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+
+*** START OF THE PROJECT GUTENBERG EBOOK 75213 ***
+
+
+
+  Transcriber’s Notes
+
+  Text transcribed between _underscores_ represents text printed in
+  italics in the source doument. Small capitals have been replaced with
+  ALL CAPITALS. ^{text} and _{text} represent superscript and subscript
+  text resepecively. Text between ~tildes~ represents marginalia.
+
+
+[Illustration: SKERRYVORE LIGHTHOUSE.]
+
+
+
+
+  ACCOUNT
+  OF THE
+  SKERRYVORE LIGHTHOUSE,
+  WITH
+  NOTES ON THE ILLUMINATION OF LIGHTHOUSES;
+
+  BY
+
+  ALAN STEVENSON, LL.B., F.R.S.E., M.I.C.E.,
+  ENGINEER TO THE NORTHERN LIGHTHOUSE BOARD.
+
+  [Illustration: ·NORTHERN LIGHTHOUSES·
+
+  IN SALUTEM OMNIUM.]
+
+  “ΥΠΕΡ · ΤΩΝ · ΠΛΩΙΖΟΜΕΝΩΝ”
+  _Inscription on the Ancient Pharos of Alexandria._
+
+  BY ORDER OF THE COMMISSIONERS OF NORTHERN LIGHTHOUSES.
+
+  ADAM AND CHARLES BLACK, NORTH BRIDGE, EDINBURGH.
+  LONGMAN AND CO., LONDON.
+
+  MDCCCXLVIII.
+
+
+  PRINTED BY NEILL AND COMPANY, EDINBURGH.
+
+
+
+
+PREFACE.
+
+
+I am unwilling to dismiss the following pages from my hands without
+saying a few words in extenuation of the defects which they contain.
+My chief plea in defence is, that the preparation of this _Account
+of the Skerryvore Lighthouse_, and the _Notes on the Illumination
+of Lighthouses_ which follow it, was not chosen or assumed by me,
+but was a task imposed by the express desire of the Lighthouse
+Board, to whose enlightened and liberal views the Mariner owes the
+erection of the Lighthouse itself. My labours were also continually
+interrupted by the urgent calls of my official duties; and, on several
+occasions, I was forced to dismiss unfinished chapters from my mind
+for a period of several months--circumstances which, I hope, will in
+some measure account for the desultory character of the performance,
+the disproportion of some of its parts, and more especially for
+repetitions and perhaps omissions which would otherwise have been quite
+unpardonable.
+
+Having said thus much by way of apology for this Volume, I must
+acknowledge my many and great obligations to my Father who preceded
+me as Engineer to the Board of Northern Lighthouses, and of whose
+experience, as the Architect of no fewer than twenty-five Lighthouses,
+including that of the Bell Rock, I had the full benefit during the
+erection of the Skerryvore Lighthouse. To the generosity of my esteemed
+friend, M. LEONOR FRESNEL, I owe all that I know of the Dioptric System
+of Illumination, invented by his late illustrious Brother; but this
+general acknowledgment will not supersede the necessity of frequent
+repetitions of my obligations to him, as occasion offers, in the course
+of these pages. I have also derived much assistance, as a careful
+reader will easily trace, from the valuable little work of M. PECLET,
+entitled _Traité de l’Eclairage_. There are, besides, many other
+obligations, which I cannot attempt to acknowledge individually, but
+which those, who kindly conferred them, well know how much I value.
+
+       *       *       *       *       *
+
+In the _Account of the Skerryvore Lighthouse_, which forms the first
+part of this Volume, there is an important omission; and, in this
+short prefatory notice, I gladly embrace the only opportunity, which
+now remains, of supplying the defect. Although, in the course of the
+Narrative, I have occasionally noticed some special deliverances
+from danger, I have altogether neglected to record the remarkable
+fact, that, amidst our almost daily perils, during six seasons on the
+Skerryvore Rock, there was no loss of either life or limb amongst
+us. Those who best know the nature of the service in which we were
+engaged,--the daily jeopardy connected with landing weighty materials
+in a heavy surf and transporting the workmen in boats through a
+boisterous sea, the risks to so many men, involved in mining the
+foundations of the Tower in a space so limited, and above all, the
+destruction, in a single night by the violence of the waves, of our
+temporary barrack on the Rock, which had cost the toils of a whole
+season, will not wonder that I am anxious to express, what I know to
+have been a general feeling amongst those engaged in the work--that
+of heartfelt thankfulness to ALMIGHTY GOD for merciful preservation
+in danger, and for the final success which terminated our arduous and
+protracted labours.
+
+  EDINBURGH, _March 25, 1848_.
+
+
+
+
+CONTENTS.
+
+
+  PART I.
+
+  ACCOUNT OF SKERRYVORE LIGHTHOUSE.
+
+                                                                    Page
+
+  Introduction -- Constitution of the Lighthouse Board -- Lights
+  established since 1821 -- Improvements in the mode of
+  illumination -- Dioptric Lights -- Beacons and Buoys,                9
+
+
+  CHAPTER I.
+
+  Topographic notice of the Skerryvore Rock,                          19
+
+
+  CHAPTER II.
+
+  Preliminary arrangements and works, including survey of the rocks,
+  and opening of quarries from 1834 to 1837 -- Survey of the
+  Skerryvore rocks -- Disadvantages of Tyree -- Pier and workyard at
+  Hynish, Tyree -- Quarries at Hynish -- Skerryvore Committee
+  appointed,                                                          37
+
+
+  CHAPTER III.
+
+  On the construction of Lighthouse Towers,                           45
+
+
+  CHAPTER IV.
+
+  OPERATIONS OF 1838.
+
+  Temporary Barrack on Rock -- Tools and machinery -- Steam Tender
+  for the works -- Employment and wages of workmen -- Progress of
+  the outfit for the season’s operations -- Embark for Skerryvore --
+  Lay down moorings, and try to land on the Rock -- Driven to Mull
+  -- First day’s work on the Rock -- Shipment of materials at
+  Glasgow and Greenock -- Reach Tyree -- Driven to Mull -- Return to
+  Tyree -- First good day’s work on the Rock -- Sudden gale and
+  great peril to the vessels -- Reach Hynish in safety -- Detained
+  by bad weather four days at Hynish -- Return to the Rock and have
+  six days of good weather -- Erection of the pyramid of the wooden
+  barrack -- Mode of determining the length of the beams, and the
+  sites for their fixtures -- Pyramid completed -- Mode of living
+  while erecting the barrack -- Shoals of Medusæ seen -- Driven by
+  a gale to Mull -- Return to Hynish and are driven to Coll --
+  Return to the Rock -- Driven to Tyree -- Return to the Rock --
+  Horizontal braces fixed -- Driven to Mull -- Heavy gale -- Timber
+  cast on Tyree -- Return to Rock and further progress of barrack --
+  Last day’s work on Rock this season -- Precaution for the benefit
+  of shipwrecked seamen -- View from top of pyramid -- Destruction
+  of the barrack during a gale -- Letter from Mr Hogben -- Proceed
+  to Skerryvore -- State in which the Rock was found -- Cause of the
+  destruction of the barrack -- Preparations for a new barrack --
+  Works at Hynish -- Hynish quarries,                                 71
+
+
+  CHAPTER V.
+
+  OPERATIONS OF 1839.
+
+  Shipping station and pier at Hynish -- Granite quarries in Mull --
+  Observations on the quarrying of granite -- Dressing of the
+  Lighthouse blocks -- Excavation of foundation for the Lighthouse
+  Tower on the Skerryvore Rock -- Fitting up of the second barrack
+  on the Rock -- Sudden death of George Middlemiss -- Wharf and
+  landing-place on the Rock -- Ring-bolts, water-tanks, and railways
+  -- Incidents of the season -- Effects of a gale from the
+  south-west -- Mutiny of the crew -- Near approach of the vessels
+  to the Rock, and other circumstances shewing the importance of a
+  Light on the Skerryvore,                                           107
+
+
+  CHAPTER VI.
+
+  OPERATIONS OF 1840.
+
+  Hynish workyard -- Hynish pier -- The Rock -- Life in the barrack
+  -- Foundation-pit -- Landing of the materials on the Rock --
+  Laying the first stone,                                            140
+
+
+  CHAPTER VII.
+
+  OPERATIONS OF 1841.
+
+  Hynish workyard -- The Rock -- The waves -- Colours of the
+  breaking waves -- The seals,                                       151
+
+
+  CHAPTER VIII.
+
+  OPERATIONS OF 1842.
+
+  State of the Rock in Spring of 1842 -- Commencement of Rock
+  operations -- Last stone -- The Lantern,                           163
+
+
+  CHAPTER IX.
+
+  CONCLUDING OPERATIONS AND EXHIBITION OF THE LIGHT.
+
+  Harbour works -- Bo Pheg beacon -- Light-keepers’ and seamen’s
+  houses -- Concluding works on the Rock, such as pointing, &c. --
+  Interior fittings of the Tower -- Light-room apparatus, and first
+  exhibition of the Light -- Removal of the barrack from the Rock --
+  Expense,                                                           169
+
+
+  PART II.
+
+  NOTES ON THE ILLUMINATION OF LIGHTHOUSES, WITH SHORT NOTICES OF
+  THEIR HISTORY, 181.
+
+  Early history, 181 -- Colossus of Rhodes, 182 -- Pharos of Alexandria,
+  183 -- Coruna Tower, 187 -- Lighthouse at the mouth of the
+  Quadalquivir, 188 -- Ancient Phari in Britain, 188 -- Tour de Corduan,
+  189 -- Eddystone, 189 -- Bell Rock, 192 -- Carlingford, 194 -- Iron
+  lighthouses, 194 -- Early modes of illumination, 195 -- Flame, 196 --
+  Drummond and Voltaic Lights, 199 -- Mr Gurney’s Lamp, 200 -- Argand
+  Burners, 200.
+
+
+  CATOPTRIC SYSTEM OF LIGHTS, 204.
+
+  Application of Paraboloidal Mirrors, 205 -- Reflection, 207 --
+  Paraboloidal Mirrors, 209 -- Divergence of Paraboloidal Mirrors, 212
+  -- Effect of Paraboloidal Mirrors, 217 -- Power of ditto, 218 --
+  Manufacture of reflectors, 218 -- Testing of mirrors, 219 -- Argand
+  Lamps used in reflectors, 220 -- Arrangements for raising or lowering
+  the Argand wick, 222 -- Flowing of the lamp, 223 -- Placing
+  the lamp in the focus, 226 -- Distinctions of Catoptric Lights, 227 --
+  Colour as a distinction for lights, 229 -- Arrangement of reflectors
+  on the frame, 230 -- Bordier Marcet’s reflectors, 232 -- Fanal
+  sidéral, 232 -- Fanal à double effet, 234 -- Fanal à double face, 236
+  -- Mr Barlow’s spherical mirrors, 237 -- Captain Smith’s mirrors in
+  the form of a parabolic spindle, 238.
+
+
+  DIOPTRIC SYSTEM OF LIGHTS, 239.
+
+  Early history of Lighthouse lenses, Condorcet, Buffon, Brewster,
+  Fresnel, 239 -- Refraction, 242 -- Lenses, 245 -- Spherical
+  aberration, 248 -- Fresnel’s formulæ for annular lenses, 249 --
+  Testing lenses, 255 -- Divergence of lenses, 256 -- Illuminating power
+  of lenses, 257 -- Arrangement of lenses in a Lighthouse, 258 --
+  Pyramidal lenses and mirrors, 259 -- Curved mirrors, 260 -- Cylindric
+  refractors of fixed Lights, 263 -- Application of crossed prisms to
+  cause flashes, 264 -- True cylindric form given to refractors, and
+  other improvements in their construction, 264 -- Catadioptric zones,
+  the mode of computing their elements, &c., 267 -- Testing of zones,
+  282 -- Framing of zones, 286 -- Mechanical lamp, 286 -- Height of
+  flame of mechanical lamp, 289 -- Position of flame in reference to
+  focus, 290 -- Working of the pumps, 291 -- Choice of focal point for
+  various parts of apparatus, 292 -- Choice of a focal point for zones,
+  292 -- Application of spherical mirrors to fixed Dioptric Lights, 293
+  -- Arrangement of Dioptric apparatus, 293 -- Arrangement of Dioptric
+  apparatus in Lightroom, 294 -- Power of Dioptric instruments, 298 --
+  Orders of French Lights, 298 -- Distinctions of Dioptric Lights, 299
+  -- Comparison of Dioptric and Catoptric apparatus for revolving
+  lights, 301 -- Comparison for fixed lights, 303 -- Summary of views as
+  to two systems for revolving lights, 306 -- Summary of views as to two
+  systems for fixed lights, 306 -- Advantages and disadvantages of both
+  systems under certain circumstances, 308 -- Distinctions of the
+  Dioptric Lights and the application of coloured media, 311 -- Captain
+  Basil Hall’s proposal for fixed lights, 313 -- Effects of rapid motion
+  on the power of lights, 315 -- Connection of experiments with
+  irradiation, 320.
+
+
+  VARIOUS GENERAL CONSIDERATIONS CONNECTED WITH LIGHTHOUSES, 320.
+
+  Masking Lights, 320 -- Double Lights, 322 -- Leading Lights, 323 --
+  Distribution of Lights on a coast, 325 -- Height of Lighthouse Tower,
+  and its relation to range of light, 328 -- Diagonal Lantern, 330 --
+  Glazing of Lantern, 331 -- Ventilation of Lanterns, 331 --
+  Arrangements and Management of a Lighthouse, 334 -- Cleansing of
+  apparatus, 335 -- Mode of measuring relative power of lights, 336 --
+  More accurate comparison of intensity of lights, 338 -- Floating
+  Lights, 346 -- Beacons and Buoys, 347.
+
+
+  APPENDIX.
+
+   1. Table of Co-ordinates of Hyperbolic Column.
+
+   2. Notes on the Making of Paraboloïdal Mirrors.
+
+   3. Notes on the Grinding and Polishing of Dioptric Instruments for
+      Lighthouses.
+
+   4. Table of the Elements of the Catadioptric Zones for Lights of the
+      first order in the system of Augustin Fresnel.
+
+   5. Notice to Mariners of the Exhibition of the Skerryvore Light.
+
+   6. Detailed Account of the Expense of the Skerryvore Lighthouse.
+
+   7. Excerpts from Account of Experiments on the Force of the Waves of
+      the Atlantic and German Oceans, by Thomas Stevenson, F.R.S.E.,
+      Civil Engineer.
+
+   8. Annual List for 1848 of Lighthouses, Beacons, and Buoys, in the
+      District of the Northern Lights Board.
+
+   9. Annual Report by the Secretary as to the Income and Expenditure of
+      the Northern Lights Board for 1846.
+
+  10. Instructions to the Light-keepers in the Service of the
+      Commissioners of the Northern Lighthouses.
+
+
+
+
+PLATES.
+
+
+       I. Chart shewing the situation of the Skerryvore Lighthouse.
+
+      II. Chart shewing the position of the Skerryvore Rocks and foul
+          ground.
+
+     III. Plans of the Skerryvore Rock at high and low water of spring
+          tides.
+
+      IV. Curves for Lighthouse Towers -- Marine Dynamometer.
+
+       V. Barrack of timber on the Skerryvore Rock.
+
+      VI. Details of fixtures of timbers at the top of the Timber
+          Barrack.
+
+     VII. Elevation of Skerryvore Lighthouse.
+
+    VIII. Section of Skerryvore Lighthouse.
+
+      IX. Balance Crane used at Skerryvore.
+
+       X. Plan shewing the Lighthouse Establishment of Barracks,
+          Harbour, &c., at Hynish, in the Island of Tyree.
+
+      XI. Elevation and Section entrance to Dock at Hynish.
+
+     XII. Plan and Section of Annular Lens.
+
+    XIII. Perspective Elevation of Revolving Dioptric Apparatus of First
+          Order.
+
+     XIV. Plan of Revolving Dioptric Light of First Order, with Mirrors.
+
+      XV. Vertical Section of fixed Dioptric Lights of First Order, with
+          Mirrors.
+
+     XVI. Elements of Concave Mirrors for Dioptric Lights of First
+          Order, and arrangement on the Frame.
+
+    XVII. Perspective View of Fixed Dioptric Light of First Order, with
+          Catadioptric Zones.
+
+   XVIII. Vertical Section of Fixed Dioptric Light of First Order, with
+          Catadioptric Zones.
+
+     XIX. Vertical Section of Catadioptric Light of Fourth Order, with
+          Framing.
+
+      XX. Elevation of Mechanical Lamp for Dioptric Lights of First
+          Order.
+
+     XXI. Enlarged Views of Oil-Pumps of Mechanical Lamp.
+
+    XXII. Enlarged Views of Oil-Pumps of Mechanical Lamp.
+
+   XXIII. Details of Clock-work of Mechanical Lamp.
+
+    XXIV. Details of Clock-work of Mechanical Lamp.
+
+     XXV. Flame of Mechanical Lamp of First Order at full size.
+
+    XXVI. Elevation of Diagonal Lantern, and details of Astragals.
+
+   XXVII. Elevation of Ardnamurchan Lighthouse.
+
+  XXVIII. Plan of Ardnamurchan Lighthouse.
+
+    XXIX. Lines of a Floating Light Vessel belonging to the Corporation
+          of Trinity House of Deptford Strond.
+
+     XXX. Elevation of Covesea Skerries Beacon.
+
+    XXXI. Details of Covesea Skerries Beacon.
+
+   XXXII. Elevations and Sections of Stone and Iron Beacons.
+
+  XXXIII. Elevations of Buoys.
+
+
+
+
+ERRATA.
+
+  Page  52, line 8, _for_ Redelet _read_ Rondelet
+   ... 178, line 6, _for_ L.93,306:8:10 _read_ L.86,977:17:7
+   ... 292, line 30, _for_ radius rector _read_ radius vector
+   ... 294, line 13, _for_ give _read_ gives
+   ... 329, line 3, _for_ earth _read_ sea
+   ... 347, line 29, _for_ Plate XXXII., _read_ Plate XXX.,
+
+
+
+
+PART FIRST.
+
+ACCOUNT OF THE SKERRYVORE LIGHTHOUSE.
+
+
+INTRODUCTION.
+
+In the course of preparing the account of the building of the
+Skerryvore Lighthouse, it occurred to me, that a short Introduction
+should be prefixed, embracing a concise view of the constitution
+and acts of the Board of Commissioners of Northern Lights, more
+especially from 1824, when my Father’s work on the Bell Rock Lighthouse
+was published, up to the present time. This object will be best
+accomplished, by presenting to the reader, in the first place, an
+account of the constitution and powers of the Lighthouse Board, chiefly
+drawn from the “Introduction to the Bye-Laws, Rules, and Regulations of
+the Commissioners of Northern Lighthouses,” prepared by a Committee of
+their number; and by afterwards briefly noticing the principal works of
+the Board since 1824, and stating generally the nature of the changes
+and improvements made within that period on the mode of illumination,
+of which I propose, in a subsequent part of this volume, to give a
+somewhat detailed account.
+
+       *       *       *       *       *
+
+  ~Constitution of the Lighthouse Board.~
+
+The trade of Scotland had begun to increase very soon after the
+settlement of the civil war in 1745; but it was not till the year 1784
+that the general establishment of Sea Lights upon the Coast appears to
+have been brought under the notice of the Legislature. In that year,
+the subject was first mentioned at a meeting of the Convention of the
+Royal Burghs of Scotland, by Mr DEMPSTER of Dunichen, M.P., the Provost
+of the burgh of Forfar; and, in the year 1786, that gentleman brought a
+bill into Parliament, and an Act was obtained establishing the present
+Board of Northern Lights.
+
+This Act sets forth, that “it would conduce greatly to the security of
+navigation and the fisheries, if four Lighthouses were erected in the
+Northern parts of Great Britain, one on Kinnaird’s Head, Aberdeenshire,
+one in the North Isles of Orkney, one on the point of Scalpa, in the
+Island of Harris, and a fourth on the Mull of Kintyre, Argyllshire;”
+and it accordingly authorises the erection of those four Lighthouses.
+The Commissioners appointed for carrying this Act into execution were,
+the Lord Advocate and Solicitor-General of Scotland, the Lord Provost
+and first Bailie of Edinburgh, the Lord Provost and first Bailie
+of Glasgow, the Provosts of Aberdeen, Inverness, and Campbeltown,
+the Sheriffs of the counties of Edinburgh, Lanark, Renfrew, Bute,
+Argyll, Inverness, Ross, Orkney and Zetland, Caithness, and Aberdeen.
+An Act was subsequently passed, which authorised the Commissioners,
+when any new Lighthouse was established on any part of the coast of
+Scotland, to add to their number the Provost or Chief Magistrate of
+the nearest Royal Burgh, and also the Sheriff-Depute of the nearest
+county; and, by the exercise of this power of assumption, the board now
+includes the Sheriffs of the counties of Ayr, Fife, Forfar, Wigtown,
+Sutherland, Kincardine, and Kirkcudbright. To enable the Board to
+carry on the intended works and to provide the means of maintaining
+the Lights, those Acts gave power to the Commissioners to levy a duty
+of 1d. per ton on British vessels, and 2d. per ton on foreign vessels;
+and liability to pay this duty was incurred by all vessels passing
+any of the Lighthouses in the course of a voyage; but this single
+payment freed them from any farther exaction, although they should
+pass more than one Lighthouse in the course of the voyage. The Board
+held its first meeting at Edinburgh on 1st August 1786. A Secretary
+and Engineer were appointed, and a resolution was adopted to borrow
+L.1200. For this sum the Magistrates of the five Royal Burghs named in
+the Act interposed their security; and, at the same time, assigned,
+in farther security, the duties under the Act of Parliament. After
+appointing a Committee to prepare matters for a general meeting, they
+adjourned till the 23d of January 1787. Some inconvenience having been
+felt in conducting the business of the Board, particularly in the
+holding of stock and other property, by reason of its not being an
+incorporated body, an Act was obtained for erecting the Commissioners
+into a body politic, by the name of the “Commissioners of the Northern
+Lighthouses.” Several Acts have been subsequently passed, in order to
+facilitate the erection of particular Lighthouses, and for the purpose
+of granting duties for their support. All those duties, however,
+are now abolished, and others have been substituted, the collection
+of which is regulated by an Act, 6th and 7th William IV., cap. 79,
+intituled, “An Act for vesting Lighthouses, Lights, and Sea-marks on
+the Coasts of England, in the Corporation of Trinity-House of Deptford
+Strond, and for making provision respecting Lighthouses, Lights, Buoys,
+Beacons, and Sea-marks, and the Tolls and Duties payable in respect
+thereof.” This Act declares, “That from the first day of January one
+thousand eight hundred and thirty-seven, the tolls now payable by or
+in respect of vessels for or towards the maintenance of the several
+lighthouses at present under the management of the Commissioners
+of Northern Lighthouses shall cease to be payable, and that, in
+lieu thereof, there shall thenceforth for ever be paid to the said
+Commissioners of the Northern Lighthouses, for every vessel belonging
+to the United Kingdom of Great Britain and Ireland (the same not
+belonging to his Majesty, his heirs or successors, or being navigated
+wholly in ballast), and for every foreign vessel which, by any Act
+of Parliament, order in Council, convention, or treaty, shall be
+privileged to enter the ports of the said United Kingdom, upon paying
+the same duties of tonnage as are paid by British vessels (the same not
+being vessels navigated wholly in ballast), which shall pass any of the
+said lighthouses, or derive benefit thereby, the toll of one halfpenny
+per ton of the burden of every such vessel for each time of passing
+every such lighthouse, or deriving benefit thereby, and of one penny
+per ton for each time of passing the Bell Rock Lighthouse, and double
+the said tolls for every foreign vessel not so privileged.” And with
+regard to any new Lighthouses to be hereafter erected, it is provided,
+that there “shall be paid to the Commissioners by the owner, or other
+person having the command of any vessel not belonging to His Majesty,
+which shall pass such lighthouse, or derive benefit thereby, such
+reasonable toll as shall have been first approved in that behalf by His
+Majesty in Council.” Before the passing of this Act, the Commissioners
+had been uncontrolled in the selection of stations for Lighthouses, or
+in choosing the characteristic appearance for the Lights; but it being
+considered desirable to have a systematic arrangement in the three
+kingdoms, the Irish Lighthouse Board, as well as the Commissioners, are
+now required to give notice to the Corporation of the Trinity-House
+of Deptford Strond, before altering the character of any Light, or
+erecting any new Lighthouse; and that Corporation must, within the
+period of six months after receiving such notice, signify their
+opinion as to the propriety of the change, or the utility of any new
+Lighthouses submitted for their consideration. The Act, however,
+provides, that, if the Commissioners are dissatisfied with the opinion
+of the Trinity-House, they may appeal to the Privy Council, whose
+determination is final. By this Act, also, an important power is given
+to the Commissioners to control the exhibition of all harbour and local
+Lights, or other sea-marks, and to prevent the exhibition of any Lights
+or fires on the sea-coast, which might be mistaken for the regular
+Lights exhibited by the Board. In the Appendix I have given a copy of
+the Annual Statement of the Income and Expenditure of the Board for the
+year 1846, prepared by Mr ALEXANDER CUNINGHAM, the Secretary to the
+Commissioners.
+
+       *       *       *       *       *
+
+  ~Lights established since 1821.~
+
+Since the Sumburghhead Lighthouse in Zetland was lighted in the year
+1821, with a notice of which the account of the Bell Rock Lighthouse
+concludes, the Commissioners have been engaged in the establishment of
+seventeen new Lighthouses, and the remodelling of several old ones;
+and they have, more particularly, effected important changes in the
+mode of illumination, and have begun to place Beacons and Buoys on the
+coast. They have, besides, executed several considerable improvements,
+for the purpose of facilitating the communication with the Lighthouses
+at Kintyre in Argyllshire, Cape Wrath in Sutherlandshire, and
+Dunnethead in the county of Caithness, by the establishment of
+landing-piers and the formation of roads, varying in length from three
+to ten miles, in connection with those Stations. Of those works, many
+interesting details might be given, were it not desirable that the
+introduction to an account of a single Lighthouse should be restricted
+within a very moderate compass; and I have, therefore, thought it
+sufficient to lay before the reader the most important circumstances of
+each Lighthouse Station belonging to the Board in a tabular form in the
+Appendix.
+
+  ~Improvements in the mode of illumination.~
+
+I shall not, in this place, enter on any exposition of the general
+principles which regulate the illumination of Lighthouses, and still
+less will it be proper to discuss the advantages of the different
+methods of illumination by Reflection and Refraction, as I shall, in
+the sequel, find a more convenient opportunity for speaking somewhat
+in detail on those subjects. It will be enough to present a very brief
+notice of the improvements in the mode of illuminating Lighthouses,
+which the Northern Lights Board have introduced since 1824, up to which
+time, as already mentioned, a sketch of their works is already before
+the public. One of the most important changes in Lighthouse apparatus
+was, unquestionably, the introduction of Revolving Lights at the Tour
+de Corduan about the year 1780, by which the means of distinguishing
+one light from another were greatly extended, and a marked difference
+in the appearance of contiguous lights was at once simply obtained.
+The mere variation of the velocity of the revolution is so simple
+as to afford an obvious source of distinction among lights; and yet
+it is remarkable, that it was only lately that one of its principal
+advantages was perceived by my Father, who first applied it in the
+year 1827 as a means of distinction for the Light of Buchanness. This
+distinction consists in giving the frame a greater number of sides
+or faces, and a more rapid revolution, so as to cause a flash in
+every five seconds of time, which produces an effect so marked and
+characteristic as to afford by far the most effective distinction which
+has been exhibited since the introduction of Revolving Lights. Under
+the auspices of the Board, this distinction has been since applied
+at the Rhinns of Islay Lighthouse, and has given much satisfaction
+wherever it has been tried. The late King of the Netherlands, a great
+patron of the useful arts, was so much pleased with this device that he
+presented the author of it with a splendid gold medal, in token of his
+approbation. The only other improvement on the Reflecting Lights, which
+I shall notice in this place, is that called the _intermittent light_,
+which is due to the same officer, and was by him introduced at the
+stations of Mull of Galloway, Tarbetness, and Barrahead. It consists
+of the apparatus of a fixed Light, in front of which two cylindric
+shades are alternately shut and opened by a vertical movement, so as to
+produce a sudden extinction and exhibition of the light, in a manner
+very difference from the gradual decline and growth of the flash,
+which is produced in revolving Lights by the attenuating effects of
+divergence on the penumbral portions of the light reflected from the
+mirror.
+
+  ~Dioptric Lights.~
+
+The introduction of lenticular apparatus into Lighthouses has been the
+last great improvement effected in their illumination. So far back as
+the year 1823, the attention of the Commissioners was first called by
+their Engineer to the invention of the late AUGUSTIN FRESNEL, who had
+succeeded in building polyzonal lenses of large dimensions, and in
+adapting to them a lamp of great power, having four concentric wicks
+supplied with oil by a clock-work movement like that of the Carcel
+lamp. A committee was appointed to consider this subject; and under its
+direction a long train of experiments was made with those instruments
+and with the paraboloidal mirrors which are generally used in British
+Lighthouses. The results of the experiments led the Board, in the
+summer of 1834, to send me on a mission to France, with instructions
+to report my opinion as to the comparative merits of the dioptric and
+catoptric apparatus for the illumination of Lighthouses. Through the
+kindness of my friend M. LEONOR FRESNEL, Secretary of the _Commission
+des Phares_, who in the most liberal manner put me in possession of
+all the information which I required, and afforded me an opportunity
+of visiting the most important Lighthouses on the French coast, I was
+enabled on my return to report very fully my views on the various
+topics whose investigation had been committed to me by the Lighthouse
+Board.
+
+The characteristics of the two systems of illumination by Reflection
+and Refraction may be briefly described as follows: In the reflecting
+apparatus, the lamp is placed in _front_ of the mirror, whose surface
+is so formed that the rays which fall upon it, and are reflected from
+it, must afterwards move in lines parallel to the axis of the mirror;
+while in using Refracting instruments, the flame is placed _behind_
+the lens, whose action is simply to bend the rays in their passage
+through it, in such a manner that they come out from its face parallel
+to a line drawn from the focus to the centre of the lens. In Revolving
+Lights, on the reflecting principle, the mirrors containing the lamps
+are placed on a frame which revolves on its centre, and carries them
+round in succession to the different points of the horizon, so that
+each mirror produces a bright flash when it crosses the line drawn from
+an observer’s eye to the centre of the Lighthouse; but in Refracting
+Lights, a single lamp of great power is fixed in the centre of the
+lightroom, while the lenses, placed on a revolving frame, intercept and
+modify the rays which fall upon them from the Lamp, as they pass in
+front of it, and thus produce successive flashes whenever the centre
+of the lens crosses the imaginary line already noticed, as joining the
+observer’s eye and the lightroom.
+
+In Fixed Lights, on the Reflecting plan, the mirrors are ranged around
+a fixed chandelier in tiers, one above another, their centres being
+placed in spiral lines, so that each shall subtend an equal arc of
+the horizon, and thus distribute the light with as little inequality
+as is consistent with the application of such an instrument as the
+paraboloidal mirror to this purpose. This object of distributing the
+light equally over the horizon, which, next to intensity, is the main
+object of a fixed light, and ought, indeed, to be strictly co-ordinate
+with it, is much better effected by using dioptric instruments. That
+apparatus consists of successive rings or bent prisms arranged in the
+form of a hoop or belt, which may be described as a cylinder, generated
+by the revolution of the central section of a polyzonal lens about
+its focus as a vertical axis, and which consequently acts only in a
+vertical direction, leaving the natural horizontal divergence of the
+light unchanged, and thus distributing it with perfect equality in
+every direction.
+
+Those two systems of illumination possess advantages and defects
+peculiar to each. The lenticular instruments insure greater intensity
+when applied to revolving lights; but this advantage is in part
+counterbalanced by the greater duration of the flash caused by the
+reflectors, whose divergence is greater; while in fixed lights, the
+refracting instruments not only produce at least an equal intensity
+of light, but, what is of the greatest importance, afford the same
+quantity of light in all directions, a property which fixed Lights on
+the reflecting principle employed in Britain cannot possess.
+
+On my return from France I made a Report, which was printed by order of
+the Commissioners; and the views which I gave of the superiority of the
+refracting apparatus, led the Board to adopt the resolution of at once
+converting the revolving light of Inchkeith from the catoptric to the
+dioptric system, as its nearness to Edinburgh offered good opportunity
+of observation as to the effect of the change. In October 1835, the
+new light was exhibited to the public, and I was forthwith instructed
+to make a similar change on the fixed light of the Isle of May; but
+in carrying this into effect, I introduced an important modification
+of the form of the refracting part of the apparatus, with the view of
+obtaining a still nearer approach to the equal distribution of the
+light. The only other considerable change in the lightroom apparatus
+which has since been effected, is the substitution of catadioptric
+zones in room of the mirrors hitherto used in the subsidiary parts of
+the larger French lights, which, as will appear in the sequel, was
+suggested by me in 1841, and finally carried into effect in 1843,
+agreeably to the computations of M. LEONOR FRESNEL. A Table of the
+Elements of those zones computed by myself, and closely verifying
+M. FRESNEL’S results, will be found in the Appendix. The lenticular
+apparatus has been applied at the new Lighthouse stations of the Little
+Ross and the Skerryvore, and, still more recently, at Covesea Skerries,
+Cromarty Point, Chanonry Point, Loch Ryan, and Girdleness.
+
+  ~Beacons and Buoys.~
+
+The establishment of a system of Beacons and Buoys on the coast
+of Scotland for the purpose of affording additional facilities to
+navigation, had long been looked upon as a desirable extension of
+the operations of the Northern Lights Board; and the increase of the
+trade and shipping of the kingdom having, some years ago, directed
+particular attention to the subject, a committee was named, on the 12th
+January 1839, to take special superintendence of that department. In
+1840, the Engineer reported to the committee upwards of fifty stations
+for Beacons, and nearly a hundred for Buoys, as auxiliaries to the
+navigation in situations where the establishment of a Lighthouse was
+either too expensive or not warranted by the wants of the district; and
+means were immediately taken for erecting three Beacons in the Frith of
+Forth, two in the Clyde, one in Loch Ryan, and two in Cambeltown Loch.
+Beacons were also erected on the Iron Rock or Skervuile in the Sound of
+Jura, and on the Covesea Skerries in Morayshire, in connection with the
+Lighthouse of that name. Those works, notwithstanding many obstacles
+arising from doubts as to the powers of the Board, have been carried
+on with great vigour. In the Appendix, I have given drawings of three
+of those Beacons, one being of masonry, and the other two of iron; and
+also Tables which shew the positions of the various Beacons and Buoys
+at present belonging to the Board.
+
+
+CHAPTER I.
+
+TOPOGRAPHIC NOTICE OF THE SKERRYVORE ROCK.
+
+From the great difficulty of access to the inhospitable rock of
+Skerryvore, which is exposed to the full fury of the Atlantic, and
+is surrounded by an almost perpetual surf, the erection of a Light
+Tower on its small and rugged surface has always been regarded as
+an undertaking of the most formidable kind. So discouraging was the
+consideration of expense, and the uncertainty of the final success
+of such a work, that the Commissioners of the Northern Lighthouses,
+after successfully completing the arduous and somewhat similar work on
+the Bell Rock, were induced to proceed with other operations of less
+magnitude, but probably, in some respects, of no less utility; and to
+delay the construction of the Skerryvore Lighthouse till the present
+time, although the Act of Parliament authorising its erection was
+obtained so long ago as 1814.
+
+The cluster of Rocks, of which that called the Skerryvore is the
+largest, has ever been a just cause of terror to the mariner. Its
+dangers have long been known, and the means of removing these dangers,
+by converting its dark horrors into a cheering guide for the benighted
+mariner, have often occupied the attention of the Lighthouse Board, and
+especially of my predecessor in the office of their Engineer, with whom
+it was a constant subject of interest, from its similarity to his own
+work on the Bell Rock.
+
+The first landing that my Father, in the course of his annual voyages
+round the coast, as Engineer of the Northern Lighthouse Board, effected
+on Skerryvore, was in the year 1804. In 1814, he visited it a second
+time, while accompanying a committee of the Commissioners on a tour
+of inspection to the Lighthouses all round the coast, from the Frith
+of Forth to the Clyde. On that occasion, Sir Walter Scott was of the
+party, and we find in his diary the following record of his impressions
+at the time, expressed in the terse and humorous language by which
+this interesting relic of the poet is characterised; and as the hasty
+observations of that great man seem worthy of a place in a work
+descriptive of the means which have been taken to obviate the dangers
+to which he refers, no apology seems necessary for introducing it in
+this place.
+
+  “Having crept upon deck about four in the morning,” says Sir Walter,
+  “I find we are beating to windward off the Isle of Tyree, with the
+  determination, on the part of Mr Stevenson, that his constituents
+  should visit a reef of rocks called _Skerry Vhor_, where he thought
+  it would be essential to have a Lighthouse. Loud remonstrances, on
+  the part of the Commissioners, who, one and all, declare they will
+  subscribe to his opinion, whatever it may be, rather than continue
+  the infernal buffeting. Quiet perseverance on the part of Mr S., and
+  great kicking, bouncing, and squabbling, upon that of the yacht, who
+  seems to like the idea of Skerryvore as little as the Commissioners.
+  At length, by dint of exertion, come in sight of this long ridge
+  of rocks (chiefly under water) on which the tide breaks in a most
+  tremendous style. There appear a few low broad rocks at one end of
+  the reef, which is about a mile in length. These are never entirely
+  under water, though the surf dashes over them. To go through all the
+  forms, Hamilton, Duff,[1] and I, resolve to land upon these bare
+  rocks, in company with Mr Stevenson. Pull through a very heavy swell
+  with great difficulty, and approach a tremendous surf dashing over
+  black pointed rocks. Our rowers, however, get the boat into a quiet
+  creek between two rocks, where we contrive to land well wetted. I
+  saw nothing remarkable in my way excepting several seals, which we
+  might have shot, but, in the doubtful circumstances of the landing,
+  we did not care to bring guns. We took possession of the rock in name
+  of the Commissioners, and generously bestowed our own great names on
+  its crags and creeks. The rock was carefully measured by Mr S. It
+  will be a most desolate position for a Lighthouse--the Bell Rock and
+  Eddystone a joke to it, for the nearest land is the wild island of
+  Tyree, at fourteen miles distance. So much for the Skerry Vhor.”
+
+  [1] The Sheriffs-Depute of Lanark and Edinburgh.
+
+Notwithstanding those occasional visits, however, it was not till the
+year 1834, that the Commissioners directed their Engineer to make a
+survey of the whole of this extensive reef, preparatory to taking
+measures for the erection of a Lighthouse on that part of it which
+might be found, after careful inspection, to afford the most suitable
+site; and, at the same time, the shores of part of the Island of
+Tyree were surveyed, with the view of establishing a Signal Tower for
+communicating with the Lighthouse, and of forming a small harbour, of
+shelter for the vessels to be employed in attending it. From these
+surveys the general view of the Reef which is given in Plate II., and
+the enlarged plan shewn in Plate III. of the Skerryvore or principal
+Rock, on which the Lighthouse has been built, were constructed.
+
+       *       *       *       *       *
+
+The Skerryvore or principal Rock of this remarkable group, is situated
+in North Lat. 56° 19′ 22″, and West Long. 7° 6′ 32″.[2] It is about 11
+Nautic miles W.S.W ¹⁄₄ W. of the island of Tyree, which is the nearest
+land, 20 miles W.N.W ³⁄₄ N. of the island of Iona, 33 miles S. ¹⁄₄ E.
+of the Lighthouse of Barrahead, the most southern of the Hebrides,
+and 53¹⁄₂ miles N.E. by N. of Mallinhead, in the county of Donegal in
+Ireland. It may also be added, that the principal rock is about 50
+miles from the nearest point of the main land of Scotland. The extent
+of the Reef, and its situation in reference to the general position of
+the coast, will be best understood by referring to Plate I., which is a
+small Map of the British Isles. From this it will be seen that it lies
+in an irregular semicircular sea, inclosed by the southern extremity of
+the Hebrides, the rugged shores of Argyllshire, and the northern coast
+of Ireland on the one side, but open on the other to the Atlantic.
+
+  [2] According to information for which I am indebted to Captain
+  Yolland, R.E., of the Ordnance Survey.
+
+       *       *       *       *       *
+
+The importance of the Skerryvore as a station for a Lighthouse is so
+evident as to require but little comment. Although the smaller class of
+coasting vessels almost invariably sail through the sheltered Sounds
+of Mull, Loing, and Islay, to avoid the difficulties and dangers
+(Skerryvore among the number) of the rough navigation of the outward
+passage, yet these rocks lie much in the track of the larger vessels
+bound over seas round the North of Ireland from the Clyde and the
+Mersey. Government Cruisers and Ships of War are also necessarily
+often within a short distance of its dangers. But for homeward-bound
+vessels sailing for the Clyde, or for any of the Ports in the Irish
+sea, and directing their course for the North Irish Channel, the
+establishment of a light at this place is of the last importance. When
+such vessels happened to encounter bad weather before making land, and
+so had difficulty in ascertaining their true position in relation to
+the coast, they often, in the event of being driven so far north from
+their course, as to miss the lights of Ireland or that of Barrahead,
+continued their progress onwards in the direction of the Skerryvore
+Rocks; and thus, while running in apparent safety, and probably, from
+the state of the weather, not within sight of Tyree, which it is often
+difficult to see, they were very liable to encounter some of the many
+detached rocks and shoals which form this broken reef of nearly seven
+miles in extent.
+
+       *       *       *       *       *
+
+In estimating the risks to which vessels were exposed from this cause,
+the peculiarly insidious nature of the danger must be kept in view.
+A headland, or line of coast, which rises to some height above the
+surface of the sea can be seen in most states of the weather, at a
+sufficient distance, even during the night, to enable the seaman to
+avoid danger; but, in approaching a sunken reef or a low rock, in
+the dark, there is no object to warn the crew of their position,
+until their vessel gets unexpectedly among breakers, after which it
+is generally too late to bring her round again. And even the very
+knowledge of the existence of a reef, such as this, often causes the
+seaman, in ignorance of its exact position, to give it too wide a
+berth; in which case his ship is liable to be carried away by the force
+of tides or winds, perhaps on a lee shore, where, although the crew may
+be saved, the vessel generally goes to pieces.
+
+       *       *       *       *       *
+
+The exhibition of a Light, however, altogether changes the case.
+Instead of shunning as a danger those dreaded rocks, vessels will steer
+boldly on their course, until checked by the Light, availing themselves
+of which they will be enabled to _lie off-and-on_ during the night,
+and so wait the return of daylight, in perfect confidence as to their
+position, and without the necessity of endeavouring to avoid hidden
+dangers. Thus, that which was formerly an obstruction and a danger, is
+rendered an aid and a safety, to the navigation of the western coasts
+of our country.
+
+       *       *       *       *       *
+
+That this source of danger to shipping was by no means imaginary, and
+the consequent terror of mariners far from being ill founded, there is
+a too melancholy proof in the following list of disasters caused by the
+Skerryvore Rock, and the neighbouring dangers off the coast of Tyree:--
+
+  In 1790. The Ship Rebecca of 700 tons lost; crew saved.
+
+  1804. Ship Brigand of Nova Scotia, Wright, master, of 600 tons, lost
+        off Hough, in Tyree; crew saved.
+
+  1804. _A Brig_, M‘Iver, master, lost off Hough; crew saved.
+
+  1806. Ellen of Bath, Paterson, master, of 90 tons, lost off Balaphuil,
+        in Tyree; one man drowned.
+
+  1809. Brig Mary, Sanders, master, lost off Balaphuil; crew saved.
+
+  1813. Sloop, Penelope of Wick, 60 tons, lost at Gott Bay, Tyree; crew
+        saved.
+
+  1810. A Brig from New York, Greenlees, master, lost off Hynish Point,
+        Tyree; crew all drowned.
+
+  1813. _A Sloop_, Eugene M‘Intyre, master, lost off Balaphuil; one man
+        drowned.
+
+  1814. Brig, Betsey of Leith, Ross, master, lost off Hough; crew saved.
+
+  1817. _A Brig_, of 400 tons, foundered off Kennavarah, Tyree; crew all
+        drowned. Numerous casks of butter came ashore.
+
+  1818. Sloop, Benlomond of Greenock, M‘Lauchlan, master, lost off
+        Balaphuil; crew all drowned.
+
+  1819. Sloop, Bee, Coice, master, of 60 tons, lost off Hough; crew
+        saved.
+
+  1820. _A Sloop_, M‘Donald, master, of 50 tons, lost in Reef Bay,
+        Tyree; crew saved.
+
+  1820. Ship, Masters, of Port-Glasgow, Martin, master, of 700 tons,
+        foundered off Skerryvore Rocks, and came ashore at Clate Hynish,
+        in Tyree; crew saved.
+
+  1821. Sloop, Catharine, M‘Rae, master lost; crew saved.
+
+  1821. _A Sloop_, of 60 tons, lost off Hough; master and three men
+        drowned.
+
+  1825. Sloop, Dan of Campbelltown, M‘Innes, master, of 50 tons, lost;
+        crew saved.
+
+  1828. Sloop, Delight, of 70 tons, Stevenson, Master, lost.
+
+  1828. _An Irish Schooner_ of 100 tons, Montgomery, master, lost off
+        Hough; crew saved.
+
+  1828. Jane of Sligo, Collins, master, lost off Balaphuil.
+
+  1829. Van Scapan of Stockholm, Fisherton, master, of 700 tons, lost
+        off Hough; fourteen people drowned.
+
+  1834. Confidence of Dundee, Wesley, master, lost off Hough; crew
+        saved.
+
+  1834. _A Schooner_ of 70 tons, lost; three men drowned.
+
+  1835. Peggy, Bitters, master, of 500 tons, lost off Beist, Tyree; crew
+        saved.
+
+  1841. April 2. Majestic of North Shields, Tait, master, of 400 tons,
+        foundered _by a sea_ off Boinshly Rock, and came ashore at Gott
+        Bay; captain and four men washed overboard and drowned, and the
+        mate and one seaman had their legs broken when the vessel was
+        struck by the sea.
+
+  1842. Fleurs of Liverpool, Thomson, master, of 300 tons, lost off
+        Kennavarah; crew saved.
+
+  1842. March 14. Two deck beams, a knee, and some pieces of deck-plank
+        of a _North American built vessel_, came ashore at Clate Hynish.
+
+  1842. _A Barra Boat_ wrecked, and four corpses washed ashore; two men,
+        a woman and a child.
+
+  1842. Pieces of wreck were seen in the Sound of Coll, and at the same
+        time the shores of Tyree were strewed with candles, mostly of
+        wax, supposed to be altar candles for the West Indies.
+
+  1843. September 2. The Prussian Barque Formosa, of 326 tons, P. R.
+        Reick, master, lost off Hough; two seamen drowned.
+
+  1844. December 1. The Hull of _a Sloop_ of about 70 tons, was washed
+        ashore off Clate Hynish. The Hull was very much broken up by
+        being in contact with the rocks; and one of the planks,
+        apparently off the taffrail, had the words “Port of Dundee”
+        lettered upon it; the crew supposed to be all drowned.
+
+This list is made up chiefly from data kindly furnished to me by the
+Rev. Neil Maclean, the Minister of Tyree and Coll, whose long residence
+on the former island has afforded him ample opportunity for making
+observations on the subject. It is not to be imagined, however, that
+Mr Maclean’s list, which is made up from recollection, contains a full
+catalogue of the disasters caused by the Skerryvore, within the dates
+which it cites. Very many vessels were wrecked on this dangerous reef
+whose names could never be learned, and of which nothing but portions
+of the drift wood or cargo came ashore; and there have, no doubt, been
+many shipwrecks of which not a single trace has been left. Nothing,
+indeed, is more probable than that many of the foreign vessels whose
+course lay through the North Irish Channel, and whose fate has been
+briefly and vaguely described, as “foundered at sea,” have met their
+fate on the _infames scopuli_ of the Skerryvore. It is also well known
+that the Tyree Fishermen were in the constant practice of visiting
+the Skerryvore, after gales, in quest of wrecks and their produce, in
+finding which they were but too often successful.
+
+       *       *       *       *       *
+
+The natives of Tyree have many traditions of vessels having struck on
+the Skerryvore and gone to pieces; but, as might have been anticipated,
+few traces of this were to be found on the Rocks themselves, the
+breach of sea which sweeps over them during storms being sufficient to
+remove any heavy bodies which might be left there after a shipwreck.
+Some relics, however, were found during the progress of the works, and
+among the rest an anchor which was fished up close to the Rock, and
+which appeared to have belonged to a vessel of about 150 tons burden.
+It had been wasted to a perfect shadow by the action of the sea, and
+was covered with a thick coating of seaweed and barnacles. Although,
+however, the Rocks themselves do not retain the proofs of the disasters
+of which they have been the cause, the shores of the neighbouring
+Islands, during the progress of the works, were frequently strewed with
+drift wreck in such a manner as clearly to indicate what had taken
+place on the shoals round the Skerryvore.
+
+       *       *       *       *       *
+
+On examining Plate II., it will be seen that what I have hitherto
+denominated the Skerryvore Reef, is a tract of foul ground, consisting
+of various small rocks, some always above the level of the sea, others
+covered at high water, and exposed only at low water, and others,
+again, constantly under the surface, but on which the sea is often seen
+to break after heavy gales from the westward. This cluster of rocks
+extends from Tyree in a south-westerly direction, leaving, however,
+between that island and the rock called Boinshly, the first of the
+great Skerryvore cluster, a passage of about five miles in breadth, and
+having a depth of thirteen fathoms at low water of spring tides, but
+not without hidden dangers, which line the rugged shores of Tyree from
+Kennavarah to Ben Hynish, and some of which lie farther off than might
+be expected. This passage is called the passage of Tyree; but it is by
+no means safe during strong and long continued gales, as the sea which
+rises between Tyree and Skerryvore, is such that no vessel can _live_
+in it. I have myself often seen it one field of white broken water, the
+whole way from Tyree to the Rock; and we know that the wreck of the
+Majestic, which occurred in 1841, during the progress of the works, was
+entirely caused by the heavy seas which she encountered off Boinshly.
+
+       *       *       *       *       *
+
+The principal rocks of the group, are called Boinshly, Bo-rhua, and
+Skerryvore, while those lying to the westward, which have been more
+recently laid down, have received the names of Mackenzie, Fresnel, and
+Stevenson.
+
+       *       *       *       *       *
+
+The rock called Boinshly lies about 3³⁄₄ miles from Skerryvore, and
+is of considerable extent. The origin of the names of the different
+rocks in the vicinity of Tyree is by no means clear, and very little
+assistance or information is to be obtained in this matter from the
+natives. The name of Boinshly is probably derived from the Gaelic words
+_boun_, signifying _bottom_, and _slighe_, _deceitful_, as indicative
+of the dangers of the place; but other interpretations have been put
+on it, and that which has been now given is by no means certain. In
+the course of the survey, several soundings were at considerable risk
+obtained, both upon this Rock itself, and in its immediate vicinity.
+The sea in that exposed situation is seldom so tranquil as to warrant
+an attempt to approach very near this Rock. The swell, which, in a
+greater or less degree, almost constantly prevails, is apt to impel,
+or seemingly draw the boat as by a kind of suction, upon the rock;
+and sometimes such accidents cannot be prevented, even although the
+greatest caution is used. Sudden _lifts_ of the sea, during an apparent
+calm, are common in all the more exposed parts of the coast, more
+especially in the Orkney and Zetland Isles, and on the shores of the
+most western of the Hebrides; and any one much accustomed to the use of
+boats on these shores, must have experienced the hazard of encountering
+such unexpected risings of the sea, more especially near shelving
+rocks, or in rapid tide-ways. In some places the boatmen apply the
+name of _lumps_ to these sudden waves. This effect is not felt to the
+same extent in attempting to reach a rock which is partially uncovered
+at low water, as a landing can, in such a case, often be effected on
+one side, at a time when the same rock on the opposite side, or a
+sunk rock just topping with the water, would, on every side, be quite
+unapproachable. From the soundings marked on the plan, it will be
+seen that shoal water extends all round Boinshly to distances varying
+from a quarter to half a mile. The sea breaks on the rock with great
+violence, and its position can easily be discovered from the island of
+Tyree by the white foam with which it is almost constantly surrounded,
+and which, in the heavy swells which sometimes accompany a dead calm,
+before or after a heavy gale of wind, rises to a prodigious height in
+a column or jet, resembling, at a distance, the play of a gigantic
+fountain. So high, indeed, does the sea rise on this shoal after heavy
+gales, that it often quite obscures the larger and more distant object
+of the Rock and Tower of the Skerryvore, even when viewed from the top
+of Ben Hynish in Tyree. The wooden barrack erected on the Skerryvore
+for the use of the workmen during the progress of the operations,
+although about sixty feet in height, was often lost sight of at Tyree
+by the uprising of the sea on Boinshly, and could be seen only during
+the calm that intervenes between returning waves.
+
+       *       *       *       *       *
+
+The next Rock that occurs is Bo-rhua, a name derived from the Celtic,
+and signifying, according to the natives, Red Rock. It lies about
+2³⁄₄ miles from Boinshly, and about one mile from the Skerryvore. The
+passage between it and Boinshly is clear, and has a depth of about
+fourteen fathoms; but it is too narrow to be safely navigated except
+by daylight, even under the most favourable circumstances, and then
+no mariner would run the risk of taking such a passage, but would
+prefer, even at some sacrifice of time, the fairway of the passage of
+Tyree. Bo-rhua is completely covered at high, but is dry at low water.
+The extent of rock uncovered is about forty feet by twenty feet, and
+the highest point of it is about six feet above low water level of
+spring tides. A small outlying pinnacle, about ten feet square, is
+also uncovered at low water. The depth immediately round Bo-rhua is
+considerable, from three to seven fathoms being found within fifty feet
+of it; and in this respect it differs from Boinshly, which, as already
+mentioned, is surrounded by shoal water for some distance. Between
+Bo-rhua and Skerryvore, however, which is a distance of about a mile,
+there cannot properly be said to be any clear navigable channel, as
+will be distinctly seen by referring to the plan. The whole of this
+tract may, in fact, be termed _foul ground_.
+
+       *       *       *       *       *
+
+The Skerryvore or chief rock, and the detached rocks immediately
+surrounding it, were surveyed with greater minuteness than the others,
+as it was at once apparent, that on this part of the reef alone could a
+suitable site for a lighthouse be found. The name is derived from the
+Gaelic, and signifies the Great Rock. It is very much wasted and cut
+up; the number of detached rocks, sunk and exposed, in its immediate
+neighbourhood, whose positions were determined during the survey,
+amounting to no fewer than 130. The depth of water between those
+different detached fragments, which extend over a surface of about a
+mile in length, by half a mile in breadth, is considerable, varying
+from 2¹⁄₂ to 8¹⁄₂ fathoms at low water of spring tides.
+
+       *       *       *       *       *
+
+The surface of the main or principal rock, on which the Lighthouse has
+been placed, measures, at the lowest tides, about 280 feet square. It
+is extremely irregular, and is intersected by many gullies or fissures,
+of considerable breadth, and of unlooked for depth, and which leave
+it solid only to the extent of 160 feet by 70 feet. The extremity of
+one of these gullies, at the south-east corner of the rock, forms the
+landing-creek, which is a narrow track of 30 feet wide, having deep
+water; and, with the help of some artificial clearing and dressing,
+which was executed with much difficulty, by blasting under water,
+while the other works were in progress, its sides and bottom are now
+comparatively smooth. At this place a landing can often be effected
+when the rock is unapproachable from any other quarter, although great
+inconvenience is felt from the surge, which finds its way from the
+opposite side of the rock, through the westward opening of the gulley
+in which the landing-place is situated.
+
+       *       *       *       *       *
+
+Another of the gullies, immediately to the south-east of the
+Lighthouse, was found, on examination, to undermine the rock to the
+extent of eight or ten feet, and to terminate in a hollow submarine
+chamber, which threw up a spout or jet of water about twenty feet high,
+resembling in appearance the Geyser of Iceland, and accompanied by a
+loud sound like the snorting of some sea monster. The effect of this
+marine _jet d’eau_ was at times extremely beautiful, the water being
+so much broken as to form a snow-white and opaque pillar, surrounded
+by a fine vapour, in which, during sunshine, beautiful rainbows
+were observed. But its beauties by no means reconciled us to the
+inconvenience and discomfort it occasioned, by drenching us whenever
+our work carried us near it. One calm day I contrived, at a very low
+tide, by means of ropes and a ladder, to explore the interior of the
+cavern, from which this fountain rose, and found it to terminate in a
+polished spherical chamber, about seven feet in diameter, its floor
+filled with boulders, whose incessant play had hollowed it out of the
+veined rock, and rendered its interior beautifully smooth and glassy.
+As I considered that this curious cavern penetrated too far, and came
+too close to what I had selected as the best foundation, I changed the
+site of the tower, so as to avoid any chance of its being undermined.
+I also deemed it prudent to fill up the cavity, to prevent its further
+extension, and at the same time to rid ourselves of the discomfort of
+being drenched by the column of water which spouted up from it, even
+during fine weather, when the sea was apparently calm. This gulley
+affords a good example of the power of pebbles kept constantly in play
+by the waves to wear down the hardest rock, and shews what extensive
+effects so insignificant an agent may effect in the course of time.
+
+       *       *       *       *       *
+
+Before the excavation for the foundation of the tower was made, a
+single conical loaf of rock, about five feet in diameter, rose to the
+height of eighteen feet above the level of high water, the greater part
+of the rest of its surface being about six feet above the tide mark.
+
+       *       *       *       *       *
+
+In addition to its shattered and disjointed appearance, the Skerryvore
+Rock presents, in another respect, a striking example of the action
+of the sea, which no one, on first landing on the rock, can fail
+to perceive. I allude to the glassy smoothness of its surface, a
+feature that existed to so remarkable an extent as to have proved
+throughout the whole duration of the work, but more especially at its
+commencement, a serious obstacle and hindrance to the operations.
+It may, at first sight, appear strange that this grievance should
+have been so much felt; but, when I mention that the landings
+were often made in very bad weather, it will be obvious that there
+was considerable danger in springing ashore from a boat in a heavy
+surf upon an irregular mass of rock as smooth and slippery as ice.
+The workmen were, in that respect, often sorely tried, and many
+inconvenient accidents occurred from falls. It was after one of these
+trials of patience, that the foreman of the masons was heard very
+graphically to describe a landing on the rock as “like climbing up
+the side of a bottle.” Instead of a weather-beaten rock, whitened by
+the dung of sea-fowls, and with marine crustacea adhering to it, the
+surface of the Skerryvore is smoothly polished by the action of the
+waves, every projecting angle or point is worn down, and the whole
+presents more the appearance of a mass of dark-coloured glass than a
+reef of gneiss-rock. Excepting in some of the more sheltered crevices,
+no marine crustacea find shelter; but different kinds of sea-plants
+grow upon it, in great abundance, at and below the low water mark.
+These plants are, doubtless, enabled to resist the action of the waves
+in the same way as the sapling, yielding to the blast, is preserved
+during the storm that uproots the aged and more stubborn oak.
+
+       *       *       *       *       *
+
+The rocks of Skerryvore have the same characteristics as those of the
+neighbourhood of Tyree, being what we may, perhaps, call a syenitic
+gneiss, as it consists of quartz, felspar, hornblende, and also mica.
+It will be seen, from the narrative of the progress of the works, that
+this rock was, from its hardness, exceedingly difficult and tedious
+to excavate. The only variation in the geology of the Skerryvore, is
+the presence of a trap rock, in the form of a dyke of basalt, which
+intersects the strata, and exhibits a fine specimen of the intrusion of
+igneous rocks. It is shewn in Plate, No. III., by a thick black line.
+
+       *       *       *       *       *
+
+Connected with this general view of the appearance and geology of the
+rock, it may be interesting also to notice, that a considerable mass
+of foreign matter, somewhat resembling, in its structure, a deposit
+of lime, was found in different places resting in horizontal layers
+of various thickness and size. This substance was found in pools or
+sheltered parts of the rock, about the level of high water mark, and,
+in some cases, even a little below it. It was so hard as to admit of a
+pretty high degree of polish; and emitted an offensive odour on being
+burned in the fire, or rubbed on a stone with water. It gave other
+clear indications of containing animal matter, and in other respects
+resembled the bergmeal and guano. To account for its presence in such a
+situation, seems rather a difficult problem. On sending a specimen of
+this material to my friend the Rev. Dr Fleming, Professor of Natural
+Philosophy in King’s College, Aberdeen, I received from him an analysis
+of the substance, and a concurrence in the opinion I had formed as to
+its containing animal matter; and Dr Fleming, indeed, expressed his
+belief that the matter in question is the indurated soil of birds, and
+had been deposited when the reef was more extensive, and the resort,
+and probably the breeding-place of sea-fowls.[3] How this singular
+formation should be found on the verge of the ocean, and even within
+the high water mark, in spite of winds and waves, or how it should
+have assumed the stratified structure which seems to indicate the
+depositation of successive layers in still water, are matters very
+difficult to be explained, without coming to the conclusion, that
+the uncovered surface of Skerryvore Rock must at some distant period
+have been much more extensive than at present, so as to permit the
+deposit to go on in an interior basin or lagoon, sheltered from the
+waves, and somewhat similar to those which Dr Darwin has described as
+characteristic of the Coral Isles of the Pacific. This supposition
+seems not at all improbable, as it does not require a great stretch of
+fancy to conceive, that at some period, the whole of the rocks in the
+immediate vicinity of Skerryvore, and extending perhaps even so far
+as Bo-rhua, may have been connected by a matrix of softer materials,
+which have gradually yielded to the action of the sea, leaving the
+harder portions to be smoothed and polished by the waves, and to assume
+the characteristic features of permanent rocks and sunk reefs which
+they now possess. There is also some countenance to such a view to be
+derived from the features of the neighbouring Island of Tyree, which
+contains numerous small lagoons, in which such deposits might be formed
+by the flocks of sea fowl which frequent them. Some of these pools are
+so near the shore, as to make it no difficult matter to conceive that
+their walls might be broken by the sea, and that they might eventually
+become part of it, and thus exhibit the phenomenon of deposits
+apparently lacustrine within the verge of the ocean.
+
+  [3] Dr Fleming has since obtained from Ichaboe indurated bird-soil or
+  guano, closely resembling that from the Skerryvore.
+
+       *       *       *       *       *
+
+Another remarkable feature which I observed in the Skerryvore Rock,
+was a deposit of gravel in the narrow crevices of the rock, which run
+nearly from north-east to south-west, dipping at an angle of 80° to
+the westward. In almost all of the fissures we found great quantities
+of small water worn boulders, less in size than a horsebean, and
+generally of the same materials as the rock itself. The boulders bore
+the appearance of having been forced into the fissures of the rock by
+some very powerful pressure, and were wedged hard into the crevices. In
+some cases a considerable quantity of softer matter containing iron was
+found, and in it the pebbles were imbedded. In the upper parts of the
+rock the crevices swarmed with centipedes of a reddish-brown colour.
+The rock was covered with sea fowl when first visited, and during heavy
+gales seals resorted to it.
+
+       *       *       *       *       *
+
+About three miles to the westward of Skerryvore lie Mackenzie’s Rock,
+Fresnel’s Rock, and Stevenson’s Rock, which, as will be seen from Plate
+II., are connected by a tract of foul ground of about a mile and a
+quarter in length. Those rocks are the western limit of what we have
+already denominated the Skerryvore Reef. The passage between them and
+the Skerryvore or main rock is clear, and has a depth of water varying
+from eleven to twenty-eight fathoms.
+
+       *       *       *       *       *
+
+Mackenzie’s Rock, which derives its name from the celebrated Marine
+Surveyor, is uncovered, at low water, to the extent of about forty
+yards, and consists of scattered patches of rock, one of which, at
+its highest part, rises about ten feet above high water mark of
+spring-tides. Fresnel’s and Stevenson’s Rocks are always under water;
+but the sea is often seen to break violently over them, as well as
+over the whole stretch of the sunken reefs which extend between them.
+The first of those rocks is indebted for its name to the great optical
+philosopher, who so greatly improved lighthouses; and the second bears
+the name of the surveyor who first laid down the rock,--the late
+Engineer of the Northern Lights Board.
+
+       *       *       *       *       *
+
+During the progress of the survey, a register of the rise and fall of
+the tides was regularly kept at Hynish on the neighbouring Island of
+Tyree; and from those observations it was determined, that the rise at
+that place is between twelve and thirteen feet at high spring tides,
+and three feet at dead low neap tides; and observations subsequently
+made while the works were in progress, gave the same results at the
+Rock of Skerryvore. It is high water at the Rock at full and change of
+the moon, at five hours and twenty-five minutes. The tides round the
+Skerryvore are not remarkable for their rapidity. In spring-tides the
+velocity is between four and five miles, and in neap-tides between two
+and three miles an hour. The flood sets to the N.N.E., and the ebb to
+the S.S.W.
+
+
+CHAPTER II.
+
+PRELIMINARY ARRANGEMENTS AND WORKS, INCLUDING SURVEY OF THE ROCKS, AND
+OPENING OF QUARRIES, FROM 1834 to 1837.
+
+  ~Survey of the Skerryvore Rocks.~
+
+In this chapter I shall very briefly notice those preliminary
+arrangements which may be said to have been in a great measure
+preparatory to the commencement of the work itself. It has been already
+stated, that the erection of the Lighthouse was provided for in the Act
+of 1814; but so formidable did this work appear, that although it was
+repeatedly under consideration, it was not until the General Meeting
+of the Board, on the 8th July 1834, that any measures were taken to
+carry into effect the provisions of the Act. On that occasion it was
+moved by the late Mr MACONOCHIE, Sheriff of Orkney and Zetland, that
+the Engineer should be instructed to make the necessary survey, and to
+report as to the expense of erecting the Lighthouse. In terms of this
+remit, the survey of the Rocks was commenced in the autumn of 1834; but
+from the broken state of the weather, little was effected at that time
+beyond making the triangulation; and it was not until the summer of
+1835 that the survey was completed from which the Chart, Plate No. II.
+was constructed. This survey was attended with much more labour than
+its extent would lead one to suppose, in consequence of its embracing
+the entire range of operations required in a more extensive nautical
+survey, and combining with the ordinary details required for a Chart,
+the minute accuracy in regard to surface and levels, which are always
+necessary for the purposes of the Engineer.
+
+       *       *       *       *       *
+
+The first step was the measurement of a base line in the low lands
+of the adjoining Island of Tyree, which, owing to the distance and
+disadvantageous position of that island, could not be satisfactorily
+extended to the Rock without fixing stations in some of the more
+distant islands; and in the course of the work not fewer than twenty
+land triangles were measured. The calculations of the distances founded
+on this triangulation agreed with those afterwards obtained from the
+data of the Trigonometrical Survey, which were kindly furnished to me
+by Captain Yolland of the Royal Engineers, in 1843. For the purpose
+of making the soundings and laying down the sunken rocks, an entirely
+separate triangulation, based upon and connected with that which has
+already been noticed, became necessary, as the land objects were
+too distant, and their relative positions were such as to render it
+difficult by observations from them alone to determine any stations on
+the sea. Buoys were therefore moored at convenient points, and their
+positions determined by a subsidiary triangulation, so as to form a
+net-work of triangles between the shore and the Skerryvore Rock. The
+distances between these buoys were afterwards used as the bases of
+imaginary triangles, having points of sounding or shoals in their apex;
+and the angles subtended by those distances being measured by the
+sextant, the positions of the shoals or soundings were thence easily
+deduced and protracted on the Chart.[4] In connection also with the
+soundings whose positions were determined in the way above described,
+a complete set of tide observations was made, extending over a period
+of about six weeks. Those tide observations were connected in point of
+time, with the soundings, and were employed as the means of correcting
+the observed depths taken with the sounding-line, so as to give the
+true depth in reference to the high or low water of a given tide.
+Accurate measurements, and minute sections, were also made of the rocks
+in reference to the tide-level, and more especially of the main rock,
+on which alone it was obvious, from the first inspection, that the
+Lighthouse Tower could be erected. In the course of this survey, the
+positions of upwards of 140 rocks were determined, and laid down on the
+Chart, and 500 soundings were taken, and their positions protracted.
+An interesting fact was also noticed regarding the mean level of all
+the tides which had been watched during the period of about six weeks,
+as above noticed, viz., that the point half way between the high and
+low water of every tide is on _one and the same level_. This fact
+regarding the tides was, it is believed, first detected by my Father,
+in the course of some tidal observations which he made in the Dornoch
+Frith in 1830, and has since been observed in the Frith of Forth in
+1833, and again on the shores of the Isle of Man, and at Liverpool. The
+agreement of so many observations by various persons at places on the
+opposite shores of the Kingdom, seems to imply the universality of this
+phenomenon in the British Seas; and the position of Skerryvore would
+lead to the belief, that it is not confined to narrow seas, but that
+it exists in the ocean. I cannot dismiss the subject of the survey,
+without mentioning the late Mr James Ritson, who acted as principal
+assistant surveyor, and to whose zeal and intelligence so much of its
+accuracy is to be attributed. The deep gulley which intersects the
+main Rock from N.E. to S.W., and across which he one day sprang while
+it was filled with a breaking wave, bears his name, as a memorial of
+his activity and perseverance. At the close of the survey in 1835,
+the station-pole was left wedged and batted into one of the fissures
+or crevices of the Rock, and a cask of water was firmly _lashed_ to
+ring-bolts in a cleft of the highest part of the Rock, in the hope that
+it might possibly prove useful to some shipwrecked seamen.
+
+  [4] _Vide_ Stevenson’s Marine Surveying and Hydrometry. Edinburgh,
+  1842, p. 144.
+
+       *       *       *       *       *
+
+For the purposes of navigation generally, a survey merely indicating
+the position and extent of the foul ground would have been sufficient.
+But in connection with the work which was about to be commenced,
+it was particularly desirable to have exact details of the depths,
+rocks, and shallows of the surrounding sea, with the nature of the
+bottom, accurately laid down; and our experience during the course of
+the work, more than once shewed how essential was the possession of
+minute topographic information to the safety of the shipping attending
+the works; more especially as some of the vessels lay very near the
+rocks, and were frequently driven, by a sudden change of wind, to seek
+shelter, during the darkest nights, among the neighbouring islands.
+
+       *       *       *       *       *
+
+Until this time the greatest ignorance prevailed amongst seamen as to
+the extent of the Reef, which had never before been minutely surveyed.
+Of this some proofs occurred even during the progress of the survey;
+for several vessels came so near the Rocks as to cause, in the minds
+of the surveyors, who witnessed their temerity, serious fears for
+their safety. On one occasion, in particular, a large vessel belonging
+to Yarmouth, with a cargo of timber, was actually boarded between
+Mackenzie’s Rock and the main Rock of Skerryvore by the surveyors,
+who warned the master of his danger in having so nearly approached
+these rocks, of the existence of which his chart gave no indication.
+On another occasion, a vessel belonging to Newcastle was boarded while
+passing between Bo-Rhua and the main Rock; and so little, indeed, had
+the master (whose chart terminated with the main Rock, and shewed
+nothing of Bo-Rhua) been dreaming of danger, or fancying that he was
+within a cable’s length of the reef, that he was found lying at ease
+on the companion, enjoying his pipe, with his wife sitting beside him
+knitting stockings.
+
+       *       *       *       *       *
+
+  ~Disadvantages of Tyree.~
+
+Much preliminary investigation was necessarily occasioned by the
+difficulties and disadvantages arising from the remote situation of
+the island in which a great part of the works was to be carried on.
+Not only is the Rock itself often inaccessible and dangerous, being
+surrounded by numerous shoals, and visited by the heaviest seas of
+the Atlantic; but what gave rise to no small part of the difficulties
+which attended this work, was the nature of the neighbouring Island
+of Tyree. This island is unhappily destitute of any shelter for
+shipping, a fact which was noticed as a hinderance to its improvement,
+upwards of 140 years ago, by Martin, in his well-known description
+of the Western Islands.[5] Nor is its interior more attractive; for
+although some parts of the soil when cultivated are excellent, the
+greater part of its surface is composed of sand. It was therefore
+obvious, at a glance, that Tyree was one of those places to which
+every thing must be brought; and this is not much to be wondered at,
+as the population, who, on a surface not exceeding 27 square miles,
+amounted in 1841 to 4687 souls, labour under all the disadvantages of
+remoteness from markets, inaccessible shores and stormy seas, and the
+oft-recurring toil of seeking fuel (of which Tyree itself is destitute)
+from the Island of Mull, nearly 30 miles distant, through a stormy
+sea. It is said that this total absence of fuel in Tyree is the result
+of the reckless manner in which it was wasted, in former days, in the
+preparation of whisky; but, however this may be, certain it is that
+the want of fuel greatly depresses the condition of the people. For
+our works, therefore, craftsmen of every sort were to be transported,
+houses were to be built for their reception, provisions and fuel were
+to be imported, and tools and implements of every kind were to be made.
+
+  [5] A Description of the Western Islands of Scotland, &c., by M.
+  Martin, Gent. London, 1703. _Vide_ 2d Edition of 1716, p. 267.
+
+       *       *       *       *       *
+
+  ~Pier and workyard at Hynish Tyree.~
+
+In the course of the survey, much attention had been bestowed upon
+the selection of a convenient place for a workyard in Tyree for the
+preparation of materials, and in examining its rugged shores in quest
+of the best site for a Harbour, for the shipment of the building
+materials for the Rock, and for the all-important purpose of enabling
+the future attending vessel to lie in safety within sight of signals
+from the Rock, when the Light should come to be exhibited to the
+public. The point chosen for this establishment was Hynish, which,
+though twelve miles distant, is, nevertheless, the nearest creek to the
+Skerryvore Rock, and which, however exposed it may be, if compared
+with creeks elsewhere dignified with the name of Harbour, certainly
+affords as good prospect of shelter as any other part of the Island of
+Tyree, and is, in this respect, greatly to be preferred to any other
+place within sight of the Rock. A deputation of the Commissioners
+visited the Skerryvore in the month of July 1836, and concurred with
+the Engineer in regard to his choice of Hynish as a site for the
+Harbour and establishment.
+
+       *       *       *       *       *
+
+  ~Quarries at Hynish.~
+
+Another most important point of inquiry was regarding the materials
+for building the Lighthouse; and on this subject the suggestions in a
+Report by the Engineer, of the 31st December 1835, were followed, which
+proposed the opening of quarries among the gneiss rocks around Hynish.
+Much facility was afforded by the liberality of the late Duke of
+Argyll, the proprietor of Tyree, who granted to the Commissioners free
+permission “to quarry materials for the purpose of the Lighthouse, on
+any part of the Argyll estates.” This freedom was generously continued
+by the present Duke, who has all along taken a lively interest in
+the success of the works. In terms, therefore, of the Engineer’s
+recommendations contained in the above noticed Report, Mr James Scott
+and fourteen quarriers were employed, during the summers of 1836 and
+1837, in opening quarries, with very promising appearances of final
+success, among the gneiss rocks near Hynish Point. In the summer of
+1837, Mr Scott and his party turned out about 3800 cubic feet of rock,
+capable of being applied to the purposes of squared masonry, and a very
+large quantity of stones fit for rubble work. This produce, although
+small, if contrasted with that of established quarries, is by no means
+despicable, when the _force_ employed and all the disadvantages of the
+situation are considered; and if the nature of the material, which is
+full of rents and fissures (technically called _dries_ and _cutters_),
+the frequent deceptions attending the opening of new quarries, the
+excessive hardness and unworkable nature of the rock, the quality and
+size of the blocks required to entitle them to claim a place in a
+marine tower, and the great loss of time, caused by the badness of the
+weather, be considered, it will not appear that Mr Scott and his party
+had been eating the bread of idleness.
+
+       *       *       *       *       *
+
+In the mean time, measures had been taken for obtaining from his
+Grace the Duke of Argyll a feu of fifteen acres of ground at Hynish,
+for carrying on the works, with a view to its being finally occupied
+as an establishment for the crew of the vessel which was to attend
+the Lighthouse, and the families of the four lightkeepers, as well
+as for the site of the harbour. To this was added a lease of thirty
+acres, for the various purposes connected with a workyard, and such
+an establishment as seemed necessary for carrying on the work. A
+subject of anxious deliberation with the Board, was the construction
+of the harbour at Hynish for the vessels engaged in the service of
+the work; and the Commissioners, on the 24th May 1837, authorized the
+Engineer to make arrangements for commencing the formation of the
+Pier. The work was, accordingly, undertaken, in terms of his Reports
+of the 31st December 1835, and 27th February 1836; and the summer of
+1837 was chiefly occupied in preparing a wharf, mostly composed of
+_pierres-perdues_,[6] and in the opening of the quarry already noticed.
+Such may serve as a brief and somewhat desultory notice of the work
+during the seasons of 1836 and 1837, after which it appeared to the
+Board that the operations must soon assume such an aspect as to require
+the superintendence of a committee of their number, as well as that of
+an Engineer specially entrusted with the management of the work.
+
+  [6] Blocks rough from the quarry, which are dropt or thrown
+  promiscuously into the sea.
+
+       *       *       *       *       *
+
+  ~Skerryvore Committee appointed.~
+
+At the meeting of the Board, on the 8th December 1837, a Committee
+of their number was accordingly named, to superintend the erection
+of the Lighthouse. This Committee consisted of--ROBERT BRUCE, Esq.,
+Sheriff of Argyllshire; ANDREW MURRAY, Esq., Sheriff of Aberdeenshire;
+ROBERT THOMSON, Esq., Sheriff of Caithness; and the late JAMES
+MACONOCHIE, Esq., Sheriff of Orkney and Zetland; and, shortly after its
+appointment, the Committee, on the motion of Mr BRUCE, the Chairman,
+appointed me Engineer for the work.
+
+       *       *       *       *       *
+
+Among the first matters which engaged the attention of this Committee,
+was a Report from the Engineer, dated the 30th January 1838, in which
+the necessity of erecting a wooden barrack, as a place of shelter for
+the workmen on the Rock, was pointed out; the general arrangements
+for carrying on the operations were described; and the building of
+a steam-tender, to act as a towing vessel for the stone lighters
+between the workyard in Tyree and the Rock, was also recommended.
+The Report was accompanied by a detailed requisition or estimate for
+the operations of the ensuing season, amounting to L.15,000 : 3 : 3;
+of which sum it was proposed to expend about one-third in building
+a steam-tender, and the rest in erecting the wooden barrack on the
+Rock, and in providing tools and materials for the work, as well as
+in the wages of men to be employed in preparing the foundation of the
+Lighthouse Tower, and in building the Pier, and dressing stones at
+Hynish.
+
+       *       *       *       *       *
+
+The Committee, after considerable deliberation, sanctioned the various
+items of the estimate, but hesitated to embark in the expense of
+building a steamer, until a fruitless correspondence with various ports
+of the kingdom, with the view of purchasing an old vessel, satisfied
+them of the necessity of building a tender expressly for the purpose.
+
+       *       *       *       *       *
+
+Offers were immediately received from various parties at Greenock
+for the preparation of the wooden barrack, which was soon afterwards
+commenced by the late Mr John Fleming, house-carpenter, who was the
+successful competitor.
+
+
+CHAPTER III.
+
+ON THE CONSTRUCTION OF LIGHTHOUSE TOWERS.
+
+In this chapter I purpose, in the first place, to make a few
+observations regarding the construction of Lighthouse Towers in
+situations which are exposed to the assault of the waves, and
+afterwards to give a short notice of the design which I adopted for
+the Tower on the Skerryvore Rock. In making a design for a Lighthouse
+Tower in an exposed situation, numerous considerations at once present
+themselves to the Engineer; and it is difficult to assign to any one
+of them a priority in the train of thought which eventually conducts
+him to the formation of his plan. These considerations, however, may
+be conveniently divided into two classes:--_1st_, Those which refer
+to elements common to Lighthouses in all situations, and differ only
+in amount, such as the height of the Tower necessary for commanding
+a given visible horizon, and the accommodation required for the
+Lightkeepers and the Stores; and, _2d_, Those which are peculiar to
+Towers in exposed situations, and which refer solely to their fitness
+to resist the force of the waves which tend to destroy them. The
+first class of considerations is so extremely simple, as to require
+few remarks in this place. The distance at which it is desirable that
+a light should be visible being ascertained, with reference to the
+nature of the surrounding seas and the extent to which any dangerous
+or foul ground lies seaward of the proposed Lighthouse, the height
+of the Tower is at once determined by means of the known relations
+which subsist between the spheroidicity of the earth, the effects
+of atmospheric refraction, and the height required for an object
+which is to be seen from a given distance. The question regarding
+the space to be provided in the interior of the Tower, can only be
+properly answered by a person who has a minute practical acquaintance
+with the peculiar wants and the internal economy of Lighthouses. The
+accommodation required for Lighthouses in exposed situations must,
+in a considerable degree, depend upon the greater or less facility
+of access to them, and the opportunities for replenishing the stores
+of all kinds which are in daily consumption. In such places, also,
+the risk of accidents naturally leads to the precaution of retaining
+additional Lightkeepers, and of having duplicates or even triplets of
+those parts of the apparatus that are liable to be injured. Of such
+circumstances, corresponding extension of the space devoted to the
+reception of Stores and the accommodation of the Lightkeepers, is the
+necessary consequence. In the long nights of a Scotch winter, when the
+lamps are kept burning for about seventeen hours, during which time
+they are never left for a moment without the superintendence of at
+least one Keeper, the care of the light, even in the most favourable
+situations, necessarily occupies at least two persons; but in places
+like the Eddystone, the Bell Rock, and the Skerryvore, where it
+sometimes happens that six or eight weeks elapse without its being
+possible to effect a landing, it has been thought necessary that there
+should never be fewer than three Keepers on duty. This addition to
+the ordinary establishment of a Lighthouse calls for a greater number
+of sleeping-cabins, and, at the same time, involves a corresponding
+increase in the supply of water, fuel and other provisions, requiring
+much additional stowage. So far, therefore, a Light Tower in an exposed
+situation, differs from one on shore only in the extent of its internal
+accommodation.
+
+The second class of considerations, which must guide the Engineer in
+framing a design for a Light Tower which is exposed to the force of
+the waves, refers solely to the stability of the building.
+
+The first observation which must occur to any one who considers the
+subject is, that we know little of the nature, amount and modifications
+of the forces, on the proper investigation of which the application
+of the principle which regulates the construction must be based.
+When it is recollected, that, so far from possessing any accurate
+information regarding the momentum of the waves, we have little more
+than conjecture to guide us, it will be obvious, that we are not in
+a situation to estimate the power or intensity of those shocks to
+which Sea Towers are subject; and much less can we pretend to deal
+with the variations of these forces which shoals and obstructing rocks
+produce, or to determine the power of the waves as destructive agents.
+No systematic or intelligible attempt has been made practically to
+measure the force of the waves, so as to furnish the Engineer with a
+_constant_ to guide him in his attempts to oppose the inroads of the
+ocean. The only experiments, indeed, on the subject, with which I am
+acquainted, are those of Mr Thomas Stevenson, Civil-Engineer, who had
+long entertained the idea of registering the force of the impulse of
+the waves, and lately contrived an instrument for the purpose, which
+he has applied at various parts of the coast. I therefore gladly avail
+myself of the present opportunity, to give a brief statement of the
+results indicated by it, as contained in a paper by the inventor, which
+appeared in the Transactions of the Royal Society of Edinburgh of 20th
+January 1845, and of which a digest will be found in the Appendix, as
+any attempt to throw light upon this most obscure, but highly important
+subject, cannot fail to be interesting, not merely to the philosopher,
+but to the Marine Architect. It would naturally be expected, that
+the force of the waves should vary according to the season of the
+year, and the nature of the exposure, and this expectation is fully
+justified by the indications of the Marine Dynamometer. Thus it
+appears, that during five summer months of 1843 and 1844, the average
+indications registered at different places near Tyree and Skerryvore,
+gave 611 lb. of pressure per square foot of surface exposed to the
+waves; while the average for the winter months for the same places
+during those two years, gave 2086 lb. per square foot, or upwards of
+_three times_ that of the summer months. It also appears, that the
+greatest result as yet obtained at Skerryvore Rock was 4335 lb. per
+square foot; while that observed on the Bell Rock was 3013 lb., or
+_one-fourth part_ less than that of Skerryvore. But these experiments
+have not been continued long enough as yet to render them available
+for the Engineer. In the present state of our information, therefore,
+we cannot be said to possess the elements of exact investigation, and
+must consequently be guided chiefly by the results of those numerous
+cases which observation collects, and which reason arranges, in the
+form which constitutes what is called _professional experience_. This
+kind of experience can only be acquired by long habit in carefully
+observing the appearance and effects of waves in different situations,
+and under various circumstances. We must attend to their magnitude
+and velocity, their level in regard to the rocks on which they break,
+the height of the spray caused by their collision against the shore,
+the masses of rock which they have been able to move, and those which
+have successfully resisted their assault; as also, where such exist,
+the slopes of the shores produced by the waves, viewed in connection
+with the nature of the materials composing the beach, with many other
+transient features which an experienced eye seizes and fixes in the
+mind as elements of primary importance in determining the power of
+the sea to produce certain effects. Such phenomena, with all their
+features and circumstances, we may carry in our recollection; and by
+comparing them with what has been observed at places where we know that
+artificial works have resisted the shocks of the waves, we may in some
+cases successfully arrive at a conclusion as to what works will, at
+all events, be within the bounds of safety. We must not, however, in
+any case, venture to approach too near the limit of stability, so long
+as we continue to labour under our present disadvantages of defective
+information on some of the most important elements in the inquiry. If
+it be asked, therefore, how the size and form of buildings exposed to
+the shock of the waves are to be determined, the answer must be, that,
+in any given case, the problem is to be solved chiefly by the union of
+an extensive knowledge of what the sea has done against man, and how,
+and to what extent, man has succeeded in controlling the sea; together
+with a cautious comparison of the circumstances which modify and affect
+_any given case_ which has not been the object of direct experience;
+nor does it seem possible as yet to found the art of Engineering, in
+so far as it refers to this class of works, upon any more exact basis.
+The uncertainty which must ever attend such reasoning can only, it is
+obvious, be dispelled by actual experience of the result; and time only
+can test the success of our schemes in cases of difficulty.
+
+       *       *       *       *       *
+
+A primary inquiry, in regard to Towers in an exposed situation, is the
+question, whether their stability should depend upon their _strength_
+or their _weight_; or, in other words, on their _cohesion_, or their
+_inertia_? In preferring _weight_ to _strength_, we more closely
+follow the course pointed out by the analogy of nature; and this must
+not be regarded as a mere notional advantage, for the more close the
+analogy between nature and our works, the less difficulty we shall
+experience in passing from nature to art, and the more directly will
+our observations on natural phenomena bear upon the artificial project.
+If, for example, we make a series of observations on the force of the
+sea, as exerted on masses of rock, and endeavour to draw from these
+observations some conclusions as to the amount and direction of that
+force, as exhibited by the masses of rock which resist it successfully
+and the forms which these masses assume, we shall pass naturally to
+the determination of the _mass_ and _form_ of a building which may be
+capable of opposing similar forces, as we conclude, with some reason,
+that the mass and form of the natural rock are exponents of the amount
+and direction of the forces they have so long continued to resist.
+It will readily be perceived, that we are in a very different and
+less advantageous position when we attempt, from such observations of
+natural phenomena, in which _weight_ is solely concerned, to deduce
+the _strength_ of an artificial fabric capable of resisting the same
+forces; for we must at once pass from one category to another, and
+endeavour to determine the _strength_ of a comparatively _light_ object
+which shall be able to sustain the same shock, which we know, by direct
+experience, may be resisted by a given _weight_. Another very obvious
+reason why we should prefer _mass_ and _weight_ to _strength_, as a
+source of stability, is, that the effect of mere _inertia_ is constant
+and unchangeable in its nature; while the _strength_ which results,
+even from the most judiciously disposed and well executed fixtures of a
+comparatively light fabric, is constantly subject to be impaired by the
+loosening of such fixtures, occasioned by the almost incessant tremor
+to which structures of this kind must be subject, from the beating of
+the waves.[7] Mass, therefore, seems to be a source of stability, the
+effect of which is at once apprehended by the mind, as more in harmony
+with the conservative principles of nature, and unquestionably less
+liable to be deteriorated than the _strength_, which depends upon the
+careful proportion and adjustment of parts.
+
+  [7] It was chiefly on these grounds that the Commissioners of
+  Northern Lights, after consulting a Committee of the Royal Society of
+  Edinburgh, and Messrs Cubitt and Rennie, Civil Engineers, rejected
+  the design of Captain Sir Samuel Brown, R. N., who volunteered a
+  proposal to build an Iron Pillar at the time that the erection of the
+  Skerryvore Lighthouse was determined on in 1835.
+
+       *       *       *       *       *
+
+Having satisfied himself that _weight_ is the most eligible source of
+stability, the next step of the Engineer is to inquire what quantity
+of matter is necessary to produce stability, and what is the most
+advantageous form for its arrangement in a tower. The first question,
+which respects the mass to be employed, is, as already stated, one of
+the utmost difficulty, and can be solved by experience alone, directed
+by that natural sagacity which Smeaton, in his account of his own
+thoughts on the subject, with much _naïveté_, terms ‘_feelings_,’ in
+contradistinction to that more accurate process of deduction which he
+calls ‘_calculation_.’ It is very difficult, for example, to conceive
+that the waves could displace a cylindric block of granite, 25 feet
+in diameter and 10 feet high, which would contain about 380 tons, and
+we almost _feel_ that they could not do so. If, in order to test the
+soundness of this expectation, we appeal to such experience as we
+possess, and apply to the _largest vertical section_ of such a solid,
+the greatest force yet indicated by my brother’s Marine Dynamometer,
+which, as already stated, is 4335 lb. per square foot, we shall obtain
+a pressure of 484 tons, which, being reduced by _one-half_[8] for the
+loss of force occasioned by the convexity of the opposing cylindric
+surface, gives 242 tons, as the greatest force of the waves tending to
+displace the cylinder. But in the extreme case we have now supposed
+the solid will be entirely immersed in the water, and its efficient
+weight will thus be reduced by 140 tons, or the weight of an equal bulk
+of sea-water; and the remaining weight of 240 tons, by which it will
+resist the force of the waves, will be almost exactly equal to the
+pressure which they exert. This imaginary cylinder may, however, be
+regarded as still within the limits of safety, because the waves could
+not overturn it, unless their pressure exceeded the weight of the block
+in a ratio greater than that of its diameter to its height, which in
+this case is that of 25 to 10, or 2¹⁄₂ times. In order, therefore, to
+endanger the stability of the solid by overturning it, the pressure,
+instead of being 240 tons, must be 600 tons.[9] We have thus seen, that
+the cylinder is secure from the chance of being overturned; but we have
+yet to consider how far it is exempt from the risk of being displaced
+by the pressure of the waves, causing it to slide along the surface of
+the Rock, owing to deficiency of friction between the two surfaces
+in contact. The block, for our present purposes, may be regarded as
+_monolithic_, either being really so or as a mass composed of parts
+so united by joggles, treenails and mortar, as to be free from any
+tendency to disintegration by the force of the waves; and in this case
+the stability of the cylinder will depend upon the amount of friction
+opposing the pressure of the waves which tends to produce a sliding
+movement. It appears, by some experiments of M. Rondelet,[10] that the
+friction of a block of stone sliding on a chiselled floor of rock is
+equal to ⁷⁄₁₀ths of its own weight; and we should thus obtain in the
+present instance 168 tons, as the amount of friction tending to resist
+the pressure of the waves, which would therefore exert a power superior
+to that resistance by 74 tons.[11] But this excess of force would be
+easily neutralized by the adhesion of the mortar and the abutment of
+the block against the sides of the foundation pit into which Lighthouse
+Towers in such exposed places are generally sunk in the solid rock.
+When, in addition to these considerations, we learn that the solid
+frustum, or lower part of the Eddystone Tower, which has weathered so
+many storms for the last ninety years, does not greatly exceed in mass
+the imaginary cylindric block which I have spoken of, our confidence in
+the stability of the cylinder is greatly increased. Our belief receives
+a still farther confirmation from the fact, that the strongest instance
+recorded of the power of the waves, falls considerably short of the
+case which we have just imagined. The instance alluded to is given
+in Mr Lyell’s Geology, on the authority of the Reverend George Low,
+of Fetlar, in Zetland, who mentions, that a block, whose dimensions
+seem to give us reason to estimate its weight at nearly 300 tons (or
+about _one-fifth_ less than that of the cylinder), was moved over a
+point, and thrown into the sea; and it must be remembered, that the
+form of this block, which was only 5 feet thick and about 40 feet long,
+rendered it very susceptible of a sliding motion, and must have greatly
+aided its transport. We may therefore not unreasonably conclude, that,
+in designing such a tower, it is safe to assume a mass which our own
+judgment and recorded facts seem to concur in pronouncing beyond the
+power of the greatest waves, as fixing the _lowest_ limit to which the
+contents of the proposed edifice may be reduced.
+
+   [8] This reduction seems to be warranted by the results of some
+  experiments of Bossut.
+
+   [9] This is the product of 240 tons, by the ratio of 2·5.
+
+  [10] L’art de bâtir.
+
+  [11] The number 168 is ⁷⁄₁₀ths of 240, which is the weight of the
+  cylinder, reduced by the weight of an equal bulk of salt water; and
+  74 is the excess of 242 tons, the pressure of the waves, above 168,
+  the amount of friction.
+
+       *       *       *       *       *
+
+There are several circumstances, however, which tend to increase or
+diminish the stability of the same mass exposed to the same forces.
+Of these a very prominent one is the _form_ of the mass, which may be
+so modified as to offer more or less resistance to the forces which
+assault the building. Thus a parallelopiped would be a much less
+suitable form for a sea tower than a cylinder, and so proportionally of
+all the polygonal prisms which may occur between these two extremes.
+I remember having heard it proposed, in the course of conversation,
+by a non-professional friend, that Lighthouse Towers might be formed
+in such a manner, that each horizontal section should be a wedge with
+its narrow end directed to the greatest assaulting force. This notion
+is in itself not destitute of ingenuity; for, if the circumstances to
+which it is to be adapted were constant, we should thereby present the
+form of least resistance, and, at the same time, the greatest depth
+and strength of the building to the line of greatest impulse. But the
+notion is wholly impracticable, because the direction of the winds and
+waves is so variable, as to render it almost certain that a Tower so
+constructed would, on some occasion, be assaulted in the line of its
+thinnest section; and thus, what might in one case be an advantage,
+would, in the event of such a change in the point of attack, become
+a great source of weakness, as the flat side of the wedge would then
+be opposed to the force, thereby presenting to the direct assault
+of the waves the largest surface, with, at the same time, the most
+disadvantageous disposition of the resisting matter. There seems little
+reason, therefore, for any doubt as to the circular section being
+practically the most suitable for a Tower exposed in every direction to
+the force of the waves.
+
+       *       *       *       *       *
+
+Next to this, and hardly to be separated from it, inasmuch as it
+involves the question regarding the form of the Tower, is the position
+of the centre of gravity. The stability of any solid will, in general,
+greatly depend upon its centre of gravity being placed as low as
+possible; and the general sectional form which this notion of stability
+indicates is that of a triangle. This figure revolving on its vertical
+axis, must, of course, generate a cone as the solid, which has its
+centre of gravity most advantageously placed, while its rounded contour
+would oppose the _least_ resistance which is attainable in _every_
+direction. Whether, therefore, we make _strength_ or _weight_ the
+source of stability, the conic frustum seems, abstractly speaking,
+the most advantageous form for a high Tower. But there are various
+considerations which concur to modify this general conclusion, and, in
+practice, to render the conical form less eligible than might at first
+be imagined. Of these considerations, the most prominent theoretically,
+although, I must confess, not the most influential in guiding our
+practice, is, that the base of the cone must in many cases meet the
+foundation on which the Tower is to stand, in such a manner, as to form
+an angular space in which the waves may break with violence. The second
+objection is more considerable in practice, and is founded on the
+disadvantageous arrangement of the materials, which would take place
+in a conic frustum carried to the great height which Lighthouse Towers
+must generally attain, in order to render them useful as sea-marks.
+Towards its top, the Tower cannot be assaulted with so great a force as
+at the base, or, rather, its top is entirely above the shock of heavy
+waves; and, as the conoidal solid should be prolate in proportion to
+the intensity of the shock which it must resist, it follows that, if
+the base be constructed as a frustum of a given cone, the top part
+ought to be formed of successive frusta of other cones, gradually less
+prolate than that of the base. But it is obvious, that the union of
+frusta of different cones, independently of the objection which might
+be urged against the _sudden_ change of direction at their junction,
+as affording the waves a point for advantageous assault, would form
+a figure of inharmonious and unpleasing contour, circumstances which
+necessarily lead to the adoption of a curve osculating the outline of
+the successive frusta composing the Tower; and hence, we can hardly
+doubt, has really arisen in the mind of Smeaton the beautiful form
+which his genius invented for the Lighthouse Tower of the Eddystone,
+and which subsequent Engineers have contented themselves to copy, as
+the general outline which meets all the conditions of the problem
+which they have to solve. And here I cannot help observing, as an
+interesting, and by no means unusual, psychological fact, that men
+sometimes appear to be conducted to a right conclusion by an erroneous
+train of reasoning; and such, from his “Narrative,” we are led to
+believe, must have been the case with Smeaton in his own conception
+of the form most suitable for his great work. In that “Narrative” (§
+81), he seems to imply, that the trunk of an oak was the counterpart
+or antitype of that form which his (§ 246) “feelings, rather than
+_calculations_,” led him to prefer. Now, there is no analogy between
+the case of the tree and that of the Lighthouse, the tree being
+assaulted at the top, and the Lighthouse at the base; and although
+Smeaton goes on, in the course of the paragraph above alluded to, to
+suppose the branches to be cut off, and water to wash round the base of
+the oak, it is to be feared the analogy is not thereby strengthened;
+as the _materials_ composing the tree and the tower are so different,
+that it is impossible to imagine that the same opposing forces can
+be resisted by similar properties in both. It is obvious, indeed,
+that Smeaton has unconsciously contrived to obscure his own clear
+conceptions in his attempt to connect them with a fancied natural
+analogy between a tree which is shaken by the _wind_ acting on its
+_bushy top_, and which resists its enemy by the _strength_ of its
+fibrous texture and wide-spreading ligamentous roots, and a tower of
+masonry, whose _weight_ and _friction_ alone enable it to meet the
+assault of the _waves_ which wash round its _base_; and it is very
+singular, that, throughout his reasonings on this subject, he does
+not appear to have regarded those properties of the tree which he has
+most fitly characterized as “its elasticity,” and the “coherence of
+its parts.” One is tempted to conclude that Smeaton had, in the first
+place, reasoned quite soundly, and arrived by a perfectly legitimate
+process at his true conclusion; and that it was only in the vain
+attempt to justify these conclusions to others, and convey to them
+conceptions which a large class of minds can never receive, that he has
+misrepresented his own mode of reasoning. In the paragraph preceding
+that which refers to the tree (§ 80), he has, in point of fact, clearly
+developed the true views of the subject; and, with the single exception
+of the allusion to the oak, he has discussed the question throughout in
+a masterly style.
+
+       *       *       *       *       *
+
+In a word, then, the sum of our knowledge appears to be contained in
+this proposition--_That, as the stability of a sea-tower depends_,
+cæteris paribus, _on the lowness of its centre of gravity, the general
+notion of its form is that of a cone; but that, as the forces to which
+its several horizontal sections are opposed decrease towards its top in
+a rapid ratio, the solid should be generated by the revolution of some
+curve line convex to the axis of the tower, and gradually approaching
+to parallelism with it_. And this is, in fact, a general description of
+the Eddystone Tower devised by Smeaton.
+
+       *       *       *       *       *
+
+[Illustration: No. 1.]
+
+It is deserving of notice, as one of the many proofs which the records
+of antiquity afford of the similarity of the results of human thought
+in all ages, and of the truth of the Wise Man’s saying, that “there is
+nothing new under the sun,” that the ancient Egyptians appear to have
+had the same conceptions of the solid of stability that were present
+to the mind of the modern Engineer of the Eddystone Lighthouse. In the
+admirable work recently published by Sir J. Gardner Wilkinson on the
+Manners and Customs of the Ancient Egyptians, he gives, in the first
+volume of his second series, at page 253, a wood-cut, shewing the
+figure of the deity Pthah, under the symbol of stability, according to
+Egyptian conceptions. This symbol so closely and strikingly resembles
+the general appearance of the Eddystone, that I willingly give it a
+place in the text, (No. 1) denuded, however, of the arms and head-dress
+of the deity whom it shrouds.
+
+       *       *       *       *       *
+
+In applying these general notions to the design of a Tower for the
+Skerryvore Rock, I was, of course, guided by numerous circumstances,
+which modified my views and produced the individual form of Tower which
+I have adopted. Since the days of Smeaton, when his magnificent Tower
+was lighted by common candles, the application of optical apparatus
+to Lighthouses has greatly altered the state of the case; and the
+improvement of the system in modern times has, in most instances,
+rendered a greater altitude of Tower desirable, in order to extend, as
+much as possible, the benefit of a system capable of illuminating the
+visible horizon of any Tower which human art can reasonably hope to
+construct. In the particular case of the Skerryvore, also, the great
+distance of the outlying rocks (some of which, as will be seen from
+the chart, are 3 miles right seaward of the Lighthouse) concurs with
+the improvement of the Lights, in making it desirable that the Tower
+should be of considerable height, and that the light should command an
+extensive range. It was, therefore, from the first consideration of the
+subject, determined that the Light should be elevated about 150 feet
+above high water of spring tides, so as to illuminate a visible horizon
+of not less than 18 miles of radius; and, after much deliberation,
+and a full consideration of the infrequency of communication with the
+proposed Lighthouse from the great difficulty of landing on the Rock,
+and the consequent uncertainty of keeping up the supplies, I found
+that, for the convenient accommodation of the Lightkeepers and the
+suitable stowage of the stores, a void space of about 13,000 cubic feet
+would be required. These elements being fixed, the general proportions
+of the Tower came next to be considered.
+
+       *       *       *       *       *
+
+In the Eddystone the radius of the base, at the level of high water
+of spring tides, is somewhat less than _one-fifth_ of the height
+of the Tower above that level; while in the Bell Rock, at the same
+level, it is little more than _one-seventh_ of the height. If, again,
+we suppose the curve of the Eddystone to be continued downwards to
+the level of low water, the radius (in so far as we may judge from
+sketching the continuation of a curve undefined by any geometrical
+property) would be rather more than _one-fourth_ of the whole height
+above that level; while in the Bell Rock the proportion, in reference
+to the same level, is a little more than _one-fifth_. Viewing the
+whole height of the Skerryvore Tower above _high water_ of spring
+tides as equal to 142 feet, and finding that, in the cases of the
+Eddystone and the Bell Rock, the radius of the horizontal section at
+that level is respectively _one-fifth_ and _one-seventh_ of the whole
+height; and again, viewing the extreme height of the Skerryvore Tower
+above _low water_ of spring tides as equal to about 155 feet, and
+considering the proportionate radii of the Bell Rock and Eddystone (in
+so far as the latter is ascertainable) as respectively _one-fifth_ and
+_one-fourth_ of the heights of the top of the masonry above the level
+of low water, I finally decided upon giving the Tower at the Skerryvore
+such dimensions as would not be widely discordant with these general
+proportions. In this view, I determined that the radius of the base
+should not exceed 22 feet, on the level of about 4 feet above the high
+water mark, where I expected to obtain a solid foundation--a base which
+bears to the whole height of the Tower a proportion somewhat _less_
+than that of the Bell Rock, which is _one-fifth_. It so happens, that
+the diameter adopted is nearly the greatest which the Rock affords;
+for, although a glance at the accompanying plan of the Rock at high
+water (Plate, No. III.) would lead one to suppose that a more extended
+base might have been obtained, I found, after many careful examinations
+of the gullies and fissures which intersect it, that some of the
+concealed fissures run much farther into the Rock than might at first
+be imagined. The adoption of a much larger base, even had it been
+otherwise advisable, would therefore have involved some risk of the
+external ring of stones of the lowest course giving way by the yielding
+of an unsound part of the outer portion of the Rock to the pressure
+of the superincumbent mass, and might eventually have led to the
+destruction of the Tower.
+
+[Illustration: No. 2.]
+
+The height of the Pillar having been finally fixed at 138·5 feet,
+and the radius of the base, at the level of about 4 feet above high
+water, at 21 feet, I next proceeded to consider the details of its
+proportions. Of the whole height of 138·5 feet, 18 were to be absorbed
+in a suitable capital for the Pillar, consisting of a parapet for the
+Lantern, an abacus, a cavetto, and a belt separating these from the
+shaft. The internal void I determined should be 12 feet in diameter, as
+the size most suitable for the reception of the lantern and apparatus;
+and this, combined with the choice of about 13,000 cubic feet of void
+already mentioned, fixed the height of the solid frustum at the base of
+the Tower at about 26 feet above the foundation. Having farther decided
+that the thinnest part of the walls, immediately under the belt-course
+which separates the capital from the shaft, should not be less than
+2 feet thick, as necessary to give due solidity and strength to the
+walls, and prevent, by the breadth of the joints, the percolation
+through the walls of the water which might be furiously dashed against
+them in storms, I had nothing farther to do but to determine the nature
+of the line which should connect the extremities of the top and bottom
+radii of the Pillar. As I had already concluded that this line must, as
+in the Eddystone and Bell Rock, be a curve line, concave to the sea,
+I next proceeded to try the effects of various curves traced between
+these points, in giving a convenient and advantageous disposition of
+the materials, with regard to both the thickness of the walls and the
+mass of the solid frustum at the base of the Tower. These two points,
+as will be better understood by means of the accompanying diagram (No.
+2), are separated from each other vertically 120·25 feet, and are
+horizontally distant from each other 13 feet, which is the excess of
+the bottom radius over that of the top of the shaft, or the consequent
+amount of what may be called the _aggregate slope_ of the wall. The
+solid generated by the revolution of some curve line about the vertical
+axis of the building then becomes the shaft of the pillar. For this
+purpose I tried four different curves, the Parabola, Logarithmic,
+Hyperbola, and Conchoid, figures of which, upon the same scale, will be
+found in Plate, No. IV., with the position of the centre of gravity,
+which was carefully calculated, marked on each. The logarithmic curve
+I at once rejected, from its too near approach to a conic frustum, and
+the excessive thickness of the walls which such a figure would produce,
+where the hollow cylindric space for the internal accommodation
+commences at the level of 26 feet above the base. The parabolic form
+displeased my eye by the too rapid change of its slope near the base;
+and I had some difficulty in reconciling myself to the condition of
+the exterior ring of stones at the base, too much of the outer portion
+of each stone being left without the advantage of direct pressure from
+the superincumbent mass of the wall above. The two remaining pillars,
+derived from the hyperbolic and conchoidal[12] frusta, are nearly
+identical in form; and of these two curves I preferred the former,
+which gives the most advantageous arrangement of materials, in regard
+to stability, of all the four forms. This quality of advantageous
+proportion exists in these forms, in the ratio of the numbers in
+the last column of the following table:[13] which shews a slight
+superiority of the Hyperbolic over any of the other forms.
+
+  +------------+------+-----------+--------+---------+-----+----------+
+  |            |      |           | Volume | Distance|     |          |
+  |            |Height|  Diameter |    of  |   of    |     |          |
+  |            |of the|     |     |  solid |centre of|     | Economic |
+  |            | Tower|  at |  at |  Tower | Gravity |     |Advantage.|
+  |            |  in  | Base| Top |in cubic|  from   |  H  |   G·M.   |
+  |Hypothetical| feet.|  in |  in | feet.  |  Base.  |  -  |  ------  |
+  |  Towers.   |  (H.)|feet.|feet.|   M.   |   G.    |  G  |  G′·M′.  |
+  +------------+------+-----+-----+--------+---------+-----+----------+
+  |Hyperbolic, | 120  |  42 |  16 | 62,915 |  41·227 |2·911| 1·00000  |
+  |Conchoidal, | 120  |  42 |  16 | 62,984 |  41·336 |2·903| 0·99627  |
+  |Parabolic,  | 120  |  42 |  16 | 63,605 |  43·400 |2·765| 0·93963  |
+  |Logarithmic,| 120  |  42 |  16 | 74,742 |  42·460 |2·826| 0·81608  |
+  |Conical,    | 120  |  42 |  16 | 84,737 |  43·280 |2·773| 0·70725  |
+  +------------+------+-----+-----+--------+---------+-----+----------+
+
+  [12] The solid, in this case, would have been formed by the
+  revolution of the interior conchoid of Nicomedes about its directrix;
+  and its co-ordinates were kindly calculated for me by my late revered
+  preceptor, Dr WALLACE, Professor of Mathematics in the University of
+  Edinburgh, who employed so many hours of his latter years in labours
+  of kindness among his friends. This act of the Professor was the
+  result of a conversation I had with him on the subject. Before I
+  received his friendly communication, however, I had resolved to adopt
+  the rectangular hyperbola, whose co-ordinates I had myself determined
+  with this view some time before; and when I found that the conchoid
+  and the hyperbola, traced between the two fixed points by means of
+  the calculated co-ordinates, were so nearly coincident, that it was
+  difficult to prevent their running into each other, even when drawn
+  out on a large scale, I determined to adhere to my original purpose
+  of adopting the latter curve as my guide.
+
+  [13] The last column of this table is derived as follows:--Assuming
+  that the economic advantage of any proposed tower of given height
+  and diameter at base and top, is _inversely_ as the mass and the
+  height of the centre of gravity above the base, and denoting these
+  quantities by M and G respectively, the fraction
+
+   1
+  ---
+  G·M
+
+  may be taken as an indication of the economic advantage of the
+  proposed tower. Let
+
+    1
+  -----
+  G′·M′
+
+  express the economic advantage of another tower; then the advantage
+  of the second tower, compared to that of the first, taken as unity,
+  will be
+
+   G·M
+  -----,
+  G′·M′
+
+  by which expression, the last column in the table was calculated.
+
+The shaft of the Skerryvore Pillar, accordingly, is a solid, generated
+by the revolution of a rectangular hyperbola about its asymptote as a
+vertical axis. Its exact height is 120·25 feet, and its diameter at
+the base 42 feet, and at the top 16 feet. The ordinates of the curve,
+at every foot of the height of the column, were carefully determined in
+feet to three places of decimals; and the Appendix contains a tabular
+view of the co-ordinates from which the working drawings were made at
+full size. The first 26 feet of height is a solid frustum, containing
+about 27,110 cubic feet, and weighing about 1990 tons.[14] Immediately
+above this level the walls are 9·58 feet thick, whence they gradually
+decrease throughout the whole height of the shaft, until at the belt
+they are reduced to 2 feet in thickness. Above the shaft rests a
+cylindric belt 18 inches deep; and this is surmounted by a cavetto
+6 feet high, and having 3 feet of projection. The contour of this
+cavetto is that resulting from a quadrant of an ellipse revolving about
+the centre of the tower, with a radius of 8 feet on the level of its
+transverse axis; and the moulds for this curve were drawn at full size
+from co-ordinates calculated for the purpose. The cavetto supports an
+abacus 3 feet deep, the upper surface of which forms the balcony of the
+tower, and above it rest the parapet-wall and lantern.
+
+  [14] At the rate of 13·62 cubic feet of granite to a ton.
+
+It may, perhaps, be not uninteresting to the reader to examine the
+woodcuts (No. 3), which shew, on one scale, the elevations of the
+Lighthouses of the Eddystone, the Bell Rock, and the Skerryvore, and
+exhibit the level of their foundations in relation to high water. They
+will also serve to give some idea of the proportionate masses of the
+three buildings. The position of the centre of gravity, as calculated
+from measurements of the solids, is also marked by a round black dot on
+each tower; and in the table following, I have given the cubic contents
+of each of these towers, the height of the centre of gravity above the
+base and the ratio of that quantity to the height of the tower.
+
+[Illustration: No. 3.
+
+EDDYSTONE.
+
+SKERRYVORE.
+
+BELL ROCK.]
+
+  +-----------+-------+--------+----------+----------+----+
+  |           | Height|        |          |          |    |
+  |           |   of  |        |          | Distance |    |
+  |           | Tower |        |          |    of    |    |
+  |           | above |        |          |centre of |    |
+  |           | first |        |          | gravity  |    |
+  |           | entire|Contents| Diameter | in feet  |  H |
+  |           |course.|   of   |  at | at |from Base.|  - |
+  |Lighthouse.|  (H)  | Tower. |Base.|Top.|   (G)    |  G |
+  +-----------+-------+--------+-----+----+----------+----+
+  |Eddystone, |  68   | 13,343 |  26 | 15 |  15·92   |4·27|
+  |Bell Rock, | 100   | 28,530 |  42 | 15 |  23·59   |4·24|
+  |Skerryvore,| 138·5 | 58,580 |  42 | 16 |  34·95   |3·96|
+  +-----------+-------+--------+-----+----+----------+----+
+
+I come now to notice the few subordinate points in which the design of
+the Skerryvore Tower may be regarded as differing from those of the
+Eddystone and the Bell Rock. In glancing at the contrasted figures of
+the three buildings, it will be at once observed that the outline of
+the Skerryvore approaches more nearly to that of a conic frustum than
+the other two. To the adoption of this form, various considerations
+induced me; and these I shall very briefly detail. In the first place,
+it seemed to me that, in both the Bell Rock and the Eddystone, the
+thickness of the walls had been reduced to the lowest limits of safety
+towards the top; and the effects of the sea and wind acting upon a
+heavy cornice, cause a degree of tremor which I felt satisfied would
+not occur in a building with thicker walls. The effect of thickening
+the walls at the top, is, of course, _cæteris paribus_, to diminish the
+projection of the base, and thus to produce less concavity of figure,
+and consequently a nearer approximation to the contour of a conic
+frustum. I have already stated, that this excess of the bottom radius
+over that of the top, is in the Skerryvore Tower 13 feet, and that the
+height of the shaft is 120·25 feet. The quotient resulting from the
+division of the height by the excess of bottom radius over that at the
+top is 9·27; and, if the figure had been conical, this number would
+have given a measure of the slope of the walls throughout. There can
+be little doubt that the more nearly we approach to the perpendicular,
+the more fully do the stones at the base receive the effect of the
+pressure of the superincumbent mass as a means of retaining them in
+their places, and the more perfectly does this pressure act as a bond
+of union among the parts of the Tower. This consideration materially
+weighed with me in making a more near approach to the conic frustum,
+which, next to the perpendicular wall, must, other circumstances being
+equal, possess the property of pressing the mass below with a greater
+weight, and in a more advantageous manner, than a curved outline in
+which the stones at the base are necessarily farther removed from
+the line of the vertical pressure of the mass at the top.[15] This
+vertical pressure operates in preventing any stone being withdrawn
+from the wall in a manner which, to my mind, is much more satisfactory
+than an excessive refinement in _dovetailing_ and _joggling_, which I
+consider as chiefly useful in the early stages of the progress of a
+work, when it is exposed to storms, and before the superstructure is
+raised to such a height as to prevent seas from breaking right over it.
+
+  [15] It is most satisfactory to find that the views expressed above,
+  regarding the eligibility of the conical form, seem to have the
+  sanction of the late Dr Thomas Young, who appears to have connected
+  his preference of this form with its greater efficiency as a source
+  of friction among the parts of a building. In his syllabus of
+  Lectures, under the section “Architecture,” he thus speaks: “For a
+  Lighthouse where a great force of wind and water was to be resisted,
+  Mr Smeaton chose a curve convex to the axis. In such a case, the
+  strength depends more on weight than on cohesion, and also in a
+  considerable degree on the friction which is the effect of that
+  weight. Perhaps a cone would be an eligible form.”
+
+If these views be substantially correct, it may not, perhaps, be
+altogether inadmissible (without, however, venturing to enunciate
+any general law) to conclude, that, in the three Lighthouses of the
+Eddystone, the Bell Rock, and the Skerryvore, this source of union
+among the outer stones of the lower courses must bear some proportion
+to the numbers 753, 659, and 927, which are the quotients of the height
+of the column, divided by the difference of the top and bottom radii
+of the shaft in each case respectively. This consideration seems too
+important to be entirely overlooked; and I conceive that, by following
+out this view, I have been enabled to depart with perfect safety from
+the intricate and elaborate work required for the connection of the
+materials by means of dovetailing and joggling, which the adoption of
+a more concave outline (in which the vertical pressure could not have
+been so advantageously transmitted to the outer stones of the base),
+would perhaps have rendered advisable. In the case of the Bell Rock,
+however, whose construction, in regard to this property, is the least
+advantageous of the three buildings, it must be borne in mind that the
+Tower is covered to the depth of 15 feet at spring tides, and that this
+principle of vertical pressure could not have been safely appealed to
+during the whole time which intervened between the commencement of
+the building and the attainment of a height sufficient to render it
+available, which, in a Tower having so great a part submerged, was of
+necessity much prolonged. The stones were thus exposed to the full
+effect of heavy seas, at all levels, during two entire winters, and
+could not therefore have been safely left, without being kept together
+by numerous ties and dovetails. It also seemed important, in designing
+that Tower, with reference to the rise of tide, to give its lower part
+a sloping form, as the least likely to obstruct the free passage of
+the waves. The outer stones of the lower courses were also selected of
+unusual length _inwards_, so as to bring them more under the influence
+of the vertical pressure of the upper wall.
+
+Before leaving this subject, I may remark, that it is quite possible to
+construct a Tower of a curved form, in such a manner, that the pressure
+of the upper part of the pillar shall be distributed to the greatest
+advantage on every stone, by building the outer walls as inverted
+arches, so that the section of each stone shall be that of a voussoir,
+with joints perpendicular to the successive tangents of the curve.
+This arrangement of the stones is, in fact, practised in sea walls of
+various kinds, and has even been recommended for circular Towers in an
+ingenious paper in the Transactions of the Royal Scottish Society of
+Arts. But in many situations, and at Skerryvore in particular, this
+mode of transmitting the pressure, so as to throw it perpendicular to
+the beds of the stones, is inadmissible, as conducing to or involving
+a greater evil. The evil has already been noticed, and consists in the
+thrust of the lowest stone (which is of course inclined to the horizon)
+having a tendency to push out the sides of the Rock on which the Tower
+is built. This fear, where the Towers are to be placed on small steep
+rocks or pinnacles, and more especially when these Rocks are traversed
+by veins nearly vertical, is by no means visionary; and there is
+good reason to apprehend, that the pressure thus resulting in a line
+considerably inclined to the plane of _cleavage_, might throw outwards
+a thin portion of rock, which, under the more conservative influence
+of a vertical pressure, might continue to retain its connection with
+the rest of the Rock unimpaired for ages.
+
+Another method of, in some degree, increasing the resistance of a Sea
+Tower to a horizontal thrust, if such aid be required, is to give
+the line of courses a continuous spiral form, instead of building
+them in successive horizontal layers. Were there reason to fear that
+the entire dislocation of the building might take place in a plane
+nearly horizontal, this method seems more calculated to counteract
+the danger than the use of dowels or joggles passing from the course
+below to the course above; but, as this is one of the accidents least
+to be apprehended, there does not seem any good ground for resorting
+to a mode of structure which would lead to considerable intricacy of
+workmanship, and would, in practice, be attended with difficulty in
+obtaining a proper vertical bond or union among the several stones.
+
+The only remaining point, in which the example furnished by the
+Eddystone and Bell Rock Lighthouses has been at all materially departed
+from, is (as has already been hinted at by an unavoidable anticipation)
+the mode of uniting the different parts of the masonry together. In
+both these Towers the stones were dovetailed throughout the buildings,
+chiefly (at least in the case of the Bell Rock where the foundation
+was so much below the tide) with the view of preventing the sea from
+washing away the courses which might be left exposed to the winter
+storms before the weight of the superstructure had been brought to bear
+upon them. In the upper part of the Bell Rock my father also introduced
+a kind of band joggle, which consists of a flat ribband of stone raised
+upon the upper bed of one course, and fitting into a corresponding
+groove cut in the under bed of the course above; and this system of
+tying the adjoining courses together also forms a chief feature in his
+design for a Lighthouse on the Wolf Rock.[16] When the great pressure
+of the superstructure of these Towers, however, and the effect of the
+mortar are considered, there seems little probability of one course
+being dislocated, in defiance of the friction resulting from the
+weight of the column. An impulse sufficient to produce such an effect
+would tend to overset the whole superstructure from mere deficiency
+in weight, and in this case the joggle would have little effect. But
+if joggles be thought necessary for this purpose, the ribband form
+certainly produces a better arrangement than that of the cubic joggles
+employed by Smeaton for connecting the adjoining courses of his
+building together, as the sectional strength of these scattered square
+joggles is very small compared to the effect of a shock which could
+be supposed capable of moving the whole mass of a Tower. In the lower
+parts of the Skerryvore Tower, I entirely dispensed with dovetailing
+and _joggles between the courses_, and thus avoided much expensive
+dressing of materials. The stones were retained in their places during
+the early progress of the work, chiefly by common diamond joggles, and
+the courses were temporarily united to each other by wooden treenails,
+like those used in the Eddystone and Bell Rock. These treenails had
+split ends, with small wedges of hardwood loosely inserted, which being
+forced against the bottom of the holes in the course below, into which
+the treenails were driven, expanded their lower ends until they pressed
+against the sides of the holes; while their tops were made tight by
+similar wedges driven into them with a mallet. I have, however, adopted
+the ribband-joggle in the higher part of the Tower, where the walls
+begin to get thin in the very same manner as at the Bell Rock, where it
+was used, partly that it might counteract any tendency to a _spreading_
+outwards of the stones, and partly that it might operate as a kind
+of _false joint_ to exclude the water which, when pressed with great
+violence against the Tower, is apt to be forced through a straight or
+plain joint. The stones in the higher courses throughout each ring are
+also connected at the ends by double dovetailed joggles, which unite
+the two adjoining stones; and the walls are, besides, tied together at
+various points by means of the floor stones, which are all connected by
+dovetails let into large circular stones which form the centres of the
+floors. I also ventured to leave out the metallic ties at the cornice,
+which consisted, at the Eddystone, of chains, and, at the Bell Rock,
+of copper rings. The reasons which induced me to adopt this change I
+need not here enlarge upon. It is sufficient to state, that I believe
+I have nearly balanced the forces which would have tended to throw the
+cornice outwards, had a greater disproportion existed in the weight of
+the outer and inner parts of the cavetto, and to point out (Plate VII.)
+that the Lightroom or highest floor occurs, at such a level, as of
+itself to answer all the ends which metallic ties could have served.
+
+  [16] Account of the Bell Rock Lighthouse, Plate XXI.
+
+
+CHAPTER IV.
+
+OPERATIONS OF 1838.
+
+  ~Temporary Barrack on Rock.~
+
+The hazardous nature of the anchorage, and the consequent difficulty of
+mooring a vessel in the neighbourhood of the Skerryvore Rock, induced
+me, from the first, to consider it as a matter of great importance,
+even at a large expenditure of time and money, to erect some temporary
+dwelling on the Rock for the accommodation of the people engaged in the
+work, with the view of rendering the operations less dependent on the
+state of the sea, which varied with every wind. So important, indeed,
+did this object appear to me, that I was at times apt to look upon it
+as an indispensable step towards ultimate success. That opinion was
+amply confirmed during our first season’s operations, by the experience
+of the oft-recurring difficulty of returning to the moorings when
+driven away by stress of weather, together with the daily risk and loss
+of time in landing the workmen in small boats, even in weather when
+they could be profitably occupied if once placed on this small _terra
+firma_. With this view, I naturally turned to the same plan which had
+been adopted at the Bell Rock, where the temporary barrack stood the
+test of five winters. That structure, which is represented in Plate
+No. V., and is particularly described in the Appendix to my father’s
+Account of the Bell Rock Lighthouse, consisted of an open framework
+of six logs, about 47 feet long and 13 inches square, assembled in
+such a manner as to form by their union a hexagonal pyramid, on the
+top of which rested a wooden turret; the whole erection rising to the
+height of about 60 feet above the rock. This pyramidal framework was
+strongly trussed and tied; and, being open at the lower part, offered
+little resistance to the waves. The upper part contained a gallery for
+keeping various stores and such materials as could not be safely left
+on the Rock, even in the finest weather; but it was framed of lighter
+materials, so as to admit of its yielding easily to any extraordinary
+waves, without involving injury to the principal part of the structure,
+by offering great resistance to the sea. The turret on the top was in
+the form of a twelve-sided prism, 12 feet in diameter, and 30 feet
+high, and was securely attached, by means of the ties and braces shewn
+in the drawing, to the apex of the pyramid, which entered into the
+lower part of it. The small space which the turret afforded was, with
+the utmost economy of room, divided into three storeys, of which the
+lower was entirely taken up by the kitchen and the bread-store, a great
+deal of room being occupied by the main beams of the pyramid which
+passed through its centre. The next storey was subdivided into two
+chambers, of which one was appropriated to the foreman of the works and
+the landing-master, while the other was set apart for myself; and the
+top storey, which was surmounted by a small lantern and ventilator,
+formed a barrack room, capable of containing 30 people. Of the comforts
+and discomforts of this habitation I shall at some future time have
+occasion to speak. I merely draw attention to its erection at present,
+as an operation, which it was most desirable should precede every
+other work on the Rock. One of the first proceedings, therefore, was
+to obtain estimates for the preparation of this log-house, which, in
+order to avoid loss of time in making adjustments on the Rock, was to
+be carefully fitted up in the workyard of the contractor before being
+shipped. Drawings and a specification were accordingly prepared, and
+submitted to several carpenters in Greenock, who gave in offers for the
+work; and it was finally commenced in the month of March, by the late
+Mr John Fleming, who was the successful offerer.
+
+  ~Tools and Machinery.~
+
+It was also necessary to provide a large assortment of quarriers’
+and masons’ tools of every kind; and many cranes, crabs, anchors,
+mooring buoys and other implements were ordered, according to detailed
+specifications and drawings. These preparations necessarily occupied
+the early part of the year 1838.
+
+  ~Steam Tender for the Works.~
+
+From the extent of the foul ground round the Skerryvore, and the
+absence of good harbours in the neighbourhood, it was foreseen at the
+outset that the operation of landing about 6000 tons of materials on
+the Rock could not be accomplished by means of sailing vessels with
+that degree of certainty or regularity which was desirable, in order to
+obtain the full benefit of the short working season which the climate
+of the Western Hebrides affords; and the necessity for providing a
+steam tender was, therefore, generally admitted. It has already been
+stated, that, in order to avoid the expense attending the building
+of a vessel for this purpose, application was made at the principal
+ports of the kingdom, with the view of purchasing a suitable vessel;
+but, although twenty-four vessels of nearly the required dimensions
+were offered for sale, not one of them was considered fit for such a
+service, the great majority being light craft, such as are generally
+used in river and port navigation. It was therefore found necessary to
+build a steamer; for which purpose, specifications and drawings were
+prepared, and after receiving various tenders from respectable parties,
+a contract was entered into with Messrs Menzies and Sons, shipbuilders,
+and Messrs J. B. Maxton and Co., engineers, both of Leith, for building
+a steamer of 150 tons, with two engines of 30 horse power each.
+
+The use of a steamer, at the very outset of the works, would doubtless
+have proved of the greatest service in the erection of the barrack
+on the Rock, and would have materially lightened our cares and
+toils; but I am not sure that I should have acquired so thorough an
+acquaintance with the difficulties and dangers of the Skerryvore, or
+that I should have been so well prepared for all the obstacles that
+presented themselves in the after parts of the work, had the first
+season’s operations been conducted under those advantages which are
+always derived from the use of steam-power. As it was, we had much to
+bear from the smallness of the Lighthouse Tender, named the _Pharos_,
+a vessel of 36 tons, new register, which was all the regular shipping
+attendance we possessed during this first season; and the inconvenience
+arising from her heavy pitching, was, to landsmen, by no means the
+least evil to be endured. But the frequent loss of opportunities, of
+which we might easily have availed ourselves, if we had possessed the
+command of steam-power, and the danger and difficulty of managing
+a sailing vessel in the foul ground near the Rock, and between it
+and Tyree, were, perhaps, even more felt by the seamen than by the
+landsmen; and if the experience of a single year’s work can form any
+ground for an estimate of the length of time required for building the
+Skerryvore Lighthouse, with a sailing vessel, I should say, we must
+still (even in 1845) have been engaged in the masonry part of the work,
+which was finished on the 25th July 1842.
+
+  ~Employment and Wages of Workmen.~
+
+About the middle of April, arrangements were made with Mr Charles
+Neilson, a builder in Aberdeen, to select granite masons for the works
+at the Skerryvore, as it was expected that the operation of dressing
+stones for the Tower would be begun in the ensuing summer; and it was
+also obvious, that their services would be required in excavating
+seats for the supports of the Barrack-house on the Rock. Masons were
+accordingly selected, and engaged on the terms stated in the following
+letter to Mr James Scott, the Foreman, who was sent to Aberdeen to
+assist in choosing the men:--“Although it is difficult to fix the
+precise number of men who may be required, during the progress of the
+works, as this must, in some measure, depend upon the produce of the
+quarries at Hynish, and of those to be opened in Mull, you may, in the
+mean time, engage thirty masons or stone-cutters, twelve quarriers,
+and three or four smiths, for two years of certain employment. With
+regard to the rate of wages to be paid to the men, this will, in some
+measure, depend upon the demand for the season at Aberdeen; it is, at
+all events, expected, that they will on no account exceed the rate of
+3s. 10d. per day for masons, and 2s. 6d. per day for quarriers, as paid
+last season during the long day, or from the 1st of February till 31st
+of October; and for the short day during the remaining three months,
+3s. for the masons, and 2s. for the quarriers, from 1st November till
+31st January.
+
+“It is intended that subsistence money shall be paid to such of the
+families or relatives of the workmen as may require it; and that their
+wages shall be fully settled monthly, deducting the subsistence money
+advanced to their relatives. A Store will be kept at the works by the
+Lighthouse Board, from which provisions will be served out at stated
+periods, to be fixed by the storekeeper; and these provisions shall be
+sold to the workmen at the cost prices at which such stores are laid
+in. Barrack accommodation or lodgings, with cooking, will also, as
+formerly, be allowed to the men free of expense.”
+
+  ~Progress of the outfit for the season’s operations.~
+
+Early in the month of May the preparation of the wooden barrack for
+the Rock had been completed, and the whole had been set up in the
+workyard at Greenock; and when I visited it for the last time about the
+5th of that month, I found it all ready for shipment, excepting some
+additional iron ties, which I ordered for securing the turret to the
+top of the pyramid, which were to be applied at the level of the floor
+of the upper or barrack-room storey. I also found that the moorings,
+including the mushroom anchors and chains, and the workyard materials,
+consisting of several cranes, trucks, a janker for the transport of
+timber, and a Woolwich sling-cart for carrying stones to the various
+sheds, were in the course of preparation. A large assortment of
+masons’ and quarriers’ tools was at the same time ready for shipment
+at Aberdeen. Early in June, a vessel called the Duke of Montrose was
+chartered to carry coals to Tyree, both for household purposes and for
+the work; and two small portable smiths’ forges were prepared for use
+on the Rock.
+
+  ~Embark for Skerryvore.~
+
+In providing the means of efficiently carrying on so many complicated
+operations in a situation so difficult and remote, it is impossible,
+even with the greatest foresight, to avoid omissions; while delay of
+a most injurious kind may result from very trivial wants. Even the
+omission of a handful of sand, or a piece of clay, might effectually
+stop for a season the progress of plans, in the maturing of which
+hundreds of pounds had been expended. Accordingly, although I had
+bestowed all the forethought which I could give to the various details
+of the preparation for the season (of which I found it absolutely
+indispensable to be personally aware, even to the extent of the cooking
+dishes), new wants were continually springing up, and new delays
+occasioned, so that it was not until the evening of the 23d of June
+that I could embark at Tobermory in the _Pharos_ Lighthouse Tender,
+commanded by Mr Thomas Macurich, with all the requisites on board for
+commencing the season’s operations. Next morning we moored off Hynish
+Point about three o’clock, and, from the roughness of the passage, were
+not unwilling to land at that early hour. Here I found that Mr Scott,
+the foreman of the workyard, had, notwithstanding the unworkable nature
+of the Rock, more particularly afterwards noticed, procured about sixty
+fine blocks of gneiss, as the produce of the Tyree quarries, which
+had been wrought for upwards of 15 months; and had at the same time
+completed the masonry of a range of buildings for stores and barracks,
+capable of containing upwards of 100 men, and had built about 100 feet
+in length of a landing-pier, reaching nearly to low-water mark. A
+magazine for gunpowder, of which a considerable stock was required for
+quarrying purposes, had also been built; and a piece of garden ground
+had been inclosed and stocked for the use of the people to be employed
+at the works. Measures had also been taken for inclosing the ground,
+which had been feued by the Board from the Duke of Argyll. This day
+being Sunday, nothing was done at Hynish, and we waited until next
+morning before sailing for the Rock.
+
+_25th June._--Sailed in the _Pharos_ from Hynish Bay this morning about
+six, with Mr Scott, the foreman of the workyard, and one or two masons
+on board; but, having a foul wind during the early part of the day,
+and the weather falling afterwards calm, it was not until three in the
+morning of the 26th that we reached the Rock.
+
+  ~Lay down Moorings, and try to land on the Rock.~
+
+_26th June._--Our first step was to lay down moorings for the tender
+as near the Rock as seemed to be consistent with safety. The position
+chosen by Mr Macurich, who commanded the vessel, was to the S.S.E. of
+the Rock, about a quarter of a mile off, and in 13 fathoms water, on
+an irregular rocky bottom. About half-past five I attempted a landing
+on the Rock, but there was a great deal too much sea. The vessel was
+pitching the bowsprit under at her moorings, and the surf broke into
+the creek where landings are generally made, in such a manner as to
+render it quite impossible to get near the Rock. After hanging on our
+oars in the boat for nearly an hour, in the hope of a smooth lull
+between the heavy seas, we returned to the vessel, and, as the wind
+still freshened from the S.E., we reefed the mainsail and set the first
+jib, and steered for the Mull shores, where, about ten at night, we
+came to an anchor in Loch Loich, not far from the Island of Iona.
+
+  ~Driven to Mull.~
+
+_27th June._--Next day also being unsuitable for attempting to reach
+the Skerryvore, the vessel lay in North Bay, and the early part of the
+day was spent in a careful examination of the granite Rocks of the
+district called _Ross of Mull_, with the view of establishing quarries
+there; as our experience of the unsatisfactoriness of working the Tyree
+quarries during fifteen months had frequently led me to anticipate the
+necessity of soon seeking a supply of materials in some other quarter.
+In this district an almost inexhaustible supply of flesh-coloured
+granite was found, not certainly of the hardest description, but
+singularly equal and homogeneous in its texture. I therefore made a
+general survey of the neighbouring localities, with a view to select
+the best position for opening quarries and establishing a landing
+place or wharf for shipping the materials, as well as for erecting
+barracks for the workmen. In the afternoon, I embarked at the call of
+Mr Macurich, to attempt another landing on the Skerryvore; but as the
+wind soon fell calm, we did very little good until evening, when some
+progress was made in stretching across towards the Rock.
+
+  ~First day’s work on the Rock.~
+
+_28th June._--At nine this morning, we reached our moorings at the
+Rock, but there was still so much surf that a landing could not be
+attempted till mid-day, when I went with Mr Macurich in the boat, and
+with some difficulty contrived to spring on the Rock, after which the
+boat returned to the vessel for the rest of the party. While left
+alone on this sea-beaten Rock, on which I had landed with so much
+difficulty, and as I watched the waves, of which every succeeding
+one seemed to rise higher than the last, the idea was for a few
+minutes forcibly impressed on my mind, that it might, probably, be
+found impracticable to remove me from the Rock, and I could not avoid
+indulging in those unaccountable fancies which lead men to speculate
+with something like pleasure upon the horrors of their seemingly
+impending fate. These reflections were rendered more impressive by
+the thought that many human beings must have perished amongst those
+rocks. A consideration, however, of the rarity of an opportunity of
+landing on the Rock, and the necessary shortness of our stay, soon
+recalled me to my duty, and before the boat returned with a few of the
+workmen, I had projected some arrangements as to the first step to
+be taken in erecting the framework of the barrack-house. The second
+landing was more easily effected, as the tide had fallen, and the
+landing-place was more sheltered, so that we were the more emboldened
+to make a fair commencement of operations. It was a day of great bustle
+and interest, the work consisting in chalking out and marking on the
+Rock with paint, the sites of the Lighthouse-Tower, and the wooden
+barrack, and the positions for cranes, crabs, and ring-bolts for guys
+and other tackling, as well as ascertaining such dimensions as would
+enable me at once to proceed to fit up the log-house, or barrack, at
+our next landing. In that way, we spent four hours on the Rock, much
+to the annoyance of the seals and the innumerable sea-fowl, which we
+drove from their favourite haunts. During the whole day, the sun had
+great power; and the smell from the cast-away feathers and the soil
+of the sea-fowl was extremely disagreeable. I was amazed to find that
+those animals should select, as their place of repose, a rock in the
+Atlantic, intersected by deep gullies which are never dry, with only
+one pinnacle, about 5 feet in diameter, raised about 16 feet above the
+sea. while the greater part is only 5 feet above high water. Yet, in a
+crevice of this Rock, I found an egg resting on a few downy feathers,
+which the first wave must have infallibly washed away! After the day’s
+work on the Rock, we sailed for Tyree, but did not reach the workyard
+till next morning at nine; and a long day of bustle and hurry was spent
+there in preparing provisions, timber, ring-bolts, chains and all
+sorts of tackling for the operations connected with the erection of
+the barrack on the Rock. On the evening of the 30th June, I sailed for
+Greenock, whence I trusted soon to return to the Skerryvore with the
+whole of the materials, to commence operations.
+
+  ~Shipment of all the materials at Glasgow and Greenock.~
+
+  ~Reach Tyree.~
+
+  ~Driven to Mull.~
+
+  ~Return to Tyree.~
+
+It seldom happens that human expectations are fully realised,
+especially in matters which excite a strong interest in the mind, and
+thus lead one to desire a more rapid progress than usual. But this is
+peculiarly true in all arrangements which depend on the co-operation of
+many persons; and so I experienced on my visit to Greenock and Glasgow,
+where I had given orders for shipping all the machinery and apparatus
+required for carrying on the works, such as cranes, trucks, boats,
+blocks and tackle, anchors, coals, grindstones, stucco, pavement,
+mats and fascines for blasting, clay for puddling, shear-poles, and
+innumerable small utensils, some of no great value, but all necessary
+to the success of the work. The great bulk of those materials were
+despatched by a vessel called the _New Leven_, and part by the _Mary
+Clark_, on the 24th July; but it was not until the 30th that the
+_Pharos_ Lighthouse tender was fully loaded, on the morning of which
+day I again embarked at Greenock for the Skerryvore Rock. The weather
+proving somewhat unfavourable, we were forced (being very heavily
+laden) to pass through the Crinan Canal, instead of going round the
+Mull of Kintyre, so that it was not till the morning of the 4th August
+that we landed at Hynish, in Tyree. Here I found some farther progress
+had been made in building the barracks for the men, some of the houses
+being already roofed and slated. The quarries, too, had turned out
+stones sufficient for about four of the lowest courses of the Tower, a
+quantity which might be estimated at about 7920 cubic feet. Next day
+(August 5th), the wind blowing strong from the S.S.W., we were forced
+to leave Hynish Bay, and retreat before a very heavy sea to Tobermory.
+We immediately sailed again, and made for Loch Erin, a small creek
+in the Island of Coll, as being nearer to Hynish and better adapted
+for enabling us to take advantage of any sudden improvement in the
+weather. On our arrival at this singular natural haven, at nine in the
+evening, I was glad to find the _New Leven_, before mentioned as having
+loaded materials at Greenock lying already there, waiting a favourable
+change of wind. Next morning we weighed anchor, and sailed along with
+that vessel for Hynish, where she was immediately discharged of her
+cargo, which was chiefly intended for the workyard there, and took in
+materials for the erection of the barrack on the Skerryvore Rock.
+
+  ~First good day’s work on the Rock.~
+
+_7th August._--We this morning took on board various tools and
+implements for the Rock, together with workmen to the number of four
+carpenters, sixteen masons and quarriers, and a smith, along with Mr
+George Middlemiss, as foreman. Having sailed with a northerly wind, we
+made a landing about noon, and had what may be called our first entire
+day of work on the Rock. Our work was by no means easy, as we had to
+erect _shear-poles_ and fix _crabs_ for landing the materials, and to
+lash every article that was landed, with great care down to ring-bolts
+on the Rock, which a few of the masons were fixing, while the rest of
+the people were discharging the vessel. All this was attended with a
+good deal of trouble, and it required my constant attention to keep
+everything going on in a fair train, so as to prevent one party of
+workmen requiring to wait for another; but, after eight hours of very
+hard work, I had the satisfaction of seeing all the materials which
+had been landed left in a secure state. The extreme smoothness of the
+surface of the Rock greatly impeded the landing of materials; for as
+yet we had no tramways on which wheeled trucks could be moved, and the
+transport by hand of heavy materials over so irregular and slippery a
+surface was attended with considerable danger. A short trial was this
+day made of boring one of the holes for the stancheons or bats, by
+which the timbers of the Barrack were to be secured to the Rock; and
+I found, that with a jumper of 3¹⁄₂ inches diameter, a depth of about
+3 inches was bored in one hour. The commencement of the operations
+involved much labour and considerable discomfort; but it invariably
+happened throughout the work, that in spite of all the fatigue and
+privation attending a day’s work on this unsheltered Rock, the landsmen
+were for the most part sorry to exchange it for the ship, which rolled
+so heavily as to leave few free from sea-sickness, and to deprive most
+of the workmen of sleep at night, even after their unusually great
+exertions during the day.
+
+On leaving the Rock at night we had the greatest difficulty in boarding
+the _Pharos_ with two boats containing upwards of thirty-two persons,
+as the vessel rolled so heavily, that there was great danger of the
+boats being thrown right upon her deck. Next morning (8th August) we
+landed, with some sea running, about nine o’clock, before which hour it
+was impracticable, owing to the surf in the landing creek. Our first
+work was to prepare the tackling for landing the heavy materials from
+the _New Leven_, which came up about eleven o’clock, and was made fast
+by a warp to the _Pharos_. We next took means for fixing the smith’s
+forge on the Rock and preparing the fixtures for the crab, which stood
+on the point of rock to the westward (see Plate III.), and served
+chiefly for raising the beams of the log-house into their places. The
+greater part of the day, till half-past eight in the evening (when it
+became dark), was spent in lining off with accuracy the site of the
+supports of the wooden barrack, and in landing and fixing by strong
+lashings to the Rock, all the principal timbers and iron fixtures.
+The spot in which the framework of the first barrack was placed, will
+be seen by reference to Plate III. The Rock was at this place a good
+deal lower than the site afterwards adopted for the barrack. The high
+water of spring-tides rose 2¹⁄₂ feet upon the legs or main beams; but
+this site had many advantages, as it left more room for operations at
+or near the Tower itself than could have been obtained in any other
+position.
+
+  ~Sudden gale, and great peril to the vessels.~
+
+  ~Reach Hynish in safety.~
+
+We also made some progress in erecting a wooden shed round the smith’s
+forge, to protect him and his fire from the wind and the spray of the
+sea. As we left the Rock in the boats, speculating on the prospect
+of getting the whole of the materials discharged in the course of
+next day, it was remarked that the northern sky was very clear, and
+that the wind had entirely fallen. The great and sudden stillness of
+the air, which permitted every ripple on the ocean to be heard, was
+regarded by Mr Macurich and the seamen generally, as the forerunner of
+a change; and the moon, which rose red and fiery, confirmed their fears
+of a gale. Nor were they wrong in their forebodings. About midnight
+there was a stiff breeze from the S.E., which induced the master of
+the _New Leven_ to hoist sail, cast loose from us, and run; and had
+not the seaman on watch on the deck of the _Pharos_ fallen asleep in
+consequence of excessive fatigue, there can be little doubt we should
+have been at once called to follow her example, if, indeed, we had
+not led the way. No sooner, however, did Mr Macurich become aware of
+the state of the wind, which was blowing very strong at S.S.E. right
+into the landing place, than he roused me about two o’clock. At this
+time there was a very heavy sea; the little vessel was pitching her
+forecastle under, and we had to contend with a strong tide combined
+with the wind against us in working clear of the Rock, from which our
+moorings were not more than a quarter of a mile to windward; while
+from the place where we lay, half of the horizon was foul ground, all
+lying to our leeward. We soon set sail, but in vain tried to weather
+the sunk rock Bo-Rhua, whose large black mass (after having imagined
+ourselves past it) we discovered encircled by a wreath of white foam
+within less than a cable’s length of us. The heavy seas we encountered
+had greatly deceived us as to our progress, and thick blinding showers
+of rain made it difficult to see far beyond the vessel’s head. Such
+was the precarious and dangerous position of the vessel, that had an
+attempt been made to _tack_ her amidst the surf which came rolling off
+the Rock, she would most probably have missed stays, the consequence of
+which would have been the inevitable loss of the vessel and of every
+soul on board. In this dilemma we were obliged to resort to a less
+dangerous expedient, by _wearing_ the ship and running her through the
+narrow passage between Bo-Rhua and the sunk rocks, about 300 yards to
+the W.N.W. of it, although this was a most hazardous attempt, as we had
+then little or no knowledge of that dangerous and intricate passage.
+A more anxious night I never spent; there being upwards of thirty
+people on board, with the prospect, during several hours, of the vessel
+striking every minute. And here I must award due praise to Mr Macurich
+for the coolness and intrepidity which he on this occasion displayed,
+and the calmness with which he gave his orders to the crew; and as
+I stood in the companion, telling him the time at intervals of five
+minutes, so as to enable him the better to judge of the vessel’s way
+through the water, I could not but remark the necessity for silence on
+the part of the master of a vessel in cases of difficulty. The workmen
+were told to be getting ready for landing, but we did not make them
+aware of the full extent of the danger; and to avoid confusion, they
+were not permitted to come on deck. We had no sooner cleared the sunk
+rocks already alluded to, than we were in fear of the great reef of
+Boinshly, and the heavy seas which were breaking over the foul ground
+all round it. In this way we spent a night of almost uninterrupted
+anxiety until daylight, and at eight in the morning we came to the
+moorings in Hynish Bay, after a hard struggle against wind and tide
+and a very heavy sea, which made us hang _dead_ a long time off Hynish
+Point. At one time I feared we should have been forced, as I had been,
+when returning from my first unsuccessful and discouraging attempt to
+land on the Skerryvore in 1836, to go round the west side of Tyree
+and Coll, which is a very foul coast; and when we did round Hynish
+Point, it was almost at the expense of our boat, which the heavy sea
+had nearly swept away from us. After all this anxiety about our safety
+and discomfort from rain, wind, and spray, during five or six hours,
+we were not sorry to set foot even on the wild shores of Tyree; and I
+trust there were none who did not gratefully acknowledge the protecting
+care of Almighty God, in preserving us through such peril.
+
+  ~Detained by bad weather four days at Hynish.~
+
+  ~Return to the Rock, and have six days of good weather.~
+
+It was not until Monday the 13th that a landing was again effected on
+the rock, as the wind continued to blow strongly from the south; and
+the intervening four days were spent in Hynish Bay, landing in the
+morning, and again returning to the vessel in the evening. During this
+time I was engaged in making drawings of some of the lower courses of
+the Lighthouse Tower, with a view to fix finally upon dimensions, from
+which working drawings and wooden moulds for cutting the stones could
+be made. The only alleviation of my impatience at being detained at
+Hynish was the satisfaction of seeing some 20 feet of the pier founded
+at low water. Late in the evening of the 13th August we again landed on
+the Rock, when we found time, before dark, to complete the fixture of
+the smith’s forge, which I had been forced to leave unfinished. Even
+the short period of work this evening was curtailed by a very heavy
+shower, which drenched us to the skin--a great evil, where there are
+many people to be accommodated in a small vessel, without room for much
+spare clothing, or the means of getting any thing quickly dried. After
+this we had an uninterrupted tract of good weather for six days; and as
+we landed every morning at four o’clock, and remained on the Rock until
+eight, taking only half an hour for breakfast, and the same time for
+dinner, we had thus the work of twenty-eight persons for about ninety
+hours.
+
+  ~Erection of the Pyramid of the wooden Barrack.~
+
+After carefully setting out the radial directions in which the six
+legs, or main beams were to stand, our next step was to lay off their
+approximate distances from the centre of the Barrack, and to clear a
+space in the solid Rock of sufficient extent to admit of adjusting the
+exact positions of the bats before boring the holes. This operation
+involved the necessity of blasting parts of the Rock by very small
+shots, the bores being about 1¹⁄₂ inch diameter, and 15 inches in
+depth, and so directed as to have the effect of throwing off a thin
+superficial crust without shaking the solid part below. The materials
+thus quarried in forming the seats for each post were thrown, by means
+of tackle, into the deepest pools, to prevent their being driven by the
+sea against the timbers of the barrack, and so injuring them.
+
+[Illustration: No. 4.]
+
+[Illustration: No. 5.]
+
+  ~Mode of determining the length of the Beams, and the sites for their
+  fixtures.~
+
+For ascertaining the exact length of each of the six beams, which
+formed by their union a pyramid of about 21° 30′ of inclination, and,
+at the same time, for determining its exact place, in reference to the
+centre of the hexagon, both of which elements necessarily varied with
+the level of the irregular surface of the Rock, I used the following
+simple arrangement:--Each beam being of the greatest length that could
+be required, the level and distance from the centre were ascertained
+for the longest beam, which, of course, had the lowest seat or rest,
+by means of a wooden frame, shewn in the diagram (No. 4), in which
+_a a_ is a vertical rod of iron firmly batted into the rock, so as
+to coincide with the centre of the pyramid to be formed by the main
+beams, and of sufficient length to exceed the greatest variation of
+level between the different points where the beams are likely to stand;
+_c c_ is a horizontal board which can be freely turned about _a a_
+horizontally, and resting upon a small shoulder _d_, and which is equal
+in length to the radius of the hexagon, on the horizontal plane at the
+level of the lowest beam. On this board is a spirit-level _s_, which
+regulates its horizontality; _e e_ is the approximate position of the
+lower end of the beam; _f f_ is a _pitched board_, representing the
+section of the permanent beam, on a vertical plane passing through
+the axis of the pyramid, and also shewing its inclination towards
+the centre of the pyramid. As this _pitched board_ is capable of
+being moved up or down by sliding through a groove at _g_, it may be
+successively applied to the rough surface at _e e_ in the course of
+cutting it down, and thus be made truly to represent the position of
+the beam, and, at the same time, give the inclination of the surface
+_e e_, which must be at right angles to the axis of the beam _f f_.
+In this way, by repeated trials, the surface was truly dressed to its
+proper inclination, and the length ascertained which required to be
+cut from the beam, so as to make it rest on that surface when in its
+true position. Hence, also, in the case of all the other beams, the
+length which the pitch-board _f f_ was moved upwards through the groove
+_g_, beyond the level _c c_, indicated the quantity to be cut from
+the end of any given beam.[17] The surface of the Rock, dressed for
+the seat of the beam, being thus brought to its proper inclination,
+the sliding-board correctly set and the centre line _a a_ of the
+beam carefully marked on the Rock, a square board (see fig. No. 5)
+representing the cross section of one of the beams, was then put down
+at the proper distance, so as to cover the space indicated by the
+_pitch-board_ as the site of the beam, and with its centre coinciding
+with the radius already traced on the dressed seat or bed. When so
+placed, the small round knobs, or ears, _d_ _d_ (No. 5) on this board,
+shewed the position of the holes to be bored for the bats or side
+fixtures, which, as afterwards shewn in figure (No. 8, p. 88), spread
+outwards from the axis of the beam, and thus formed a kind of dovetail.
+In order to make the holes capable of receiving the bats and, at the
+same time, embracing the timbers of the barrack, a quoin of wood (Nos.
+6 and 7) _e_, was put down, with bevelled faces or grooves _g_, cut in
+it for directing the motion of the jumper or boring iron _i_, thus:--
+
+[Illustration: No. 6.]
+
+[Illustration: No. 7.]
+
+These holes were bored with jumpers, 3¹⁄₂ inches in diameter, and were
+sunk 2 feet deep in the rock. The boring of each hole took upwards of
+eight hours, in consequence of the hardness of the material, which
+is gneiss, a stone considerably more difficult to bore than even
+the granite of Aberdeenshire. The bats or stancheons, although very
+accurately forged, were occasionally found not to fit truly, owing to
+unavoidable twists in the holes, which arose from _dries_ or veins in
+the Rock crossing the line of the hole, and thus disturbing the motion
+of the jumper. This gave us much trouble, and shewed that, had we
+determined, as I at first contemplated, to cut a lewis-hole, swelling
+towards the base, the work would have been almost impracticable. The
+mode which I had proposed for executing this operation was to bore a
+number of very small holes, inclined at the proper angle, all round the
+outside of this lewis chamber, and then to cut out between them; but
+this, as our after experience in cutting the foundation of the Tower
+proved, would have occupied an extent of time which we should have been
+very unwilling to bestow upon a merely temporary erection like the
+wooden barrack. Even as it was, and with all the retrenchments that
+could be safely adopted, the preparation of the seats for the six outer
+or main beams, and those for the six inner braces, employed twelve men
+for four days.
+
+  [17] The accented letters _e′_, _c′_, _f′_, _g′_, _o′_, _s′_,
+  in the figure (No. 4), page 85, denote the various parts of the
+  gauging-rule, when applied to the beam, opposite that to which the
+  letters _e_, _c_, _f_, _g_, _o_, _s_, in the text, refer.
+
+[Illustration: No. 8.]
+
+After the seats for the timbers had been dressed in this manner, the
+carpenters were employed cutting the beams to their respective lengths,
+the piece to be cut off being measured, as already stated, by the
+length through which the sliding-board _f f_ (No. 4, p. 85) had been
+raised above its position on the level platform on which the pyramid
+had been erected in the workyard at Greenock. At the same time, the
+stancheons (_k k_) in the figure (No. 8, p. 88), and the glands or
+collars _e_ _e_ (in figure No. 8), were let into grooves in the beam,
+and the holes admitting the screwed bolts _a_ _a_, to pass through the
+two stancheons and the beam between them, were bored with an auger,
+and widened with a red hot iron. The tops of the beams _b_ _b_ (see
+fig. No. 9), having been already fitted in the workyard at Greenock,
+so as to meet a hexagonal quoin of hardwood _e_, round which they were
+assembled as shewn in the figure (No. 9), straps of iron _d d_, were
+made to pass over the top of the whole, and were secured to the beams
+with bolts, and a spike at _a_ was driven into the centre to wedge the
+timbers tightly up, so as to fill a ring which embraced the exterior
+of the whole. It was obvious, that if the sliding-board (described on
+p. 85) had indicated the true inclination of the seat on the Rock for
+the end of the beam to rest on, as well as its radial distance from
+the centre of the pyramid and the corresponding length of the beams,
+the top of each beam must necessarily meet in its exact place around
+the central hexagonal quoin. The operation of determining the positions
+and lengths of such beams on a rugged rock, and placing them with the
+accuracy requisite, to insure their _mitering_ truly at the top, was
+attended with a good deal of trouble; and I have judged it advisable to
+give these details, as they may prove useful to others who may have a
+similar work in hand.
+
+[Illustration: No. 9.]
+
+After a good deal of trouble, owing to the lowness of the Rock and
+the smallness of its surface, the six main beams, each nearly 50 feet
+long, were raised on end by means of shear-poles, and the iron straps
+which passed over the top of them, and the ring which embraced the
+whole so as to secure them at the top, were fixed with much care. The
+temporary guys were removed on the afternoon of the 18th August. A
+plummet suspended from the centre of the quoin, after all the six beams
+were in their places and the stancheons had been run up with lead, came
+within half-an-inch of the centre bar, which was about 40 feet below
+the point of suspension, thus indicating an angular deviation of less
+than 4′. This is a very good approximation, under all the circumstances
+with which we had to contend; and it is chiefly to be imputed to the
+very accurate measures pursued in the workyard of the contractor at
+Greenock, by Mr George Middlemiss, foreman of the carpenters (who then
+acted as superintendent of the contract works), and whose intelligence
+and zeal made him, at all times, able and ready to do full justice to
+all my suggestions for incurring as little loss of time on the Rock
+as possible. The operation of fixing these six beams, which formed,
+by their union, a hexagonal pyramid of about 44 feet high, and about
+34 feet in diameter at the base, occupied only six days, including
+the cutting of the seats and the boring of the holes in the Rock.
+Much labour and time were consumed in the mere moving of beams, each
+weighing about 13 cwt., over the rugged surface of the Rock, for which
+purpose we could only use a small set of shear-poles, with crabs and
+blocks, and tackle purchase; and it sometimes happened, that merely
+for the purpose of moving a beam, it was necessary to place a special
+ring-bolt for holding a _snatch-block_ for a few minutes, in spite of
+all the care and forethought which had been bestowed, in selecting
+the most advantageous positions for placing them, before the work of
+raising the beam was begun. Nor was the necessity for securing every
+loose material by means of lashings to the Rock, before leaving for the
+night, an insignificant source of delay; for we were sometimes forced
+by the waves or the darkness, which drove us from our work, to lower a
+beam which was just ready for being fixed and to replace it in a safe
+situation.
+
+  ~Pyramid completed.~
+
+On Saturday the 18th August, the pyramid having been successfully
+erected, the men were busied for two hours, before embarking for the
+vessel, in collecting and lashing all the loose materials to the Rock,
+for the sky gave some indications of a change. As we took to the boats,
+I looked at the result of our labours with some satisfaction, not
+unmingled with gratitude.
+
+  ~Mode of living while erecting the Barrack.~
+
+During the week, while we had been engaged in fitting up the main
+timbers of the barrack, the weather had been very fine; and except the
+long hours of toil and the sea-sickness on board the vessel, there was
+nothing to complain of; but the economy of our life while moored for
+days off the Rock, was somewhat singular. We landed at four o’clock
+every morning to commence work, and generally breakfasted on the Rock
+at eight, at which time the boat arrived with large pitchers of tea,
+bags of biscuit, and _canteens_ of beef. Breakfast was despatched in
+half an hour and work again resumed, till about two o’clock, which hour
+brought the dinner, differing in its materials from breakfast only in
+the addition of a thick pottage of vegetables, and the substitution
+of beer for tea. Dinner occupied no longer time than breakfast, and
+like it, was succeeded by another season of toil, which lasted until
+eight and sometimes till nine o’clock, when it was so dark that we
+could scarcely scramble to the boats, and were often glad to avail
+ourselves of all the assistance we could obtain from an occasional
+flash of a lantern and from following the voices. Once on the deck of
+the little tender and the boats hoisted in, the materials of breakfast
+were again produced under the name of supper; but the heaving of the
+vessel damped the animation which attended the meals on the Rock, and
+destroyed the appetite of the men, who, with few exceptions, were so
+little _sea-worthy_ as to prefer messing on the Rock even during rain,
+to facing the closeness of the forecastle. As I generally retired to
+the cabin to write up my notes, when that was practicable, and to wait
+the arrival of my own refection, I was sometimes considerably amused
+by the regularity with which the men chose their mess-masters, and the
+desire which some displayed for the important duties of carving and
+distributing the rations. Even the short time that could be snatched
+from the half-hour’s interval at dinner, was generally devoted to a
+nap; and the amount of hard labour and long exposure to the sun, which
+could hardly be reckoned at less than 16 hours a-day, prevented much
+conversation over supper: yet, in many, the love of controversy is so
+deeply rooted, that I have often, from my small cabin, overheard the
+political topics of the day, with regard to Church and State, very
+gravely discussed on deck, over a pipe of tobacco. Perhaps the great
+heat below, where upwards of twenty people were confined, might in some
+measure account for this wakefulness on board the Tender.
+
+  ~Shoals of Medusæ seen.~
+
+One beautiful morning, during our stay of six days at the Rock, we
+had a visit from a shoal of small fish, whose novel appearance made
+me take them for a fleet of some species of Nautilus. Those animals
+came in such numbers, that the pale blue silky membranes or sails,
+which wafted them before a gentle breeze over the glassy surface of
+the ocean, literally covered the water as far as we could see. One of
+those animals I sent in a small phial to my friend, Professor Fleming,
+then of King’s College, Aberdeen, who assigns to it the Linnean name of
+_Medusa velilla_, and says it is noticed by Dr Walker and Mr Pennant,
+as a native of Scotland.
+
+  ~Driven by a gale to Mull.~
+
+  ~Return to Hynish, and are driven to Coll.~
+
+  ~Return to the Rock.~
+
+The threatening of the previous night was fully verified by the
+succeeding Sunday morning, as a strong southerly wind with heavy
+showers, forced us to part from our moorings at the Rock at break of
+day, and make sail for Hynish Bay, where we anchored at seven. On
+Monday I landed at Hynish; but as the wind, which had increased to a
+strong gale, was still rising and inclining more to E., Mr Macurich
+summoned me to the boat, when, with much difficulty, and at the expense
+of shipping several seas, we reached the vessel which was pitching the
+bowsprit under. This soon forced us to run for the Sound of Mull, where
+we were detained until Saturday the 25th, on the morning of which day
+we again made Hynish Bay; but the wind, which had been less violent
+when we started from Tobermory the night before, again commencing to
+blow strong from the same unpropitious quarter, we had only time to
+land at Hynish, and take on board a salted sheep (which proved a rather
+unpalatable addition to our provisions), when we were forced to seek
+shelter in our old quarters at Loch Erin in Coll. As we entered Loch
+Erin, we saw the _Regent_ (the General Lighthouse Tender) leave the
+Sound of Mull, and again put back to Tobermory. Next day (the 26th
+August) we left Loch Erin, and boarded the Regent; but the weather
+proving boisterous, we were again forced into our old anchorage, while
+the _Regent_ proceeded with the Engineer, who was then on his annual
+voyage, to Barrahead Lighthouse, without attempting to go near the
+Skerryvore. From this date the weather did not prove favourable for
+a landing until the 30th, when the wind being N.W., we sailed from
+Loch Erin at daybreak, and reached the Skerryvore at ten. We now
+discharged all the remaining materials which had been shipped for the
+Rock with a view to complete the pyramid of the barrack, which it was
+intended should stand the test of a winter, deferring the fixing of the
+habitable part till next spring.
+
+  ~Driven to Tyree.~
+
+  ~Return to the Rock.~
+
+  ~Horizontal braces fixed.~
+
+  ~Driven to Mull.~
+
+  ~Heavy gale.~
+
+  ~Timber cast on Tyree.~
+
+  ~Return to Rock, and farther progress of barrack.~
+
+_31st August._--The last day of August was one of considerable
+discomfort. Our landing at four in the morning was attended with great
+difficulty and some danger; and throughout the day we were a good
+deal incommoded by a thick drizzling rain, which continued without
+intermission. About mid-day the sea rose so much as to render it no
+longer prudent to delay leaving the Rock, and we therefore embarked.
+After lying at our moorings until half-past two, in what, to landsmen,
+was a most distressing sea, we slipped and ran for Hynish Bay, which
+we reached at 5¹⁄₂ P.M. The weather continued boisterous until next
+evening (1st September), when the wind went round to the north, and
+at eight all the men were summoned on board; but although we sailed
+at daybreak, we could not reach the moorings with daylight; and it
+was not till the morning of the 4th September, about four o’clock,
+that we could again land on the Rock. We succeeded, in spite of a
+very unfavourable day, in remaining till three o’clock, during which
+time we fixed the whole of the horizontal braces, and got everything
+which we had not been able to secure in its place firmly lashed to the
+ring-bolts on the Rock, after which we were forced to leave it for
+Mull. The gale continued to blow very hard, without any intermission,
+for some days; and on the 6th, some wreck-timber, covered with
+goose-barnacles, came ashore among the surf at the beach at Hynish, but
+no trace of its history was ever found, nor did any rumour reach us
+of a shipwreck having occurred on this coast. It was not till the 8th
+that we could again attempt to reach the Skerryvore; when, sailing from
+Mull with a fair wind, and taking on board at Hynish nine masons, and
+Mr C. Barclay, foreman of the quarriers, we again landed on it at 2¹⁄₂
+P.M. We succeeded in getting up the mortar gallery (see Plate V.), and
+in fixing some of the diagonal braces, and left the Rock about eight.
+A marrot perched on the vessel’s side this afternoon, much fatigued
+and evidently desirous to get on board; but the sailors, from some
+superstitious dread, would not admit the poor bird.
+
+_10th September._--We landed at four o’clock, and had a long and good
+day’s work until daylight left us. We were now within twenty-four
+hours at most of completing all that could be expected to be done this
+season; and it was with no small anxiety that I observed a change of
+wind from N.E. to S.S.W., accompanied by a fall of the sympiesometer;
+as in the event of a change of weather at that season, it seemed very
+uncertain when we might again land, and still more uncertain whether
+our work, in its incomplete state, could resist the winter’s seas.
+
+  ~Last day’s work on Rock this season.~
+
+  ~Precaution for the benefit of shipwrecked seamen.~
+
+  ~View from top of pyramid.~
+
+_11th September._--This was our last day’s work on the Rock this
+season. We landed at four o’clock with very great difficulty, and some
+danger of having our boats swamped; and we were forced, owing to the
+heavy sea which broke upon it, to leave the Rock at high water; but,
+about one o’clock, we were enabled to return, as the sea fell a little.
+By dint of great exertions, we got the last of the diagonal braces
+fixed, and the bats run up with lead and painted, for their protection
+against corrosion. We also contrived to remove the greater part of
+the tools from the Rock, but some we were forced to leave to their
+fate. To the upper part of the pyramid we lashed a water-tight chest,
+containing biscuits and a cask of water, to serve as a means of support
+to any shipwrecked mariners who might chance to reach the Rock. I also
+caused some spars to be lashed at various levels, by way of testing the
+effects of the sea; but to how little purpose, the sequel will shew.
+Before leaving the Rock, I climbed to the top of the pyramid, from
+which I now, for the first time, got a bird’s eye view of the various
+shoals which the stormy state of the sea so well disclosed; and my
+elevation above the Rock itself decreased the apparent elevation of
+the rugged ledge so much, that it seemed to me as if each successive
+wave must sweep right over its surface, and carry us all before it
+into the wide Atlantic. So loud was the roaring of the wind among the
+timbers of the barrack, and so hoarse the clamour of the waves, that
+I could not hear the voices of the men below; and I, with difficulty,
+occasionally caught the sharp tinkle of the hammers on the Rock. When I
+looked back upon the works of the season, upon our difficulties, and,
+I must add, dangers, and the small result of our exertions--for we had
+only been 165 hours at work on the Rock between the 7th August and
+the 11th September--I could see that, in good truth, there were many
+difficulties before us; but there was also much cause for thankfulness,
+in the many escapes we had made.
+
+After a somewhat precarious embarkation in the boats, and shipping
+several seas in our way, we reached the vessel, and immediately set
+sail with three cheers, rejoicing to have thus concluded our season’s
+work.
+
+  ~Destruction of the barrack during a gale.~
+
+  ~Letter from Mr Hogben.~
+
+After spending a few days at Hynish in making various arrangements
+for the operations of the next season, which were to embrace the
+extension of the pier, the completion of the barracks and the erection
+of sheds and workshops for carrying on the dressing of the materials
+for the Lighthouse Tower, I left Tyree with the pleasing belief that
+the successful termination of our first season’s labours might be
+taken as an omen of future success. But how uncertain are even the
+most rational sources of satisfaction which Time can furnish! On the
+12th November, I received from Mr Hogben, the clerk and store-keeper
+at Tyree, the unwelcome intelligence that the Barrack-house had been
+destroyed, as was supposed, by the heavy sea of the 3d November; and
+as his letters contain all the facts of the case in so far as they
+could be collected at the time, I cannot do better than quote them
+at full length:--“_Skerryvore Lighthouse Works, Tyree, 5th November
+1838._--Dear Sir,--I am extremely sorry to inform you, that the barrack
+erected on Skerryvore Rock has totally disappeared. It was seen on
+the 31st of October, when I observed no change in its appearance. On
+the two following days the weather was showery, with haze, so that
+the Rock was not seen; and on the 3d it rained almost all day, with
+strong breezes. In the evening the wind increased to a gale, with a
+great swell, and an extraordinary high tide. Yesterday (Sunday the
+4th) the weather was moderate, but the swell prevented the Rock being
+seen from the low ground. Mr Scott and Charles Barclay, however,
+having gone to the top of Ben Hynish, got a momentary glimpse of the
+Rock through the spray, and both were of opinion that the barrack was
+gone. This was not credited by the workmen who had been employed at
+it, but this morning we found it to be the case; the Rock was pretty
+clearly seen, but no trace of the barrack. From the circumstance of
+the yard of a large vessel, and also a piece of a boom, having come
+ashore in the direction of the Rock, we think it is not improbable
+that some wreck has happened, and that some part of it has been thrown
+upon the barrack by the force of the sea. Should any opportunity
+occur for going out to the Rock, we shall take advantage of it, in
+order to give you farther information on the subject. I remain, &c.
+(Signed) WM. S. HOGBEN.” A subsequent letter from Mr Hogben is of the
+following tenor:--“_Skerryvore Lighthouse Works, Tyree, 10th November
+1838._--Dear Sir,--This morning, Charles Barclay, with a boat and four
+men, went out to the Rock to view the site of the barrack; and, the
+weather being moderate, he got a good landing. The following is the
+state in which he found everything:--The whole barrack timbers had been
+carried away, excepting the long beam next the place where the crab
+stood which drew up the beams, and about seven feet of the long beam
+opposite the place where the other crab stood. The former of these
+beams had fallen in the direction of the highest part of the Rock, and
+had drawn one of the iron stancheons 16 inches. The latter was all
+in splinters, with one of the iron stancheons broken, and the other
+bent. The rest of the stancheons were broken at the point between the
+round and the flat, and some of them were drawn about 9 inches. The
+iron hoop which bound the top of the beams was lying at the distance
+of about the length of the beams to the eastward of the centre of the
+barrack, having one of its screws broken. Five large wooden knees were
+remaining, a ladder partly broken, some moulds for taking the angle of
+the beams, and most of the quarry and masons’ tools. The grindstone
+was thrown from the top of the Rock into a deep hole on the side next
+Tyree, a distance of about 12 yards, apparently whole. The smith’s
+forge had disappeared, and the anvil had been thrown about 8 yards
+to the N.E. of the place, where it was left; it was brought ashore,
+along with the hoop which encircled the top of the barrack. The iron
+posts which supported the bellows were standing. The crab on the S.W.
+side was thrown from its place to the east side of the site of the
+barrack, a distance of about 15 or 20 yards, and was dashed to pieces,
+excepting the axle, handles, pinion, and the trunk of the barrel. The
+other crab was thrown from its place to the N.E., over a part of the
+rock 5 or 6 feet high, to a distance of about 6 yards, and was found
+in a similar state to the former. A stone measuring three-fourths
+of a ton was found near the seat of one of the beams; it had been
+thrown up from the hole where it had been deposited while cutting the
+seats for the barrack timbers. One of the ring-bolts near the top of
+the Rock to which the chain binding the wood had been made fast, was
+broken close by the surface of the Rock, and the wood was all gone. The
+mooring buoy has also disappeared. The barrack was seen from the top
+of Ben Keen-na-vara, by some men on Saturday, 3d November, so that the
+succeeding night, which was truly awful, must have done the damage. I
+may mention, that many of the islanders say that they have not seen
+such a swell as on that evening for about sixteen years. I am happy to
+say that no damage has been done to the works on shore here, as on that
+evening the wind was about S.W., and we are pretty much sheltered from
+the wind in that direction. The shore on the S.W. side of the island is
+strewed with sea-weed, which has been carried up far beyond the usual
+reach of the tide. Hoping that the above information will suffice, I
+remain, &c.
+
+  (Signed) “WM. S. HOGBEN.”
+
+  ~Proceed to Skerryvore.~
+
+  ~State in which the Rock was found.~
+
+On the day on which I received this discouraging intelligence, I
+requested a special meeting of the Committee, for the purpose of
+deliberating as to the best course to be pursued, when I received
+instructions to proceed to the Rock, and for that purpose to hire
+a steamer at Glasgow. I accordingly started that very evening for
+Skerryvore, with the intention at the same time of removing such of
+the men from Tyree as were not to be employed during the winter. I
+left Greenock in the steamer _Tobermory_, accompanied by Mr Macurich
+of the Lighthouse tender, at midnight of the 14th November, after some
+delay in repairing a leak in the boiler, which was discovered in time
+before starting, and reached Hynish at 11 on the forenoon of the 16th,
+having got a good passage round the Mull of Kintyre. The weather was,
+however, in every other respect most unfavourable for the purpose; and
+having merely touched, in passing Tyree, at the workyard at Hynish, to
+inquire whether any thing farther had transpired, and to take on board
+Mr Charles Barclay, who had visited the Rock after the loss of the
+barrack, we at once proceeded and reached Skerryvore about 4 o’clock
+in the afternoon. The sea ran very high, and there was not the most
+remote chance of landing, but, having got into the boat, I approached
+near enough to the Rock to enable me to survey the melancholy remains
+of our labours, which seemed to be in the same state in which they were
+described by Mr Hogben. The beam which lay back on the inclined ledge
+still kept its place, having been firmly lashed by Mr Charles Barclay
+to a ring which was near it when he landed on the 10th November; and
+I could see the remains of some of the stancheons and of the crabs
+which the sea had left. After waiting, in the hope of a change in the
+state of the sea, until it was nearly dark, we again turned towards
+Tyree, in all the gloom of a stormy night, and depressed by mingled
+disappointment and sad forebodings, occasioned by the fate of our
+intended asylum from the waves. Owing to the heavy sea, and a strong
+gale against us, we hung for a long time off Hynish Point, and did not
+reach the Bay till midnight. Next morning about 7, we came off Hynish,
+in order to take in the men who were to go home for the winter. The
+ground was deeply covered with snow, which made the embarkation of so
+many persons and so much baggage a tedious and uncomfortable operation;
+and when we sailed, we experienced all the inconveniences of a strong
+gale and a heavy sea, with the concomitant of a deck covered with
+passengers, all very sick and much dispirited. Many of the men, indeed,
+seemed to be as deeply concerned for the loss we had sustained as I
+myself was. To add to our difficulties, the vessel, under the care of
+a native pilot, had touched slightly on a rock off Hynish Point, and
+gave some indications of leaking. We, however, reached Oban in safety.
+
+[Illustration: No. 10.]
+
+  ~Cause of the destruction of the barrack.~
+
+Various conjectures were made as to the cause of the destruction of the
+barrack. Those who saw it erected were so confident of its stability,
+that they could not avoid connecting its failure with some injury
+received from the wreck-timber, which had come ashore on the island
+of Tyree, two days after the supposed date of the accident. In this
+opinion they were strengthened by the total destruction of the cranes
+and other objects on the rock, forgetting that the timber of the
+barrack itself, when once let loose, must of necessity have proved even
+a more powerful agent of destruction than the driftwood of the wreck.
+But whatever doubt may exist as to the first cause of the injury, there
+seems good reason to suppose that the dismemberment of the parts of
+the structure had commenced with the removal of the horizontal braces,
+and that the beams, having thus more liberty for play and tremor,
+had gradually shaken loose the fixtures at the top, which consisted
+of straps _c_ _c_, passing right over the tops _a_ _a_, of the beams
+and _b b_, the hexagonal quoin of hardwood already noticed at p. 88,
+which were secured by means of a central bolt _d_, and finally girt
+outside by a ring, _e_ _e_, as shewn in the annexed woodcut (No.
+10.) The moment this dismemberment occurred, the beams would be free
+to work their own destruction; and the enormous leverage which they
+exerted, when dashed to and fro by the breakers, would soon snap the
+iron stancheons at the base, and throw all loose to the waves. The only
+remaining beam was that which was supported against a ledge of rock,
+and which had received the sea from the opposite direction to that in
+which it was found lying. That beam, however, although firmly lashed
+to the rock by the men who first visited it after the accident, along
+with Mr Charles Barclay, also disappeared in the course of the winter.
+As a proof how severely these beams had been dashed by the waves, I
+may state, that the only remaining part of a beam which I saw attached
+to the iron stancheons, when I landed in the following spring, was so
+thoroughly riven and _shaken_ as to be quite like a bundle of lathwood.
+
+  ~Preparations for a new barrack.~
+
+[Illustration: No. 11.]
+
+These circumstances by no means shook my belief in the suitableness
+of the plan adopted for obtaining a temporary dwelling on the rock;
+but they induced me, as soon as I received authority from the
+Commissioners, whose confident expectation of final success was not
+damped by the unhappy issue of our season’s labours, to examine very
+carefully the whole details of the ties and fastenings. In preparing a
+similar structure for next season, I resolved to strengthen the ties
+at the top, where I imagined the former failure to have occurred, by
+adding six strong stancheons _a_, _a_ (Plate V.), one to each beam,
+with heads passing through a centre-plate (H), which united them in one
+as a cap and to which they were secured by strong screws and keys. The
+nature of those fixtures will be more easily understood by a reference
+to the figures (1) and (2) in Plate VI., which shew an elevation and
+plan of the upper part of the beams. In the elevation only the beams A,
+B, C, are shewn; but in the plan, all the six beams appear _mitering_
+at their heads _n_, _n_, to the central beam or tie _o_, _o_ (see
+also Plate V.), which was introduced to counteract the tendency of
+the heavy seas that might burst inside the pyramid, and by exerting a
+powerful force in the vertical direction, might separate the beams at
+the top. In the Plate (VI.), _a_, _a_, are strong stancheons of iron
+attached to the outside of the beams by bolts, and also by collars _r_,
+_r_, attached to ears _g_, _g_. These stancheons being bent into the
+vertical direction and rounded at the top, passed through the malleable
+iron plate H, which was held down, and, as already stated, bound the
+beams together by nuts _c_, _c_, and wedges _b_, _b_. Through a hole in
+the centre of this plate, a large spike _p_ was driven, which produced
+an expansion of the central beam, and thus wedged up or tightened all
+the joints formed by the _mitering_ of the seven timbers. On each of
+those stancheons, _snugs_ were formed at _e_, capable of receiving and
+retaining in its place against any tendency to move upwards, a strong
+metallic ring _g_, which was tightly keyed by wedges at _k_. Additional
+ties of iron D, E, F, were also provided, which connected the six beams
+together in pairs. Each end of those ties was attached to the timbers
+by three spikes; one tie, D, is shewn a little fore-shortened; another,
+E, is seen only on the end; while the third F, is shewn as cut off at
+the middle. Lastly, an important change was made, by the substitution
+of malleable iron for wooden braces (see Plate V.) _b_, _b_, _b_, _b_,
+in the horizontal direction. Fixtures of this kind held the whole more
+firmly together; and their construction was such that they might firmly
+embrace each beam, without requiring any means of attachment beyond
+wedging tightly up; and thus the entire strength of the timbers was
+unimpaired by the driving of spikes or bolts. Those braces (No. 11),
+_a_, _a_, had, at each end, double knobs, and were pushed up along the
+beams, until they squeezed the timbers _x_, _x_, _x_ between them;
+plates _p_, _p_ (having holes in them through which the double knobs of
+the braces were made to pass), were then put on and keyed and screwed,
+as shewn in the figure, so that each beam was quite enclosed by
+fixtures, which were thus independent of spikes or bolts. Thin hardwood
+wedges were afterwards driven in, wherever they could be inserted
+between the iron and the timber; and those wedges were “_stitched_” to
+the beams with common nails, merely to prevent their dropping downward,
+after any temporary contraction of the timber from the state of the
+atmosphere. In all this, I have anticipated what more properly belongs
+to the works of the season 1839; but I consider it best, for the sake
+of clearness, to connect this account of the new with the destruction
+of the old Barrack.
+
+       *       *       *       *       *
+
+  ~Works at Hynish.~
+
+While the operations already described were in progress at the Rock,
+various works were going forward at the workyard in Tyree. About 16
+masons, 12 quarriers, and 4 carpenters, were employed in building
+the barracks for the workmen and in erecting smiths’ and carpenters’
+shops. A large room, paved with a stone floor, for drawing out at
+full size the courses of the Tower and making the moulds for dressing
+the stones, was also provided; and a platform of squared masonry was
+set in the workyard, on which the courses were to be laid, before
+being shipped for the Rock. During the season, the pier had also been
+carried out 256 feet, to a point 15 feet within the low-water mark. It
+was also necessary to provide depositories for the security of tools
+and other implements, as well as a large coal-shed for the supply of
+the Steamer which was then in the course of being built. It had, as
+already noticed, been determined that the stores were to be served
+out at the cost prices of the Greenock market, to be paid for once
+a month, at the same time that the wages of the men were paid. That
+arrangement had been carried into effect on a small scale, from the
+very beginning of the works; but this season it became necessary, owing
+to the increased number of men, to conduct it on a more extended and
+systematic plan; and, for that purpose, a person was required to act
+as storekeeper and clerk. In order also to preserve the provisions
+from injury by damp and to secure them from the inroads of the needy
+Celts and from innumerable rats which overrun that part of Tyree, it
+was found necessary to set apart, as a storehouse, a large room on the
+second storey of one of the workshops. The chief articles served out in
+the store were meal, molasses, sugar, coffee, tea, tobacco and butter.
+The establishment of the store entailed a great deal of trouble, and
+led to some expense for carriage and packages, as well as to occasional
+trifling losses in serving out the allowances or from injury sustained
+in the transport of the goods; but the inhospitable nature of the
+country, and the remoteness of Tyree from the ordinary steam-boat
+traffic, made the adoption of some such plan unavoidable. Amongst other
+inconveniences which attended the store, not the least may be reckoned
+the frequent importunities, on the part of the native labourers whom we
+employed, to be permitted to purchase provisions at the workyard; but
+that was never acceded to, except in cases where dearths (which are of
+frequent occurrence in the island) rendered the call irresistible. Had
+their entreaties easily prevailed, we should soon have had the whole
+population of Tyree as our regular customers at the Store.
+
+  ~Hynish Quarries.~
+
+The quarries at Hynish, as already stated, were by no means productive.
+The great proportion of the materials which had been quarried, was
+found to be applicable only to the building of the pier and the
+inclosing walls, and to the various erections in the workyard; and not
+more than _one-tenth_ of the whole could be dressed as blocks for the
+Tower.
+
+During the numerous occasions on which I had been driven by stress of
+weather to the neighbouring coasts, I had visited the quarries around
+Oban and in various parts of Morven and Mull. When so forced to leave
+what I might more especially call my _post_, I had an opportunity of
+seeing the quarries at Ardentallen near Oban, which contain the old red
+sandstone strongly impregnated with clay. That stone is by no means
+suitable for the _face-work_ of a marine building, in such a situation
+as the Skerryvore; while the comparatively small quantity of _hearting_
+which could be admitted into such a work, made it inexpedient to seek
+such materials at so great a distance. In this way, the Ardentallen
+quarry seemed completely excluded from the field. At another time, in
+passing through Inverary, I devoted a day to the examination of the
+quarries which had lately been opened at that place and in which a
+beautiful porphyry is wrought; but I saw no appearance of very large
+blocks, or, at all events, nothing that could favour the expectation
+of a considerable supply. But after carefully weighing the matter,
+the great masses of granite at the Ross of Mull finally determined my
+choice in favour of that locality; and the Duke of Argyll having, with
+the greatest liberality, ratified his predecessor’s grant of liberty
+to the Lighthouse Board to quarry stones from any part of the Argyll
+estates, it was resolved to take measures early in the spring of 1839
+for opening quarries at North Bay, in Mull, where an excellent station
+for shipping had been discovered, close to the place where we saw
+the most promising appearance of rock. This measure seemed the more
+indispensable, as the last part of the quarry _terred_[18] or laid bare
+at Hynish, had greatly disappointed our expectations. The unworkable
+nature of gneiss rock also and its extreme uncertainty with regard to
+quality, farther concurred to make a change most desirable. Granite,
+indeed, is a material in many respects superior to sandstone, gneiss,
+or porphyry. The first it greatly excels in durability and weight; and,
+as a stone for the workyard, it is superior to the other two, from
+its property of being _fissile_, or easily split in any direction. In
+this respect it resembles certain parts of some sandstone strata which
+are commonly called _liver rock_, of which Craigleith quarry, near
+Edinburgh, furnishes an excellent example. Porphyry, and, I think,
+all other igneous rocks (excepting granite), gneiss also, and most of
+the other primary rocks, have not this property, being _fissile_ only
+in one plane, so that quarries of those rocks generally turn out very
+uncouth or irregular stones, which, though they may in some favourable
+cases possess good natural _beds_, will always be found to have ragged
+and irregular _joints_, which, for the most part, are incapable of
+being properly dressed.
+
+  [18] This term in Scotland denotes the removal of the soil and
+  unsolid material, in order to lay bare the rock previous to working
+  the quarry, and seems obviously to be derived from the Latin “terra,”
+  perhaps through the medium of some old charter. The quantity of
+  terring very much affects the profitable working of a quarry.
+
+
+CHAPTER V.
+
+OPERATIONS OF 1839.
+
+  ~Shipping Station and Pier at Hynish.~
+
+During the winter months which intervened between November 1838 and
+March 1839, a small detachment of men, consisting of three masons, nine
+quarriers, and one smith, were left at Hynish under the superintendence
+of Mr Charles Barclay, to clear the landing-place of several patches
+of rock which encumbered the entrance. They were also to build some
+walls of inclosure, and to quarry and dress stones for the pier
+and other buildings at Hynish. The provision of accommodation for
+shipping at that place was now naturally regarded as of more urgent
+necessity than formerly, because the importation of stones from Mull,
+which the failure of the Tyree stone had rendered unavoidable, led to
+the necessity of a reshipment of all the materials at Hynish, where
+they were dressed before being sent to the Rock. It may, perhaps, be
+naturally enough imagined, that instead of importing the materials to
+be dressed at Tyree and there reshipped in order to be carried to the
+Rock, they might have been prepared in Mull, and sent directly to the
+Skerryvore; but many things concurred to render this inexpedient, if
+not altogether impracticable. The advantage of being able, by means of
+a good telescope, in some measure to ascertain the state of the sea
+at the Rock, the comparative shortness of the passage, which gave the
+prospect of several cargoes being landed on it in one day during fine
+weather, and the convenience of communicating with the Rock by signal,
+were circumstances in themselves quite sufficient to determine my
+choice in favour of Hynish, as the place from which the materials must
+be shipped for the Rock, even if there had been no other considerations
+leading to the same conclusion. But in addition to all this, I could
+not fail to perceive that Hynish was the only place for the permanent
+station of the vessel attending on the future Lighthouse; and that on
+that account alone the construction of a Harbour there was unavoidable.
+That the arrangement, by which the future station for the Tender was
+used as the workyard for the operations, was the most judicious that
+could have been adopted, was fully proved by my subsequent experience
+of the advantage of assembling all our materials and all our force at
+a point as near to the Rock as possible, so that we might be at all
+times ready to supply defects or omissions, and take advantage of every
+favourable change of the sea or sky.
+
+In the middle of March the _Regent_ conveyed from Aberdeen a detachment
+of twenty-nine masons and quarriers and five smiths, and the foreman
+of the workyard, who, together with the men already at Hynish and the
+native labourers, were to be employed during the season of 1839, in
+the various departments of the work. On their arrival the men were
+separated into two small bands, of which the one, consisting of six
+masons, twelve quarriers, one smith and a foreman, was stationed at
+North Bay in Mull, where the new quarries were to be opened; while the
+other had its head quarters at Hynish, and, when not engaged in the
+work on the Rock itself, was subdivided into smaller parties, varying
+in number with the nature of the particular operations in which the men
+were occupied.
+
+  ~Granite quarries in Mull.~
+
+On the afternoon of the _19th April_ I sailed from Greenock in the
+_Regent_, for North Bay in Mull, where the quarries were to be opened.
+We had on board the whole materials of the new Barrack, which was to
+supply the place of that which had been destroyed in the preceding
+month of November; and we had also a party of carpenters who came to
+fit up the Barrack in a temporary manner at North Bay, as a residence
+for the masons who were to be engaged in preparing more permanent
+dwellings for the quarriers and in forming a landing-wharf for the
+shipment of the stones for Tyree. It was not till the 25th, after a
+tedious passage of six days, that we anchored at North Bay; and next
+morning we had the satisfaction of seeing the steamer, the _Skerryvore_
+(by which name she was specially set apart for the service of the
+works), arrive in the Bay with a party of masons and quarriers, who had
+been appointed to meet us in order to begin the work.
+
+The necessary arrangements with the Duke of Argyll’s tenants at the
+_Ross_ of Mull (in which district North Bay is situated) having been
+already made, no time was lost in erecting the wooden Barrack; and, in
+seven days after our arrival, the masons and quarriers entered their
+new habitation under the charge of Mr Charles Stewart, whom I left as
+foreman of the North Bay works. Mr Stewart and his party, following the
+example of diligence thus set to them, were not less expeditious in
+proceeding with the work which had been assigned to them; and by the
+beginning of August a range of barracks, capable of accommodating forty
+persons, had been erected, a landing wharf had been built, and various
+storehouses had been provided, although the quarry had to be opened,
+and the blocks of stone required for those various works were still _in
+situ_ at the time of our landing at North Bay three months before.
+
+The landing wharf is placed on a small projecting face of rock in a
+depth of 12 feet at high water of ordinary spring tides. It presents
+a face of 40 feet in length, and was provided with wooden fenders
+for the protection of the vessels loading stones. Landward of it a
+considerable space was levelled, by cutting and filling, to serve
+as a yard for storing the quarried materials, so as to be ready for
+shipment. The quarry itself was opened in the face of a hill, so steep
+as almost to deserve the name of a cliff; but advantage was taken of a
+deep gully which intersected it and in it an inclined plane was formed
+communicating directly with the landing-place. This gully was partly
+cleared by excavation of the rock and partly, where necessary, its
+inequalities were smoothed down by filling it with stone shivers; and
+along its bed thus prepared, longitudinal sleepers of timber were laid,
+to which _edge-rails_ were attached.
+
+At the top of the incline two iron drums or barrels were set, and round
+them were wound, in opposite directions, the chains by which the trucks
+or wagons, loaded with stones from the quarry, were lowered to the
+wharf below. A powerful break apparatus was attached to those barrels,
+to check the velocity of the descending wagons, which was also in part
+counteracted, by making their gravity act as a power to raise the empty
+wagons in the same manner as is usually practised in coal-mines.
+
+The quarry itself, as already stated, was opened in the face of the
+cliff, at a point where the successive beds of solid rock seemed to
+promise the fairest prospect of success. The preliminary operation was
+to remove a very thin alluvial cover which scarcely concealed from
+view a large mass of most beautiful granite, whose reddish colour
+is said to have given the name of _Ross_[19] to that part of Mull,
+the shores of which everywhere exhibit massive slopes of that fine
+rock. The granite is separated very abruptly from the basalts of the
+surrounding district, so as to leave the Ross purely granitic; but in
+no part of the whole coast, which abounds with creeks and bays, does
+the rock appear to be of equal quality, or so conveniently situated
+for shipping, and so easily accessible to quarriers, as at the spot
+we had chosen. I know of no instance of a quarry so fully answering
+the most sanguine expectations as that of the Ross of Mull; and I
+have never seen a granite quarry of equally great resources, as
+regards both the quantity and the quality of the material produced.
+The rock in general yielded easily before well-directed shots, and
+was separated into large masses, capable of being advantageously
+cut, with little loss of material, into shapely blocks, by means of
+wedges, which work remarkably well in that rock. A few weeks after the
+quarrying operations had been commenced, a single shot detached 150
+tons of excellent stone, in the cutting of which into blocks for the
+Lighthouse Tower little loss of material occurred; and in the course
+of the season of 1839, although the summer was chiefly spent in the
+preliminary works above noticed, the Mull quarries produced nearly as
+much workable material for the Lighthouse Tower as the Hynish quarries
+had done in three years. In the course of the future working of the
+quarry, when it came to be more fully opened, its resources were so
+great, that on one occasion a single shot shook about 570 tons, while
+another shot detached a mass of 460 tons. In that way, between April
+1839 and June 1840, material had been quarried in that single spot,
+sufficient to supply 4300 selected blocks, varying in weight from ³⁄₄
+ton to 2¹⁄₂ tons each. The average monthly produce of the quarries was
+about 400 tons, and there were generally employed in them 26 quarriers,
+3 labourers, and 2 smiths. The quantity of gunpowder consumed in the
+quarry was small, as it was almost exclusively employed in great bores
+about 11 feet deep, for the purpose of detaching large masses which
+had no _open side_ and could not be removed by means of the _pinch_ or
+_crow-bar_. When a mass of rock had been thus removed, it was cut up
+into various portions by means of wedges, and finally subdivided into
+blocks, _hammer_ (or as it is called _quarry_) _dressed_, according
+to rough moulds, whose dimensions exceeded those of the stones of the
+various courses of the building by a quantity which was considered
+sufficient to cover any casualty in the final dressing of the block
+by the masons at Hynish, and which allowance was generally equal to a
+film of rock about 1¹⁄₂ inch in depth. The blocks thus roughly formed
+were shipped for Hynish, distant about 26 miles, through a tempestuous
+sea, open to the full reach of the Atlantic towards the south-west,
+sometimes in a small vessel called the “Queen,” belonging to the
+Commissioners, and sometimes in undecked boats of 16 tons, belonging
+to the adventurous men of Tyree. The freight usually paid was 5s. a
+ton, and yet the whole of the blocks for the Lighthouse Tower, and many
+of those used in the pier at Hynish, were laid down to the number of
+about 5000, at the rate of 2s. 1¹⁄₂d. per cubic foot, including all the
+expense of building barracks, opening quarries, freight of stones, and
+the expense of building and maintaining the small vessel called the
+“Queen,” above noticed. The stone of the Mull quarries is a reddish
+or flesh-coloured granite, in which felspar predominates. About 13·66
+cubic feet weigh a ton, and it is not quite so hard as the granite of
+Aberdeen.
+
+  [19] Whether from any inflection of the Celtic _Rhua_, or _Roy_, or
+  directly from the Italian _Rosso_, it would, perhaps, be impossible
+  to determine.
+
+  ~Observations on the quarrying of granite.~
+
+As I am not aware that any professional work contains a detailed
+description of the quarrying of granite, some observations on that
+subject may not be unacceptable in this place; and I therefore propose,
+at the risk of appearing somewhat prolix, to give a pretty minute
+account of the mode of opening and working a granite quarry, more
+especially as practised by us at North Bay.
+
+Having laid bare the rock of earth, gravel, or other loose matter
+(which operation, as I have elsewhere mentioned, is in Scotland
+technically called _terring_), and having swept or washed clean the
+surface of the rock so as to have a good view of the natural seams or
+joints which traverse it, the next step is to fix the best place for
+putting in a bore or mine.
+
+In selecting the position of the bore, the direction of the seams and
+veins of the rock must be duly considered, with a view to employ the
+force of the explosion to the greatest advantage in separating the
+natural joints or beds of the rock, instead of shattering the solid
+_masses_ or _posts_ (as they are called in the language of the quarry)
+into shivers or fragments.
+
+One thing to be strictly borne in mind is, that the bore should never
+be in the centre of a fine or large block, but should be placed within
+a few inches of its back so as not to break the finer rock into small
+and useless fragments; and care must, at the same time, be taken to
+keep the bore clear of cracked or unsound rock, as the jumper, in
+passing through such material, is liable to be jammed by the cracks
+and fissures before it can be driven to the proposed depth. It is not
+possible to lay down precise rules for guiding the quarrier in choosing
+the place of the bore, as his plan must be regulated chiefly by the
+circumstances of each case; but it may be observed, that having first
+determined the depth of the hole, it will seldom be found advantageous
+to keep the bore farther back from the face of the rock than about
+_four-fifths_ of that depth. The depth itself, also, to which the mine
+should be carried, is a point for deliberation with the skilful and
+experienced quarrier, who will take great care not to go so deep as to
+pass through the solid rock in which he is boring and thus to touch
+a bed, unless indeed he shall think it advisable to attempt to raise
+more than one _post_ of rock by a single mine, in which case he will
+carry the bore through the first post into the second or third as the
+case may be. But in all cases the boring must be stopt at two inches
+before coming to the bed or seam of the post in which the mine is to
+terminate, lest the exploding powder should escape by the bottom of the
+bore, and thus leave the top of the rock altogether undisturbed. In
+endeavouring to procure large materials, the bores should in general be
+as deep as possible. It is only experience, however, which teaches the
+quarrier to form a sound _prognosis_ as to the direction and level of
+the beds of the rock at any particular spot, and enables him to choose
+the most advantageous position and depth for the mines.
+
+In the blasting of granite there are a few general rules which
+(although it may not be necessary to follow them in every case) may
+be considered as constituting the best practice. If the bore be a
+vertical one of the depth of 6 feet, 2¹⁄₂ inches diameter at the
+top, diminishing to 2 inches at the bottom, may be considered a
+proportionate caliber. If the bore be a deep one (perhaps of 14 feet),
+its diameter will require to be 3¹⁄₂ inches at the top, and should
+diminish to 2³⁄₄ inches at the bottom; and the quantity of powder
+required for the charge will in most cases be about as much as is
+required to fill ²⁄₅ths of the hole.[20]
+
+  [20] Miners and quarriers, who always work by empirical rules,
+  disregard entirely the _line of least resistance_ as a measure for
+  the _charge_, and invariably refer to the _depth_ of the bore.
+
+The patent _fusee_ having been inserted among the powder, with its end
+about the centre of the charge, and the upper part of the bore having
+been filled up with dried clay, well forced down with a wooden rammer
+faced with copper, a length of 3 or 4 inches of the _fusee_ should be
+left outside the bore, to which the match is to be attached. Having
+cleared away every thing near the blast which can receive any injury
+and covered up the machinery of the cranes with strong planks, the
+mine may be said to be ready for being fired; and, on a signal given,
+by blowing a horn, all hands retreat to a safe distance, with the
+exception of the fireman, who then lights the match, and follows the
+others as fast as possible.
+
+If, as already stated, the object in quarrying be to obtain large
+materials, the bores should, if possible, be deep; and, in that case,
+the rock will seldom be thrown down in fragments by the blast, but will
+merely be cracked, and intersected by rents about one inch in width.
+Recourse must therefore be had to what, in quarry language, is called
+a _Bull_, which consists in running a quantity of loose powder into
+the crack which has been made by the blast, at that part where its
+explosion seems most likely to throw out the cracked or broken mass
+in various fragments and disengage them from their place in the rock.
+In _bulling_, perhaps twice as much powder as was used in the bore is
+loosely poured into the crack, care being at the same time taken to get
+as much of it to go under the bottom of the rock as possible. After
+enough of powder has been poured into the crack, a quantity of dried
+smithy ashes, or dry sand, is run in over the powder, so as completely
+to cover it, except so much as is required to fire it by; and that
+coating, which is merely superficial, is employed partly to keep down
+the powder, and partly for security against its being accidentally
+fired before all things are ready. The fireman having seen every thing
+cleared away, gives notice to sound the alarm, when all hands escape
+to a distance in the direction which is supposed to be the safest. The
+match is then applied, and the fireman retires, as fast and as far as
+he can, yet so as if possible to keep in view, during his retreat, the
+progress of the match. The operation of _bulling_ is far more dangerous
+than the firing of a bore, as the charge is much greater, and not so
+well confined, so that many splinters are thrown off, and the direction
+in which they fly varies continually with the direction of the cracks
+which the original bore may have produced. As might be expected, by far
+the greater part of the accidents which occur to firemen in granite
+quarries, arise from that practice.
+
+[Illustration: No. 12]
+
+Should it happen, as it sometimes does, that after having gone through
+those operations, the quarrier fails in getting the cracked mass
+thrown down to the bottom of the quarry, he varies his mode of attack,
+and proceeds to bore a row of _plug-holes_ on the face of the rock
+in such a line as to cut off a part from one end of the shaken mass;
+and for that purpose he is often obliged to hang a scaffold over the
+face of the rock on which to stand while boring the holes. Those
+plug-holes should be slightly inclined, so that, when the wedges,
+called _plugs_[21] and _feathers_, are driven into them, they may rend
+the rock in such a direction that the piece intended to be cut off may
+be a little narrower on the inner than the outer face, so that, thus
+resting on an incline it may be more easily taken out. The plug-holes
+should be cut at one foot asunder, and bored with a jumper 1¹⁄₂ inch
+diameter to the depth of 9 inches; and if the plug-holes be deep, and
+some difficulty in driving be expected, the plugs should be carefully
+greased or oiled previously to being driven. Having cut off a block
+as above described, an attempt may be made, if the mass be great, to
+throw it down by means of _bulling_; but if it be of lesser dimensions,
+and there be reason to expect that it may be removed in the ordinary
+way, the power of the crane may be applied to draw it down. For that
+purpose, the quarrier employs an instrument called a _Dog_, which is
+a strong short hook, armed like a pick on the point with steel, and
+having a ring in the end of it for the hook of the crane-chain to pass
+through. Having cut a small hole with a pick, on the upper part of the
+block which is meant to be removed, the _steeled_ point of the dog is
+inserted into it, in such a manner that the weight of the crane-chain
+may retain it steadily in its place. Five or six men then heave on
+the crane a strain just as much as they suppose it may bear, without
+danger of carrying away any of its fixtures; and as many men as can
+find room are, at the same time, employed at the top of the rock,
+working with crow-bars behind the block, so as to shake it and loosen
+its hold. The two parties continue their work reciprocally, leading
+and following,--the men at the crane, still keeping up the strain, and
+taking care not to heave so much as to break any of the chains, while
+those on the top continue to shake the block by means of the crow-bars,
+or throw in stones into the opening, which is always getting wider
+between the block and the cliff, so as to prevent the loosened mass
+from falling back into its old place. When the block has been drawn as
+far forward as to appear just ready to fall over the cliff, one of the
+most expert men at the crane stands carefully watching the movement of
+the block; and whenever the stone begins to fall, he instantly throws
+the crane _out of the gear_, so as to prevent the wheelwork being
+pulled to pieces by the tumbling mass getting entangled in the chains,
+on which it frequently falls and breaks them to pieces. The operation
+of taking down large blocks from a great height is very tedious, and
+is often attended with much danger, as the stone, when it falls on the
+bottom of the quarries, makes the shivers among which it alights fly in
+all directions with a force which nothing can withstand.
+
+  [21] The _plug_ (fig. 12, _c_ _c′_), and _feathers_ (fig. 12,
+  _d_ _d′_), are flat pieces of malleable iron, slightly tapered, and
+  forming together a kind of compound wedge, the two feathers being
+  first inserted into the hole, and the plug being driven between them
+  by a series of gentle blows, from malls of the weight of from 30 lb.
+  to 35 lb.
+
+An opening being made in the manner above described, by getting one
+piece brought down, the same process is continued by cutting off and
+taking down pieces of eight or ten tons weight, until there be as many
+blocks in the floor of the quarry as can be easily managed at one time.
+Those masses are then arranged by means of the crane in convenient
+positions for being cut up into blocks of the requisite sizes; and as
+all of them are within range of the crane, they can with its assistance
+be easily turned over or set in any position. While some of the men
+are employed in cutting up those blocks, others are clearing away the
+rubbish, and others are boring holes or making ready for a fresh blast.
+
+[Illustration: No. 13.]
+
+If those blocks, which we have supposed to be brought down to the
+quarry floor and to be ready for cutting, exceed seven feet in depth
+of cut, their farther subdivision will require the use of the plugs
+and feathers already described; but if their depth or thickness fall
+short of that, the ordinary iron wedges will answer. If the cut be of
+the depth of about 6 feet, the wedges must be placed about 3 inches
+apart from side to side; but if the depth of cut be less, they may be
+set 4 or 5 inches asunder. The method of setting in those wedges is
+as follows:--The person who cuts the wedge-holes generally works in
+a sitting posture, and if the block will admit of it, he prefers to
+bestride it, with a stone, as a stool, under each foot. He works with a
+pick of 16 lb. weight, having a handle only 16 inches long, with which
+he cuts the first hole generally about 3 inches from the end of the
+block. The holes are for the most part about 2¹⁄₂ inches deep, and 3¹⁄₂
+inches long, and must be well cleared out at the bottom with a sharp
+pick; and the wedges must be set in a line as fair and straight as
+possible. Cutting wedges of that kind are of iron, from 7 to 9 inches
+long, and 2¹⁄₂ inches broad, and weigh about 7 lb. weight each. When
+in good order they must not be sharp in the mouth, but about ³⁄₈ of an
+inch thick, to prevent their _grounding_ in the bottom of the hole; for
+if they but touch the bottom of the hole, they fly out at the first
+touch of the mall. When the wedges have been all properly arranged for
+a cut, the workman proceeds to give each of them in succession a gentle
+tap, so as to make them all fast; and for that purpose he uses a mall
+about 30 lb. weight (fig. No. 13), and having a handle 2 feet 9 inches
+long. He then goes over all the wedges, giving each of them a smart
+blow in regular, yet not too rapid succession, but allowing a little
+time for the parts of the stone to separate gradually. If the wedges be
+forced too quickly, there is great danger of the cut being spoiled by
+its flying out obliquely at one side, and thus not reaching throughout
+the whole depth of the block. The blocks, when thus subdivided by
+means of the wedges, are generally nearly of the size required by the
+rough moulds sent from the workyard, and are fit to be carried to the
+stone-cutter’s shed.
+
+[Illustration: Fig. 14.]
+
+As a conclusion to the above account of quarrying, it may perhaps be
+thought desirable to give some notion of the probable time required to
+perform certain parts of that sort of work. In boring holes of 1 inch
+to 1¹⁄₄ inch in diameter, it may be observed that they are generally
+done with the _hand mall_ (fig. No. 14), one and the same person
+striking with the mall with one hand, and turning the boring tool for
+himself with the other; and in most cases a man will bore 9 or 10
+inches an hour in granite rock. If the bore be 1¹⁄₂ inch diameter, as
+for plugs, three men will generally bore two plug holes in one hour,
+each hole being about 9 inches deep. If the bore be for blasting and of
+2 or 2¹⁄₂ inches diameter, three men will bore, at the rate of one foot
+per hour, to the depth of 6 or 7 feet; but if the bore be for a large
+blast of 13 or 14 feet deep, the hole must be 3¹⁄₂ inches in diameter
+at the top (diminishing to 2³⁄₄ inches at bottom), and will employ
+three men working hard between two and three days. Bores of that sort,
+indeed, cannot be made (at least by hand) to a greater depth than 14
+or 15 feet, as the weight of a rod of iron, 17 feet in length, and 2
+inches in diameter, makes it quite unmanageable for one man either to
+turn or to lift; while, from its great mass, the strokes of the mall
+produce little effect on it. The malls used in boring holes, which
+require three men, are 7 or 8 lb. weight, having handles 3 feet long
+(fig. No. 15), and are swung over the shoulder, while striking for
+_down bores_, in the same manner as a smith’s forehammer is used. An
+expert cutter with the wedges will make good wages by cutting holes at
+the rate of 2¹⁄₂d. for a dozen of holes, taking light and heavy cuts as
+they come to hand.
+
+[Illustration: No. 15.]
+
+What has been said above of boring and blasting refers only to
+_downright_ or vertical bores; but, in the lower parts of a quarry, it
+is often necessary to have recourse to what are called _breast-bores_,
+from their running in a nearly horizontal direction and piercing the
+front or breast of the rock. Those bores are not so easily made as
+the _downright_ bores and, in general, are only used where the rock
+is low, or in taking up bottom rock. They can seldom be carried to
+a greater depth than about 9 or 10 feet, owing to the difficulty of
+turning the jumper, and can never be bored quite horizontally, but
+require as much dip as will retain a little water in the hole to keep
+the jumper moving. Instead of throwing the mass outward, as is done
+by _down-bores_, those _breast-bores_ generally only cut or break the
+stone in the direction or line of the bore, so that the block always
+requires to be afterwards removed by _bulling_, in the manner already
+described.
+
+  ~Dressing of the Lighthouse blocks.~
+
+The dressing of the blocks for the Lighthouse Tower, as already
+mentioned, was one of the most important operations in the workyard
+at Hynish; and as no writer with whom I am acquainted has given any
+account of the mode now practised of dressing granite, I hope I shall
+be excused for attempting, in this place, to give some idea of the
+method employed by the masons of Aberdeenshire, whose skill in that
+department of workmanship is well known both in our own and in other
+countries. As the whole of the materials for the Tower were to be
+dressed in such a manner as to avoid the necessity of any fitting
+on the Rock, by the introduction of what are technically called
+_closers_, the greatest accuracy in the formation of the moulds
+from which the stones were to be shaped became necessary. With that
+view, I had a _trainer_ or _radius_ made with a moveable _vernier_,
+capable of sliding along it, so as to give the differences between
+the _readings_ of the feet, as far as to the _thirtieth_ part of an
+inch; and I was thus enabled to lay off the _batter_ or slope on each
+course (according to the quantities in the Table of Co-ordinates in
+the Appendix) with great nicety, and so to trace very distinctly the
+contour of the intended column.[22] On the stone floor of an apartment
+in one of the workshops, the _quadrant_ of each course of the building
+was carefully drawn out, at full size, and divided into the sectors
+which were required for preserving a due _bond_ among the joints of
+the adjoining courses. The form of each stone in the tower having been
+thus determined by those full-sized draughts, moulds, representing the
+_beds_ and _sides_ of each stone, were prepared according to them,
+of seasoned timber, well shielded at the angles with sheet-iron, to
+prevent their being injured. Those moulds having been marked with
+reference to the number of the course, and the position of the stones
+in the wall, were given to the foreman of the workyard, who regulated
+the work of each of the stone-cutters, often to the number of 70 men.
+A proper block having been selected for each stone, leaving about 1¹⁄₂
+inch all round the extremity of the moulds when applied to its several
+faces, it was conveyed, by means of the sling-cart, to the shed where
+it was to be dressed. The shed for dressing granite stones differs in
+no respect from an ordinary mason’s shed, except in its greater height;
+but, as the stone cutter, in order to wield his tools to advantage,
+must, at certain parts of the work, stand on the top of the block, it
+has been found, that a height of about 15 feet is required for the
+back-wall of a granite mason’s shed. Each man also requires, for large
+blocks, a space of about 10 feet (measured along the front of the
+shed), as his peculiar territory.
+
+  [22] Such nicety, I would observe, was by no means superfluous,
+  because the arrangements of the Tower precluded the possibility of
+  using a trainer in building; and as the whole was done by means of
+  _plumb-templets_, the greatest accuracy in tracing the curve of the
+  Tower became necessary, as the only true basis of good workmanship on
+  the Rock.
+
+When a block has been brought to the shed, the first thing to be
+done, if it is a large stone of 1¹⁄₂ or 2 tons weight, is to lay it
+nearly level on the ground, with the side which is to be first dressed
+uppermost. The form or _plan_ is then sketched upon it according to the
+mould, and the stone is _blocked_ out with a large hammer weighing 30
+or 35 lb. (fig. No. 16), which is the most suitable weight for ordinary
+men, although a stout man will manage one of 40 lb. well enough, if
+the block be lying in an advantageous position. When the stone has
+been thus rudely _blocked_ out, it is set upon its edge with a gentle
+inclination to one side, so that the mason, who mounts on the top of
+it, may conveniently use a pick of 18 lb. weight, having a handle three
+feet long, to dress off very roughly the most prominent parts of its
+irregular surface. In doing that he makes a great many deep ruts in
+a downward direction, at the same time taking care that none of them
+shall be so deep as to fall below the general surface of the stone when
+finished. When he has in that style dressed as far down the surface of
+the stone as he can conveniently reach, (and that is generally about
+half way,) the stone is then thrown over and set up on the opposite
+edge, when he again mounts upon it, and goes over the rest of the
+surface in the same manner, until the whole shall be reduced to one
+rough plane, so that in spite of numerous partial inequalities, the
+general face may be straight, or what is technically termed _out of
+winding_. A stone in that state is also said to be _well opened_.
+
+[Illustration: No. 16.]
+
+[Illustration: No. 17.]
+
+[Illustration: No. 18.]
+
+The next step is to raise the stone so that it may incline at about 30°
+or 40° with the horizon; after which the mason, standing at the higher
+side, commences to put on the _draughts_ or _guide-lines_ all round the
+edge of the face which he has just _opened_. For that purpose he first
+employs a pick of about 12 lb. weight, having a handle about 2 feet in
+length (fig. No. 17), with which he dresses a band of about 3 inches
+broad, taking care that this band or draught be straight and _out of
+winding_. He then, with the pick, goes over the whole face between
+the draughts, dressing off all the ridges which still remain between
+the ruts which he had made while the stone was standing on edge, as
+before noticed, so that the whole surface will present the appearance
+of a pretty regularly _dabbed_ face. Having arrived at that stage, he
+next proceeds to put on the _true draughts_ (as round the edges of the
+stone, as in the case of the _guide-lines_), with the cast-steel chisel
+or _punch_ (_a_, _a′_, fig. No. 18), and a small iron-mall of 3¹⁄₂ lb.
+weight; and afterwards with the axe, he carefully _axes_ a band about
+2¹⁄₂ inches broad, so as to be quite out of winding, and as straight as
+possible all round. The dressing is then completed between those bands.
+If the block be a broad one, the mason will probably be able to take
+in only one half of the face at a time; and, in that case, the stone
+must be let down at the high side, and the other one raised as high as
+may be necessary to enable him to work to advantage. If the surface
+thus dressed, which is in this case supposed to be the largest side, be
+intended for the _bed_ of a stone, the knobs or high points between the
+_pick-dabs_ are merely roughly dressed down with a blunt axe, so as to
+be all as low as the axed lines or draughts round the extremities, and
+thus to present no convexity on which the stone, when laid, could rock;
+but if the surface should be meant for a fine _face_, the dressing
+must be commenced with a bluntish axe, taking care that all the axe
+marks be made quite across the stone, at right angles to the side
+where the workman stands. The whole face having been once gone over in
+that manner with a blunt axe, a sharper and well ground axe is next
+used for crossing the first axing in such a manner that all the second
+axe-marks may be inclined at an angle of 45°, or thereby, with the
+first. The whole face having been thus brought to a smoother and more
+uniform surface, the third and last axing follows; and then the mason
+uses his shortest and lightest axe, which must, for that work, be well
+ground and sharp. That axing must be done right across the block, or in
+the same direction as the first axing had been done, and in that state
+the surface of the stone may be supposed to be fine enough for most
+kinds of work used in housebuilding or in public works; but for very
+fine work, such as some sepulchral monuments, or for surfaces which are
+afterwards to be polished, it is not unusual to axe four or even five
+times, care being always taken that how often soever that operation may
+be performed, the axing should never be made twice consecutively in
+the same direction, for by that precaution alone can a true and even
+surface be obtained. (The form of the axe is shewn in fig. No. 19.)
+
+[Illustration: No. 19.]
+
+[Illustration: No. 20.]
+
+The dressing of the first face being finished in the manner described,
+the block is laid flat on the ground, and the plan or form of the stone
+is then accurately drawn on it, according to the mould, with some
+substance that makes a bright or good mark, such as a piece of tile
+ground sharp, or a thin splinter of logwood. If there be much _waste_
+to be taken off beyond the lines so drawn, a hammer, whose weight must
+be in proportion to the piece to be struck off, is applied; but care
+must be taken not to come too near the lines with the hammer, and it
+is generally safe to leave at least an inch outside of them. The piece
+which is left gives a good hold for the _chipper_ or _pincher_ (fig.
+No. 20), which is next carefully applied along the line, being steadily
+held within one hand, and with the other sharply struck with a small
+iron mall of 3¹⁄₂ lb. weight, having a short handle about 8 inches in
+length. While the _chipper_ receives sharp strokes in succession with
+the mall, it must be slowly moved several times along the line from
+one end of the stone to the other, till the piece projecting beyond
+the line, or a part of it, breaks off. Such is the power of this small
+instrument, that it not infrequently cuts down to a depth of 9 or
+even 12 inches, thereby doing more execution and to greater purpose,
+than a heavy hammer can generally accomplish, even in the hands of a
+skilful workman. The _chipper_ is a tool lately introduced; but has
+now become a most important article in every hewer’s _kit_. It makes a
+regular and clean cut, and leaves little to be done by the punches and
+chisels (fig. No. 18, in p. 122), in preparing the _arris_ of the next
+face of the stone. The block is now raised a little from the ground,
+and the workman standing at its higher side, the axing of which he
+has just finished, puts on with the punches and chisel a fine band or
+draught along the side next to that just dressed. He then applies to
+the finished face the _square_ or _bevel_, according to the inclination
+of the faces, and dresses a band across the stone at each end of the
+block; and, finally, joins those two cross bands by means of another
+band along the back. In that way the external draughts on the second
+side are completed. He then with the pick and axe dresses away the
+material between those draughts until the second face is finished;
+and the same process is repeated for each side of the block which
+requires to be dressed. If the block be a large one, and it require
+to be dressed on all its sides, it will, lastly, be cut to the proper
+thickness or height, which is regulated by means of a gauge, known,
+in the technical language of the shed, as “_a grippers_” (fig. No.
+21),[23] from its embracing the stone on three sides. It is simply
+a three-sided iron templet, having one long and one short tail (at
+right angles to the connecting piece), the space between the two tails
+shewing the thickness of the stone.
+
+  [23] The figure shews “_a grippers_” for a stone 14 inches thick.
+
+[Illustration: No. 21.]
+
+The practical reader will readily see, that what has been said above
+about the hewing of granite, is chiefly applicable to the dressing
+of the large stones used in public works, such as docks, bridges, or
+marine towers; and it may be proper to add, that such heavy materials
+are always dressed on the ground, and that a piece of wood is placed
+under each end of the stone as a necessary precaution to prevent its
+being split by the blows of the mall. In dressing the lighter materials
+for house building, where a good deal of fine work is generally
+required, the stones are laid on what is called a _banker_, similar to
+that which is used in hewing freestone. The banker is a bench of stone
+2¹⁄₂ or 3 feet long, and 2 feet broad, and is raised about 2 feet above
+the ground, so as to suit the workman’s convenience.
+
+In dressing one of the outside stones of the first or lowest courses
+of the Skerryvore Tower, a mason was occupied _eighty-five_ hours (see
+Plans of courses, Plate VIII.); and in dressing one of the largest of
+the hearting or inner stones of the same courses, _fifty-five_ hours.
+But as the work proceeded, owing to the greater readiness which the
+men had acquired in the application of the moulds, gauges and bevels,
+the time occupied, gradually decreased to the extent of about _ten
+hours_ for each stone, until the work had been carried on as far as
+to the thirteenth course, where the number of outside stones was
+reduced to twenty-four, at which stage of the work, the time required
+for dressing increased to about _one hundred and twenty hours_ for
+each outside stone. From that point upwards, the time again gradually
+decreased till we reached the sixty-fourth course, where it may be
+stated, that, on an average, a man was employed _sixty-three_ hours in
+dressing each stone; but the time gained in the last instance seemed
+to depend less on the readier application of the implements, than on
+the gradual diminution in the size of the stones, which, from that
+level upwards, decreased along with the thickness of the wall. But
+above the sixty-fourth course, a very marked increase in the time
+of dressing took place, owing to the introduction of the _ribband
+or ring joggles_ (shewn in the Plans of the 84th and 94th courses,
+Plate VIII.); and to the substitution of the _dovetailed joggles_ in
+the place of the _square_ or _diamond joggles_, which were used in
+the lower parts of the building. The time required for dressing a
+stone of the sixty-fifth course was _ninety-three_ hours of one man,
+a circumstance which strikingly shews, that a small, and, apparently,
+trifling alteration in the style of workmanship may sometimes increase
+to a considerable extent, the expense of a great work. Each radiating
+stone of the _eighty-fourth_ course, which forms the floor that goes
+quite through the wall, required _one hundred and sixty-one hours_ for
+its completion; and the other radiating floor-stones, which did not
+pass quite through the wall to the outside, occupied one man about _one
+hundred and twenty hours_. Each centre stone of the floors into which
+the others were dovetailed, required about _three hundred and twenty
+hours_ of one man’s time. The time of a labourer occupied in cutting a
+hole for the dovetailed Lewis bats, by which the stones were raised,
+was about _three hours_.
+
+The tools necessary fully to equip a granite mason are as follows:--One
+dressing hammer about 16 or 18 lb. weight; 6 dressing picks, from 12 to
+20 lb. weight; one small hand-mall, or mash-hammer, about 4 lb. weight;
+3 stone axes about 7 lb.; 16 or 18 cast-steel punches and chisels,
+with one or two chippers or pinchers of 2¹⁄₂ lb. weight. One large
+blocking-hammer of 30 or 32 lb., may very well serve for eight men. The
+value of a granite mason’s _kit_ may be estimated, when in good working
+order, at about L.7. A very great revolution has taken place during a
+few years in the method of working granite. The most important change
+is the substitution of the hand-mall and chisel in the operation of
+putting the _drafts_ or bands on the stones, in place of _arris-picks_,
+which made the workmanship clumsy, tedious and imperfect, by slowly
+grinding down the stone at a great expense of labour to the hewer,
+who was forced to remain bent forward in an irksome posture, without
+the relief which is obtained by occasionally shifting his position, a
+change, which, every one who has been long employed in any laborious
+occupation, knows well how to value. The introduction of the _chipper_
+may also be regarded as one of the most important modern improvements
+in the art of working granite; and had it not been for those changes,
+the actual expense of dressing the blocks for the Skerryvore Tower, as
+ascertained from the journals of the works, would have been exceeded
+by a sum of between L.4000 and L.5000; and it may even be questioned
+whether it would have been at all practicable with such tools to cut
+the dovetailed spaces of the floors out of the solid stone.
+
+  ~Excavation of Foundation for the Lighthouse Tower on the Skerryvore
+  Rock.~
+
+The excavation of the foundation of the Lighthouse Tower was the
+first operation which engaged my attention at Skerryvore Rock, at
+the beginning of the season of 1839. It was commenced on the 6th of
+May, and was continued up to the last hour of our remaining on the
+Rock, on the 3d of September. A more unpromising prospect of success
+in any work than that which presented itself at the commencement of
+our labours, I can scarcely conceive. The great irregularity of the
+surface, and the extraordinary hardness and unworkable nature of the
+material, together with the want of room on the Rock, greatly added to
+the other difficulties and delays, which could not fail, even under
+the most favourable circumstances, to attend the excavation of a
+foundation-pit on a rock at the distance of 12 miles from the land. The
+Rock, as already noticed, is a hard and tough gneiss, and required the
+expenditure of about _four times_ as much labour and steel for boring
+as are generally consumed in boring the Aberdeenshire granite.
+
+After a careful survey of the Rock, and having fully weighed all the
+risks of injuring the foundation, I determined at once to enter upon a
+horizontal cut, so as to lay bare a level floor of extent sufficient
+to contain the foundation pit for the Tower. The very rugged and
+uneven form of the Rock made this an almost necessary precaution, in
+order to prevent any misconception as to its real state, for it was
+traversed by numerous veins and bands inclined at various angles, on
+the position and extent of which the stability of the foundation in no
+small degree depended. That operation occupied 30 men for 102 days, and
+required the firing of no fewer than 246 shots, chiefly horizontal,
+while the quantity of material removed did not greatly exceed 2000
+tons. It was a work of some hazard; for the small surface of the
+Rock confined us within 30, and sometimes within a dozen yards of the
+mines, while its form afforded us no cover from the flying splinters.
+The only precautions we could adopt were to cover the mines with
+mats and with coarse nets, which I had caused to be made during the
+previous winter, of the old ropes of one of the Lighthouse Tenders,
+and in each blast to apportion very carefully the charge of powder to
+the work that was to be done. That was managed with great skill by
+Charles Barclay, the foreman of the quarriers, who charged all the
+bores, and, along with myself, fired all the shots. So completely did
+the simple expedient of covering the bores with nets and mats check the
+flight of the stones, that, except on one or two occasions, none of
+the splinters reached us, and all the damage done was a slight injury
+to one of the cranes. Perhaps, also, our safety may, in some measure,
+be attributed to a change which I introduced into the mode of charging
+the horizontal shots, by which all the risk of pushing home the powder
+in the ordinary mode with the _tamping rod_ is avoided. That change
+consisted in using a kind of shovel, formed of a rod, armed with a
+hollow half-cylinder of sheet copper, which contained the powder, and
+being inverted by giving the rod half a turn round its axis, made the
+powder drop out when the cylinder reached the bottom of the bore. It
+was, in all respects, excepting size, the same as the charging-rod used
+for great guns. The amount of materials removed by blasting, as nearly
+as I could ascertain, was only about 1000 cubic yards; and, taking
+all the circumstances into account, it may be doubted whether there
+be any instance in modern engineering of an operation _of so small
+an extent_ occupying so much time, and involving so great risk. The
+blasting of the Rock, however, was not the only difficulty with which
+we had to contend, for it also became necessary to remove the quarried
+materials, amounting to about 2000 tons, into the deep water round
+us, to prevent their being thrown by the waves upon the Rock, and so
+endangering the future temporary Barrack. That was rather a laborious
+work, and occupied two cranes, with temporary runs and trucks, during
+the greater part of the time we spent on the Rock. I am well aware that
+the quantity of materials which I have just mentioned, will be apt
+to produce a smile from those who have been chiefly conversant with
+the gigantic but simple operations which generally characterize the
+great railways of this country; but if it be remembered that we were
+at the mercy of the winds and waves of the wide Atlantic, and were
+every day in the expectation of a sudden call to leave the Rock, and
+betake ourselves to the vessel, and on several occasions had our cranes
+and other tools swept into the sea, the slowness of our progress will
+excite less surprise; and still less will those who duly weigh the
+dangers of our daily life, both in our little vessel and on the Rock,
+and who, at the same time, reflect on the many striking proofs which
+we almost every hour experienced of the care of an Almighty hand, be
+disposed to withhold their sympathy from the heartfelt expressions of
+gratitude which often went round our little circle in the boats, as we
+rowed in the twilight from the Rock to the ship. Isolation from the
+world, in a situation of common danger, produces amongst most men a
+freer interchange of the feelings of dependence on the Almighty, than
+is common in the more chilly intercourse of ordinary life.
+
+With a view to lessen the dangers of blasting in such a situation,
+I had provided a galvanic battery on the plan proposed by Mr Martyn
+Roberts, but I used it less frequently than I intended. The attachments
+of the wires were very liable to be broken from various causes, where
+there were many men congregated in a small space; and as we could not
+venture to leave the apparatus on the Rock, the frequent re-shipment of
+it in a heavy sea was another cause of the derangement of its parts. I
+soon, therefore, laid it aside, and only had recourse to it when any
+work was to be done under water, or in cases where the simultaneous
+firing of several mines (for which it is admirably adapted) was of
+importance in effecting any special purpose.
+
+When the floor had been roughly levelled I again carefully surveyed the
+Rock, with the view of fixing precisely the site of the foundation-pit,
+and of taking advantage of its form and structure to adopt the largest
+diameter for the Tower of which the Rock would admit. In some places
+I found that parts of the Rock, apparently solid, had been undermined
+by the constant action of the waves, to the distance of 13 feet inward
+from its face; but none of those cavernous excavations reached the main
+nucleus, so that, after much deliberation and repeated examinations of
+all the veins and fissures, I was enabled to mark out a foundation-pit
+42 feet in diameter, on one level throughout. That was a point of no
+small importance; and although it had cost great labour at the very
+outset, much time was saved by it in the subsequent stages of the
+work. Not only was the labour thereby avoided of cutting the rock into
+separate terraces, and fitting the blocks to each successive step,
+as was done by Smeaton at the Eddystone; but the certainty that we
+had a level foundation to start from, enabled us at once to commence
+the dressing of stones without regard to any irregularities in the
+surface of the Rock; and the building operations, when once commenced,
+continued unimpeded by the necessity for accommodating the courses to
+their places in the foundation-pit, so that the Tower soon rose above
+the level, at which there was the greatest risk of the stones being
+removed by the waves before the pressure of the superincumbent building
+had become great enough to retain them in their places.
+
+The outline of the circular foundation pit, 42 feet in diameter, having
+been traced with a trainer on the rock, numerous jumper-holes were
+bored in various places, having their bottoms all terminating in one
+level plane, so as to serve as guides for the depth to which the basin
+was to be excavated. The depth did not exceed 15 inches below the
+average level, already laid bare by the cutting of the rough horizontal
+floor which has just been described; and before the close of the season
+of 1839, about _one-third_ of the area of the circle had been cleared,
+and was ready for the final pick-dressing which prepared it for the
+reception of the first course. The excavation of this circular basin
+was conducted with the greatest caution, and few shots were permitted
+to be fired lest the foundation should in any place be shaken by the
+action of the gunpowder on any of the natural fissures of the Rock. The
+work was chiefly done by means of what are called _plugs and feathers_,
+the form of which has already been shewn in the woodcuts (No. 12,
+p. 115). In that part of the work the bores were nearly horizontal,
+and the action of the _plug and feathers_ was to throw up a thin
+superficial shelf or paring of rock of from 6 to 12 inches in depth,
+and not more than 2 feet square. By that painful process an area of
+about 1400 superficial feet was cleared. The chief trouble connected
+with that operation was cutting, by means of the pick, a vertical
+face for the entrance of the horizontal _jumpers_ or boring rods; and
+wherever advantage could be taken of natural fissures it was gladly
+done. Another considerable source of labour was the dressing of the
+vertical edges of the basin, as that implied cutting a _square check_,
+15 inches deep and about 130 feet long, in the hardest gneiss rock; and
+the labour attending which, can only be fully estimated by a practical
+stone-cutter who has wrought in such a material. The plan employed was
+to bore all around the periphery of the circle, 1⁵⁄₈ inch vertical
+jumper-holes, 6 inches apart, to the required depth, and to cut out
+the stone between them. The surface thus left was afterwards carefully
+dressed, so as to admit vertical and horizontal moulds, representing
+truly the form of the masonry which the check was intended to receive.
+The experience of the labour attending that operation gave me great
+reason for congratulation on having adopted a foundation on one level
+throughout, instead of cutting the rock into several terraces, at each
+of which the same labour of cutting angular checks must necessarily
+have been encountered. The cutting of the foundation occupied 20 men
+for 217 days in all, whereof 168 days were in the season of 1839, and
+the rest in the summer of 1840.
+
+  ~Fitting up of the Second Barrack on the Rock.~
+
+  ~Sudden death of George Middlemiss.~
+
+The minute details given in my account of the destruction of the
+first Barrack, have entirely superseded the need for any particular
+description of the fitting up of the second Barrack on the Rock; and
+I shall therefore confine myself to a brief notice of the work in the
+chronological order in which it occurred. On the 1st of July, after the
+level floor for the foundation of the Tower had been roughly cleared,
+and all risk of injury from the firing of mines was past, the boring
+of holes for the fixtures of the second Barrack was begun; and so
+great were our exertions, that in the short period of fourteen days,
+the pyramidal frame-work on which the Barrack-house was to stand (see
+Plate V.), consisting of 13 beams, of about 50 feet in length, with all
+their braces, ties and stancheons, and the malleable iron cap which
+secured their union at the top, was firmly fixed on the Rock. After
+the pyramid was completed, the Barrack-house (which had previously
+been removed from North Bay, where, as already noticed, it had served
+as a temporary abode for the men who opened the quarries there), was
+transported, piece-meal, from Hynish to the Rock as required; for it
+was not considered prudent, after the experience of last year, to
+trust, even in the finest part of the season, a great quantity of
+timber to _lashings_ on the Rock. The fitting-up of the Barrack-house
+was completed on the 3d September and occupied only eleven days; so
+that the whole work extended to only twenty-five days, a remarkably
+short time for such a work, in such a situation. That despatch, indeed,
+was only obtained by working (as we did both during the excavation of
+the foundation and the erection of the Barrack), at all times when the
+weather would permit, from four o’clock in the morning till eight, and
+even nine in the evening, with an interval of only half-an-hour for
+breakfast and the same for dinner. The erection of the Barrack was a
+work of great difficulty and anxiety; for, as every thing depended on
+the exact union of all its parts, the slightest error in any dimension
+would have stopped the work until it could be remedied, a delay which,
+in such a situation, would, at certain stages of its progress, have
+proved fatal to the whole structure. I cannot, therefore, omit this
+opportunity of paying a tribute, in passing, to the memory of the
+late Mr George Middlemiss, the foreman of the carpenters who fitted
+up the Barrack, whose zeal for the completion of the work was very
+conspicuous. Poor Middlemiss died very suddenly at Hynish, about a
+fortnight after the completion of his labours on the Rock. He had
+received some instructions from me, so late as 11 o’clock, on the night
+of the 20th September; and when one of the men went to call him next
+morning at 6 o’clock, he was found dead, and in such a state as led Mr
+Moxey, the surgeon attached to the works, after a careful examination,
+to conclude, that he had died of paralysis of the heart, about three
+hours before he was found, or not more than four hours after I had seen
+him, to all appearance, in perfect health!
+
+  ~Wharf and Landing-place on the Rock.~
+
+No inconsiderable part of the labour of this season was devoted to the
+clearing of the landing-place, which was formed in a natural creek
+(see Plate III.) and in excavating the rocks in front of the line of
+wharf, so as to admit the vessels carrying the building materials to
+come alongside of it. That work could only be done at certain times of
+tide and during very fine weather, and was, therefore, tedious as well
+as hazardous. After two entire days spent in cutting with a sickle,
+mounted on a long pole, the thick cover of gigantic sea-weed, which hid
+the true form of the Rock from view, we were able to mark out the line
+of the wharf; and after all the mines were bored and charged and the
+tide had risen, and every one had retired from the spot, the whole were
+fired at the same instant, by means of the galvanic battery, to the
+great amazement and even terror of some of the native boatmen, who were
+obviously much puzzled to trace the mysterious links which connected
+the drawing of a string at the distance of about 100 yards, with a low
+murmur, like distant thunder, and a sudden commotion of the waters in
+the landing-place, which boiled up, and then belched forth a dense
+cloud of smoke; nor was their surprise lessened, when they saw that
+it had been followed by a large rent in the rock; for so effectually
+had the simultaneous firing of the mines done its work, that a flat
+face for a quay had been cleared in a moment, and little remained to be
+done, to give the appearance of a regular wharf and to fit it for the
+approach of a stone lighter, except attaching wooden fenders and a trap
+ladder.
+
+  ~Ring-bolts, Water-Tanks, and Railways.~
+
+A good deal of time was also spent in fixing a great many ring-bolts
+on various parts of the Rock and its _outlyers_, for the use of the
+shipping, which we expected to carry stones to the Rock the next
+season and in clearing a line for a permanent iron railway, about
+50 yards long, from the landing wharf to the Tower, the position of
+which is shewn in Plate III. The railway was used for the conveyance
+of materials from the stone-lighters to the building, and is now the
+_highway_ for all the stores which pass from the wharf to the Tower.
+Means were also taken for laying down two cast-iron water-tanks on the
+Rock in tolerably sheltered positions, as shewn in Plate III. One of
+those tanks was completed and filled with water, but the sole-plate
+only of the other was fixed, as unfortunately one of the plates dropped
+from the vessel’s side into the water, while the seamen were lowering
+it into one of the boats, a loss which prevented the second tank from
+being finished till the next year. Those tanks, together, held about
+900 gallons, and contained our chief supply of water during the whole
+subsequent progress of the works, when there were often about fifty men
+on the Rock.
+
+  ~Incidents of the Season.~
+
+I shall conclude this Chapter, by noticing a few incidents which
+occurred during the season of 1839, serving, in some degree to throw
+light upon the peculiar difficulties we had to encounter, or tending to
+shew the importance of the work in which the Commissioners had engaged.
+
+  ~Effects of a gale from the S.W.~
+
+On the 9th of August a strong gale suddenly sprang up from the S.W.,
+which, while it lasted, caused us much alarm and anxiety at Hynish,
+whither we had been driven from our station at the Rock to seek shelter
+at the commencement of the storm. Several small pieces of timber,
+which we had left on the Rock when we were forced to leave it, came
+ashore in Balaphuil Bay; and it was generally reported in the Island
+that the Barrack had, for the second time, been destroyed. That report
+I did not credit, as I had great confidence in the fixtures which
+attached it to the Rock; but my anxiety to ascertain the true state of
+the case, led me to examine the south-eastern shore of Tyree, when all
+that could be discovered was a few pieces of loose timber, and one of
+the smith’s cooling tubs, which had been washed from the Rock. Next
+day, however, the smith’s bellows came ashore in the same Bay, and so
+little injured, that we had them repaired and put in use again on the
+Rock. On the 12th of August, when the weather permitted us to return
+to our station at the Skerryvore, we found all the timbers which had
+been lashed down with chains to the Rock scattered in every direction
+around the beams of the Barrack, the smith’s forge overturned, the
+bellows of course gone; one of the cranes also which had been used
+for the removal of the excavated materials had been swept away, and
+not a vestige of it left, except a small piece of one of the wooden
+stays, which the force of the waves had broken. But that which most
+of all surprised us, and gave us the greatest concern, as an alarming
+proof of the force of the sea and a source of great inconvenience and
+hazard during the rest of the season, was the disappearance of our
+moorings, which had been lost by the _foundering_ of the cask buoy in
+the heavy surf which the gale had raised. During all the rest of our
+stay at the Rock that season, we were forced to ride at anchor in foul
+rocky ground of the worst and most irregular description, over which
+the vessel frequently drifted to a considerable distance, occasioning
+us no small fear for our safety. That was the second set of moorings
+which had disappeared at Skerryvore; and a stronger proof of the very
+great power of the western swell can hardly be imagined, as nothing of
+the kind had happened during the whole time the Bell Rock works were
+in progress. That circumstance also convinced us of the necessity of
+adopting vessels of small burden for landing the materials. So great,
+indeed, was the difficulty of _hanging_ even the boats at the Rock,
+that on two occasions (on the nights of the 4th May and 12th July) we
+had both the boats half filled by the sea, and nine or ten men thrown
+out on the Rock by the _kanting_ of one of the boats at the recoil
+of the wave. The landing department was indeed, throughout the whole
+season, attended with great difficulty, and was to me a source of
+constant anxiety; for, in the daily transport to and from the vessel
+and the Rock of 30 men, unaccustomed to boating, during a period of
+four months, it was more than could have been expected that we should
+have been preserved from the loss of either life or limb. On the night
+of the 3d September, when we left our anchorage at the Skerryvore
+for the season, every heart was full of rejoicing, and many cordial
+expressions of gratitude to our Almighty Protector were uttered in deep
+whispers by the more seriously disposed men, whose number bore a goodly
+proportion to our whole band. I cannot omit saying, in this place, that
+both Mr Macurich, who acted as landing-master on the Rock, and the
+late Mr Heddle, the master of the steam-tender, conducted the boating
+department in a most masterly style.
+
+  ~Mutiny of the Crew.~
+
+As an aggravation of our difficulties, we were occasionally much
+annoyed by the unprincipled and cowardly conduct of a few of the
+seamen, who, despite the contempt of their comrades, fearing or
+pretending to fear the risk of lying all night so near the face of the
+Rock, spared no pains to spread alarm, and made several attempts, by
+threatening desertion, to extort a rise of wages. They even spoke of
+leaving the vessel at the Rock, which they could easily have done by
+some of the native boats which called in passing to see the progress
+of the works; and Mr Heddle, the master of the steamer, was forced to
+dismiss the mutineers on the first occasion when the vessel was driven
+for shelter to the land, and to rely during the rest of the season
+on the native boatmen to supply their place. That firm conduct had,
+for some time afterwards, the desired effect on those who remained;
+but the spirit of disaffection having spread pretty widely, we had
+subsequently several other instances of sudden desertion from the
+service.
+
+  ~Near approach of Vessels to the Rock, and other circumstances
+  shewing the importance of a Light on the Skerryvore.~
+
+In the course of my residence for four months on board the tender
+moored off the Rock, I had opportunities of witnessing many proofs
+of the great necessity which existed for a Light on the Skerryvore;
+and if I had ever entertained any doubt as to the beneficial effects
+of such an establishment, the experience of the season of 1839 must
+have entirely removed it. It often happened that for several days
+successively, not fewer than five or six vessels of large size, both
+outward and homeward bound, were visible at distances varying from
+3 to 6 miles from the Rock; and much anxiety was often felt by us
+for the safety of those vessels, several of which approached so near
+the outlying rocks as to keep us for some time in the most painful
+suspense. On two occasions, more especially, I was about to direct the
+steam to be raised, in order that the Skerryvore tender might be sent
+to warn the masters of vessels of their danger, or if too late for
+that, to afford them assistance in case of accident. On the 29th of May
+a large schooner, and on the 13th of June a large brig ran right down
+upon the western _outlyers_, called FRESNEL’S Rocks (which were covered
+at the time), and just _put about_ in time to avoid striking; and on
+the 12th June, a fine foreign barque (apparently a Prussian) passed so
+close to Bo-Rhua as to leave us for a short time in doubt whether or
+not she had struck on it. On the 21st of June, also, a large brig came
+very near the rocks which lie off Tyree, at the base of Ben-Hynish,
+in trying to avoid Boinshley Rock, which lies about 5 miles to the
+N.W. of the Skerryvore. Those circumstances, together with the list
+of shipwrecks already given at page 23, afford strong proofs that the
+Skerryvore Rock occupies a most fatal position in a great fairway much
+frequented by large vessels bound to or from ports in the Irish Sea and
+in the Clyde.
+
+There cannot be a doubt that many vessels have been wrecked on the
+Skerryvore and its numerous _outlyers_, being borne down upon the reef
+by the strong tide which runs at the rate of between four and five
+miles an hour at the height of spring tides; and the natives of Tyree
+have many stories about chains and anchors and hidden treasures, with
+which their fancy has filled every nook of the Rocks. To what extent
+those stories, which are often most circumstantially told, may be true,
+it is not easy to determine; but in the end of July 1839, we succeeded,
+under the guidance of a native boatman, in raising from a creek in one
+of the detached shelves to the south-west of the main Rock, an anchor
+worn by the action of the sea to a mere skeleton, a circumstance which
+so far corroborates the truth of their traditions.
+
+
+CHAPTER VI.
+
+OPERATIONS OF 1840.
+
+In describing the progress of the works during the season of 1840,
+I shall speak of the various departments separately, as in the last
+chapter, beginning with the workyard at Hynish.
+
+  ~Hynish Workyard.~
+
+During the preceding winter months, the establishment at Hynish was
+reduced to about fifty persons, of whom twenty-seven were masons
+employed chiefly in dressing blocks for the Lighthouse, in laying the
+stone platform in the workyard (on which each course was adjusted
+previously to its being shipped for the Rock, to prevent the occurrence
+of mistakes which might not be easily remedied there), and in building
+some additional barracks, masons’ sheds and a limekiln for the
+summer of 1840. The quarriers and labourers formed a party of about
+eighteen, and were engaged in cutting blocks in the Tyree quarries,
+which, although unfit for the Lighthouse Tower, were very suitable
+for the completion of the Pier at Hynish; while nine carpenters
+had full occupation in making moulds for dressing the Lighthouse
+blocks, preparing oaken treenails to be used in the lower courses
+of the Lighthouse Tower, and in dressing handles for the masons’
+and quarriers’ tools. In the month of April, a reinforcement of
+thirty-seven masons from Aberdeen arrived at Hynish; and the greater
+number of them were at once employed in the dressing of stones for
+the Tower; while a few assisted in building the dressed materials
+in a temporary manner on the stone platform in the workyard already
+mentioned. The number of masons in the workyard, during the summer
+months, varied considerably, according to the state of the works on
+the Rock, where seldom fewer than thirty men were stationed throughout
+the whole working season. But the dressing of the stones for the Tower
+proceeded with considerable vigour; and notwithstanding the inroads
+necessarily made upon the men’s time, by their being frequently
+required to assist in the landing of materials from Mull, a work for
+which few of the Tyree men were fit, from their awkwardness in the
+management of cranes and all kinds of machinery or tackling, and also
+by the constant detachment of a considerable number both of men and
+of tools for the laborious work of dressing the foundation-pit at the
+Rock, upwards of 20,000 cubic feet of granite had been dressed and
+fitted on the platform, when I left Hynish in the end of October 1840.
+
+  ~Hynish Pier.~
+
+During the whole of the summer, the traffic at the pier at Hynish
+was so great in landing materials from the Mull quarries, and in
+shipping stones for the Rock, that much inconvenience was felt from
+want of room. Nearly 4000 tons were shipped and discharged at the
+quay, independently altogether of the ballasting of each vessel which
+discharged at the pier, and the receiving, storing, and finally
+supplying coals to the steamer, which formed no inconsiderable item
+of the labour. Every exertion was made to extend the pier, so soon as
+the works at the Rock were closed for the season and the stone trade
+with Mull had ceased; and by great perseverance on the part of Mr James
+Scott, the foreman of the workyard, whom I always found ready, night
+and day, to second and even to anticipate my wishes in regard to the
+progress of the works, an additional length of 36 feet was added to the
+berthage of the quay before the winter had set in.
+
+  ~The Rock.~
+
+The first landing on the Rock, for the purpose of resuming the work
+in 1840, was on the 30th April, when all things connected with the
+Barrack were found in nearly the same state in which we had left them
+seven months before. The red paint with which we had coated it had
+become nearly white, partly by a covering of sea-salt, and by blanching
+of the paint itself, but chiefly towards the top by the soil of the
+numerous sea-fowl which had perched on the roof. The timbers, also,
+bore the signs of being wave-washed, and in the more sheltered parts
+were tufted with the finer kinds of seaweed; the iron-work was much
+rusted and entirely divested of paint. The door had been firmly secured
+with lashings and bolts, and some difficulty was experienced in forcing
+an entrance into the interior, about the state of which, as our future
+abode, much curiosity was naturally felt by the men, who were desirous
+to know how it had weathered a seven months’ exposure to the waves of
+the Atlantic. It was with no small pleasure, therefore, that, when the
+door was opened and the windows unbarred and the sunshine admitted
+to dispel its gloom and chilly damp, we found, that although the
+water had forced its way through some of the imperfect seams in the
+window-frames, the interior shewed evident signs of the stability of
+the fabric, and was in some places so dry, that the greater part of the
+biscuits which we had left the year before, as a store for shipwrecked
+seamen who might find their way to the Rock, although some of them were
+wet and pulpy on the side nearest the outer walls, admitted of being
+dried, and when a little toasted at the fire, were palatable enough
+to hungry men, so that, in fact, we consumed the greater part of that
+stock before we entered on our new supply.
+
+The most important change which had occurred during the winter, was the
+removal of a mass of rock in the neighbourhood of the foundation-pit,
+which had been shaken by the effects of the blasting operations of
+the previous year. That mass, the moving of which shewed that a great
+weight of water had passed over the Rock, weighed about five tons,
+and had been detached from its bed during a heavy gale from the N.W.,
+in the month of March, and carried right across the foundation-pit
+to the Barrack, against one of the beams of which it had rested, and
+had partially injured the iron _collars_ or _glands_ by which the
+beam was secured. The stone was broken into small fragments by a
+party of men, who had been appointed to visit the Rock after heavy
+gales, and had landed on the 27th of March, to see the state of the
+Barrack. The men, in their anxiety to break down the block, which they
+feared might injure the Barrack, if thrown against it by the waves,
+and allured by the smoothness of the sea, most imprudently remained
+all night, mooring their boat in the landing creek, and trusting to
+the scanty stock of provisions which they had brought out, with the
+intention of at once returning to Hynish. The risk involved in such
+a proceeding, we afterwards had many opportunities of knowing during
+our stay on the Rock, as we were often forced to make fast all our
+materials, to prevent their being washed away by the sudden rising of
+the waves, especially about the time of high-water in spring-tides. The
+discomforts, however, experienced by the men on that occasion while in
+the Barrack, without fire, light or bedding, in a cold dark night of
+spring were such, that several of them did not afterwards much affect
+the Rock as a residence even in summer.
+
+  ~Life in the Barrack.~
+
+Owing to the great difficulty of landing on the Rock in the early
+part of May, few opportunities occurred of preparing the Barrack as
+a habitation; and it was not until the 14th of that month that we
+were enabled to take up our quarters in it; and even then we were
+most uncomfortably lodged, as many of the smaller fittings which
+are essential to a _wind-and-water-tight_ habitation had not been
+completed. During the first month we suffered much from the flooding of
+our apartments with water, at times when heavy sprays lashed the walls
+of the Barrack with great violence and also during rainy weather; and
+in northerly gales we had much difficulty in keeping ourselves warm. On
+one occasion, also, we were fourteen days without communication with
+the shore or the steamer; and during the greater part of that time we
+saw nothing but white fields of foam as far as the eye could reach,
+and heard nothing but the whistling of the wind and the thunder of the
+waves, which were at times so loud as to make it almost impossible
+to hear any one speak. For several days, the seas rose so high as
+to prevent our attempting to go down to the Rock; and the cold and
+comfortless nature of our abode reduced all hands to the necessity of
+seeking warmth in bed, where (rising only to our meals) we generally
+spent the greater part of the day listening to the howling of the
+winds and the beating of the waves, which occasionally made the house
+tremble in a startling manner. Such a scene, with the ruins of the
+former barrack not 20 yards from us, was calculated only to inspire
+the most desponding anticipations; and I well remember the undefined
+sense of dread that flashed across my mind, on being awakened one night
+by a heavy sea which struck the Barrack, and made my cot or hammock
+swing inwards from the wall, and was immediately followed by a cry of
+terror from the men in the apartment above me, most of whom, startled
+by the sound and tremour, immediately sprang from their berths to the
+floor, impressed with the idea that the whole fabric had been washed
+into the sea. The alarm, however, was very short and the solemn pause,
+which succeeded the cry, was soon followed by words of reassurance
+and congratulation. Towards the end of the fourteen days I began to
+grow very uneasy, as our provisions were drawing to a close; and when
+we were at length justified, by the state of the sea on the rock, in
+making the signal to those on shore (at the hour fixed for pointing the
+telescope at Hynish on the Barrack), that a landing could be effected,
+we had not more than twenty-four hours’ provision on the Rock, so that
+when the steamer came in sight she was hailed by all hands with the
+greatest joy!
+
+The construction of the Barrack has already been very fully described,
+and a glance at Plate V. will be sufficient to give a pretty correct
+idea of the nature of our singular dwelling. Immediately under the
+wooden tower was an open gallery, the floor of which was removed at
+the end of each season, so as to allow free space for the passage of
+the sea during the storms of winter, but on which, during the summer,
+we kept the stock of coals, the tool-chests, the beef and beer casks,
+and other smaller materials which we could not, even at that season,
+safely leave on the Rock itself. Next came the kitchen and provision
+store, a six-sided apartment about 12 feet in diameter and somewhat
+more than 7 feet high, in which small space, curtailed as it was by
+the seven beams which passed through it, stood a _caboose_, capable
+of cooking for forty men, and various cupboards and lockers, lined
+with tin, for holding the biscuits, meal, flour, barley and other
+things needful for the sustenance of the human frame. That apartment,
+for protection against fire, was coated, partly with tin and partly
+with sheet-lead, which latter, although not in all respects the most
+desirable material to come in contact with that element, was found to
+be the only one which we could in some parts conveniently apply. The
+next storey was divided into two apartments, whereof one was shared by
+Mr Thomas Macurich, who superintended the landing of all the materials
+and Mr Charles Stewart, the foreman of the builders, and the other
+was allotted to myself. The apartments thus occupied consisted of
+a twelve-sided narrow space twisted around a centre pyramid, whose
+bevelled faces formed, as will in part be seen by inspecting Plate V.,
+their sloping walls on one side. The half of that space constituted
+my apartment, which, I think, would be generally pronounced not over
+commodious; and when it is added that it contained my bed, desk, chair
+and table, and a stock of groceries, it will readily be imagined I had
+little room to spare for myself. So much attention was paid to economy
+of space, that the recesses of the pyramid formed by the meeting of
+the beams were boarded over and made into cupboards; while my _cot_,
+or framed hammock (which, during the night, rested upon brackets which
+could be folded close to the wall when not required), was, during the
+day, hoisted by pullies to the roof of the apartment, so as to leave me
+as much space to move about in as a prisoner could expect. The cornice
+of the apartment consisted of a narrow shelf adorned with books, which
+I found very needful helps to solitary life. The highest apartment was
+also twelve-sided, surmounted by a pyramidal roof and a small six-sided
+lantern or ventilator, and was lined round the sides with four tiers
+of berths, capable of accommodating thirty people. The closeness of
+that room was most intolerable, especially during the heat of fine
+weather in summer, at which time several of the men preferred taking
+a nap on the rock, with the clear blue sky for a canopy. The economy
+of our life on the Rock was strange enough. At half-past three in the
+morning we were called, and at four the work commenced, continuing
+till eight, when half-an-hour was given for breakfast: after which it
+was carried on till two, when another half-hour was given for dinner;
+and the work was again resumed and continued till seven, eight, and
+even nine o’clock, when anything urgent was in hand. Supper was then
+produced and eaten with more leisure and comfort in the cool of the
+evening. Such protracted exertion produced a continual drowsiness,
+and almost every one who sat down fell fast asleep. I have myself
+repeatedly fallen asleep in the middle of breakfast or dinner; and have
+not unfrequently awakened, pen in hand, with a half-written word on
+the paper! Yet life on the Skerryvore Rock was by no means destitute
+of its peculiar pleasures. The grandeur of the ocean’s rage, the deep
+murmur of the waves, the hoarse cry of the sea-birds, which wheeled
+continually over us, especially at our meals, the low moaning of the
+wind, or the gorgeous brightness of a glassy sea and a cloudless sky,
+and the solemn stillness of a deep blue vault, studded with stars, or
+cheered by the splendours of the full moon, were the phases of external
+things that often arrested our thoughts in a situation where, with all
+the bustle that sometimes prevailed, there was necessarily so much time
+for reflection. Those changes, together with the continual succession
+of hopes and fears connected with the important work in which we were
+engaged, and the oft-recurring calls for advice or direction, as well
+as occasional hours devoted to reading and correspondence, and the
+pleasures of news from home, were more than sufficient to reconcile me
+to, nay, to make me really enjoy, an uninterrupted residence, on one
+occasion, of not less than five weeks on that desert Rock.
+
+  ~Foundation-pit.~
+
+During the first half of the season 30 men were engaged 14 hours a day
+in the preparation of the foundation-pit, which, as already said, was
+a work of the greatest labour. The Rock, indeed, was in many places
+so hard as often to make it seem hopeless that tools could make any
+impression on it. The time employed in the excavation and the number
+of tools expended on it, were very great, as a pick seldom stood more
+than three strokes in the harder quartzose veins; but our perseverance
+was at length amply rewarded by obtaining a foundation so level and
+so fairly wrought throughout the whole area of a circle 42 feet in
+diameter, as to present to the view the appearance of a gigantic basin
+of variegated marble; and so much pleased were the workmen themselves
+with the result of their protracted toil, that many of them expressed
+serious regret that the foundation must soon be covered up so, as (we
+trusted), never to be seen again. In the dressing of the Rock much
+inconvenience arose from the small splinters which flew out before the
+tools, sometimes rising to the height of 40 feet, and coming in at the
+windows of the Barrack; and after several injuries had been sustained,
+I at length found it necessary to send to Glasgow for fencing masks to
+protect the men’s faces. In all our work, nothing was more grudged than
+the occasional loss of half a day in _baling_ out the water from the
+foundation-pit after it had been filled by a heavy sea.
+
+  ~Landing of materials on the Rock.~
+
+Before we had made an actual trial of landing stones on a Rock at the
+distance of 12 miles from the nearest shore, exposed to the incessant
+beating of Atlantic waves, there was much room for doubt as to the
+measure of success to be expected; and, as the time approached, I
+naturally looked to the attempt with increasing anxiety, as to an
+experiment in a great measure decisive of the future complexion of our
+operations. Four small vessels, carrying from 16 to 19 tons, had been
+built at Leith and Dumbarton, for the purpose of carrying the stones
+on their decks, so as to admit of their being easily lifted by the
+crane, and so to avoid the risk which would have been incurred by any
+attempt to raise stones by a crane from the hold of a vessel moored
+to a rock in the open sea and moving about with every wave. Had that
+been attempted, the crane would, on many occasions, have been pulled
+down before the stone could be cleared from the hold. The vessels were
+very similar to those which were used for the same purpose at the Bell
+Rock; and I therefore beg leave to refer the reader to page 509, and
+to Plate XI. of my Father’s account of that work, for a description of
+them. Being decked all over, to give room for cargo (for they carried
+nothing in the hold but empty casks for the purpose of floating them
+in the event of their sustaining any injury), they were towed between
+Hynish and the Rock by the steamer, and being _cast off_ as near the
+landing-place as possible, were taken by the boats to the creek, and
+moored with warps to the fenders at the quay.
+
+The first trial of the lighters in landing stones on the Rock was
+made on the 20th of June, on which occasion both the steamer and the
+stone craft were decorated with flags; and due honour was done to
+the occasion of landing the first stone, by firing a salvo shot and
+drinking success to the works. The landing service throughout the
+whole progress of the works was one of much difficulty and anxiety and
+many narrow escapes were made; but it was managed with great prudence,
+and at the same time with unremitting energy, by Messrs Macurich and
+Heddle, in their several departments, both ashore and afloat. On many
+occasions the men who steered the lighters ran great risks; and it was
+often found necessary to lash them to the rails, to prevent their being
+thrown overboard by the sudden bounds of the vessels, or being carried
+away by the weight of water which swept their decks as they were towed
+through a heavy sea. Sometimes, also, we were forced, owing to the
+rush of the sea into the creek, which threatened to lift the vessels
+on the top of the Rock, to draw out the loaded lighters from the wharf
+without landing a single stone, after they had been towed through a
+stormy passage of 13 miles; and one day, during the very best part of
+the season, so sudden was the bounding of the vessel before the sea,
+that eight large warps were snapped like threads as the lighter was
+carried violently before a crested wave which rolled unexpectedly into
+the creek, while those who stood on her deck were thrown flat on their
+faces and imagined that the vessel had been laid _high and dry_ on the
+top of the Rock. During the whole season, however, in the course of
+landing 800 tons of masonry on the Rock, too often in that dangerous
+manner, none of the dressed stones received any great damage, nor was
+any other injury of importance sustained.
+
+  ~Building the first stone.~
+
+The building of the Tower was commenced on the 4th July; but it was
+not till the 7th that the ceremony of laying the foundation-stone was
+performed by His Grace the Duke of Argyll, who, as proprietor of the
+adjacent Island of Tyree, took a great interest in the success of
+the works, and on that day visited the Skerryvore with the Duchess
+of Argyll, the Marquis of Lorne, Lady Emma Campbell, and a party of
+friends, in the Toward Castle steamer. On that occasion His Grace
+expressed himself much pleased with the works and kindly left with me a
+donation of L.10 for the workmen.
+
+The building operations in 1840 were entirely carried on by means of
+two cranes with moveable jibs, of which one was fixed just beyond the
+foundation, at the place shewn in Plate III., between the landing quay
+and the Tower, and was chiefly used in bringing forward the materials;
+and the other, placed in the centre of the Tower, served for laying
+the stones, and was raised along with the rise of the building. So
+perfectly had the stones been dressed in the workyard at Tyree, that
+no alteration or paring of the beds or joints was required; and such
+was the facility afforded by the building apparatus, that by working
+14 hours, we occasionally _set_, through the activity of Mr Charles
+Stewart, the foreman builder, so many as 85 blocks in a day. The first
+course of masonry was laid by means of a wooden trainer; but the place
+of all the subsequent stones was, as already noticed, regulated by the
+use of _plumb-templets_, whose inner faces were arcs of the generating
+hyperbola. By those means we succeeded in _setting_, in a most perfect
+manner, six courses, which carried the building to the height of 8
+feet 2 inches, and contained a mass equal to 10,780 cubic feet. That
+quantity is not greatly less than the whole materials of the Eddystone
+Lighthouse Tower, which, according to my computations from the drawings
+of SMEATON, do not exceed 13,300 cubic feet, and is somewhat more than
+_one-third_ of the contents of the Bell Rock Tower, which are about
+28,500 cubic feet. That frustum was also nearly equal to _one-fifth_
+part of the whole mass of the proposed building, which is about 56,000
+cubic feet. Of the six courses, the first three are of Hynish gneiss,
+and the rest are of granite from the Ross of Mull. The comparative
+merits of those two materials may be stated as follows:--The Hynish
+stone is harder, and susceptible of finer workmanship, and perhaps its
+most perfect blocks are more durable; but it requires much more labour
+in dressing than the Mull granite, which is more homogeneous in its
+structure and is not intersected by hard veins, like those which occur
+in the gneiss of Tyree. There is good reason also for concluding that
+the Mull stone is sufficiently durable, because it contains but a small
+proportion of micaceous matter, and in its texture closely resembles
+some of the blocks of St Oran’s chapel in the neighbouring Island of
+Iona, which have resisted the action of the weather, it is believed,
+for more than 600 years and still retain the marks left by the tools of
+the workmen. I had also carefully compared the density of the Hynish
+and Mull stones, by weighing blocks of known dimensions, and found that
+it requires 13·16 cubic feet of the former, and 13·66 cubic feet of the
+latter to weigh one ton, a difference much less than the appearance of
+the stone would lead one to expect. A Tower of the dimensions of that
+at Skerryvore, built entirely of Hynish stone, would have weighed about
+4308 tons, while the same mass of Mull stone would weigh 4252 tons,
+leaving a difference of not more than 156 tons in favour of the Hynish
+stone.
+
+The mortar employed in the building was composed of equal parts of
+Aberdda lime and Pozzolano earth, and was therefore identical, in its
+composition, with that used by Smeaton at the Eddystone. Not having
+been able, after searching the neighbouring islands, to obtain good
+sand, I found it inexpedient to adopt the proportion of equal parts
+of lime, sand, and Pozzolano, which were so successfully used at the
+Bell Rock; but so perfect was the adhesion of the mortar used at the
+Skerryvore, that in that mass of 800 tons only two small leaks were
+discernible, which being _ripped_ or opened with an _iron_, and allowed
+to run dry, were afterwards carefully repointed, and have never since
+shewn the slightest symptoms of leaking.
+
+
+CHAPTER VII.
+
+OPERATIONS OF 1841.
+
+  ~Hynish workyard.~
+
+The workyard at Hynish presented a very busy scene during the summer
+and winter of 1840; and the desolation and misery of the surrounding
+hamlets of Tyree seemed to enhance the satisfaction of looking on our
+small colony, where about 150 souls were collected in a neat quadrangle
+of cleanly houses, conspicuous by their chimnies and windows amongst
+the hovels of the poor Hebrideans, who generally make no outlet for
+the smoke in their gloomy dwellings, but permit it to escape by the
+doors. The regular meals and comfortable lodgings and the cleanly and
+energetic habits of the Lowland workmen, whose days were spent in toil
+and their evenings, most generally, in the sober recreations of reading
+and singing, formed a cheering contrast to the listless, dispirited,
+and squalid look of the poor Celts, who have none of the comforts of
+civilized life and are equally ignorant of the value of time and the
+pleasures of activity.
+
+The number of masons employed in 1841, varied from 60 to 84 and they
+were chiefly engaged in dressing blocks for the Lighthouse-Tower, in
+discharging the cargoes of vessels loaded with stone from Mull and also
+in shipping stones for the Rock, in which operation, their acquaintance
+with the handling of dressed materials and their readiness in working
+the cranes, made them very useful in directing and also in working
+along with the native labourers, who, partly from incapacity and
+partly from excessive indolence, could not be trusted for a moment to
+themselves. During that year, upwards of 38,000 cubic feet of granite
+were dressed into blocks with straight beds and joints, and with faces
+of double curvature, so as to suit the contour of the Tower, when
+arranged in the wall. The blocks were also fitted with stone joggles,
+for retaining them in their places, and with lewis-holes for raising
+them in the manner usually practised in building materials of that
+description. Of those materials upwards of 70 blocks were floor-stones
+(see Plans of 84th and 85th courses, Plate VIII.), _dovetailed_ on
+the heads, _checked_ on the joints and having a plain surface on the
+upper and a concave one on the under bed. The necessity of preserving
+throughout their entire joints a perfect uniformity of bearing, made
+the dressing of those materials a work of great nicety; and each
+stone, as before noticed, being cut according to moulds, was fitted
+temporarily in its place on the platform at Hynish, previously to its
+being laid aside as ready for transport to the Rock. Those various
+operations were conducted with great care; and the stones, which were
+regularly arranged and numbered according to a schedule, formed, at the
+time I left the workyard in the end of October, a considerable pile,
+bearing ample testimony to the diligence and zeal of Mr James Scott,
+the foreman of the workyard and leader of the party ashore.
+
+  ~The Rock.~
+
+Owing to the uncertain and stormy weather in spring, it was not till
+the 13th of May, that the first landing was effected on the Rock. The
+result of our visit, however, was most satisfactory. We found the
+Barrack quite as we had last seen it six months before; and not one
+joint of the pile of masonry, which we had left exposed to the waves,
+had been shaken or _started_. The Railway and Landing Wharf, although
+much exposed to the breach of the sea, had survived the winter’s storms
+with no greater damage than the loss of one of the sleepers or beams,
+on which the rails rested, which had been torn by the waves from its
+fixtures to the rock. It was not till a week after our first landing
+that we were enabled again to take up our quarters on the Rock; for
+we had few landings in the mean time, and some of them, owing to the
+heavy surf which played round the Rock, were of no very satisfactory
+kind. Our first experience of this season was indeed far from inviting.
+So difficult was the first landing, that we were forced to direct
+all our endeavours to laying in a small stock of provisions in the
+Barrack, before being left on the Rock; and, considering the scanty
+nature of the supplies which the weather permitted us to secure, it
+was thought prudent to restrict the number of men to eight masons and
+myself, with as many tools as we could land, to enable them to make the
+necessary repairs and arrangements before fairly commencing for the
+season the works of a more strictly progressive character. The vessel
+then returned to Tyree with the rest of the men and all the heavy
+apparatus which we could not land; and, to add to the unpleasantness
+of being left in such a position, with the improbability of a visit
+from the vessel for several days, one of the masons took alarmingly
+ill soon after the steamer was too far off for a signal, and suffered
+so acutely during the whole night, that his piercing cries in the
+spasms which accompanied his disorder, combined with the howling of a
+strong _north-wester_ and the incessant lash of the waves, deprived
+the whole party of sleep during the first night. In this uncomfortable
+predicament, until the steamer returned on the 22d, we spent two days
+exposed to winds piercingly cold and in apartments soaked with spray,
+which found its way through inlets which had been made by the winter’s
+storms. We were not sorry, at the same time, to have an opportunity
+of removing the poor man to the care of Dr Campbell, the surgeon who
+was attached to the workyard at Hynish and of reinforcing our stock of
+provisions and the detachment of men. We also succeeded in landing the
+cranes and other building apparatus, which, owing to the heavy surf on
+the 20th, we had not been able to accomplish.
+
+The few first days after getting fairly established in our habitation
+for the season, were occupied in extending the railway to a point on
+the northern part of the Rock, somewhat sheltered during certain seas
+(see Plate III.), where a crane for stowing the materials previously
+to building them had been erected; and thus it was not till the 25th of
+May that the first cargo of stones was landed. Next day a crane (then
+thirty-four years old), which had been used in the building of the Bell
+Rock Lighthouse, was placed on the top of the masonry, and the more
+cheering operations of mixing the mortar and of _setting_ stones were
+begun.
+
+In spite of the unfavourable state of the weather and the continual
+distraction of our exertions, occasioned by storms and the landing of
+materials, we continued our operations with such vigour as to complete
+the solid part of the masonry of the Tower on the 8th July. Until the
+building had reached to the level of 15 feet, the work was carried on
+by the use of two jib-cranes, one on the Rock and the other on the
+Tower, by means of which latter the stones were _set_, after being
+_brought to hand_ by the first. But above that level, _shear-legs_
+similar to those used at the Eddystone, were employed. Those shear-legs
+were about 50 feet high, and were erected in the situation, at the side
+of the Tower, shewn in Plate III. They consisted of two spars attached
+at the base to _jointed_ sockets _batted_ into the Rock, and connected
+at the top by means of a crosshead of timber. The jointed sockets
+permitted the shears to hang forward at any angle suited to the level
+and distance of the part of the Tower to be reached; and chain guys
+both in front and behind, secured them from falling either backwards or
+forwards. At the crosshead hung an iron sheave with a chain, one end
+of which was provided with a hook for raising stones, while the other
+was wound around the barrel of a _crab machine_ well batted down to the
+rock, by working which the blocks were raised to such a level as to
+be within reach of the building crane on the top of the masonry. The
+_shear-poles_ were used, until the building of the Tower was completed,
+to raise the stones the first lift of forty feet above the Rock. In
+the later stages of the work, the stones, instead of being taken by
+the building cranes directly from the _shear-poles_, were raised from
+storey to storey by means of crabs placed inside the Tower, which
+worked chains, _reeved_ through sheaves hanging from the end of beams
+projecting from the windows. Such beams are called _needles_, and are
+described at page 504, and shewn in Plate IX., fig. 3, of my Father’s
+Account of the Bell Rock Lighthouse, where they were used for the same
+purpose.
+
+  ~The Waves.~
+
+  ~Colours of breaking Waves.~
+
+During the early part of the season the weather was intensely cold,
+with showers of sleet and heavier showers of spray, which dashed round
+us in all directions, to the great discomfort of the poor masons, whose
+apartments did not admit of a large wardrobe, while they had not the
+benefit of much room for drying their clothes at the small _coboose_
+or cooking-stove in the Barrack. For days together, also, the men
+were left without building materials, owing to the impossibility of
+landing them, or, what was worse, without the power of building what we
+had on hand in consequence of the violence of the winds. During such
+times we often felt much anxiety about the safety of the stones which
+we had piled on the rock ready for being built; and it took no small
+trouble, by the occasional application of the crane, to save them from
+being swept into the sea by the surf. Nothing struck me more than the
+illusive effect produced on the mind by the great waves which rolled
+past the rock. The rapidity of their movements, and the noise which
+accompanied their passage through the gullies and rents of the rugged
+reef, seemed to give them the appearance of being much larger than they
+really were; and, even when viewed from the Tower, after it had risen
+to the height of 30 feet, they seemed, on approaching the rock, to be
+on the eve of washing right over the top of the building and sweeping
+all before them into the sea. It was a long time before, by continually
+watching the waves and comparing their apparent height with the results
+of their impact on the rock, we were enabled to correct our notions of
+their magnitude, so as to mark the approach of their crested curling
+heads with composure; and some of the party never became sufficiently
+familiarized with those visitors, to avoid suddenly looking round when
+the rush of a breaker was heard behind them, or recoiling a few paces
+when they saw its towering crest apparently about to burst in a torrent
+over their heads. It was only after a long residence on the rock and
+continual experimental observation, that I acquired confidence to
+approach within a few feet of the point which I expected the breakers
+to reach. I occasionally suffered for my temerity, by being thoroughly
+drenched with spray; but by long perseverance, I attained considerable
+skill in predicting the limits of their influence, though ever and anon
+an extraordinary wave overthrew all our confidence, by bursting far
+above the boundaries which we had assigned in our minds. That, however,
+did not generally occur in calm weather, but after strong gales from
+the N.W., when the waves had assumed the larger and more flattened form
+known by the name of the _ground-swell_. To gauge the height of those
+waves by means of a vertical rod, graduated with large divisions, so
+as to be read at a little distance, as the waves washed it in passing,
+was an object I had long in view; but I found it utterly impossible
+to apply any fixture in the deep water, in a situation fitted for the
+purpose. By making numerous comparisons, however, of the waves, with
+various known points of rock near the main Rock, and by availing myself
+of the observations of some of the more intelligent of the masons, I
+was led to conclude, that the greatest elevation of an unbroken wave,
+measuring from the hollow to the crest, does not, in the sea around the
+Skerryvore, exceed 15 feet; but the sailors, perhaps from their being
+less accustomed to accurate measurement, generally estimated it at 30
+or even 40 feet. I was often much interested, while I sat watching the
+waves that boiled round us on every side, to observe the peculiar tints
+which they assumed at the moment of breaking, passing as they did from
+the bluish-green colour of solid water by very rapid changes, to a
+delicate and very evanescent _blush_ of rose colour, which invariably
+accompanied their greatest state of comminution or disintegration.
+Those appearances I have often observed in other places, and I
+supposed them to be produced by _reflection from the thin plates of
+water_; and took them for indications of the perfect homogeneousness of
+the sea-water, in regard to density, and also of the similarity of its
+condition at the _moment_ of breaking.
+
+  ~The Seals.~
+
+Amongst the many wonders of the “great deep,” which we witnessed at the
+Skerryvore, not the least is the agility and power displayed by the
+unshapely seal. I have often seen half a dozen of those animals round
+the Rock, playing on the surface or riding on the crests of curling
+waves, come so close as to permit us to see their eyes and head, and
+lead us to expect that they would be thrown _high and dry_ at the
+foot of the Tower; when suddenly they performed a somersault within a
+few feet of the Rock, and diving into the flaky and wreathing foam,
+disappeared and as suddenly reappeared a hundred yards off, uttering
+a strange low cry, as we supposed, of satisfaction at having caught
+a fish. At such times the surf often drove among the crevices of the
+Rock a bleeding cod, from whose back a seal had taken a single moderate
+bite, leaving the rest to some less fastidious fisher.
+
+The latter part of the season, although not so stormy as the first,
+was far from being favourable for the building operations which, on
+one occasion, even during the month of July, were suspended for five
+days by a violent gale, which made it unsafe to attempt standing on the
+Tower. Happily the wind was from the N.E., a quarter from which it has
+comparatively little power in raising heavy seas, otherwise we should
+infallibly have lost a large part of the dressed materials which lay
+piled on the Rock, and, in all probability, should have had our work
+thus prematurely cut short in the middle of summer.
+
+After building a few courses above the level of the solid part of the
+Tower, the jib-crane could no longer be conveniently used, and recourse
+was had to a _balance-crane_, which, during the previous winter, I
+had caused to be constructed at Edinburgh, in the workshop of Mr
+James Dove. That apparatus, which, except as to its greater size and
+strength, in order to suit the greater dimensions of the Tower, was
+almost identical with that which was used at the Bell Rock, is shewn
+in Plate IX.; and it is only necessary, in this place, to notice its
+general construction and mode of working, which is also shewn in Plate
+XVII. of my Father’s Account of the Bell Rock Lighthouse. In the hollow
+of the Tower, a cast-iron pipe or pillar was erected, susceptible of
+being lengthened as the Tower rose, by means of additional pieces of
+pillar let in by _spigot and faucet joints_; and on the pillar a frame
+of iron was placed capable of revolving freely round it, and carrying
+two trussed arms and a double train of barrels and gearing. On the one
+arm hung a cylindric weight of cast-iron, which could be moved along
+it by means of the gearing, so as to increase or diminish by leverage
+its effect as a counterpoise; and on the other was a roller. The roller
+was so connected with the weight on the opposite arm, as to move along
+with it, receding from, or approaching to, the centre pillar of iron in
+the same manner as the weight did. From the roller hung a sheave, over
+which a chain moved, with a hook at the end for raising the stones.
+When a stone was to be raised, the weight and the sheave were drawn
+out to the end of the arms of the crane, which projected over the
+outside of the walls of the Tower, and they were held in their places
+by simply locking the gearing which moved them. The second train of
+gearing was then brought into play to work the chain which hung over
+the sheave, and so to raise the stone to a height sufficient to clear
+the top of the wall. When in that position, the first train of gearing
+was slowly unlocked and the slight declivity inwards from the end of
+the arms formed an _inclined plane_, along which the roller carrying
+the sheave was allowed slowly to move (one man using a break on the
+gearing to prevent a rapid run), while the first train of gearing was
+slowly wound by the others, so as to take up the chain which passed
+over the sheave, and thus to keep the stone from descending too low in
+proportion as it approached the centre of the Tower. When the stone so
+raised had reached such a position as to hang right over the wall, the
+crane was made to turn round the centre column in any direction that
+was necessary, in order to bring it exactly above the place where it
+was to be _set_; and by working either train of gearing, it could be
+moved horizontally or vertically in any way that was required. The men
+who wrought the crane, stood on two small stages of planks attached to
+either side of the framework, and moving round the shaft along with it.
+
+The balance-crane was safely landed on the Rock on the 20th July and
+on the 25th it was erected in working order on the top of the masonry.
+On the afternoon of that day, I had the satisfaction of seeing it put
+to a severe trial in raising a stone of nearly two tons weight and
+drawing it from the _shear-poles_ already noticed to the top of the
+building. As that trial was made at an earlier stage of the works than
+was originally intended, the Tower was of larger diameter than was
+quite suited to the arrangements of the crane, which was consequently
+subjected to the weight of the stone at the very point of the jib. I
+felt no small anxiety as to the result, and had taken the precaution
+to relieve the centre pillar or shaft, on which the crane swung, from
+part of its burden, by means of a guy attached to a lewis-bat on the
+top of the building; yet even with that aid, the point of the jib was
+depressed 6 or 8 inches on a length of 14 feet. That test, however,
+having been successfully passed and not the slightest trace of any
+injury having been discoverable in any part of the crane, we continued
+to work it with perfect confidence and in the most satisfactory manner
+throughout the whole season until the close of the Rock operations for
+the year on the 17th of August.
+
+The mass of masonry built during the season was 30,300 cubic feet, a
+quantity considerably more than double that contained in the Eddystone
+and somewhat more than the mass of the Bell Rock. The whole was very
+carefully _set_ and when gauged at the upper bed of each course was
+found to preserve the diameter due to the height, according to the
+calculated dimensions, within a fraction rarely exceeding ¹⁄₁₆th of
+an inch. The height of the mass also, when measured, exceeded the
+specified height only by _half an inch_. The mortar employed was
+composed of equal parts of lime from the Halkin Mountain in North
+Wales and Pozzolano; and I consider it if possible superior to that
+produced from the lime of Aberdda. When we left the Rock this season,
+two apartments were covered in and the third was nearly completed, as
+will appear from the section (Plate III.) (on which the progress of the
+several seasons is marked), and only about _one-third_ of the whole
+Tower remained to be built.
+
+Our last work on the Rock before leaving it for the season on the 17th
+August, was to cover the balance-crane with a strong tarpaulin in order
+to protect it as much as possible from the weather and also to make a
+temporary lightning-conductor from the top of the building to the sea.
+
+The extent of work done during the season of 1841 at the Rock, must in
+a great measure be attributed to the advantage of steam attendance,
+without which numerous favourable opportunities of landing materials
+must necessarily have been lost, from the uncertainty which pervades
+all the movements of sailing craft. The number of lighters towed out
+and discharged at the Rock was 120; and it is remarkable that no
+accident of importance occurred, although many risks were run, from
+the breaking of warps while the craft lay moored to the landing quay
+during heavy seas. I cannot omit in this place to record my sense of
+the services rendered to the works by the late Mr James Heddle, who
+commanded the steamer and who died from some consumptive disease soon
+after the close of the season’s operations. Mr Heddle’s health had
+been somewhat enfeebled towards the latter part of the autumn; and his
+excessive exertions and continued exposure during his arduous service,
+in some measure, I fear, hastened the crisis of his disease, which at
+length terminated suddenly by the rupture of an abscess in the lungs.
+Of his anxiety to forward the work, and his unwearied exertion in the
+discharge of his harassing duty at Skerryvore, which frequently allowed
+him less than twenty hours sleep in a week, I cannot speak too highly,
+as I consider his intrepidity and zeal to have been one of the most
+efficient causes of our success ever since the commencement of the
+works on the Rock in 1839. Mr Heddle possessed attainments superior
+to those generally found among persons in his walk of life and was in
+every respect a most estimable man.
+
+
+CHAPTER VIII.
+
+OPERATIONS OF 1842.
+
+  ~State of the Rock in Spring of 1842.~
+
+On the 17th of April 1842, I made my first landing on the Skerryvore,
+for the season, and found traces of very heavy seas having passed over
+the Rock during the preceding winter. Its surface was washed quite
+clean from all the scattered materials which were left lying on it at
+the end of the last season; and the building, to the height of 6 or 8
+feet from the foundation, was covered with a thick coating of green
+sea-weed. The railway had suffered considerably from large stones
+having been thrown upon it; and several blocks of about half a ton
+in weight were found wedged into the deep fissures of the Rock, and
+lying among the main timbers of the Barrack. Heavy sprays had been
+playing over the Tower, in the upper uncovered apartment of which a
+great number of water-worn pebbles or boulders were found. Those stones
+had been raised by the heavy surf and deposited on the floor of the
+apartment and on the top of the wall at a height of no less than 60
+feet above high watermark; but the balance-crane, which had stood all
+winter on the top of the Tower, had sustained no damage, although the
+canvass cover was torn to shreds by the action of the weather. In the
+Barrack every thing was in good order except the smoke-funnel, which,
+from the effects of the sea-water, was riddled full of holes and
+required to be completely renewed.
+
+  ~Commencement of Rock operations.~
+
+As I had resolved to keep, during the summer of 1842, a complement
+of about eighteen or twenty seamen on the Rock, in addition to the
+usual detachment of masons, in order to work the crabs for raising
+the materials to the top of the Tower by successive stages; my first
+step was to set about preparing additional accommodation in the
+Barrack, by converting the open gallery (called _store for coals_,
+&c., in Plate V.), immediately below the cook-house, into a covered
+apartment for lodgings for the additional hands. I accordingly landed
+on the 20th of April, with a stock of provisions, water and fuel and
+a party of joiners and a smith, to prepare that apartment by simply
+flooring over the joists of the gallery and closing the _triangular_,
+or rather _trapezoïdal_, spaces between the uprights of the Barrack,
+with double planking, protected on the seams with painted canvass,
+so as to render them impervious to the heavy sprays which, even in
+summer, dashed forcibly on the lower parts of the Barrack. Windows
+were formed on the sides least exposed to the intrusion of the sea;
+but, with all our precautions, we could not succeed in keeping dry
+even the cots or hammocks, which were suspended there; and it must be
+admitted that the addition to the Barrack proved, in bad weather, but a
+comfortless retreat, the inconveniences of which few but seamen would
+have patiently endured. Those discomforts, however, were to a certain
+extent, counterbalanced by some advantages which that singular abode
+possessed in hot weather; for, at such times, its inhabitants enjoyed
+more room, freer air, and more tolerable temperature, than any of their
+neighbours in the highest storey could obtain, owing to the greater
+number of persons in that part of the Barrack and its exposure to the
+heat of the cook’s stove.
+
+During the remainder of the month of April and the commencement of May
+we had frequent stiff gales; and it often happened that the men could
+not venture out of the Barrack, owing to the heavy sea which swept
+over the Rock. The crane, too, which had been erected at the wharf for
+unloading the stones, although its top stood about 8 feet above the
+Rock, was often buried in the breakers and seemed in hourly danger of
+being carried away, an event which we were the more ready to fear from
+our experience in a former season, when the crane disappeared during a
+heavy westerly gale. The sea on those occasions also broke so heavily
+on the Barrack, that the windows of my apartment, which were about 55
+feet above the sea, were often darkened by the sheet of water which
+flowed over them after the house had been struck by a wave. From those
+causes it was not till the 18th May that we were enabled to occupy the
+Rock in full force; and on the day following we commenced building the
+38th course on the top of the last year’s work.
+
+After that period we had a long continuance of north-easterly winds,
+which always brought both smooth water for landing materials and dry
+weather for building; so that by the 23d of May our work had made
+such progress and the Tower had risen so high, that the chain of the
+balance-crane, which had been raised along with the building, by
+sliding it upwards on the cast-iron pillar or shaft placed in the
+centre of the Tower, could not reach the top of the _shear-poles_, by
+which the stones were raised to the level of about 40 feet above the
+Rock; and it was found necessary to rig from the lowest window a beam
+or _needle_ (in the manner described at page 155, and as also shewn in
+Plate IX. of my Father’s _Account of the Bell-Rock Lighthouse_), as an
+intermediate stage between the top of the Tower and the shear-poles on
+the Rock. The needle, as already noticed, projected horizontally from
+the window and the stones were raised by a chain which passed over the
+sheave at its outer end and was wrought by means of a crab placed in
+the interior of the Tower. In that manner we continued for about six
+weeks, with little interruption from the weather, to raise the blocks
+of stone to the top of the Tower by successive needles from storey to
+storey; while the mortar, lewis-bats and other lighter materials were
+raised at once by means of a line wrought by a windlass placed on the
+Rock.
+
+On the night of Saturday the 9th of July, however, a heavy sea, caused
+by a combination of high tides and strong gales, threw down some of
+the stones of the belt course which lay piled up round the base of
+the Tower ready to be raised for building; and they were with great
+difficulty, but most happily, saved from the insatiable deep. The loss
+of any of the stones of that course would have been a serious obstacle
+to the progress of the works and might have prevented our completing
+the erection of the lantern until next year; and indeed, as that
+course formed a prominent feature of the Tower, any slight injury even
+to the arris or corners of the outer face would have been much to be
+regretted. It was with great satisfaction, therefore, that it was found
+on examination next morning that none of the stones had sustained the
+slightest damage.
+
+  ~Last Stone.~
+
+On the 21st July the last stones of the Tower were safely landed
+on the Rock, under a salute from the steamer, as an expression, no
+doubt, of the satisfaction which the commander Mr Kerr and his crew
+naturally felt at having successfully brought out not fewer than 75
+lighter loads, or about 1500 tons, of stone during the season, as well
+as in some measure of their joy at the prospect of a speedy and happy
+termination of our arduous labours. The process of landing, indeed,
+owing to the fine weather that prevailed throughout the season, was
+very easy, compared with that of former years; in proof of which, I
+may state, that in 1841, there were often as many as five warps broken
+at a single landing, while in 1842, not a single rope was broken in
+the discharging of the stones. On the 25th July the last stone of
+the parapet or top-course was built; and immediately thereafter we
+proceeded to remove from the Tower, the balance-crane and the cast-iron
+pillar on which it was swung, and to make way for the erection of the
+Lantern.
+
+In looking back upon the works we found great cause for thankfulness
+for the successful conclusion of the building operations, without loss
+of life, or even the occurrence of any serious accident, excepting the
+destruction of the first Barrack in November 1839. It also gave me
+great satisfaction to reflect that, however difficult a rigid adherence
+to scrupulous accuracy of workmanship may be in such a situation as
+the Skerryvore, it had nevertheless, from the exactness with which
+the stones were dressed, on no occasion been necessary, throughout the
+execution of the whole work, to deviate from the rule which I had laid
+down of carefully gauging the diameter of each course and of admitting
+no variation from the true form materially exceeding ¹⁄₈ inch. Every
+part of the stone work, indeed, was fitted in an accurate manner and
+the floor stones, in particular, which serve as _ties_ across the
+building, were finely dressed and carefully set. All opportunities were
+also embraced, whenever it was practicable, to grout each course over
+night that the recent masonry might be in a state fit for building upon
+in the morning; and by those precautions and the peculiar properties
+of the mortar used, any disadvantages from very rapid building were
+entirely avoided. Even the elliptic cavetto which forms the cornice
+and which projects no less than three feet from the face of the wall,
+although bearing a very heavy _entablature_ or _plinth_, never gave any
+signs of _settling_ outwards; and when I examined it from a stage hung
+from the end of the balance-crane just before it was removed, there was
+no appearance of any change in the thickness of the joints, although
+the outer heads of the stones had been purposely kept a little high to
+allow for any tendency to settlement. The effect of the cornice is very
+bold and striking and is quite in accordance with the simple and almost
+severe style of the pillar itself. The masonry of the Tower is 137 feet
+11 inches in height and it contains 58,580 cubic feet or about 4308
+tons.
+
+  ~The Lantern.~
+
+The day after landing the last stone of the parapet, the steamer
+started from Tyree for Greenock, with two lighters in tow, for the
+transport of the Lantern; and by the 10th of August the whole was
+landed on the Rock. No time was lost in preparing the beds for the
+sole-plates of the Lantern, and that operation had been nearly
+completed when my Father, in the course of his annual tour of
+inspection, as Engineer for the Northern Lights, visited the Rock, two
+days after the iron work had been landed. By the 16th the whole of the
+sashes and the frame of the roof were to their places; and on the same
+day the fixtures of the lightning-conductor were completed. On the
+18th of August Mr Bruce, the Sheriff of Argyll, and some gentlemen who
+accompanied him and had spent the preceding night at Hynish, visited
+the Rock; and, after breakfasting at the base of the Tower, ascended to
+the top and minutely inspected every part of the work. They afterwards
+returned to Hynish, whither I accompanied them and had an opportunity
+of pointing out to Mr Bruce the various works in progress there. The
+party sailed for Oban in the afternoon of the same day.
+
+From want of room on the Rock it was found necessary to build the roof
+of the Lantern in separate pieces instead of rivetting together the
+sheets of which it was composed on the ground, and raising the whole
+to the top in one mass, as is usually done; but, in spite of that
+disadvantage, the work was brought to a close for the season on the
+14th September, on which day the glazing of the Lantern was completed
+and the glass was covered with a framework of timber to protect it
+from the sea-fowls which frequent in myriads the Rock and the Tower.
+The workmen were, on the same day, removed from the Rock, although
+with much difficulty, owing to the heavy surf which broke over the
+landing-place and rendered the embarkation more perilous than almost
+any I had before experienced at the Skerryvore.
+
+
+CHAPTER IX.
+
+CONCLUDING OPERATIONS AND EXHIBITION OF THE LIGHT.
+
+  ~Harbour Works.~
+
+The shores of Tyree, as already often noticed in these pages, and as
+deplored by Martin 140 years ago, in his Account of the Hebrides,
+afford few places of safety fit even for boats. It had therefore been
+determined, by the Commissioners, that any attempt at the construction
+of a harbour should be strictly confined to the provision of a place
+of shelter for the vessel which was to attend the Lighthouse. Much
+attention had been bestowed on the subject, not merely by myself
+during my five years’ acquaintance with Tyree, but also by Mr Thomas
+Stevenson, who succeeded me in the charge of the works at Hynish, at
+the time when I was appointed Engineer to the Lighthouse Board in
+January 1843, after the completion of the masonry of the Tower. A small
+sandy beach at Hynish, which lies embayed between rugged rocks, had
+been selected as the fittest place for the pier; and all the materials
+had been landed and shipped there, so that we naturally looked to it
+as the site for the projected harbour, not only as presenting works
+already finished, which might be made available as part of a more
+extended plan, but as a place which, during an experience of some
+years, had justified our anticipations as to its being less frequently
+disturbed during stormy weather than most of the neighbouring creeks.
+All that was contemplated in the proposed plan, was to form a small
+basin in which the vessel could lie sheltered in all states of the
+weather, and from which she could find an easy departure in any
+condition of the sea which would permit a landing to be made on the
+Rock. The Skerryvore Steamer having been sold and a small vessel of
+35 tons, named the “Francis,” having been purchased at Deal, the dock
+accommodation at Hynish was, for the sake of economy, laid out with
+reference to the shelter of that vessel. It was calculated that a basin
+100 feet in length and 50 feet wide, would afford sufficient room for
+such a vessel; and as her draught of water is between 7 and 8 feet, it
+was thought sufficient to provide for a depth of about 12 feet at high
+water of spring-tides, which, it was expected, would render the dock
+accessible during good springs at about _three quarters flood_.
+
+The exposure of the shore at Hynish, to the effects of heavy westerly
+swells, made it desirable to avoid carrying the entrance of the
+basin so far seaward, as, under more favourable circumstances, would
+undoubtedly have been done; and it was accordingly determined that
+the landing pier should be extended to about 40 feet seaward of
+low-water mark, and terminated in a round head, as shewn in Plate X.,
+having a talus wall on its seaward face, composed of rough blocks,
+arranged in courses regularly receding, so as to form a slope of 45° of
+inclination, as shewn in Plate XI. The inner face of that pier, being
+nearly vertical and guarded by fenders of timber, had served as the
+quay for landing and shipping stones and other stores and it now forms
+one side of the basin or dock. The other side consists of a shorter
+talus wall, built about 60 feet to the westward of the first, and,
+together with the crossheads projecting from each wall and containing
+the gateway, completes the inclosure of the basin. In the gateway,
+_booms_ are employed, as the shifting nature of the sand and the heavy
+seas render _gates_ inadmissible. The space contained between those
+walls was left completely dry at low water of spring-tides, and was
+chiefly composed of rock, covered with a thin layer of shifting sand,
+which varied in depth with the state of the wind and sea. The rocky
+matter, consisting of decomposed gneiss, was excavated to the extent
+of about 5000 tons, in three separate compartments, protected by
+successive dams of rubble masonry, built with Pozzolano mortar, and
+presenting an aggregate area of 7339 square feet. Those dams, two feet
+thick, proved so water-tight, that by the aid of a small hand-pump, the
+excavation and the building of the entrance heads of the booms went
+regularly forward without any delay, although the men worked in the
+bottom of the pit, surrounded on all sides by the sea, which, at high
+water of spring-tides, rose 17 feet above them. The dams were sheltered
+from the action of the swell by a temporary breakwater of heavy blocks,
+which formed a convenient roadway for the transport of the materials
+during the progress of the works, and which were removed at the close
+of the operations.
+
+The talus wall for protecting the seaward side of the harbour, has
+about 60 feet of its foundation laid in a depth of water varying at low
+spring-tides from 18 inches to 3¹⁄₂ feet. The mode of its construction,
+as already stated, is shewn in Plate XI. It is surmounted by a strong
+parapet of rustic masonry of Mull granite, and is altogether a most
+substantial piece of work.
+
+The idea of a tide-basin with boom-gates facing the breach of Atlantic
+waves is somewhat novel and was not very hastily entertained by me at
+first; but the most complete success has attended the plan. During my
+occasional visits to the works in the course of the summer 1843, our
+attention had been often occupied with considering the probability of
+the sand shutting up the basin; and as a single tide during heavy winds
+from the N.W., made great changes on the appearance of the beach, we
+feared that the vessel might often be imprisoned within the boomgates
+by a bank of sand heaped against them by the sea. To such an extent
+did the accumulation go before the harbour was fully opened, that on
+many occasions there was not water for a rowboat to pass between the
+boom-heads even at the highest spring-tides. The only remedy for such
+an evil, was obviously to attempt some mode of artificial scouring; and
+for that purpose, it was proposed to divert several small streams which
+run from Ben Hynish and the neighbouring hills through the grounds at
+Hynish, into one feeder, and pen them up in a pond, so as to afford
+the means of scouring the entrance to the basin from the incumbrance
+of the loose sand which might choke it. Those streams were repeatedly
+gauged during the summer and were found to deliver from 13 to 50 cubic
+feet of water per minute, according to the state of the weather,--a
+supply which seemed ample for the purpose in view. The sand at Hynish
+is of a light nature and is easily acted on by currents of very feeble
+power. It consists of comminuted shells and requires about 25¹⁄₂ cubic
+feet to make a ton, instead of 24 feet, which is the common allowance
+for silicious sand. The leave of the Duke of Argyll and also of the
+Farmer at Hynish, having been obtained, various cuts were made and the
+stream was diverted into a pond capable of containing about 175,000
+cubic feet and provided with a waste-weir and with sluices for opening
+the communication between the pond and the scouring tunnel, from which
+the water flows in a stream of about 9 square feet of area, at the rate
+of about 260 feet per minute for a period of 1¹⁄₄ hour. The operation
+of scouring is performed at low water and is generally found quite
+sufficient for the purpose of clearing a passage down to the bare rock
+in a single tide. Nothing can be more satisfactory than to witness the
+effect of that process in opening the entrance to a basin apparently
+inaccessible; and but for such an arrangement, the dock must have
+remained permanently choked with sand and sea-weed. The position of the
+various works is marked in Plate X., which shews the ground at Hynish.
+
+On the side of the dock stands a crane, which is used for various
+purposes connected with the shipment and discharging of materials. It
+also serves for raising the booms, by means of a double hook, which can
+be attached to the chain and which embraces the pegs in the centre of
+each boom, shewn in Plate XI. The two tiers of booms are firmly lashed
+down by means of chains passing through ring-bolts in the manner shewn
+in the section (Plate XI.), so as to prevent their rising with the
+tide.
+
+The necessity of providing somewhere in the neighbouring island of
+Tyree for the proper accommodation of the vessel which was to wait
+upon the Lighthouse (if it could ever have been a matter of doubt),
+was abundantly demonstrated by the experience of 1843, and more
+especially by that of the months of November and December. Owing to the
+shortness of the day and the distance of any place of shelter from the
+Skerryvore, together with the difficulty of landing on the Rock and
+the extreme variableness and uncertainty of the climate, the Regent
+Tender, although constantly waiting on the coast and making trials on
+every occasion that seemed to offer any prospect of success, could not
+effect any communication with the people who had been left on the Rock,
+during a period of no less than seven _long_ weeks. The poor seamen
+who were living in the Barrack passed that time most drearily, for not
+only had their clothes been literally worn to rags, but they suffered
+the want of many things dearer to them than clothes, and amongst others
+of tobacco, the failure of the supply of which they had despondingly
+recorded in chalk on the walls of their prison-house, with the date
+of the occurrence! Unless, therefore, the vessel had been stationed
+near the rock, the few casual and uncertain opportunities which occur
+at intervals, during the short days of winter, would often have been
+lost, and the future maintenance of the Light rendered excessively
+precarious. The experience of subsequent years, during which the relief
+of the Light-keepers has been kept up with considerable regularity,
+shews that the small Harbour at Hynish forms a most important integral
+part of the Establishment of Skerryvore, than which I believe no
+Lighthouse on the coast is more comfortable as a residence.
+
+  ~Bo Pheg Beacon.~
+
+In connection with the Harbour at Hynish, I naturally notice the
+erection of a Beacon on a rock called Bo Pheg, which is dry only at low
+water of spring tides. It lies about one mile NE. from Hynish Point,
+(See Plates II. and X.) right in the track of the Tender in its passage
+to and from the Lighthouse. From the great difficulty of landing on
+that small rock, over which the sea almost continually breaks, even
+in very fine weather, the shortness of the time during which the men
+could remain at work, and the want of room on its irregular surface of
+about 16 yards square, the erection of a beacon proved to be a work of
+great difficulty. The Beacon consisted of an open frame-work of iron,
+(somewhat on the same plan as that which is described in the Appendix)
+and calculated to offer little opposition to the free passage of the
+waves; but before all the fixtures could be completed, the heavy storms
+of the winter of 1844, acting on its unfinished base (the bats of which
+were only partially secured), destroyed it piecemeal, at a season
+when no landing could be effected, nor any effort made to save almost
+any part of it from the sea. In the ensuing summer, a second Beacon,
+consisting of a hollow cone, composed of iron plates, united together
+by strong flanges and attached to the rock by _webbed flanges_ round
+its base with strong bats passing through them, was fixed down to the
+rock; and in order to increase its weight, the interior was filled with
+concrete gravel. That structure also has since yielded to the force of
+the waves, after giving slight indications of movement, an effect which
+I attribute chiefly to the smallness of the base, which the narrow
+limits of the rock unhappily prescribe.
+
+  ~Lightkeepers’ and Seamen’s House.~
+
+Another necessary part of the Establishment at Hynish, was the
+provision of dwelling-houses for the families of the Lightkeepers and
+Seamen and of Storehouses of various kinds. Those were partly built
+on purpose and partly consisted of altered forms of the buildings
+which had been found necessary as barracks for workmen and stores for
+materials, during the progress of the works.
+
+  ~Concluding works on the Rock, such as pointing, &c.~
+
+On landing on the Rock, on the 29th of March 1843, the Resident
+Engineer had the satisfaction of finding the whole building perfectly
+water-tight and saw not the slightest trace of a defective joint. The
+outside joints of the building were therefore carefully “ripped,” and
+repointed with mortar, composed of equal parts of Halkin lime and
+Pozzolano. That operation, from the difficulty of employing many men,
+where suspended scaffolds were necessary and from the care with which
+it requires to be executed, occupied a great deal of time.
+
+  ~Interior fittings of the Tower.~
+
+Another tedious operation was the fitting up of the interior of the
+Tower with wainscot lining and forming the various stories into
+apartments separate from the staircase. Much work was also expended
+in providing the fire-places with proper flues, in fitting up water
+tanks, coal stores, and oil tanks, and also in conveying the air-tubes
+between the Lightroom and the several apartments by which the signal
+bells are rung for summoning the keepers to mount guard. The keeper
+on duty is, by the rules of the Service, forbidden, under penalty
+of instant dismissal, to leave the Light-room, on any pretext,
+until relieved by the next who mounts guard, and who is summoned by
+means of a bell placed inside his cot or sleeping berth, which is
+rung by means of a small piston, propelled by simply blowing into a
+mouth-piece in the Light-room. The keeper in bed answers this signal by
+a “_counter-blast_,” which rings another bell in the Light-room, and
+informs the keeper there that his signal has been heard and will be
+obeyed.
+
+  ~Arrangement of the several apartments.~
+
+The general arrangement of the Tower, may be seen in the Section Plate
+VIII.; and the details of its subdivision are very similar to those
+shewn in Plate XVI. of my Father’s Account of the Bell Rock Lighthouse.
+The ascent to the outside door is by a ladder or trap of gun metal,
+26 feet high. The first apartment on the level of the entrance door,
+is chiefly appropriated to the reception of iron water-tanks, capable
+of holding a supply of 1251 gallons. The next story is set aside for
+coals, which are stowed in large iron boxes. The third apartment
+is a workshop; the fourth is the provision store; and the fifth is
+the kitchen. Above are two stories, each divided into two sleeping
+apartments, for the four Light-keepers. Over them is the room for the
+Visiting Officers; then follows the oil store, and lastly comes the
+Lightroom, making in all twelve apartments. The nearness of the oil
+store to the Lightroom is a great convenience to the Keepers, who are
+thus saved the trouble of carrying the daily supply of oil to the
+Lightroom, up a long flight of steps. The passage from story to story
+is by oaken trap ladders, passing through hatches in each floor and
+partitioned off from each apartment in order to prevent accidents and
+to check cold draughts.
+
+  ~Lightroom Apparatus, and first exhibition of the Light.~
+
+The light of Skerryvore was exhibited to the mariner on the night of
+the 1st February 1844, in terms of the Statutory Notice, which will
+be found in the Appendix. The light is revolving, appearing in its
+brightest state once in every minute of time. It is elevated 150 feet
+above the sea, and is well seen as far as the curvature of the earth
+permits; it is also frequently seen as a brilliant light from the high
+land of Barra, a distance of 38 miles. The apparatus consists of eight
+annular lenses (of the first order, in the system of AUGUSTIN FRESNEL),
+of 36·22 inches focal distance, revolving round a lamp with four
+concentric wicks, and producing a bright blaze when each lens passes
+between the lamp and the eye of a distant observer. Above those lenses
+are placed eight pyramidal lenses of 19·68 inches focal distance,
+inclined at 50° with the horizon and combined with eight plane mirrors,
+inclined in the opposite direction at 50° with the horizon. By this
+arrangement, that part of the light from the lamp which would otherwise
+escape uselessly beyond the great lenses, upwards into the sky, being
+parallelized in its passage through the smaller lenses and falling on
+the mirrors, is finally projected forwards in horizontal beams, so as
+to aid the effect of the light. Those lenses and mirrors, however,
+instead of having their axes in the same vertical plane with the axes
+of the principal lenses, are inclined about 7° horizontally to the
+right hand, and by that deviation produce small premonitory blazes,
+which, blending with the beams of the larger lenses, tend in some
+measure to lengthen the duration of the impression on the eye. So far
+the apparatus of the Skerryvore Lighthouse is identical in its general
+arrangements with that of the Tour de Corduan, and differs only in
+the superior workmanship of the lenses and the machinery, which the
+experience of more than twenty years has brought about, since FRESNEL
+designed that light in 1822. Instead, however, of employing curved
+mirrors, as has been done at Corduan, to collect the light which would
+otherwise escape below the lenses and, at the same time, to send it to
+the horizon, I determined to put in practice a plan which I had long
+contemplated, of placing totally reflecting zones below the lenses,
+similar in construction to the zones of the small Harbour Light
+Apparatus of the fourth order, which was also invented by FRESNEL. This
+was finally carried into effect, agreeably to the design of M. LEONOR
+FRESNEL, his brother, with whom I had corresponded on the subject. In
+the subsequent pages of this volume, I intend to make some observations
+explanatory of the principles and arrangement of the various optical
+instruments employed in Lighthouses; and as that will afford me a more
+convenient opportunity of describing the nature and properties of the
+_totally reflecting zones_, I shall forbear in this place to enter
+into further details as to the construction or action of the apparatus
+at the Skerryvore. It is right, however, that I should mention here
+that the lenses, mirrors and zones are from the works of M. FRANÇOIS
+of Paris, whose name I shall afterwards have occasion to notice; and
+that the machinery was constructed to my entire satisfaction, and in a
+manner worthy of his reputation as a mechanician, by Mr JOHN MILNE of
+Edinburgh.
+
+  ~Removal of the Barrack from the Rock.~
+
+In such a situation as the Skerryvore, new wants were discovered every
+day; and each summer brought its round of smaller works, which the
+experience of the preceding winter had suggested. The Barrack was found
+very useful as a place of residence for the workmen, who were engaged
+in such needful works; and it was not until the summer of 1846, that it
+was taken to pieces and removed from the Rock, after having kept its
+place for six years. Its removal, however, was then thought advisable,
+as some of its fixtures, by the continual action of the weather, had
+become very loose and precarious; and, although a very small outlay
+would have made it almost as stable as at first, it was considered
+inexpedient to attempt to perpetuate a structure confessedly temporary
+in its nature, and the sudden destruction of which by the waves, seemed
+to involve some risk of injury to the Tower itself.
+
+  ~Expense.~
+
+The expense of erecting the Skerryvore Lighthouse, including the
+opening of quarries and forming wharfs at the quarries in Mull and also
+the Harbour in Tyree, was, as appears from the Account in the Appendix,
+L.86,977 : 17 : 7.
+
+In the course of the Summer of 1844, a marble tablet, bearing an
+inscription in letters of gold, was, by order of the Commissioners,
+placed over one of the windows in the Visiting Officers’ Room. With
+a representation of the Tablet and the Inscription, which, after
+acknowledging the hand of Almighty God in the success which attended
+the work, briefly sets forth the beneficent purposes for which the
+Lighthouse was erected and records the laying of the foundation-stone
+by his Grace the Duke of Argyll, I willingly close this most defective
+narrative of the work.
+
+
+[Illustration:
+
+  IN SALUTEM OMNIUM
+  NORTHERN LIGHTHOUSES
+
+  A. D. O. M.
+
+  AUCTORITATE . ET . CONCILIIS
+  PHARORUM . SCOTIAE . COLLEGII
+  HAEC . STRUCTA . FUIT . PHAROS
+  CUJUS . DIRECTI . FLAMMA
+  NAUTAE
+  INFAMIBUS . HIS . SCOPULIS . ADHUC . MERITO . DETERRITI
+  OPTATUM . PORTUM . RECTIUS . ADVENIRENT.
+
+  JOANNES . DUX . DE . ARGYLL
+  INSULARUM . ADJACENTIUM . DOMINUS
+  LAPIDEM . AUSPICALEM . RITE . STATUIT
+  DIE . IV . MENSIS . JULII . ANNO . IV . VICT. REG.
+  M . D . C . C . C . X . L .
+  OPERUM . MAGISTRO . ALANO . STEVENSON . L.L.B.
+
+_Engraved by W. & A.K. Johnston_]
+
+
+
+
+PART SECOND.
+
+
+NOTES
+
+ON THE
+
+ILLUMINATION OF LIGHTHOUSES.
+
+
+
+
+PART SECOND.
+
+NOTES ON THE ILLUMINATION OF LIGHTHOUSES, WITH SHORT NOTICES OF THEIR
+EARLY HISTORY.
+
+
+  ~Early History.~
+
+The early history of Lighthouses is very uncertain; and some ingenious
+antiquaries, finding the want of authentic records, have been anxious
+to supply the deficiency by conjectures based upon casual and obscure
+allusions in ancient writers, and by vague hypotheses drawn from the
+heathen mythology. Some writers have gone so far as to imagine, that
+the Cyclopes were the keepers of lighthouses; whilst others have
+actually maintained that Cyclops was intended, by a bold prosopopœia,
+to represent a lighthouse itself.[24] A notion so fanciful deserves
+little consideration; and accords very ill with that mythology of which
+it is intended to be an exposition, as seems sufficiently plain from a
+passage in the ninth Odyssey, where Homer (who flourished about 907 B.
+C.), after describing the darkness of the night, informs us that the
+fleet of Ulysses actually struck the shore of the Cyclopean island,
+before it could be seen.[25]
+
+  [24] This spirit of etymological conjecture has converted _Cyclops_,
+  _Proteus_, _Cneph_, _Phanes_, _Canobus_, _Chiron_, _Tithonus_,
+  _Thetis_, _Amphitrite_, _Minotaurus_, _Chronus_, _Phrontis_, and
+  other demigods, into celebrated lighthouses, or, at all events, has
+  imagined that those mythological personages were worshipped under the
+  emblem of fire or light in buildings, which, at the same time, served
+  as guides to the benighted mariner. On the faith, also, of similar
+  obscure and finely drawn etymologies, various places, such as _Calpe_
+  and _Abyla_, the opposite points of Africa and Europe, at the Straits
+  of the Mediterranean, have been unhesitatingly recognized as the
+  sites of celebrated light-towers; and the Latin words _turris_ and
+  _columna_ have been supposed primarily to signify a lighthouse, the
+  first being written _Tor-is_, the _Tower of fire_, and the _Col-on_,
+  the _Pillar of the Sun_.
+
+  [25]
+
+     Ἔνθ’ ὄυτις τὴν νῆσον ἐσέδρακεν ὀφθαλμοῒσιν
+    Ὅυτ’ οὖν κύματα μακρὰ κυλινδόμενα ποτὶ χέρσον
+     Ἐισίδομεν πρὶν νῆας ἐϋσσέλμους ἐπικελσαι.
+
+  _Odyss._, ix., 146.
+
+Nor does there appear any better reason for supposing, that under the
+history of Tithonus, Chiron, or any other personage of antiquity,
+the idea of a lighthouse was conveyed; for such suppositions,
+however reconcileable they may appear with some parts of mythology,
+involve obvious inconsistencies with others. It seems, indeed, most
+improbable, that, in those early times, when navigation was so little
+practised, the advantages of beacon lights were so generally known and
+acknowledged as to render them the objects of mythological allegory.
+
+It must not, however, be imagined, that ancient writings are entirely
+destitute of allusions to the subject of Beacon Lights for the guidance
+of the Mariner. The venerable poet, already noticed, in speaking of
+the shield of Achilles, has beautifully described the flash of a
+beacon-light in some solitary place, as seen by seamen leaving their
+friends, in those lines, which contain ample proof of the existence of
+such a provision for the safety of the mariner in Homer’s time:--
+
+    Ὣς δ’ ὅταν ἐκ πόντοιο σέλας ναύτῃσι φανείη
+    Καιομένοιο πυρὸς, τὸ δὲ καίεται ὑψόθ’ ὄρεσφι,
+    Σταθμῷ ἐν οἰοπόλῳ· τοὺς δ’ οὐκ ἐθέλοντας ἄελλαι
+    Πόντον ἐπ’ ἰχθυόεντα φίλων ἀπάνευθε φέρουσιν.
+
+  _Il._, xix., 375.
+
+In the Holy Scriptures the word _Beacon_ occurs but once, and that in
+Prophecies of Isaiah (xxx. 17.), who lived above 200 years later than
+Homer; but it is obvious that the original term, which the Septuagint
+translate by the word ἱστος, merely imports a flagstaff or perch and
+does not at all imply the knowledge of beacon-lights among the Hebrews,
+who were not a maritime people.
+
+  ~Colossus of Rhodes.~
+
+About 300 years before the Christian era, Chares, the disciple of
+Lysippus, constructed the celebrated brazen statue, called the
+Colossus of Rhodes. It was of such dimensions as to allow vessels to
+sail into the harbour between its legs, which spanned the entrance.
+There is considerable probability in the idea that this figure served
+the purposes of a lighthouse; but there is no passage in any ancient
+writer, where this use of the Colossus is expressly mentioned. Many
+inconsistencies occur in the account of this fabric by early writers,
+who, in describing the distant objects which could be seen from it,
+appear to have forgotten the height which they assign to the figure.
+It was partly demolished by an earthquake, about eighty years after
+its completion; and so late as the year 672 of our era, the brass of
+which it was composed was sold by the Saracens to a Jewish merchant of
+Edessa, for a sum, it is said, equal to L.36,000.
+
+  ~Pharos of Alexandria.~
+
+Little is known with certainty regarding the Pharos of Alexandria,
+which was regarded by the ancients as one of the seven wonders of the
+world. It was built in the reign of Ptolemy Philadelphus, about 300
+years before the Christian era; and Strabo relates that Sostratus,
+a friend of the royal family, was the architect. He describes it as
+built in a wonderful manner in many stories of white stone, on a rock
+forming the promontory of the island Pharos (whence the Tower derived
+its name), and says that the building bore the inscription--“Sostratus
+of Cnidos, the son of Dexiphanes, to the Gods, the Saviours, for the
+benefit of seamen.” He concludes his brief notice of it by describing
+the neighbouring shores as low and encumbered with shoals and snares,
+and as calling for the establishment of a lofty and bright beacon, a
+sign to guide sailors arriving from the ocean into the entrance to the
+haven.[26]
+
+  [26] The passage from which the above description is drawn will be
+  found in the Oxford edition of Strabo, 1807, page 1123. It is as
+  follows: Ἔστι δε και ἀυτο τὸ τῆς νησίδος ἄχρον πετρα πολυκλύστος,
+  ἔχουσα πῦργον θαυμαστῶς κατεσκευασμένον λευκου λιθου, πολυοροφον,
+  ὁμωνυμον τῇ νὴσῳ· τουτον δε ἄνέθηκε Σωστρατος Κνὶδιος φιλος τῶν
+  βασιλεων, της των πλωϊζομενων σωτηριας χαριν, ὥς φησιν ἥ ἐπιγραφη
+  Επιγραμμα, ΣΩΣΤΡΑΤΟΣ ΚΝΙΔΙΟΣ ΔΕΧΙΦΑΝΟΥΣ, ΘΕΟΙΣ ΣΩΤΗΡΣΙΝ ΥΠΕΡ ΤΩΝ
+  ΠΑΩΙΖΟΜΕΝΩΝ. Ἀλιμένου γαρ ὄυσης και ταπεινῆς της ἕκατέρωθεν παραλίας,
+  ἐχουσης δε και χοιράδας και βράχη τινὰ, ἔδει σημεὶου τινος ὑψηλου
+  και λαμπρου, τοις ἀπὸ του πελάγους προσπλέουσιν, ὥστ’ ἐυστοχειν της
+  ἐισβολης του λιμενος. Strabo’s account of the position of the island
+  of Pharos at once leads to the conclusion of its having formed part
+  of the harbour of Alexandria (as is abundantly testified by Josephus,
+  Pliny, and other writers), and cannot be easily reconciled with
+  that of Homer (fourth Odyssey, l. 354), who describes the island as
+  a day’s sail with a fair wind from the mainland. His words are as
+  follows:--
+
+    Νῆσος ἔπειτά τις ἐστὶ πολυκλύστῳ ἐνὶ πόντῳ
+    Αἰγύπτου προπάροιθε (Φάρον δέ ἑ κικλήσkουσι)
+    Τοσσον δ’ ἂνευθ’ ὄσσον τεπανημέριη γλαφυρὴ νηῦς
+     Ἤνυσεν, ᾗ λιγὺς οὖρος ἐπιπνέιῃσιν ὂπισθεν.
+
+  _Odyssey_, iv., l. 354.
+
+  Pliny, however, does not scruple to identify the Pharos of Homer’s
+  time with that of his own day. “Pharos,” says he, “quondam diei
+  navigatione distans ab Ægypto, nunc è turri nocturnis ignibus cursum
+  navium regens.” Hist. Nat., v. 31; see also Hist. Nat., ii. 87, and
+  xiii. 21.
+
+The accounts which have come down to us of the dimensions of this
+remarkable edifice are exceedingly various; and the statements of
+the distance at which it could be seen are clearly fabulous. That
+of Josephus (who likens it to the second of Herod’s three Towers at
+Jerusalem, called Phasael, in honour of his brother) is the least
+removed from probability; yet even he informs us, that the fire which
+burnt on the top to enable seamen to anchor in sight of it, before
+coming near the shore, and so to avoid the difficulty of the navigation
+by night, was visible at a distance equal to about thirty-four English
+miles. Such a range for a lighthouse on the low shores of Egypt, would
+require a tower about 550 feet in height![27] Ammianus Marcellinus[28]
+and Pliny[29] are both very circumstantial in their notices of the
+Pharos as a beacon-light to guide seamen in approaching the coast of
+Egypt and port of Alexandria. The latter adds the interesting fact,
+that the cost of the Tower was reckoned at a sum equal to about
+L.390,000 of our money;[30] and both of them agree in stating that a
+light was shewn from it at night. Ammianus Marcellinus differs from all
+the other writers, in attributing the erection of the Tower to Queen
+Cleopatra. Pliny mentions in passing, that there were also lighthouses
+at Ostia and Ravenna.
+
+  [27] Bell. Judaic. iv., cap. 10, sec. 5. (Havercamp’s Josephus,
+  tom. ii., p. 309. Amsterdam, 1726.) ἐν δεξιᾳ δε ἡ προσαγορευομενη
+  Φαρος νησις προκειται, πῦργον ανἐχουσα μεγιστον, εκπυρσευοντα
+  τοις καταπλὲουσιν, ἐπι τριακοσιους σταδιους, ὤς ἐν νυκτὶ πὂρρωθεν
+  ὁρμιζοιντο προς την δυσχέρειαν του καταπλοῦ. And again, in the sixth
+  Book of the same History (v. 4, sec. 3, tom. ii., p. 330), he says,
+  και τὸ μεν σχημα παρεῴκει τῳ κατα τὴν Φαρον ἐκπυρσεὐοντι τοις επ’
+  Αλεξανδρείας πλέουσι. The height of the Tower in the text proceeds on
+  the idea of the observer’s eye being ten feet above the sea.
+
+  [28] Ammianus Marcellinus, l. xxii., c. 16. (Leipsic 1807, tom.
+  i., p. 306.) Hoc littus cum fallacibus et insidiosis accessibus
+  affligeret antehac navigantes discriminibus plurimis, excogitavit
+  in portu Cleopatra turrim excelsam, quae Pharos a loco ipso
+  cognominatur, praelucendi navibus nocturna suggerens ministeria; cum,
+  quondam ex Parthenio pelago venientes aut Libyco, per pandas oras
+  et patulas, montium nullas speculas vel collium signa cernentes,
+  harenarum inlisae glutinosae mollitiae frangerentur.
+
+  [29] Plinii Hist. Nat., xxxvi. 18. (Paris, 1723, p. 739.)
+  Magnificatur et alia turris a rege facta in insula Pharo portum
+  obtinente Alexandriae, quam constitisse octingentis talentis tradunt;
+  magno animo (nequid omittamus) Ptolemai regis, quod in ea permiserit
+  Sostrati Guidii Architecti structuræ ipsius nomen inscribi. Usus
+  ejus, nocturno navium cursu ignes ostendere ad praenuncianda vada
+  portûsque introïtum: quales, jam compluribus locis flagrant, ut
+  Ostiae ac Ravennae. Periculum in continuatione ignium, ne sidus
+  existimetur, quoniam è longinquo similis flammarum aspectus est.
+
+  [30] Supposing, as is most probable, that Pliny means the _Egyptian_
+  talent; the _Attic_ talent was about one-half the value of the other.
+
+If the reports of some writers are to be believed, this Tower must
+have far exceeded in size the great Pyramid itself; but the fact that
+a building of comparatively so late a date should have so completely
+disappeared, whilst the Pyramid remains almost unchanged, is a
+sufficient reason for rejecting, as erroneous, the dimensions which
+have been assigned by most writers to the Pharos of Alexandria. Some
+have pretended that large mirrors were employed to direct the rays of
+the beacon-light on its top, in the most advantageous direction; but,
+in so far as I know, there is no definite evidence in favour of this
+supposition. Others, with greater probability, have imagined that this
+celebrated beacon was known to mariners, simply by the uncertain and
+rude light afforded by a common fire. In speaking of the Pharos, the
+poet Lucian, on most occasions sufficiently fond of the marvellous,
+takes no notice of the gigantic mirrors which it is said to have
+contained. He thus speaks of this celebrated lighthouse as having
+indicated to Julius Cæsar his approach to the Pharos of Egypt on the
+seventh night after he sailed from Troy:
+
+    Septima nox, Zephyro nunquam laxante rudentes,
+    Ostendit Phariis Ægyptia littora _flammis_.
+    Sed prius orta dies nocturna _lampada_ texit,
+    Quam tutas intraret aquas.
+
+  _Pharsal._, ix., 1004.
+
+It is true that, by using the word “_lampada_,” which can only with
+propriety be applied to a more perfect mode of illumination than an
+open fire, he appears to indicate that the “_flammis_” of which he
+speaks, were not so produced. The word _lampada_ may however, be used
+metaphorically; and _flammis_ would, in this case, not improperly
+describe the irregular appearance of a common fire.
+
+Perhaps, also, the opinion that some kind of lamp was used in the
+Pharos, may seem to receive countenance from the remarkable words of
+Pliny, in the passage above cited--“Periculum in continuatione ignium,
+ne sidus existimetur, quoniam è longinquo similis flammarum aspectus
+est.” The fear he expresses lest the light viewed from a distance
+should be mistaken for a star, could hardly be applicable to the
+diffuse, oscillating, lambent light derived from an open fire, and
+certainly gives some reason for imagining that, even at that remote
+time, the art of illuminating lighthouses was better understood than in
+the early part of the present century.
+
+Before leaving the subject of the Pharos of Alexandria, I wish to
+vindicate the memory of its architect Sostratus from the calumny of
+Lucian, who, in his Treatise on the art of writing history, with his
+usual acrimony, accuses the builder of the Pharos of a fraud, in
+cutting his own name on the solid walls of the Tower, and covering the
+inscription with plaster, on which he carved the name of his royal
+master Ptolemy.[31] Against this assertion I would oppose the testimony
+of Strabo, who calls Sostratus the “friend of the Kings” (see the
+quotation at the foot of page 183), and the direct evidence of Pliny,
+who, in the passage above cited, expressly states, as a proof of
+Ptolemy’s magnanimity, his giving the architect liberty to inscribe
+his own name on the Tower. The only other notices of the Pharos
+which I have been able to find in ancient writers are from Cæsar’s
+Commentaries, Valerius Flaccus, and Pomponius Mela.[32] At Alexandria,
+there is a modern lighthouse called the Pharos, which is maintained by
+the Pacha of Egypt.
+
+  [31] Lucian, in his Treatise (Amsterdam, 1743, vol. ii., p. 68.)
+  Πως δει ἱστοριαν συγγραφειν, thus details the merit and fraud of
+  Sostratus. Ορᾷς τον Κνίδιον ἐκεῖνον ἀρχιτεκτονα, οἶον ἐποίησεν;
+  οἰκοδομὴσας γαρ τον ἐπὶ τῇ Φαρῳ πῦργον, μεγιστον και καλλιστον ἔργων
+  ἀπαντων, ὡς πυρσεύοιτο ἀπ’ αὐτου τοις ναυτιλλομενοις, ἐπὶ πολὺ της
+  θαλασσης, και μὴ καταφέροιντο εἰς την Παραιτονίαν, παγχάλεπον,
+  ὣς φασιν, οὖσαν και ἄφυκτον, εἴ τις ἐμπεσοι εἴς τα, ἕρματα.
+  Οἰκοδομήσας οὐν το ἔργον, ἔνδοθεν μεν, κατα των λιθων, το αὐτου
+  ὄνομα ἐπέγραψεν. Ἐπιχρίσας δὲ τιτάνῳ και ἐπικαλύψας, ἐπέγραψε το
+  ὀνομα του τότε βασιλέυοντος, εἰδὼς, ὃσπερ και ἐγενετο, πάνυ ὀλιγου
+  χρονου, συνεκπεσουμενα μεν τῳ χρισματι τα γραμματα, εκφανησόμενον δε
+  ΣΩΣΤΡΑΤΟΣ ΔΕΧΙΦΑΝΟΥΣ Κνιδιος. θεοις σωτηρσιν ὑπερ των πλωΐζομεων,
+  κ.τ.λ.
+
+  [32] Cæsar de Bell. Civil., iii. 98 (Lond. 1712, p. 355). Pharus est
+  in insula turris, magna altitudine, mirificis operibus extructa, quae
+  nomen ab insula accepit.
+
+  Valerius Flaccus very distinctly sets forth the great advantage
+  of lighthouses to the seaman, and especially speaks of those at
+  Alexandria and Ostia in these lines--
+
+    Non ita Tyrrhenus stupet Ioniusve magister,
+    Qui portus, Tyberine, tuos, claramque serenâ
+    Arce Pharon præceps subiit:
+
+  _Argonaut_, vii., v. 84.
+
+  Pompon. Mela, ii. cap. 7.
+
+  ~Coruña Tower~
+
+Mr Moore, in his _History of Ireland_, vol. i., p. 16, speaks of
+the Tower of Coruña, which he says is mentioned in the traditionary
+history of that country, as a lighthouse erected for the use of the
+Irish in their frequent early intercourse with Spain. In confirmation
+of this opinion, he cites a somewhat obscure passage from Æthicus,
+the cosmographer. This in all probability is the tower which Humboldt
+mentions in his Narrative under the name of the _Iron Tower_, which was
+built as a lighthouse by Caius Saevius Lupus, an architect of the city
+of Aqua Flavia, the modern Chaves.[33] A Lighthouse has lately been
+established on this headland, for which Dioptric apparatus was supplied
+from the workshop of M. LETOURNEAU of Paris.
+
+  [33] “The traditionary history,” says Mr Moore, “of the latter
+  country (Ireland) gives an account of an ancient Pharos or lighthouse
+  erected in the neighbourhood of the port now called Coruña, for the
+  use of navigators on their passage between that coast and Ireland.
+  There is a remarkable coincidence between this tradition and an
+  account given by Æthicus, the cosmographer, of a lofty Pharos or
+  lighthouse standing formerly on the sea-coast of Gallicia, and
+  serving as a beacon in the direction of Britain. _Secundus Angulus
+  intendit ubi Brigantia civitas sita est Galliciae, et altissimum
+  Pharum et inter pauca memorandi operis ad speculum Britanniae._
+  Whether the translation I have given of the last three words of this
+  passage convey their real meaning, I know not; but they have been
+  hitherto pronounced unintelligible. The passage is thus noticed
+  by Casaubon, in a note on Strabo, lib. iii. ‘Æthicus in Hispaniae
+  descriptione altissimi cujusdam Fari meminit.’” The passage in Strabo
+  above referred to is on page 179 of the first volume of the Oxford
+  folio edition of 1807, where the geographer speaks of Cape Νεριον,
+  which Casaubon distinctly identifies with the _Cabo de Finisterra_ of
+  modern seamen.
+
+  ~Lighthouse at the mouth of the Guadalquivir.~
+
+There is also a record in Strabo of a magnificent lighthouse of stone
+at Capio, or Apio, near the Harbour of Menestheus (the modern Mesa
+Asta, or Puerto de Sta. Maria), which he describes as built on a rock
+nearly surrounded by the sea, as a guide for the shallows at the mouth
+of the Guadalquivir, in terms almost identical with those used by him
+in speaking of the Pharos of Alexandria. I am not aware of any other
+notice of this great work, for such it seems to have been, to have
+deserved the praises of Strabo.[34]
+
+  [34] The words of Strabo are (Oxon. 1807, p. 184), Και ὁ του Καπὶωνος
+  (vel Ἀπιωνος) πὺργος ἵδρυται ἐπι πέτρας ἀμφκλυστου, θαυμασιως
+  κατεσκευασμένος, ὥσπερ ό Φαρος τῆς των πλωϊζομενων σωτηριας χαριν, ῃ
+  τε γαρ ἐκβαλλομενη χους ὕπο του ποταμου βραχεα ποιει και χοιραδωδης
+  ἐστὶν ὁ πρὸ ἀυτου τοπος ὥστε δει σημειου τινος ἐπιφανοῦς.
+
+  ~Ancient Phari in Britain.~
+
+In Camden’s Britannia, a passing notice is taken of the ruins called
+_Cæsar’s Altar_, at Dover, and of the _Tour d’Ordre_, at Boulogne, on
+the opposite coast; both of which are conjectured to have been ancient
+lighthouses. Pennant describes the remains of a Roman Pharos near
+Holywell, but cites no authorities for his opinion as to its use. There
+were likewise remains of a similar structure at Flamborough-head. A
+very meagre and unintelligible account is also given of a lighthouse
+at St Edmund’s Chapel, on the coast of Norfolk, in Gough’s additions
+to Camden, by which it might seem that the lighthouse was erected in
+1272.[35]
+
+  [35] Gough’s Camden’s Britannia, vol. i., 318, and vol. ii., p.
+  198; Batcheller, in his Dover Guide (1845, p. 111), says, that the
+  Dover Pharos was built “during the lieutenancy of Aulus Plautius
+  and Ostorius Scapula, the latter of whom left Britain, A. D.
+  53.”--Pennant’s History of Whiteford and Holywell, p. 112.
+
+Such seems to be the sum of our knowledge of the ancient history of
+lighthouses, which, it must be admitted, is neither accurate nor
+extensive. Our information regarding modern lighthouses is of course
+more minute in its details and more worthy of credit. The greater part
+of it is drawn from authentic sources; and much of what is afterwards
+stated is the result of my own observation, during my visits to the
+most important lighthouses of Europe.
+
+  ~Tour de Corduan.~
+
+The first lighthouse of modern days that merits attention, is the
+_Tour de Corduan_, which, in point of architectural grandeur, is
+unquestionably the noblest edifice of the kind in the world. It is
+situated on an extensive reef at the mouth of the river Garonne, and
+serves as a guide to the shipping of Bordeaux and the Languedoc Canal,
+and indeed of all that part of the Bay of Biscay. It was founded in
+the year 1584, but was not completed till 1610, under Henri IV. It
+is minutely described in Belidor’s _Architecture Hydraulique_. The
+building is 197 feet in height, and consists of a pile of masonry,
+forming successive galleries, enriched with pilasters and friezes,
+and rising above each other with gradually diminished diameters.
+Those galleries are surmounted by a conical tower, which terminates
+in the lantern. Round the base is a wall of circumvallation, 134
+feet in diameter, in which the light-keepers’ apartments are formed,
+somewhat in the style of casemates. This wall is an outwork of
+defence, and receives the chief shock of the waves. The tower itself
+contains a chapel, and various apartments; and the ascent is by a
+spacious staircase. The first light exhibited in the Tour de Corduan
+was obtained by burning billets of oak-wood, in a chauffer at the
+top of the tower; and the use of coal instead of wood, was the first
+improvement which the light received. A rude reflector, in the form of
+an inverted cone, was afterwards added, to prevent the loss of light
+which escaped upwards. About the year 1780, M. LENOIR was employed to
+substitute paraboloïdal reflectors and lamps; and in 1822, the light
+received its last improvement, by the introduction of the dioptric
+instruments of AUGUSTIN FRESNEL, the celebrated French Academician.
+
+  ~Eddystone.~
+
+The history of the famous Lighthouse on the Eddystone Rocks is well
+known to the general reader, from the narrative of SMEATON the
+Engineer. Those Rocks are 9¹⁄₂ miles from the Ram-Head, on the coast
+of Cornwall; and from the small extent of the surface of the chief
+Rock and its exposed situation, the construction of the Lighthouse was
+a work of very great difficulty. The first erection was of timber,
+designed by Mr WINSTANLEY; and was commenced in 1696. The light was
+exhibited in November 1698. It was soon found, however, that the
+sea rose upon that tower to a much greater height than had been
+anticipated; so much so, it is said, as to “_bury under the water_”
+the lantern, which was sixty feet above the Rock; and the Engineer
+was therefore afterwards under the necessity of enlarging the Tower,
+and carrying it to the height of 120 feet. In November 1703, some
+considerable repairs were required, and Mr WINSTANLEY, accompanied by
+his workmen, went to the Lighthouse to attend to their execution; but
+the storm of the 26th of that month, carried away the whole erection,
+when the Engineer and all his assistants unhappily perished!
+
+The want of a light on the Eddystone, soon led to a fatal accident;
+for not long after the destruction of Mr WINSTANLEY’S lighthouse,
+the Winchilsea man-of-war was wrecked on the Eddystone Rocks, and
+most of her crew were lost. Three years, however, elapsed, after this
+melancholy proof of the necessity for a light, before the Trinity-House
+of London could obtain a new Act of Parliament, to extend their powers;
+and it was not till the month of July 1706, that the construction of
+a new lighthouse was begun under the direction of Mr JOHN RUDYERD of
+London. On the 28th of July 1708, the new light was first shewn, and it
+continued to be regularly exhibited till the year 1755, when the whole
+fabric was destroyed by accidental fire, after it had stood forty-seven
+years. But for this circumstance, it is impossible to tell how long the
+lighthouse might, with occasional repair, have lasted, as Mr RUDYERD
+seems to have executed his task with much judgment, carefully rejecting
+all architectural decoration, as unsuitable for such a situation, and
+directing his attention to the formation of a tower which should offer
+the least resistance to the waves. The height of the tower, which was
+of a conical form and constructed of timber, was 92 feet, including the
+lantern; and the diameter at the base, which was a little above the
+level of high water, was 23 feet.
+
+The advantages of a light on the Eddystone having been so long known
+and acknowledged by seamen, no time was permitted to elapse before
+active measures were taken for its restoration; and SMEATON, to whom
+application was made for advice on the subject, recommended the
+exclusive use of stone as the material, which, both from its weight
+and other qualities, he considered most suitable for the situation.
+On the 5th of April 1756, SMEATON first landed on the Rock and made
+arrangements for erecting a Lighthouse of stone and preparing the
+foundations, by cutting the surface of the rock into regular horizontal
+benches, into which the stones were carefully dovetailed or notched.
+The first stone was laid on 12th June 1757 and the last on the 24th
+of August 1759. The Tower measures 68 feet in height and 26 feet in
+diameter at the level of the first entire course; and the diameter
+under the cornice is 15 feet. The first 12 feet of the Tower form
+a solid mass of masonry; and the stones of which it is composed
+are united by means of stone joggles, dovetailed joints, and oaken
+treenails. It is remarkable that SMEATON should have adopted an arched
+form for the floors of his building, instead of employing the floors
+as tie-walls formed of dovetailed stones. To counteract the injurious
+tendency of the outward thrust of those arched floors, he had recourse
+to the ingenious expedient of laying, in circular trenches or grooves
+cut in the stones which form the outside casing, tie-belts of chain,
+which were heated before being set in the grooves by means of an
+application of hot lead and became tight in cooling, after they were
+fixed in the wall. The light was exhibited on the 16th October 1759;
+but such was the state of lighthouse apparatus in Britain at that
+period, that a feeble light from tallow candles was all that decorated
+this noble structure. In 1807, when the property of this lighthouse
+again came into the hands of the Trinity-House, at the expiry of a long
+lease, Argand burners, and paraboloïdal reflectors of silvered copper,
+were substituted for the chandelier of candles.
+
+  ~Bell Rock.~
+
+The dangerous reef called the Inch Cape, or Bell Rock, so long a
+terror to mariners, was well known to the earliest navigators of
+Scotland. Its dangers were so generally acknowledged, that the Abbots
+of Aberbrothwick, from which the Rock is distant about twelve miles,
+caused a float to be fixed upon the Rock with a bell attached to it,
+which being swung by the motion of the waves, served by its tolling to
+warn the mariner of his approach to the reef. From this circumstance,
+which formed the groundwork of SOUTHEY’S striking ballad of Sir Ralph
+the Rover, the Rock is said to have derived its name. Amongst the many
+losses which occurred on the Bell Rock in modern times, one of the
+most remarkable is that of the _York_, _seventy-four_, with all her
+crew, part of the wreck having been afterwards found on the Rock and
+part having come ashore on the neighbouring coast. During the survey
+of the Rock also, several instances were discovered of the extent
+of loss which this reef had occasioned; and many articles of ships’
+furnishings were picked up on it, as well as various coins, a bayonet,
+a silver shoe-buckle, and many other small objects. Impressed with the
+great importance of some guide for the Bell Rock, Captain Brodie, R.N.,
+set a small subscription on foot and erected a beacon of spars on the
+Rock, which, however, was soon destroyed by the sea. He afterwards
+constructed a second beacon, which soon shared the same fate. It was
+not, therefore, until 1802, when the Commissioners of Northern Lights
+brought a bill into Parliament for power to erect a lighthouse on it,
+that any efficient measures were contemplated for the protection of
+seamen from this Rock, which, being covered at every spring-tide to the
+depth of from twelve to sixteen feet, and lying right in the fairway
+to the Friths of Forth and Tay, had been the occasion of much loss
+both of property and life. In 1806, the bill passed into a law; and
+various ingenious plans were suggested for overcoming the difficulties
+which were apprehended, in erecting a lighthouse on a rock twelve miles
+from land, and covered to the depth of twelve feet by the tide. But
+the suggestion of Mr ROBERT STEVENSON, the Engineer to the Lighthouse
+Board, after being submitted to the late Mr RENNIE, was at length
+adopted; and it was determined to construct a tower of masonry, on the
+principle of the Eddystone. On the 17th of August 1807, Mr STEVENSON
+accordingly landed with his workmen and commenced the work by preparing
+the Rock to receive the supports of a temporary pyramid of timber,
+on which a barrack-house for the reception of the workmen (similar
+to that which has already been described in a preceding part of this
+volume) was to be placed; and during this operation, much hazard was
+often incurred in transporting the men from the Rock, which was only
+dry for a few hours at spring-tides, to the vessel which lay moored off
+it. The lowest floor of this temporary erection, in which the mortar
+for the building was prepared, was often broken up and removed by the
+force of the sea. The foundation for the tower having been excavated,
+the first stone was laid on the 10th July 1808, at the depth of sixteen
+feet below the high water of spring-tides; and at the end of the second
+season, the building was five feet six inches above the lowest part of
+the foundation. The third season’s operations terminated by finishing
+the solid part of the structure, which is thirty feet in height; and
+the whole of the masonry was completed in October 1810. The light was
+first exhibited to the public on the night of the 1st of February 1811.
+The difficulties and hazards of this work were chiefly caused by the
+short time during which the Rock was accessible between the ebbing and
+flowing tides; and amongst the many eventful incidents which render
+the history of this work interesting, was the narrow escape which the
+Engineer and thirty-one persons made from being drowned, by the rising
+of the tide upon the Rock, before a boat came to their assistance, at
+a time when the attending vessel had broken adrift. This circumstance
+occurred before the Barrack-house was erected, and is narrated by Mr
+STEVENSON, in his Account of the work, published at the expense of
+the Lighthouse Board in 1824, to which I would refer for more minute
+information on the subject of this work and the other lighthouses on
+the coast of Scotland.
+
+The Bell Rock Tower is 100 feet in height, 42 feet in diameter at the
+base, and 15 at the top. The door is 30 feet from the base and the
+ascent is by a massive copper ladder. The apartments, including the
+light-room, are six in number. The light is a _revolving red and white
+light_; and is produced by the revolution of a frame containing sixteen
+Argand lamps, placed in the foci of paraboloïdal mirrors, arranged on
+a quadrangular frame, whose alternate faces have shades of red glass
+placed before the reflectors, so that a red and white light is shewn
+successively. The machinery, which causes the revolution of the frame
+containing the lamps, is also applied to tolling two large bells,
+to give warning to the mariner of his approach to the Rock in foggy
+weather. The erection of the Bell Rock Lighthouse cost L.61,331 : 9 : 2.
+
+  ~Carlingford.~
+
+The most remarkable Lighthouse on the coast of Ireland is that of
+Carlingford, near Cranfield Point, at the entrance of Carlingford
+Lough. It was built according to the design of Mr GEORGE HALPIN, the
+Inspector of the Irish Lights; and was a work of an arduous nature,
+being founded 12 feet below the level of high-water, on the Hawlbowling
+Rock, which lies about two miles off Cranfield Point. The figure of the
+Tower is that of a frustum of a cone, 111 feet in height, and 48 in
+diameter at the base. The light, which is fixed, is from oil burned in
+Argand lamps, placed in the foci of paraboloïdal mirrors. It was first
+exhibited on the night of December 20, 1830.
+
+  ~Iron Lighthouses.~
+
+There are various other Lighthouses, which, in themselves, are
+sufficiently deserving of a separate notice, were it not that they
+have more or less something in common with those already described,
+which are unquestionably the most remarkable edifices of the kind.
+The first design for an Iron Lighthouse, is that by my Father for the
+Bell Rock, in the year 1800. The invention of Mr MITCHELL of Belfast,
+for applying the principle of the screw to the erection of Lighthouses
+on soft foundations, deserves a longer notice than is consistent with
+the nature of these notes. It must therefore be sufficient to say,
+that the principal Lighthouses on this plan (those of the Maplin,
+Fleetwood, and Belfast Lough) consist of piles or of hollow pillars of
+cast-iron, grouped together in the form of a truncated pyramid, and
+closely resembling, in the general arrangement of their parts, the
+Beacon shewn in Plate XXX., and that erected on the Carr Rock in 1821.
+The lower end of each pillar is furnished with a flat screw or worm
+and a sharp point, which is screwed into the sand, clay, or gravel,
+or other soft subsoil. Mr ALEXANDER GORDON of London also fitted up
+a Lighthouse, composed of cast-iron plates, which was erected at
+Morant, in the West Indies, a style of building in itself by no means
+eligible, and which seems suitable only where stone cannot be easily
+obtained, or conveniently applied. Both those plans (except in so far
+as the screw is concerned, which is indeed the distinguishing feature
+of Mr MITCHELL’S ingenious plan) are to be found in one of my Father’s
+designs for the Bell Rock Lighthouse (see his Account, at Plate VII.,
+figs. 2, 3, 4, and 5, and pp. 499, 500). Dr POTTS has also invented a
+method of driving piles by means of atmospheric pressure, which has
+been used at the South Galliper Beacon, on the Goodwin Sands.
+
+  ~Early modes of Illumination.~
+
+Having thus hastily described the most interesting and celebrated
+Lighthouses, I proceed to the proper object of these Notes, which are
+chiefly intended to make known the various methods now in use for the
+illumination of Lighthouses. There can be little doubt, that down
+to a very late period, the only mode of illumination adopted in the
+Lighthouses, even of the most civilized nations of Europe, was the
+combustion of wood or coal in _chauffers_, on the tops of high towers
+or hills. It consists with the personal knowledge of many persons now
+living, that the Isle of May Light, in the Frith of Forth, previous to
+its being assumed by the Commissioners of the Northern Lights in 1786,
+was of that kind; and, even in England, the art of illumination had
+made so little progress, that the magnificent Tower of the Eddystone,
+for about forty years after it came from the hands of SMEATON, could
+boast of no better Light than that derived from a few miserable
+tallow candles. Such methods were most imperfect, not only in point of
+efficiency and power, but also as respects the distinction of one light
+from another, an object which, on a difficult and rugged coast, may be
+considered as of almost equal importance with the distance at which the
+Light can be seen.
+
+  ~Flame.~
+
+Solid substances which remain so throughout their combustion, are
+only luminous at their own surface, and exhibit phenomena, such as
+the dull red heat of iron, or of most kinds of pit-coal, and are
+therefore more suited for the purpose of producing heat than light.
+But by using substances which are formed into inflammable vapours,
+at a temperature below that which is required for the ignition of
+the substances themselves, gas is obtained and _flame_ is produced.
+Much light is thus evolved at a comparatively low temperature. The
+gas necessarily rises _above_ the combustible substance from which it
+is evolved, owing to its being formed at a temperature considerably
+higher than that of the surrounding air, than which it is necessarily
+rarer. Of this description are the flames obtained by the burning of
+the various oils, which are generally employed in the illumination of
+lighthouses. In the combustion of oil, wicks of some fibrous substance,
+such as cotton, are used, into which the oil ascends by capillary
+action, and being supplied in very thin films, is easily volatilized
+into vapour or gas by the heat of the burning wick. The gas of pit-coal
+has been occasionally used in lighthouses; it is conveyed in tubes to
+the burners, in the same manner as when employed for domestic purposes.
+There are certain advantages, more especially in dioptric lights,
+where there is only one large central flame, which would render the
+use of gas desirable. The form of the flame, which is an object of
+considerable importance, would thus be rendered less variable, and
+could be more easily regulated, and the inconvenience of the clock-work
+of the lamp would be wholly avoided. But it is obvious, that gas is
+by no means suitable for the majority of lighthouses, their distant
+situation and generally difficult access rendering the transport
+of large quantities of coal expensive and uncertain; whilst in many
+of them there is no means of erecting the apparatus necessary for
+manufacturing gas. There are other considerations which must induce us
+to pause before adopting gas as the fuel of lighthouses; for, however
+much the risk of accident may be diminished in the present day, it
+still forms a question, which ought not to be hastily decided, how
+far we should be justified in running even the most remote risk of
+explosion in establishments such as lighthouses, whose sudden failure
+might involve consequences of the most fatal description, and whose
+situation is often such, that their re-establishment must be a work of
+great expense and time. Gas is, besides, far from being suitable in
+catoptric lights, to which, in many cases (especially when the frame is
+moveable, as in revolving lights), it could not be easily applied. The
+oil most generally employed in the Lighthouses of England is the sperm
+oil of commerce, which is obtained from the South Sea whale (_Physeter
+macrocephalus_). In France, the colza oil, which is expressed from the
+seed of a species of wild cabbage (_Brassica oleracea colza_), and the
+olive oil are chiefly used; and a species of the former has lately
+been successfully introduced into the Lighthouses of Great Britain.
+Of all these oils, the purified sperm oil has hitherto been generally
+considered the most advantageous for lighthouse purposes; but there is
+every reason for anticipating that the late adoption of the colza oil
+in many of the British Lights, on the suggestion of Mr JOSEPH HUME,
+M.P., while chairman of a select committee of the House of Commons
+on Lighthouses, will lead to an important saving, as its combustion
+produces an equal quantity of light at somewhat more than one-half of
+the expense for spermaceti oil. Careful trials have been made of this
+oil; and on the 10th of March 1847, I was enabled to report the results
+to the Commissioners of Northern Lighthouses in the following terms:
+
+“1. The colza oil possesses the advantage of remaining fluid at
+temperatures which thicken the spermaceti oil so that it requires the
+application of the frost lamp.
+
+“2. It appears, from pretty careful photometrical measurements of
+various kinds, that the light derived from the colza oil is, in point
+of intensity, a little superior to that derived from the spermaceti
+oil, being in the ratio of 1·056 to 1.
+
+“3. The colza oil burns both in the Fresnel lamp and the single Argand
+burner with a thick wick during seventeen hours without requiring
+any coaling of the wick or any adjustment of the damper; and the
+flame seems to be more steady and free from flickering than that from
+spermaceti oil.
+
+“4. There seems (most probably owing to the greater steadiness of the
+flame) to be less breakage of glass chimneys with the colza than with
+the spermaceti oil.
+
+“5. The consumption of oil, in so far as that can be ascertained
+during so short a period of trial, seems in the Fresnel lamp to be 121
+for colza, and 114 for spermaceti; while in the common Argand, the
+consumption appears to be 910 for colza, and 902 for spermaceti.
+
+“6. If we assume the means of these numbers, 515 for colza, and 508 for
+spermaceti, as representing the relative expenditure of these oils, and
+if the price of colza be 3s. 9d., while that of spermaceti is 6s. 9d.
+per imperial gallon, we shall have a saving in the ratio of 1 to 1·755,
+which, at the present rate of supply for the Northern Lights, would
+give a saving of about L.3266 per annum.
+
+“Of these conclusions, the three last may be considered as more or less
+conjectural, being founded on data derived from too short a trial;
+but the striking agreement of the results obtained at the six lights
+in which the experiments were made, tends in some measure to supply
+the place of a longer period of trial; and I have no hesitation,
+therefore, in recommending the Board at once to introduce the use of
+the colza oil into all the dioptric lights, except that of Skerryvore,
+where some special reasons induce me to defer the change for another
+season. In the catoptric lights, the only reason for not making an
+equally extensive trial is the necessity for renewing all the burners,
+which require to be so constructed as to receive thick wicks of brown
+cotton; and it may perhaps be considered prudent to proceed with
+some caution in changing the apparatus, so as to suit it for burning
+a patent oil, the circumstances attending the regular and extensive
+supply of which are not yet fully known. I may remark, that I have
+burnt the colza oil in the solar lamp alluded to in my last report; but
+I disapprove of it as tending to elongate the flame vertically, and
+thus to decrease its horizontal volume. The elongated form of flame
+increases the divergence vertically where the light is lost, and so far
+circumscribes its horizontal range where it is most required. I have
+therefore substituted the thick wick burner for the solar lamp, whereby
+an equally complete combustion is obtained, and the proper form of the
+flame is at the same time preserved.”[36]
+
+  [36] Since the above report was written, the price of colza oil has
+  risen; and other circumstances have occurred to justify the caution
+  as to the universal adoption of that oil.
+
+       *       *       *       *       *
+
+  ~Drummond and Voltaic Lights.~
+
+The application of the Drummond and Voltaic lights[37] to lighthouse
+purposes is, owing to their prodigious intensity, a very desirable
+consummation; but it is surrounded by so many practical difficulties
+that, in the present state of our knowledge, it may safely be
+pronounced unattainable. The uncertainty which attends the exhibition
+of both these lights, is of itself a sufficient reason for coming to
+this conclusion. But other reasons unhappily are not wanting. The
+smallness of the flame renders them wholly inapplicable to dioptric
+instruments, which require a great body of flame in order to produce a
+degree of divergence sufficient to render the duration of the flash in
+revolving lights long enough to answer the purpose of the mariner. M.
+FRESNEL made some experiments on the application of the Drummond light
+to dioptric instruments, which completely demonstrate their unfitness
+for this combination. He found that the light obtained by placing
+it in the focus of a great annular lens was much more intense than
+that produced by the great lamp and lens; but the divergence did not
+exceed 30′; so that, in a revolution like that of the Corduan Light,
+the flashes would last only 1¹⁄₃ second, and would not, therefore, be
+seen in such a manner as to suit the practical purposes of a revolving
+light. The great cylindric refractor used in fixed lights of the first
+order, was also tried with the Drummond light in its focus; but it
+gave coloured spectra at the top and bottom, and only a small bar of
+white light was transmitted from the centre of the instrument. The
+same deficiency of divergence completely unfits the combination of the
+Drummond light with the reflector for the purposes of a fixed light,
+and even if this cause did not operate against its application in
+revolving lights on the catoptric plan, the supply of the gases, which
+is attended with almost insurmountable difficulties, would, in any
+case, render the maintenance of the light precarious and uncertain in
+the last degree.
+
+  [37] The Drummond light is produced by the ignition or combustion of
+  a ball of lime (³⁄₈ inch diameter) in the united flames of hydrogen
+  and oxygen gases, and is equal to about 264 flames of an ordinary
+  Argand Lamp with the best Spermaceti oil. It derives its name from
+  the late LIEUT. DRUMMOND, R. E., who first applied it in the focus of
+  a paraboloïd for geodetical purposes, and afterwards proposed it for
+  Lighthouses. (See his Account of the Light in the Phil. Trans. for
+  1826, p. 324, and for 1830, p. 383.) The Voltaic light is obtained
+  by passing a stream of Voltaic electricity from a powerful battery
+  between two _charcoal points_, the distance between which requires
+  great nicety of adjustment, and is the chief circumstance which
+  influences the stability and the permanency of the light. The Voltaic
+  light greatly exceeds the Drummond light in intensity, as ascertained
+  by actual comparison of their effects; but the ratio of their power
+  has not been accurately determined. It was first exhibited in the
+  focus of a reflector by Mr JAMES GARDNER, formerly engaged in the
+  Ordnance Survey of Great Britain.
+
+  ~Mr Gurney’s Lamp.~
+
+In 1835, Mr GURNEY proposed the combination of a current of oxygen with
+the flame of oil, in order to obtain a powerful light of sufficient
+size to produce the divergence required for the illumination of
+lighthouses. The Trinity-House of London entertained the proposal,
+and made some experiments on this important subject; but the plan was
+finally rejected as disadvantageous in practice.
+
+  ~Argand Burners.~
+
+Until the invention by ARGAND (about the year 1784), of the lamp with a
+double current of air, the art of illumination seems to have received
+no improvement, and to have occupied very little attention from the
+time of CARDAN, or at all events of Dr HOOK, who, about the year 1677,
+in a monograph entitled “Lampas,” made some important observations on
+the constitution of _flame_, so as to make one wonder that he should
+have stopped short of the discoveries of later inventors. Before
+ARGAND’S time, every wick consisted of a solid cord, whose flame was
+fed only by the current of air on its outside; and the consequence of
+this arrangement is, that the stream of vapour or smoke, especially
+from the centre of thick wicks, escapes unburnt, because, before it
+reaches the height at which the combustion of the central stream
+can take place, its temperature has become too low to admit of its
+ignition.[38] The chief improvements which had been made, consisted
+in varying the level of the oil in the cistern, or in attempts to
+render that level constant, by mechanical means, and in lessening the
+thickness of the wick, by spreading its substance into a flat form,
+thus reducing the stream of gas which escapes from the centre of a
+thick cylindric wick without being burnt, and thereby causing a more
+complete combustion, and producing less smoke and a whiter flame. To
+ARGAND belongs the great merit of having first formed the wick into a
+hollow cylinder, thus supplying the flame with two currents of air, one
+of which, as in the case of the solid wick, envelopes the flame, and
+the other, passing through the centre of the wick, is enveloped by the
+flame itself. He also added a chimney, which served to defend the flame
+from irregular draughts of air, and to regulate the proportion between
+the velocities of the currents of air and the stream of gas. This was
+indeed a most important step in the art of illumination, and causes
+the great difference between the incomplete combustion, which, owing
+chiefly, as we have seen, to a defect in the supply of air, always
+takes place with a solid wick (from which much unburnt gas escapes in
+the form of smoke), and that more perfect combustion in which passage
+is given for a free current of air through the centre of the wick. The
+invention of ARGAND came nearly perfect from his hands; and but a few
+slight modifications of his original arrangement have been introduced.
+The Argand burner consists of two concentric tubes or cylinders,
+separated by a small annular space, which is shut at the bottom, and
+communicates by a pipe with the oil fountain, whose level ought to
+be a little _below_ the level of the upper edge of the cylinders. In
+this annular space, partly filled with oil from the fountain, stands
+a cylindric wick of cotton, loosely wove, into which the oil rises
+freely by capillary action. The wick has its lower edge fixed to a
+metallic ferule or ring, called a wickholder, which (by means of a
+peculiar arrangement, to be afterwards described) gives the power of
+raising or depressing the wick to any convenient level with regard to
+the burner. A cylinder of glass, of greater diameter than the burner,
+rests on a gallery or ring which hangs from the burner and surrounds
+it. This glass cylinder, or chimney as it is generally called, should
+stand vertically with its axis coincident with that of the burner
+itself. The effect of this arrangement is obvious, and has already
+in part been indicated. The flame is thus necessarily bounded on all
+sides by two conical concentric surfaces, one external and concave, and
+the other internal and convex, both of which receive a free current
+of air. The flame is therefore very thin in every direction; and, as
+a consequence of the mutual radiation of its different parts on each
+other, it is throughout its entire surface of more equal temperature
+than can ever be attained in the thick solid wick or the narrow flat
+one. The glass cylinder also increases the force of the two currents
+which pass outside and inside of the flame; and the union of so many
+favourable circumstances produces a greater amount of pure light than
+has yet been obtained by any other method. The contraction of the glass
+chimney (known by the technical name of the _shoulder_) at a point a
+little above the level of the wick, tends to direct the current of air
+inwards on the flame, thereby causing a more perfect combustion and the
+evolution of more light.
+
+  [38] That the form of a flame is necessarily conoidal, and that
+  its height is determined by the relation subsisting between its
+  diameter and the continually varying velocities of the currents
+  of gas and air, may be easily shewn; and the combustion of each
+  annular film of the stream of gas from the wick can take place only
+  at a level determined by, and continually varying with, the ratio
+  of the velocities of the streams of gas and air. I am unwilling to
+  offer this explanation in my own words, when those of M. Peclet,
+  in his excellent work, Traité de l’Eclairage, are at hand,--“Let
+  us conceive,” says he, “a very thin film or layer of inflammable
+  gas placed horizontally, and which rises into the air parallel to
+  itself, with a uniform motion. We shall suppose that it cannot be
+  burnt, except at its circumference, and that the top and bottom of
+  the film are, by some means, preserved from combustion (they are so
+  preserved in ordinary flames, by the films which precede and follow
+  them). If the circumference is at a high enough temperature it will
+  burn; at each instant the film or layer of air, which has assisted
+  the combustion and also the products of that combustion, being very
+  hot, will rise very rapidly, and will make room for other layers or
+  films of air, which will rise in their turn; and as the diameter
+  of the film of gas is continually diminishing, it is obvious that
+  its combustion will offer the appearance of a series of circles
+  continually growing smaller, and terminating at length in a point.
+  If we trace in thought the series of circles which the combustion
+  has successively developed, we shall form a cone whose length will
+  depend on the ratio of the velocities of the films of gas and of
+  air which escape after combustion. If, for example, the velocity
+  of the current of air were very great, compared to the velocity of
+  the cylinder of gas, the entire combustion would take place, while
+  the film of gas passes over a very small space; and the cone formed
+  by the succession of luminous circles would, consequently, be very
+  short. If, on the contrary, there were but a very small difference
+  between these velocities, the luminous circles would only appear
+  at considerable intervals from each other; for the air which had
+  served for combustion, being unable to feed it longer, the surface
+  of the cylinder could not become luminous until the difference of
+  velocity had freed it from the air which had served for the preceding
+  combustion. If, then, we imagine a set of similar films succeeding
+  each other, each of them would give rise to the same series of
+  coloured rings; and as there would be a film in each section of the
+  cone in a state of combustion at the same instant of time, the cone
+  would, of course, appear luminous throughout its height.”--Peclet,
+  _Traité de l’Eclairage_, p. 51.
+
+Great as the improvement of ARGAND undoubtedly was, the value of the
+lamp alone as a means for the illumination of lighthouses must be
+regarded as comparatively small. The primary object of a lighthouse
+is to give early notice to the mariner of his approach to the coast,
+and it is therefore necessary that the light be of such a kind that it
+may be seen at a great distance. Every one is practically acquainted
+with the fact that the rays proceed in all directions from a luminous
+body in straight lines; and if we could obtain a ball equally luminous
+in every part of its surface, it would give an equal share of light
+to every part of the inner surface of a hollow sphere, whose centre
+coincided with the centre of the ball. Again, if an opaque body were
+placed between the luminous ball and the hollow sphere, the part
+opposite that body would be deprived of the light by the interception
+of the rays, and no light would emerge from a hole bored in that
+part of the surface of the hollow sphere. The bearing of these facts
+is obvious; and no one can fail to perceive that in the case of a
+lighthouse illuminated by a single unassisted burner, a seaman could
+only receive the benefit of that small portion of light which emerges
+from the lamp in a line joining his eye and the centre of the flame.
+The other rays would be occupied partly in making the light visible
+in other parts of the horizon, and but a very small portion of them
+would be usefully employed for that purpose, while all the rest would
+be lost by escaping upwards into the sky, or downwards below the plane
+in which seamen can see a lighthouse. This state of matters would be
+little improved by increasing the number of burners, as the effective
+part of the light would only be augmented by the addition of an equally
+trifling portion of light from each burner. The small pencils of rays
+thus meeting at the eye of a distant observer, would form a very minute
+fraction of the whole quantity of light uselessly escaping above and
+below the horizon, and also at the back of each flame; and the wasteful
+expenditure of light would be enormous. By such a method no practically
+efficient sea-light could ever be obtained.
+
+
+CATOPTRIC[39] SYSTEM OF LIGHTS.
+
+  [39] From the Greek κατοπτρον, a _mirror_; a compound of κατα,
+  _opposite to_, and ὂπτομαι, _I see_.
+
+For those defects a simple remedy is found in the well known power
+possessed by most bodies, of _reflecting_ or throwing back from them
+the light which falls upon them. This property is not possessed by all
+reflecting bodies in an equal degree, some absorbing more and some
+less of the incident light. Perhaps the earliest attempts to apply
+this property as a corrective for the direction of the rays from a
+Lighthouse, would be confined to placing plane mirrors behind each
+lamp; yet this would prove but a partial remedy, as it would still
+leave the greater part of the light to stray above and below the proper
+direction. Hollow mirrors of a spherical form might next be tried;
+and if properly placed with reference to the flame, would constitute
+a very great improvement in lighthouse illumination. But those steps
+in the march of improvement are more imaginary than real; and I am
+not aware of any well authenticated records of such gradual attempts
+having preceded the adoption of the right mode of applying reflection
+as a means of rectifying the direction of the rays emerging from a
+lighthouse. There is, on the contrary, distinct evidence that the
+impulse given by ARGAND’S invention, led to an immediate adoption of
+the most perfect form of reflecting instruments.
+
+  ~Application of Paraboloïdal Mirrors into Lighthouses.~
+
+The name of the inventor of paraboloïdal mirrors and the date of their
+first application to Lighthouses, have not been accurately ascertained.
+The earliest notice which I have been able to find, is that by Mr
+WILLIAM HUTCHINSON, the pious and intelligent author of a quarto volume
+on “Practical Seamanship” (published at Liverpool in 1791), who notices
+(at p. 93) the erection of the four lights at Bidstone and Hoylake, in
+the year 1763, and describes large parabolic moulds, fashioned of wood
+and lined with mirror-glass, and smaller ones of polished tin-plate, as
+in use in those Lighthouses. Mr HUTCHINSON seems to have understood the
+nature, properties, and defects of the instruments which he describes,
+and has shewn a good acquaintance with many of the most important
+circumstances to be attended to in the illumination of Lighthouses.
+Many claims to inventions rest on more slender grounds than might be
+found in Mr HUTCHINSON’S book for concluding him to have first invented
+the paraboloïdal mirror and applied it to use in a Lighthouse;[40]
+but, in the absence of any statement as to the date when the mirrors
+were really adopted, the merit of the improvement must, in justice, be
+awarded to others.
+
+  [40] Mr HUTCHINSON seems also (“Practical Seamanship,” p. 198) to
+  have tried speculum metal as a material for Lighthouse reflectors.
+
+M. TEULERE, a member of the Royal Corps of Engineers of Bridges and
+Roads in France, is, by some, considered the first who hinted at the
+advantages of paraboloïdal reflectors; and he is said, in a memoir
+dated the 26th June 1783, to have proposed their combination with
+Argand lamps, ranged on a revolving frame, for the Corduan Lighthouse.
+Whatever foundation there may be for the claim of M. TEULERE, certain
+it is that this plan was actually carried into effect at Corduan, under
+the directions of the CHEVALIER BORDA; and to him is generally awarded
+the merit of having conceived the idea of applying paraboloïdal mirrors
+to lighthouses. These were most important steps in the improvement
+of lighthouses, as not only the power of the lights was thus greatly
+increased, but the introduction of a revolving frame proved a valuable
+source of differences in the appearance of lights, and, in this way,
+has since been the means of greatly extending their utility. The exact
+date of the change on the light of the Corduan is not known; but as it
+was made by LENOIR, the same young artist to whom BORDA, about the year
+1780, entrusted the construction of his reflecting circle, it has been
+conjectured by some that the improvement of the light was made about
+the same time. The reflectors were formed of sheet-copper, plated with
+silver, and had a double ordinate of 31 French inches. It was not long
+before these improvements were adopted in England, by the Trinity-House
+of London, who sent a deputation to France to inquire into their
+nature. In Scotland, one of the first acts of the Northern Lights Board
+in 1786, was to substitute reflectors in the room of the coal-light
+then in use at the Isle of May in the Frith of Forth, which, along with
+the light on the Cumbrae Isle in the Frith of Clyde, had, till that
+period, been the only beacons on the Scotch coast. The first reflectors
+employed in Scotland were formed of _facets_ of mirror glass, placed in
+hollow paraboloïdal moulds of plaster, according to the designs of the
+late Mr THOMAS SMITH, the Engineer of the Board, who (as appears from
+the article _Reflector_, in the Supplement to the third edition of the
+Encyclopædia Britannica) was not aware of what had been done in France,
+and had himself conceived the idea of this combination. The same system
+was also adopted in Ireland; and in time, variously modified, it became
+general wherever lighthouses are known.
+
+  ~Reflection.~
+
+To enable us to enter on the subject of the proper forms of reflectors,
+we must glance very briefly at the _laws of reflection_. Those laws
+are two in number. _1st_, The ray which falls on a reflecting surface,
+called the _incident_ ray, and the ray which leaves the reflector,
+called the _reflected_ ray, are always in one _plane_, which plane is
+perpendicular to the _reflecting surface_. _2d_, The angle which the
+_reflected_ ray makes with the reflector is always equal to the angle
+which the _incident_ ray makes with it, or, in other words, the angle
+of _incidence_ is equal to the angle of _reflection_.[41]
+
+  [41] This will be more readily understood by referring to the
+  accompanying figure (No. 22), in which CDEF is the reflecting
+  surface; GHOKI the plane of reflection perpendicular to that surface;
+  BO a line perpendicular or _normal_ to the surface CDEF; and AO the
+  incident ray. Then if in the plane GHOKI, the angle BOI be made equal
+  to AOB, OA′ is the reflected ray; BOG is then the angle of incidence;
+  and BOI the angle of reflection. GOH and IOK, which are the
+  complements of those angles, are, indeed, more strictly speaking, the
+  angles of incidence and reflection; but in cases where the reflecting
+  surface is curved, it is more convenient to refer the angles to the
+  normal BO.
+
+  [Illustration: Fig. 22.]
+
+It would lead to prolixity altogether superfluous in this place,
+to explain, in a rigorous manner, the effects produced by various
+reflecting surfaces on the direction of the rays incident on them; as
+any one who comprehends the laws of reflection just enumerated, may
+easily satisfy himself of the following truths: _1st_, That a plane
+mirror makes no change on the divergence of the rays, but merely causes
+them to emerge from its surface in the same direction as if they had
+come from a point as much behind the mirror as the luminous body lies
+in front of it. _2d_, A convex reflecting surface increases divergence,
+and disperses the rays in the same manner as if they had come directly
+from a point behind it, whose distance from the mirror increases with
+the distance of the luminous body from its surface, and diminishes
+with the degree of convexity of the mirror. _3d_, A concave surface
+diminishes the divergence of the rays incident upon it from a point
+between the surface and its centre of curvature; the distance of the
+point in which the reflected rays converge diminishing as the distance
+of the radiant point or the concavity of the mirror is increased. It is
+obvious, therefore, that concave mirrors are those which are required
+to produce a correction of the path of the rays, so as to apply them to
+most advantage in a lighthouse, the object to be attained being that
+of throwing the greatest amount of light towards given points in the
+horizon, and collecting the divergent rays, which, as we have already
+seen, are scattered above and below it.
+
+To simplify our view of this matter, I shall, in the first place,
+suppose that the object to be attained is to throw the whole rays of a
+single lamp, with an infinitely small flame, to a given mathematical
+point at a moderate distance; and, as this is a case which can hardly
+occur in the practice of Lighthouse illumination, I content myself
+with observing that this object may be attained _approximately_ by
+placing the lamp in front of a spherical mirror at any distance
+greater than half the radius of the curve surface, or _accurately_
+by placing it in one focus of an elliptical mirror; in all those
+cases the rays would meet in the opposite, or, as they are termed,
+_conjugate foci_. Let us next suppose that our object is to illuminate,
+by means of a mathematical point of light, a small circular space on
+the horizon equal in diameter to the mirror employed; this object will
+be rigorously attained only by placing the light in the focus of a
+paraboloïdal reflector. The same object may be approximately attained
+by placing the light in a spherical mirror, at a point _half-way_
+between the centre of curvature and the surface of the mirror, provided
+the surface of the mirror shall subtend only a small angle at the
+centre of curvature. The paraboloïdal mirror, on the contrary, has the
+property of converging to the focus parallel rays falling upon every
+point of its surface, however extended it may be.
+
+  ~Paraboloïdal Mirrors.~
+
+Any one practically acquainted with this subject, must at once
+perceive that the paraboloïdal mirror completely fulfils one great
+object required in a lighthouse; and to render this more obvious to
+the general reader, I shall, for the present, confine my remarks to
+the case of those lighthouses which exhibit to the mariner in every
+part of the horizon, pencils of light at certain intervals of time,
+separated by periods of darkness, reserving the consideration of Lights
+which are continually in sight all round the horizon or over a given
+portion of it, for a subsequent part of these Notes. In doing this,
+I am aware that I may appear to be departing from the strict order
+of investigation, by suddenly introducing the idea of motion; but a
+little consideration will, I think, satisfy the reader that this is,
+in reality, the more convenient mode of treating the subject. Let us
+suppose, then, that our object is to give occasional flashes of light,
+separated by intervals of darkness, to seamen in various azimuths and
+at various distances from a lighthouse. It is obvious that this may
+be most efficiently done by causing concave mirrors, which collect
+the rays from lamps placed in them and thereby increase the light in
+front of the mirror, to revolve round a vertical axis with a velocity
+suited to produce the required number of flashes in a given time. The
+paraboloïdal mirror is best adapted for producing this effect, for
+the following reasons: _1st_, Because it alone produces a rigorous
+parallelism of all rays proceeding from its focus, and falling upon
+any point of its surface, however distant the point of reflection
+from that focus, or however far _in front_ of it. _2d_, Because it
+therefore embraces in its action the greatest number of the whole
+rays coming from the focus, and, _cæteris paribus_, will produce the
+strongest light. _3d_, Because the _theoretical_ object to be attained
+is to make those flashes equally powerful at any distance, an effect
+which would be rigorously fulfilled by placing an infinitely small
+flame in a perfect paraboloïdal mirror. And, _4th_, Because, although
+absolute equality of luminousness at any distance is not attainable,
+and, in practice, is inconsistent with other conditions required in a
+useful light, we still, by using the parabolic mirror, make the nearest
+approach to parallelism of the reflected rays, and consequently obtain
+the strongest light which is consistent with a due regard to a certain
+duration of the flash on the eye of a distant observer, which is
+measured by the angle of the luminous cone projected to the horizon.
+
+Having thus so far anticipated what some might think would more
+naturally have occurred in a subsequent part of these Notes, I return
+to a more detailed consideration of the parabola itself, and its
+product, the paraboloïdal mirror. I content myself, however, with
+describing the parabola, by that property which peculiarly adapts it
+to the purposes of a lighthouse. The parabola, then, is a curve of the
+second order, obtained by cutting a cone in a plane parallel to one
+side, which possesses this remarkable property, _that a line drawn from
+the focus to any point in the curve, makes, with a tangent at that
+point, an angle equal to that which a line parallel to the axis of the
+curve makes with that tangent_.[42]
+
+  [42] See third corollary to Proposition III. of Wallace’s Conic
+  Sections, which shews that a tangent to the parabola makes equal
+  angles with the diameter which passes through the point of contact
+  and a straight line drawn from that point to the focus. The curve
+  may be traced in two different ways, both dependent on the property,
+  _that the distance of any point in the parabola from the focus is
+  equal to its distance from the directrix_.
+
+  To draw the curve mechanically (fig. 23), let F be the focus, MF
+  the focal distance (chosen at pleasure according to rules which I
+  shall afterwards notice), KMX is the axis, and AB the directrix (the
+  dotted line _f_ F _e_, bounded by the curve at either end, would then
+  be the _parameter_ or _latus rectum_). Place the edge of the straight
+  ruler AKHB along the directrix; and let LHB be a square ruler which
+  may slide along the fixed ruler AKHB, so that the edge HL may be
+  constantly perpendicular to AB, or parallel to MX, the axis; let LDF
+  be a string equal in length to HL, and having one end fixed in F, and
+  the other at L, a point in the sliding square. Then if the string be
+  stretched by a pencil D, so as to keep the part DL close to the edge
+  of the square, and if at the same time the square be gently pushed
+  along the line AB, the point D will be forced to move along the
+  edge LH of the square, and will trace out a curve which will be the
+  required parabola. This is obvious from the consideration, that the
+  string LDF being equal in length to LH, and LD being common to both,
+  the remainder DF must be equal to the remainder DH, so that the point
+  which traces the curve being equidistant from the directrix and the
+  focus must, in terms of the above definition, describe a parabola.
+
+  [Illustration: Fig. 23.]
+
+  In the second place, the same property, as already stated, furnishes
+  us with the means of tracing the curve by finding successive points
+  therein. Draw a line _a b_ perpendicular to the axis OX, and the
+  position in this line, of a point _p_ through which the curve passes,
+  is easily found thus: Describe from F the focus as a centre with a
+  radius equal to the perpendicular distance O _d_ of the line _a b_
+  from the directrix AB, a circle cutting the line _a b_ in two points
+  _p_ and _p′_; then both these points are in the curve. By repeating
+  the same process, any number of points in the curve may be obtained.
+
+  [Illustration: Fig. 24.]
+
+  Lastly, from the equation to the curve, the length _y_ of any
+  ordinate may be computed, in terms of _m_ its principal focal
+  distance, and x its abscissa, by the simple expression,--
+
+  _y_ = √(4 _m_ _x_).
+
+It is easy to see, that if this curve revolve about its axis, it will
+generate a parabolic conoid, which we may conceive to be concave or
+convex, as we please. If the surface be concave, we obtain the mirror
+of which we are in search; for every principal section, or that passing
+through the axis of such a mirror, will necessarily possess the same
+properties as that of the plane curve, and will each have a focus
+meeting in one and the same point; the union of all these sections will
+therefore form a mirror capable of reflecting, in a direction parallel
+to the axis and to each other, all the rays of light which fall on its
+surface.
+
+  ~Divergence of Paraboloïdal Mirrors.~
+
+We have already seen that a perfect paraboloïdal mirror, with a
+point of light infinitely small placed in the focus, would project
+a beam equally intense at any distance, every transverse section of
+which would be of the same superficial extent. In practice, these
+conditions can never be rigorously fulfilled. No perfect instrument
+can come from the hands of man, and every mirror must of necessity
+possess many defects. To obtain a true mathematical point of light
+is also impossible; and for the purposes of a lighthouse, it would
+be completely useless, as will appear from the following simple
+considerations. Let us suppose that a true paraboloïdal mirror, having
+a double ordinate or space of two feet, and illuminated by a point
+of light, projects a truly cylindric beam of light to the horizon,
+and that it revolves horizontally round a vertical axis, with such
+a velocity as to cause the beam to pass over the eye of an observer
+stationed at the distance of 100 feet in one second of time, and we
+shall find that another observer, at a distance of 15 miles from the
+mirror, would not see the light at all, although of equal size, because
+its velocity at that distance would be so great as only to be present
+to his eye for ¹⁄₇₉₂d of a second, a space of time far too short to
+make a perceptible impression on the eye of a distant observer. This
+is no mere hypothesis unsupported by facts; for I shall have occasion,
+in another part of these Notes, to describe certain experiments, by
+which it was ascertained that a beam of light emerging from a lens, and
+passing over the eye of an observer at 14 miles distance, in a space of
+time equal to ¹⁄₁₆₆th of a second, became altogether invisible at that
+distance.
+
+For this evil, happily a very simple and efficient remedy may be
+found in what may be said to constitute a _theoretical_ defect in
+the combination of the Argand burner with the reflector. The burner,
+instead of being a mathematical point, has generally a diameter of
+about one inch, and a ray proceeding from the edge of the flame to
+any point on the surface of the mirror, makes with the line joining
+that point and the principal focus an angle which, being repeated by
+reflection, gives the effective divergence of _each_ side of the mirror
+at that point.[43]
+
+  [43] This is easily understood by reference to the accompanying
+  figure (No. 25.), in which AOB is a central section of a paraboloïdal
+  mirror.
+
+  [Illustration: Fig. 25.]
+
+  PF = distance from the focus F to a point in the curve P, and PG a
+  tangent drawn from P to the surface of the flame at G;
+
+  FG = radius of the wick or flame;
+
+  and GPF = G′PF′ = divergence of one side of mirror, and consequently
+  2 GPF = the whole effective divergence of the mirror at that cross
+  section.
+
+                GF
+  Now sin GPF = --
+                PF
+
+  or the sine of the divergence from each point
+
+                 Radius of flame.
+  = -------------------------------------------
+    Distance from focus to point of reflection.
+
+  [Illustration: Fig. 26.]
+
+  It is obvious that this quantity which varies _inversely_ with the
+  distance of the reflecting surface from the focus, is greatest
+  at the vertex of the curve, and least at the sides or edges of
+  the paraboloïd. The most useful part of the light, or that which
+  conduces to the strongest part of the flash in a revolving light,
+  is that which is derived from the cone of rays which is bounded by
+  the limits of this _minimum_ divergence; for the faint light which
+  first reaches the eye of a distant observer, in the revolution of a
+  reflector, is not that which is reflected by the sides or edges, as
+  might at first be supposed, but proceeds from the centre. The light,
+  in fact, gradually increases in power in proportion as additional
+  rays of reflected light are brought to bear on the observer’s eye,
+  until, last of all, the extreme edge of the mirror adds its effect.
+  The light continues in its best state until the opposite limit of
+  minimum divergence has been reached, when it begins gradually to
+  decline, receding from the margin of the mirror towards the centre,
+  and, having at length reached the limit of its maximum divergence,
+  it finally disappears at the centre. The increase and decline of the
+  power of a mirror in the course of its movement round the circle of
+  the lantern, as seen by a distant observer, will, therefore, in all
+  its different states, be measured by the areas of a series of circles
+  described from its focus, with radii equal to the distance of the
+  focus from the point of the mirror which reflects to the observer’s
+  eye the extreme ray which can reach him in any given position of
+  the mirror. This will be more easily understood by referring to the
+  accompanying diagram, Fig. 26, in which _e a e′_ is the principal
+  section of a paraboloïdal mirror, F its focus, αFA its axis, and FK
+  the radius of the flame. If the reflector revolve round a vertical
+  axis at O, an observer placed in front of it (at a distance so great
+  that the subtense of the mirror’s width would be small enough to
+  allow us safely to consider the lines drawn from _e_ and _e′_ to
+  his eye as parallel), would receive the first ray of light in the
+  direction _a_ D, as reflected at _a_, from a single point on the
+  edge of the flame (where a tangent to the flame would pass through
+  _a_); and conversely he would lose the last ray at D′, as reflected
+  at _a_, from a single point on the opposite margin of the flame; and
+  hence, as above, the greatest divergence is measured by the angle
+  which the flame subtends at the vertex a of the mirror, being the
+  sum of the angles _α_ and _α′_. We shall next suppose the mirror to
+  move a little, so that the observer may receive at G a ray of light
+  from some other point in the flame which is reflected at _b_; while
+  another ray from an opposite point reflected at _b′_ would be seen
+  in the parallel direction _b′_ G′, thus indicating the boundary of
+  a circular portion of the mirror _b a b′_, the whole of which would
+  reflect light to the distant observer’s eye. Again, let us suppose
+  a ray to come from another part of the flame, and be reflected at
+  the mirror’s edge _e_ into the direction _e_ H, and another from
+  the opposite side of the flame to be reflected at its opposite edge
+  _e′_, into the direction _e′_ G″, and we obtain the full effect of
+  the whole reflecting surface, which will continue unabated until
+  the mirror in the course of its revolution shall reflect at _e′_ to
+  the observer’s eye, a ray from a point in the margin of the flame
+  (through which a tangent drawn from _e′_ to the flame would pass)
+  in such a direction, that the angle which it makes with the axis of
+  the mirror is equal to that subtended by the radius of the flame at
+  the distance F _e_ or F _e′_. After this the light would recede from
+  the edges of the mirror in the same gradual manner, until it should
+  vanish in the direction _a_ D′, which is the opposite limit of the
+  extreme divergence of the instrument. In the above explanation, I
+  have confined myself simply to the effects of the outer ring of the
+  flame, which is the source of divergence; but I need not remind the
+  reader that every portion of the flame radiates light, which, being
+  reflected, conduces to the effect. Some rays also are passing from
+  the opposite sides of the flame through the true focus, so as to be
+  normally reflected in lines parallel to its axis. The solid lines
+  in the diagram shew the theoretical reflection of rays proceeding
+  from F to _b_, _b′_, _e_, _e′_, where they are diverted into the
+  directions _b_ B, _b′_ B′, _e_ E, and _e′_ E′; and by contrast with
+  the dotted lines, serve to render more perceptible the path of the
+  divergent rays which come from the edge of the flame. The Greek
+  letters indicate the angles of divergence, and point out their
+  relations to each other on either side of the mirror. The arcs of
+  greatest and least divergence are marked in the diagram. This subject
+  will be found treated less directly, but, certainly, more concisely
+  and neatly, by Mr W. H. BARLOW, in a paper on the Illumination of
+  Lighthouses in the London Transactions for 1837, p. 218.
+
+It is still more obvious that a perfect paraboloïdal figure, and a
+luminous _point_ mathematically true, would render the illumination
+of the whole horizon by means of a fixed light _impossible_; and it
+is only from the divergence caused by the size of the flame which
+is substituted for the _point_, that we are enabled to render even
+revolving lights practically useful. But for this aberration, the
+slowest revolution in a revolving light would be inconsistent with a
+continued observable series, such as the practical seamen could follow,
+and would, as we have seen, render the flashes of a revolving light too
+transient for any useful purpose; whilst fixed lights, being visible
+in the azimuths only in which the mirrors are placed, would, over the
+greater part of the distant horizon, be altogether invisible. The size
+of the flame, therefore, which is placed in the focus of a paraboloïdal
+mirror, when taken in connexion with the form of the mirror itself,
+leads to those important modifications in the paths of the rays and the
+form of the resultant beam of light, which have rendered the catoptric
+system of lights so great a benefit to the benighted seamen.
+
+In order to obtain a mirror capable of producing a given divergence of
+the reflected beam, therefore, we must proportion its focal distance to
+the diameter of the flame in such a manner, that the sine of _one-half_
+of the whole effective divergence of the mirror, may be equal to the
+_quotient of the radius of the flame, divided by the distance of a
+given point on the surface of the mirror from the focus_. The best
+proportions for paraboloïdal mirrors depend on the objects which they
+are meant to attain. Those which are intended to give great divergence
+to the resultant beams, as in fixed lights, capable of illuminating
+the whole horizon at one time, should have a short focal distance;
+while those mirrors which are designed to produce a nearer approach to
+parallelism (as in the case of revolving lights which illuminate but a
+few degrees of the horizon at any one instant of time), will have the
+opposite form. Those two objects may, no doubt, be attained with the
+same mirror, by increasing or diminishing the size of the burner; but
+that is by no means desirable, as any change on the size of a burner,
+which is found to be the best in other respects, must be considered as
+to some extent disadvantageous.
+
+What I have stated above as to the use of mirrors with a short focal
+distance for lights of great divergence, proceeds on the assumption,
+that the penumbral portion of the light on each side of the strongest
+beam (which is confined within the limits of the least divergence, due
+to that portion of the mirror where the focal distance is the greatest)
+is to be pressed into service in the illumination of the horizon;
+and it is the chief inconvenience which attends the application of
+paraboloïdal mirrors to fixed lights, that because it is impracticable
+to apply a number of mirrors sufficient to light the whole horizon with
+an equally strong light, spaces occur on either side of each reflector
+in which the mariner has a light sensibly inferior to that which
+illuminates the sector near the axis of each mirror. This will be best
+explained by stating the numerical results of the computations of the
+divergence of the mirrors used in the Northern Lights for this purpose,
+both at the vertex and the sides. In a mirror whose focal distance is
+4 inches, and its greatest double ordinate 21 inches, illuminated by
+a flame 1 inch in diameter, we find by computation, that the greatest
+divergence is 14° 22′, and that the strongest arc of light is only 5°
+16′; a difference so great, that while the one may admit of the horizon
+being imperfectly illuminated by means of 26 reflectors, the superior
+light which would result from confining the duty of each instrument
+within the range of its best effect, could only be obtained by the
+use of 68 reflectors, and the expenditure of a proportionately great
+quantity of oil, not to speak of the great practical difficulty which
+would attend the arrangement of so many lamps in a lantern of moderate
+size. In revolving lights, the mirrors are not, as in fixed lights,
+inconveniently taxed for horizontal divergence, because each portion of
+the divergent beam visits successively each point of the horizon. In
+this view of the merits of _fixed_ and _revolving_ lights, I should be
+disposed to recommend, in any new organisation of lights with parabolic
+reflectors, the adoption, in fixed lights, of reflectors with a short
+focal distance and small span, so as to admit of many being ranged
+around the frame; while in revolving lights, it would be my aim to
+approach the largest size of reflector that could be made, so as if
+possible to illuminate each face of the revolving frame by means of a
+large lamp in a single mirror, with a great focal distance, thereby
+diminishing the difference between the divergence of the powerful cone
+of rays reflected from the more distant parts of the mirror and that of
+the feebler and more diffuse light from its apex.
+
+  ~Effect of Paraboloïdal mirrors.~
+
+The maximum luminous effect of the reflectors ordinarily employed in
+fixed lights, as determined by observation, is generally equal to
+about 350 times the effect of the unassisted flame which is placed in
+the focus; while for those employed in revolving lights, which are of
+larger size, it is valued at 450. This estimate, however, is strictly
+applicable only at the distances at which the observations have been
+made, as the proportional value of the reflected beam must necessarily
+vary with the distance of the observer, agreeably to some law dependent
+upon the unequal distribution of the light in the illuminous cone
+which proceeds from it. The effect also varies very much in particular
+instruments. The ordinary burners used in lighthouses are one inch
+in diameter, and the focal distance generally adopted is 4 inches,
+so that the extreme divergence of the mirror in the horizontal plane
+may be estimated at about 14° 22′; while the divergence of the most
+luminous cone is 5° 16′ for the small reflectors, and 4° 25′ for the
+larger size. In arranging reflectors on the frame of a fixed light,
+however, it is advisable to calculate upon a less amount of effective
+divergence, for beyond 11° the light is very feeble; but the difficulty
+of placing many mirrors on one frame, and the great expense of oil
+required for so many lamps, have generally led to the adoption of the
+first valuation of the _effective_ divergence.
+
+  ~Power of Paraboloïdal Mirrors.~
+
+The measure of the illuminating power of a paraboloïdal mirror may be
+estimated as the _quotient of the_ SURFACE _of the circle which cuts it
+in the plane of its greatest double ordinate, divided by the surface of
+the largest vertical section of the flame, and diminished by the loss
+of light in the process of reflection_. This estimate will be found
+near enough for all practical purposes; but it is obviously inaccurate,
+inasmuch as it overlooks the circumstance of the focal distance of each
+portion of the mirror being different, and the consequent increase in
+the length of the various trajectories at each point of the surface
+as you recede from the axis; and the only correct rule, therefore,
+is, to find an imaginary focal distance which must be the radius of a
+spherical segment which shall answer the double condition of having
+its surface equal to that of the greatest cross section of the mirror,
+and of including, at the same time, a number of degrees equal to those
+which are brought under the influence of the reflecting action of the
+paraboloïd. This subject, however, as I have already hinted, is not
+of great practical importance; and I shall not therefore dilate on it
+farther, but content myself with saying, that such a line will be found
+to be a _mean proportional_ between the _greatest_ and _least_ focal
+distances of the mirror.[44] The large mirrors used in the Northern
+Lights have about ¹²⁄₁₇ths of the whole light of the lamp incident on
+their surface; the rest escapes in the comparatively useless state of
+naturally radiating light.
+
+  [44] This subject is treated in detail in M. BARLOW’S Paper already
+  noticed. (London Transactions for 1837, p. 212.)
+
+  ~Manufacture of Reflectors.~
+
+The reflectors used in the best lighthouses, are made of sheet-copper
+plated in the proportion of six ounces of silver to sixteen ounces
+of copper. They are moulded to the paraboloïdal form, by a delicate
+and laborious process of beating with mallets and hammers of various
+forms and materials, and are frequently tested during the operation
+by the application of a mould carefully formed. After being brought
+to the curve, they are stiffened round the edge by means of a strong
+bizzle, and a strap of brass which is attached to it for the purpose of
+preventing any accidental alteration of the figure of the reflector.
+Polishing powders are then applied, and the instrument receives its
+last finish. The details of this manufacture are given in the Appendix.
+
+  ~Testing of Mirrors.~
+
+Two gauges of brass are employed to test the form of the reflector.
+One is for the back, and is used by the workmen during the process of
+hammering, and the other is applied to the concave face as a test,
+while the mirror is receiving its final polish. It is then tested, by
+trying a burner in the focus, and measuring the intensity of the light
+at various points of the reflected conical beam. Another test may also
+be applied successively to various points in the surface, by masking
+the rest of the mirror; but as it proceeds upon the assumption that the
+surface of the reflector is perfect, and that we can measure accurately
+the distance from a radiant coincident with the focus to the point of
+the mirror to be tried, it is in practice almost useless. For such a
+trial we must place a screen in the line of the axis of the mirror
+at some given distance from it, and ascertain whether the image of a
+very small object placed in the conjugate focus, which is due to the
+distance of the screen in front of the focus, be reflected to any point
+considerably distant from the centre of the screen through which the
+prolongation of the axis of the mirror should pass. We thus obtain a
+measure of the error of the instrument. For this purpose, we must find
+the position of the conjugate focus, which corresponds to the distance
+of the screen. If _b_ be the distance to which the object should be
+removed outwards from the principal focus of the mirror, _d_ the
+distance from the focus to the screen, and _r_ the distance from the
+focus to that point of the mirror which is to be tested, we shall have
+
+        _r_²
+  _b_ = ----
+        _d_
+
+as the distance to which the object must be removed outwards from the
+true focus on the line of the axis.[45]
+
+  [45] The truth of this equation may be easily ascertained as follows
+  (See fig. 27):--Let AP be the mirror, F its principal focus, and PH
+  the line of reflection of the ray FP; then an object at I will be
+  reflected at P to the conjugate focus O, where the screen is supposed
+  to be placed. But by construction, FPI = HPO = POF, and the angle at
+  F being common, the triangle FPI is similar to FPO, and hence FO ∶
+  PF ∷ PF ∶ FI, and
+
+       PF²
+  FI = ---;
+       FO
+
+  and substituting the letters in the text, we get _d_ ∶ _r_ ∷ _r_ ∶
+  _b_, and
+
+        _r_²
+  _b_ = ----.
+        _d_
+
+  [Illustration: Fig. 27.]
+
+[Illustration: Fig. 28.]
+
+[Illustration: Fig. 29.]
+
+[Illustration: Fig. 30.]
+
+[Illustration: Fig. 31.]
+
+  ~Argand Lamps used in Reflectors.~
+
+The flame generally used in reflectors, is from an Argand
+fountain-lamp, whose wick is an inch in diameter. Much care is bestowed
+upon the manufacture of the lamps for the Northern Lighthouses, which
+sometimes have their burners tipped with silver to prevent wasting
+by the great heat which is evolved. The burners are also fitted with
+a sliding apparatus, accurately formed, by which they may be removed
+from the interior of the mirror at the time of cleaning them, and
+returned exactly to the same place, and locked by means of a key. This
+arrangement, which is shewn in figs. 28, 29, and 30, is very important,
+as it insures the burner always being in the focus, and does not
+require that the reflector be lifted out of its place every time it
+is cleaned; so that, when once carefully set and screwed down to the
+frame, it is never altered. In these figs. _a a a_ represents one of
+the reflectors, _b_ is the burner, and _c_ a cylindric fountain, which
+contains 24 ounces of oil. The oil-pipe, the fountain _c_ for supplying
+oil, and the burner _b_, are connected with the rectangular frame _d_,
+which is moveable in a vertical direction upon the guide-rods _e_ and
+_f_, by which it can be let down, so that the burner may be lowered
+out of the reflector, by simply turning the handle _g_ (as will be
+more fully understood by examining figs. 28 and 29), which has the
+effect of forcing a _thread_ (like that of a screw) on the outside
+of the guide into a groove in the frame, or withdrawing it, and thus
+allows it to slide down or locks it at pleasure. An aperture of an
+elliptical form, measuring about two inches by three, is cut in the
+upper and lower part of the reflector, the lower serving for the free
+egress and ingress of the burner, and the upper, to which the copper
+tube _h_ is attached, serving for ventilation; _i_ shews a cross
+section and a back view of the main bar of the chandelier or frame on
+which the reflectors are ranged, each being made to rest on knobs of
+brass, one of which, as seen at _k k_, is soldered to the brass band
+_l_, that clasps the exterior of the reflector. Fig. 28 is a section
+of the reflector _a a_, shewing the position of the burner _b_, with
+the glass chimney _b′_, and oil-cup _l_, which receives any oil that
+may drop from the lamp. Fig. 30 shews the apparatus for moving the
+lamp up and down, so as to remove it from the reflector at the time of
+cleaning it. In the diagram (fig. 30) the fountain _c_ is moved partly
+down; _d d_ shews the rectangular frame on which the burner is mounted,
+_e e_ the elongated socket-guides through which the guide-rods slide,
+and _f_ the guide-rod, connected with the perforated sockets on which
+the _checking-handle g_ slides. The oil-cup _l_ (covered with a lid
+and wick-holder, as shewn in fig. 31) also serves as a _frost-lamp_
+during the long nights of winter, when the oil is apt to turn thick.
+It is attached to the lower part of the oil-tube by the arm _h_; and
+is lighted about an hour before sunset, so as to prepare the reflector
+lamp for lighting at the proper time. The communication between the
+burner and the fountain is easily opened or shut in the burners used
+in the Scotch Lighthouses, by simply giving the fountain a turn of one
+quadrant of the horizon round its own vertical axis by means of the
+round knob at its top, and thereby moving a simple slide-valve, which
+shuts off the communication between the fountain-tube and lamp-tube.
+By this mode, the oil is cut off about fifteen minutes before
+extinguishing the lights, so that when that is done, the burner is
+quite free of oil.
+
+[Illustration: Fig. 32.]
+
+  ~Arrangements for Raising or lowering the Argand Wick.~
+
+It would needlessly occupy much time and space to describe the various
+means (many of them sufficiently clumsy) which have been employed,
+and in many places are still in use, for raising and depressing the
+wick; it will be enough to say, that they all involve some application
+of the rack and pinion. I shall, therefore, only describe the method
+(invented, it is believed, by M. VERZY) which is adopted in all the
+Lighthouses in the district of the Commissioners of Northern Lights.
+The arrangement is as follows (see figs. 32, 33, 34, 35, 36):--The
+inner tube _t_ of the burner is enclosed by a strong tube _s_, which
+fits to it tightly, so as not to be easily moved. This strong tube has
+a spiral groove cut on its outer or convex surface. The wick-holder has
+two small pegs projecting from it, the one on the inside (not seen),
+and the other on the outside at _a_ (fig. 33). That on the inside
+works in the spiral groove of the tube S (figs. 32 and 33), already
+described as embracing the inner tube _t_; and all that is required for
+raising the wick is to make the wick-holder turn round on its vertical
+axis. This is effected by means of the small external peg _a_ of the
+wick-holder (fig. 33), which moves in a vertical slit _a_ (figs. 32 and
+34), cut in a tube standing in the burner, and concentric with it, and
+which also moves freely round its axis. Small knobs _n_ _n_ (figs. 32,
+34, and 36), at the top of this tube, fit into a notch in the upper
+ring of the gallery, which supports the glass chimney. By turning this
+gallery _g_ (see figs. 33 and 36), therefore, motion is given to the
+tube, with its knobs _n_ _n_, whose vertical slit _a_ (while it holds
+the external peg of the wick-holder, and also turns it round along with
+it) permits that peg _a_ to slide upwards or downwards, and thus the
+wick-holder rises or falls, according as its own internal peg moves up
+or down the spiral groove in the tube S. In fig. 32, C shews the glass
+chimney resting on the gallery _g g_.
+
+[Illustration: Fig. 33.]
+
+[Illustration: Fig. 34.]
+
+[Illustration: Fig. 35.]
+
+[Illustration: Fig. 36.]
+
+  ~Flowing of the Lamp.~
+
+An important point in the economy of the Argand lamp, is the level at
+which the outlet for the oil, in its passage from the fountain to the
+burner, should be cut. The cutting of this hole (generally called
+the _flow-hole_) in the pipe is termed the _flowing_ of the lamp, and
+is commonly done by successive trials, until the oil stands at the
+proper level of the burner, before the wick is put in. A more ready and
+accurate method of accomplishing this object and at once determining
+the level at which the _flow-hole_ should be cut, was introduced by Mr
+JAMES MURDOCH, the Foreman of Lightroom Repairs to the Scotch Board,
+and is generally employed in the Northern Lighthouses. Its nature will
+be readily understood by a reference to the accompanying diagram, No.
+37:
+
+[Illustration: Fig. 37.]
+
+The _hatched_ surface represents a metallic ruler, with a spirit-level
+at L; C is the cup in which the bottom of the fountain _f_ (shewn in
+dotted lines) rests. When the fountain is removed, and the ruler rests
+on the edge of the cup C, the screw at A is used to adjust the level at
+L; and a gauge GG is allowed to fall until a notch in it at _x′_ rests
+on the outer tube of the burner F; the pinching-screw B retains this
+ruler in its place, and the point _x′_ indicates the level at which
+the oil should stand in the burner. The level line _x′ x_ indicates
+the level on which the top of the _flow-hole_ H should be cut in the
+fountain-tube, which is shewn in dotted lines within the outer tube,
+or _body_ of the lamp. In other words, _y′ x′_ measures the level at
+which the oil should stand in the burner _below_ the lower edge of the
+metallic ruler, while the corresponding line _y x_, at the opposite
+end, shews the level of the top of the _flow-hole_ H, below the edge
+of the cup C. The gauge GG applied to that point of the fountain which
+coincides with the edge of the cup (so that _y′_ coincides with _y_)
+measures the length _yx_ = _y′ x′_; and a _set-square_ applied at _x_
+gives the position of H on the fountain-tube. The round dot at _a_
+shews the position of the air-hole in the body of the lamp, which
+establishes a connection between the external air and the surface of
+the oil. The rods SS′ shew the sliding gear (described as _d_ and _f_,
+page 221), and are only introduced to identify this diagram with those
+of the fountain and burner which have preceded it.
+
+The most advantageous level of the flow-hole depends on many
+circumstances too obscure and complicated to admit of any systematic
+elucidation; and it is enough for all practical purposes, to know that
+the capillary powers of the wick, and the greater or less viscidity of
+the oil, are the chief circumstances which determine that level. Actual
+experience is the only sure guide to the best practice in this respect;
+and I therefore content myself with stating, that it is generally found
+that the sperm oil should stand in the empty burner at about ³⁄₈ inch
+below its top. For colza oil ²⁄₈ inch is sufficient. In summer, owing
+to the oil being more fluid, there is sometimes a tendency to overflow
+the burner; but any inconvenience arising from it is avoided by the
+plan adopted in the Northern Lights, of shutting off the oil (by means
+of the apparatus already alluded to on p. 222) about fifteen minutes
+before extinguishing the lights in the morning.
+
+[Illustration: Fig. 38.]
+
+The arrangement for cutting off the oil is very simple, as will be
+seen from the annexed diagram (fig. 38), in which F is the fountain,
+T the oil-tube leading to the burner, and V the _flow-hole_, with its
+sliding valve. By turning the handle H one quadrant of the circle, the
+whole fountain F and tube T turn round their vertical axis, while the
+valve V, which rests in a notch in the cup of the lamp, remains still,
+and sliding over T, opens the _flow-hole_. S is the screw-plug which
+retains the oil in the fountain, and which is unscrewed and removed
+when the fountain is to be filled.
+
+  ~Placing the Lamp in the Focus.~
+
+[Illustration: Fig. 39.]
+
+[Illustration: Fig. 40.]
+
+In the reflecting apparatus of the Northern Lighthouses, the focal
+position of the lamp is not, as we have already seen, liable to
+derangement, by the removal of the burner for the purpose of cleaning,
+as the sliding gear described at p. 221 insures the return of the lamp
+to its true place. The burner is originally set by means of a gauge,
+which touches four points of the mirror’s surface (one of them being
+its vertex, and the other three in the vertical plane of its greatest
+double ordinate). This gauge being provided with a short tube or collar
+properly placed for the purpose of receiving the burner, at once
+verifies its true position, both vertical and horizontal. The diagrams
+39 and 40 shew the nature of the apparatus for adjusting the burners,
+the one being a plan and the other a section. The four points which
+touch the curve are one _g_ at the vertex, two in the same horizontal
+plane with the focus, and near the edge of the mirror at PP, and the
+fourth, also near the edge, and in the same vertical plane with the
+focus. F is the focus. The horizontal arms are graduated, and fitted
+with sliding pieces and clamping screws at R, so as to admit of being
+varied with the width of the mirror; but each gauge applies only to
+curves of the same focal distance; the distance F _g_ being fixed. The
+gauge, when applied to the mirror, is properly secured by the screws
+at R, R, and R′; and the burner which is attached to the oil-tube in a
+temporary manner at A, is raised into the interior of the mirror. If
+the tube of the burner ascends into the circular tube at F until (when
+fixed by the checking handle already noticed at p. 221) its upper edge
+just touches a narrow projection inside the tube F (so placed that the
+rim of the burner should just touch it when it is on the level required
+for putting the brightest part of the flame in the focus), then the
+burner is in the proper position; but if, on the one hand, the axis of
+the burner stands beyond F, at some point between it and N (which lies
+in the plane of the mirror’s edge), the bent tube O from the fountain
+must be shortened at A; and if it rise too high, that tube must be bent
+down (and _vice versa_), until, by successive trials, it shall exactly
+fit into the tube F, and stand at the proper level. A skilful workman
+soon comes to guess those quantities very accurately; and, almost at
+the first trial, curtails the tube to the proper length, and bends it
+to the suitable level. All that is needful is to proceed cautiously, so
+as not to cut the tube too short, for this leads to some trouble.
+
+  ~Distinctions of Catoptric Lights.~
+
+The great advantage derived by seamen from the establishment of lights
+on a coast, soon makes the calls for additional lights so frequent,
+that their very number itself produces a new evil, in the difficulty
+of distinguishing the lights from each other. As the object of a light
+is to make known to the benighted mariner the land he has made, with
+as much certainty as the sight of a hill or tower would shew him his
+position during the day, it becomes an object of the first importance
+to impress upon each light a distinctive character, which shall
+effectually prevent the possibility of its being mistaken for any
+other.
+
+Catoptric lights are susceptible of nine separate distinctions, which
+are called _fixed_, _revolving white_, _revolving red and white_,
+_revolving red with two whites_, _revolving white with two reds_,
+_flashing_, _intermittent_, _double fixed lights_, and _double
+revolving white lights_. The first exhibits a steady and uniform
+appearance, which is not subject to any change; and the reflectors
+used for it (as already noticed) are of smaller dimensions than those
+employed in revolving lights. This is necessary, in order to permit
+them to be ranged round the circular frame, with their axes inclined at
+such an angle, as shall enable them to illuminate every point of the
+horizon. The revolving light is produced by the revolution of a frame
+with three or four sides, having reflectors of a larger size grouped
+on each side, with their axes parallel; and as the revolution exhibits
+once in two minutes, or once in a minute, as may be required, a light
+gradually increasing to _full strength_, and in the same gradual manner
+decreasing to total darkness, its appearance is extremely well marked.
+The succession of _red_ and _white_ lights is caused by the revolution
+of a frame whose different sides present red and white lights; and
+these, as already mentioned, afford three separate distinctions,
+namely, alternate red and white; the succession of two white lights
+after one red, and the succession of two red lights after one white
+light. The _flashing_ light is produced in the same manner as the
+_revolving_ light; but owing to a different construction of the frame,
+the reflectors on each of eight sides are arranged with their rims or
+faces in one vertical plane, and their axes in a line inclined to the
+perpendicular, a disposition of the mirrors which, together with the
+greater quickness of the revolution, which shews a flash once in five
+seconds of time, produces a very striking effect, totally different
+from that of a revolving light, and presenting the appearance of
+the flash alternately rising and sinking. The brightest and darkest
+periods being but momentary, this light is farther characterised by a
+rapid succession of bright flashes, from which it gets its name. The
+_intermittent_ light is distinguished by bursting suddenly into view
+and continuing steady for a short time, after which it is suddenly
+eclipsed for half a minute. Its striking appearance is produced by the
+perpendicular motion of circular shades in front of the reflectors, by
+which the light is alternately hid and displayed. This distinction,
+as well as that called the _flashing light_, is peculiar to the
+Scotch coast, having been first introduced by the late Engineer of
+the Northern Lights Board. The double lights (which are seldom used
+except where there is a necessity for a _leading_ line, as a guide for
+taking some channel or avoiding some danger) are generally exhibited
+from two Towers, one of which is higher than the other. At the Calf
+of Man, a striking variety has been introduced into the character of
+leading lights, by substituting, for two _fixed_ lights, two lights
+which revolve in the same periods, and exhibit their flashes at the
+same instant; and these lights are, of course, susceptible of the other
+variety enumerated above, that of two revolving red and white lights,
+or flashing lights, coming into view at equal intervals of time. The
+utility of all these distinctions is to be valued with reference to
+their property of at once striking the eye of an observer and being
+instantaneously obvious to strangers.
+
+The introduction of colour, as a source of distinction, is necessary,
+in order to obtain a sufficient number of distinctions; but it is in
+itself an evil of no small magnitude; as the effect is produced by
+interposing coloured media between the burner and the observer’s eye,
+and much light is thus lost by the absorption of those rays, which are
+held back in order to cause the appearance which is desired. Trial
+has been made of various colours; but red, blue, and green alone have
+been found useful, and the two latter only at distances so short as to
+render them altogether unfit for sea-lights. Owing to the depth of tint
+which is required to produce a marked effect, the red shades generally
+used absorb from ⁴⁄₇ths to ⁵⁄₆ths of the whole light, an enormous loss,
+and sufficient to discourage the adoption of that mode of distinction
+in every situation where it can possibly be avoided. The red glass
+used in France absorbs only ⁴⁄₇ths of the light; but its colour
+produces, as might be expected, a much less marked distinction to the
+seaman’s eye. In the Lighthouses of Scotland, a simple and convenient
+arrangement exists for colouring the lights, which consists in using
+chimneys of red glass, instead of placing large discs in front of the
+reflectors.
+
+  ~Arrangement of Reflectors on the Frame.~
+
+[Illustration: Fig. 41.]
+
+After what has been already said on the subject of divergence, it
+will at once be seen, that in revolving lights the reflectors are
+placed with their axes parallel to each other, so as to concentrate
+their power in one direction; whilst in fixed lights it is necessary,
+in order to approach as near as possible to an equal distribution of
+the light over the horizon, to place the reflectors, with their axes
+inclined to each other, at an angle somewhat less than that of the
+divergence of the reflected cone. For this purpose, a brass gauge (see
+fig. 41), composed of two long arms, AM, AM, somewhat in the form of a
+pair of common dividers, connected by a means of a graduated limb A,
+is employed. The arms having been first placed at the angle, which is
+supplemental to that of the inclination of the axes of the two adjacent
+mirrors at O, are made to span the faces of the reflectors, one of
+which is moved about till its edges are in close contact with the flat
+surface of one of the arms of the gauge.
+
+[Illustration: Fig. 42.]
+
+[Illustration: Fig. 43.]
+
+Figs. 42 and 43 shew an elevation and plan of a revolving apparatus on
+the catoptric principle. In these figures, _n n_ shews the reflector
+frame or chandelier; _o o_, the reflectors with their oil-fountains
+_p_ _p_. The whole is attached to the revolving axis or shaft _q_.
+The copper tubes _r_ _r_ convey the smoke from the lamps; _s_ _s_ are
+cross bars which support the shaft at _t t_; _u u_ is a copper pan for
+receiving any moisture which may accidentally enter at the central
+ventilator in the roof of the light-room; _l_ is a cast-iron bracket,
+supporting the cup in which the pivot of the shaft turns; _m_ _m_ are
+bevelled wheels, which convey motion from the machine to the shaft. The
+machinery does not require any particular notice, being that of common
+clock-work, moved by the descent of a weight.
+
+[Illustration: Fig. 44.]
+
+Fig. 44 shews a plan of one tier of reflectors arranged in the manner
+employed in a fixed catoptric light; _n_ _n_ shews the chandelier,
+_q_ the fixed shaft in the centre, which supports the whole, _o_ _o_
+the reflectors, and _p_ _p_ the fountains of their lamps. In this
+figure (in order to prevent confusion) only one tier of reflectors is
+shewn; the other tiers are so arranged, that their axes divide into
+equal angles the arcs intercepted between the axes of the adjoining
+reflectors on the first tier, thereby producing the nearest approach
+to an equal distribution of the light, which is attainable by this
+arrangement.
+
+In lighthouses of moderate height, the proper position for the
+reflector itself is perfect horizontality of its axis, which may be
+ascertained with sufficient accuracy, by trying with a plummet, whether
+the lips of the instrument, which we may conclude to be at right
+angles to the plane of its axis, be truly vertical. In lightrooms very
+much elevated above the sea, however, the dip of the horizon becomes
+notable; and a slight inclination forwards should be given to the face
+of the reflectors, so that their axes produced may be tangents to the
+earth at the visible horizon of the light-room. This, however, must not
+be permitted to interfere with the perfect horizontality of the top of
+the burner, which is indispensable to its proper burning.
+
+  ~Bordier Marcet’s Reflectors.~
+
+  ~Fanal Sidéral.~
+
+Various forms of the parabolic mirror were invented by M. BORDIER
+MARCET, the pupil and successor of ARGAND, who has laboured with
+much enthusiasm in perfecting catoptric instruments, more especially
+with a view to their application in the illumination of lighthouses
+and the streets of towns. Amongst many other ingenious combinations,
+he has invented and constructed an apparatus which is much used in
+harbour-lights on the French coast, where it is known by the fanciful
+name of _Fanal[46] sidéral_. The object is to fulfil, as economically
+as possible, the conditions required in a fixed light, by illuminating,
+with perfect equality, every part of the horizon, by means of a single
+burner; and M. BORDIER MARCET has in his work-shop an instrument of
+this kind, eight feet in diameter, which he constructed on speculation.
+The apparatus used in harbour-lights, on the French coast, is of much
+smaller dimensions, and does not exceed fifteen inches in diameter.
+A perfect idea of the construction and effect of this instrument may
+be formed, by conceiving a parabola to revolve about its parameter as
+a vertical axis, so that its upper and lower limbs would become the
+generating lines of two surfaces possessing the property of reflecting,
+in lines parallel to the axis of the parabola, all the rays incident
+upon them, from a light placed in the point where the parameter and
+axis of the generating parabola intersect each other. This point
+being the focus of each parabolic section of this apparatus, light
+is equally dispersed in every point of the horizon, when the axis of
+the parabolic section is in a plane perpendicular to a vertical line.
+But however perfectly this apparatus may attain its important object,
+it necessarily produces a feeble effect; because as its action is
+entirely confined to the vertical direction, the light distributed by
+it decreases directly as the distance of the observer. This beautiful
+little instrument is shewn at fig. 45, in which _b_ shews the burner,
+_p p_ the upper reflecting surface, and _p′ p′_ the lower reflecting
+surface, both generated in the manner above described by the revolution
+of a parabola about its parameter _x b_; F is the focus of the
+generating parabola; and _l_ _l_ are small pillars, which connect the
+two reflecting plates, and give strength to the apparatus.
+
+  [46] Fanal, from φανεν, a lantern.
+
+[Illustration: Fig. 45.]
+
+  ~Fanal à double effet.~
+
+M. BORDIER MARCET has also prepared an ingenious modification of the
+paraboloïdal mirror, which he has described under the name of _fanal
+à double effet_; and the object of which is to obtain a convenient
+degree of divergence from parabolic mirrors, by the use of two flames
+and two reflecting surfaces, each of which is acted upon by its own
+flame, and also by that of the other. This modification consists in
+the union of two portions of hollow paraboloïdal mirrors, generated by
+the revolution of two parabolas about a common horizontal axis, and
+illuminated by two lamps placed in the focus of each. The first surface
+is generated by the revolution on its axis of a segment of a paraboloid
+intercepted between the parameter and some double ordinate greater
+than it, and may, from its form, be called the ribbon-shaped mirror.
+The second surface is that of a parabolic conoid, which is cut off by
+a vertical plane passing through a double ordinate, which is equal to
+the parameter of the parabolic ribbon, which is placed in front of it.
+The elements of the curve which forms the conoïdal mirror, must be so
+chosen as to have its focus at a convenient distance in _front_ of
+that of the ribbon-shaped mirror, so as to admit of placing the two
+lamps separate from each other, as well as to produce the necessary
+degree of divergence, which is to be obtained by the action of these
+mirrors respectively on the flame placed in the focus of the other.
+These two mirrors are joined together in the line of the parametric
+section of the ribbon, which coincides with the lips of the conoid at
+some double ordinate _behind_ its parameter. Each mirror produces, by
+means of the lamp placed in its focus, an approach to parallelism of
+the reflected rays, which M. BORDIER MARCET has not inaptly termed
+the _principal effect_; whilst the action of each surface on the lamp
+which is placed in the focus of the other, causes what the inventor
+calls the _secondary_ or _lateral effect_. Their secondary action may
+be described thus: The lamp, which is in the focus of the ribbon, is
+much nearer the vertex of the conoid than its own focus; so that its
+rays making, with normals to the surface of the conoid, angles greater
+than those which are formed by the rays proceeding from its focus, are
+of necessity reflected in lines diverging from the axis of the mirror.
+Those, on the contrary, which proceed from the focus of the conoid,
+meet the ribbon-shaped surface, so as to make angles with its normals
+more acute than those which the rays from its own focus could do, and
+which are, therefore, reflected in lines converging to the axis of the
+mirror. Those reflected rays must therefore cut the axis, and diverge
+from it on the other side. This apparatus has been used at La Hève
+and some other lights on the French coast; but it is impossible not
+to perceive the great loss of light which results from the use of two
+flames in one mirror; and it must not be forgotten, that the divergence
+which is obtained by means of it is not confined to the horizontal
+direction in which only it is wanted; but that the light is at the same
+time scattered in every direction round the edge of the mirror.
+
+Arrangements of a similar kind were proposed and executed for the
+same purpose of uniting greater divergence with considerable power in
+the central parts of the resultant beam, by ARGAND himself, in 1806,
+and also in 1808, by M. HAUDRY, _Ingénieur des Ponts et Chaussées_.
+ARGAND proposed the union of a paraboloid, and an ellipsoid having
+their foci coincident in one point, which being the posterior focus
+of the latter curve, was illuminated by the rays reflected to it by
+means of the ellipsoïdal surface from the lamp placed in the anterior
+focus. From the _optical focus_ thus obtained, some rays would fall
+on the paraboloïdal surface and produce, by reflection, a cylinder of
+parallel rays, while the rest would diverge from the axis, and form a
+zone of spreading rays. M. HAUDRY’S plan consisted of a combination of
+a conical with a paraboloïdal mirror, so placed, that the rays from the
+front part of the hollow cone might be nearly parallel to those sent
+out by the paraboloid; while the rays from its base diverging from the
+axis might produce a ring of divergent rays, similar to that obtained
+from the ellipsoid of ARGAND’S apparatus.
+
+It would occupy much time to exhibit all the disadvantages of the
+arrangements in the _fanal à double effet_ of M. BORDIER MARCET, and
+also in those of ARGAND and HAUDRY; and I shall therefore dismiss the
+subject by observing, that the loss of light due to the position of
+the flame in the apparatus of ARGAND, is so great as to induce one
+to wonder that such combinations should ever have been attempted.
+There can be no doubt, that the most efficient mode of obtaining due
+divergence from mirrors, is to adopt the paraboloid, with a short focal
+distance, which has the double advantage of increasing the divergence
+which is due inversely to the focal distance, and, at the same time,
+subjecting to the action of the mirror a larger portion of the luminous
+sphere proceeding from the flame.
+
+[Illustration: Fig. 46.]
+
+  ~Fanal à double face.~
+
+Lastly, I shall notice M. BORDIER MARCET’S _fanal à double face_,
+which consists of two paraboloïdal mirrors, truncated in the vertical
+plane of the parameter, and united together back to back, so as to
+be illuminated by the same lamp placed in their common focus. To
+save the light which would otherwise escape the catoptric action, he
+adds a parabolic conoid of greater focal distance, and so placed,
+that while its focus may coincide with the common focus of the other
+mirrors, its size may be so restricted, that it shall not interfere
+with the effect of the truncated mirror opposite which it is placed.
+The obvious consequence of such an arrangement is, that the rays (see
+fig. 46) produced from a lamp in the common focus of the three mirrors,
+will produce in opposite directions a luminous ring from each of the
+truncated mirrors AC, BC, and A′C′, B′C′, while the central or conoïdal
+mirror MN will fill the interior of one of those luminous rings with
+a cone of rays, whose intensity will be in the inverse ratio of MN²
+to _a_ _b_² (or FM² to F _a_²), which latter surface represents the
+whole amount of naturally divergent rays, which strike on _a_ _b_, and
+which are spread over MN. Two sets of reflectors of this form facing
+in opposite directions (each set arranged in one plane, and fixed on
+a frame which could be made to revolve round a vertical axis), would
+thus present their brightest effect after considerable intervals of
+darkness; but, by arranging them with their axes slightly inclined,
+they were made to prolong the light periods and curtail the dark ones.
+M. BORDIER MARCET speaks of this apparatus with all the satisfaction
+generally felt by inventors; but it is no difficult matter to identify
+its effect with that of the common paraboloïdal mirrors. It is obvious,
+that all the rays which fall from a true focal point on the three
+reflectors AC, BC, A′C′, B′C′, and MN, are merely those which would
+fall on a single reflector, whose double ordinate and the portion of
+the abscissa between that ordinate and the focus, are equal to those
+of the first reflector of the compound system, so that the quantity of
+light reflected by the three reflectors is neither more nor less than
+that which would be projected by one. All the difference that can exist
+is, that in the case of a flame which has a notable size, the surface
+MN being farther distant than _a_ _b_, would produce less aberration
+and, consequently, a very slight increase of intensity in the small
+portion of the reflected beam of parallel rays due to that part of the
+compound mirror. We cannot, therefore, sensibly err in rejecting any
+advantage to be derived from this arrangement as insignificant.[47]
+
+  [47] See Peclet′s Traité de l′Eclairage, p. 302, from which fig. 46
+  is copied.
+
+  ~Mr Barlow′s Spherical Mirrors.~
+
+Spherical mirrors have been employed in Lighthouses chiefly when they
+can be introduced to aid the effect of refracting apparatus: and it
+will not be necessary to say much of them in this place. I must,
+however, notice an ingenious proposal of Mr W. H. BARLOW,[48] who
+suggests placing in front of the flame a small spherical reflector,
+whose centre is coincident with the focus of a paraboloïd, and
+whose subtense is the parameter of the generating curve. The small
+mirror, being somewhat less than a hemisphere, would cause the light
+falling upon it to be returned through the focus so as to reach the
+paraboloïdal surface and to be finally reflected from that portion of
+it which is embraced between the limits of its extreme divergence. If
+there were no loss of light at the surface of the small mirror, its
+effect would be to increase the power of the beam of parallel rays
+by an amount equal to the sum of the rays incident on the spherical
+surface, but at the same time to diminish it by intercepting a portion
+of the light reflected from the paraboloïd. I am not aware that such
+a combination has been tried, as it applies most advantageously to
+reflectors whose span does not exceed the parameter of the generating
+curve, a form rarely adopted in lighthouses; but it might also be
+adapted to reflectors which intercept a larger portion of light, by
+making the spherical reflector some segment less than the hemisphere.
+
+  [48] In an excellent paper above noticed, on the Illumination of
+  Lighthouses, in the London Transactions, for 1837.
+
+  ~Captain Smith’s Mirrors in the form of a parabolic spindle.~
+
+CAPTAIN SMITH of the Madras Engineers, has described in the
+“Professional papers of the ‘Corps of Royal Engineers,’[49] a new
+system of fixed lights,” which consists in placing a flat wick in
+the focus of one-half of a hollow parabolic spindle generated by the
+rotation of a parabola about its parameter as a vertical axis. The
+action of the instrument is obvious, for each vertical section being
+parabolic, effects a change only in the _vertical_ divergence of the
+rays incident on it from the focus, and suffers their horizontal
+direction to remain unaltered; thus each vertical plate of reflected
+rays passes through the parameter of the curve and illuminates the
+opposite point of the horizon by means of a narrow strip or line of
+light. Two hollow spindles of that form, each lighting 180° and facing
+opposite azimuths, would, therefore, be sufficient to illuminate the
+whole horizon. The author of the paper, however, appears to contemplate
+the employment of a series of those mirrors ranged one above another
+and _breaking joint_ vertically, somewhat in the manner already
+described in speaking of the arrangement of the paraboloïdal mirrors
+used in fixed lights. The advantages of this mode of illumination are
+much overrated by CAPTAIN SMITH, who seems to magnify beyond its real
+importance the risk attending the use, in the dioptric apparatus,
+of a single lamp, whose sudden extinction would deprive at once the
+whole horizon of the benefit of the light; while, on the contrary, he
+reckons the security obtained by his arrangement as an advantage of the
+highest value. In certain situations, where no regular establishment of
+trained light-keepers is maintained, that security may be an object of
+more importance and may warrant a greater sacrifice, than is necessary
+in Great Britain; but I have no hesitation in saying, that I know of
+no situation in which the plan proposed by CAPTAIN SMITH could bear
+comparison with the mode of illumination for fixed lights by means of
+the catadioptric instruments of FRESNEL.
+
+  [49] Vol. v., p. 56.
+
+
+DIOPTRIC[50] SYSTEM OF LIGHTS.
+
+  [50] Most probably directly derived from the Greek διόπτρον, an
+  optical instrument with holes for looking through, whose name is a
+  compound of διὰ, through, and ὄπτομαι, _I see_.
+
+One of the earliest notices of the application of lenses to lighthouses
+is that recorded by SMEATON in his Narrative of the Eddystone
+Lighthouse, where he mentions a London optician, who, in 1759, proposed
+grinding the glass of the lantern to a radius of seven feet six
+inches; but the description is too vague to admit of even a conjecture
+regarding the proposed arrangement of the apparatus. About the middle
+of the last century, however, lenses were actually tried in several
+lighthouses in the south of England, and in particular at the South
+Foreland in the year 1752; but their imperfect figure and the quantity
+of light absorbed by the glass, which was of impure quality and of
+considerable thickness, rendered their effect so much inferior to
+that of the parabolic reflectors then in use, that after trying some
+strange combinations of lenses and reflectors, the former were finally
+abandoned. Lenses were also tried at the lights of Portland, Hill
+of Howth, and Waterford, by Mr Thomas Rogers, a glass manufacturer
+in London; who possessed, it is said, the art of blowing mirrors of
+glass, “and by a new method silvered over the convex side without
+quicksilver.”[51]
+
+  [51] Hutchinson’s Practical Seamanship, p. 200. See also the notice
+  of the spherical mirrors made by Messrs François and Letourneau of
+  Paris in a subsequent part of this volume.
+
+The object to be attained by the use of lenses in a Lighthouse is, of
+course, identical with that which is answered by employing reflectors;
+and both instruments effect the same end by different means, collecting
+the rays which diverge from a point called the _focus_, and projecting
+them forward in a beam, whose axis coincides with the produced axis of
+the instrument. We have already seen that, in the case of _reflection_,
+this result is produced by the light being _thrown back_ from a surface
+so formed as to make all the rays to proceed in one and the same
+required direction. In the case of _refraction_, on the other hand, the
+rays pass through the refracting medium, and are _bent_ or _refracted_
+from their natural course into that which is desired.
+
+The celebrated BUFFON, to prevent the great absorption of light by
+the thickness of the material, which would necessarily result from
+giving to a lens of great dimensions a figure continuously spherical,
+proposed to grind out of a solid piece of glass, a lens in steps or
+concentric zones. This suggestion of BUFFON regarding the construction
+of large burning glasses, was first executed, with tolerable success,
+about the year 1780, by the Abbé ROCHON; but such are the difficulties
+attending the process of working a solid piece of glass into the
+necessary form, that it is believed the only other instrument ever
+constructed in this manner, is that which was made by Messrs COOKSON of
+Newcastle-upon-Tyne, for the Commissioners of Northern Lighthouses.
+
+The merit of having first suggested the building of lenses in separate
+pieces, seems to be due to CONDORCET, who, in his _Eloge de Buffon_,
+published so far back as 1773, enumerates the advantages to be derived
+from this method. Sir DAVID BREWSTER also described this mode of
+building lenses in 1811, in the _Edinburgh Encyclopædia_; and in
+1822, the late eminent FRESNEL, unacquainted with the suggestions of
+CONDORCET or the description by Sir DAVID BREWSTER, explained, with
+many ingenious and interesting details, the same mode of constructing
+those instruments. To FRESNEL belongs the additional merit of having
+first followed up his invention, by the construction of a lens and, in
+conjunction with MM. ARAGO and MATHIEU, of placing a powerful lamp in
+its focus, and indeed of finally applying it to the practical purposes
+of a Lighthouse.
+
+The great advantages which attend the mode of construction proposed by
+CONDORCET are,--the ease of execution, by which a more perfect figure
+may be given to each zone and spherical aberration in a great measure
+corrected, and the power of forming a lens of larger dimensions than
+could easily be made from a solid piece. Both BUFFON and CONDORCET,
+however, chiefly speak of reducing the thickness of the material, and
+do not seem to have thought of determining the radius and centre of
+the curvature of the generating arcs of each zone, having contented
+themselves with simply depressing the spherical surface in separate
+portions. FRESNEL, on the other hand, determined those centres,
+which constantly recede from the vertex of the lens in proportion as
+the zones to which they refer are removed from its centre; and the
+surfaces of the zones of the annular lens, consequently, are not parts
+of concentric spheres, as in BUFFON’S lens. It deserves notice, that
+the first lenses constructed for FRESNEL by M. SOLEIL had their zones
+polygonal, so that the surfaces were not annular, a form which FRESNEL
+considered less accommodated to the ordinary resources of the optician.
+He also, with his habitual penetration, preferred the plano-convex
+to the double-convex form, as more easily executed.[52] After mature
+consideration, he finally adopted crown glass, which, notwithstanding
+its greenish colour, he preferred to flint glass, as being more free
+from _striæ_. All his calculations were made in reference to an index
+of refraction of 1·51, which he had verified by repeated experiments,
+conducted with that patience and accuracy for which, amidst his higher
+qualities, he was so remarkably distinguished.[53] The instruments have
+received the name of _annular_ lenses, from the figure of the surface
+of the zones.
+
+  [52] The plano-convex lens, with its curved side towards the parallel
+  rays, is also a form producing small spherical aberration, a
+  circumstance which may also have influenced his choice.
+
+  [53] My friend, Mr WILLIAM SWAN, carefully examined, by his new
+  and ingenious method, described in the Edinburgh New Philosophical
+  Journal, January 1844, several specimens of the St Gobain glass
+  (which is now used in the manufacture of the lenses), and found its
+  refractive index to be 1·51793, the _difference_ between the greatest
+  and least values being only 0·00109.
+
+  ~Refraction.~
+
+A ray of light, in passing _obliquely_ from one transparent body
+into another of different density, experiences at the point of the
+intersection of the common surface of the two planes, a sudden change
+of direction, to which the name of _refraction_ has naturally been
+given, in connection with the most familiar instance of the phenomenon,
+which is exhibited by a straight ruler with one half plunged into a
+basin of water while the other remains in the air. The ruler no longer
+appears straight, but seems to be _bent_ or _broken_ at the point where
+it enters the water. It may not be out of place to call attention to
+the laws which regulate the change of direction in the incident light,
+which are _three_ in number.
+
+1. Incidence and refraction, in uncrystallized media of homogeneous
+structure such as glass, always occur in a plane perpendicular to that
+of the refracting surface.
+
+2. In the same substances, the angle formed with the perpendicular by
+the ray at its entering the surface of the second medium, has to the
+angle which it makes with the normal after it has entered the surface,
+such a relation, that their sines have a fixed ratio, which is called
+the _refractive index_. When a ray falls normally on the surface of any
+substance, it suffers no refraction.
+
+3. The effect of passing from a rare to a dense medium, as from air
+into water or glass, is to make the angle of _refraction_ less than the
+angle of _incidence_; and those angles are measured with reference
+to a normal to the plane which separates the media at the point of
+incidence. The converse phenomenon, of course, takes place in the
+passage from a dense to a rare medium, in which case the angle of
+_incidence_ is less than the angle of _refraction_. To this rule there
+are a few exceptions; for there are certain combustible bodies, such as
+diamond, whose refractive powers are much greater than other substances
+of equal density.
+
+[Illustration: Fig. 47.]
+
+The diagram (fig. 47) will serve to render those laws more
+intelligible. Let a ray of light _a_ O meet a surface of water _n m_
+at O, it will be immediately bent into the direction O _a′_; and if,
+from the centre O, we describe any circle, and draw a line _b_ O _b′_,
+perpendicular to _nm_; then _ab_ and _a′ b′_, perpendiculars drawn to
+the normal _bb′_, from the points _a_ and _a′_ where the circle cuts
+the incident and refracted rays, will be the sines of the angle of
+incidence _b_ O _a_, and of the angle of refraction _b′_ O _a′_, and
+the ratio of those sines to each other, or
+
+   _b a_
+  -------
+  _b′ a′_
+
+will be the relative index of _refraction_ for the two media.
+
+4. It may perhaps be added, for convenience, as a _fourth_ law,
+deducible from the others, that since rays passing from a dense into a
+rare medium, have their angle of refraction greater than the angle of
+incidence, there must be some angle of incidence whose corresponding
+angle of refraction is a right angle; beyond which no refraction can
+take place, because there is no angle whose sine can be greater than
+the radius. In such circumstances, _total reflection_ ensues. For
+common glass, whose index of refraction is 1·5, we have (in the case of
+emergent rays) sine of
+
+              sine of refraction
+  incidence = ------------------;
+                     1·5
+
+but, as no sine can exceed radius or unity, the angle of incidence must
+be limited to 41° 49′; beyond which total reflection will take place,
+and the light will return _inwards_ into the glass, being _reflected_
+at its surface.
+
+Thus, if a ray proceed from a point O (fig. 48), within a piece of
+glass, to a point C, at its surface A B; and if O C _b_, its incidence,
+be less than 41° 49′, it will be _refracted_ in some direction C _f_;
+but if this angle be greater than 41° 49′, as O C′ _b′_, the ray will
+be _reflected_ back into the glass in the direction C′ O′.
+
+[Illustration: Fig. 48.]
+
+The material hitherto employed in the construction of lighthouse
+apparatus is crown glass, which, although it possesses a lower
+refractive power than flint glass and has, besides, a slightly
+greenish tinge, offers the great practical advantages of being more
+easily obtained of homogeneous quality; and, being less subject to
+deterioration from atmospheric influences, it is peculiarly suitable
+for use in the exposed situations generally occupied by Lighthouses.
+The refractive index of crown glass, as already noticed, is about 1·5.
+
+Any one may easily satisfy himself by a careful protraction of the
+angles of _incidence_ and _refraction_, in the manner above described,
+as to the truth of the following general propositions resulting from
+those laws:--
+
+1. A ray of light passing through a plate of some diaphanous
+substance such as glass, with parallel surfaces, suffers no change
+of _direction_, but emerges in a line parallel to its original path,
+merely suffering a _displacement_, depending on the obliquity of the
+incident ray, and the refractive power and thickness of the plate. The
+effect of this displacement is merely to give the ray an apparent point
+of origin different from the true one. This will be easily understood
+by the diagram (fig. 49), in which _a b_ is a normal to the plate,
+whose surfaces _x x_ and _x′ x′_ are parallel, _r r r r_ shews the path
+of the ray, _r r_ the displacement, and _r′_ the apparent point of
+origin resulting from its altered _direction_.
+
+[Illustration: Fig. 49.]
+
+2. When a ray passes through a triangular prism _a b c_, the
+inclination of the faces _a c_ and _c b_ causes the emergent ray _r′_
+to be bent towards _a b_, the base of the prism, in a measure depending
+on the inclination of the sides of the prism and the obliquity of the
+incident ray to the first surface.
+
+[Illustration: Fig. 50.]
+
+3. When parallel rays fall on a concave lens, they will, at their
+emergence, be divergent. The section of the diaphanous body _a b c d_
+may be regarded as composed of innumerable frusta of prisms, having
+their apices directed towards the centre line _x r_; and the rays which
+pass through the centre, being normal to the surface, will be unchanged
+in their direction, while all the others will (as shewn in the figure)
+suffer a change of direction, increasing with their distance from the
+centre, owing to the increasing inclination of the surfaces of the lens
+as they recede from its axis.
+
+[Illustration: Fig. 51.]
+
+4. Lastly, when divergent rays fall on a convex lens _a b_, from a
+point _f_, called the principal focus, they are made parallel at their
+emergence; while, _conversely_, parallel rays which fall on the lens
+are united in that point.[54] This effect, which is the opposite of
+that caused by the concave lens, may be explained in a similar manner,
+by conceiving the section _a b_ of the convex lens to be composed of
+innumerable frusta of prisms, arranged with their _bases_ towards the
+centre of the lens.
+
+  [54] It is, of course, to be understood that only rays incident near
+  the axis of the lens are refracted accurately to a focus.
+
+[Illustration: Fig. 52.]
+
+Now, it is obvious, that we can derive no assistance, in economising
+the rays of a lamp for Lighthouse purposes, from concave lenses, whose
+property is to increase the dispersion of the rays incident on them.
+With concave lenses, therefore, we have no concern; and we shall
+confine ourselves to the consideration of the convex or converging
+lenses.
+
+The lens always used in Lighthouses is (for reasons already noticed)
+plano-convex, and differs from the last only by having a plane and
+a curve surface, instead of two curve surfaces, whose radii are on
+opposite sides of the lens. The plano-convex is generally regarded, by
+writers on optics, as a _case_ of the double convex having one side of
+an _infinite_ radius. Both forms cause parallel rays to converge to a
+focus.
+
+We commence with a general view of the relations which exist between
+the position of the _radiant_ and the focus.
+
+[Illustration: Fig. 53.]
+
+Let Q _q_ be a section of a lens, and _f_ A _r_ its optical axis, or
+the line in which a ray of light passes unchanged in its direction
+through the lens, from its being normal to both surfaces, whether the
+lens be double-convex as above, or plano-convex (see fig. 53), then the
+_principal focus f_ is that point where the rays from _r r r_, which
+fall parallel to the optic axis on the outer face of the lens, meet
+after refraction at the two faces,--or, to speak more in the language
+of the art which is under consideration, the _principal focus f_ is the
+point whence the rays of light, proceeding in their naturally divergent
+course, fall on the inner surface Q A _q_ of the lens, and are so
+changed by refraction there and at the outer face, that they finally
+emerge parallel to the _optic axis_ in the directions Q _r_, _q r_. The
+position of this point depends partly on the refractive power of the
+substance of which the lens is composed and partly on the curvature of
+the surface or surfaces which bound it.
+
+It would be quite beyond the scope of these Notes to attempt to present
+the subject of refraction at spherical surfaces before the reader’s
+view in a rigorous or systematic manner, and thus to advance, step by
+step, to the practical application of refracting instruments, as a
+means of directing and economising the light in a Pharos. This would
+involve the repetition, in a less elegant form, of what is to be
+found in all the works on optics; and instead of this, I am content
+to refer, where needful, to those works, and shall confine myself
+simply to what concerns Lighthouse lenses and their use. It would
+also be superfluous to determine the position of the principal focus
+of a plano-convex lens, in terms of the refractive index and radius
+of curvature,[55] as it can be very accurately found in practice by
+exposing the instrument to the sun, in such a manner that his rays may
+fall upon it in a direction parallel to its axis. The point of union
+between the converging and diverging cones of rays (where the spectrum
+is smallest and brightest), which is the _principal focus_, is easily
+found by moving a screen behind the lens, farther from or nearer to
+it as may be required. The path of the Lighthouse optician, moreover,
+generally lies in the opposite direction; and his duty is not so much
+to find the focal distance of a ready-made lens, as to find the best
+form of a lens for the various circumstances of a particular Pharos,
+whose diameter, in some measure, determines the focal distance of the
+instruments to be employed. All, however, that I shall really have to
+do is to give an account of what has been done by the late illustrious
+FRESNEL, who seems to have devoted such minute attention to every
+detail of the Dioptric apparatus, that he has foreseen and provided
+for every case that occurs in the practice of Lighthouse illumination.
+His brother, Mons. LEONOR FRESNEL, who succeeded him in the charge of
+the Lighthouses of France, has, with the greatest liberality, put me
+in possession of the various formulæ used by his lamented predecessor,
+in determining the elements of those instruments which have so greatly
+improved the lighthouses of modern days.
+
+  [55]
+
+        _r_
+  F = -------
+      _m_ - 1
+
+  in which _r_ is the radius of curvature, and _m_ is the refractive
+  index.--_Coddington’s Optics_, Chap. VIII. If the radiant be brought
+  near the lens, so as to cast divergent rays on its surface, then the
+  conjugate focus will recede behind the _principal focus_; and when
+  the luminous body reaches the _principal_ focus _in front_ of the
+  lens, the rays will emerge from its posterior surface in a direction
+  parallel to its axis. If it be brought still nearer the lens, the
+  rays would emerge as a divergent cone. Hence converging lenses can
+  only collect rays into a focus, when they proceed from some point
+  _more_ distant than the principal focus.
+
+Spherical lenses, like spherical mirrors, collect truly into the focus
+those rays only which are incident near the axis; and it is, therefore,
+of the greatest importance to employ only a small segment of any sphere
+as a lens. The experience of this fact, among other considerations,
+led CONDORCET, as already noticed, to suggest the building of lenses
+in separate pieces. FRESNEL, however, was the first who actually
+constructed a lens on that principle; and he has subdivided, with such
+judgment, the surface of the lens into a centre lens and concentric
+annular bands and has so carefully determined the elements of curvature
+for each, that no farther improvement is likely to be made in their
+construction. For the drawings of the great lens, I have to refer to
+Plate XII., which also contains a tabular view of the elements of its
+various parts. The central disc of the lens, which is employed in
+lights of the first order, and whose focal distance is 920 millimètres,
+or 36·22 inches, is about 11 inches in diameter; and the annular rings
+which surround it vary slightly in breadth from 2³⁄₄ to 1¹⁄₄ inches.
+The breadth of any zone or ring is, within certain limits, a matter of
+choice, it being desirable, however, that no part of the lens should
+be much thicker than the rest, as well for the purpose of avoiding
+inconvenient projections on its surface, as to permit the rays to pass
+through the whole of the lens with nearly equal loss by absorption. The
+objects to be attained in the polyzonal or compound lens, are chiefly,
+as above noticed, to correct the excessive aberration produced by
+refraction through a hemisphere or great segment, whose edge would make
+the parallel rays falling on its curve surface converge to a point much
+nearer the lens than the principal focus, as determined for rays near
+the optical axis, and to avoid the increase of material, which would
+not only add to the weight of the instrument and the expense of its
+construction, but would greatly diminish by absorption the amount of
+transmitted light. Various modes of removing similar inconveniences in
+telescopic lenses have been devised; and the suggestions of DESCARTES,
+as to combinations of hyperbolic and elliptic surfaces with plane and
+spherical ones, more especially fulfil the whole conditions of the
+case; but the excessive difficulty which must attend grinding and
+polishing those surfaces, has hitherto deprived us of the advantages
+which would result from the use of telescopic lenses entirely free
+from spherical aberration. In Lighthouse lenses, where so near an
+approach to accurate convergence to a single focus is unnecessary,
+every purpose is answered by the partial correction of aberration which
+may be obtained, by determining an average radius of curvature for
+the central disc, and for each successive belt or ring, as you recede
+from the vertex of the lens. In the lenses originally constructed for
+FRESNEL by SOLEIL, the zones were united by means of small _dowels_
+or _joggles_ of copper, passing from the one zone into the other; but
+the greater exactness of the workmanship now attained, has rendered it
+safe to dispense with those fixtures; and the compound lens is now held
+together solely by a metallic frame and the close union between the
+concentric faces of the rings, which, however, are in contact with each
+other at surfaces of only ¹⁄₄ inch in depth, as shewn in Plate XII. It
+is remarkable, that an instrument, having about 1300 square inches of
+surface, and weighing 109 lb., and which is composed of so many parts,
+should be held together by so slender a bond as two narrow strips of
+polished glass, united by a thin film of cement.
+
+I now proceed to the formulæ employed by FRESNEL, to determine the
+elements of the compound lens,[56] in the calculation of which two
+cases occur, viz., the central disc and a concentric ring. The focal
+distance of the lens and the refractive index of the glass are the
+principal data from which we start.
+
+  [56] It may be proper to mention that, while the formulæ given
+  in the text are those of M. FRESNEL, I am responsible for the
+  investigations in the Notes; I have, at the same time, much pleasure
+  in acknowledging my obligations, at various times (about ten years
+  ago), to Mr EDWARD SANG, and (more recently) to Mr WILLIAM SWAN, for
+  their kind advice on this part of the subject.
+
+[Illustration: Fig. 54.]
+
+I begin with the case of the central disc or lens round which the
+annular rings are arranged. Its principal section is a mixtilinear
+figure (fig. 54) composed of a segment _b_ _a_ _c_, resting on a
+parallelogram _b_ _c_ _d_ _e_, whose depth _b_ _d_ or _c_ _e_ is
+determined by the strength which is required for the joints which unite
+the various portions of the lens. Those particulars have, as I already
+stated, been determined with so much judgment by FRESNEL and the
+dimensions of the lenses so varied to suit the case of various lights,
+that nothing in this respect remains to be done by others.
+
+[Illustration: Fig. 55.]
+
+Referring to fig. 55, we have, for obtaining the radius of the central
+disc, the following formulæ, in which
+
+_r_ = AB, half the aperture of the lens
+
+_r′_ = AB′
+
+φ = AF, the focal distance
+
+_t′_ = A _a_, the thickness of the lens at the vertex
+
+_t″_ = B _b_, the thickness of the joint
+
+μ = the index of refraction
+
+ρ = the radius of curvature.
+
+Then for the radius of curvature near the axis we have:
+
+              (    _t′_)
+  ρ′ = (μ - 1)(φ + ----)
+              (     μ  )
+
+and for that near the margin we have:
+
+             r
+  tan _i′_ = -
+             φ
+
+            sin _i′_
+  sin _e_ = --------
+                μ
+
+  _r′_ = _r_ - _t″_ . tan _e_
+
+            _r′_
+  tan _i_ = ----
+              φ
+
+          sin _i_
+  sin ε = -------
+             μ
+
+          _r_
+  ρ″ = ---------√(μ² - 2 μ cos _e_ + 1)
+       μ sin _e_
+
+and, finally
+
+      ρ′ + ρ″[57]
+  ρ = -------
+         2
+
+  [57] The following steps lead to the formulæ given in the text. Let
+  APQB (fig. 56) represent a section of the central lens by a plane
+  passing through its axis AF; F the focus for incident rays; and FQPH
+  the path of a ray refracted finally in the direction PH, parallel to
+  the axis. Let C be the centre of curvature, then PC is a normal to
+  the curve at P; and, producing PQ to meet the axis in G, we have G
+  the focus of the rays, after refraction at the surface BQ.
+
+  [Illustration: Fig. 56.]
+
+  Then
+
+      sin PCG   PG
+  μ = ------- = --;
+      sin GPC   CG
+
+  and also
+
+      sin QFG   QG
+  μ = ------- = --
+      sin QGF   QF
+
+  Now, as P approaches A, we have ultimately PG = AG, QG = BG, and QF =
+  BF;
+
+  Therefore, putting AG = θ and AC = ρ′
+
+      AG =    θ        BG   θ - _t′_
+  μ = -- = ------; μ = -- = --------,
+      CG = θ - ρ′      BF      φ
+
+  from which μ θ - μ ρ′ = θ; and μ φ = θ - _t′_ and eliminating θ, we
+  have μ² φ + μ ρ′ = μ φ + _t′_, whence, as above,
+
+              (    _t′_)
+  ρ′ = (μ - 1)(φ + ----)
+              (     μ  )
+
+  But as this value of the radius of curvature, as already stated,
+  is calculated for rays near the axis, it would produce a notable
+  aberration for rays incident on the margin of the lens. In order,
+  therefore, to avoid the effects of aberration as much as possible, a
+  second radius of curvature must be calculated, so that rays incident
+  on the margin of the lens may be refracted in a direction parallel to
+  the axis. This second value of the radius is called ρ″ in the text,
+  and is found as follows (referring to fig. 57):
+
+  Let FB′ _b_ _x_ be the course of a ray refracted in the direction
+  _b_ _x_ parallel to the axis A _x′_. This ray meets the surface AB in
+  the point B′, whose position may be found approximately by tracing
+  the path of the ray FB, on the supposition that the surface of the
+  refracting medium is produced in the directions AB, _a′_ _b′_.
+
+  [Illustration: Fig. 57.]
+
+  Let C be the centre of curvature (see fig. 57)
+
+  α = AC _b_ the angle of emergence
+
+  η = B′_b_ C the second angle of refraction
+
+  ε = B b B′ the first angle of refraction
+
+  _i_ = B′FA the first angle of incidence
+
+  _i′_ = BFA
+
+  _e_ = _b′_ B _b_
+
+  AB = _r_
+
+  AB′ = _r′_
+
+  B _b_ = _t″_ the thickness of the lens at the edge
+
+  AF = φ the focal distance.
+
+  Then
+
+             _r_            sin _i′_
+  tan _i′_ = ---; sin _e_ = --------
+              φ                μ
+
+  whence _b_ _b′_ = _t″_ tan _e_ becomes known.
+
+  Now, since BB′ = _b_ _b′_ nearly, AB′ = AB - _b_ _b′_ or _r′_ = _r_ -
+  _t″_ tan _e_.
+
+  From this is obtained the angle of incidence _i_, and the first angle
+  of refraction ε; for
+
+            _r′_             sin _i_
+  tan _i_ = ---- and sin ε = -------.
+              φ                 μ
+
+  Next B′ _b_ C = B _b_ C - B _b_ B′ or η = α - ε and sin α = μ sin η =
+  μ sin (α - ε)
+
+                                          sin α
+  from which, sin α cos ε - cos α sin ε = -----
+                                            μ
+
+               (        1)
+  whence sin α (cos ε - -) = cos α sin ε; and
+               (         μ)
+
+         (         2 cos ε    1)
+  sin² α (cos² ε - ------- + --) = cos² α sin² ε =
+         (            μ      μ²)
+
+  (1 - sin² α) sin² ε = sin² ε - sin² α sin² ε
+
+  Then transposing we have
+
+         {                    2 cos ε    1}
+  sin² α {(cos² ε + sin² ε) - ------- + --} = sin² ε
+         {                       μ      μ²}
+
+  and because (cos² ε + sin² ε) = 1 we have, by dividing,
+
+                 sin² ε              μ² sin² ε
+  sin² α = ------------------ = ------------------
+           {    2 cos ε    1}   μ² - 2 μ cos ε + 1
+           {1 - ------- + --}
+           {       μ      μ²}
+
+  and
+
+                 μ sin ε
+  sin α = ---------------------
+          √(1 - 2 μ cos ε + μ²)
+
+  Next, since
+
+           _a′_ _b_     _r_
+  _b_ C = ---------- = -----,
+          sin AC _b_   sin α
+
+  putting C _b_ = _ρ″_, and substituting we have
+
+           _r_
+  _ρ″_ = ------- √(μ² - 2 μ cos ε + 1)
+         μ sin ε
+
+  and, taking for the radius of curvature, the mean of _ρ′_ and _ρ″_
+  the values calculated for the central and marginal rays, we have
+  finally
+
+      ρ′ + ρ″
+  ρ = -------
+         2
+
+[Illustration: Fig. 58.]
+
+I come next to the _second_ case, which concerns the calculation of
+the elements of a concentric ring. The section _a_ _b_ _c_ _d_ _e_
+(fig. 58) of one of those rings includes a mixtilinear triangle
+_a_ _b_ _e_, and a rectangle _b_ _c_ _e_ _d_, the thickness _b_ _c_
+being the same as that of the edge of the central disc; and the
+elements to be determined are the radius of the curve surface, and the
+position of the centre of curvature, with reference to the vertex of
+the lens.
+
+[Illustration: Fig. 59.]
+
+The radius of curvature of the zone may be calculated by the following
+formulæ, in which (see fig. 59)
+
+_r_₁ = AB the distance of the outer margin of the zone from the axis of
+the lens
+
+_r_₂ = AE the distance of the inner margin from the axis
+
+_l_ = BE the breadth of the zone = _r_₁ - _r_₂
+
+ρ = the radius of curvature = _b_ C = _m_ C
+
+φ = focal distance AF
+
+_t_ = thickness of the joint B _b_
+
+_t″_ = B _b_
+
+μ = refractive index of the glass
+
+_i_₁ = BFA
+
+_i_₂ = EFA
+
+                   _r_₁              _r_₂
+  Then tan _i′_₁ = ----; tan _i′_₂ = ----
+                     φ                 φ
+
+             sin _i′_₁             sin _i′_₂
+  sin _e_₁ = ---------; sin _e_₂ = ---------
+                _μ_                   _μ_
+
+  _r′_₁ = _r_₁ - _t″_ sin _e_₁; _r′_₂ = _r_₂ - _t″_ sin _e_₂
+
+             _r′_₁             _r′_₂
+  tan _i_₁ = -----; tan _i_₂ = -----
+               φ                 φ
+
+          sin _i_₁           sin _i_₂
+  sin ε = --------; sin ε′ = --------
+              μ                  μ
+
+                  μ sin ε
+  sin α = ---------------------;
+          √(μ² - 2 μ cos ε + 1)
+
+                  μ sin ε′
+  sin α′ = ---------------------; η = α′ - ε′
+           √(μ² - 2 μ cos ε′ + 1)
+
+                                2 cos ε′
+  and lastly ρ = --------------------------------------
+                 2 cos {η + ¹⁄₂(α - α′)} sin ¹⁄₂(α - α′)
+
+which is FRESNEL’S value of the radius of curvature.[58]
+
+  [58] The following steps will conduct us to this expression:
+
+  [Illustration: Fig. 60.]
+
+  Let B _b_ _f_ E (fig. 60) represent the section of a zone by a plane
+  passing through the axis of the lens AF, C the centre of curvature,
+  F the radiant point, and FB′ _b_ _x_, FE′ _m_ _x′_ the course of the
+  extreme rays which are transmitted through the zone (and the latter
+  of which passes from E′ to _e_ through a portion of the zone or lens
+  in contact with that under consideration). Then putting
+
+  AB = _r_₁; AB′ = _r′_₁; C _b_ = ρ
+
+  AE = _r_₂; AE′ = _r′_₂; B _b_ = _t″_; BE = _r_₁ - _r_₂ = _l_
+
+  ε = the first angle of refraction _b_ B′ _k_
+
+  η = the second angle of refraction B′ _b_ C
+
+  ε′ = the first angle of refraction _e_ E _k′_
+
+  η′ = the second angle of refraction _e_ _m_ C
+
+  α = the angle of emergence _b_ C _q_
+
+  α′ = the angle of emergence _m_ C _q_
+
+  _i′_₁ = BFA; _i′_₂ = EFA; _i_₁ = B′FA; _i_₂ = E′FA
+
+  _e_₁ = B _b_ B′; _e_₂ = E _e_ E′.
+
+  Proceeding exactly as in the case of the central lens we shall have
+
+              BA   _r_₁              EA   _r_₂
+  tan _i′_₁ = -- = ----; tan _i′_₂ = -- = ----
+              AF     φ               AF     φ
+
+             sin _i′_₁             sin _i′_₂
+  sin _e_₁ = ---------; sin _e_₂ = ---------
+                  μ                    μ
+
+  _r′_₁ = _r_₁ - _t″_ sin _e_₁; _r′_₂ = _r_₂ - _t″_ sin _e_₂
+
+             _r′_₁             _r′_₂
+  tan _i_₁ = -----; tan _i_₂ = -----
+               φ                 φ
+
+          sin _i_₁           sin _i′_₂
+  sin ε = --------; sin ε′ = ---------
+              μ                  μ
+
+                 μ sin ε                             μ sin ε′
+  sin α = ---------------------; and sin α′ = ----------------------
+          √(μ² - 2 μ cos ε - 1)               √(μ² - 2 μ cos ε′ + 1)
+
+  Now, the angle _b_ C _m_ = α - α′ from which (since the triangle
+  _b_ _m_ C is isosceles) _b_ _m_ C = 90° - ¹⁄₂ (α - α′); also, in the
+  triangle _b_ _m_ _e_, the angle _b_ _m_ _e_ = _b_ _m_ C - _e_ _m_ C =
+  90° - ¹⁄₂ (α - α′) - η and _b_ _e_ _m_ = _k′_ _e_ E′ = 90° - ε′
+
+  We have therefore in the triangle _b_ _m_ _e_
+
+            _b_ _e_ sin _b_ _e_ _m_         _l_ cos ε′
+  _b_ _m_ = ----------------------- = ---------------------
+               sin _b_ _m_ _e_        cos {η + ¹⁄₂ (α - α′)}
+
+  and in _b_ _m_ C
+
+          _b_ _m_ sin _b_ _m_ C      _l_ cos ε′ cos ¹⁄₂ (α - α′)
+  _b_ C = --------------------- = ----------------------------------
+              sin _b_ C _m_       cos (η + ¹⁄₂ (α - α′)) sin (α - α′)
+
+                  _l_ cos ε′ cos ¹⁄₂ (α - α′)
+  = --------------------------------------------------------
+    cos {η + ¹⁄₂ (α - α′)} 2 sin ¹⁄₂ (α - α′) cos ¹⁄₂ (α - α′)
+
+  from which, putting _b_ C = ρ
+
+                    _l_ cos ε′
+  ρ = ---------------------------------------
+      2 cos {η + ¹⁄₂ (α - α′)} sin ¹⁄₂ (α - α′)
+
+Lastly, the position of C the centre of curvature for a ring is easily
+determined by two co-ordinates in reference to their origin, A, which
+is the vertex of the lens (see fig. 60 below), by the equations:
+
+  CG = ρ . sin α - _a_ _b_ = ρ . sin α - _r_₁
+
+  CQ = ρ . cos α - _q_ Q = ρ . cos α - _t″_
+
+The elements of each successive zone are determined in the same manner.
+The annular lens of the first order of lights in FRESNEL’S system
+consists, as already stated, of a central disc 11 inches in diameter,
+and 10 concentric rings, all of which have a common principal focus,
+where the rays of the sun meet after passing through the lens. With
+such accuracy are those rings and the disc ground and placed relatively
+to each other, that the position of the actual conjugate focus of the
+entire surface of the compound lens, differs in a very small degree
+from that obtained by calculation in the manner described below.[59]
+
+  [59]
+
+  ~Testing Lenses.~
+
+  The tests generally applied for examining the lenses used in
+  Lighthouses, is to find the position of the conjugate focus _behind_
+  the lens, due to a given position of a lamp in _front_ of it. This
+  test depends on the following considerations:--Draw a line from an
+  object O in front of a lens, to any point Q in the lens; and from A,
+  the centre of the lens, draw AR parallel to OQ, and cutting a line
+  RF _r_ which passes through the principal focus F, at right angles
+  to the axis of the lens; then join the points Q and R, and produce
+  the line joining them: I, the image of O must be in that line. In
+  the same way, draw a line from O to _q_, another point in the lens
+  on the other side of its axis, and parallel to it draw A _r_ from
+  the centre of the lens, cutting the plane of the principal focus in
+  _r_. Join _q_ _r_, in which line the image will lie; and hence the
+  intersection of OR and _q_ _r_, in I, will be the point in which the
+  image of O is formed, or will be the conjugate focus of the lens due
+  to the distance OA. This mode will serve to give the distance of
+  the conjugate focus of a lens (_neglecting its thickness_) for rays
+  falling on its surface at any angle.
+
+  [Illustration: Fig. 61.]
+
+  We shall suppose QA (fig. 61) to represent the half of a lens, and
+  remembering the conditions described in reference to the last figure,
+  we shall at once perceive the truth of the following analogy (fig.
+  62):--
+
+  [Illustration: Fig. 62.]
+
+  OA ∶ AF ∷ AQ ∶ FR ∷ AI ∶ FI, and putting OA = δ, AI = φ′, and AF
+  = φ, we have δ ∶ φ ∷ φ′ ∶ φ′ - φ, and, consequently, δ φ′ - δ φ =
+  φ φ′; and hence the following equations, which express the relations
+  subsisting between the principal focus of the lens and the distance
+  of any object and its corresponding image:
+
+  1_st_, To find the principal focal distance of a lens from the
+  measured position of its object and its image refracted through it,
+  we have,
+
+       δ φ′
+  φ = ------.
+      δ + φ′
+
+  2_d_, For the distance of the object, when that of the image is
+  known, we have,
+
+        φ φ′
+  δ = ------.
+      φ′ - φ
+
+  3_d_, For the position of the image, when that of the object is
+  known, we have,
+
+        δ φ
+  φ′ = -----.
+       δ - φ
+
+  [Illustration: Fig. 63.]
+
+  In testing lenses, of course, it is this last equation which we use,
+  because the value of φ or the principal focus is always known, and
+  is that whose accuracy we wish to try, while δ may be chosen within
+  certain limits at will. I have found that the best mode of proceeding
+  is the following:--In front of the lens Q _q_ (see fig. 63) firmly
+  fixed on a frame, place a lamp at O at the distance of about 50
+  yards. Calculate the value of φ′ due to 50 yards, which in this case
+  is equal to AF′, OA being equal to δ; and move a screen of white
+  paper backwards and forwards until you receive on it the smallest
+  image that can be formed, which is at the point where the cones of
+  converging and diverging rays meet. The image will always increase
+  in size whether you approach nearer to the lens or recede farther
+  from it, according as you pass from the converging into the diverging
+  cone of rays, or _vice versa_; and hence the intermediate point is
+  easily found by a very little practice. The distance from the centre
+  of the lens to the face of the screen, which must be adjusted so as
+  to be at right angles to a line joining the centre of the lens and
+  the lamp, is then measured; and its agreement with the calculated
+  length of φ′, is an indication of the accuracy of the workmanship of
+  the lens. When the measured distance is greater than the calculated
+  φ′, we know that the lens is too flat; and it is on this side the
+  error generally falls. On the other hand, when φ′ is greater than the
+  measured distance, we know that the lens has too great convexity. I
+  have only to add, that an error of ¹⁄₆₀ on the value of φ′ may be
+  safely admitted in Lighthouse lenses; but I have had many instruments
+  made by M. FRANÇOIS SOLEIL, whose error fell below ¹⁄₈₀ of φ′. Owing
+  probably to the mode of grinding, the surfaces of all the lenses I
+  have yet examined are somewhat too flat.
+
+  ~Divergence of Annular Lenses.~
+
+In the combination of lenses with the flame of a lamp, similar
+considerations must influence us in making the necessary arrangements,
+as in the case of reflectors. We have already seen that the size of
+the flame and its distance from the surface of reflecting instruments
+have an important practical bearing on the utility of the instrument,
+and that the divergence of the resultant beam materially affects its
+fitness for the purpose of a Lighthouse. So also, in the case of the
+lens, unless the diameter of the flame of the lamp has to the focal
+distance of the instrument a relation such as may cause an appreciable
+divergence of the rays refracted through it, it could not be usefully
+applied to a Lighthouse; for, without this, the light would be in sight
+during so short a time, that the seaman would have much difficulty
+in observing it. To determine the amount of this divergence of the
+refracted beam, therefore, is a matter of great practical importance,
+and I shall briefly point out the conditions which regulate its amount,
+as they are nearly identical with those which determine the divergence
+of a paraboloïdal mirror illuminated by a lamp in its focus. The
+divergence, in the case of lenses, may be described as _the angle which
+the flame subtends at the principal focus of the lens_, the maximum of
+which, produced at the vertex of FRESNEL’S great lens by the lamp of
+four concentric wicks, is about 5° 9′.[60]
+
+  [60]
+
+  This will be easily seen by examining the annexed figure (64), in
+  which Q _q_ represents the lens. A its centre, F the principal
+  focus, _b_ F and _b′_ F the radius of the flame; then is the angle
+  _b_ A _b′_ equal to the maximum divergence of the lens.
+
+               _b_ F                  Rad. of flame
+  Sin _b_ AF = ----- = sin _b′_ AF = --------------;
+                AF                   Focal distance
+
+  and twice _b_ AF = the whole divergence at A. Then for the divergence
+  at the margin of the lens, or at any other point, we have, FQ = √(AQ²
+  + AF²) and Q _x_ = √(QF² + F _x_²); and for any angle at Q, we have
+
+               F _x_
+  sin FQ _x_ = -----.
+                 FQ
+
+  [Illustration: Fig. 64.]
+
+  ~Illuminating Power of Lenses.~
+
+On the subject of the illuminating power of the lenses, it seems
+enough to say, that the same general principle regulates the estimate
+as in reflectors. Owing to the square form of the lens, however,
+there is a greater difficulty in finding a _mean focal distance_
+whereby to correct our estimate of the angle subtended by the light,
+so as to equate the varying distance of the several parts of the
+surface; but, practically, we shall not greatly err if we consider the
+_quotient of the surface of the lens divided by the surface of the
+flame_ as the increased power of illumination by the use of the lens.
+The illuminating effect of the great lens, as measured at moderate
+distances, has generally been taken at 3000 Argand flames, the value
+of the great flame in its focus being about 16, thus giving its
+increasing power as nearly equal to 180. The more perfect lenses have
+produced a considerably greater effect.
+
+  ~Arrangement of the Lenses in a Lighthouse.~
+
+The application of lenses to Lighthouses is so obvious as scarcely
+to admit of farther explanation than simply to state, that those
+instruments are arranged round a lamp placed in their centre, and on
+the level of the focal plane in the manner shewn in Plates XIII. and
+XIV.,[61] so as to form by their union a right octagonal hollow prism,
+circulating round the flame which is fixed in the centre, and shewing
+to a distant observer successive flashes or blazes of light, whenever
+they cross a line joining his eye and the lamp, in a manner similar to
+that already noticed in describing the action of the mirrors. The chief
+difference in the effect consists in the greater intensity and shorter
+duration of the blaze produced by the lens; which latter quantity is,
+of course, proportional to the divergence of the resultant beam. Each
+lens subtends a central horizontal pyramid of light of about 46° of
+inclination, beyond which limits the lenticular action could not be
+advantageously pushed, owing to the extreme obliquity of the incidence
+of light; but FRESNEL at once conceived the idea of pressing into the
+service of the mariner, by means of two very simple expedients, the
+light which would otherwise have uselessly escaped above and below the
+lenses.
+
+  [61] The Plates shew the nature of the mechanical power which gives
+  movement to the lenses. It consists of a clockwork movement driven
+  by a weight which sets in motion a plate bearing brackets that carry
+  the lenses. All this, however, can be seen from the Plates; and I am
+  unwilling to expend time in a detailed explanation of what is obvious
+  by inspection.
+
+  ~Pyramidal Lenses and Mirrors.~
+
+For intercepting the upper portion of the light, FRESNEL employed
+eight smaller lenses of 500 mm. focal distance (19·68 inches) inclined
+inwards towards the lamp, which is also their common focus and thus
+forming, by their union, a frustum of a hollow octagonal pyramid of
+50° of inclination. The light falling on those lenses is formed into
+eight beams parallel to the axis of the smaller lenses, and rising
+upwards at an angle of 50° inclination. Above them are ranged eight
+plane mirrors, so inclined (see Plates XIII. and XIV.) as to project
+the beams transmitted by the small lenses in the horizontal direction,
+so as finally to increase the effect of the light. In placing those
+upper lenses, it is generally thought advisable to give their axis an
+horizontal deviation of 7° or 8° from that of the great lenses and in
+the direction contrary to that of the revolution of the frame which
+carries the lenticular apparatus. By this arrangement, the flashes of
+the smaller lenses precede that of the large ones, and thus tend to
+correct the chief practical defect of revolving lenticular lights by
+prolonging the bright periods. The elements of the subsidiary lenses
+depend upon the very same principles, and are calculated by the same
+formulæ as those given for the great lenses. In fixing the focal
+distance and inclination of those subsidiary lenses, FRESNEL was guided
+by a consideration of the necessity for keeping them sufficiently
+high to prevent interference with the free access to the lamp. He also
+restricted their dimensions within very moderate limits, so as to avoid
+too great weight. The focal distance is the same as that for lenses of
+the third order of lights.
+
+  ~Curved Mirrors.~
+
+[Illustration: Fig. 65.]
+
+Owing to the necessary arrangements of a lantern, only a very small
+portion of those rays, which escape from below the lenses, can be
+rendered available for the purposes of a Lighthouse; and any attempt
+to subject it to lenticular action, so as to add it to the periodic
+flashes, would have led to a most inconvenient complication of the
+apparatus. FRESNEL adopted the more natural and simple course of
+transmitting it to the horizon in the form of flat rings of light, or
+rather of divergent pencils, directed to various points of the horizon.
+This he effected by means of small curved mirrors, disposed in tiers,
+one above another, like the leaves of a Venetian blind--an arrangement
+which he also adopted (shewn in Plates XV. and XVI.) for intercepting
+the light which escapes above as well as below the dioptric belt in
+fixed lights. Those curved mirrors are, strictly speaking, generated
+(see fig. 65) by portions, such as a b, of parabolas, having their
+foci coincident with F, the common flame of the system. In practice,
+however, they are formed as portions of a curved surface, ground by the
+radius of the circle, which osculates the given parabolic segment.[62]
+The mirrors are plates of glass, silvered on the back and set in
+flat cases of sheet-brass. They are suspended on a circular frame
+by screws, which are attached to the backs of the brass cases, and
+which afford the means of adjusting them to their true inclination, so
+that they may reflect objects on the horizon of the Lighthouse to an
+observer’s eye, placed in the common focus of the system.[63]
+
+  [62] To find the radius and centre of a circle, which shall osculate
+  a given parabola, whose focus is in F, draw the normals to the curve
+  from _p_ and P, meeting in O, and draw N _e_ parallel to a tangent
+  of the curve, or to _p_ P, then P O or _p_ O is the radius required.
+  Now, we have similar triangles P _p_ _d_ and N _e_ _n_, and P H
+  and _p_ _h_ are (proximate) ordinates; hence we have the following
+  analogies:--
+
+  P _d_ ∶ P _p_ ∷ PH ∶ PN
+
+  N _e_ ∶ N _n_ ∷ PH ∶ PN
+
+  [Illustration: Fig. 66.]
+
+  Hence compounding those ratios (in which P _d_ = N _n_ nearly)
+
+  N _e_ ∶ P _p_ ∷ PH² ∶ PN²
+
+  also N _e_ ∶ P _p_ ∷ NO ∶ PO,
+
+  (for O P _p_ and N _o_ _e_ are similar triangles)
+
+  PH² ∶ PN² ∷ NO ∶ OP,
+
+  then PN²- PH² = HN²
+
+  and PO - NO = NP,
+
+  therefore HN² ∶ PN² ∷ NP ∶ PO,
+
+  and finally,
+
+       PN³
+  PO = ---.
+       HN²
+
+  Then put FP = HC = FN = ρ; HN = ρ - _z_; then as FP² - FH² = PH² = ρ²
+  - _z_²
+
+  PN² = PH² + HN² = (ρ² - _z_²) + (ρ² - 2 ρ _z_ + _z_²)
+
+  = 2 ρ² - 2 ρ _z_
+
+  PN = √(2 ρ (ρ - _z_))
+
+  Therefore
+
+       √{2 ρ (ρ - _z_)}³
+  PO = ----------------
+          (ρ - _z_)²
+
+    √({2 ρ (ρ - _z_)}³)
+  = ------------------
+        (ρ - _z_)⁴
+
+                          (   ρ³  )
+  and finally, PO = 2 √2 √(-------)
+                          (ρ - _z_)
+
+  [Illustration: Fig. 67.]
+
+  To find the versed sine of the curvature (which may be useful in the
+  examination of the mirrors by a mould) we may proceed (see fig. 67) to
+
+  put AG = _f_; BE = C; AC = R
+
+  then BG² = AG . GD
+
+  4 BG² = BE² = 4 AG . GD
+
+  C² = 4 _f_ . (2 R - _f_)
+
+  C² = 8 _f_ R - 4 _f_²
+
+  From which equation,
+
+                                  C²      C⁴
+  2 _f_ - 2 R = ± √(4 R² - C²) = ---  - ----- &c.
+                                 4 R    64 R³
+
+           C²     C⁴
+  2 _f_ = --- - -----
+          4 R   64 R³
+
+         C²      C⁴
+  _f_ = --- - -------.
+        8 R    128 R³
+
+  [Illustration: Fig. 68.]
+
+  In order to test the accuracy of the workmanship of the mirrors,
+  recourse must again be had, as in the case of the lenses and
+  parabolic mirrors, to the formula of conjugate foci, in which we
+  shall call R = the radius of curvature of the mirror M _m_ (fig. 68);
+  _a_ = the distance of a light, _f_, which is arbitrarily placed in
+  front of the mirror; and _b_ = the distance of a moveable screen S,
+  on which the rays reflected from the mirror may converge in a focus.
+  We must find the distance _b_, at which, with any given distance _a_,
+  such convergence should take place.
+
+  _f_ M′ = _a_
+
+  SM′ = _b_
+
+  OM′ = R
+
+  Then (because _f_ MS is bisected by OM, and for points near the
+  vertex of the mirror at M′)
+
+  SM′ ∶ _f_ M′ ∷ SO ∶ O _f_
+
+  or _b_ ∶ _a_ ∷ R - _b_ ∶ _a_ - R
+
+  _a_ _b_ - R _a_ = R _b_ - _a_ _b_.
+
+                     R _a_
+  From which _b_ = ---------,
+                   2 _a_ - R
+
+  the distance required, in which an error of ¹⁄₃₀ (of its whole
+  length) may be safely admitted.
+
+  [63] At such times when the horizon cannot be seen, the mirror may
+  be placed, by means of a _clinometer_, with a spirit-level, set to
+  the proper angle, which may be easily mechanically determined as
+  follows: Draw a line from the focus F through the point O, where the
+  centre of the mirror is to be, producing it beyond that point to a
+  convenient distance at I; through O draw HOH, parallel to the horizon
+  FH; bisect IOH by MOM, which coincides with a tangent to the mirror
+  at its centre O; and MOH is the angle required to be laid off, or its
+  complement.
+
+  [Illustration: Fig. 69.]
+
+  ~Cylindric Refractors for Fixed Lights.~
+
+Having once contemplated the possibility of illuminating Lighthouses by
+dioptric means, FRESNEL quickly perceived the advantage of employing
+for fixed lights a lamp placed in the centre of a polygonal hoop,
+consisting of a series of refractors, _infinitely small_ in their
+length and having their axes in planes parallel to the horizon. Such a
+continuation of vertical sections, by refracting the rays proceeding
+from the focus, only in the vertical direction, must distribute a zone
+of light _equally brilliant_ in every point of the horizon. This effect
+will be easily understood, by considering the middle vertical section
+of one of the great annular lenses, already described, abstractly
+from its relation to the rest of the instrument. It will readily be
+perceived that this section possesses the property of simply refracting
+the rays _in one plane coincident with the line of the section_ and
+in a direction parallel to the horizon, and cannot collect the rays
+from either side of the vertical line; and if this section, by its
+revolution about a vertical axis, becomes the generating line of the
+enveloping hoop, above noticed, such a hoop will of course possess the
+property of refracting an equally diffused zone of light round the
+horizon. The difficulty, however, of forming this apparatus appeared so
+great, that FRESNEL determined to substitute for it a vertical polygon,
+composed of what have been improperly called _cylindric lenses_, but
+which in reality are mixtilinear and horizontal prisms, distributing
+the light which they receive from the focus nearly equally over the
+horizontal sector which they subtend. This polygon has a sufficient
+number of sides to enable it to give, at the angle formed by the
+junction of two of them, a light not very much inferior to what is
+produced by one of the sides; and the upper and lower courses of curved
+mirrors are always so placed as partly to make up for the deficiency of
+the light at the angles. The effect sought for in a fixed light is thus
+obtained in a much more perfect manner, than by any combination of the
+parabolic mirrors used in the British Lighthouses.
+
+  ~Application of crossed prisms to cause occasional flashes.~
+
+An ingenious modification of the fixed apparatus is also due to
+the inventive mind of FRESNEL, who conceived the idea of placing
+one apparatus of this kind in front of another, with the axis of
+the cylindric pieces crossing each other at right angles. As those
+cylindric pieces have the property of refracting all the rays which
+they receive from the focus, in a direction perpendicular to the
+mixtilinear section which generates them, it is obvious that if two
+refracting media of this sort be arranged as above described, their
+joint action will unite the rays which come from their common focus
+into a beam, whose sectional area is equal to the overlapped surface
+of the two instruments, and that they will thus produce, although in
+a disadvantageous manner, the effect of an annular lens. It was by
+availing himself of this property of crossed prisms, that FRESNEL
+invented the distinction for lights, which he calls _a fixed light
+varied by flashes_; in which the flashes are caused by the revolution
+of cylindric refractors with vertical axes, ranged round the outside of
+the fixed light apparatus already described.
+
+  ~True Cylindric form given to the Refractors and other improvements
+  in their Construction.~
+
+Having been directed by the Commissioners of the Northern Lighthouses
+to convert the fixed catoptric light of the Isle of May, into a
+dioptric light of the first order, I proposed, that an attempt should
+be made to form a true cylindric, instead of a polygonal belt for the
+refracting part of the apparatus; and this task was successfully
+completed by Messrs COOKSON of Newcastle in the year 1836. The
+disadvantage of the polygon lies in the excess of the radius of
+the circumscribing circle over that of the inscribed circle, which
+occasions an unequal distribution of light between its angles and the
+centre of each of its sides; and this fault can only be fully remedied
+by constructing a cylindric belt, whose generating line is the middle
+mixtilinear section of an _annular_ lens, revolving about a vertical
+axis passing through its principal focus. This is, in fact, the only
+form which can possibly produce an equal diffusion of the incident
+light over every part of the horizon.
+
+I at first imagined that the whole hoop of refractors might be built
+between two metallic rings, connecting them to each other solely by
+the means employed in cementing the pieces of the annular lenses;
+but a little consideration convinced me that this construction would
+make it necessary to build the zone at the lighthouse itself, and
+would thus greatly increase the risk of fracture. I was therefore
+reluctantly induced to divide the whole cylinder into ten arcs, each of
+which being set in a metallic frame, might be capable of being moved
+separately. The chance of any error in the figure of the instrument
+has thus a probability of being confined within narrower limits;
+whilst the rectification of any defective part becomes at the same
+time more easy. One other variation from the mode of construction at
+first contemplated for the Isle of May refractors, was forced upon
+me by the repeated failures which occurred in attempting to form the
+middle zone in one piece; and it was at length found necessary to
+divide this belt by a line passing through the horizontal plane of the
+focus. Such a division of the central zone, however, was not attended
+with any appreciable loss of light, as the entire coincidence of the
+junction of the two pieces with the horizontal plane of the focus,
+confines the interception of the light to the fine joint at which they
+are cemented. With the exception of those trifling changes, the idea
+at first entertained of the construction of the instrument was fully
+realised at the manufactory of Messrs COOKSON. I also, at a subsequent
+period, greatly improved the arrangement of this apparatus, by giving
+to the metallic frames which contain the prisms, a rhomboidal,[64]
+instead of a rectangular form. The junction of the frames being thus
+inclined from the perpendicular, do not in any azimuth intercept the
+light throughout the whole height of the refracting belt, but the
+interception is confined to a small rhomboidal space, whose area is
+inversely proportional to the sine of the angle of inclination; and if
+the helical joints be formed between the opposite angles of the old
+rectangular frames, the amount of intercepted light becomes absolutely
+equal in every azimuth.[65]
+
+  [64] The form would not be exactly rhomboidal, but would be a portion
+  of a flat helix intercepted between two planes, cutting the enveloped
+  cylinder at right angles to its axis.
+
+  [65] See my Report on the Refractors of the Isle of May Light, 8th
+  October 1836.
+
+[Illustration: Fig. 70.]
+
+Such an apparatus is shewn in Plate XVII.; and the accompanying
+diagram (fig. 70) shews an elevation ABCD, a section BD, and a plan
+ABD, of a single pannel of this improved compound belt. AC and BD
+are the diagonal joints above described. Time and perseverance, and
+the patience and skill of Monsieur FRANÇOIS SOLEIL, whom I urged to
+undertake the task, were at length crowned with success; and I had the
+satisfaction at last of seeing a fixed light apparatus, having its form
+truly cylindric, and its central belt in one piece, while the joints
+were inclined to the horizon at such an angle as to render the light
+perfectly equal in every azimuth.
+
+  ~Catadioptric Zones.~
+
+The loss of light by reflection at the surface of the most perfect
+mirrors, and the perishable nature of the material composing their
+polish, induced me, so far back as 1835, in a Report on the Light
+of Inchkeith, which had just been altered to the dioptric system,
+to propose the substitution of _totally reflecting_ prisms, even in
+lights of the first order or largest dimensions. In this attempt I was
+much encouraged by the singular liberality of Mr LEONOR FRESNEL, to
+whose friendship (as I have often, with much pleasure, acknowledged)
+I owe all that I know of dioptric Lighthouses. He not only freely
+communicated to me the method pursued by his distinguished brother
+AUGUSTIN FRESNEL, in determining the forms of the zones of the small
+apparatus, introduced by him into the Harbour Lights of France, and
+his own mode of rigorously solving some of the preliminary questions
+involved in the computations; but put me in possession of various
+important suggestions, which substantially embrace the whole subject.
+Another friend also helped me, by pointing out certain less direct
+methods of determining some of the elements, which greatly abridged the
+labours of computation. Mr FRESNEL agreed with me in anticipating a
+considerable increase of the light derived from the accessory part of
+the apparatus; but he expressed his opinion, that in order to prevent
+great absorption, the rings should not greatly exceed those of the
+small apparatus in their sectional area. This would have required about
+_forty_ rings to intercept the same quantity of light acted upon by
+the curved mirrors; and, although the difficulties of grinding were
+somewhat similar to those which had already been encountered in forming
+the cylindric belt for the Isle of May apparatus, there were also some
+special difficulties attending the formation of the catadioptric
+zones, which appeared so formidable as to deter me by the expense of
+grinding so many zones, and led me to think of adopting flint glass.
+Considerable masses, of a very pure and homogeneous appearance, had
+been shewn to me by the late Dr RITCHIE of the London University, who
+calculated upon the uniform and permanent success of his process;
+but, whatever foundation there might have been for this hope, it was
+removed by his death, which occurred soon afterwards, and I was forced
+to return to the idea of using crown glass. In order, therefore, to
+enable me to estimate more correctly the advantage of the zones, I
+procured from Messrs COOKSON of Newcastle, an average specimen of
+crown glass, of the thickness of 40 mm. (about 1¹⁄₂ inch), which is
+the distance traversed by the ray between its immergence into and its
+emergence out of the zones of the small apparatus; and having had it
+carefully polished, with both faces parallel, I found, as the result
+of numerous trials, conducted with every precaution I could think of,
+that the loss of light due to the transmission through it, was somewhat
+less than ²⁄₇ths of the incident light. According to the experiments
+of BOUGEUR, the loss by the two refractions may be assumed at ¹⁄₂₀th;
+so that we could not sensibly err in concluding that the whole loss
+due to the transmission of the light through the zones would not much
+exceed ²⁄₇ths of the incident light. In the lights of the first order,
+the loss by reflection from the surface of the mirrors, and by the
+escape of light through the interstices which separate them, is not
+less than ²⁄₃ds of the light incident on that part of the apparatus. On
+the most moderate expectation, therefore, which this proportion seemed
+to warrant, it appeared that, without any allowance for imperfections
+in the figure of the zones, at least _twice_ as much light would be
+transmitted through the zones as can be reflected by the mirrors. The
+prospect even of a part of this increase being obtained without the
+expenditure of more oil, seemed too important to be readily renounced,
+more especially when it was considered that the fixed lights, to which
+it chiefly applies, are necessarily much feebler than the revolving
+lights, as well as more numerous and more expensive. So many motives
+pressed me to the work, that I commenced my labours (during my leisure
+hours while engaged at the Skerryvore), and computed Tables of the
+Elements of 45 zones, whose lesser sides were 40 millimètres in
+length, which were printed in 1840. In 1841, in consequence of having
+seen at Paris specimens of purer crown glass, I printed other Tables
+from computations of larger zones, which I had made in 1838, but
+had discarded as unsuited to the inferior quality of English glass,
+whose absorption rendered the use of smaller dimensions of the zone
+imperative. In the first Table, I had adopted the form of isosceles
+triangles, to avoid the difficulty of grinding _annular_ surfaces with
+radii of great length (which I found required to be nearly 30 feet),
+but in the second Table, I adopted a suggestion, conveyed to me in
+a letter from M. LEONOR FRESNEL, by giving each zone the form of an
+oblique triangle whose base is the chord of the circle which osculates
+the surface of the reflecting side of the zone. Some attempts were made
+by Messrs COOKSON at Newcastle to execute the largest of the zones; but
+the forms differed so widely from the dimensions assigned in the Table,
+that I had begun to despair of success. About this time, I received a
+communication from M. FRESNEL, pointing out several inaccuracies in my
+Tables, and more especially directing my attention to the disadvantage
+of choosing, for the focus of the upper series of zones, a high part
+of the flame, as I had done with the view of throwing _all_ the light
+_below_ the horizon, so that none might be lost. He, at the same time,
+informed me of the success of M. FRANÇOIS SOLEIL, in executing zones
+for the smaller apparatus, known by the name of the Third Order; and
+put me in possession of the results of his computations of large zones
+of the First Order, suited to the greatly improved quality of the crown
+glass of St Gobain, with an invitation, before I should adopt his
+dimensions, to verify his calculations. This I willingly undertook,
+and computed the elements of the zones in M. FRESNEL’S Table afresh,
+with results differing from his only in one or two instances, to an
+amount whose angular value does not exceed more than 2″. The Table
+in the Appendix contains the result of my calculations, which are
+verifications of those of M. FRESNEL. The subject of the zones has
+thus been very fully weighed; and it is most satisfactory to think
+that complete success has attended the perseverance and ardour of
+M. FRANÇOIS SOLEIL, who at once boldly undertook to furnish for the
+Skerryvore Lighthouse the first catadioptric apparatus ever constructed
+on so magnificent a scale. On the 23d December 1843, M. FRESNEL
+announced, in a letter to me, the complete success which had attended
+a trial of the apparatus at the Royal Observatory at Paris, whereby it
+appeared that the illuminating effect of the cupola of zones, was to
+that of the seven upper tiers of mirrors of the first order, as 140
+to 87. Nothing can be more beautiful than an entire apparatus for a
+fixed light of the first order, such as that shewn in Plates XVII. and
+XVIII. It consists of a central belt of refractors, forming a hollow
+cylinder 6 feet in diameter, and 30 inches high; below it are six
+triangular rings of glass, ranged in a cylindrical form, and above a
+crown of thirteen rings of glass, forming by their union a hollow cage,
+composed of polished glass, 10 feet high and 6 feet in diameter! I know
+no work of art more beautiful or creditable to the boldness, ardour,
+intelligence, and zeal of the artist.
+
+I must now endeavour to trace the various steps by which the elements
+of the zones given in the appended Table have been determined; and
+this, I fear, I cannot do without considerable prolixity of detail.
+Referring to Plates XV., XVI., XVII., and XVIII., in which F shews the
+flame, RR, the refractors, and MRM and MRM, the spaces through which
+the light would escape uselessly _above_ and _below_ the lens, but for
+the corrective action of the mirrors MM, which project the rays falling
+on them to the horizon, I have to observe that a similar effect is
+obtained, but in a more perfect manner, by means of the zones ABC and
+A₂B₂C₂ (fig. 71, on page 271), whose action on the divergent rays of
+the lamp causes the rays FC, FB and FC₂, FB₂ to emerge horizontally, by
+refracting them at the inner surfaces BC, B₂C₂, reflecting them at AB,
+A₂B₂, and a second time refracting them at AC, A₂C₂.
+
+[Illustration: Fig. 71.]
+
+The problem proposed is, therefore, the determination of the elements
+and position of a triangle ABC, which, by its revolution about a
+vertical axis, passing through the focus of a system of annular
+lenses or refractors in F, would generate a ring or zone capable of
+transmitting in an horizontal direction by means of _total reflection_,
+the light incident upon its inner side BC from a lamp placed in the
+point F. The conditions of the question are based upon the well-known
+laws of _total reflection_, and require that all the rays coming from
+the focus F shall be so refracted at entering the surface BC, as to
+meet the side BA at such an angle, that instead of passing out they
+shall be _totally reflected_ from it, and passing onwards to the side
+CA shall, after a second refraction at that surface, finally emerge
+from the zone in an horizontal direction. For the solution of this
+problem, we have given the positions of F the focus, of the apex C of
+the generating triangle of the zone, the length of the side BC or CA,
+and the refractive index of the glass. The form of the zone must then
+be such as to fulfil the following conditions:--
+
+1. The extreme ray FB must suffer refraction and reflection at B, and
+pass to C, where being a second time refracted, it must follow the
+horizontal direction CH.
+
+2. The other extreme ray FC must be refracted in C and passing to A,
+must at the point be reflected, and a second time reflected, so as to
+follow the horizontal course AG (see fig. 72, on opposite page).
+
+These two propositions involve other two in the form of corollaries.
+
+1. That every intermediate ray proceeding from F, and falling upon BC
+in any point E, between B and C, must, after refraction at the surface
+BC in E into the direction EW, be so reflected at W from AB into the
+direction WI, that being parallel to BC, it shall, after a second
+refraction in I, at the surface AC, emerge horizontally in the line IK.
+
+And, 2. That the paths of the two extreme rays must therefore trace the
+position of the generating triangle of the zone.
+
+To these considerations it may be added, that as the angles BCH and FCA
+are each of them solely due to the refraction at C, as their common
+cause, they must be equal to each other, and BCA being common to both,
+the remaining angle ACH = the remaining angle BCF.
+
+We naturally begin by the consideration of the lowest ray FC, whose
+path being traced gives the direction of the two refracting sides BC
+and AC, leaving only the direction of the reflecting side BA to be
+determined. I shall not now explain the reason for neglecting entirely
+the consideration of the reflecting side at present, as I could not
+do so without anticipating what must be more fully discussed in the
+sequel; but I may content myself with stating, that as the positions of
+BC and AC depend upon the direction of the incident ray FC, and on the
+refractive index of the glass, this part of the investigation may be
+carried on apart from any interference with the reflecting side.
+
+As we know the relation existing between the angles of incidence and
+refraction, we might determine the relative positions of the sides AC
+and BC, by means of successive corrections obtained by protraction,
+tracing the paths of the rays from the horizontal directions backwards
+through the zones to the focus. This method, however, depends entirely
+upon accurate protraction, and is therefore unsatisfactory as a final
+determination, or if employed for any other purpose than that of
+affording a rough approximation to the value of the angle, a knowledge
+of which may occasionally save trouble in the employment of more exact
+means of determination. I have not, however, on any occasion employed
+this process, as I found that a little practice enabled me to make my
+first estimation very near the truth. I shall therefore at once proceed
+to give a view of the reasoning employed in the investigation.
+
+[Illustration: Fig. 72.]
+
+Referring to fig. 72, which shews the _first_ and _second_ zone of the
+upper series, we have
+
+            FL
+  Tan LCF = --;
+            CL
+
+and if we make
+
+  the known angle, SCF = α
+
+                   OCF = ξ = the complement of BCF = the angle of
+                             incidence for FC.
+
+                   DCΟ = γ = angle of refraction.
+
+                   LCF = θ = (HCF - 90°) = (2 α - 90°)
+
+                   SCD = (α + γ - ξ)
+
+               And _m_ = the index of refraction for crown glass,
+
+we obtain the means of determining the angles γ and ξ in two equations,
+which are based upon the relation between the angles of incidence and
+refraction, and on the interdependence of the various angles about C.
+These primary equations are:
+
+sin ξ = _m_ . sin γ
+
+and
+
+[66]γ = 2 ξ - θ (making 2 α - 90° = θ)
+
+  [66] The truth of the first of these equations (sin ξ = _m_ . sin
+  γ) which merely expresses the ratio of the sines of the angles of
+  incidence and refraction is obvious; but owing to the great number
+  of small angles about C, a little consideration may be required to
+  enable one to perceive the truth of the second. I therefore subjoin
+  the steps by which I reached it. It is obvious (see fig. 72), that
+  as ACH and BCF are equal, the line SC bisecting HCF must bisect
+  ACB. But the production of AC clearly gives SCD opposite and equal
+  to ACW and SCD is by construction = (α - ξ + γ) = (α + γ - ξ), and,
+  therefore, ACB, which is twice ACW or SCD = (2 α + 2 γ - 2 ξ). Now,
+  by construction OC is a normal to the refracting surface CB and its
+  production C _g_ gives AC _g_ = γ. But γ = ACB - _g_ CB = (2 α + 2 γ
+  - 2 ξ) - _g_ CB = (2 α + 2 γ - 2 ξ) - 90°, hence
+
+  γ = {2 α + 2 γ - 2 ξ} - 90°,
+
+  and γ - 2 γ = -γ = -2 ξ + (2 α - 90°) by transposition, and finally
+  changing signs, we have as above:
+
+  γ = 2 ξ - (2 α - 90°)
+
+    = 2 ξ - θ.
+
+Eliminating γ between these two equations we obtain:
+
+sin ξ = _m_ . sin (2 ξ - θ)
+
+an expression, which, after various transformations of circular
+functions, assumes the form
+
+            1                   (  1       )
+  sin⁴ ξ - --- sin θ . sin³ ξ + (------ - 1) . sin² ξ +
+           _m_                  (4 _m_²    )
+
+    1
+  ------ sin θ . sin ξ + ¹⁄₄ sin² θ = 0[67]
+  2 _m_
+
+  [67] This expression is equivalent to that of M. Fresnel, but
+  owing to a simplification in the fractional coefficients, it is
+  not _literally_ the same. I was led to it by the following steps,
+  starting from the original equation sin ξ = _m_ sin (2 ξ - θ)
+
+  sin ξ = _m_ sin (2 ξ - θ)
+
+  = _m_ {sin 2 ξ . cos θ - cos 2 ξ sin θ}
+
+  = _m_ cos θ . sin 2 ξ - _m_ sin θ . cos 2 ξ
+
+  = _m_ cos θ . 2 sin ξ . cos ξ - _m_ sin θ . {1 - 2 sin² ξ}
+
+  = 2 _m_ cos θ . sin ξ . cos ξ - _m_ sin θ + 2 _m_ sin θ . sin² ξ.
+
+  Therefore, _m_ sin θ + sin ξ - 2 _m_ sin θ sin² ξ =
+  2 _m_ cos θ . sin ξ . cos ξ.
+
+  Then:
+
+  _m_² sin² θ + 2 _m_ sin θ . sin ξ - 4 _m_² sin² θ sin² ξ + sin² ξ -
+  4 _m_ sin θ . sin³ ξ + 4 _m_² sin² θ . sin⁴ ξ =
+  4 _m_² cos² θ sin² ξ (1 - sin² ξ) = 4 _m_² . cos² θ . sin² ξ - 4 _m_²
+  cos² θ sin⁴ ξ.
+
+  Hence we have:
+
+  _m_² sin² θ + 2 _m_ sin θ . sin ξ + (1 - 4 _m_²) . sin² ξ -
+  4 _m_ sin θ . sin³ ξ + 4 _m_² sin⁴ ξ = 0
+
+  Then dividing by 4 _m_² and arranging according to powers of ξ, we
+  have as above:
+
+            1                   (   1      )              1
+  sin⁴ ξ - --- sin θ . sin³ ξ + (------ - 1) . sin² ξ + ----- . sin θ .
+           _m_                  (4 _m_²    )            2 _m_
+
+  sin ξ + ¹⁄₄ sin² θ = 0
+
+The solution of this equation, which is of the fourth degree, is
+somewhat tedious; but as the root, which will satisfy the optical
+conditions of the question, must be the sine of an angle, and
+necessarily lies between _zero_ and _unity_; and as the protraction,
+if conducted with due care in the manner already described, affords
+the means of at once assuming a probable value of ξ not very distant
+from the truth, the labour of the calculation, in this particular case,
+is not quite so great as might be expected. But notwithstanding all
+the abridgments of which the particular case admits, a considerable
+amount of labour is required, and a corresponding risk of error
+incurred, in merely introducing the numerical values into the equation
+preparatory to its solution; and any other method requiring less
+arithmetical operation, is, of course, greatly to be preferred. I
+therefore willingly adopted the suggestion of a friend, the benefit of
+whose advice I have on many occasions experienced, and made use of the
+following ordinary method of approximating to the root of the equation.
+
+If the equation sin ξ - _m_ sin (2  - θ) = 0 (see page 274) be regarded
+as an expression for the error, when the true value of ξ which would
+satisfy the equation has been introduced into its first member, we may
+consider any error in the value of ξ as expressed by the equation:
+
+  sin ξ - _m_ . sin (2 ξ - θ) = ε
+
+and differentiating this expression we have:
+
+  _d_ ε = cos ξ . _d_ ξ - 2 _m_ cos (2 ξ - θ) . _d_ ξ
+
+       = {cos ξ - 2 _m_ cos (2 ξ - θ)} . _d_ ξ
+
+Then dividing by the differential coefficient we obtain
+
+                   _d_ ε
+  _d_ ξ = ---------------------------
+          cos ξ - 2 _m_ cos (2 ξ - θ)
+
+But when ξ becomes ξ + _d_ ξ, ε will also become ε + _d_ ε; but
+
+ε + _d_ ε = 0
+
+therefore _d_ ε = -ε
+
+hence by substitution we have
+
+                      -ε
+  _d_ ξ = ---------------------------
+          cos ξ - 2 _m_ cos (2 ξ - θ)
+
+          -{sin ξ - _m_ sin (2 ξ - θ)}
+        = ----------------------------
+           cos ξ - 2 _m_ cos (2 ξ - θ)
+
+           -sin ξ + _m_ sin (2 ξ - θ)
+  _d_ ξ = ---------------------------
+          cos ξ - 2 _m_ cos (2 ξ - θ)
+
+By substituting, therefore, in this last equation the known values of
+_m_ and θ, and the assumed value of ξ, a correction is obtained, which
+being applied to ξ and the same process repeated, new corrections may
+be found until the value of _d_ ξ falls within the limits of error,
+which may be considered safe in the particular case. I need hardly say,
+that where so great a body of flame is employed as in the lights of
+the first order, these limits are soon passed, more especially as one
+soon acquires by a little experience the means of guessing a value of
+ξ not very far from the truth. It is this method I have employed in
+calculating the appended tables of the zones, in which I have on all
+occasions, though, perhaps, with needless exactness, pushed my angular
+determinations to _seconds_.
+
+Having in this manner determined the angles of BCF, the obtuse angle
+BCA of the generating triangle of the zone is easily and directly
+deduced by the following expression, which results from the obvious
+relations existing among the known angles about C; and we have (see
+fig. 73),
+
+  BCA = 90° + γ = 90° + 2 ξ - θ.
+
+We next proceed to consider the form of BA, the reflecting side of the
+zone, which is a point of the greatest consequence, as an error in the
+inclination of any part of its surface is doubled in the resulting
+direction of the reflected rays. The conditions of the question
+require, that every ray EW, after reflection at the surface AB, shall,
+like WI, be parallel to the first ray, which is reflected in the
+direction BC, and after a second refraction at C, emerges horizontally
+in CH. But, let us trace backwards the rays as they emerge in their
+horizontal directions IK, and it is obvious that if BA be made a
+straight line, then will every ray EW meet the first refracting side
+BC at the same angle, and there suffering the same refraction, they
+will go on parallel to each other, and never meet in the focus F. This
+convergence to F, which is a necessary condition of the problem, may,
+however, be produced by a curvature of AB, such that all the rays shall
+have a degree of convergence before falling on BC, sufficient to cause
+them to be finally refracted, so as to meet in F. On this account,
+they will occupy _less_ space in passing through BC, than they did
+in passing through AC; and thus BC will be _shorter_ than AC by some
+quantity which shall give to that part of AB which is at B the amount
+of _downward_ inclination required for causing the ray BF finally to
+converge to F; and the line joining B and A must be a curve, every
+point of which has its tangent inclined so as to serve the same purpose.
+
+[Illustration: Fig. 73.]
+
+To trace tangents to this curve, is therefore the next step in the
+process. The direction of the first tangent AZ depends upon very simple
+considerations; and all that is necessary to be done is to draw a line
+AU (fig. 73), parallel to BC (which is the parallel to the direction
+of the reflected rays), and forming an angle CAU, which is, of course,
+equal to the inclination of the extreme rays refracted by CB at C,
+with rays reflected from the arc which we have yet to trace. The line
+AX bisecting this angle, must therefore be a normal to the reflecting
+surface at A, and AB drawn perpendicular to AX, is consequently a
+tangent to the reflecting arc.
+
+We must next find the direction of the second tangent Z _b_, which must
+be so inclined that the ray F _b_ will, after refraction at _b_, be
+reflected into the direction, _b_ C; but as the rigorous determination
+of this is difficult, I shall describe two approximations suggested to
+me by M. LEONOR FRESNEL. The first method is based upon assuming the
+inclination of the ray refracted at _b_ to the ray refracted at C as
+equal to:
+
+  _b_ FC
+  ------
+    _m_
+
+(in which expression, _m_ is the refractive index of the glass); a
+supposition which obviously differs very little from the truth, as
+small arcs may be assumed as nearly equal to their sines. Now, it will
+be recollected, that the rays refracted at C and _b_, must be reflected
+at A and _b_, in a direction parallel to C _b_, and therefore the
+inclination of the reflecting surfaces, or that which should be formed
+by the tangents ZA and Z _b_, being half that of the incident rays, is,
+according to the assumption, equal to
+
+  _b_ FC
+  ------,
+   2 _m_
+
+which may be expressed by ¹⁄₃ _b_ FC, _m_ being equal to 1·51. But as
+the inclination of the two radii AX and BX is equal to the inclination
+of the tangents of the reflecting surfaces to which they are normals,
+we obtain for the excess B β of the secant of the reflecting arc over
+its radius the following expression:
+
+  B β = ¹⁄₂ AB . tan ¹⁄₃ BFC.[68]
+
+The value of B _b_ gives, of course, the direction of the second tangent
+Z _b_ (which must be equal in length to AZ), whence we easily deduce the
+chord of the reflecting side A _b_.
+
+  [68] The following steps will shew the mode of obtaining this
+  expression: Suppose (fig. 74, on opposite page) F _n_ to be a ray
+  incident on the surface BC very near _b_ or B (which, although
+  exaggerated in the figure for more easy reference, are close
+  together), and let this ray F _n_ be refracted in the direction _n_ O,
+  and draw _n n′_ parallel to CA, the ray which is refracted at C,
+  then will _n′_ _n_ O = _m_ . _b_ FC = ²⁄₃ _b_ FC. But the tangent
+  AZ should make with the tangent _b_ Z an angle equal ¹⁄₃ _b_ FC, or
+  _one-half_ the inclination of the rays refracted at _b_ and C, which
+  are afterwards by the agency of those tangents, to be reflected in
+  the directions parallel to _b_ C and to each other. Hence we have
+  AX _b_ (which is the inclination of the normals to those tangents),
+
+                       _b_ FC   _b_ FC
+  or AX _b_ = BZ _b_ = ------ = ------ nearly.
+                        2 _m_      3
+
+  [Illustration: Fig. 74.]
+
+  But putting AXB (fig. 73, p. 277) for AX _b_, and BFC for _b_ FC,
+  a supposition which may be safely made when the differences are so
+  small, and founding upon the analogy AX∶ AB ∷ R ∶ tan AXB, we have BA
+  = AX . tan AXB = AX . tan ¹⁄₃ BFC. Then
+
+  AB² = B β (B β + 2 AX)
+
+      = B β² + 2 B β . AX
+
+  and neglecting B β², which is very small, we have:
+
+  BA² = B β . 2 AX nearly,
+
+               BA²
+  hence B β = ----
+              2 AX
+
+                        BA
+  But as above AX = -------------
+                    tan (¹⁄₃ BFC)
+
+  and substituting this value of AX we obtain:
+
+             BA²
+  B β = -----------------
+        (       BA      )
+        (2 -------------)
+        (  tan (¹⁄₃ BFC))
+
+  hence we have, as in the text,
+
+  B β = ¹⁄₂ BA . tan(¹⁄₃ BFC)
+
+The second mode proposed by M. FRESNEL, and that which I found most
+convenient in practice, consists in forming successive hypotheses as to
+the length of the side BC, and tracing the path of the incident ray FB,
+which being refracted at B, so as to make with the normal BK an angle
+= BKY = _y′_, and finally reflected in the direction BC, must make
+the angle YBZ = MBC. I shall describe it as follows: In the annexed
+figure (fig. 75) MBZ is a tangent to the reflecting surface at B, and
+KBF is the angle of incidence of the ray BF before its refraction at B.
+If KBF = _x´_, and the angle of incidence of FC = ECF = _x_, we have
+BFC (which is the inclination of those rays to each other, and must
+be equal to the difference of their angles of incidence to the same
+surface) = _x_ - _x´_, whence knowing _x_, we easily find a value of
+_x´_ corresponding to the length of BC. Then for finding the angle of
+refraction KBY = _y´_ we have:
+
+             sin _x´_
+  sin _y´_ = --------
+                _m_
+
+[Illustration: Fig. 75.]
+
+Now, if FB be refracted, so as to make with the reflecting side an
+angle equal to ZBY, it must (if the position of B be rightly chosen),
+be reflected so as to follow BC, thus making MBC = YBZ, and calling
+each of these angles = μ, we have the right angle NBZ made up of μ +
+_y´_ + NBK. But NBK clearly equals μ, because it is the inclination of
+the normals to BC and BZ, and hence _y´_ + 2 μ = 90°. This, therefore,
+forms a crucial test for the length of BC. I may only remark, that we
+already know the numerical value of _y_; and that of μ is easily found,
+for μ = CBA + ABM = CBA + BAM = CBA + (MAC - BAC) = CBA + ¹⁄₂ (180° -
+υ) - BAC. Thus knowing μ and _y´_, we have only to see whether
+
+  (_y´_ - 2 μ) - 90° = 0
+
+We have now only to find the length of the radius AX or _b_ X (see fig.
+73, p. 277), which will describe the reflecting surface or arc AZ _b_,
+and to determine the position of its centre X. We already know the
+values of _y′_ and _y_, the angles of refraction of C and _b_, and
+their difference _y_ - _y′_ gives us the inclination of the rays which
+are to be reflected (into directions parallel to C _b_) at _b_ and at
+A. This quantity is, of course, double the inclination of tangents to
+the reflecting surface AZ and _b_ Z, and of their normals AX and _b_ X.
+Again, we have the chord line
+
+               sin (AC _b_)
+  A _b_ = AC . ------------;
+               sin (_b_ CA)
+
+and, as above,
+
+  AX _b_ = ¹⁄₂ (_y_ - _y′_) = φ
+
+                               sin (¹⁄₂ (180° - φ))
+  And AX = _b_ X = ρ = A _b_ . ------------------- =
+                                      sin φ
+
+  ¹⁄₂ A _b_ . cosec(¹⁄₂ φ).
+
+And, lastly, for the co-ordinates to X, the centre of curvature for the
+reflecting arc, we have
+
+      OX = ρ . sin OAX
+
+  and OA = ρ . cos OAX.[69]
+
+  [69] The angle OAX is easily found, as will be seen by referring to
+  fig. 73, p. 277; for, AH being horizontal by construction and AO
+  vertical, HAO = 90°; and HAC and CAU being both known, we have
+
+  OAX = 90° - (HAU + UAX) = 90° - (HAU + ¹⁄₂ CAU).
+
+[Illustration: Fig. 76.]
+
+The positions of the apices A and B of the angles of the zones are also
+easily found in reference to the focus, and are given in the Table in
+the Appendix. In fig. 76 we may, in reference to the known position of
+C, find that of A or B, by simply adding the quantities AH, HC, and BK,
+to C _y_ or C _x_, and by deducting CK from C _y_; while it is obvious
+that those quantities are respectively proportional to the length of
+the known sides AC and BC, modified by the inclination of those sides
+with the horizon. Hence we have AH = AC . sin ACH; HC = AC . cos ACH;
+BK = BC . sin BCK; and CK = BC . cos BCK.
+
+In the process of grinding the zones, it is found convenient for the
+workman to give a curved form to the refracting sides BC and AC, the
+one being made convex and the other concave, so that both being ground
+to the same radius, the convergence of the rays produced by the first
+shall be neutralized by the divergence caused by the second. By this
+arrangement we have three points given in space from which, with given
+radii, to describe a curvilinear triangle whose revolution round the
+vertical axis of the system generates the zone required. Co-ordinates
+to those two centres of curvature for the surfaces AC and BC were
+determined in reference to arris A of each zone, and will be found in
+the Appendix. The mode of finding those co-ordinates is, of course,
+similar to that already given; and, the radii being assumed at 4000
+millimètres, the co-ordinates are respectively proportional to the sine
+and cosine of the inclination of the radius at A to the vertical line,
+which inclination depends upon the relations of known angles around A
+and C.
+
+The section ABC (fig. 71, p. 271) of the first zone being thus
+determined, we proceed by fixing the point C₂ of the second zone, which
+is at the intersection of the horizon GAG₂ with the ray FBC₂ passing
+through B. This arrangement prevents any loss of light between the
+adjacent zones. The calculation of the elements of the second and of
+every following zone, is precisely similar to that of the first.
+
+  ~Testing of Zones.~
+
+The mode of grinding the zones I shall not notice here; but shall
+refer the more curious reader to the Appendix, in which I have given
+the details of the process followed by M. THEODORE LETOURNEAU, who now
+manufactures the apparatus for the Northern Lights Board, in the room
+of M. FRANÇOIS SOLEIL, who is engaged at St Petersburg in the same
+work. I accordingly proceed to consider what mode should be followed in
+testing the accuracy of the zones. For this purpose, various expedients
+suggested themselves, such as the application of gauges in the form
+of a radius, having at one end a plate with a triangular space cut
+through it, equal and similar to the cross section of the zone. The
+horizontal motion of this arm would, of course, detect the inaccuracies
+of the successive sections of the inclosed zone. The application of
+such a gauge, however, seemed difficult, and in order to test the
+_form_ of the zones, I satisfied myself with using callipers (similar
+to the sliding rules used by shoemakers) for measuring the _length_
+of the sides of the zone, and a goniometer for the angles, which is
+represented in the figure (fig. 77), in which ABC represents the prism,
+with one angle inclosed between the arms AC and AB, moveable round a
+centre O, and RR the graduated limb. This instrument is inconvenient
+and defective, as the convexity of the sides AB and BC of the zone
+requires some skill in getting the arms to be tangents to them.
+
+[Illustration: Fig. 77.]
+
+[Illustration: Fig. 78.]
+
+A practical test, however, yet remained to be made of the zones when
+fixed in the brass frames (shewn at Plate XVIII.), and assembled around
+the common focus of the system, by measuring the final inaccuracy in
+the path of the rays emergent from them. I have successfully used the
+following mode. Having mounted the frames containing the zones on a
+carriage revolving round a small flame placed truly in the common
+focus, I carefully marked with a piece of soap the centre of the
+emergent _surface_ of each zone; and having attached to a vertical rod
+of metal a telescope, provided with a spirit-level and cross-hairs
+(for cutting the centre of the image of the flame reflected through
+the zone) in such a manner as to be capable of sliding on the rod, I
+observed the cutting of the centre of the flame by the cross-hairs. In
+the case of any aberration from a normal emergence of the central ray,
+I had thus the means of at once determining its amount and direction.
+The telescope was moved up or down, and its vertical inclination was
+varied until the axis of the instrument coincided with the direction
+of the ray emergent from the centre of each zone, which was made to
+circulate round the flame, the observer noting any change in the
+position of the reflected image of the flame, and causing an attendant
+to mark the zones in which the change occurred, that they might again
+be subjected to separate examination of the same kind, by adjusting
+the telescope to the error of each. The vertical inclination of the
+telescope and the consequent aberration of the ray, was then measured
+by a graduated arc, with an adjusting spirit-level, moved by a rack and
+pinion. The accompanying figure (fig. 78) shews the arrangement just
+described. E is the small flame in the focus; ABC is the zone; TT is
+the telescope; and R a graduated limb, on which is read the angular
+deviation θ of the axis of the telescope from the horizon. In the
+figure, the ray emergent from the centre of AC is shewn dipping below
+the _true level_, to which the line TC is supposed to be parallel. I
+have succeeded by this method in detecting the inaccurate position
+of some of the zones in the frame; and the error has been reduced by
+carefully resetting them, so as to diminish considerably the error
+of a great proportion of the emergent rays. Another mode, and that
+which, owing to its convenience, was chiefly employed in preference to
+that just described, was to measure the vertical inclination (given
+in the Table in the Appendix), of each surface of the zone, and more
+especially the reflecting surface, by means of the instrument, shewn
+in figures 79 and 80, after the zones were fixed in their place. The
+figure (No. 79) shews the mode of gauging the reflecting side AB of a
+zone of the upper series; and the second (No. 80) shews the position
+of the instrument in gauging the reflecting side AB of a zone of the
+under series. In those figures, L is a spirit-level; R, a graduated
+limb for reading the angular deviation from the true inclination of the
+tangents to each surface; and SS are studs which rest on the convex
+surfaces AB and BC of the zones, so as to make the ruler parallel to
+the tangents of those sides. I have only to add, that I have restricted
+the error, in the position of the reflecting side of the zones, to 50′
+as an extreme limit; and I have invariably endeavoured, in altering the
+position of the zone in the frame, to throw any error on the side of
+safety, by causing the rays to _dip_ below the horizon, rather than to
+rise above it.[70]
+
+[Illustration: Fig. 79.]
+
+[Illustration: Fig. 80.]
+
+  [70] In connection with the use of the clinometer, I determined the
+  inclinations of the tangents or chords of the three curve surfaces
+  AB, BC, and AC of each zone with NP, the axis of the system, by means
+  of the obvious relations of the known angles about C, A, and B. Those
+  inclinations (fig. 81) are shewn by the angles BNO, BON, and CPF; and
+  are given in the Table of the Zones in the Appendix.
+
+  [Illustration: Fig. 81.]
+
+  ~Framing of Zones.~
+
+The mode of framing the greater zones is shewn in Plate XVIII. and is
+nearly the same as that used for the Small Harbour Light apparatus
+of the fourth order (Plate XIX.). The chief difference consists in
+the diagonal framing, which I adopted for supporting the cupola of 13
+zones, which, from its great weight, could not be safely made to rest
+on the dioptric belt below. That frame is seen in Plates XVII. and
+XVIII. and is in accordance with the mode of jointing the refractors
+already described. This system has now been rendered still more
+complete by the adoption of lanterns composed of diagonal framework,
+afterwards described and shewn at Plate XXVI.
+
+  ~Mechanical Lamp.~
+
+We have next to consider the great Lamp, to the proper distribution
+of whose light, the whole of the apparatus, above described, is
+applied. FRESNEL immediately perceived the necessity of combining
+with the dioptric instruments which he had invented, a burner capable
+of producing a large volume of flame; and the rapidity with which he
+matured his notions on this subject and at once produced an instrument
+admirably adapted for the end he had in view, affords one of the many
+proofs of that happy union of practical with theoretical talent, for
+which he was so distinguished. FRESNEL himself has modestly attributed
+much of the merit of the invention of this Lamp to M. ARAGO; but
+that gentleman, with great candour, gives the whole credit to his
+deceased friend, in a notice regarding lighthouses, which appeared in
+the _Annuaire du Bureau des Longitudes_ of 1831. The lamp has four
+concentric burners, which are defended from the action of the excessive
+heat, produced by their united flames, by means of a superabundant
+supply of oil, which is thrown up from a cistern below by a clockwork
+movement and constantly overflows the wicks, as in the mechanical lamp
+of Carcel. A very tall chimney is found to be necessary, in order to
+supply fresh currents of air to each wick with sufficient rapidity to
+support the combustion. The carbonisation of the wicks, however, is by
+no means so rapid as might be expected, and it is even found that after
+they have suffered a good deal, the flame is not sensibly diminished,
+as the great heat evolved from the mass of flame, promotes the rising
+of the oil in the cotton. I have seen the large lamp at the Tour de
+Corduan burn for seven hours without being snuffed or even having the
+wicks raised; and, in the Scotch Lighthouses, it has often, with Colza
+oil, maintained, untouched, a full flame for no less a period than
+seventeen hours.
+
+[Illustration: Fig. 82.]
+
+[Illustration: Fig. 83.]
+
+[Illustration: Fig. 84.]
+
+The annexed diagrams will give a perfect idea of the nature of the
+concentric burner. The first (fig. 82) shews a plan of a burner of
+four concentric wicks. The intervals which separate the wicks from
+each other and allow the currents of air to pass, diminish a little
+in width as they recede from the centre. The next (fig. 83) shews a
+section of this burner. C, C′, C″, C‴ are the rack-handles for raising
+or depressing each wick; AB is the horizontal duct which leads the
+oil to the four wicks; L, L, L, are small plates of tin by which the
+burners are soldered to each other, and which are so placed as not
+to hinder the free passage of the air; P is a clamping screw, which
+keeps at its proper level the gallery R, R, which carries the chimney.
+The last figure (No. 84) shews the burner with its glass chimney and
+damper. E is the glass chimney; F is a sheet-iron cylinder, which
+serves to give it a greater length, and has a small damper D, capable
+of being turned by a handle, for regulating the currents of air; and
+B is the pipe which supplies the oil to the wicks. The only risk in
+using this lamp arises from the liability to occasional derangement
+of its leathern valves that force the oil by means of clockwork; and
+several of the lights on the French coast, and more especially the
+Corduan, have been extinguished by the failure of the lamp for a few
+minutes, an accident which has never happened, and scarcely can occur
+with the fountain lamps which illuminate the reflectors. To prevent the
+occurrence of such accidents, and to render their consequences less
+serious, various precautions have been resorted to. Amongst others,
+an alarum is attached to the lamp, consisting of a small cup pierced
+in the bottom, which receives part of the overflowing oil from the
+wicks, and is capable, when full, of balancing a weight placed at
+the opposite end of a lever. The moment the machinery stops, the cup
+ceases to receive the supply of oil, and, the remainder running out
+at the bottom, the equilibrium of the lever is destroyed, so that it
+falls and disengages a spring which rings a bell sufficiently loud
+to waken the keeper should he chance to be asleep. It may justly be
+questioned whether this alarum would not prove a temptation to the
+keepers to relax in their watchfulness and fall asleep; and I have,
+in all the lamps of the dioptric lights on the Scotch coast, adopted
+the converse mode of causing the bell to cease when the clockwork
+stops. There is another precaution of more importance, which consists
+of having always at hand in the light-room a spare lamp, trimmed and
+adjusted to the height for the focus, which may be substituted for
+the other in case of accident. It ought to be noticed, however, that
+it takes about twenty minutes from the time of applying the light to
+the wicks to bring the flame to its full strength, which, in order to
+produce its best effect, should stand at the height of nearly four
+inches (10^{cm.}). The inconveniences attending this lamp have led to
+several attempts to improve it; and, amongst others, M. DELAVELEYE has
+proposed to substitute a pump having a metallic piston, in place of the
+leathern valves, which require constant care, and must be frequently
+renewed. A lamp was constructed in this manner by M. LEPAUTE, and
+tried at Corduan; but was afterwards discontinued until some further
+improvements could be made upon it. It has lately been much improved by
+M. WAGNER, an ingenious artist whom M. FRESNEL employed to carry some
+of his improvements into effect. In the dioptric lights on the Scotch
+coast, a common lamp, with a large wick, is kept constantly ready for
+lighting; and, in the event of the sudden extinction of the mechanical
+lamp by the failure of the valves, it is only necessary to unscrew and
+remove its burner, and put the reserve-lamp in its place. The height
+of this lamp is so arranged, that its flame is in the focus of the
+lenses, when the lamp is placed on the ring which supports the burner
+of the mechanical lamp; and as its flame, though not very brilliant,
+has a considerable volume, it will answer the purpose of maintaining
+the light in a tolerably efficient state for a short time, until the
+light-keepers have time to repair the valves of the mechanical lamp.
+Only three occasions for the use of this reserve-lamp have yet occurred.
+
+  ~Height of the flame of the Mechanical Lamp.~
+
+The most advantageous heights for the flames in dioptric lights are as
+follows:--
+
+                                        Inches.
+  1st Order,  10 to 11 centimètres = 3·94 to 4·33
+  2d Order,    8 to  9   ......    = 3·15 to 3·54
+  3d Order,    7 to  8   ......    = 2·76 to 3·15
+
+Those heights of flame can be obtained only by a careful adjustment
+of the heights of the wicks and the relative levels of the _shoulder_
+of the glass-chimney and the burner, together with a due proportion
+for the area of the opening of the iron-damper which surmounts it.
+The wicks must be gradually raised during the first hours of burning
+to the level of 7 millimètres (0·27 inch) above the burner, a height
+which they may only very rarely and but slightly exceed. By raising the
+shoulder of the glass-chimney the volume of the flame is increased;
+but, after a certain height is exceeded, the flame, on the other hand,
+becomes reddish, and its brilliancy is diminished. The height of the
+flame is decreased, and it becomes whiter by lowering the chimney. The
+chimney is lowered or raised by simply turning to the right or to the
+left the cylindric _glass-holder_ in which it rests (see Plate XXV.).
+In regulating the flame, however, recourse is most frequently had to
+the use of the damper, by enlarging the opening of which the flame
+falls and becomes whiter and purer; while by diminishing its aperture,
+the contrary effect is produced. The area of the opening depends on the
+inclination of a circular disc capable of turning, vertically through
+a quadrant, on a slender axle of wire, which is commanded by the
+light-keeper by means of a fine cord which hangs from it to the table
+below. When the disc (see fig. 84, p. 287) is in a horizontal plane
+the chimney is shut, when in a vertical plane it is open; and each
+intermediate inclination increases or decreases the aperture.
+
+  ~Position of flame in reference to focus of apparatus.~
+
+I need scarcely add, that in order to produce the proper effect of a
+system of lenses or refractors, the vertical axis of the flame should
+coincide with their common axis; and it is further necessary, in order
+to bring the best portion of the flame into a suitable position with
+reference to the apparatus, that the top of the burner should be quite
+level, and should stand _below_ the plane of the focus in the following
+proportions, viz.:--
+
+  For 1st order, 28 millimètres = 1·10 inches.
+  ... 2d  order, 26    ...      = 1·02  ...
+  ... 3d  order, 24    ...      = 0·95  ...
+
+[Illustration: Fig. 85.]
+
+For the purpose of placing the lamp in the centre of the apparatus,
+a plumbet with a sharp point suspended in the axis of the apparatus,
+is used to indicate, by its apex, the place for the centre of the
+burner. The lamp is then raised or lowered as required by means of
+four adjusting screws Q at the bottom of its pedestal (Plate XX.); and
+the top of the burner is made horizontal by a spirit-level, the most
+convenient form of which is that of the spherical segment, which acts
+in every azimuth. Its application to this purpose is due, I believe,
+to M. LETOURNEAU, the successor of M. FRANÇOIS in the construction of
+dioptric apparatus at Paris. This level is shewn in the annexed figure
+(fig. 85), in which _a_ _b_ is the brass frame containing the level,
+and O the air-bubble; and _e_ shews circles of equal altitudes engraved
+on the glass. After the first application of this level, the adjustment
+of the burner as to its central position is carefully repeated by means
+of a centre gauge (shewn at fig. 90, p. 295), with reference to the
+vertex of each lens, or to many points on the internal surface of the
+refractors; and being found correct, the level is again applied to the
+top of the burner, to detect any deviation from horizontality that may
+have occurred during the process of adjusting it to the axis.
+
+The lamp is subject to derangement, chiefly from the stiffness of the
+clack-valves for want of regular cleaning, bursting of the leathern
+valves of the oil-box, stiffness of the regulator, and the wearing of
+the bevelled gearing which gives motion to the connecting-rod that
+works the valves of the oil-pumps.
+
+  ~Working of the Pumps of the Lamp.~
+
+The pumps of the lamp should raise, in a given time, _four_ times the
+quantity of oil actually consumed by burning during that time. Their
+hourly produce should be,
+
+                                  lb. avoirdupois.
+  For the lamp with four wicks,        6·615
+        ......      three wicks,       4·410
+        ......      two wicks,         1·675
+
+This surplus of _three_ times what is burned is necessary to prevent
+the wick from being carbonised too quickly; and it has been found
+quite sufficient for that purpose. The discharge from the pumps is, of
+course, regulated by changes in the angle of the fans of the regulator,
+or in the amount of the moving weight.
+
+Care must be taken, in preparing the leathern valves of the pump-box or
+chamber, shewn in Plate XXII., that they be neither too flaccid from
+largeness nor too tense from smallness; and also that, after being
+fitted, they draw no air. To remove the old valves and replace them
+by fresh ones, is a very simple process, more especially when a proper
+die or mould is used, which at once cuts the kid-leather, of which the
+valves are formed, to the required size and squeezes them into the
+proper shape. In Plates XX., XXI., XXII., XXIII., XXIV., and XXV., the
+most minute details are given as to the clockwork, pumps, burners, and
+flame of the great lamp.[71]
+
+  [71] See also M. LEONOR FRESNEL’S _Instructions sur l’organisation et
+  la surveillance du service des Phares et Fanaux de France_. Paris,
+  1842, pp. 12, 13, 14, and 15.
+
+  ~Choice of Focal Point for various parts of the apparatus.~
+
+The focal point for the lenses and refractors is in the centre of the
+flame and on the level of its brightest film, as shewn in Plate XXV.
+The choice of a focus for the zones naturally formed a most important
+practical consideration in their arrangement; and the judicious remarks
+of M. LEONOR FRESNEL on that subject, already noticed, would alone have
+induced me to discard my former calculations in favour of his. For
+the upper zones, M. FRESNEL had adopted a point in the centre of the
+flame 10 millimètres above the focus of the lenses, so that all the
+light _below_ that point necessarily falls between the horizon and the
+Lighthouse; but for the lower zones, it was necessary, owing to their
+arrangement for convenience in a cylindric form, to adopt a separate
+focus for each zone in the direction of the centre of gravity of that
+part of the flame which would light each zone. In this manner (fig. 86)
+the foci of the zones recede upwards from _a_ to _f_ in proportion to
+the depression of the zones _a_, _b_, _c_, _d_, _e_, _f_, so that the
+line joining each zone and its focus, must revolve as a _radius vector_
+round some point O between them. The details of this arrangement
+are shewn in Plate XVIII.; and are also given in the Table of the
+Catadioptric Zones in the Appendix.
+
+[Illustration: Fig. 86.]
+
+  ~Application of Spherical Mirrors to fixed Dioptric Lights.~
+
+[Illustration: Fig. 87.]
+
+In the arc next the land, in fixed lights, a great loss of light ensues
+from the escape of the rays uselessly in that direction. So far back
+as 1834, I suggested the placing a segment of a spherical mirror, with
+its centre of curvature coincident with F the focus of the system, so
+that the luminous pyramid MFM, of which the mirror MM forms the base,
+might be thrown back through the focal point and finally refracted into
+such a direction as to contribute to the effect of the lens QA _q_ in
+seaward and opposite arc. In the diagram (fig. 87), _r_ _ r_ indicate
+rays proceeding directly from F; _r′_ _r′_ rays reflected from MM
+through F, and finally refracted at QA _q_; and _r″_ _r″_ is the beam
+compounded of both. In the best glass-silvered mirrors, this accession
+of light would amount to nearly half of the light incident on them. In
+such an arrangement, a considerable radius is desirable to decrease
+the amount of aberration produced by a large flame. In the case of
+revolving lights of the first order, the radius would, of course, be
+limited to somewhat less than three feet, which is the focal distance
+of the lenses, between which and the focus, the reflecting segment must
+be placed; but in fixed lights, the lantern is the limit of radius,
+so that a focal length of five feet ten inches may be obtained. M.
+FRANÇOIS ground some beautiful mirrors of three feet radius, which were
+afterwards _tinned_ by his successor, M. LETOURNEAU, by a new process
+discovered by himself;[72] and that gentleman is at present engaged in
+the construction of reflecting spherical segments 1200^{mm.} square
+(about 16 superficial feet), to a radius of 1770^{mm.} (5 feet 10
+inches), which subtend a vertical arc of about 40°.
+
+  [72] See notice of a similar process practised about the year 1750 by
+  Mr ROGERS of London, _ante_, p. 240.
+
+  ~Arrangement of Dioptric Apparatus.~
+
+The arrangements of the dioptric apparatus in the lightroom will be
+more fully understood by referring to the Plates.
+
+Plate XIII. shews an elevation of a revolving dioptric apparatus of
+the first order; F is the focal point, in which the flame is placed;
+L, L great annular lenses, forming by their union an octagonal prism,
+with the lamp in its axis, and projecting, in horizontal beams, the
+light which they receive from the focus; L′L′, the upper lenses,
+forming by their union a frustum of an octagonal pyramid of 50° of
+inclination, and having their foci coinciding in the point F. They
+parallelise the rays of light which pass over the lenses. M, M are
+plane mirrors, placed above the pyramidal lenses L′L′, and so inclined
+as to project the beams reflected from them in planes parallel to
+the horizon; Z, Z are the lower zones, first used at Skerryvore, in
+the room of the curved mirrors which were used at Corduan. The lower
+part of Plate XIII. shews the moveable framework which carries the
+lenses and mirrors, and the rollers on which it circulates, with the
+clockwork which gives motion to the whole. Plate XIV. is the plan of
+the apparatus shewn in Plate XIII.
+
+Plate XV. shews a section of a fixed dioptric light of the first order.
+F is the focal point in which the flame is placed; R, R cylindric
+refractors, forming by their union a prism of thirty-two sides, or
+a true cylinder, with the lamp in its axis, and producing a zone of
+light of equal intensity in every point of the horizon; M, M, curved
+mirrors, ranged in tiers above and below the cylindric refractors, and
+having their foci coinciding in the point F; the effect of the mirrors
+increases the power of the light, by collecting and transmitting
+the rays which would otherwise pass above and below them, without
+increasing the effect of the light. Plate XVI. gives the elements of
+the curved mirrors MM of Plate XV.
+
+After the details given of the nature of the catadioptric zones, all
+that is needful is briefly to refer to Plate XVII., in which ABC and
+A′B′C′ shew the upper and lower zones which supply the place of the
+mirrors shewn at M, M, in Plate XV.; while DEF shews the cylindric
+belt as lately improved, with the diagonal joints M, N, C; and X,
+X, represent the diagonal supports for the cupola ABC. This plate,
+in connection with the enlarged view of the same apparatus at Plate
+XVIII., affords a complete explanation of the arrangement of all the
+parts.
+
+  ~Arrangement of the Dioptric Apparatus in the Lightroom.~
+
+For the purpose of arranging the various parts of the dioptric
+apparatus in their proper positions, _three_ gauges are employed. The
+first (fig. 88) is for ascertaining that the lenses _l_, _l_, meet at
+the proper horizontal angle, so that their axes shall meet with the
+proper inclination in F the focus. This is done by means of two arms,
+whose projecting points _r_, _r_, _r_, _r_ touch the backs of the
+lenses, while the graduated arc _c_ indicates the inclination of _l_,
+_l_, to _l_, _l_, or the complement of that inclination at F.
+
+[Illustration: Fig. 88.]
+
+[Illustration: Fig. 89.]
+
+Again, for ascertaining the verticality of the main lenses, or for
+setting the subsidiary lenses or mirrors shewn in Plates XIII. and
+XIV., at the required angle of inclination, recourse is had to a
+clinometer (fig. 89) touching the back of the lens LL by means of studs
+at A, A, while the spirit-level S indicates, on the graduated limb,
+the amount of deviation from the vertical position of the instrument,
+whether accidental or intentional.
+
+[Illustration: Fig. 90.]
+
+Lastly, to test the true position of the lamp itself, with reference to
+the lenses thus properly arranged, we apply a radius or trainer (fig.
+90) which fits into the centre burner at F, while its point A touches
+the centre of the lens _l_, _l_; at B is a graduated slide, which
+admits of the trainer being lengthened or shortened to suit various
+focal distances; and the spirit-level at _c_ at once corrects any error
+in the length of the trainer arising from depression or elevation,
+and also serves to indicate the proper level for the burner which is
+noticed at page 290, in speaking of the lamp. The dotted line F _c′_B′A′
+shews the position of the trainer in reference to an adjacent lens.
+
+The elegant apparatus invented by AUGUSTIN FRESNEL for Harbour Lights,
+on the same principle as that just described for Sea Lights, is shewn
+beneath (fig. 91). It consists of thirteen rings of glass of various
+diameters arranged one above another, in an oval form. The five middle
+rings have an interior diameter of 11·81 inches (30^{cm.}), and like
+those of the larger apparatus, refract equally over the horizontal
+plane of the focus the light which they receive from it. The other
+rings or prisms, five of which are upper and three lower, are ground
+and set in such a manner, that they project all the light derived
+from the focus in a direction parallel to the other rays by _total
+reflection_.
+
+[Illustration: Fig. 91.]
+
+The arrangements of this apparatus, which is distinguished by the
+addition of external refractors arranged vertically, will be more fully
+understood by a reference to fig. 91, which shews its section and plan.
+F is the focal point in which the flame is placed; _r_, _r_ cylindric
+refractors, forming by their union a cylinder with a lamp in its axis,
+and producing a zone of light of equal intensity all round the horizon;
+_x_, _x_ are catadioptric prismatic rings acting by _total reflection_,
+and giving out zones of light of equal intensity at every point of the
+horizon. The dotted lines shew the course traversed by the rays of
+light which proceed from the lamp, and are acted upon by the rings of
+glass. The letters _r′_ _r′_ shew the external prisms, having their
+axes at right angles to those of the principal bent prisms, composing
+the refractors at _r_, _r_, and revolving around them. This ingenious
+application of the property of crossed prism is already described at
+page 264.
+
+When this apparatus is employed to light only a part of the horizon,
+the rings are discontinued on the side next the land, and room is
+thus obtained for using a common fountain lamp; but when the whole
+horizon is illuminated, the apparatus must inclose the flame on every
+side; and it has in that case been found most convenient to employ the
+hydrostatic lamp of THILORIER, which has a balance of _sulphate of zinc
+in solution_.
+
+An instrument differing from this small apparatus only in size, has
+lately been introduced into the Lighthouses in France, and has also
+been adopted in Scotland for lights in narrow seas. It has the same
+number of rings of glass as the small apparatus, and of the same
+_proportional_ dimensions. Its internal diameter, however, is 500
+millimètres (about 19¹⁄₂ inches). Drawings of the smaller apparatus
+are given at Plate XIX., which also contains the radii and the centre
+of curvature for the rings of the central dioptric belt; while the
+following Table gives the elements of the eight prismatic zones
+(above and below the belt), with the co-ordinates to their centres of
+curvature, measured from the arris A of the outer or emergent surfaces,
+in whatever position the zone may lie on the lathe. The dimensions are
+in millimètres; but may be easily converted into imperial inches, in
+the manner described in the Table of the Great Zones, which will be
+found in the Appendix:--
+
+  +------+-------+--------+--------++------+-------+--------+--------+
+  |      |       |  Hori- |        ||      |       |  Hori- |        |
+  |      |       | zontal |        ||      |       | zontal |        |
+  |      |       |distance|Vertical||      |       |distance|Vertical|
+  |      | Radii |from the|distance||      | Radii |from the|distance|
+  |Number|   of  | axis of|from the||Number|   of  | axis of|from the|
+  |  of  | curva-|   the  | outer  ||  of  | curva-|   the  | outer  |
+  | Zone.| ture. | system.| arris. || Zone.| ture. | system.| arris. |
+  +------+-------+--------+--------++------+-------+--------+--------+
+  |                  REFLECTING SURFACES (CONVEX).                   |
+  |   I. | 1094·5|  723·5 |  833·78||    V.|1222·9 |  523·6 | 1169·1 |
+  |  II. | 1045·7|  652·8 |  891·01||   VI.|1249·4 |  544·0 | 1192·1 |
+  | III. | 1044·5|  598·4 |  933·67||  VII.|1150·4 |  593·5 | 1062·9 |
+  |  IV. | 1087·3|  551·9 | 1010·20|| VIII.|1113·6 |  650·5 |  985·9 |
+  +------+-------+--------+--------++------+-------+--------+--------+
+  |               OUTER REFRACTING SURFACES (CONCAVE).               |
+  |   I. | 1250·0| 1290·7 |  303·19||    V.|1250·00| 1100·22|  829·52|
+  |  II. | 1250·0| 1274·2 |  445·89||   VI.|1250·00| 1112·74|  821·16|
+  | III. | 1250·0| 1234·0 |  587·05||  VII.|1250·00| 1190·50|  698·00|
+  |  IV. | 1250·0| 1173·0 |  717·71|| VIII.|1250·00| 1251·90|  557·22|
+  +------+-------+--------+--------++------+-------+--------+--------+
+  |              INNER REFRACTING SURFACES (CONVEX).                 |
+  |   I. | 1250·0|  150·67 |1211·90||    V.|1250·00|  452·23| 1184·20|
+  |  II. | 1250·0|  228·19 |1208·80||   VI.|1250·00|  453·07| 1185·20|
+  | III. | 1250·0|  305·10 |1203·35||  VII.|1250·00|  374·60| 1196·00|
+  |  IV. | 1250·0|  381·00 |1195·30|| VIII.|1250·00|  294·35| 1203·80|
+  +------+-------+---------+-------++------+-------+--------+--------+
+
+  ~Power of Dioptric Instruments.~
+
+The effect of an annular lens, in combination with the great lamp, may
+be estimated at moderate distances to be nearly equal to that of 3000
+Argand flames of about an inch diameter; that of a cylindric refractor
+at about 250; and that of a curved mirror may perhaps on an average be
+assumed at about 10 Argand flames.
+
+  ~Orders of the French Lights.~
+
+The dioptric lights used in France are divided into four orders,
+in relation to their power and range; but in regard to their
+characteristic appearances, this division does not apply, as, in each
+of the orders, lights of identically the same character may be found,
+differing only in the distance at which they can be seen, and in the
+expense of their maintenance. The four orders may be briefly described
+as follows:--
+
+1_st_, Lights of the first order having an interior radius or focal
+distance of 36·22 inches (92^{cm.}), and lighted by a lamp of four
+concentric wicks, consuming 570 gallons of oil per annum.
+
+2_d_, Lights of the second order having an interior radius of 27·55
+inches (70^{cm.}), lighted by a lamp of three concentric wicks,
+consuming 384 gallons of oil per annum.
+
+3_d_, Lights of the third order, lighted by a lamp of two concentric
+wicks, consuming 183 gallons of oil per annum. The instruments used in
+those lights are of two kinds, one having a focal distance of 19·68
+inches (50^{cm.}), and the other of 9·84 inches (25^{cm.}).
+
+4_th_, Lights of the fourth order, or harbour-lights, having an
+internal radius of 5·9 inches (15^{cm.}), and lighted by a lamp of one
+wick, or Argand burner, consuming 48 gallons of oil per annum. This
+apparatus is, as already noticed, now more generally used of a larger
+scale, having a focal distance of 9·84 inches (25^{cm.}), and a lamp of
+two concentric wicks, consuming about 130 gallons of oil per annum.[73]
+
+  [73] An apparatus of 0^{m.}·185^{cm.} was recently added to the list
+  of French lights under the name of the _Fifth_ order; while that of
+  25^{cm.} radius has been called the _Fourth_, and that of 15^{cm.}
+  radius is styled the _Sixth_ order. Those minute subdivisions I
+  consider to be unnecessary.
+
+  ~Distinctions of the Dioptric Lights.~
+
+Those four orders are not intended as distinctions; but are
+characteristic of the power and range of lights, which render them
+suitable for different localities on the coast, according to the
+distance at which they can be seen. This division, therefore, is
+analogous to that which separates our lights into _sea-lights_,
+_secondary lights_, and _harbour-lights_, terms which are used to
+designate the power and position, and not the appearance of the lights
+to which they are applied.
+
+Each of the above orders is susceptible of certain combinations, which
+produce various appearances, and constitute the distinctions used for
+dioptric lights; but the following are those which have been actually
+employed as the most useful in practice:--
+
+The first order contains, 1_st_, Lights producing, once in every
+minute, a great flash, preceded by a smaller one, by the revolution of
+eight great lenses and eight smaller ones combined with eight mirrors;
+2_d_, Lights flashing once in every half minute, and composed of
+sixteen half lenses. Those lights may have the subsidiary parts simply
+catoptric, or diacatoptric; and, 3_d_, Fixed lights, composed of a
+combination of cylindric pieces, with curved mirrors or catadioptric
+zones ranged in tiers above and below them.
+
+The second order comprises revolving lights with sixteen or twelve
+lenses, which make flashes every half minute; and fixed lights varied
+by flashes once in every four minutes, an effect which, as already
+noticed, is produced by the revolution of exterior cylindrical pieces.
+
+The third order (larger diameter) contains common fixed lights, and
+fixed lights varied by flashes once in every four minutes.
+
+The third order (smaller diameter) contains fixed lights, varied by
+flashes once in three minutes.
+
+The fourth order has fixed lights varied by flashes once in every three
+minutes, and fixed lights of the common kind. It has been thought
+necessary to change the term “fixed lights varied by flashes,” for
+“fixed light with short eclipses,” because it has been found that, at
+certain distances, a momentary eclipse precedes the flash.
+
+These distinctions depend upon the periods of revolution, rather than
+upon the _characteristic appearance_ of the light; and therefore seems
+less calculated to strike the eye of a seaman, than those employed
+on the coasts of Great Britain and Ireland. In conformity with this
+system, and in consideration of the great loss of light which results
+from the application of coloured media, all distinctions based upon
+colour have been discarded in the French lights.
+
+The distinctions are, in fact, only _four_ in number, viz.: Fixed;
+Fixed, varied by flashes;[74] Revolving, with flashes once a minute;
+and Revolving, with flashes every half minute. To those might be
+added, Revolving, with bright periods once in two minutes, and perhaps
+_Flashing_ once in _five seconds_ (as introduced by me at the Little
+Ross, but I cannot say with such complete success as would induce me to
+recommend its general adoption). My own experience would also lead me
+to reject the distinction called “Fixed, varied by flashes,” which I do
+not consider as possessing a marked or efficient character.
+
+  [74] The “Feu fixe, varié par des éclats,” or “Feu fixe, à courtes
+  éclipses,” of Fresnel.
+
+  ~Comparison of Dioptric and Catoptric Apparatus for Revolving Lights.~
+
+Having thus fully described the nature of the catoptric and dioptric
+modes of illuminating lighthouses, I shall next compare the merits of
+both systems, with a view to determine their eligibility in revolving
+or in fixed lights.
+
+Repeated experiments were made at Gullan-hill, which is distant
+from Edinburgh about fifteen miles, during the winters of 1832 and
+1833, under the inspection of the Commissioners of Northern Lights,
+the result of which was, that the light of one of the great annular
+lenses used in the revolving lights of the first order, was equal to
+the united effect of about eight of the large reflectors employed in
+the revolving lights on the Scotch coast. It may be said, however,
+that the dia-catoptric[75] combination of pyramidal lenses and plane
+mirrors of Corduan, adds the power of more than two reflectors to
+the effect of the great lens; but it ought to be remembered that in
+the French lights, this additional power is used only to compensate
+for one of the defects of the system by lengthening the duration
+of the flash, and therefore contributes, if at all, only in a very
+indirect manner, to render the light visible to the mariner at a
+greater distance. M. FRESNEL found, from the smaller divergence of
+the lens, that the eclipses were too long and the bright periods of
+the revolution too short; and he therefore determined to adopt the
+horizontal deviation of 7° for the upper lenses, with a view to remedy
+this defect. Assuming, therefore, that it were required to increase
+the number of reflectors in a revolving light of three sides, so as to
+render it equal in power to a dioptric revolving light of the first
+order, it would be necessary to place eight reflectors on each face,
+so that the greatest number of reflectors required for this purpose
+may be taken at _twenty-four_. M. FRESNEL has stated the expenditure
+of oil in the lamp of four concentric wicks at 750 grammes of colza
+oil per hour; and it is found by experience at the Isle of May and
+Inchkeith, that the quantity of spermaceti oil consumed by the great
+lamp, is equal to that burned by from fourteen to sixteen of the
+Argand lamps used in the Scotch lights. It therefore follows that, by
+dioptric means, the consumption of oil necessary for between fourteen
+and sixteen reflectors, will produce a light as powerful as that which
+would require the oil of twenty-four reflectors in the catoptric
+system of Scotland; and, consequently, that there is an excess of oil
+equal to that consumed by ten reflectors, or 400 gallons in the year,
+against the Scotch system. But in order fully to compare the economy
+of producing two revolving lights of equal power by those two methods,
+it will be necessary to take into the calculation the interest of the
+first outlay in establishing them.
+
+  [75] I use this word to designate the arrangement of pyramidal lenses
+  and plane mirrors, by which the light is first _refracted_, and then
+  _reflected_.
+
+The expense of fitting up a revolving light with twenty-four
+reflectors, ranged on three faces, may be estimated at L.1298, and
+the annual maintenance, including the interest of the first cost of
+the apparatus, may be calculated at L.418, 8s. 4d. The fitting up a
+revolving light with eight lenses and the dia-catoptric accessory
+apparatus, may be estimated at L.1459, and the annual maintenance at
+L.354, 10s. 4d. It therefore follows, that to establish and afterwards
+maintain a catoptric light of the kind called _revolving white_, with
+a frame of three faces, each equal in power to a face of the dioptric
+light of Corduan, an annual outlay of L.63, 18s. more would be required
+for the reflecting light than for the lens light; while for a light of
+the kind called _revolving red and white_, whose frame has four faces,
+at least thirty-six reflectors would be required in order to make the
+light even approach an equality to that of Corduan; and the catoptric
+light would in that case cost L.225 more than the dioptric light.
+
+The effect produced by burning an equal quantity of oil, in revolving
+lights on either system, may be estimated as follows:--In a revolving
+light, like that of Skerryvore, having eight sides, each lighting with
+its greatest power a horizontal sector of 4°, we have 32° (or _units_)
+of the horizon illuminated with the full power of 3200 Argand flames,
+and consequently an aggregate effect of 102,400 flames, produced by
+burning the oil required for _sixteen_ reflectors; while in a catoptric
+apparatus, like that of the old light at Inchkeith, having seven sides
+of one reflector, each lighting with its greatest power a sector of
+4°·25′, we have nearly 31° (or _units_) of the horizon illuminated with
+the full power of 400 Argand flames, and consequently an aggregate
+effect of 12,400 flames as the result of burning the oil required for
+_seven_ reflectors. Hence, the _effect_ of burning the same quantity
+of oil in revolving lights on either system, will be represented
+respectively by (¹⁶⁄₇) 12,400 = 28,343 for the catoptric, contrasted
+with 102,400 for the dioptric light; or, in other words, revolving
+lights on the dioptric principle use the oil more _economically_ than
+those on the catoptric plan, nearly in the ratio of 3·6 to 1.
+
+  ~Comparison of Catoptric and Dioptric Apparatus for Fixed Lights.~
+
+I shall now speak of fixed lights, to which the dioptric method is
+peculiarly well adapted. The effect produced by the consumption of a
+gallon of oil in a fixed light, with twenty-six reflectors, which is
+the smallest number that can be properly employed, may be estimated as
+follows:--The _mean_ effect of the light spread over the horizontal
+sector, subtended by one reflector, as deduced from measurements made
+at each horizontal degree, by the method of shadows, is equal to 174
+unassisted Argand burners. If, then, this quantity be multiplied by 360
+degrees, we shall obtain an aggregate effect of 62,640, which, divided
+by 1040 (the number of gallons burned during a year in _twenty-six_
+reflectors), would give 60 Argand flames for the effect of the light
+maintained throughout the year by the combustion of a gallon of oil.
+On the other hand, the power of a catadioptric light of the first
+order, like that lately established at Girdleness, may be estimated
+thus:--The _mean_ effect of the light produced by the joint effect of
+both the dioptric and catadioptric parts of a fixed light apparatus,
+may be valued at 450 Argand flames, which, multiplied by 360 degrees,
+gives an aggregate of 162,000; and if this quantity be divided by 570
+(the number of gallons burned by the great lamp in a year), we shall
+have about 284 Argand flames for the effect of the light produced by
+the combustion of a gallon of oil. It would thus appear that in fixed
+lights, the French apparatus, as lately improved, produces, as the
+_average_ effect of the combustion of the same quantity of oil over
+the whole horizon, upwards of _four times_ the amount of light that
+is obtained by the catoptric mode; although, in certain directions,
+opposite the axis of each reflector, the catoptric light be fully 50
+_per centum_ more powerful than the dioptric light.
+
+But the great superiority of the dioptric method chiefly rests upon
+its _perfect_ fulfilment of an important condition required in a
+fixed light, by distributing the rays _equally_ in every point of
+the horizon. In the event of the whole horizon not requiring to be
+illuminated, the dioptric light would lose a part of its superiority
+in economy, and when half the horizon only is lighted, it would be
+more expensive than the reflected light; but the greater power and
+more equal distribution of the light, may be considered of so great
+importance, as far to outweigh the difference of expense. In the
+latter case, too, an additional power (as noticed p. 293) can be
+given to the dioptric light, by placing at the landward side of the
+lightroom, spherical mirrors with their centres in the focus of the
+refracting apparatus.[76] The luminous cones, or pyramids of which
+such reflectors would form the bases, instead of passing off uselessly
+to the land, would thus be thrown back through the focal point, and
+finally refracted, so as to increase the effect of the light seaward,
+by nearly _one-third_ of the light which would otherwise be lost.
+
+  [76] A similar arrangement can also be made in revolving lights by
+  making the radius of the mirrors somewhat less than that of the
+  inscribed circle of the octagon bounded by the lenses, so that they
+  may circulate freely round the backs of the mirrors. The shortness of
+  the radius of the reflecting surface would, of course, increase the
+  divergence of the beam of light refracted through the lenses, as the
+  flame would, in this case, subtend a greater angle at the face of the
+  mirrors.
+
+The expense of establishing a fixed light composed of twenty-six
+reflectors, may be estimated at L.950, and its annual maintenance,
+including interest on the first cost of the apparatus, may be reckoned
+at L.425, 10s.: and the expense of fitting up a fixed light on the
+dioptric principle with catadioptric zones is L.1511, while its annual
+maintenance may be taken at L.285, 6s. 4d. It thus appears that the
+annual expenditure of the dioptric fixed light is L.140, 3s. 8d. less
+than that of a fixed light composed of twenty-six reflectors; while the
+_average_ effect, equally diffused over the horizon, is _four times_
+greater.
+
+The comparative views already given of the catoptric and dioptric modes
+of illuminating lighthouses, demonstrate that the latter produces more
+powerful lights by the combustion of the same quantity of oil; while it
+is obvious that the catoptric system insures a more certain exhibition
+of the light, from the fountain-lamps being less liable to derangement
+than the mechanical lamps used in dioptric lights. The balance,
+therefore, of real advantages or disadvantages, and, consequently, the
+propriety of adopting the one or the other system, involves a mixed
+question, not susceptible of a very precise solution, and leaving room
+for different decisions, according to the value which may be set upon
+obtaining a cheaper and better light, on the one hand, as contrasted,
+on the other, with less certainty in its exhibition.
+
+  ~Summary of considerations as to the fitness of the two systems for
+  Revolving Lights.~
+
+A few general considerations, serving briefly to recapitulate the
+arguments for and against the two systems, may not be out of place.
+And, first, regarding the fitness of dioptric instruments for revolving
+lights, it appears from the details above given,--
+
+1_st_, That by placing eight reflectors on each face of a revolving
+frame, a light may be obtained as brilliant as that derived from the
+great annular lens; and that, in the case of a frame of three sides,
+the excess of expense by the reflecting mode, would be L.63, 18s.; and
+in the case of a frame of four sides, the excess would amount to L.225.
+
+2_d_, That for burning oil economically in revolving lighthouses, which
+illuminate every point of the horizon successively, the lens is more
+advantageous than the reflector in the ratio of 3·6 to 1.
+
+3_d_, That the divergence of the rays from the lens being less than
+from the reflector, it becomes difficult to produce, by lenses, the
+appearance which characterises the catoptric revolving lights, already
+so well known to British mariners; and any change of existing lights
+which would, of course, affect their appearance, must, therefore,
+involve many grave practical objections which would not at all apply to
+the case of new lights.
+
+4_th_, That the uncertainty in the management of the lamp renders it
+more difficult to maintain the revolving dioptric lights without risk
+of extinction, an accident which has several times occurred at Corduan
+and other lighthouses both in France and elsewhere.
+
+5_th_, That the extinction of one lamp in a revolving catoptric light
+is not only less probable, but leads to much less serious consequences
+than the extinction of the single lamp in a dioptric light; because, in
+the first case, the evil is limited to diminishing the power of _one
+face_ by an _eighth part_; whilst, in the second, _the whole horizon
+is totally deprived of light_. The extinction of a lamp, therefore, in
+a dioptric light, leads to evils which may be considered _infinitely
+great_ in comparison with the consequences which attend the same
+accident in a catoptric light.
+
+  ~Summary of considerations as to the fitness of the two systems for
+  Fixed Lights.~
+
+In comparing the fixed dioptric, and the fixed catoptric apparatus, the
+results may be summed up under the following heads:--
+
+1_st_, It is impossible, by means of any practicable combination of
+paraboloïdal reflectors, to distribute round the horizon a zone of
+light of exactly _equal intensity_; while this may be easily effected,
+by dioptric means, in the manner already described. In other words,
+the qualities required in fixed lights cannot be so fully obtained by
+reflectors as by refractors.
+
+2_d_, The _average_ light produced in every azimuth by burning
+one gallon of oil in Argand lamps, with reflectors, is only about
+_one-fourth_ of that produced by burning the same quantity in the
+dioptric apparatus; and the annual expenditure is L.140, 3s. 8d. less
+for the entire dioptric light than for the catoptric light.
+
+3_d_, The _characteristic_ appearance of the fixed reflecting light in
+any one azimuth would not be changed by the adoption of the dioptric
+method, although its increased _mean_ power would render it visible
+at a greater distance in almost every direction; the only exception
+being in the azimuths opposite the axis of each reflector, where the
+catoptric light has an _excess_ of power equal to about 50 _per centum_.
+
+4_th_, From the equal distribution of the rays, the dioptric light
+would be observed at equal distances in every point of the horizon; an
+effect which cannot be fully attained by any practicable combination of
+paraboloïdal reflectors.
+
+5_th_, The inconveniences arising from the uncertainty which attends
+the use of the mechanical lamp, are not perhaps so much felt in a
+fixed as in a revolving light, because the greater simplicity of the
+apparatus admits of easier access to it, in case of accident.
+
+6_th_, But the extinction of a lamp in a catoptric light, leaves only
+one _twenty-sixth part_ of the horizon without the benefit of the
+light, and the chance of accident arising to vessels from it, may,
+therefore, be considered as incalculably less than the danger resulting
+from the extinction of the single lamp of the dioptric light, which
+deprives the whole horizon of light.
+
+7_th_, There may also, in certain situations, be some risk arising from
+irregularity in the distances at which the same fixed catoptric light
+can be seen in the different azimuths. This defect, of course, does not
+exist in the dioptric light.
+
+  ~Advantages and disadvantages of both systems under certain
+  circumstances.~
+
+There can be little doubt, that the more fully the system of FRESNEL is
+understood, the more certainly will it be preferred to the catoptric
+system of illuminating lighthouses, at least in those countries where
+this important branch of administration is conducted with the care
+and solicitude which it deserves. It must not, however, be imagined,
+that there are no circumstances in which the catoptric system is not
+absolutely preferable to illumination by means of lenses. We have
+hitherto attended only to horizontal divergence and its effects, and
+this is unquestionably the more important view; but the consideration
+of vertical divergence must not be altogether overlooked. Now, while
+it is obvious that vertical divergence, at least above the horizon,
+involves a total loss of the light which escapes uselessly upwards into
+space, it is no less true, that if the sheet of light which reaches
+the most distant horizon of the lighthouse, however brilliant, were as
+thin as the absence of all vertical divergence would imply, it would be
+practically useless; and some measure of dispersion in the arc _below_
+the horizon is therefore absolutely indispensable to constitute a
+really useful light. In the reflector, the greatest vertical divergence
+below the horizontal plane of the focus is 16° 8′, and that of the lens
+is about 4° 30′.
+
+Let us consider for a moment the bearing of those facts upon the
+application of the two modes of illumination to special circumstances.
+The powerful beam of light transmitted by the lens, peculiarly fits
+that instrument for the great sea-lights which are intended to warn
+the mariner of his approach to a distant coast which he first makes on
+an _over-sea_ voyage; and the deficiency of its divergence, whether
+horizontal or vertical, is not practically felt as an inconvenience
+in lights of that character, which seldom require to serve the double
+purpose of being visible at a great distance, and at the same time of
+acting as guides for dangers near the shore. For such purposes, the
+lens applies the light much more economically than the reflector,
+because, while the duration of its _least_ divergent beam is nearly
+equal to that of the reflector, it is _eight_ times more powerful.
+A revolving system of eight lenses illuminates an horizontal arc of
+32° with this bright beam. The reflector, on the other hand, spreads
+the light over a larger arc of the horizon; and, while its _least_
+divergent beam is much less powerful than that of the lens, the
+light which is shed over its _extreme_ arc is so feeble as to be
+practically of little use in lights of extensive range, even during
+clear weather. When a lighthouse is placed on a very high headland,
+however, the deficiency of divergence in the vertical direction is
+often found to be productive of some practical inconvenience; but this
+defect may be partially remedied by giving to the lenses a slight
+inclination outwards from the vertical plane of the focus, so as to
+cause the most brilliant portion of the emergent beam to reach the
+_visible horizon_ which is due to the height of the lantern. It may
+be observed, also, that a lantern at the height of 150 feet, which,
+taking into account the common height of the observer’s eye at sea,
+commands a range of upwards of 20 English miles, is sufficient for
+all the ordinary purposes of the navigator, and that the intermediate
+space is practically easily illuminated, even to within a mile of
+the lighthouse, by means of a slight inclination of the subsidiary
+mirrors, even where the light from the principal part of the apparatus
+passes over the seaman’s head. For the purpose of leading lights,
+in narrow channels, on the other hand, and for the illumination of
+certain narrow seas, there can be no doubt that reflectors are much
+more suitable and convenient. In such cases, the amount of vertical
+divergence below the horizon, forms an important element in the
+question, because it is absolutely necessary that the mariner should
+keep sight of the lights even when he is very near them; while there is
+not the same call for a very powerful beam which exists in the case of
+sea-lights. Yet even in narrow seas, where low towers, corresponding
+to the extent of the _range_ of the light, are used, but where it is,
+at the same time, needful to illuminate the whole or the greater part
+of the horizon, the use of dioptric instruments will be found almost
+unavoidable, especially in fixed lights, as well from their equalizing
+the distribution of the light in every azimuth, as from their much
+greater economy in situations where a large annual expenditure would
+often be disproportionate to the revenue at disposal. In such places,
+where certain peculiarities of the situation require the combination of
+a light equally diffused over the greater portion of the horizon, along
+with a greater vertical divergence in certain azimuths, than dioptric
+instruments afford, I have found it convenient and economical to add
+to the fixed refracting apparatus a single paraboloïdal reflector, in
+order to produce the desired effect, instead of adapting the whole
+light to the more expensive plan for the sake of meeting the wants of
+a single narrow sector of its range. In other cases, where the whole
+horizon is to be illuminated, and great vertical divergence is at the
+same time desirable, a slight elevation of the burner, at the expense,
+no doubt, of a small loss of light, is sometimes resorted to, and is
+found to produce, with good effect, the requisite depression of the
+emergent rays.
+
+In certain situations, where a great range and, consequently, a
+powerful light must be combined with tolerably powerful illumination
+in the immediate vicinity of the lighthouse, we might, perhaps,
+advantageously adopt a variation of the form and dimensions of the
+mirrors employed, so as to resemble those formerly employed at the
+Tour de Corduan, which were of considerably larger surface and longer
+focal distance than those which are used in Britain. If such a form
+were adopted, the power of the light for the purpose of the distant
+range would be increased; and I would propose to compensate for the
+deficiency of divergence consequent on a long focal distance, by
+placing a second burner in some position between the parameter and the
+vertex, and slightly elevated above the axis of the instrument, so as
+to throw the greater portion of the beam resulting from this second
+burner below the horizontal plane of the focus. Such an expedient
+is no doubt somewhat clumsy and would at the same time involve the
+consumption of twice the quantity of oil used in an ordinary catoptric
+light; but I can still conceive it to be preferable, in certain
+situations, to the use of lenses alone.
+
+Thus it appears that we must not too absolutely conclude against one,
+or in favour of the other mode of illumination for lighthouses; but, as
+in every other department of the arts, we shall find the necessity of
+patiently weighing all the circumstances of each particular case that
+comes before us, before selecting that instrument, or combination of
+instruments, which appears most suitable.
+
+  ~Distinctions of the Dioptric Lights, and the application of coloured
+  media.~
+
+The mode of distinguishing lights in the system of FRESNEL, depends
+more upon their _magnitude_ and the _measured interval_ of the time
+of their revolution, than upon their _appearance_; and no other very
+marked distinctions, except Fixed and Revolving, have been successfully
+attempted in France. As above stated, I consider the distinction of
+the _fixed light varied by flashes_, to possess an appearance too
+slightly differing from that of a revolving light, to admit of its
+being safely adopted in situations where revolving lights are near.
+The trial which I made at the Little Ross, in the Solway Frith, of
+producing, by means of lenses, a light flashing once in five seconds of
+time, although successful so far as mere distinction is concerned, has
+several practical defects, arising from the shortness of the duration
+of the flashes, compared with the powerful effect of the fixed part
+of the apparatus, which I consider sufficient to prevent its adoption
+in future, especially considering that a much more marked appearance
+can be produced, by means of reflectors, as has been done at the
+Buchanness in Aberdeenshire, and the Rhinns of Islay in Argyllshire.
+Coloured media have never, so far as I know, been applied to Dioptric
+apparatus, except in the case of the Maplin Light at the mouth of
+the Thames, and Cromarty Point Light at the entrance to the Cromarty
+Frith, and in both instances successfully. The enormous loss of light,
+however, amounting to no less than 0·80 of the whole incident rays,
+forms a great bar to the adoption of colour as a distinction; and any
+means which could tend to lessen that absorption, and at the same
+time produce the characteristic appearance, would be most valuable.
+I have tried some glasses of a pink tinge, prepared by M. LETOURNEAU
+of Paris, whose absorption does not exceed 0·57 of the incident rays;
+but the appearance of the light, at a distance, is much less marked
+than that produced by the glasses used in Britain.[77] Such deficiency
+of characteristic colour might lead to serious consequences, as the
+transmission of white rays, through a hazy atmosphere, too often
+produces, by absorption, a reddish tinge of the light, for which
+the less marked appearance given by the paler media might be easily
+mistaken. This colouring power of absorption is so well known, that red
+lights are seldom used except in direct contrast with white ones; but,
+on a coast so thickly studded with Lighthouses as that of Britain, the
+number of distinctions is insufficient to supply all our wants, so that
+we are sometimes reluctantly compelled to adopt a _single red light_
+in some situation of lesser importance, or which, from some local
+circumstances and the appearance of the lights which must be seen by
+the mariner before passing it, is not likely to be mistaken. The great
+loss of light by coloured media causes the red beam, in a revolving
+light, to be seen at a shorter distance than the white; and it is
+conceivable that, in certain circumstances, this might lead the mariner
+to mistake a _red and white light_ for a _white_ light revolving at
+half the velocity. Such a mistake might perhaps prove dangerous; but
+the lights are generally so situated that there is ample time for the
+mariner, after first discovering the red light, and thus correcting
+any mistake, to shape his course accordingly. All other coloured media
+except _red_ have been found useless as distinctions for any lights
+of extensive range, and fail to be efficient, owing to the necessity
+of absorbing almost all the light before a marked appearance can be
+obtained. In a few pier or ferry lights, green and blue media have been
+tried, and found available at the distance of a few cables’ lengths.
+
+  [77] See page 229, _ante_.
+
+  ~Captain BASIL HALL’s proposal for producing the appearance of Fixed
+  Lights by rapid movement.~
+
+It seems to be a natural consequence of the physical distribution
+of light, that fixed lights, which illuminate the whole horizon,
+should be less powerful than revolving lights which have their effect
+concentrated within narrow sectors of the horizon. Any attempt to
+increase the power of fixed lights is, therefore, worthy of attention;
+and when the late Captain BASIL HALL proposed a plan for effecting
+this object, it received, as it deserved, the full consideration of
+the Lighthouse Board, who authorised me to repeat Captain HALL’S
+experiments, and verify his results by observations made at a
+considerable distance. As some interesting phenomena of irradiation
+were evolved in the course of those trials, I think it right to
+give some account of the results which were obtained, as they bear
+upon various questions connected with the practical arrangements of
+Lighthouses, under certain circumstances.
+
+In revolving lights on the dioptric principle, the annular lens of
+Fresnel, as formerly stated, is employed. This instrument, as the
+reader already knows, possesses the property of projecting to the
+horizon, in the form of _one_ pencil or beam, all the light which falls
+on its inner surface from a lamp placed in its principal focus. The
+consequence of this action is, that when several lenses are so arranged
+as to form a right prism which circulates round a lamp placed in the
+common focus, a distant observer receives from each lens, as its axis
+crosses his line of vision, a bright flash, which is succeeded by total
+darkness, when one of the dark spaces intermediate between the lenses
+passes over his eye; and this succession of bright flashes alternating
+with dark intervals, produces the characteristic appearance of a
+revolving light.
+
+The fixed light, on the other hand, presents to the eye a steady
+and unchanging appearance; and the chief object to be obtained in
+its construction, is to unite the greatest brilliancy with an equal
+distribution of the light in every direction. The condition of perfect
+distribution, as already said, is most rigorously fulfilled by the use
+of refracting zones or belts, which form, by their union, a cylinder
+enveloping the flame placed in its centre, and possess the property of
+refracting the light in the vertical direction only, without affecting
+its natural divergence horizontally. The light from the focus which
+is incident on the inner surface of the belt is therefore projected
+forwards in the shape of a flat ring of equal brilliancy all round the
+horizon.
+
+This repetition may seem needless, but it is hoped it will be found
+useful in rendering intelligible the following outline of the plan
+proposed by Captain HALL for the improvement of fixed lights, and the
+account of the trials that were made with that object in view.
+
+The familiar experiment of whirling a burning stick quickly round the
+head, so as to produce a ribbon of light, proves the possibility of
+causing a continuous impression on the retina by intermittent images
+succeeding each other with a certain rapidity. From the moderate
+velocity at which this continuity of impression is obtained, we should
+be warranted in concluding, _a priori_, that the time required to make
+an impression on the retina is considerably less than the duration of
+the impression itself; for the continuity of effect must, of course,
+be caused by fresh impulses succeeding each other before the preceding
+ones have entirely faded. If it were otherwise, and the time required
+to make the impression were equal to the duration of the sensation, it
+would obviously be impossible to obtain a series of impulses so close
+or continuous in their effects as to run into and overlap each other,
+and thus throw out the intervals of darkness; because the same velocity
+which would tend to shorten the dark intervals, would also curtail
+the bright flashes, and thus prevent their acting on the eye long
+enough to cause an impression. Accordingly, we find that the duration
+of an impression is in reality much greater than the time required
+for producing the effect on the retina. It is stated by Professor
+WHEATSTONE, in the London Transactions for 1834, that only about
+_one millionth part_ of a second is required for making a distinct
+impression on the eye; and it appears, from a statement made by Lamé,
+at p. 425 of his Cours de Physique, that M. PLATEAU found that an
+impression on the retina preserved its intensity unabated during _one
+hundredth_ of a second, so that, however small those times may be in
+themselves, the one is yet 10,000 greater than the other.
+
+It has been ascertained by direct experiment,[78] that the eye can
+receive a fresh impression before the preceding one has faded; and,
+indeed, if this were impossible, absolute continuity of impression
+from any succession of impulses, however rapid, would seem to be
+unattainable; and the approach to perfect continuity would be inversely
+as the time required to make an impression.
+
+  [78] Lamé, Cours de Physique, p. 424. “L’impression peut subsister
+  encore lorsque la suivante a lieu.”
+
+  ~Effects of rapid motion on the power of Lights.~
+
+From this property which bright bodies passing rapidly before the
+eye possess of communicating a continuous impression to the sense of
+sight, Captain HALL conceived the idea, not merely of obtaining all
+the effects of a fixed light, by causing a system of lenses to revolve
+with such a velocity as to produce a continuous impression, but, at
+the same time, of obtaining a much more brilliant appearance, by
+the compensating influence of the bright flashes, which he expected
+would produce impulses sufficiently powerful and durable to make the
+deficiency of light in the dark spaces almost imperceptible. The
+mean effect of the whole series of changes would, he imagined, be
+thus greatly superior to that which can be obtained from the same
+quantity of light equally distributed, as in fixed lights, over the
+whole horizon. Now this expectation, if it be considered solely in
+reference to the physical distribution of the light, involves various
+difficulties. The quantity of light subjected to instrumental action
+is the same whether we employ the refracting zones at present used in
+fixed dioptric lights, or attempt to obtain continuity of effect by
+the rapid revolution of lenses; and the only difference in the action
+of those two arrangements is this, that while the zones distribute
+the light equally over the whole horizon, or rather do not interfere
+with its natural horizontal distribution, the effect of the proposed
+method is to collect the light into pencils, which are made to revolve
+with such rapidity, that the impression from each pencil succeeds the
+preceding one in time to prevent a sensible occurrence of darkness.
+To expect that the mean effect of the light, so applied, should be
+greater than when it is left to its natural horizontal divergence,
+certainly appears at first to involve something approaching to a
+contradiction of physical laws. In both cases, the same quantity of
+light is acted upon by the instrument; and in either case, any one
+observer will receive an impression similar and equal to that received
+by any other stationed at a different part of the horizon; so that,
+unless we imagine that there is some loss of light peculiar to one
+of the methods, we are, in the physical view of the question, shut
+up to the conclusion, that the impressions received by each class of
+observers must be of equal intensity. In other words, the same quantity
+of light is by both methods employed to convey a continuous impression
+to the senses of spectators in every direction, and in both methods
+equality of distribution is effected, since it does not at all consist
+with our hypothesis, that any one observer in the same class should
+receive more or less than his equal share of the light. Then, as to
+the probability of the loss of light, it seems natural to expect that
+this should occur in connection with the revolving system, because the
+velocity is an extraneous circumstance, by no means necessary to an
+equal distribution of the light, which can, as we already know, be more
+naturally and at the same time perfectly, attained by the use of the
+zones.
+
+On the other hand, it must not be forgotten, that although the effect
+of both methods is to give each part of the horizon an equal share
+of light, there is yet this difference between them, that while the
+light from the zones is equally intense at every instant of time,
+that evolved by the rapidly circulating lenses is constantly passing
+through every phase between total darkness and the brightest flash of
+the lens; and this difference, taken in connection with some curious
+physiological observations regarding the sensibility of the retina,
+gives considerable countenance to the expectation on which Captain
+HALL’S ingenious expedient is based. The fact which has already
+been noticed, and which the beautiful experiments of M. PLATEAU and
+Professor WHEATSTONE have of late rendered more precise, that the
+duration of an impression on the retina is not only appreciable,
+but is much greater than the time required to cause it, seems to
+encourage us in expecting, that while the velocity required to produce
+continuity of effect would not be found so great as to interfere
+with the formation of a full impression, the duration of the impulse
+from each flash would remain unaltered, and the dark intervals which
+do not excite the retina would, at the same time, be shortened, and
+that, therefore, we might in this manner obtain an effect on the
+senses exceeding the brilliancy of a steady light distributed equally
+in every direction by the ordinary method. Some persons, indeed, who
+have speculated on this subject, seem even to be of opinion, that,
+so far from the whole effect of the series of continuous impressions
+being weakened by a blending of the dark with the bright intervals,
+the eye would in reality be stimulated by the contrast of light and
+darkness, so as thereby to receive a more complete and durable impulse
+from the light. It is obvious, however, that this question regarding
+the probable effect to be anticipated from a revolution so rapid as
+to cause a continuous impression, could only have been satisfactorily
+answered by an appeal to experiment.
+
+In experimenting on this subject, I used the apparatus formerly
+employed by Captain HALL. It consisted of an octagonal frame, which
+carried eight of the discs that compose the central part of Fresnel’s
+compound lens, and was susceptible of being revolved slowly or quickly
+at pleasure, by means of a crank-handle and some intermediate gearing.
+The experiments were nearly identical with those made by Captain HALL,
+who contrasted the effect of a single lens at rest, or moving very
+slowly, with that produced by the eight lenses, revolving with such
+velocity as to cause an apparently continuous impression on the eye.
+To this experiment I added that of comparing the beam thrown out by
+the central portion of a cylindric refractor, such as is used at the
+fixed light of the Isle of May, with the continuous impression obtained
+by the rapid revolution of the lenses. Captain HALL made all his
+comparisons at the short distance of 100 yards; and in order to obtain
+some measure of the intensity, he viewed the lights through plates of
+coloured glass until the luminous discs became invisible to the eye.
+I repeated those experiments at Gullan, under similar circumstances,
+but with very different results. I shall not, however, enter upon the
+discussion of those differences here, although they are susceptible
+of explanation, and are corroborative of the conclusions at which I
+arrived, by comparing the lights from a distance of 14 miles; but shall
+briefly notice the more important results which were obtained by the
+distant view. They are as follows:--
+
+1. The flash of the lens revolving slowly was very much larger than
+that of the rapidly revolving series; and this decrease of size in the
+luminous object presented to the eye, became more marked as the rate of
+revolution was accelerated, so that, at the velocity of eight or ten
+flashes in a second, the naked eye could hardly detect it, and only
+a few of the observers saw it; while the steady light from the fixed
+refractor was distinctly visible.
+
+2. There was also a marked falling off in the brilliancy of the rapid
+flashes as compared with that of the slow ones; but this effect was by
+no means so striking as the decrease of volume.
+
+3. Continuity of impression was not attained at the rate of five
+flashes in a second, but each flash appeared to be distinctly separated
+by an interval of darkness; and even when the nearest approach to
+continuity was made, by the recurrence of eight or ten flashes in a
+second, the light still presented a twinkling appearance, which was
+well contrasted with the steady and unchanging effect of the cylindric
+refractor.
+
+4. The light of the cylindric refractor was, as already stated, steady
+and unchanging, and of much larger volume than the rapidly revolving
+flashes. It did not, however, appear so brilliant as the flashes of the
+quickly revolving lenses, more especially at the lower rate of five
+flashes in a second.
+
+5. When viewed through a telescope, the difference of volume between
+the light of the cylindric refractor and that produced by the lenses
+at their greatest velocity was very striking. The former presented a
+large diffuse object of inferior brilliancy, while the latter exhibited
+a sharp pin-point of brilliant light.
+
+Upon a careful consideration of these facts it appears warrantable to
+draw the following general conclusions:--
+
+1. That our expectations as to the effects of light, when distributed
+according to the law of its natural horizontal divergence, are
+supported by observed facts as to the visibility of such lights,
+contrasted with those whose continuity of effect is produced by
+collecting the whole light into bright pencils, and causing them to
+revolve with great velocity.
+
+2. It appears that this deficiency of visibility seems to be chiefly
+due to a want of volume in the luminous object, and also, although in
+a less degree, to a loss of intensity, both of which defects appear
+to increase in proportion as the motion of the luminous object is
+accelerated.
+
+3. That this deficiency of volume is the most remarkable optical
+phenomenon connected with the rapid motion of luminous bodies, and that
+it appears to be directly proportional to the velocity of their passage
+over the eye.
+
+4. That there is reason to suspect that the visibility of distant
+lights depends on the volume of the impression in a greater degree than
+has perhaps been generally imagined.
+
+5. That, as the size and intensity of the radiants causing these
+various impressions to a distant observer were the same, the volume
+of the light and, consequently, _cæteris paribus_, its visibility,
+are, within certain limits, proportionate to the time during which the
+object is present to the eye.
+
+Such appear to be the general conclusions which those experiments
+warrant us in drawing; and the practical result, in so far as
+lighthouses are concerned, is sufficient to discourage us from
+attempting to improve the visibility of fixed lights in the manner
+proposed by Captain HALL, even supposing the practical difficulties
+connected with the great centrifugal force generated by the rapid
+revolution of the lenses to be less than they really are.
+
+  ~Connection of the experiments with Irradiation.~
+
+This decrease in the volume of the luminous object caused by the rapid
+motion of the lights is interesting, from its apparent connection with
+the curious phenomenon of irradiation. When luminous bodies, such as
+the lights of distant lamps, are seen by night, they appear much larger
+than they would do by day; and this effect is said to be produced by
+irradiation. M. PLATEAU, in his elaborate essay on this subject, after
+a careful examination of all the theories of irradiation, states it
+to be his opinion, that the most probable mode of accounting for the
+various observed phenomena of irradiation is to suppose, that, in the
+case of a night-view, the excitement caused by light is propagated over
+the retina beyond the limits of the day-image of the object, owing to
+the increased stimulus produced by the contrast of light and darkness;
+and he also lays it down as a law confirmed by numerous experiments,
+that irradiation increases with the duration of the observation. It
+appears, therefore, not unreasonable to conjecture, that the deficiency
+of volume observed during the rapid revolution of the lenses may have
+been caused by the light being present to the eye so short a time, that
+the retina was not stimulated in a degree sufficient to produce the
+amount of irradiation required for causing a large visual object. When,
+indeed, the statement of M. PLATEAU, that irradiation is proportional
+to the duration of the observation, is taken in connection with the
+observed fact, that the volume of the light decreased as the motion
+of the lenses was accelerated, it seems almost impossible to avoid
+connecting together the two phenomena as cause and effect.
+
+
+VARIOUS GENERAL CONSIDERATIONS CONNECTED WITH LIGHTHOUSES.
+
+  ~Masking Lights.~
+
+In the course of supplying the numerous wants of navigation, it will
+often be found necessary to _cut off_, on a given bearing, the beam
+proceeding from a Lighthouse, as a guide to the seaman to avoid some
+shoal, or as a hint to put about and seek the opposite side of a
+channel. This is attended with some little practical difficulty,
+especially in lights from reflectors arranged externally on a circle,
+because a certain portion of light, chiefly due to the divergence
+caused by the size of the flames, and partly from the effects of the
+diffraction or inflexion of the light, spreads faintly over a narrow
+sector between the light arc and the dark one. It becomes necessary,
+of course, to make allowance for this penumbral arc by increasing
+the masked portion of the lantern; and, where a very sharp line of
+demarcation is required, a board is sometimes placed on the outside of
+the Lightroom, in such a position, and of such length, that while it
+does not enter the boundaries of the luminous sector, it prevents the
+more powerful part of the penumbral beam from reaching the observer’s
+eye. This effect is, of course, more conveniently produced, where the
+circumstances admit of its adoption, by distributing the reflectors
+round the concave side of the lantern, towards the land; but such an
+arrangement is inapplicable when the illuminated sector exceeds the
+dark one. I have found, by observation, that the sector intercepted
+between the azimuth on which the lantern is masked and that on which
+total darkness is produced to an observer, at moderate distances, may
+be estimated at not less than 3° for dioptric, and 7° for catoptric
+lights of the highest class.[79]
+
+  [79] The method which I adopted for determining those quantities, was
+  to mask a certain portion of the lantern of a lighthouse subtending
+  an horizontal sector of about 30° or 40°, and at night to fix, by
+  actual observation, at the distance of 5 or 6 miles, two points on
+  the coast between which the light so masked was obscured. The angle
+  included between the lines joining those points and the centre of the
+  lantern was then determined by triangulation next day, and _half the
+  difference_ between the observed angle (which is always the _lesser_
+  of the two) and the computed subtense of the masked sector of the
+  lantern, is, in each case, the amount of the allowance stated in the
+  text.
+
+Those quantities may therefore serve to guide the Lighthouse engineer
+to approximate more rapidly to his object, as he will generally be safe
+in increasing the dark sector, by one or other of the above constants,
+according to the kind of apparatus employed. I need not add, that in a
+matter of this kind, a final appeal to actual observation is, in all
+cases, indispensable.
+
+  ~Double Lights.~
+
+A few words on the subject of double lights, naturally spring out
+of what has been said about the masking of lights. The term _double
+lights_ is properly and distinctly confined to lights on different
+levels, but not _necessarily_ (as _leading-lights_ are) in separate
+towers. The sole object of using double lights is for _distinction_
+from neighbouring lights; and they are unquestionably most effective in
+this respect, when they are placed in the same tower. In this point of
+view, therefore, I shall speak of them; and it is obvious that all that
+peculiarly belongs to them is, that the difference of level between
+them shall be sufficiently great to present the lights as separate
+objects to the eye of the seaman, when placed at the greatest distance
+at which it may be desirable that he should be able to recognise their
+characteristic appearance. In many cases it is not necessary (but
+it is certainly always desirable) that the lights should, from the
+first moment of their being seen, be known as _double lights_; but
+in others, it may well consist with safety, that two lights, which
+appear as a single light when first seen at the distance of 20 miles,
+shall at 15 or 10 miles distance be discovered to be _double_. Now we
+should at first be apt hastily to imagine, that all that is required
+to produce that effect, is to raise the one light above the other to
+such an extent, that the distance between them shall be somewhat more
+than a _minimum visibile_ at the most distant point of observation,
+or, in other words, that the difference of the height of the lights
+should be such as to subtend to the eye at the point of observation,
+an angle greater than 13″·02, which is the subtense of a _minimum
+visibile_ during the day.[80] But the effect of irradiation, to which
+I have already alluded, tends to blend together the images of the
+lights long before their distance apart has become so low a fraction
+of the observer’s distance from the Lighthouse, as to subtend so
+small an angle; and I have accordingly found by experiments, conducted
+under various circumstances, and at various distances, that repeated
+observations gave me 3′ 18″ as the mean of the subtenses calculated in
+reference to the distances at which the lights began to be blended into
+_one_.
+
+  [80] This quantity is deduced from observations made by my friend
+  Mr JAMES GARDNER, while engaged on the Ordnance Survey, and may
+  be regarded as the _extreme_ limit of visibility, under the most
+  favourable circumstances as to the state of the atmosphere and also
+  the contrast of colours. The observed object, also, was a pole, not
+  a _round_ disc; and it is familiar to every one accustomed to view
+  distant objects, that _vertical length_ is an important constituent
+  in their visibility.
+
+Adopting this as the smallest angle which the two lights should subtend
+at the observer’s eye, we may find the least vertical distance between
+them which will cause them to appear as separate objects by the
+following formula:
+
+  H = 2 Δ . tan θ
+
+in which Δ is the observer’s distance in feet; θ, half the subtense, =
+1′ 39″; and H the required height of the tower between the two lights
+in feet. The following Table gives the height in feet corresponding
+to the distance in nautic miles, from 1 to 20 inclusive: the heights,
+which are the bases of _similar_ isosceles triangles, increase, of
+course, in an arithmetical series:
+
+  +---------------+-----------------++---------------+-----------------+
+  |Distance of the|Vertical distance||Distance of the|Vertical distance|
+  |  observer in  | in feet between ||  observer in  | in feet between |
+  | Nautic Miles. |   the Lights.   || Nautic Miles. |   the Lights.   |
+  +---------------+-----------------++---------------+-----------------+
+  |        1      |       6·02      ||       11      |      66·22      |
+  |        2      |      12·04      ||       12      |      72·24      |
+  |        3      |      18·06      ||       13      |      78·26      |
+  |        4      |      24·08      ||       14      |      84·28      |
+  |        5      |      30·10      ||       15      |      90·30      |
+  |        6      |      36·12      ||       16      |      96·32      |
+  |        7      |      42·14      ||       17      |     102·34      |
+  |        8      |      48·16      ||       18      |     108·36      |
+  |        9      |      54·18      ||       19      |     114·38      |
+  |       10      |      60·20      ||       20      |     120·40      |
+  +---------------+-----------------++---------------+-----------------+
+
+  ~Leading Lights.~
+
+Akin to the subject of _Double Lights_, is that of _Leading Lights_,
+the object of which is to indicate to the mariner a given line of
+direction by their being seen _in one line_. In most instances, this
+line of direction is used to point out the central part of a narrow
+channel; and the alternate _opening_ of the lights, on either side of
+their _conjunction_, serves to indicate to the mariner (who ought to
+conjoin with his watching of the lights the observation of the elapsed
+time and also frequent soundings) the proper moment for changing his
+tack. In some places, the line of conjunction of the lights is placed
+nearer to one side of a channel than the other, according as the set
+of the tides, or the position of shoals, may seem to require. In other
+situations, this line only serves as a _cross-bearing_ to shew the
+mariner his approach to some danger, or to indicate his having passed
+it, and thus to assure him of his entry on wider _sea-room_. Similar
+considerations to those which determine the difference of elevation for
+_double lights_ regulate the choice of the distance between two leading
+lights; but the question is less narrow, and may be generally solved
+graphically by simply drawing the lines on an accurate chart of the
+locality. In some few situations, the configuration of the coast does
+not admit of a separation between the lights, sufficient to cause what
+is called a _sharp intersection_; but, in most cases, there is room
+enough to place them so far apart, that but a few yards of deviation
+in the vessel’s course, from the exact line of the conjunction of
+the lights _in one_, produces a distinct opening between them on the
+opposite side of that line. In order to insure the requisite sharpness
+of intersection, the distance between the lights, wherever attainable,
+should be not less than _one-sixth_ of the distance between the more
+seaward of the two Towers and that point at which the seaman begins to
+use the line of conjunction as his guide. I have only to add, that in
+situations where the land prevents a considerable separation between
+leading lights, they should be placed as nearly on _one level_ as is
+consistent with their being seen as _vertically_ separated, so as in
+some measure to compensate for their horizontal nearness, by rendering
+their intersection more sharp and striking than it can be where the
+observer must draw from the upper light an imaginary perpendicular
+in his mind, and then estimate the separation of the lights by the
+sine of an angle, which decreases as the difference of their apparent
+elevations increases.
+
+  ~Distribution of Lights on a Coast.~
+
+The considerations which enter into the choice of the position and
+character of the Lights on a line of coast, are either, on the one
+hand, so simple and self-evident as scarcely to admit of being stated
+in a general form, without becoming mere truisms; or are, on the
+other hand, so very numerous and often so complicated as scarcely to
+be susceptible of compression into any general laws. I shall not,
+therefore, do more than very briefly allude to a few of the chief
+considerations which should guide us in the selection of the sites and
+characteristic appearance of the Lighthouses to be placed on a line of
+coast. Perhaps those views may be most conveniently stated in the form
+of distinct propositions:--
+
+1. The most prominent points of a line of coast, or those first made
+on _over-sea_ voyages, should be first lighted; and the most powerful
+lights should be adapted to them, so that they may be discovered by the
+mariner as long as possible before his reaching land.
+
+2. So far as is consistent with a due attention to distinction,
+revolving lights of some description, which are necessarily more
+powerful than fixed lights, should be employed at the outposts on a
+line of coast.
+
+3. Lights of precisely identical character and appearance should not,
+if possible, occur within a less distance than 100 miles of each other
+on the same line of coast, which is made by over-sea vessels.
+
+4. In all cases, the distinction of colour should never be adopted
+except from absolute necessity.
+
+5. Fixed lights and others of less power, may be more readily adopted
+in narrow seas, because the _range_ of the lights in such situations is
+generally less than that of open sea-lights.
+
+6. In narrow seas also, the distance between lights of the same
+appearance may often be safely reduced within much lower limits than is
+desirable for the greater sea-lights; and there are many instances in
+which the distance separating lights of the same character need not
+exceed 50 miles, and there are peculiar cases in which even a much less
+separation between similar lights may be sufficient.
+
+7. Lights intended to guard vessels from reefs, shoals, or other
+dangers, should in every case be placed, where practicable, to the
+seaward of the danger itself, as it is desirable that seamen be enabled
+to make the lights with confidence.
+
+8. Views of economy in the first cost of a Lighthouse should never be
+permitted to interfere with placing it in the best possible position;
+and, when funds are deficient, it will generally be found that the
+wisest course is to delay the work until a sum shall have been obtained
+sufficient for the erection of the lighthouse on the best site.
+
+9. The elevation of the lantern above the sea should not, if possible,
+for sea-lights, exceed 200 feet; and about 150 feet is sufficient,
+under almost any circumstances, to give the range which is required.
+Lights placed on high headlands are subject to be frequently wrapped in
+fog, and are often thereby rendered useless, at times when lights on a
+lower level might be perfectly efficient. But this rule must not, and
+indeed cannot, be strictly followed, especially on the British coast,
+where there are so many projecting cliffs, which, while they subject
+the lights placed on them to occasional obscuration by fog, would also
+entirely and permanently hide from view lights placed on the lower land
+adjoining them. In such cases, all that can be done is carefully to
+weigh all the circumstances of the locality, and choose that site for
+the lighthouse which seems to afford the greatest balance of advantage
+to navigation. As might be expected, in questions of this kind, the
+opinions of the most experienced persons are often very conflicting,
+according to the value which is set on the various elements which enter
+into the inquiry.
+
+10. The best position for a sea-light ought rarely to be neglected for
+the sake of some neighbouring port, however important or influential;
+and the interests of navigation, as well as the true welfare of the
+port itself, will generally be much better served by placing the
+sea-light _where it ought to be_, and adding, on a smaller scale, such
+subsidiary lights as the channel leading to the entrance of the port
+may require.
+
+11. It may be held as a general maxim, that the fewer lights that
+can be employed in the illumination of a coast the better, not only
+on the score of economy, but also of real efficiency. Every light
+needlessly erected may, in certain circumstances, become a source of
+confusion to the mariner, and, in the event of another light being
+required in the neighbourhood, it becomes a _deduction_ from the means
+of distinguishing it from the lights which existed previous to its
+establishment. By the needless erection of a new Lighthouse, therefore,
+we not only expend public treasure, but waste the means of distinction
+among the neighbouring lights.
+
+12. Distinctions of lights, founded upon the minute estimation of
+intervals of time between flashes, and especially on the measurement of
+the duration of light and dark periods, are less satisfactory to the
+great majority of coasting seamen, and are more liable to derangement
+by atmospheric changes, than those distinctions which are founded on
+what may more properly be called the _characteristic appearance_ of the
+lights, in which the times for the recurrence of certain appearances
+differ so widely from each other as not to require for their detection
+any very minute observation in a stormy night. Thus, for example,
+flashing lights of five seconds interval, and revolving lights of half
+a minute, one minute, and two minutes, are much more characteristic
+than those which are distinguished from each other by intervals varying
+according to a slower series of 5″, 10″, 20″, 40″, &c.
+
+13. Harbour and local lights, which have a circumscribed range, should
+generally be fixed instead of revolving; and may often, for the same
+reason, be safely distinguished by coloured media. In many cases also,
+where the purpose of guiding into a narrow channel is to be gained, the
+leading lights which are used, should, at the same time, be so arranged
+as to serve for a distinction from any neighbouring lights.
+
+14. Floating lights, which are very expensive and more or less
+uncertain from their liability to drift from their moorings, as well
+as defective in power, should never be employed to indicate a turning
+point in a navigation in any situation where the conjunction of lights
+on the shore can be applied at any reasonable expense.
+
+  ~Height of Lighthouse Tower, and its relation to range of Light.~
+
+The spheroïdal form of the Earth requires that the height of a
+Lighthouse Tower should increase proportionally to the difference
+between the Earth’s radius and the secant of the angle intercepted
+between the normal to the spheroïd at the Lighthouse and the normal
+at the point of the light’s occultation from the view of a distant
+observer. The effect of atmospheric refraction, however, is too
+considerable to be neglected in estimating the _range_ of a light, or
+in computing the height of a Tower which is required to give to any
+light a given range; and we must, therefore, in accordance with the
+influence of this element, on the one hand _increase_ the range due
+to any given height, and _vice versa reduce_ the height required for
+any given range, which a simple consideration of the form of the globe
+would assign. In considering this height, we may proceed as follows:--
+
+[Illustration: Fig. 92.]
+
+Referring to the accompanying figure (No. 92), in which S′ _d_ L′ is
+a segment of the ocean’s surface, O the centre of the earth, L′L a
+Lighthouse, and S the position of the mariner’s eye, we obtain the
+value of LL′ = H′, the height of the tower in feet by the formula,
+
+       2 _l_²
+  H′ = ------  (1.)
+          3
+
+in which _l_ = the distance in English miles L′ _d_ at which the light
+would strike the ocean’s surface. We then reduce this value of H′ by
+the correction for mean refraction, which permits the light to be seen
+at a greater distance, and which =
+
+  2 _l_²
+  ------,  (2.)
+    21
+
+                    2 _l_²   2 _l_²   4 _l_²
+  So as to get, H = ------ - ------ = ------   (3.)
+                      3        21       7
+
+an expression which at once gives the height of the tower required, if
+the eye of the mariner were just on the surface of the water at _d_,
+where the tangent between his eye at S and the light at L would touch
+the sea. We must, therefore, in the first instance, find the distance
+_d_ S = _l′_, which is the radius of the visible horizon due to the
+height SS′ = _h_ of his eye above the water, and is, of course, at once
+obtained conversely by the expression:--
+
+         √(7 _h_)
+  _l′_ = --------  (4.)
+             2
+
+Deducting this distance from SL, the whole effective range of the
+light, we have L _d_ = _l_, and operating with this value in the former
+equation,
+
+      4_l_²
+  H = -----
+        7
+
+we find the height of the tower which answers the conditions of the
+case.[81] From the above data the following Table has been computed.
+
+  [81] In the above expressions _l_ and _l′_ are given in English
+  miles, which in Scotland may be considered as bearing to nautical
+  miles the ratio of 5280 to 6088. In order to convert a distance given
+  in nautical miles to English miles, all that is needful is to add the
+  log of the number of nautical miles to log 5280, and subtract log
+  6088.
+
+  +-------+--------+--------++-------+--------+--------+
+  |       |   λ    |   λ′   ||       |   λ    |   λ′   |
+  |   H   | Lengths|Lengths ||   H   | Lengths|Lengths |
+  |Heights|    in  |   in   ||Heights|    in  |   in   |
+  |  in   |English |Nautical||  in   |English |Nautical|
+  | Feet. | Miles. | Miles. || Feet. | Miles. | Miles. |
+  +-------+--------+--------++-------+--------+--------+
+  |    5  |  2·958 |  2·565 ||  110  | 13·874 | 12·03  |
+  |   10  |  4·184 |  3·628 ||  120  | 14·490 | 12·56  |
+  |   15  |  5·123 |  4·443 ||  130  | 15·083 | 13·08  |
+  |   20  |  5·916 |  5·130 ||  140  | 15·652 | 13·57  |
+  |   25  |  6·614 |  5·736 ||  150  | 17·201 | 14·91  |
+  |   30  |  7·245 |  6·283 ||  200  | 18·708 | 16·22  |
+  |   35  |  7·826 |  6·787 ||  250  | 20·916 | 18·14  |
+  |   40  |  8·366 |  7·255 ||  300  | 22·912 | 19·87  |
+  |   45  |  8·874 |  7·696 ||  350  | 24·748 | 21·46  |
+  |   50  |  9·354 |  8·112 ||  400  | 26·457 | 22·94  |
+  |   55  |  9·811 |  8·509 ||  450  | 28·062 | 24·33  |
+  |   60  | 10·246 |  8·886 ||  500  | 29·580 | 25·65  |
+  |   65  | 10·665 |  9·249 ||  550  | 31·024 | 26·90  |
+  |   70  | 11·067 |  9·598 ||  600  | 32·403 | 28·10  |
+  |   75  | 11·456 |  9·935 ||  650  | 33·726 | 29·25  |
+  |   80  | 11·832 | 10·26  ||  700  | 35·000 | 30·28  |
+  |   85  | 12·196 | 10·57  ||  800  | 37·416 | 32·45  |
+  |   90  | 12·549 | 10·88  ||  900  | 39·836 | 34·54  |
+  |   95  | 12·893 | 11·18  || 1000  | 41·833 | 36·28  |
+  |  100  | 13·228 | 11·47  ||       |        |        |
+  +-------+--------+--------++-------+--------+--------+
+
+If the distance at which a light of given height can be seen by a
+person on a given level be required, it is only needful to add together
+the two numbers in the column of lengths λ or λ′ (according as Nautical
+or English miles may be sought) corresponding to those in the column of
+heights H, which represent respectively the height of the observer’s
+eye and the height of the lantern above the sea. When the height
+required to render a light visible at a given distance is required,
+we must seek first for the number in λ or λ′ corresponding to the
+height of the observer’s eye, and deduct this from the whole proposed
+range of the light, and opposite the remainder in λ or λ′ seek for the
+corresponding number in H.
+
+  ~Diagonal Lantern.~
+
+A considerable practical defect in all the lighthouse lanterns which
+I have ever seen, with the exception of those recently constructed
+for the Scotch Lighthouses, consists in the vertical direction of
+the astragals, which, of course, tend to intercept the whole or a
+great part of the light in the azimuth which they subtend.[82] The
+consideration of the improvement which I had effected in giving a
+diagonal direction to the joints of the fixed refractors, first led
+me (as stated at p. 266, _ante_), to adopt a diagonal arrangement of
+the framework which carries the cupola of zones and afterwards for the
+astragals of the lantern. Not only is this _direction_ of the astragals
+more advantageous for equalising the effect of the light; but the
+greater stiffness and strength which this arrangement gives to the
+frame-work of the lantern make it safe to use more slender bars and
+thus also absolutely _less_ light is intercepted. The panes of glass
+at the same time become triangular, and are necessarily stronger than
+rectangular panes of equal surface. This form of lantern is extremely
+light and elegant, and is shewn, with detailed drawings of some of its
+principal parts, in Plate XXVI. To avoid the necessity of painting,
+which, in situations so exposed as those which lighthouses generally
+occupy, is attended with many inconveniences and no small risk, the
+framework of the lantern is now formed of gun-metal and the dome is
+of copper; so that a first order lantern of 12 feet diameter and 10
+feet height of glass costs, when glazed, about L.1260. In order to
+give the lightkeepers free access to cleanse and wash the upper panes
+of the lantern (an operation which in snowy weather must sometimes
+be frequently repeated during the night), a narrow gangway, on which
+they may safely stand, is placed on the level of the top of the lower
+panes, and at the top of the second panes, rings are provided of which
+the lightkeepers may lay hold for security in stormy weather. A light
+trap-ladder is also attached to the outside of the lantern by means of
+which there is an easy access to the ventilator on the dome.
+
+  [82] I must also except the small pier light at Kirkcaldy, erected (I
+  believe in 1836) by my friend Mr EDWARD SANG.
+
+  ~Glazing of the Lantern.~
+
+Great care is bestowed on the glazing of the lantern, in order that
+it may be quite impervious to water, even during the heaviest gales.
+When iron is used for the frames, they are carefully and frequently
+painted; but gun-metal, as just noticed, is now generally used in the
+Scotch Lighthouses. There is great risk of the glass plates being
+broken by the shaking of the lantern during high winds; and as much as
+possible to prevent this, various precautions are adopted. The arris
+of each plate is always carefully rounded by grinding; and grooves
+about ¹⁄₂ inch wide, capable of holding a good thickness of putty, are
+provided in the astragals for receiving the glass, which is ¹⁄₄ inch
+thick. Small pieces of lead or wood are inserted between the frames and
+the plates of glass against which they may press, and by which they
+are completely separated from the more unyielding material of which
+the lantern-frames are composed. Panes glazed in frames padded with
+cushions, and capable of being temporarily fixed in a few minutes, in
+the room of a broken plate, are kept ready for use in the Store-room.
+Those framed plates are called _storm-panes_, and have been found very
+useful on several occasions, when the glass has been shattered by large
+sea-birds coming against it in a stormy night, or by small stones
+violently driven against the lantern by the force of the wind.
+
+  ~Ventilation of the Lanterns.~
+
+The ventilation of the lanterns forms a most important element in the
+preservation of a good and efficient light. An ill-ventilated lantern
+has its sides continually covered with the water of condensation,
+which is produced by the contact of the ascending current of heated
+air; and the glass thus obscured obstructs the passage of the rays,
+and diminishes the power of the light. In the Northern Lighthouses,
+ventilators, capable of being opened and shut at pleasure, so as to
+admit from without a supply of air when required, are provided in
+the parapet-wall on which the lantern stands; the lantern roof also
+is surmounted by a cover which, while it closes the top of an open
+cylindric tube against the entrance of rain, and descends over it only
+so far as is needful for that purpose, still leaves an open air-space
+between it and the dome. This arrangement permits the current of
+heated air, which is continually flowing from the lantern through the
+cylindric tube, to pass between it and the outer cover, from which it
+finally escapes to the open air through the space between the cover and
+the dome. The door which communicates from the lightroom through the
+parapet to the balcony outside, is also made the means of ventilating
+the lightroom; and, for that purpose, it is provided with a sliding
+bolt at the bottom, which, being dropped into one or other of the
+holes cut in the balcony for its reception, serves to keep the door
+open at any angle that may be found necessary. A useful precaution was
+introduced by my predecessor, as Engineer to the Northern Lights Board,
+in order to prevent the too rapid condensation of heated air on the
+large internal surface of the lantern roof, which consists in having
+two domes with an air-space between them, as shewn in the enlarged
+diagrams in Plate XXVI.
+
+An important improvement in the ventilation of Lighthouses was some
+years ago introduced by Dr FARADAY into several of the Lighthouses
+belonging to the Trinity House, and has since been adopted in all the
+dioptric lights belonging to the Commissioners of Northern Lighthouses.
+After mentioning several proofs of extremely bad ventilation in
+Lighthouses, Dr FARADAY thus describes his apparatus:[83]
+
+  [83] Minutes of Institution of Civil Engineers, vol. i., p. 207.
+
+“The ventilating pipe or chimney is a copper tube, 4 inches in
+diameter, not, however, in one length, but divided into three or four
+pieces; the lower end of each of these pieces for about 1¹⁄₂ inch
+is opened out into a conical form, about 5¹⁄₂ inches in diameter at
+the lowest part. When the chimney is put together, the upper end of
+the bottom piece is inserted about ¹⁄₂ inch into the cone of the next
+piece above, and fixed there by three ties or pins, so that the two
+pieces are firmly held together; but there is still plenty of air-way
+or entrance into the chimney between them. The same arrangement holds
+good with each succeeding piece. When the ventilating chimney is fixed
+in its place, it is adjusted so that the lamp-chimney enters about ¹⁄₂
+inch into the lower cone, and the top of the ventilating chimney enters
+into the cowl or head of the lantern.
+
+“With this arrangement, it is found that the action of the ventilating
+flue is to carry up every portion of the products of combustion into
+the cowl; none passes by the cone apertures out of the flue into the
+air of the lantern, but a portion of the air passes from the lantern
+by these apertures into the flue, and so the lantern itself is in some
+degree ventilated.
+
+“The important use of these cone apertures is that when a sudden gust
+or eddy of wind strikes into the cowl of the lantern, it should not
+have any effect in disturbing or altering the flame. It is found that
+the wind may blow suddenly in at the cowl, and the effect never reaches
+the lamp. The upper, or the second, or the third, or even the fourth
+portion of the ventilating flue might be entirely closed, yet without
+altering the flame. The cone junctions in no way interfere with the
+tube in carrying up all the products of combustion; but if any downward
+current occurs, they dispose of the whole of it into the room without
+ever affecting the lamp. The ventilating flue is in fact a tube, which,
+as regards the lamp, can carry everything _up_ but conveys nothing
+_down_.”
+
+The advantages of this arrangement, as applied to the Northern
+Lighthouses, were much less palpable than those which are described in
+the beginning of Dr FARADAY’S paper, because their ventilation was very
+good before its introduction; and the flame in particular was perfectly
+steady, being by no means subject to derangement from sudden gusts of
+wind from the roof in the manner noticed above.
+
+  ~Arrangements and internal management of a Lighthouse.~
+
+All the Lighthouses in the district of the Commissioners are under
+the charge of at least two Lightkeepers, whose duties are to cleanse
+and prepare the apparatus for the night illumination, to mount guard
+singly after the light is exhibited, and to relieve each other at
+stated hours, fixed by the printed regulations and instructions, under
+which they act. The rule is, that no keeper on watch shall, under any
+circumstances, leave the Lightroom until relieved by his comrade; and,
+for the purpose of cutting off all pretext for the neglect of this
+universal law, the dwelling-houses are built close to the Light Tower,
+and means are provided for making signals directly from the Lightroom
+to the sleeping apartments below. These signals are communicated by
+air-tubes, through which, by means of a small piston, or a puff of wind
+from the mouth, calls can be exchanged between the keepers, enabling
+the man on guard in the Lightroom, at the end of the watch, or on any
+sudden emergence, to summon his comrade from below, who, on being thus
+called, answers by a counter-blast, to shew that the summons has been
+heard and will be obeyed. For the purpose of greater security, in
+such situations as the Bell Rock and the Skerryvore, four keepers are
+provided for one lightroom; one being always ashore on leave with his
+family, and the other three being at the Lighthouse, so that, in case
+of the illness of one lightkeeper, an efficient establishment of two
+keepers for watching the light may remain. At all the land-lighthouses
+also, an agreement is made with some steady person residing in the
+neighbourhood, who is instructed in the management of the light and
+cleansing of the apparatus, and comes under an obligation to be ready
+to do duty in the light-room when called upon, in the event of the
+sickness or absence of one of the lightkeepers. This person is called
+the _occasional keeper_, and receives pay only while actually employed
+at the Lighthouse; but in order to keep him in the practice of the
+duty, he is required to serve in the lightroom for a fortnight annually
+in the month of January. The details of the lightkeeper’s duty may be
+seen by referring to the instructions already alluded to, which will
+be found in the Appendix.
+
+Each of the two lightkeepers has a house for himself and family, both
+being under a common roof, but entering by separate doors, as shewn
+in Plates XXVII. and XXVIII., which exhibit the buildings for the
+new Lighthouse at Ardnamurchan Point, on the coast of Argyllshire.
+The principal keeper’s house consists of six rooms, two of which are
+at the disposal of the visiting officers of the Board, whose duty in
+inspecting the Lighthouse, or superintending repairs, may call them to
+the station; and the assistant has four rooms, one of which is used as
+a barrack-room for the workmen, who, under the direction of the Foreman
+of the lightroom works, execute the annual repairs of the apparatus.
+
+The early Lighthouses contained accommodation for the lightkeepers in
+the Tower itself; but the dust caused by the cleaning of those rooms in
+the Tower was found to be very injurious to the delicate apparatus and
+machinery in the lightroom. Unless, therefore, in situations such as
+Skerryvore, where it is unavoidable, the dwellings of the lightkeepers
+ought not to be placed in the Light Tower, but in an adjoining building.
+
+Great care should be bestowed to produce the utmost cleanliness in
+everything connected with a Lighthouse, the optical apparatus of which
+is of such a nature as to suffer materially from the effect of dust in
+injuring its polish. For this purpose covered ash-pits are provided at
+all the dwelling-houses, in order that the dust of the fire-places may
+not be carried by the wind to the lightroom; and for similar reasons,
+iron floors are used for the lightrooms instead of stone, which is
+often liable to abrasion, and all the stonework near the lantern is
+regularly painted in oil.
+
+  ~Cleansing of Apparatus.~
+
+If, in all that belongs to a lighthouse, the greatest cleanliness be
+desirable, it is in a still higher degree necessary in every part of
+the lightroom apparatus, without which the optical instruments and
+the machinery will neither last long nor work well. Every part of
+the apparatus, whether lenses or reflectors, should be carefully
+freed from dust before being either washed or burnished; and without
+such a precaution, the cleansing process would only serve to scratch
+them. For burnishing the reflectors, prepared _rouge_ (tritoxide of
+iron) of the finest description, which should be in the state of an
+impalpable powder of a deep orange-red colour, is applied, by means
+of soft chamois skins, as occasion may require; but the great art of
+keeping reflectors clean consists in the daily, patient, and skilful
+application of manual labour in rubbing the surface of the instrument
+with a perfectly dry, soft, and clean skin, without rouge. The form
+of the hollow paraboloid is such, that some practice is necessary in
+order to acquire a free movement of the hand in rubbing reflectors; and
+its attainment forms one of the principal lessons in the course of the
+preliminary instruction, to which candidates for the situation of a
+light-keeper are subjected at the Bell Rock Lighthouse. For cleansing
+the lenses and glass mirrors, spirit of wine is used. Having washed
+the surface of the instrument with a linen cloth steeped in spirit
+of wine, it is carefully dried with a soft and dry linen rubber, and
+finally rubbed with a fine chamois skin, free from any dust which would
+injure the polish of the glass, as well as from grease. It is sometimes
+necessary to use a little fine rouge with a chamois skin, for restoring
+any deficiency of polish which may occur from time to time; but in
+a well-managed lighthouse this application will seldom, if ever, be
+required.
+
+The machinery of all kinds, whether that of the mechanical lamp or the
+revolving apparatus, should also be kept scrupulously clean, and all
+the journals should be carefully oiled.
+
+  ~Mode of measuring the relative intensity and power of Lights.~
+
+As I have had frequent occasion to speak of the comparative power of
+lights, it will not be out of place to present the reader with a few
+practical observations, chiefly drawn from the excellent work of M.
+PECLET to which I have so often referred, on the measurement of the
+intensity of lights by the method of shadows.
+
+[Illustration: Fig. 93.]
+
+The intensity of light decreases as the observer recedes from the
+luminous body, in proportion to the square of his distance. Suppose
+a beam of light to proceed from a radiant at F, and we shall have the
+rays which, of course, move in straight lines, gradually receding
+from each other, as _b_, _b′_, _b″_, _b‴_, and _c_, _c′_, _c″_, _c‴_,
+so that the section of the beam will increase with the distances
+F _b_, and F _c_; and the same number of rays, being thus spread over
+spaces continually increasing, will illuminate the surfaces with a
+less intensity. This decrease of intensity will, therefore, be in the
+inverse ratio of the extent of the transverse parallel sections of
+the luminous cones at _b_ and _c_, which, we know, increase as the
+square of their distances from the apex of the cone at F. Hence we
+conclude, that the _intensity of any section of a divergent beam of
+light decreases as the square of its distance from the radiant_. This
+law furnishes us with a simple measure of the comparative intensity of
+lights. If we suppose two lights so placed that they may separately
+illuminate adjacent portions of a vertical screen of paper, we may, by
+repeatedly comparing the luminousness of those surfaces, and moving
+one of the lights farther from, or nearer to the screen, at length
+cause the separate portions of the paper to become equally luminous.
+This arrangement, however, has many practical difficulties, which I
+shall not wait to specify; but shall at once indicate a more simple
+and equally correct mode of obtaining the same result, by means of the
+shadows cast by the lights from an opaque rod, in a vertical position
+at O (fig. 94), placed between them, and a screen covered with white
+paper on which the shadows fall. It is obvious that the light at F
+would cause the object O to cast a shadow at SS, while the light at
+F′ would cast a shadow at S′S′. But while the shadow at S would still
+receive light from F′, S′ would receive light from F, so that those two
+shadows are, in fact, the only portions of the screen which are each
+illuminated only by one of the lights, while every other portion of
+its surface receives light from both the radiants at F and F′. If we
+suppose F to be the weaker light, we can bring it nearer the screen,
+until the shadow S′S′, shall become similar in appearance to the shadow
+SS; and we shall have the ratio of the intensity of the light at F to
+that of the light at F′, as (FS′)² is to (F′S)², which distances must
+be measured with the greatest exactness. Such is the mode commonly used
+in estimating the comparative intensities of two lights; but there
+are various precautions which are needful in order to prevent errors
+in comparing the deepness of the shadows, and to insure the greatest
+attainable accuracy in the estimate of the power of the lights, which I
+shall endeavour briefly to describe.
+
+[Illustration: Fig. 94.]
+
+  ~More accurate comparison of the intensity of Lights.~
+
+The difficulties of estimating the deepness or sharpness of the shadow
+is very great, and many persons seem quite incapable of arriving at
+any right judgment in this matter. The same person also will discover
+such unaccountable variations in his decision after observations made
+at short intervals of time, as, one would think, can only arise from
+a sudden change of the intensity of one or both lights. M. Peclet, in
+his _Traité de l’éclairage_, gives, as the result of his experience
+(and I can fully confirm his result by my own), that those differences
+depend less frequently on any real difficulty of estimating the
+deepness of the shadows, than on variations in the position of the
+observer, or rather in the angle at which he views the shadows, and
+that, consequently, in proportion to the distance between the two
+shadows, this source of error is increased. Any thing like a glossy
+texture of the surface of the screen, which then, of course, becomes a
+reflector, also tends to aggravate this evil. Thus, if the two lights
+which are to be compared be placed on a table, in such situations as
+to spread pretty far apart on the screen the shadows of a vertical rod
+placed between them; and if the shadow nearer to the observer seem to
+be a little deeper or sharper than the other, let the observer look
+at them from the other side of the table, and their difference will
+be reversed, and that which seemed the paler, will become the deeper.
+Again, if the difference between the two shadows be very great when
+seen from the right side of the screen, it may happen that, on viewing
+them from the left hand, the difference may still be in favour of the
+same shadow, but in a much less degree.
+
+“When I observed this effect,” says M. Peclet,[84] “I tried to view
+the shadows through a transparent screen, but I remarked the same
+variations. They were indeed even more sensible; for a variation in the
+distance of the eye of a few centimètres, made a prodigious change in
+the deepness of the shadows. I observed also that the shadow was much
+deeper when seen in the line of the light, and that in every other
+direction, it became paler in proportion as the eye receded from that
+direction.
+
+  [84] Traité de l’éclairage, p. 214.
+
+“In all the cases which I have just described, the differences of
+the tints when the position is changed, increase in proportion as
+the shadows are farther separate; and they grow very minute when the
+shadows are almost touching each other.
+
+[Illustration: Fig. 95.]
+
+“Let AB (fig. 95) be a white opaque surface, _a_, a luminous body, and
+_m_, a black opaque body, then the shadow _b′_ cast on AB, will appear
+deeper when observed from P, than as seen from Q. This is a fact which
+may be easily verified, and the cause of which is easily conceived.
+In fact, the surface AB, although it disperses the light, must still
+reflect more of it, in the directions in which the regular reflection
+takes place; and hence the rays which are reflected round about the
+shadow, must have a greater intensity in the direction of P than in
+that of Q, and, consequently, the shadow _b′_ must appear deeper from
+the point P than from Q.
+
+[Illustration: Fig. 96.]
+
+“If we now place (fig. 96) two lights in front of the screen AB, at
+such distances that the two shadows _a′_ and _b′_ should have equal
+intensities, it is evident that if the eye be placed at P, the shadow
+_b′_ must appear more intense than the shadow _a′_, and that the
+reverse will take place if the eye be at Q. But the difference which is
+then observed, arises not only from the difference in the brightness of
+the parts surrounding the shadows, but also from a difference in the
+intensity of the shadows themselves; for the shadow _b′_ is illuminated
+by _b_, and radiates much more towards Q than towards P; and, on the
+contrary, the shadow _a′_, which is illuminated by _a_, radiates much
+more towards P than towards Q. We perceive also why the _differences_
+of the tints increase with the separation of the two shadows, and
+why they become very small when the shadows touch each other; it is
+because, in proportion as the shadows are farther apart, each of them
+is illuminated more obliquely, and a greater quantity of light is
+radiated (by reflection) in the regular direction. When they touch each
+other, on the contrary, they are illuminated almost perpendicularly,
+and consequently the shadows radiate light almost equally on either
+side.
+
+“Those anomalies of a like kind which are observed when the shadows
+are viewed through a translucent body, such as paper or linen, may
+be referred to a similar cause. We know, in fact, that, in looking
+through a translucent medium, we always, more or less, distinctly
+perceive the luminous body behind it, and, also, that there is a very
+large proportion of the rays which traverse the body, which stray but
+a little from the direction which they would follow if the substance
+were absolutely transparent. Consequently, the space which surrounds
+the shadow is more luminous in proportion as we come nearer to the
+direction of the shadow; and as the absolute intensity of the shadows
+diminishes as we come nearer to the direction of the rays which light
+them, those two effects concur to increase the intensity of that shadow
+to which the eye is nearer.
+
+“As the dispersion by reflection is much more complete than by
+refraction, the variations of which we have just spoken are much
+greater with a transparent screen, through which the shadows are
+viewed, than with an opaque screen (from which they are reflected).
+
+“This, then, is the mode of observing which has appeared to me the
+best, and by means of which we may obtain very great precision in
+measuring the intensity of two lights. I view, first, the two shadows
+in such a manner that both of them may be seen in succession from
+either side of the body which produces them, and at equal distances.
+For this purpose I use a good opera-glass. I alter the distance of
+the flames until in those two positions I perceive the differences
+(of the intensity in the shadows) to be in opposite directions. The
+distances of the lamps may then be considered as very nearly in the
+proper proportion for producing equal shadows, and to make them exactly
+so, the differences, which are observed on either side (of the centre
+line between them), should be equal; and, of course, the two shadows
+themselves, seen at one moment from either side of the opaque body,
+should be perfectly equal also.[85] These three observations, which
+mutually serve to verify or correct each other, will lead, with a
+little practice, to very great precision in the result. We may, also,
+by using a narrow screen, bring the shadows sufficiently near to touch
+each other; the variations of the tints then become very small by any
+change of our position, and we may, in this case, rest content with
+observing them from one point. To get rid of large penumbrae which are
+always an obstacle in forming a right estimate of the tints of the
+shadows, I place the opaque body very near the screen.
+
+  [85] I prefer to view the exterior portions of both shadows from the
+  central line itself, in which case the opaque rod stands between
+  them, because, in this manner, I obtain a more correct comparison by
+  the direct contrast of the surfaces than by successive views of them,
+  however quickly taken.
+
+[Illustration: Fig. 97.]
+
+“When we wish to make a great many observations, it is very convenient
+to mark divisions on the table (which carries the lights), in order
+to read off, by means of them, the distance of the lamps from the
+shadows which they illuminate. By this means, each observation need
+not occupy more than two minutes. I generally use a table CC DD (fig.
+97), about two mètres long (6 feet 6 inches), by 80 centimètres wide (2
+feet 8 inches). At one end I place the screen AB, covered with white
+paper, dull (or not glazed), and kept in a vertical plane by two small
+pieces P and Q. Through the point M, the centre of the opaque body,
+I draw two lines M _f_ and M _g_, equally inclined to the central line
+_x_ _y_, whose extremities _b′_, _a′_ are the axes of the two shadows.
+These lines must be inclined in such a manner that the distance of the
+shadows may be a little less than the diameter of the opaque body, or
+so that they may actually touch each other, according to the mode of
+observing which you wish to follow. These lines M _f_, M _g_ I divide
+into decimètres and centimètres, starting from the points _a′_, _b′_
+and over these lines I place the centres of the flames; the distance
+between the shadows remains always the same, whatever may be the
+distance of the lamps: to determine the distance of each lamp from the
+shadow which it illuminates, we ought, strictly speaking, to take the
+distance of the centre of the flame _b_ from the point _a′_; but as
+the distance from the point _b_ to the point _a′_ differs little from
+the distance between the points _b_ and _b′_, we assume the latter
+for the former, without causing any sensible error. That distance may
+be obtained very conveniently by taking the half of the sum of the
+distances of the two extremities _z_ and _z′_ of the diameter of the
+pedestal of the lamp. When the burner is not placed over the centre of
+the pedestal, we may suspend from it a small plummet, whose point will
+touch some division and indicate the distance between the centre of the
+burner and the shadow.
+
+“When the lights are coloured, the shadows are coloured also, and it is
+then far more difficult to judge accurately of their intensity. They
+may in that case be much better seen from the point _x_, as the black
+opaque body which is interposed between them renders the difference of
+colour less sensible to the eye.
+
+“The opaque body M is a cylindric rod of iron, whose upper part is
+blackened in the flame of a lamp, in order to prevent the reflection
+which might interfere with the _sharpness_ (_netteté_) of the shadows,
+and to make them more distinct when they are viewed from the point
+x.”[86]
+
+  [86] Those who feel a curiosity to look farther into this subject may
+  consult Count Rumford’s elaborate paper in the Phil. Trans. for 1794,
+  p. 67.
+
+I shall make a few trifling additions to M. Peclet’s clear description
+of his excellent mode of measuring the intensity of lights. It is, of
+course, presumed throughout, that the centres of the flames should be
+on one level; and I have found it most convenient to place the lamps
+on small carriages with rollers, which are guided by means of fine
+strips of wood nailed along the table in the directions _g_ M and _f_ M,
+and carrying the divided scales of centimètres. This affords the means
+of making any slight change in the position of the lamps so easily,
+as entirely to avoid the disturbance of the flame which ensues from
+lifting the lamp and readjusting it in another position; and will,
+in practice, be found very convenient when many observations are to
+be made. I have already said that my own experience has satisfied me
+that, with the aid of a good opera-glass, the central observation
+of the two shadows, with the opaque rod between them, is by far the
+best, and conducts, at once, to a result which is confirmed by the
+observations of two assistants who watch the shadows at the same time
+on opposite sides of the table, and at equal distances from them. I
+have found it convenient in comparing lights, to cover the table with
+dull black linen cloth, and to surround it with curtains of the same
+material, hung from slender brackets, in such a manner as to leave
+space for the observer to move freely round the table within them. The
+curtains prevent reflection from the walls of the chamber in which the
+experiments may be conducted, and also lessen the disturbing effects
+of currents of air. When a comparison of the _intensity_, and not of
+the _aggregate power_ of two flames, is to be made, it is necessary
+to adopt the precaution of inclosing the lights in opaque boxes, with
+slits of equal area in each, placed on the same level, and so arranged,
+in reference to the flames, as to be directly opposite the brightest
+portion of each. After what has been said, it will be almost needless
+to add that the _quotient of the square of the greater observed
+distance divided by the lesser, is the ratio of the illuminating
+power of the two flames_. The most convenient mode of registering
+observations, and that which is generally practised, is in the form of
+a Table like the following:--
+
+  +-------+---------------+---------------+---------------+
+  |       |               |               | Illuminating  |
+  |       |               |               |    Power,     |
+  |       |               |  Squares of   |  or Quotient  |
+  |       |   Distance.   |  Distances.   |  of Squares.  |
+  |       +-------+-------+-------+-------+-------+-------+
+  |Trials.|Lamp A.|Lamp B.|Lamp A.|Lamp B.|Lamp A.|Lamp B.|
+  +-------+-------+-------+-------+-------+-------+-------+
+  |   1   |  143  |  140  |20,449 |19,700 | 1·00  | 0·958 |
+  |   2   |  117  |  114  |13,689 |12,996 | 1·00  | 0·949 |
+  +-------+-------+-------+-------+-------+-------+-------+
+
+As a standard lamp by which to test others, I believe few will be found
+superior to the best Carcel lamp, which has a clockwork movement, and
+whose flame continues to increase in power for about four hours after
+it is lighted; after which it maintains its state permanently, until
+the supply of oil fails. This fact was verified by M. Peclet with the
+greatest care. “I took,” says he, “two similar lamps. They were lighted
+at the same time, and their relative intensities were measured. One
+was then extinguished, without touching the wick, and its clockwork
+movement was stopped. One hour afterwards, I set the clockwork in
+motion and relighted the lamp, but without touching the wick. It was
+found in the same state as at the first comparison, and I measured its
+intensity in reference to the first. Those experiments I repeated
+every hour, and these are the results which I obtained. The lamp which
+I call No. 1, is that which remained continually burning; No. 2, is
+that which was only lighted during the continuance of the (successive)
+observations.”
+
+  +------------++-------------------------+
+  |            ||      Intensities.       |
+  |  Times of  ++------------+------------+
+  |Observation.||Lamp, No. 1.|Lamp, No. 2.|
+  +-----+------++------------+------------+
+  | H.  |  M.  ||            |            |
+  |  5  |  30  ||    100     |    100     |
+  |  6  |  30  ||    103     |    100     |
+  |  7  |  30  ||    106     |    100     |
+  |  8  |  30  ||    110     |    100     |
+  |  9  |  30  ||    117     |    100     |
+  | 10  |  30  ||    117     |    100     |
+  | 11  |  30  ||    117     |    100     |
+  | 12  |  30  ||    117     |    100     |
+  +-----+------++------------+------------+
+
+This curious scale of increase in power, seems to be solely due to a
+peculiarity of the manner in which the lamp, that derives its supply
+of oil by clockwork, becomes heated; and the effect may be described
+as follows: The heating of the wicks, the chimney, and the oil in this
+burner, as in that of all other lamps, tends to increase the light;
+but, in an ordinary lamp, acting by a constant pressure, this _maximum_
+of heat is soon attained; whereas in the clockwork-lamp, into the
+burner of which the oil is thrown up by a pump, the whole of the oil in
+the cistern must reach its maximum temperature before the _best_ effect
+of that lamp is produced. After this state has been reached, there is
+no disturbing influence at work, and the lamp burns steadily as long as
+the oil lasts.
+
+I have myself tried what may naturally appear to be the most simple
+mode of obtaining an unvarying standard-light, by employing a
+gas-burner, supplied from a gasometer under a constant pressure;
+but I found it very difficult to obtain satisfactory proof of the
+constancy of the pressure; and in a large town, where there are many
+burners around one, their lighting or extinction is found to exercise
+a material influence in changing the condition of the flame. I must
+confess that I have always been disappointed in attempting to use a
+gas-flame as a standard of comparison.
+
+  ~Floating Lights.~
+
+There are various dangers on the shores of Britain, more especially
+at the entrance of the great estuaries of England and also in
+Ireland, whose position is such as to put them beyond the reach of
+regular lighthouses. Sand-banks which are too soft to sustain a solid
+structure, and have too deep water on them to admit of the erection of
+screw-pile lighthouses, are often the sites for mooring light-vessels,
+to guide the mariner into the entrance of some estuary, or enable him
+to thread his way through the mazes of _gats_ and channels, which, even
+during the daytime, baffle the mariner, who sees no natural object on
+the low sandy shores of the neighbouring coast to help him to guess at
+his true position. The first Light-vessel moored on the coast of Great
+Britain, was that at the Nore in 1734. There are now no fewer than 26
+floating lights on the coast of England.
+
+By the kindness of the Elder Brethren of the Corporation of Trinity
+House of Deptford Strond, I am enabled to give the following brief
+sketch of the nature and peculiarities of Floating Lights which was
+communicated to me by Mr Herbert, the secretary of the Corporation:--
+
+“The annual expense of maintaining a Floating Light, including the
+wages and victualling of the crew, who are eleven in number, is,
+on an average, L.1000; and the first cost of such a vessel, fitted
+complete with lantern and lighting apparatus, anchors, cables, &c.,
+is nearly L.5000. The lanterns are octagonal in form, 5 feet 6 inches
+in diameter; and, where fixed lights are exhibited, they are fitted
+with eight Argand lamps, each in the focus of a parabolic reflector of
+twelve inches diameter; but, in the revolving lights, four lamps and
+reflectors only are fitted. The greatest depth of water in which any
+light-vessel belonging to the Corporation of Trinity House of Deptford
+Strond at present rides, is about 40 fathoms (which is at the station
+of the _Seven Stones_ between the Scilly Islands and the coast of
+Cornwall).
+
+“The Corporation’s light-vessels are moored with chain-cables of 1¹⁄₂
+inch diameter, and a single mushroom anchor of 32 cwt., in which cases
+the chain-cables are 200 fathoms in length; some of the said vessels
+are moored to _span-ground_ moorings, consisting of 100 fathoms of
+chain to each arm, and a mushroom anchor of similar weight at the end
+of each; a riding cable of 150 fathoms being in such cases attached to
+the centre ring of the ground chain. The tonnage and general dimensions
+of the light-vessel are given on the drawing of the lines.” (See Plate
+XXIX.)
+
+  ~Beacons and Buoys.~
+
+Still lower in the scale of “signs and marks of the sea,” are Beacons
+and Buoys, which are used to point out those dangers which, either
+owing to the difficulty and expense that would attend the placing
+of more efficient marks to serve by night as well as by day, are
+necessarily left without lights, or which, from the peculiarity of
+their position, in passages too intricate for navigation by night,
+are, in practice, considered to be sufficiently indicated by day-marks
+alone. Beacons, as being more permanent, are preferred to Buoys; but
+they are generally placed only on rocks or banks which are dry at some
+period of the tide. On rocks, in exposed situations, the kind of Beacon
+used is generally that of squared masonry, secured by numerous joggles
+(as shewn at Plate XXXII.); and in situations difficult of access,
+and in which works of uncompleted masonry could not be safely left
+during the winter season, an open framework of cast-iron pipes, firmly
+trussed and braced, and secured to the rock with strong _louis-bats_,
+is preferred. The details of this framework are shewn at Plates XXX.
+and XXXI. A stone Beacon of the form and dimensions shewn in Plate
+XXXII., may be erected for about L.700, and the iron Beacon shewn at
+Plate XXX., for about L.640. In less exposed places, where the bottom
+is gravel or hard sand, a conical form of Beacon, composed of cast-iron
+plates, united with flanges and screws, with rust-joints between them,
+is sometimes used. A Beacon of this kind is shewn at Plate XXXII.,
+which can be erected for about L.400.
+
+Lastly, Buoys, which may be regarded as the least efficient kind
+of mark, and as bearing the same relation to a Beacon that a
+Floating-light does to a Lighthouse, are used to mark by day _dangers_
+which are always covered even at low water, and also to line out the
+fair-ways of channels. They are, for the most part, of one of the three
+forms shewn in Plate XXXIII., viz., the _Nun-buoy_, in the form of a
+parabolic spindle, generally truncated at one end, so as to carry a
+mast or frame of cage-work, and loaded at the other end, so as to float
+in a vertical position; the _Can-buoy_, which is a conoid floating
+on its side; and, lastly, the _Cask-buoy_, which is a short frustum
+of a spindle truncated at both ends, but almost exclusively used for
+carrying the warps of vessels riding at moorings. Those buoys are of
+various sizes and differ in cost. Mast-buoys, from 10 to 15 feet in
+length, cost from L.23, 15s. to L.48; and those of the Ribble and the
+Tay, which are 21 and 24 feet long, cost respectively L.105 and L.79;
+the _Can-buoys_ are from 5 to 8 feet long, and cost from L.13, 13s. to
+L.20, 5s. Large buoys are often built on _kneed_ frames resembling the
+timbers of vessels. The Cask-buoy is generally 6 feet long, and costs
+L.22, 15s. All these buoys are formed of strong oaken barrel-staves,
+well hooped with iron rings, and shielded with soft timber; and the
+nozzle-pieces at the small end of the _Nun_ and _Can_ buoys are
+generally solid quoins of oak, formed with a _raglet_ or groove to
+receive the ends of the staves. Much skill, on the part of the cooper,
+is required in heating and moulding the staves to the required form;
+and great care must be taken that they be of well-seasoned timber.
+Buoys are not caulked with oakum, but with dry flags closely compressed
+between the edges of the staves, which swell on being wet; and they are
+carefully proved by _steaming_ them like barrels, to see if they be
+quite tight. Buoys are also formed of sheet-iron, in which case they
+are sometimes protected with fenders of timber; but they have been
+found more troublesome for transport, and, for most situations, are
+considered less convenient than those of timber.
+
+In the beginning of 1845, I suggested the idea of rendering Beacons and
+Buoys useful during night, by coating them with some phosphorescent
+substance, or surmounting them with a globe of strong glass filled with
+such a preparation, whose combustion is very slow, and emits a dull
+whitish light and little heat. Some experiments were accordingly made
+by my suggestion; but I cannot add that any practically useful result
+has been obtained.
+
+In laying down Beacons or Buoys, their position is fixed, as may be
+seen in the Table in the Appendix, either by the intersection of two
+lines drawn through two leading objects on the shore (the magnetic
+bearings of which are given for the sake of easy reference on the spot,
+in finding out the marks), or by means of the angles contained between
+lines drawn to various objects on the shore, which meet at the Beacon
+or Buoy from which they are measured by means of a sextant. In the
+latter case, the angles are always measured around the whole horizon,
+thus affording a check by the difference of their sum from 360°.
+The magnetic bearing of one of those lines is afterwards carefully
+ascertained, by means of the prismatic compass (if possible from one
+of the objects on shore, and if not, conversely from the Beacon or
+Buoy), so as to afford the means of translating the whole into magnetic
+bearings for the use of seamen. The buoys are moored, as shewn in
+Plate XXXIII., by means of chains and iron sinkers, with a sufficient
+allowance in the length of the chain to permit them to _ride_ easily.
+
+
+
+
+APPENDIX.
+
+
+APPENDIX, No. I.
+
+TABLE OF CO-ORDINATES OF AN HYPERBOLIC COLUMN WHOSE DIAMETER AT THE TOP
+= 16 FEET, AT THE BASE = 42 FEET, AND HEIGHT = 120·25 FEET.
+
+The column is generated by the revolution of a rectangular hyperbola
+about one of its asymptotes. In the annexed figure (No. 98), _a_ _f_ is
+the height of the column, _a_ _c_ and _f_ _h_ the radii of its base and
+top; and we have to determine the particular hyperbola which will pass
+through the points _c_, _h_.
+
+Putting _b_ _e_ = _x_; _e_ _g_ = _y_, the equation to the curve,
+referred to its asymptotes, is
+
+            _a_²
+  _x_ _y_ = ----,
+              2
+
+in which the value of the constant
+
+  _a_²
+  ----
+    2
+
+is to be found. For this purpose we have the conditions _a_ _c_ = 21;
+_f_ _h_ = 8; and _a_ _f_ = 120·25. Let the co-ordinates of the point
+_c_ be _x′_, _y′_, and of _h_, _x″_, _y″_, then _y′_ = 21; _y″_ = 8;
+_x″_ = _x′_ + 120·25.
+
+[Illustration: Fig. 98.]
+
+                        _a_²
+  And since _x′_ _y′_ = ---- = _x″_ _y″_
+                          2
+
+  we have 21 _x′_ = 8 (_x′_ + 120·25)
+
+  from which _x′_ = 74
+
+      _a_²
+  and ---- = _x′_ _y′_ = 74 × 21 = 1554.
+        2
+
+  Therefore _x_ _y_ = 1554.
+
+Transferring the origin to _a_, _x_ becomes _x_ - _x′_ = _x_ - 74, and
+_y_ (_x_ - 74) = 1554, and the required equation by which the following
+Table was computed is,
+
+          1554
+  _y_ = --------.
+        _x_ - 74
+
+TABLE _of the Radii of the Hyperbolic Column at each foot of its
+Height_.
+
+  +-------+-------++-------+-------++-------+-------++-------+-------+
+  |Height.|Radius.||Height.|Radius.||Height.|Radius.||Height.|Radius.|
+  +-------+-------++-------+-------++-------+-------++-------+-------+
+  |    0  | 21·000||   31  | 14·800||   62  | 11·426||  93   | 9·305 |
+  |    1  | 20·720||   32  | 14·660||   63  | 11·343||  94   | 9·250 |
+  |    2  | 20·447||   33  | 14·523||   64  | 11·261||  95   | 9·195 |
+  |    3  | 20·182||   34  | 14·389||   65  | 11·180||  96   | 9·141 |
+  |    4  | 19·923||   35  | 14·257||   66  | 11·100||  97   | 9·088 |
+  |    5  | 19·671||   36  | 14·127||   67  | 11·021||  98   | 9·035 |
+  |    6  | 19·425||   37  | 14·000||   68  | 10·944||  99   | 8·983 |
+  |    7  | 19·185||   38  | 13·875||   69  | 10·867|| 100   | 8·931 |
+  |    8  | 18·951||   39  | 13·752||   70  | 10·792|| 101   | 8·880 |
+  |    9  | 18·723||   40  | 13·632||   71  | 10·717|| 102   | 8·830 |
+  |   10  | 18·500||   41  | 13·513||   72  | 10·644|| 103   | 8·780 |
+  |   11  | 18·282||   42  | 13·397||   73  | 10·571|| 104   | 8·730 |
+  |   12  | 18·070||   43  | 13·282||   74  | 10·500|| 105   | 8·681 |
+  |   13  | 17·862||   44  | 13·170||   75  | 10·430|| 106   | 8·633 |
+  |   14  | 17·659||   45  | 13·059||   76  | 10·360|| 107   | 8·586 |
+  |   15  | 17·461||   46  | 12·950||   77  | 10·291|| 108   | 8·539 |
+  |   16  | 17·267||   47  | 12·843||   78  | 10·224|| 109   | 8·492 |
+  |   17  | 17·077||   48  | 12·738||   79  | 10·157|| 110   | 8·446 |
+  |   18  | 16·891||   49  | 12·634||   80  | 10·091|| 111   | 8·400 |
+  |   19  | 16·710||   50  | 12·532||   81  | 10·026|| 112   | 8·355 |
+  |   20  | 16·532||   51  | 12·432||   82  |  9·962|| 113   | 8·310 |
+  |   21  | 16·358||   52  | 12·333||   83  |  9·898|| 114   | 8·266 |
+  |   22  | 16·188||   53  | 12·236||   84  |  9·835|| 115   | 8·222 |
+  |   23  | 16·021||   54  | 12·141||   85  |  9·774|| 116   | 8·179 |
+  |   24  | 15·857||   55  | 12·046||   86  |  9·712|| 117   | 8·136 |
+  |   25  | 15·697||   56  | 11·954||   87  |  9·652|| 118   | 8·094 |
+  |   26  | 15·540||   57  | 11·862||   88  |  9·593|| 119   | 8·052 |
+  |   27  | 15·386||   58  | 11·773||   89  |  9·534|| 120   | 8·010 |
+  |   28  | 15·235||   59  | 11·684||   90  |  9·476|| 120·25| 8·000 |
+  |   29  | 15·087||   60  | 11·597||   91  |  9·418||  ...  |  ...  |
+  |   30  | 14·942||   61  | 11·511||   92  |  9·361||  ...  |  ...  |
+  +-------+-------++-------+-------++-------+-------++-------+-------+
+
+
+APPENDIX, No. II.
+
+NOTES ON THE MANUFACTURE OF PARABOLOÏDAL REFLECTORS,
+
+from Information furnished by Mr JAMES MURDOCH, OF THE NORTHERN LIGHTS
+SERVICE.
+
+[Illustration: Fig. 99.]
+
+The reflector-plate consists of virgin-silver and the purest copper
+(from the ingot), in the proportion of 6 oz. of silver to 16 oz. of
+copper. The two metals are in pieces, forming a flat parallelopepid
+of about nine inches of surface. Being first thoroughly scraped and
+cleared from rust with a file, they are tied together with wire and
+placed in the furnace, where they are united by means of a flux
+composed of burnt borax and nitre, mixed to the consistence of cream.
+Their thickness is sufficient to admit of their being repeatedly
+passed through the rolling-mill, so as at last to come out a plate
+twenty-eight inches square. Every time it is passed through the
+rollers, the plate is annealed in the furnace before being again
+pressed. It is then cut into a circular disc ready for working; and
+great care should be taken to keep the metal perfectly clean during
+the whole of the hammering and polishing processes. The first step
+towards forming the plate to the curve, is to raise the back or copper
+side to a slight convexity by beating, with the boxwood mallet (fig.
+99), rounded at each end, _c_ and _d_, its inner or silver side upon a
+large block of beechwood, of a form slightly concave. This beating is
+begun at the edge of the plate, and gradually reaches the centre. After
+the disc has been raised to the proper height on the wooden block,
+the next step is to take it to the _horse_ (fig. 103, opposite page),
+where it is beaten with the wooden mallet (fig. 100), its concave face
+being in contact with the bright steel-head _a_ (fig. 103), until it
+has nearly reached the proper height for the reflector, for which
+the workman has a gauge or mould to guide him; in this course of
+_raising_, as it is called, the _peened_ face _b_ _a_ _b_ (fig. 100)
+is first used, and then recourse is had to the opposite or flat face
+for smoothing it after being raised. In this last course of raising, as
+well as in the process of smoothing the reflector all over, the workman
+bestrides the _horse_.
+
+[Illustration: Fig. 100.]
+
+[Illustration: Fig. 101.]
+
+During the process of raising with the peened side of the mallet,
+an external mould FGHF (fig. 101), with a needle-point P, at its
+vertex, is applied, to indicate its proper position with reference
+to the mould; and allowance is made on the height and diameter
+of the reflector to meet the expansion of the metal during the
+_hard-hammering_ which is to follow. After each course of the raising
+with the wooden mallets, the reflector must be annealed in the
+following manner:--The reflector is first damped with clean water, and
+its surface dusted over with a powder, composed of one pint of powdered
+charcoal to one ounce of saltpetre, which is applied by means of a thin
+flannel bag. The reflector is then put on a clear charcoal fire, where
+it is turned round as the powder flies off, which is an indication that
+the metal is duly heated. Over-heating is very injurious. When removed
+from the fire, the reflector is plunged into a large tub, containing
+what is called the _pickle_, which is a solution of one quart of
+vitriol in five or six gallons of water. After this it is washed with
+clean water, and scoured with Calais sand.
+
+The next step is to put the reflector, thus raised _nearly_ to its
+true form, into an iron stool, where a small hole being drilled in its
+vertex, a circle is described from this point with a beam-compass, so
+as to cut the paraboloïd to the proposed size.
+
+[Illustration: Fig. 102.]
+
+[Illustration: Fig. 103.]
+
+[Illustration: Fig. 104.]
+
+[Illustration: Fig. 105.]
+
+The reflector is next _hard-hammered_ all over (or _planished_, as
+it is technically termed) on the bright steel-head _a_ (fig. 103),
+with the planishing hammer (fig. 102); and to facilitate working, the
+reflector is slung in a flexible frame SS, and counterbalanced by
+a weight _w_, hanging by a cord over the pulleys _p_ _p_. When the
+reflector is all _planished_ over, the next process is the _smoothing_,
+which is done on the steel-head _a_, with a lighter hammer (fig. 104),
+muffled with fine parchment at each end. After it is smoothed comes the
+_finishing_, or what is called the _filling up to the mould_. This is a
+tedious process, and the workman requires continually to have recourse
+to the marble table at M, on which he lays the reflector, as shewn in
+fig. 105, and applies to successive portions of its surface the mould
+_g_ _n_, which has a needle-point centred at _n_, in the small hole
+drilled in the vertex. During this examination, he marks with a fine
+slate-pencil those portions of the reflector which do not meet the
+mould _g_ _n_. The parts, so marked, are gently gone over with the
+muffled hammer, until every point touches the mould. This last process
+requires great caution; for, if any part of the surface be raised above
+the gauge, it is hardly possible to remedy it. Such a mistake, indeed,
+can only be corrected by annealing the reflector afresh, and bringing
+it back to the true form with the mallet; but reflectors so _cobbled_
+are never good. The table M (fig. 105) rests on a square box C, in
+which the tools and moulds are kept.
+
+[Illustration: Fig. 106.]
+
+When thus finished from the hammer, the reflector is put into the
+apparatus shewn in fig. 106, which is placed at the end of a long
+dark corridor. RR is a wooden frame fixed to the wall with projecting
+brackets at K, which carry the reflector, fixed at E, E, by means of
+screws, so as always to have a definite position with reference to the
+bracket B, which carries the lamp and its fountain _f_, so arranged
+that its flame may admit of perfect adjustment to the point which
+_ought_ to be the focus of the reflector. For the purpose of this
+adjustment, S shews screws for raising and depressing the level of
+the burner; and the lines or marks M, M′ shewn at the sockets J being
+brought _into line_, regulate the _position_ of the burner in _the
+plane of the focus_, after it has been raised to the level of that
+plane by means of the screws at S. The lamp being lighted and thus
+properly placed, its effect on the reflector’s surface is observed by
+some one stationed at a convenient distance; and if the whole surface
+appear luminous, the instrument is considered fit for polishing;
+but if any dark spaces be found in it, the whole reflector must be
+again carefully tested by means of the mould, and the defective parts
+remedied in the manner above described.
+
+The next step is to turn over the edge of the reflector, so as to
+stiffen it. For this purpose it is placed in the matrix P′P′ (fig.
+107), and the needle-point at V is adjusted by the screw at D, so as
+just to enter the small hole formerly drilled in the vertex of the
+reflector. The die-plate PP (which is worked by means of the arms AA,
+which turn the screw S) then descends and presses the edge _over_,
+which is finished with a finely polished tool C, revolving round
+the axis of the instrument, which coincides with the centre of the
+matrix and die. In order to ensure a steady vertical movement of the
+die-plate PP, cross-arms FF, which are provided with sockets HH, which
+slide over the rods GG, GG, are added to prevent any lateral shake or
+derangement. The whole frame is stiffened by the cross-head in which
+the screw S works.
+
+[Illustration: Fig. 107.]
+
+[Illustration: Fig. 108.]
+
+[Illustration: Fig. 109.]
+
+The reflector is then placed on the circular cast-iron table (figs.
+108, 109), to which it is attached by the clamp-screws S, S. In this
+position, the bizzle W (fig. 108) and back-belt NAN (fig. 109), are
+soldered on. After this the reflector is ready for being finally
+polished; for which purpose, it is placed in a _chaise percée_,
+padded round the edges, and is first scoured all over with a piece of
+pure charcoal of hard wood, and next with a mixture of Florence oil
+and finely washed rottenstone, applied by means of a large ball of
+superfine cloth. It is then carefully cleansed with a piece of fine
+flannel dipped in Florence oil, and afterwards dusted over with the
+powder of well washed whiting, and wiped out with a soft cotton cloth.
+Lastly, it is carefully rubbed by the naked hand, with finely washed
+rouge and clean water, and wiped with a smooth chamois skin. In all
+the polishing and cleansing processes, some skill in manipulation
+is required, as the hand is generally moved in such a manner as to
+describe successive circles with their planes parallel to the lips of
+the reflector, and their centres in the axis of the generating curve.
+
+The prices paid to the workmen for the various departments of the
+reflector-making are generally as follows:--
+
+  Raising the plate to the curve, with the wooden mallet,     L.0 10 0
+  Hammering and smoothing to the mould,                         1  5 0
+  Finishing in the die, and putting on bizzle and back-belt,    0  6 0
+  Polishing,                                                    0 12 0
+                                                               -------
+                                                              L.2 13 0
+
+The prices paid to the manufacturer were for the large reflectors of 24
+inches aperture, L.43; for the small ones of 21 inches, L.31, 12s. The
+lamp with the sliding-carriage, required for each, costs L.6.
+
+
+APPENDIX, No. III.
+
+NOTES ON THE GRINDING OF THE VARIOUS PIECES COMPOSING THE INSTRUMENTS
+USED IN DIOPTRIC LIGHTHOUSES, CHIEFLY FROM NOTES FURNISHED BY M.
+THEODORE LETOURNEAU OF PARIS.
+
+The glass used in all the parts of the optical apparatus of the
+dioptric Lighthouses is that of St Gobain, whose index of refraction is
+1·51.
+
+As well on account of the difficulty experienced in producing at
+all times regular castings of glass from the moulds, as in order
+to compensate for the frequent accidents, which occur in the first
+application of the rubbers to the inequalities of the surface of the
+glass, the castings, whether for rings of lenses or prisms, are made
+from moulds, exceeding the intended size of the finished pieces by
+_one-eighth part_.
+
+We shall take as an example, which is well calculated to illustrate the
+difficulties of the grinding process, one of the prismatic rings of a
+Catadioptric Light of the first order. The first operation will be to
+take off the rough arris at the angles of the pieces as they come from
+the moulds, and to reduce to equality the length of each of the four
+quadrantal prisms or segments by removing from each the quantity that
+may be necessary to make those four pieces, when placed on a circle,
+exactly equal to that of the finished zones. Each of them must have an
+excess of material at the various surfaces just sufficient to insure
+the rubber having scope enough to remove all the flaws or defects of
+the two surfaces to be first ground, which are the (concave and convex)
+refracting faces of the zone (the sides AC and BC in the Table in the
+Appendix, No. IV.)
+
+[Illustration: Fig. 110.]
+
+The pieces must be placed end to end on the horizontal plane or table
+of the lathe at AA (fig. 110), and must rest on the exterior arris
+A of the reflecting side, on which arris there is ground a narrow
+plane whose width is proportionate to the projection of the outer edge
+beyond the inner edge of the zone, _foreshortened_ by the _bevel_ or
+inclination of the reflecting side, when resting (as in fig. 110) on
+the circular iron belt, which is screwed to the table of the lathe
+provided for its reception. This narrow plane at the arris A should
+be sufficient to give the prism a solid and regular bearing on the
+circular iron belt. In this figure (fig. 110) _a_ _b_ is the vertical
+axis of the lathe, _n_ the point from which the co-ordinates for O,
+the grinding centre for the exterior _concave_ refracting surface
+AC, are measured, and _e_ AC the arc swept by the grinding surface.
+Conversely, _n′_ is the origin of the co-ordinates for the grinding
+centre O of the interior _convex_ refracting surface BC, and _e_ CB the
+arc swept by its grinding surface. Some skill is required in fixing
+the prism on the belt, for, on the one hand, there is an obstacle to
+correct workmanship from the dragging motion of the platform, and, on
+the other, by the unequal subdivision of the weight of the glass, which
+should be nearly balanced. This narrow plane being perfectly adjusted
+for all the segments so as to bed them quite level, the circular iron
+belt on which the ring should be ground, is placed on its platform, in
+the manner represented in the figure. It should be as truly levelled
+as possible, otherwise all the subsequent operations will be deranged
+by it. This iron belt is heated by means of heating _pans_; and the
+degree of heat may be practically judged of by the ebullition of drops
+of water let fall on it. The segments of glass are also at the same
+time placed in a stove heated with steam, and are generally raised to
+about 120° centigrade. The difference between the time required for
+the two operations of heating the iron belt and the glass segments is
+employed in laying or bedding a quantity of cement on the reflecting
+side of the segment, so as to fill up the angular space between the
+glass and the iron belt, and also to serve as a seat for the segment in
+the manner shewn in fig. 110. This operation is performed on a plane
+surface, in order that the lower part of the mastic may be precisely
+on a level with the narrow plane already ground on the outer arris of
+the reflecting side. After being sure that the heat is equally spread
+over every part of the circular iron belt, the segment is arranged on
+it; and the workman must, at this juncture, exert all his skill in
+placing the parts of the segment in a position nearly concentric with
+the belt, or in a truly circular form, making due allowance, however,
+for the inequalities existing at various parts of the rough material,
+and at the same time taking care that there should be an interval of at
+least two millimètres (or about ¹⁄₁₂th inch) between the ends of each
+of the two adjacent segments. Without this interval the heat evolved
+during the polishing would either dilate the glass so much as to cause
+the ends of the segments to fly into splinters, or make it needful
+to remove the zone before this should take place, the inevitable
+consequence of which would be the fracture of the pieces. Those
+intervals between the segments are filled with statuary’s plaster,
+which must be carefully washed and brushed at each change of the emery
+employed in grinding.
+
+The exterior diameter of the circular iron belt must be precisely
+equal to that of the ring, because, if larger, the free movement of
+the rubbers to and fro on the concave refracting surface AC (fig. 110)
+could not take place.
+
+By what is already said, it will be obvious that the grinding process
+is begun at the refracting sides AC and BC, and a few words will shew
+that this could hardly be otherwise. If a commencement be made on
+the reflecting side, which appears at first sight more natural, the
+consequence is obvious. Having provided for an excess of material
+in every direction, the segment must consequently be larger than it
+will be when finished; and the surfaces therefore cannot be true and
+perfect, except they be ground throughout their entire segmental
+section, from their centres of curvature, in reference to some given
+apex of the generating triangle. Now, if the reflecting side were
+finished first, it might continue to possess this excess of size after
+being finished, and would, therefore, afford no accurate starting
+point for the grinding of the other surfaces; it would also present
+no _surface_ or narrow plane for resting firmly on the iron belt, but
+would then depend merely on its own finished plane, which, being curved
+and considerably inclined, would not give a solid bearing for the
+glass. The other mode of commencing with the two refracting sides, on
+the contrary, gives a solid bearing on the narrow plane already ground
+on the reflecting side at A; and after these surfaces have been ground,
+and the segments inverted (as shewn in fig. 111), the outer edge of
+this narrow plane at the arris A, which has been fully defined by the
+intersection of the finished surface AC just ground, and also the apex
+at C, which has been determined by the intersection of AC and BC,
+combine to fix an accurate starting point for the rubber, in grinding
+the reflecting surface AB.
+
+[Illustration: Fig. 111.]
+
+
+_Dressing off the rough part of the Ring._
+
+The ring is generally reduced from the rough state by means of fixed
+rubbers, the adjustment of which is more easily regulated than that
+of the moveable beam or radius of the arc, which is used to give the
+exact curvature of the surface. Those fixed rubbers are 150 millimètres
+(nearly 6 inches) wide, by 200 millimètres (nearly 8 inches) long,
+and are of cast-iron. Three such rubbers are placed at equidistant
+points of the circle. Two cutters of sheet-iron attached to arms placed
+vertically (as are also those which carry the rubbers), and moving in
+grooves radiating towards the centre of the lathe, so as to admit of
+adjustment to suit the varying radii of the zones, serve gradually to
+abrade the outer and inner arrises of the segments, so as to prevent
+the splintering to which, from becoming too sharp, those arrises,
+without this precaution, would be liable. Those rubbers are, besides,
+fixed by stems to frames, in the form of quadrants of the circle, which
+allow of a change in the direction of the planes, as occasion may
+require.
+
+Instead of the siliceous sand formerly used, the powder of pounded
+freestone is employed, as it is found to wear the tools less, and to
+form a better preparation for the subsequent grinding operations. It
+is easy to conceive that the action of the fixed rubbers necessarily
+produces ruts or inequalities in the circular direction. The operation
+of rough dressing, therefore, is not finished until, when those first
+rubbers are removed, the surfaces of the segments have been subject,
+for the required time, to the action of moveable rubbers, attached to
+arms working as radii of curvature, in a plane at right angles to the
+horizontal movement of the lathe, which carries the zones.
+
+
+_The Emery Grinding._
+
+The form of the segment should be nearly perfect, after the rough
+grinding is finished. The lathe and the zone are then subjected to an
+extremely careful washing. Every place where the stone-powder might
+adhere is dusted. The radius of curvature is verified afresh, agreeably
+to the co-ordinates (Appendix, No. IV.); and emery is used instead of
+powdered stone; beginning with that called No. 1, which is drawn after
+suspension in water for one minute. Brushes are used for spreading the
+emery on the surface of the glass. The quantity ought always to be
+sufficient to prevent the direct contact of the cast-iron rubber with
+the glass. Splintering or scratching, which cannot be easily effaced,
+may result from the neglect of this precaution.
+
+Practice alone, and an eye duly trained by continual experience,
+can determine the point of time at which each kind of emery must be
+discontinued. The celerity of the work depends on circumstances very
+difficult to appreciate, such as the amount of the pressure of the
+rubbers, or the degree of accuracy with which the radius of curvature
+has been adjusted, during the rough grinding. Each kind of emery in
+succession thus corrects the form of the zone and refines the grain of
+the surface of the glass; and each change to a fresh material requires
+the same attention to cleanliness, so as to remove every trace of the
+substance last used in grinding, and thus to give each successive
+process its full and legitimate effect. The _douci_ is the _fifth_
+and _last_ kind of emery which precedes the _polish_. It is drawn off
+after ten minutes’ suspension in water, and is extremely fine. Before
+applying it, the greatest care is necessary to insure cleanliness,
+as a single grain of any of the preceding kinds of emery might cause
+scratches, which the polish cannot remove.
+
+
+_The Polish._
+
+The same considerations which induce the workman most carefully to
+cleanse the lathe and everything connected with it, before employing
+the last emery called the _douci_, are still more urgent in the case
+of the final _polish_. The only change which is made at this last
+stage of the work is to replace the first rubber by a new one, both
+longer and wider by about 50 millimètres (nearly 2 inches). On its
+lower face is attached with cement a piece of soft carpet, whose edges
+are fixed to the rubber by means of flat bands of iron, attached with
+screws. This security, added to that given by the cement, is necessary
+to fit it to resist the great pressure it must sustain. A practical
+question, which experience alone can resolve, occurs at this stage, as
+the operation of polishing may, in the hands of unskilful persons, be
+so inopportunely commenced, as to make that work almost endless. Thus,
+the mere circumstance of spreading at the beginning too thick layers
+of rouge, or using unsuitable kinds of carpet, would cut scratches in
+the glass, and thus perhaps make it necessary to return to the use of
+the emery called _douci_. Sometimes, also, if the carpets be not washed
+at the very time of using them, scratches are formed by the dust which
+they may contain. This shews, that the use of rouge should be rather
+sparing than otherwise, at the commencement of the polish; and that the
+carpet-cloths should be brushed and washed _twice_ rather than _once_.
+In all cases, the quality of the carpet forms an important element in
+the success of the working.
+
+When the _polish_ is finished, the ring is detached from the circular
+belt, simply by the tap of a hammer, on the inner edge of the circle.
+The division of the zones (which are quarters of the circle) into
+_eighths_, is done by means of a sawing machine consisting of a flat
+copper-wheel, one-half millimètre (¹⁄₅₀th inch) in thickness, attached
+to an arm with a counterpoise. This wheel descends and cuts the zone by
+means of emery, which is continually applied to it; the direction of
+the cut is radial. The two halves of the zone are detached from each
+other, as soon as their weight exceeds the resistance of the part which
+remains to be sawn.
+
+
+_Adjustment of the Prisms._
+
+The adjustment of the prisms in the frames, involves an operation
+which is not without risk. Much care is required in handling the sharp
+arrises of the glass, which are very acute and delicate and at the
+same time lie in a curved direction, which makes them liable to be
+splintered in the hands of unskilful persons.
+
+With the exception of the plane vertical surfaces of the annular
+lenses, and the central band and rings of the dioptric belts of
+fixed lights, which are ground by means of vertical rubbers with a
+reciprocating movement, every other plane surface is executed by hand
+on a flat table.
+
+
+_Composition of the Cement for fixing the glass on the lathe._
+
+  8 parts Swedish pitch.
+  1  do.  of wood ashes.
+
+The whole is heated in an iron pot until fully liquified and thoroughly
+mixed. This cement is used almost in a state of ebullition, so that it
+cannot be handled without the precaution of continually dipping the
+hands in cold water.
+
+
+_Composition of cement used for the adjustment of the pieces of glass
+which touch each other._
+
+  12 parts white lead.
+   1  do.  minium or red lead.
+   5  do.  boiled lintseed oil.
+
+The whole is pounded on an iron table by means of a flat mullet, like
+that used by painters (fig. 112), whose grinding surface is _a_ _b_,
+and _c_ the knob for the hand. This cement is applied liquid so as
+to offer no resistance to the close union of the pieces, which it is
+intended to unite.
+
+[Illustration: Fig. 112.]
+
+
+_Cement for filling up voids, and fixing the rings in the frames._
+
+  12 parts white lead.
+   3  do.  whiting.
+   1  do.  minium.
+   4  do.  boiled lintseed oil.
+
+This last composition differs from the former only in the introduction
+of whiting, which, while like minium it has a desiccative property,
+gives more body to the cement and prevents the formation of cracks. The
+oil is also decreased in quantity, as the cement must be used in a more
+compact state. The trituration of this cement is performed by means of
+a cylindric iron roller _a_ _b_, with a centre-spoke _c_ _d_ for the
+hand (fig. 113).
+
+[Illustration: Fig. 113.]
+
+It is essential for the production of good cement, that the mixture of
+the ingredients be complete.
+
+
+_Prices of the various parts of the Dioptric Apparatus._
+
+The expense of the various parts of the Dioptric apparatus is as
+follows: Great lens of first order, L.58 (8 of which are required);
+pyramidal lens and mirror, L.14, 12s. (8 of which are required);
+catadioptric cupola, L.480; catadioptric rings below lenses, L.360;
+pannel of dioptric belt for fixed light of first order, L.56 (of which
+8 are required for the whole circle); apparatus of fourth order, for a
+fixed light, for whole horizon, L.128; apparatus of sixth order, for
+whole horizon, L.44. The expense of the mechanical lamp of the first
+order with four wicks, as made for the Scotch Lighthouses by Mr JOHN
+MILNE of Edinburgh, is L.30.
+
+
+_Diagrams illustrative of the Table, Appendix, No. IV._
+
+[Illustration: Fig. 114.]
+
+[Illustration: Fig. 115.]
+
+[Illustration: Fig. 116.]
+
+[Illustration: Fig. 117.]
+
+
+APPENDIX, No. IV.
+
+TABLE OF THE ELEMENTS OF CATADIOPTRIC ZONES SUITED FOR LIGHTS OF THE
+FIRST ORDER IN THE SYSTEM OF AUGUSTIN FRESNEL.
+
+  NOTE.--The Six co-ordinates of the Generating Triangle of each Zone
+  in these Tables have the Focus of the Principal Lenses of the System
+  for their origin; it being considered more convenient, in executing
+  the necessary protractions, preparatory to the construction of the
+  grinding apparatus, at once to refer the whole of the grinding
+  machinery to the axis of the apparatus. To prevent the appearance of
+  any inconsistency, however, it is proper to mention, that the radiant
+  points of the series of Zones, do not exactly coincide with the Focus
+  of the Lenses nor with each other; and that to avoid the parallax
+  which the distance of the radiant points from the origin of the
+  co-ordinates would occasion, it is necessary to make some corrections
+  upon the linear dimensions, so as to find the line corresponding
+  to the angles θ, ξ, and the distance Δ. In the Hyperpyral series,
+  which stands _above_ the flame, the Zones have the radiant point
+  10 millimetres above the Focus of the Lenses, and each _y_ of this
+  series, therefore, requires a reduction of that quantity; while the
+  _x_ remains unchanged. In the Hypopyral series, which stands _below_
+  the flame, the Focus or radiant points of each Zone, varies its place
+  in the flame, moving upwards as the Zone is lower, so that the line
+  joining the Zones and the Foci, revolves as a radius vector round a
+  point between them. In this way, the _x_’s remain unaltered; but the
+  _y_’s will be lengthened successively by the addition of 10, 14, 19,
+  25, 32, and 40 millimetres. As these Tables contain the dimensions of
+  Zones which are intended as an addition to the apparatus of FRESNEL,
+  I have adopted the metric scale, so as to render them at once
+  applicable to the existing protractions of that system. It is only
+  necessary to add, that the conversion of millimetres into imperial
+  inches, is easily effected by adding the log. millimetres to the log.
+  ̅2·59516, the sum being the log. of the equivalent of the first term
+  in imperial inches.
+
+  +-------+-----++--------+--------++---------+--------+--------++
+  |       |     ||   θ    |   ξ    ||   BCA,  |  ABC,  |   BAC, ||
+  |       |     ||        |        ||         |        |        ||
+  |       |     ||        |        ||         |        |        ||
+  |       |     ||        |        ||         |        |        ||
+  |       |     ||        |        ||         |        |        ||
+  |       |     ||        |        ||         |        |        ||
+  |       |     ||        |        ||         |        |        ||
+  |       |     ||        |        ||         |        |        ||
+  |       |     ||        |        ||         |        |        ||
+  |       |     ||        |        ||         |        |        ||
+  |       |     ||        |        ||         |        |        ||
+  |       |     ||        |        ||         |        |        ||
+  |       |     || Incli- |        ||         |        |        ||
+  |       |     || nation |        || Obtuse  |        |        ||
+  |       |     ||   of   |  Inci- ||  Angle  |        |        ||
+  |       |     || Ray FC |  dence ||  of the |        |        ||
+  |       |     || to the | of Ray ||  Gener- |Angle of|Angle of||
+  |       |     ||Vertical|  FC on ||  ating  | Gener- | Gener- ||
+  |       |     ||  Axis  |  Side  || Triangle|  ating |  ating ||
+  |       |     || of the |  BC of || of the  |Triangle|Triangle||
+  |       |     || System.|  Zone. ||  Zone.  |of Zone.|of Zone.||
+  |       | No. ||        |        ||         |        |        ||
+  |       | of  ||  (Fig. |  (Fig. ||  (Fig.  |  (Fig. |  (Fig. ||
+  |       |ZONE.||  114.) |  114.) ||  114.)  |  114.) |  114.) ||
+  |       +-----++--------+--------++---------+--------+--------++
+  |       |     || °  ′  ″| °  ′  ″||  °  ′  ″| °  ′  ″| °  ′  ″||
+  |       |  1  ||60 45 38|44 06 09||117 26 40|31 48 10|30 45 10||
+  |       |  2  ||56 55 38|41 28 10||116 00 42|32 32 01|31 27 17||
+  |       |  3  ||53 05 38|38 48 29||114 31 20|33 17 30|32 11 10||
+  |       |  4  ||49 15 38|36 07 09||112 58 40|34 04 36|32 56 44||
+  |HYPER- |  5  ||45 25 38|33 24 19||111 23 00|34 53 07|33 43 53||
+  | PYRAL |  6  ||41 35 38|30 40 05||109 44 32|35 42 57|34 32 31||
+  |SERIES |  7  ||37 45 38|27 54 34||108 03 30|36 34 01|35 22 29||
+  |  OF   |  8  ||33 55 38|25 07 52||106 20 06|37 26 11|36 13 43||
+  |ZONES. |  9  ||30 05 38|22 20 07||104 34 36|38 19 23|37 06 01||
+  |       | 10  ||26 15 38|19 31 25||102 47 12|39 13 27|37 59 21||
+  |       | 11  ||22 25 38|16 41 54||100 58 10|40 07 14|38 54 36||
+  |       | 12  ||18 42 02|13 56 26|| 99 10 50|40 59 53|39 49 17||
+  |       | 13  ||15 06 03|11 16 04|| 97 26 07|41 51 03|40 42 49||
+  +=======+=====++========+========++=========+========+========++
+  |       |     || °  ′  ″| °  ′  ″||  °  ′  ″| °  ′  ″| °  ′  ″||
+  |       |  1  ||59 49 16|43 27 36||117 05 56|31 58 37|30 55 27||
+  | HYPO- |  2  ||55 48 55|40 42 01||115 35 07|32 44 43|31 40 09||
+  | PYRAL |  3  ||51 48 33|37 54 32||114 00 31|33 28 16|32 27 13||
+  |SERIES.|  4  ||47 51 11|35 07 32||112 23 53|34 20 23|33 15 44||
+  |       |  5  ||43 59 40|32 23 06||110 46 32|35 08 23|34 05 05||
+  |       |  6  ||40 16 34|29 43 19||109 10 04|35 55 37|34 54 18||
+  +-------+-----++--------+--------++---------+--------+--------++
+
+  +-------+-----++-------+-------+-------++
+  |       |     ||  BA,  |  BC,  |  AC,  ||
+  |       |     ||       |       |       ||
+  |       |     ||       |       |       ||
+  |       |     ||       |       |       ||
+  |       |     ||       |       |       ++
+  |       |     ||       |       |       ||
+  |       |     ||       |       |       ||
+  |       |     ||       |       |       ||
+  |       |     ||       |       |       ||
+  |       |     ||  Re-  |       |       ||
+  |       |     || flect-|       |       ||
+  |       |     || ing   |       |       ||
+  |       |     ||Side of|       |       ||
+  |       |     ||Zone in| Inner | Outer ||
+  |       |     || Milli-|  Re-  |  Re-  ||
+  |       |     || metres| fract-| fract-||
+  |       |     || being |  ing  |  ing  ||
+  |       |     || Chord |Side of|Side of||
+  |       |     ||   of  |Zone in|Zone in||
+  |       |     ||the Arc| Milli-| Milli-||
+  |       |     ||_b_ A. |metres.|metres.||
+  |       | No. ||       |       |       ||
+  |       | of  || (Fig. | (Fig. | (Fig. ||
+  |       |ZONE.|| 115.) | 115.) | 115.) ||
+  |       +-----++-------+-------+-------++
+  |       |     ||       |       |       ||
+  |       |  1  ||160·331| 92·379| 95·209||
+  |       |  2  ||155·430| 90·249| 93·011||
+  |       |  3  ||151·551| 88·729| 91·434||
+  |       |  4  ||148·580| 87·768| 90·424||
+  |HYPER- |  5  ||146·444| 87·332| 89·947||
+  | PYRAL |  6  ||145·087| 87·403| 89·986||
+  |SERIES |  7  ||144·481| 87·977| 90·536||
+  |  OF   |  8  ||144·609| 89·060| 91·604||
+  |ZONES. |  9  ||145·476| 90·671| 93·209||
+  |       | 10  ||147·089| 92·843| 95·384||
+  |       | 11  ||145·361| 93·000| 95·413||
+  |       | 12  ||143·362| 93·000| 95·271||
+  |       | 13  ||141·379| 93·000| 95·127||
+  +=======+=====++=======+=======+=======++
+  |       |     ||       |       |       ||
+  |       |  1  ||159·369| 92·000| 94·806||
+  | HYPO- |  2  ||158·051| 92·000| 94·783||
+  | PYRAL |  3  ||156·592| 92·000| 94·719||
+  |SERIES.|  4  ||155·083| 92·000| 94·619||
+  |       |  5  ||153·489| 92·000| 94·488||
+  |       |  6  ||151·863| 92·000| 94·334||
+  +-------+-----++-------+-------+-------++
+
+  +-------+-----++--------------------------------------------------++
+  |       |     ||   Co-ordinates of the Apices of the Generating   ||
+  |       |     || Triangle, in Millimetres, having the Axis of the ||
+  |       |     ||  System cut by the horizontal plane of the focus ||
+  |       |     ||of the Annular Lenses, for its origin. (Fig. 116.)||
+  |       |     ++--------+-------+--------+-------+--------+-------++
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       |     ||        |       |        |       |        |       ||
+  |       | No. ||        |       |        |       |        |       ||
+  |       | of  ||        |       |        |       |        |       ||
+  |       |ZONE.|| A_{_y_}|A_{_x_}| B_{_y_}|B_{_x_}| C_{_y_}|C_{_x_}||
+  |       +-----++--------+-------+--------+-------+--------+-------++
+  |       |     ||        |       |        |       |        |       ||
+  |       |  1  || 593·369|986·260| 551·481|831·497| 525·000|920·000||
+  |       |  2  || 663·063|957·410| 617·423|808·832| 593·369|895·816||
+  |       |  3  || 734·313|926·908| 684·958|783·619| 663·063|869·605||
+  |       |  4  || 807·357|894·222| 754·267|755·451| 734·313|840·920||
+  |HYPER- |  5  || 882·445|858·858| 825·547|723·921| 807·357|809·337||
+  | PYRAL |  6  || 959·847|820·325| 899·011|688·608| 882·445|774·426||
+  |SERIES |  7  ||1039·852|778·108| 974·899|649·051| 959·847|735·730||
+  |  OF   |  8  ||1122·784|731·645|1053·471|604·730|1039·852|692·742||
+  |ZONES. |  9  ||1209·000|680·322|1135·025|555·059|1122·784|644·900||
+  |       | 10  ||1298·900|623·433|1219·892|499·354|1209·000|591·556||
+  |       | 11  ||1390·290|559·378|1308·183|439·428|1288·900|531·963||
+  |       | 12  ||1482·755|490·169|1398·007|374·538|1390·290|467·217||
+  |       | 13  ||1576·048|415·991|1488·972|304·611|1482·755|397·403||
+  +=======+=====++========+=======+========+=======+========+=======++
+  |       |     ||        |       |        |       |        |       ||
+  |       |  1  || 593·815|985·212| 550·915|831·725| 525·000|920·000||
+  | HYPO- |  2  || 682·731|981·810| 634·862|831·183| 610·872|920·000||
+  | PYRAL |  3  || 779·464|978·917| 726·831|830·694| 704·730|920·000||
+  |SERIES.|  4  || 885·046|974·441| 827·926|830·261| 807·657|920·000||
+  |       |  5  ||1000·663|970·608| 939·385|829·882| 920·871|920·000||
+  |       |  6  ||1127·665|966·771|1062·591|829·557|1045·740|920·000||
+  +-------+-----++--------+-------+--------+-------+--------+-------++
+
+  +-------+-----++--------------------------++
+  |       |     || Inclination of the Sides ||
+  |       |     ||of the Generating Triangle||
+  |       |     ||  to the Vertical Axis of ||
+  |       |     ||  the System. (Fig. 117.) ||
+  |       |     ||--------+--------+--------++
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     ||        |        |        ||
+  |       |     || Incli- | Incli- | Incli- ||
+  |       | No. || nation | nation | nation ||
+  |       | of  ||  of    |   of   |   of   ||
+  |       |ZONE.||  AB.   |   BC.  |   AC.  ||
+  |       +-----++--------+--------+--------++
+  |       |     || °  ′  ″| °  ′  ″| °  ′  ″||
+  |       |  1  ||74 51 19|73 20 31|44 06 09||
+  |       |  2  ||72 55 27|74 32 32|41 28 10||
+  |       |  3  ||70 59 39|75 42 51|38 48 29||
+  |       |  4  ||69 03 53|76 51 31|36 07 09||
+  |HYPER- |  5  ||67 08 12|77 58 41|33 24 19||
+  | PYRAL |  6  ||65 12 36|79 04 27|30 40 05||
+  |SERIES |  7  ||63 17 03|80 08 56|27 54 34||
+  |  OF   |  8  ||61 21 35|81 12 14|25 07 52||
+  |ZONES. |  9  ||59 26 08|82 14 29|22 20 07||
+  |       | 10  ||57 30 46|83 15 47|19 31 25||
+  |       | 11  ||55 36 30|84 16 16|16 41 54||
+  |       | 12  ||53 45 43|85 14 24|13 56 26||
+  |       | 13  ||51 58 53|86 10 02|11 16 04||
+  +=======+=====++========+========+========++
+  |       |     || °  ′  ″| °  ′  ″| °  ′  ″||
+  |       |  1  ||74 23 03|73 38 20|43 27 36||
+  | HYPO- |  2  ||72 22 10|74 53 06|40 42 01||
+  | PYRAL |  3  ||70 21 45|76 05 59|37 54 32||
+  |SERIES.|  4  ||68 23 16|77 16 21|35 07 32||
+  |       |  5  ||66 28 11|78 23 26|32 23 06||
+  |       |  6  ||64 37 37|79 26 45|29 43 19||
+  +-------+-----++--------+--------+--------++
+
+  +-------+-----++----------------------------------------++
+  |       |     ||                                        ||
+  |       |     ||                                        ||
+  |       |     ||    AB, Reflecting Surfaces (convex).   ||
+  |       |     ||                (Fig. 115.)             ||
+  |       |     ++-------+-------+-------+-------+--------++
+  |       |     ||       |       | Verti-|       |        ||
+  |       |     ||       | Hori- |  cal  |       |        ||
+  |       |     ||       | zontal|  dis- |       |        ||
+  |       |     ||       |  dis- | tance |       |        ||
+  |       |     ||       | tance |   of  |       |        ||
+  |       |     ||       |   of  | centre|       |        ||
+  |       |     ||       | centre|   of  |       |        ||
+  |       |     ||       |   of  | curva-|       |        ||
+  |       |     ||       | curva-| ture X|       |        ||
+  |       |     ||       |  ture |_below_|       |        ||
+  |       |     ||       | X from|  the  |       |        ||
+  |       |     || Radius|  the  |_outer_|       |Inclina-||
+  |       |     ||   of  |  axis | arris |  In-  |  tion  ||
+  |       |     || Curva-| of the| of the| clina-| of the ||
+  |       |     ||ture in| System| _Zone_|tion of|  Outer ||
+  |       |     || Milli-|   in  |at A in|the Two| Radius ||
+  |       | No. ||metres,| Milli-| Milli-| Radii |  in A  ||
+  |       | of  || XA or | metres| metres|  in A | to the ||
+  |       |ZONE.|| X _b_.| = OX. | = OA. | and B.| Vertex.||
+  |       +-----++-------+-------+-------+-------+--------++
+  |       |     ||       |       |       |°  ′  ″| °  ′  ″||
+  |       |  1  ||8750·19|3194·76|8466·88|1 02 59|14 38 11||
+  |       |  2  ||8253·90|3306·80|7909·94|1 04 45|16 32 11||
+  |       |  3  ||7850·30|3411·75|7446·67|1 06 22|18 27 11||
+  |       |  4  ||7527·08|3514·22|7056·39|1 07 51|20 22 11||
+  |HYPER- |  5  ||7275·23|3617·56|6730·66|1 09 12|22 17 11||
+  | PYRAL |  6  ||7082·17|3723·81|6459·63|1 10 25|24 12 11||
+  |SERIES |  7  ||6944·09|3835·23|6234·93|1 11 31|26 07 11||
+  |  OF   |  8  ||6857·03|3954·67|6052·36|1 12 30|28 02 11||
+  |ZONES. |  9  ||6817·87|4081·70|5902·53|1 13 20|29 57 11||
+  |       | 10  ||6824·46|4226·67|5795·68|1 14 05|31 52 11||
+  |       | 11  ||6880·52|4385·63|5718·52|1 12 37|33 47 11||
+  |       | 12  ||6980·89|4558·83|5672·64|1 10 36|35 38 59||
+  |       | 13  ||7123·05|4747·24|5654·92|1 08 15|37 26 59||
+  +=======+=====++=======+=======+=======+=======+========++
+  |       |     ||       |       |       |°  ′  ″| °  ′  ″||
+  |       |  1  ||8674·74|3243·48|8375·64|1 03 09|15 05 22||
+  | HYPO- |  2  ||8419·60|3456·44|8047·72|1 04 31|17 05 32||
+  | PYRAL |  3  ||8278·82|3685·41|7823·68|1 05 01|19 05 13||
+  |SERIES.|  4  ||8252·95|3941·89|7701·00|1 04 36|21 04 24||
+  |       |  5  ||8335·86|4228·06|7673·05|1 03 18|23 00 10||
+  |       |  6  ||8522·64|4549·97|7732·80|1 01 15|24 51 43||
+  +-------+-----++-------+-------+-------+-------+--------++
+
+  +-------+-----++----------------------------------------++
+  |       |     ||                                        ||
+  |       |     ||                                        ||
+  |       |     ||                                        ||
+  |       |     ||AC, Outer Refracting Surfaces (concave).||
+  |       |     ++-------+-------+-------+-------+--------++
+  |       |     ||       |       | Verti-|       |        ||
+  |       |     ||       |       |  cal  |       |        ||
+  |       |     ||       | Hori- |  dis- |       |        ||
+  |       |     ||       | zontal| tance |       |        ||
+  |       |     ||       |  dis- |   of  |       |        ||
+  |       |     ||       | tance | centre|       |        ||
+  |       |     ||       |  of   |   of  |       |        ||
+  |       |     ||       | centre| curva-|       |        ||
+  |       |     ||       |  of   |  ture |       |        ||
+  |       |     ||       | curva-|_above_|       |        ||
+  |       |     ||       |  ture |  the  |       |   In-  ||
+  |       |     ||       |  from | outer |       | clina- ||
+  |       |     ||       |  the  | arris |  In-  |  tion  ||
+  |       |     || Radius|  axis | of the| clina-| of the ||
+  |       |     ||   of  | of the| _Zone_|  tion |  Outer ||
+  |       |     || Curva-| System|   at  | of the| Radius ||
+  |       | No. ||ture in|   in  |  A in | Radii |  at A  ||
+  |       | of  || Milli-| Milli-| Milli-|  in A | to the ||
+  |       |ZONE.||metres.|metres.|metres.| and C.| Vertex.||
+  |       +-----++-------+-------+-------+-------+--------++
+  |       |     ||       |       |       |°  ′  ″| °  ′  ″||
+  |       |  1  ||4000·00|3825·31|2817·77|1 21 50|45 12 56||
+  |       |  2  ||  ...  |3923·65|2683·55|1 19 56|47 51 52||
+  |       |  3  ||  ...  |4015·06|2542·31|1 18 34|50 32 14||
+  |       |  4  ||  ...  |4098·54|2394·23|1 17 42|53 14 00||
+  |HYPER- |  5  ||  ...  |4173·08|2239·64|1 17 18|55 57 02||
+  | PYRAL |  6  ||  ...  |4237·70|2078·82|1 17 20|58 41 15||
+  |SERIES |  7  ||  ...  |4291·45|1912·18|1 17 48|61 26 32||
+  |  OF   |  8  ||  ...  |4333·30|1740·12|1 18 44|64 12 46||
+  |ZONES. |  9  ||  ...  |4362·26|1563·10|1 20 06|66 59 50||
+  |       | 10  ||  ...  |4377·24|1381·63|1 21 58|69 47 36||
+  |       | 11  ||  ...  |4376·72|1194·94|1 22 00|72 37 06||
+  |       | 12  ||  ...  |4360·70|1009·41|1 21 12|75 22 58||
+  |       | 13  ||  ...  |4329·31| 828·19|1 21 46|78 03 02||
+  +=======+=====++=======+=======+=======+=======+========++
+  |       |     ||       |       |       |°  ′  ″| °  ′  ″||
+  |       |  1  ||4000·00|3855·83|2785·60|1 21 28|45 51 40||
+  | HYPO- |  2  ||  ...  |3983·21|2644·16|1 21 28|48 37 15||
+  | PYRAL |  3  ||  ...  |4104·84|2494·82|1 21 24|51 24 46||
+  |SERIES.|  4  ||  ...  |4218·56|2340·02|1 21 20|54 11 48||
+  |       |  5  ||  ...  |4322·95|2182·17|1 21 12|56 56 18||
+  |       |  6  ||  ...  |4416·91|2023·99|1 21 04|59 36 09||
+  +-------+-----++-------+-------+-------+-------+--------++
+
+  +-------+-----++----------------------------------------++-------++
+  |       |     ||                                        ||   Δ,  ||
+  |       |     ||                                        ||       ||
+  |       |     ||                                        ||       ||
+  |       |     || BC, Inner Refracting Surfaces (convex).||       ||
+  |       |     ++-------+-------+-------+-------+--------++       ||
+  |       |     ||       |       |       |       |        ||       ||
+  |       |     ||       |       | Verti-|       |        ||       ||
+  |       |     ||       | Hori- |  cal  |       |        ||       ||
+  |       |     ||       | zontal|  dis- |       |        ||       ||
+  |       |     ||       |  dis- | tance |       |        ||  Dis- ||
+  |       |     ||       | tance |   of  |       |        || tance ||
+  |       |     ||       |   of  | centre|       |        ||   of  ||
+  |       |     ||       | centre|   of  |       |        || C from||
+  |       |     ||       |   of  | curva-|       |        ||  the  ||
+  |       |     ||       | curva-|  ture |       |        || Focus ||
+  |       |     ||       |  ture |_below_|       |   In-  ||for the||
+  |       |     ||       |  from |  the  |       | clina- || Zones,||
+  |       |     ||       |  the  | outer |  In-  | tion of||   in  ||
+  |       |     || Radius|  axis | arris | clina-| of the || Milli-||
+  |       |     ||   of  | of the| of the|  tion | Outer  || metres||
+  |       |     || Curva-| System| _Zone_| of the| Radius || = FC. ||
+  |       | No. ||ture in|   in  |at A in| Radii |  in C  ||       ||
+  |       | of  || Milli-| Milli-| Milli-|  in C | to the || (Fig. ||
+  |       |ZONE.||metres.|metres.|metres.| and B.| Vertex.|| 114.) ||
+  |       +-----++-------+-------+-------+-------+--------++-------++
+  |       |     ||       |       |       |°  ′  ″| °  ′  ″||       ||
+  |       |  1  ||4000·00|2021·19|3777·07|1 19 24|15 58 47||1054·34||
+  |       |  2  ||  ...  |1918·37|3797·40|1 17 34|14 48 41||1069·02||
+  |       |  3  ||  ...  |1813·60|3815·77|1 16 16|13 39 01||1087·52||
+  |       |  4  ||  ...  |1707·55|3831·95|1 15 26|12 30 46||1109·85||
+  |HYPER- |  5  ||  ...  |1599·72|3846·04|1 15 04|11 23 47||1136·14||
+  | PYRAL |  6  ||  ...  |1489·62|3858·14|1 15 08|10 17 59||1166·57||
+  |SERIES |  7  ||  ...  |1376·71|3868·30|1 15 36| 9 13 16||1201·46||
+  |  OF   |  8  ||  ...  |1260·38|3876·59|1 16 32| 8 09 30||1241·16||
+  |ZONES. |  9  ||  ...  |1139·94|3883·03|1 17 56| 7 06 33||1286·15||
+  |       | 10  ||  ...  |1014·67|3887·66|1 19 48| 6 04 19||1336·99||
+  |       | 11  ||  ...  | 884·95|3893·00|1 19 56| 5 03 46||1394·36||
+  |       | 12  ||  ...  | 752·78|3897·32|1 19 56| 4 05 38||1457·22||
+  |       | 13  ||  ...  | 618·37|3901·10|1 19 56| 3 10 00||1525·43||
+  +=======+=====++=======+=======+=======+=======+========++=======++
+  |       |     ||       |       |       |°  ′  ″| °  ′  ″||       ||
+  |       |  1  ||4000·00|2002·52|3781·91|1 19 04|15 42 08||  --   ||
+  | HYPO- |  2  ||  ...  |1918·55|3801·51|1 19 04|14 27 22||  --   ||
+  | PYRAL |  3  ||  ...  |1836·22|3818·93|1 19 04|13 14 29||  --   ||
+  |SERIES.|  4  ||  ...  |1756·33|3834·20|1 19 04|12 04 07||  --   ||
+  |       |  5  ||  ...  |1679·85|3847·38|1 19 04|10 57 02||  --   ||
+  |       |  6  ||  ...  |1607·39|3858·56|1 19 04| 9 53 43||  --   ||
+  +-------+-----++-------+-------+-------+-------+--------++-------++
+
+
+APPENDIX, No. V.
+
+NOTICE TO MARINERS.--SKERRYVORE LIGHTHOUSE.
+
+The Commissioners of the Northern Lighthouses hereby give notice, that
+a Lighthouse has been erected upon the Skerryvore Rock, which lies off
+the Island of Tyree, in the county of Argyll, the Light of which will
+be exhibited on the Night of the 1st February 1844, and every Night
+thereafter, from sunset to sunrise.
+
+A specification of the bearings of the Lighthouse and character of the
+Light will be found on the next page.
+
+And the Commissioners hereby further give notice, that by virtue of a
+Warrant from the Queen in Council, of date the 13th December 1843, the
+following Tolls will be levied for voyages in respect of which benefit
+will be derived from this Light, viz., from every British Vessel
+(the same not belonging to Her Majesty, or being navigated wholly in
+ballast), and for every Foreign Vessel which, by any Act of Parliament,
+Order in Council, Convention, or Treaty, shall be privileged to enter
+the Ports of the United Kingdom of Great Britain and Ireland, upon
+paying the same duties of tonnage as are paid by British Vessels (the
+same not being navigated wholly in ballast), the Toll of One Penny per
+Ton of the Burden of every such Vessel; and for every Foreign Vessel
+not so privileged, the Toll of Two Pence per Ton.
+
+  _By Order of the Commissioners_,
+
+  (Signed) C. CUNINGHAM,    }
+           ALEX. CUNINGHAM, } _Joint Secs._
+
+  EDINBURGH, _23d December 1843_.
+
+  The following is a Specification of the Position of the Lighthouse,
+  and the Appearance of the Light, by Mr ALAN STEVENSON, Engineer to
+  the Commissioners.
+
+The Skerryvore Rock lies off the Island of Tyree, in Lat. 56° 19′ 22″
+N.; Long. 7° 6′ 32″ W.
+
+By Compass, the Lighthouse bears from Barrahead Lighthouse S. ¹⁄₄ E.,
+distant 33 nautic miles; from Hynish Point, in Tyree, WSW. ¹⁄₂ W.,
+distant 10¹⁄₃ miles; from Iona Island, WNW. ³⁄₄ N., distant 20 miles;
+from Rhinns of Islay Lighthouse, N. ¹⁄₄ E., distant 44 miles; and from
+Innistrahull Lighthouse in Ireland, NE. by N., distant 53¹⁄₂ miles.
+
+Owing to the distance to which the foul ground extends on every side of
+the rock on which the Lighthouse is placed, and the weight of sea which
+breaks on the shallow ground all round it, it is necessary to give
+the Light a wide berth. The better to enable seamen to judge of this,
+their attention is called to the prefixed Chart,[87] which exhibits
+the relative position of the Skerryvore Rock, and the various dangers
+around it. In particular, it is necessary to notice the position of
+those rocks which lie seaward of the Lighthouse, viz. Mackenzie’s Rock,
+about 3 miles W. by S. ¹⁄₄ S. from the Lighthouse; Stevenson’s, 2¹⁄₄
+miles W. ¹⁄₂ N.; and Fresnel’s, which lies between these two Rocks. To
+the left of the prefixed Chart is a small diagram, which exhibits the
+position of the Skerryvore Rock in reference to the principal landmarks
+above noticed.
+
+  [87] A copy of the Chart referred to will be found at Plate II. at
+  the end of this volume.
+
+The Skerryvore Light will be known to mariners as a Revolving Light,
+producing a Bright Flash once every minute. The Lantern, which is
+open all round, is elevated 150 feet above the level of the sea. In
+clear weather the flashes of the Light will be seen at the distance
+of six leagues, and at lesser distances according to the state of the
+atmosphere; and to a near observer, in favourable circumstances, the
+Light will not wholly disappear between the flashes.
+
+
+APPENDIX, No. VI.
+
+ACCOUNT OF THE EXPENSE OF ERECTING THE SKERRYVORE LIGHTHOUSE AND OF THE
+SUBSIDIARY WORKS.
+
+  ESTABLISHMENT AT HYNISH.
+
+  Wages of the different workmen quarrying
+  and dressing the stones, and building
+  the dwelling-houses, barracks,
+  storehouses, inclosure and subdivision
+  dykes, draining and trenching the
+  ground, &c., at Hynish, and the wages of
+  joiners preparing and fitting up the
+  joiner work,                             £2996  7  7
+
+  Timber, pavement, bricks, ironmongery,
+  glass, &c., &c., used in the erections,   1376 16  9¹⁄₂
+
+  Slater, plaster, and plumber work of
+  the houses,                                436  1  0
+
+  Paid the tenant of Hynish for a barn
+  which was used as a barrack to
+  accommodate the workmen when they first
+  landed at Tyree,                           13   0  0
+                                          ---------------
+                                                          £4822  5  4¹⁄₂
+
+  NOTE.--Although these buildings had been erected for
+  the purposes of the works, yet the greater part of them
+  were designed to serve as part of the permanent
+  accommodation required at Tyree in connection with the
+  Lighthouse Establishment, and have accordingly been so
+  applied.
+
+  ROCK BARRACK, No. 1.
+
+  Cost of the barrack on the Rock, which
+  was destroyed, including the
+  contractor’s account for extra work,
+  &c.,                                      £742 17  7
+
+  Lead for running up the bats and for
+  other purposes about the barrack,           14 11  6¹⁄₂
+
+  A smith’s forge, bellows, anvil, and
+  smith’s tools used at Rock in erecting
+  the barrack,                                32 19  1¹⁄₄
+                                          ---------------
+                                                            790  8  2³⁄₄
+
+  ROCK BARRACK, No. 2.
+
+  Cost of the carpenter and joiner work
+  on the second barrack, the expense of
+  fitting and erecting it at Greenock,
+  the wages of four joiners and a smith,
+  furnished by the contractor to assist
+  in its erection at Skerryvore,
+  including sundry other minor charges,     £911 14  4
+
+  Cost of the iron-work of the barrack,      369 11  8
+
+  Lead for running up the bats and
+  protecting the timber of cooking
+  apartment, &c.,                             29 11 10
+
+  Cooking apparatus for the cook-room of
+  barrack, sheet-iron smoke tube, cooking
+  utensils, &c.,                              54 16  6
+
+  Bedding for beds of barrack,                90  9  1
+
+  Expense of upholding and making sundry
+  small repairs on the barrack since its
+  erection,                                   22 18  6¹⁄₂
+                                          ---------------
+                                                           1479  1 11¹⁄₂
+
+  Cost of the furniture, bedding, and
+  other utensils required for the
+  dwelling-houses, barracks, &c.,
+  connected with the different
+  establishments of the works,                              830 19  2
+
+  ESTABLISHMENT AT NORTH BAY.
+
+  Wages of the quarriers, masons,
+  joiners, &c., quarrying stones,
+  building the barracks, storehouses,
+  &c., &c., and fitting up the joiner
+  work,                                     £378 11  9
+
+  Timber and other furnishings for the
+  erections, the expense of making the
+  doors and windows, including
+  furnishings required for erecting the
+  habitable part of Skerryvore Barrack at
+  North Bay as a temporary accommodation
+  for the workmen, and sundry other
+  charges,                                   361  4  7
+
+  Sundry furnishings--such as utensils
+  for provision store, smithy, &c.,           13  2  5
+                                          ---------------
+                                                            752 18  9
+
+  QUARRIES AT NORTH BAY.
+
+  Cost of rails and timber for railway
+  and timber, &c., for shipping-pier at
+  North Bay,                                £131  5  1
+
+  Wages of workmen who were employed at
+  quarries in North Bay, quarrying the
+  lighthouse blocks, constructing the
+  pier, railway, &c.,                       1752  5  3
+                                          ---------------
+                                                           1883 10  4
+
+  TEMPORARY WHARF AND RAILWAY AT THE SKERRYVORE ROCK.
+
+  Cost of timber used in the wharf and
+  railway at the Skerryvore Rock,           £103 18  6
+
+  Iron bats, bolts, &c., for fastening
+  the timber, rails for railway, and
+  sundry furnishings connected with an
+  apparatus for blasting under water,        119  7  6
+
+  Wages of the workmen constructing the
+  railway, fastening the timber of wharf,
+  &c.,                                        34 10  5
+                                          ---------------
+                                                            257 16  5
+
+  EXCAVATION AT ROCK AND PLATFORM, &c.
+
+  Wages of the workmen excavating the
+  foundation for the Lighthouse Tower, on
+  the Skerryvore Rock,                      £609  2  3¹⁄₂
+
+  A portable forge, and other smith’s
+  tools, used at the rock for this work,      21 15 10
+
+  Wages of the workmen excavating the
+  site of a platform at the workyard in
+  Hynish, and quarrying and dressing
+  stones for sill of platform,              £107 16  5
+
+  Cost of freestone from Garscube Quarry,
+  Glasgow, for part of the sill of
+  platform,                                   24 14  0
+                                          ---------------
+                                                            763  8  6¹⁄₂
+
+  DRESSING LIGHTHOUSE BLOCKS.
+
+  Wages of masons, including the
+  assistance of labourers, carters, &c.,
+  in dressing the blocks for the
+  Lighthouse Tower at Hynish,              £8589  8  7¹⁄₂
+
+  Timber for moulds of the various
+  blocks, and the joiners’ wages making
+  the moulds,      384 18 10
+
+  Timber, &c., and wages of joiners in
+  erecting sheds for the masons,             955  4  5
+                                          ---------------
+                                                           9929 11 10¹⁄₂
+
+  Expense of victualling the workmen and
+  others who were employed at the rock
+  during the operation of the whole
+  works,                                                   1503 18  6
+
+  IMPLEMENTS AND TOOLS FOR MASONS, SMITHS, &c.
+
+  Amount paid to sundry persons for the
+  implements and tools used by the
+  workmen in all the departments of the
+  works,                                   £1176  9  6¹⁄₂
+
+  Wages of the smiths and their hammermen
+  keeping these tools in repair and
+  making others,                             908 16  5
+                                          ---------------
+                                                           2085  5 11¹⁄₂
+
+  MACHINERY FOR THE WORKS AT THE ROCK, HYNISH, AND NORTH BAY.
+
+  Cost of cranes, crabs, winches, trucks,
+  iron blocks, chains, rope-guys, &c.,
+  with sundry other furnishings connected
+  with these articles,                     £1516  9  5
+
+  1 Woolwich or sling-cart, a janker for
+  wood, and four jack-screws,                 89  6  4
+
+  Large balance crane used in building
+  the Lighthouse Tower,                      533 10  0¹⁄₂
+
+  Hoisting beams or needles, and a pair
+  of strong sheer-poles, used in building
+  the Lighthouse Tower,                       42 11  2
+                                          ---------------
+                                                           2181 16 11¹⁄₂
+
+  CARTAGE ACCOUNT.
+
+  Cost of 3 large draught horses and a
+  pony, for the use of the works,           £127  9 10¹⁄₂
+
+  Carts and stable utensils,                  65 14  2¹⁄₂
+
+  Harness and other furniture, and
+  keeping them in repair,                     52  2  3¹⁄₂
+
+  Provender for the horses for seven
+  years,                                     858 14  8
+                                          ---------------
+                                                           1104  1  0¹⁄₂
+
+  MORTAR ACCOUNT.
+
+  Cost of the lime which was used for all
+  the departments of the works,             £331  9  8
+
+  Pozzolano which was used for the
+  building of the Lighthouse Tower,
+  excepting a small portion for the works
+  of the harbour or dock,                    376 16  4
+
+  Mastic, cements, and stucco,                39  6 10
+
+  Wages of labourers grinding and sifting
+  Pozzolano at Hynish, and burning and
+  sifting a portion of the lime,             121 18  8
+
+  Packages to contain Pozzolano, to
+  prevent its admixture with other cargo
+  when on board ship,                         20  0  1
+                                          ---------------
+                                                            889 11  7
+
+  SIGNAL TOWER AT HYNISH.
+
+  Expense of quarrying, dressing, and
+  building the stones, and executing the
+  joiner work of the Signal Tower at
+  Hynish,                                   £370 13  2
+
+  Pavement and bricks for the interior,       32 13  1
+
+  Cast-iron floor, with lintels and sole
+  plates for windows, and cast-iron
+  supports for do.,                          110 13  4
+
+  Timber for joisting of floors, lining
+  of walls and windows, including the
+  glazing of them, a wooden trap,
+  flag-pole, and other furnishings for
+  interior,                                  284  9  0
+
+  Plumber work of roof,                       35  9  6
+
+  A 5 feet achromatic telescope, with
+  stand, &c., for Signal Tower,               35 10  0
+
+  Cost of a code of signals, flags,
+  return books, and other furnishings,        11 10  6
+                                          ---------------
+                                                            880 18  7
+
+  LIGHTS ACCOUNT.
+
+  Expense of the apparatus required for
+  the lights at the Pier and Signal Tower
+  at Hynish, including fitting up, &c.,      £66  7  0
+
+  Cost of oil and other requisites for
+  upholding these lights,                    136  5  8
+
+  Salary of the Lightkeepers, &c.,           131 11  7
+                                          ---------------
+                                                            334  4  3
+
+  “SKERRYVORE” STEAMER.
+
+  First cost and complete outfit of the
+  steamer Skerryvore,                      £5930  0 11
+
+  Alteration on the engines, by raising
+  the shafts, &c.,                           423  5  0
+
+  Repairs on the hull and engines, on
+  various occasions, during the progress
+  of the works,                             1057  4  2
+
+  Sailing expenses (exclusive of the cost
+  of coals supplied when the steamer was
+  at Hynish), and sundry other minor
+  charges,                                  5538 10 11¹⁄₄
+                                          ---------------
+                                                         12,949  1  0¹⁄₄
+
+  “QUEEN” TENDER.
+
+  First cost and complete outfit of the
+   “Queen” Tender,                          £935 13  3
+
+  Sailing expenses and other charges,       1010  7  9
+
+  Repairs on the hull, rigging, sails,
+  &c.,                                        77 12  8¹⁄₄
+                                          ---------------
+                                                           2023 13  8¹⁄₄
+
+  STONE LIGHTERS
+
+  First cost and outfit of four lighters
+  for transporting the Lighthouse blocks,
+  &c., from Hynish to the Skerryvore Rock, £1666 15  6¹⁄₂
+
+  Hawsers for towing, mooring-ropes,
+  heaving-lines, &c., used in the course
+  of transporting the stones to the Rock,    249  1  6
+
+  Upholding the lighters in repair, and
+  sundry other charges,                      178  9  9¹⁄₂
+
+  Expense transporting the lighters on
+  various occasions to different places,      58 15 10
+
+  Expense shifting and attending upon the
+  lighters when lying at Leith, and
+  advertising them for sale,                  19  9 10¹⁄₂
+                                          ---------------
+                                                           2172 12  6¹⁄₂
+
+  MOORINGS.
+
+  Cost of the buoys for mooring the
+  vessels belonging to the works in
+  Hynish Bay, and at the Rock, when lying
+  there,                                    £240  1  3
+
+  Cast-iron mushroom anchors for mooring
+  the buoys,                                 118  7  4
+
+  Wrought-iron common anchors, grapnels,
+  &c., for mooring the vessels, warping,
+  kedging, &c.,                               48 16  1
+
+  Chains and shackles for do., &c.,          354  2  7
+
+  Upholding and keeping in repair the
+  buoys,                                       4 17  1
+                                          ---------------
+                                                            766  4  4
+
+  BOATS AND ATTENDANCE.
+
+  Cost of 8 boats, with oars, sails,
+  tackling, &c.,                            £207 19 11¹⁄₂
+
+  Upholding these boats in repair,            28 13  9
+
+  Amount paid for the use of boats and
+  their crews assisting to discharge
+  cargoes from vessels previous to the
+  pier being built,                          119  6  0
+                                          ---------------
+                                                            355 19  8¹⁄₂
+
+  Amount paid the owners of hired
+  vessels, as freights of the Lighthouse
+  blocks from the quarries at North Bay,
+  in Mull, to the workyard at Hynish,                      1300 14  8¹⁄₂
+
+  FREIGHT AND SAILING EXPENSES.
+
+  Freights and other charges paid the
+  owners of hired vessels, vessels, for
+  the materials which were imported for
+  the use of various departments of the
+  works, exclusive of the Lighthouse
+  blocks from North Bay,                                   4045  9  7¹⁄₂
+
+  Wages of labourers, &c., discharging
+  the cargoes from the vessels at the
+  Pier at Hynish, and the wages of
+  workmen quarrying stones for ballast,
+  and putting it on board the vessels,                      933 12 10
+
+  Amount paid for travelling expenses,
+  and other charges connected with the
+  transport of the workmen, including the
+  expenses of the Officers, &c.,
+  travelling on the business of the works,                 1711 11  2
+
+  Cost of the coals supplied to the
+  steamer “Skerryvore,” when plying
+  between the Skerryvore Rock, Hynish,
+  &c., for the household purposes of the
+  different departments of the works, and
+  also for the smith’s forge,                              1463  0  7¹⁄₂
+
+  Cost of the blasting powder used for
+  the purpose of quarrying stones,
+  excavating rocks, &c.                                     375 14  2¹⁄₂
+
+  LIGHTHOUSE TOWER.
+
+  Wages of the workmen who were engaged
+  at Skerryvore Rock in building the
+  Tower, and shipping the materials at
+  Hynish for Rock, including the wages of
+  masons, &c., assisting the other
+  tradesmen in the respective departments
+  of their work, after the completion of
+  the building operations,                 £2381 11  7
+
+  Cost of the wainscot and other articles
+  for the joinery of the interior of the
+  Lighthouse; the wages of the joiners
+  preparing the wood at Hynish, and
+  fitting it up at the Tower,               1415  5  1
+
+  Green heart and oak for treenails, for
+  securing the lower courses of
+  Lighthouse Tower,                           40 10  4
+
+  Plate-glass for windows and borrowed
+  lights in partitions of Tower,              84  7  4
+
+  Lewis bats, hinges, &c., for
+  entrance-door and shutters of Tower,
+  and the locks and other mounting for
+  the interior,                              218 15  2
+
+  14 Copper oil-cisterns, a copper-pump,
+  gauging-rods for do.,                      276 10  7
+
+  Cast-iron water-tanks and coal-boxes,
+  for interior of Tower,                     160 13  9
+
+  A large cooking apparatus for kitchen
+  of Tower, a stove to heat the lower
+  apartments, and cast-iron smoke-tubes
+  for both fire-places,                      117 17  7
+
+  A bell-metal railing for balcony,          341 13  1
+
+  A bell-metal ladder from rock to
+  entrance-door of Tower,                    194 13  4
+
+  A cast-iron pillar to support floor of
+  light-room,                                 17  8  7
+
+  A bell-metal lightning-conductor for
+  Tower, and fixtures,                        65 13  0
+
+  Cast-iron permanent railway on the
+  Skerryvore Rock, from the landing creek
+  to the Tower; a cast-iron platform near
+  the Tower, and stairs at landing creek,    493 11  8
+
+  A crane erected at the landing creek,
+  for landing materials on the rock,          98 13  2
+
+  A copper flagstaff and ball for the top
+  of the Lighthouse Tower, with bell-metal
+  base, fixtures, pulleys, &c.,               66 10  8
+
+  A brass force-pump, for pumping water
+  up from tanks to kitchen of Lighthouse,     31 17  5
+
+  Premiums paid the seamen who were
+  employed in the shipping department, in
+  lieu of extra time,                        454  2  6
+
+  Premiums paid 17 seamen who were
+  employed in the building works at the
+  Rock during the season of 1842, in lieu
+  of extra time,                             121 11  0
+
+  Premiums of the landing master at Rock,
+  foreman of masons, &c.,                     96 12  0
+
+  Cost of the furniture, bedding,
+  utensils, books, &c., for the
+  Lighthouse Tower,                          304  6 10
+
+  Sundry furnishings connected with the
+  building of the Lighthouse Tower,--the
+  wages of workmen quarrying stones at
+  Hynish for Lighthouse Tower, previous
+  to opening quarries at North Bay, and
+  the wages of workmen, and furnishings
+  for the general purposes of the works,    1386 18  5¹⁄₂
+
+  Cost of three models, in stucco, of
+  different forms of the Lighthouse,          22  4  6
+
+  Cast-iron water-tanks, which were built
+  and secured into recesses of the rock,
+  for the supplying of the rock
+  works,--new water-casks, and their
+  repairs, for taking off water,              17  5 11
+
+  Feu-duty, rent of ground, assessed
+  taxes, &c., for the establishment at
+  Hynish,                                    143  6  4
+                                          ---------------
+                                                           8551 19 10¹⁄₂
+
+  Cost of the iron and steel which were
+  used for all the departments of the
+  works,                                                   1299  3  5¹⁄₄
+
+  LIGHTROOM AND APPARATUS.
+
+  Cost of the lantern of cast-iron, with
+  facings of bell-metal, including the
+  cleaning and trimming paths, and
+  bell-metal ladder outside of lantern,
+  and the wages of the contractor’s
+  workmen fitting them up at Skerryvore,    £863 13  6
+
+  Plate-glass for the lantern,               268  4  6
+
+  Copper dome of lantern, including the
+  internal frame of do., drip-pan, copper
+  steps, handles, air-tubes, rain-water
+  pipes, a platform outside of dome for
+  cleaning the vents, with the wages of
+  the contractor’s workmen fitting them
+  up at Skerryvore,                          348 16  9
+
+  Machinery of the revolving apparatus,
+  and brass case for do. complete; three
+  machines for pumping the oil for
+  supplying the burner; the expense of
+  the lamps, fountains, &c.; and
+  bell-metal frames for annular lenses,
+  zones, pyramidal lenses, &c., with the
+  wages of the contractor’s workmen
+  fitting up the above apparatus at
+  Skerryvore,                               1244 10  6¹⁄₂
+
+  The charge of Mr François
+  of Paris furnishing eight
+  annular lenses, and two
+  spare do., with eight
+  catadioptric frames of the
+  first order for lower part,
+  and eight pyramidal lenses,
+  with mirrors, for upper
+  part,                      £762  0  0
+
+  Expense of transporting the
+  whole apparatus to Leith,    79  7 10
+                             ----------
+                                             841  7 10
+
+  Cost of two bells, and one
+  spare do., used during
+  foggy weather,             £107  6  3
+
+  Shafting for do.; bevel
+  wheels, levers, hammers,
+  &c., connecting with the
+  machinery of apparatus,      63 14 11¹⁄₂
+                             -------------
+                                             171  1  2¹⁄₂
+
+  Eighteen screens for lantern, cased
+  with iron, and brass mounted, with
+  rollers, &c., and the time of workmen
+  fitting them up at Skerryvore,              48  7  6
+
+  Air watch-bells from lightroom to
+  bedrooms and kitchen, time of workmen
+  fitting them up at Skerryvore, and
+  furnishings for the complete working of
+  do.,                                        34 13  0
+
+  Brass medallion heads and copper tubes
+  for ventilation of lightroom,                8  9  6
+
+  Wood and workmanship making models of
+  the catadioptric zones to a full size,
+  and a brass model of frame for zones to
+  a small scale,                              22  1  2
+                                          ---------------
+                                                           3851  5  6
+
+  SALARIES, AGENCIES, AND OFFICE EXPENSES.
+
+  Salaries of the Engineer, Surveyor,
+  Clerk, and Store-keeper, including
+  expenses of the survey of the rocks and
+  adjoining Islands,                       £3262 10  5
+
+  Agency of the Agent at Aberdeen, who
+  made the monthly payments to the
+  workmen’s relatives, and for some time
+  superintending the making of tools;
+  and the agency of the Lighthouse Agent
+  at Greenock transacting business for
+  the works,                                 294 13 11
+
+  Iron safe, &c., books, and other
+  stationery for the various departments
+  of the works,                               99 10 10
+                                          ---------------
+                                                           3656 15  2
+
+  Petty disbursements and miscellaneous
+  expenses, made on account of the
+  general purposes of the works,                            308  7  9
+
+  LIGHTKEEPERS’ HOUSES.
+
+  Wages of workmen, quarrying, dressing,
+  and building the stones of houses at
+  Hynish for light-keepers, building the
+  brick partitions and lining of walls,
+  and the wages of joiners executing the
+  joiner-work,                             £1893  6  2
+
+  Timber and other articles used in the
+  joinery of the houses,                     462 19  9
+
+  Plumber-work of roof, including the
+  expense of bringing the water into the
+  houses, &c.,                               963 18  6
+
+  Bricks for partitions, lining of
+  external walls, &c.,                        73 10  0
+
+  Pavement for floors, water-cisterns,
+  &c.,                                        51 16  0
+
+  Workmanship, executing the plaster-work
+  (the lime being charged in a special
+  account for this article),                  38 12 11
+
+  Glass for glazing the windows and
+  fan-lights,                                 20 12  3
+
+  Locks, hinges, and other mounting for
+  the doors and windows,                     101 11 11
+
+  Cans for the chimney heads,                  9 16  6
+
+  Furniture, bedding, utensils, &c.,
+  supplied for these houses,                 299  0  4
+                                          ---------------
+                                                           3915  4  4
+
+  PIER AT HYNISH.
+
+  Wages of masons, quarriers, carters,
+  labourers, &c., quarrying, dressing,
+  and building the stones of a pier at
+  Hynish for the landing and shipping of
+  materials,                               £2300 17  1¹⁄₂
+
+  Iron rails for the works of building
+  the pier,                                   53 10  1
+
+  Timbers for fenders of pier, and other
+  purposes connected with the building of
+  it,                                        130 19  4
+
+  Cost of a pont for building the pier,      106  8 11
+                                          ---------------
+                                                           2591 15  5¹⁄₂
+
+  DOCK OR HARBOUR FOR TENDER.
+
+  Wages of workmen, quarrying, dressing,
+  and building stones to form a talus
+  wall and parapet along the south side
+  and round the point of the pier at
+  Hynish; raising the pier one course;
+  excavating rock in the interior of the
+  harbour or dock and along the point of
+  pier; quarrying, dressing, and building
+  the stones of boom-heads and walls of
+  dock; excavating reservoir and forming
+  embankment of do, for scouring sand,
+  &c., from the dock; forming the feeders
+  to reservoir, and the tail-race from
+  reservoir to dock, refreshments to
+  workmen during night and tide works,
+  &c.,                                      £6676 10  6
+
+  Timber for double set of boom-gates of
+  dock, copper for sheathing their ends,
+  and mounting for booms,                     101  2  6
+
+  Timber used in constructing
+  coffer-dams, and for the general
+  purposes of the harbour works,             135 18  0
+
+  Cost of two sluices, and of the
+  machinery, &c., complete for working
+  them,                                       81 14  0
+
+  Two cast-iron ladders for sides of pier
+  and dock,                                   13  1  9
+
+  Cost of sea-boots, &c., and keeping
+  them in repair, which were used by the
+  workmen at tide works,                      26 12  0
+
+  Cost of silt-pumps, and furnishings of
+  leather, &c., for making others, and
+  keeping them in repair,                      9 10  0
+
+  Compensation paid the tenant of the
+  farm of Hynish, for liberty to cut
+  drains for a supply of water for a
+  reservoir,                                   5  0  0
+
+  Two signal lamps, two torches,
+  turpentine, &c., for signalizing when
+  the tender enters the dock at night,         5 14  8
+                                          ---------------
+                                                           7055  3  5
+                                                        ----------------
+                                           TOTAL,       £89,817  6 11
+
+  DEDUCTIONS--
+
+  Price of steamer “Skerryvore,” sold,     £1616  0  6
+
+  Do. of sloop “Queen,” sold,                200  0  0
+
+  Do. of 4 Stone Lighters, sold,             225  0  0
+
+  Do. of Horses and Carts, sold,              60  0  0
+
+  Implements sold or afterwards used at
+  other works of the Board,                  738  8 10
+                                          ---------------
+                                                           2839  9  4
+                                                        ----------------
+                                                        £86,977 17  7
+
+
+APPENDIX, No. VII.
+
+EXCERPTS FROM AN ACCOUNT OF EXPERIMENTS UPON THE FORCE OF THE WAVES
+OF THE ATLANTIC AND GERMAN OCEANS. By THOMAS STEVENSON, F.R.S.E.,
+CIVIL-ENGINEER, EDINBURGH.
+
+(From the Transactions of the Royal Society of Edinburgh, Vol. XVI.)
+
+The letters (see Plate IV.) D E F D represent a cast-iron cylinder,
+which is firmly bolted at the projecting flanges G to the rock where
+the experiments are wanted. This cylinder has a flange at D D. L L is
+a door, which is opened when the observation is to be read off. A A is
+of iron, and forms a circular plate or disc, on which the sea impinges.
+Fastened to the disc are four guide-rods B B B B. These rods pass
+through a circular plate C C (which is screwed down to the flange D D),
+and also through holes in the bottom E F. Within the cylinder there
+is attached to the plate C C a powerful steel spring, to the other or
+free end of which is fastened the small circular plate K K, which again
+is secured to the guide-rods B B B B. There are also rings of leather
+T T, that slide on the guide-rods, and serve as indices for registering
+how far the rods are pushed through the holes in the bottom; or, in
+other words, how much the spring has been drawn out or lengthened by
+the force of the sea acting upon the plate or disc A A. The object of
+having four leathern rings, where one might have answered the purpose,
+was merely that they might serve as a check upon each other; and so
+perfectly did they answer the purpose intended, that in every instance
+they were found equidistant from the bottom of the cylinder; proving
+thereby, that after the recoil of the spring, they had all kept their
+places. The guide-rods are graduated, so as to enable the observer to
+note exactly the quantity that the spring has yielded.
+
+This instrument, which may, perhaps, be not improperly termed a
+_Marine Dynamometer_, is, therefore, a self-registering apparatus
+which indicates the maximum force of the waves. In the graduation of
+the instrument, the power of the spring is ascertained by carefully
+loading the disc with weights, so that when the quantity that the
+spring has yielded by the action of the sea is known, the pressure due
+to the area of the disc exposed is known also. The discs employed were
+from 3 to 9 inches diameter, but generally 6 inches, and the powers
+of the springs varied from 10 lb. to about 50 lb. for every ¹⁄₈ inch
+of elongation. Their respective effects were afterwards reduced to a
+value per square foot. The instrument was generally placed so as to be
+immersed at about three-fourths tide, and in such situations as would
+afford a considerable depth of water. It is not desirable to have the
+instrument placed at a much lower level, as it has not unfrequently
+happened during a gale, that for days together no one could approach
+it to read off the result and readjust the indices to zero. It must,
+however, at the same time be remarked, that it is in most situations
+almost impossible to receive the force unimpaired, as the waves are
+more or less broken by hidden rocks or shoal ground before they reach
+the instrument.
+
+In connection with the apparatus above described, a graduated pole was
+erected on an outlying sunken rock, for the purpose of ascertaining the
+height of the waves; but the observations were not of so satisfactory a
+nature as could have been desired, and the poles soon worked loose from
+their attachments, and disappeared.
+
+With the instrument which has been explained, I entered upon the
+following train of observations:--
+
+In 1842 several observations were made on the waves of the Irish Sea
+at the island of Little Ross, lying off the Bay of Kirkcudbright.
+Since April 1843 till now, continued observations have been made on
+the Atlantic at the Skerryvore and neighbouring rocks lying off the
+island of Tyree, Argyllshire; and in 1844 a series of observations
+was begun on the German Ocean at the Bell Rock. It will be seen, that
+in selecting these localities a varied exposure has been embraced,
+comprising the comparatively sheltered Irish Sea, the more exposed
+eastern shore of Scotland, and the wild Rocks of Skerryvore, which are
+open to the full fury of the Atlantic, the far distant shores of North
+America being the nearest land on the west.
+
+Referring for more full information to the tables of experiments which
+are given at the end of this paper, it will be sufficient in this place
+to state generally the following as the results obtained.
+
+In the _Atlantic Ocean_, according to the observations made at the
+Skerryvore rocks, the average of results for five of the _summer_
+months during the years 1843 and 1844, is 611 lb. per square foot. The
+average results for six of the _winter_ months (1843 and 1844), is 2086
+lb. per square foot, or thrice as great as in the summer months.
+
+The _greatest result_ yet obtained at Skerryvore was during the heavy
+westerly gale of 29th March 1845, when a pressure of 6083 lb. per
+square foot was registered. The next highest is 5323 lb.
+
+In the _German Ocean_, according to the observations made at the Bell
+Rock, the greatest result yet obtained is 3013 lb. per square foot.
+
+It thus appears, that the greatest effect of the sea, which has been
+observed, is that of the Atlantic at Skerryvore, which is nearly equal
+to three tons per square foot.
+
+These experiments, amounting to 267 in number, and on the Atlantic
+alone, extending over 23 months continuously, are not intended to prove
+anything farther than the simple fact, that the sea has been known to
+exert a force equivalent to a pressure of three tons per square foot,
+however much more.
+
+It is proper, however, to observe, that there may be some objection
+to referring the action of the sea to a statical value. Although the
+instrument might perhaps be made capable of giving a dynamical result,
+it was considered unnecessary, in these preliminary experiments, to
+do anything more than represent the maximum pressure registered by
+the spring, because the effects of the waves may, from supposing them
+to have continuity of action, be perhaps regarded as similar to a
+statical pressure, rather than to the impact of a hard body. The near
+coincidence, or indeed almost perfect agreement of the results of the
+experiments made with different instruments, goes far to shew that the
+waves act in very much the same manner as a pressure, although both
+pressure and impact must obviously enter into their effect. In the
+experiments, begun February 1844, and given at the end of the paper,
+the three instruments had not only different areas of discs, but very
+different powers of springs, and yet the results were almost identical.
+Now, the same force, supposing the waves to act like the impact of
+a hard body, would, in the Marine Dynamometer, have assumed very
+different statical values, according to the spaces in which that force
+was expended or developed; so that with the same force of impact, the
+indication of a weak spring would be less than that of a stronger.
+
+In future experiments it may be interesting, however, to test the
+springs dynamically, by means of the impact of a heavy body dropped
+from a given height upon the plate or disc of the instrument. In some
+experiments lately made in this way, by dropping a cannon-ball upon the
+disc, it appeared, that, within the limits of the experiments, there
+was for each individual spring a ratio between the value registered
+by the leathern index and the calculated momentum of the impinging
+body. These ratios were, of course, found to vary in springs of
+different power, and to be constant only for springs of the same power.
+Did the waves, therefore, act by a sudden finite impact, like the
+cannon-ball employed in this instance, we could scarcely have found
+such harmony between the results of instruments with different springs,
+as the experiments alluded to afford. At the same time, the result
+cannot, perhaps, be in strictness considered correct; but, from the
+elongation of the spring being very small, the results may be regarded
+as practically correct,--the more so when we find so remarkable a
+coincidence of results as that alluded to.
+
+  EXPERIMENTS.--With reference to the following experiments I have only
+  to observe, that those which were made at Little Ross, upon the Irish
+  Sea, cannot, from the unusual fineness of the weather at the time,
+  be regarded as affording a true value of the effects of a hard gale
+  in these seas. Of the others it is to be noticed, that where two or
+  three instruments were for some time employed as a check upon each
+  other, and only one or two readings are given, the want has occurred
+  either from the instruments being under repair, or being difficult
+  of access in stormy weather, or during neap tides. It often happened
+  also, in consequence of the springs proving too weak, when new ones
+  had to be made, or the area of the disc reduced. Registers of the
+  state of the weather, apparent height of spray, &c., were generally
+  kept; but it was not considered necessary to complicate the Tables by
+  inserting these, excepting in one or two instances.
+
+  +-----------------+-----------------+
+  |                 |    lbs. to a    |
+  |      Dates.     |   Square Foot.  |
+  +-----------------+-----------------+
+  |   Observations at Little Ross.    |
+  |                 |                 |
+  |1842.            |                 |
+  |April  25        |     15          |
+  |       28        |     51          |
+  |June    1        |     36          |
+  |        4        |     81·5        |
+  |       20        |     86·5        |
+  |       24        |    840·0        |
+  |       25        |    458·0        |
+  |July   25        |    380·0        |
+  |Aug.    2        |    570·0        |
+  |        5        |    665·0        |
+  |        6        |    380·0        |
+  |        9        |    380·0        |
+  |                                   |
+  |The Observations at the Skerryvore |
+  |Rock, and the neighbouring Island  |
+  |of Tyree, distant 13 miles from the|
+  |Skerryvore, are as follows:--      |
+  |                                   |
+  |1843.            |                 |
+  |April  24        |    455          |
+  |       25        |    707          |
+  |May     7        |    243          |
+  |       11        |    182          |
+  |       12        |    243          |
+  |       16        |    364          |
+  |       20        |  { 495          |
+  |                 |  { 476          |
+  |June    3        |    182          |
+  |        4        |    519          |
+  |        7        |    428          |
+  |        8        |    855          |
+  |        9        |    173          |
+  |July    2        |    476          |
+  |        3        |  { 723          |
+  |                 |  { 866          |
+  |       30        |    433          |
+  |Aug.    9        |    346          |
+  |       22        |    723          |
+  |       30        |    389          |
+  |Sept.   5        |    866          |
+  |       21        |    952          |
+  |Oct.    5        |   1535          |
+  |        6        |   1606          |
+  |Nov.   18        |   1711          |
+  |       19        |   1497          |
+  |       27        |   1497          |
+  |       29        |   2353          |
+  |Dec.    5        |   2674          |
+  |        8        | { 3421          |
+  |                 | { At least      |
+  |       14        |   2460          |
+  |       26        |   1947          |
+  |                                   |
+  |In January, two instruments were   |
+  |placed beside each other, but not  |
+  |set parallel. These instruments    |
+  |had springs of different power,    |
+  |the one being about double that    |
+  |of the other, and one had a disc   |
+  |of 3 inches diameter, the other    |
+  |6 inches.                          |
+  |                                   |
+  |1844.            |                 |
+  |Jan.    6        |    962          |
+  |                 |    928          |
+  |        7        |   2353          |
+  |                 |    357          |
+  |        9        |   1925          |
+  |                 |   1000          |
+  |       10        |    826          |
+  |                 |   1000          |
+  |                                   |
+  |Both instruments set parallel.     |
+  |                                   |
+  |1844.            |                 |
+  |Jan.   16        |    424          |
+  |       16        |    427          |
+  |                                   |
+  |Another instrument was placed      |
+  |beside them, but the two marked    |
+  |thus* were found to be too weak,   |
+  |as the leathers were found         |
+  |flattened, and one of the          |
+  |instruments was broken, and was    |
+  |not repaired till the 15th         |
+  |February.                          |
+  |                                   |
+  |1844.            |                 |
+  |Jan.   28        |   3422*         |
+  |                 |   2285*         |
+  |                 |   3313          |
+  |Feb.    2        |    429          |
+  |                 |    457          |
+  |        3        |    429          |
+  |                 |    457          |
+  |       13        |    214          |
+  |                 |    228          |
+  |       15        |    321          |
+  |                 |    280          |
+  |                 |    321          |
+  |       16        |    428          |
+  |                 |    402          |
+  |                 |    343          |
+  |       24        |   1284          |
+  |                 |   1364          |
+  |                 |    685          |
+  |       26        |   2032          |
+  |                 |   2068          |
+  |                 |    399          |
+  |       27        |    321          |
+  |                 |    321          |
+  |                 |    342          |
+  |March   4        |   3316          |
+  |                 |   3369          |
+  |                 |   3427          |
+  |        7        |   1069          |
+  |                 |    963          |
+  |                 |    913          |
+  |       10        |   1925          |
+  |                 |   1925          |
+  |                 |   1713          |
+  |       11        |    535          |
+  |                 |    481          |
+  |                 |    456          |
+  |       12        |   3316          |
+  |                 |   4011          |
+  |                 |   2970          |
+  |       13        |   1142          |
+  |                 |   1283          |
+  |                 |   1283          |
+  |April  10        |    457          |
+  |                 |    428          |
+  |                 |    481          |
+  |       11        |    800          |
+  |       12        |    343          |
+  |                 |    321          |
+  |       14        |    571          |
+  |                 |    535          |
+  |       16        |    571          |
+  |                 |    642          |
+  |                 |    481          |
+  |       17        |    800          |
+  |                 |    856          |
+  |                 |    862          |
+  |       18        |    571          |
+  |                 |    481          |
+  |       19        |    800          |
+  |                 |    535          |
+  |                 |    481          |
+  |       22        |    913          |
+  |                 |    482          |
+  |                 |    962          |
+  |       24        |   1942          |
+  |                 |   1604          |
+  |                 |   1370          |
+  |       25        |   1283          |
+  |                 |    343          |
+  |                 |    321          |
+  |       27        |    457          |
+  |                 |    481          |
+  |               { |   Night  800    |
+  |               { |   tide          |
+  |                 |    642          |
+  |       30        |    229          |
+  |                 |    241          |
+  |May    15        |    343          |
+  |       14        |    481          |
+  |June    6        |    571          |
+  |       15        |   1828          |
+  |July   11        |   1028          |
+  |       13        |    457          |
+  |       18        |    914          |
+  |       23        |   1532          |
+  |       25        |    571          |
+  |       26        |    971          |
+  |       27        |    457          |
+  |       28        |   1142          |
+  |       29        |    286          |
+  |       30        |    914          |
+  |       31        |   1028          |
+  |Aug.    1        |    571          |
+  |        7        |    914          |
+  |       13        |    914          |
+  |       14        |    914          |
+  |       21        |    800          |
+  |       30        |   1713          |
+  |Sept.  12        |   1028          |
+  |       14        |    914          |
+  |       20        |    457          |
+  |       23        |   1142          |
+  |       25        |    685          |
+  |       30        |   1599          |
+  |Oct.    2        |   2399          |
+  |        3        |   1485          |
+  |        4        |   1828          |
+  |       11        |   3427[88]      |
+  |       14        |   1599          |
+  |       19        |   1599          |
+  |       20        |   2513          |
+  +-----------------+-----------------+
+  |1844.            |                 |
+  |Oct.   22        |    800          |
+  |       24        |   1827          |
+  |       28        |   1485          |
+  |       29        |    457          |
+  |Nov.    2        |   1942          |
+  |       10        |   1028          |
+  |       14        |   1257          |
+  |       15        |   2056          |
+  |       16        |   2056          |
+  |       22        |   2627          |
+  |       23        |   3427          |
+  |       27        |   3199          |
+  |       28        |   4112          |
+  |Dec.    7        |   1369          |
+  |        9        |   2738          |
+  |       10        |   1825          |
+  |       13        |   1925          |
+  |       14        |   1027          |
+  |       15        |   1764          |
+  +-----------------+-----------------+
+
+  [88] On this occasion, 14 stones were slightly moved, and 14
+  scattered, all of which had been built into the round-head or
+  end of Hynish Pier, which was still in an unfinished state, and
+  a Dynamometer which was attached to the Pier, registered on this
+  occasion 2557 lb. These stones weighed from 1 to 1¹⁄₂ tons, and
+  exposed, when built into the wall, about two square feet of surface.
+  The stone to which the instrument was fixed was turned upside down,
+  although it weighed about 1¹⁄₄ ton = 2800 lb.
+
+A more exposed point of the Skerryvore Rock was at this time chosen for
+experiment; and with the view of ascertaining the effect of the waves
+at different heights upon the rock, two instruments were fixed, the one
+(No. I.) several feet lower, and about 40 feet seaward of the other
+(No. II.). It was observed, that about half-flood the force of the
+waves was a good deal expended before they reached the place where No.
+I. was placed, from there being so little water on the rocks outside;
+whereas when the tide was higher, the waves were, from the greater
+depth of water, not so much broken when they reached No. II. The
+results of the Marine Dynamometer shew generally about twice the force
+at No. II. as at No. I.; a result which shews how important it would be
+to ascertain the relative forces of the waves at different levels upon
+our breakwaters and other seaworks.
+
+  +--------+-------------------------+-----------+------------+
+  |        |                         |           |Pressure in |
+  |        |                         |  No. of   |  lbs. per  |
+  | Date.  |         Remarks.        |Instrument.|Square Foot.|
+  +--------+-------------------------+-----------+------------+
+  |1845.   |                         |           |            |
+  |Jan.   7|Heavy sea.               |     I.    |    1714    |
+  |        |                         |    II.    |    4182    |
+  |      12|Very heavy swell.        |     I.    |    2856    |
+  |        |                         |    II.    |    5032    |
+  |      16|Heavy ground swell.      |     I.    |    2856    |
+  |        |                         |    II.    |    4752    |
+  |      22|A good deal of sea.      |     I.    |    2856    |
+  |        |                         |    II.    |    5323    |
+  |      28|Heavy ground swell.      |     I.    |    2627    |
+  |        |                         |    II.    |    4562    |
+  |Feb.   5|Fresh gales.             |     I.    |     856    |
+  |        |                         |    II.    |    3042    |
+  |      21|                         |     I.    |    1827    |
+  |        |                         |    II.    |    3422    |
+  |      24|Fresh breezes.           |     I.    |    1256    |
+  |        |                         |    II.    |    3802    |
+  |March  9|Ground swell.            |     I.    |    1256    |
+  |        |{Waves supposed about 10 |    II.    |    3041    |
+  |        |{feet high.              |           |            |
+  |      11|Short sea.               |     I.    |    1028    |
+  |      24|Heavy sea.               |     I.    |    2281    |
+  |        |{Waves supposed about 20 |    II.    |    4562    |
+  |        |{feet high.              |           |            |
+  |      26|Swell.                   |     I.    |    1256    |
+  |        |Waves about 6 feet high. |    II.    |    3041    |
+  |        |{Strong gale, with heavy |           |            |
+  |        |{sea, the highest waves  |     I.    |    2856    |
+  |      29|{supposed 20 feet high,  |           |            |
+  |        |{and the spray rose      |    II.    |    6083    |
+  |        |{about 70 feet.          |           |            |
+  +--------+-------------------------+-----------+------------+
+
+_Register of Observations on the force of the Sea, made at the Bell
+Rock, German Ocean._
+
+  +-----------------+-----------------+
+  |                 |    lbs. to a    |
+  |      Dates.     |   Square Foot.  |
+  +-----------------+-----------------+
+  |1844.            |                 |
+  |Sept.  15        |    853          |
+  |       20        |   2260          |
+  |Oct.    9        |   3013          |
+  |                 |   2562          |
+  |       26        |   1142          |
+  |       27        |    958          |
+  |Nov.   12        |   1680          |
+  |       13        |   1920          |
+  |Dec.   13        |   1560          |
+  |       26        |   1439          |
+  |                 |                 |
+  |1845.            |                 |
+  |Jan.    7        |   1559          |
+  |       10        |   1439          |
+  |       11        |   1439          |
+  |       15        |   1559          |
+  |       25        |    959          |
+  |       26        |    719          |
+  |Jan.   27        |   1199          |
+  |       30        |   2879          |
+  |       31        |   1559          |
+  |Feb.    6        |   2999          |
+  |       24        |   1199          |
+  |       25        |    959          |
+  |       27        |    839          |
+  |       28        |   1319          |
+  |March   4        |    959          |
+  |        7        |   1079          |
+  |       11        |   1919          |
+  |       20        |   2519          |
+  |       21        |   2759          |
+  |       24        |   1319          |
+  |       25        |    959          |
+  |       28        |    599          |
+  |       30        |   1079          |
+  +-----------------+-----------------+
+
+
+APPENDIX, No. VIII.
+
+LIST OF NORTHERN LIGHTHOUSES, BEACONS AND BUOYS.
+
+FOR 1848.
+
+  +-----------+--------------------------------------------------------+
+  |           |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  |   Name    |                                                        |
+  | of Light. |                   Situation of Light.                  |
+  +-----------+--------------------------------------------------------+
+  |INCHKEITH  |Highest Land on the Island of Inchkeith, in Fifeshire   |
+  |           |                                                        |
+  +-----------+--------------------------------------------------------+
+  |ISLE OF MAY|Highest Land on Isle of May, in Fifeshire               |
+  +-----------+--------------------------------------------------------+
+  |DO. LEADING|Placed about 130 feet below the High Light, and to the  |
+  |LIGHT      |NE. by N. of it                                         |
+  |           |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  +-----------+--------------------------------------------------------+
+  |BELL ROCK  |Bell Rock, a sunk reef, 11³⁄₄ miles S. by E. ¹⁄₃ E. off |
+  |           |Arbroath, in Forfarshire                                |
+  +-----------+--------------------------------------------------------+
+  |GIRDLENESS |Girdleness, Kincardineshire                             |
+  |           |                                                        |
+  +-----------+--------------------------------------------------------+
+  |BUCHANNESS |Buchanness, Aberdeenshire                               |
+  +-----------+--------------------------------------------------------+
+  |KINNAIRD-  |Kinnairdhead, Aberdeenshire                             |
+  |HEAD       |                                                        |
+  +-----------+--------------------------------------------------------+
+  |COVESEA    |Craighead, Morayshire                                   |
+  |SKERRIES   |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  +-----------+--------------------------------------------------------+
+  |CHANONRY   |Chanonry Point, Ross-shire                              |
+  |POINT      |                                                        |
+  +-----------+--------------------------------------------------------+
+  |CROMARTY   |Cromartyshire                                           |
+  |POINT      |                                                        |
+  +-----------+--------------------------------------------------------+
+  |TARBETNESS |Tarbetness, Cromartyshire                               |
+  |           |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  |           |                                                        |
+  +-----------+--------------------------------------------------------+
+  |NOSSHEAD   |Nosshead, Caithness-shire (building)                    |
+  +-----------+--------------------------------------------------------+
+  |DUNNETHEAD |Dunnethead, most northern point of the Mainland of      |
+  |           |Scotland, Caithness-shire                               |
+  +-----------+--------------------------------------------------------+
+  |PENTLAND   |Pentland Skerries Island, Orkney                        |
+  |SKERRIES   |                                                        |
+  +-----------+--------------------------------------------------------+
+  |START POINT|Start Point, Sanday Island, the most eastern point of   |
+  |           |Orkney                                                  |
+  +-----------+--------------------------------------------------------+
+  |SUMBURGH-  |The most southern Headland of Zetland                   |
+  |HEAD       |                                                        |
+  +-----------+--------------------------------------------------------+
+  |CAPE WRATH |Cape Wrath, north-western Headland of Sutherlandshire   |
+  |           |                                                        |
+  +-----------+--------------------------------------------------------+
+  |ISLAND     |Island Glass, one of the Harris Isles, Inverness-shire  |
+  |GLASS      |                                                        |
+  +-----------+--------------------------------------------------------+
+  |BARRAHEAD  |Highest land on Bernera Island, Inverness-shire         |
+  |           |                                                        |
+  |           |                                                        |
+  +-----------+--------------------------------------------------------+
+  |ARDNA-     |Ardnamurchan Point, Argyleshire (building)              |
+  |MURCHAN    |                                                        |
+  +-----------+--------------------------------------------------------+
+  |LISMORE    |Mousedale, small Island off Lismore, Argyleshire        |
+  +-----------+--------------------------------------------------------+
+  |SKERRY-    |Skerryvore Reef, 12 miles WSW. ¹⁄₂ W. from Tyree Island,|
+  |VORE[89]   |with foul ground all round it                           |
+  +-----------+--------------------------------------------------------+
+  |RHINS OF   |Oversay, small Island off Islay, Argyleshire            |
+  |ISLAY      |                                                        |
+  +-----------+--------------------------------------------------------+
+  |MULL OF    |South-western Headland of Argyleshire                   |
+  |KINTYRE    |                                                        |
+  +-----------+--------------------------------------------------------+
+  |PLADDA     |Pladda Isle, off south-east point of Arran, county of   |
+  |           |Bute                                                    |
+  +-----------+--------------------------------------------------------+
+  |CORSEWALL  |Western side of entrance to Loch Ryan, in Wigtonshire   |
+  |           |                                                        |
+  +-----------+--------------------------------------------------------+
+  |LOCH RYAN  |Cairn Ryan Point, within Loch Ryan, Wigtonshire         |
+  +-----------+--------------------------------------------------------+
+  |MULL OF    |Southern extremity of the Mainland of Scotland,         |
+  |GALLOWAY   |Wigtonshire                                             |
+  |           |                                                        |
+  +-----------+--------------------------------------------------------+
+  |LITTLE ROSS|Little Ross Island, Kirkcudbrightshire                  |
+  +-----------+--------------------------------------------------------+
+  |POINT OF   |Northern extremity of Isle of Man                       |
+  |AYRE       |                                                        |
+  +-----------+--------------------------------------------------------+
+  |CALF OF MAN|West side Calf Island, at the southern extremity of Isle|
+  |           |of Man                                                  |
+  +-----------+--------------------------------------------------------+
+
+  +-----------+-------+------------------------------------------------+
+  |           |       |                                                |
+  |           |       |                                                |
+  |           |       |                                                |
+  |           |       |                                                |
+  |           |       |                                                |
+  |           |       |                                                |
+  |           | Number|                                                |
+  |   Name    |   of  |                                                |
+  | of Light. |Lights.|              Appearance of Light.              |
+  +-----------+-------+------------------------------------------------+
+  |INCHKEITH  |One    |Revolving, and appearing in its brightest state |
+  |           |       |once every minute                               |
+  +-----------+-------+------------------------------------------------+
+  |ISLE OF MAY|One    |Fixed                                           |
+  +-----------+-------+------------------------------------------------+
+  |DO. LEADING|One    |Fixed                                           |
+  |LIGHT      |       |                                                |
+  |           |       |                                                |
+  |           |       |                                                |
+  |           |       |                                                |
+  |           |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |BELL ROCK  |One    |Revolving, and shewing alternately a red and    |
+  |           |       |white light every 2 minutes                     |
+  +-----------+-------+------------------------------------------------+
+  |GIRDLENESS |Two    |Fixed Lights, one above the other               |
+  |           |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |BUCHANNESS |One    |Flashing once every 5 seconds                   |
+  +-----------+-------+------------------------------------------------+
+  |KINNAIRD-  |One    |Fixed                                           |
+  |HEAD       |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |COVESEA    |One    |Revolving, and appearing in its brightest state |
+  |SKERRIES   |       |once every minute. From W. by N. ¹⁄₄ N. to SE.  |
+  |           |       |by E. ¹⁄₄ E. the light is of the natural        |
+  |           |       |appearance; but from SE. by E. ¹⁄₄ E. to SE. ¹⁄₄|
+  |           |       |S. it is coloured RED                           |
+  +-----------+-------+------------------------------------------------+
+  |CHANONRY   |One    |Fixed                                           |
+  |POINT      |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |CROMARTY   |One    |Fixed and red                                   |
+  |POINT      |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |TARBETNESS |One    |Intermittent, suddenly bursting into view, and  |
+  |           |       |continuing in sight 2¹⁄₂ min., then suddenly    |
+  |           |       |eclipsed for half a minute. But within the Moray|
+  |           |       |Frith, in Southerly and South-westerly          |
+  |           |       |directions from Tarbetness, the light does not  |
+  |           |       |intermit, but is permanently visible            |
+  +-----------+-------+------------------------------------------------+
+  |NOSSHEAD   |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |DUNNETHEAD |One    |Fixed                                           |
+  |           |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |PENTLAND   |Two    |Fixed, and 100 feet apart                       |
+  |SKERRIES   |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |START POINT|One    |Revolving, and appearing in its brightest state |
+  |           |       |once every minute                               |
+  +-----------+-------+------------------------------------------------+
+  |SUMBURGH-  |One    |Fixed                                           |
+  |HEAD       |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |CAPE WRATH |One    |Revolving, and shewing alternately a red and    |
+  |           |       |white light every 2 minutes                     |
+  +-----------+-------+------------------------------------------------+
+  |ISLAND     |One    |Fixed                                           |
+  |GLASS      |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |BARRAHEAD  |One    |Intermittent, suddenly bursting into view, and  |
+  |           |       |continuing in sight 2¹⁄₂ min., then suddenly    |
+  |           |       |eclipsed for half a minute                      |
+  +-----------+-------+------------------------------------------------+
+  |ARDNA-     |       |                                                |
+  |MURCHAN    |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |LISMORE    |One    |Fixed                                           |
+  +-----------+-------+------------------------------------------------+
+  |SKERRY-    |One    |Revolving, and appearing at its brightest once  |
+  |VORE[89]   |       |every minute                                    |
+  +-----------+-------+------------------------------------------------+
+  |RHINS OF   |One    |Flashing once every 5 seconds                   |
+  |ISLAY      |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |MULL OF    |One    |Fixed                                           |
+  |KINTYRE    |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |PLADDA     |Two    |Fixed, the one above the other                  |
+  |           |       |                                                |
+  +-----------+-------+------------------------------------------------+
+  |CORSEWALL  |One    |Revolving, and shewing alternately a red and    |
+  |           |       |white light every 2 minutes                     |
+  +-----------+-------+------------------------------------------------+
+  |LOCH RYAN  |One    |Fixed                                           |
+  +-----------+-------+------------------------------------------------+
+  |MULL OF    |One    |Intermittent, suddenly bursting into view, and  |
+  |GALLOWAY   |       |continuing in sight 2¹⁄₂ min., then suddenly    |
+  |           |       |eclipsed for half a minute                      |
+  +-----------+-------+------------------------------------------------+
+  |LITTLE ROSS|One    |Flashing once every 5 seconds                   |
+  +-----------+-------+------------------------------------------------+
+  |POINT OF   |One    |Revolving, and shewing alternately a red and    |
+  |AYRE       |       |white light every 2 minutes                     |
+  +-----------+-------+------------------------------------------------+
+  |CALF OF MAN|Two    |Revolving, and shewing white lights every 2     |
+  |           |       |minutes                                         |
+  +-----------+-------+------------------------------------------------+
+
+  +-----------+------+-------------------------------------------------+
+  |           |      |                                                 |
+  |           |      |                                                 |
+  |           | Dis- |                                                 |
+  |           | tance|                                                 |
+  |           | visi-|                                                 |
+  |           |  ble |                                                 |
+  |           |  in  |                                                 |
+  |   Name    |Nautic|                                                 |
+  | of Light. |Miles.| Points of Compass within which Light is Visible.|
+  +-----------+------+-------------------------------------------------+
+  |INCHKEITH  |  18  |All round the Compass                            |
+  |           |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |ISLE OF MAY|  21  |All round the Compass                            |
+  +-----------+------+-------------------------------------------------+
+  |DO. LEADING|  15  |When _seen in_ ONE _line_ with the High Light,   |
+  |LIGHT      |      |these two Lights bear NE. by N. ¹⁄₄ N., and SW.  |
+  |           |      |by S. ¹⁄₄ S., and in this line lead about _half a|
+  |           |      |mile_ to the Eastward of the North Carr Rock. The|
+  |           |      |Lights must on no account be opened to the       |
+  |           |      |Westward                                         |
+  +-----------+------+-------------------------------------------------+
+  |BELL ROCK  |  14  |All round the Compass                            |
+  |           |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |GIRDLENESS | 19 & |From NNE. to WSW. ¹⁄₂ W. Easterly and Southerly  |
+  |           |  16  |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |BUCHANNESS |  16  |From N. by E. to SW. by W. Easterly              |
+  +-----------+------+-------------------------------------------------+
+  |KINNAIRD-  |  15  |From WNW. to SE. Northerly                       |
+  |HEAD       |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |COVESEA    |  18  |From W. by N. ¹⁄₄ N. to SE. ¹⁄₄ S. Northerly     |
+  |SKERRIES   |      |                                                 |
+  |           |      |                                                 |
+  |           |      |                                                 |
+  |           |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |CHANONRY   |  11  |From W. ¹⁄₂ N. to N. by E. Southerly             |
+  |POINT      |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |CROMARTY   |   9  |From WNW. to SE. by E. ¹⁄₄ S. Northerly          |
+  |POINT      |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |TARBETNESS |  18  |From SW. ¹⁄₂ W. to W. ¹⁄₂ N. Easterly            |
+  |           |      |                                                 |
+  |           |      |                                                 |
+  |           |      |                                                 |
+  |           |      |                                                 |
+  |           |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |NOSSHEAD   |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |DUNNETHEAD |  23  |From SE. ¹⁄₂ E. to W. Northerly                  |
+  |           |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |PENTLAND   | 16 & |All round the Compass                            |
+  |SKERRIES   |  18  |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |START POINT|  15  |All round the Compass                            |
+  |           |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |SUMBURGH-  |  22  |From NE. by E. ¹⁄₄ E. to NW. by N. ¹⁄₄ N.        |
+  |HEAD       |      |Southerly                                        |
+  +-----------+------+-------------------------------------------------+
+  |CAPE WRATH |  25  |From SE. ¹⁄₂ E. to SW. by W. Northerly           |
+  |           |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |ISLAND     |  16  |From W. by S. to ENE. ¹⁄₂ E. Southerly           |
+  |GLASS      |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |BARRAHEAD  |  32  |From N. by E. to ENE. Westerly and Southerly     |
+  |           |      |                                                 |
+  |           |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |ARDNA-     |      |                                                 |
+  |MURCHAN    |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |LISMORE    |  15  |From E. to NE. by E. ¹⁄₄ E. Westerly             |
+  +-----------+------+-------------------------------------------------+
+  |SKERRY-    |  18  |All round the Compass                            |
+  |VORE[89]   |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |RHINS OF   |  17  |From NNE. to SE. Southerly                       |
+  |ISLAY      |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |MULL OF    |  22  |From NNE. ¹⁄₂ E. to S. by W. ¹⁄₄ W. Southerly    |
+  |KINTYRE    |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |PLADDA     | 13 & |From NW. by W. to NE. by E. Southerly            |
+  |           |  16  |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |CORSEWALL  |  15  |From NE. by E. to SW. Northerly                  |
+  |           |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |LOCH RYAN  |  10  |From S. by W. ¹⁄₈ W. to N. ⁷⁄₈ E. Westerly       |
+  +-----------+------+-------------------------------------------------+
+  |MULL OF    |  23  |From NE. to NW. ¹⁄₂ W. Southerly                 |
+  |GALLOWAY   |      |                                                 |
+  |           |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |LITTLE ROSS|  18  |From N. by E. to NW. by W. Southerly             |
+  +-----------+------+-------------------------------------------------+
+  |POINT OF   |  15  |From S. by W. to W. by N. Northerly              |
+  |AYRE       |      |                                                 |
+  +-----------+------+-------------------------------------------------+
+  |CALF OF MAN| 22 & |From NE. ¹⁄₃ to SW. W. Southerly                 |
+  |           |  24  |                                                 |
+  +-----------+------+-------------------------------------------------+
+
+  +-----------+-------+-------+-------+-------+
+  |           | Height|       |       |       |
+  |           |   of  |       |       |       |
+  |           |Lantern|       |       |       |
+  |           |in feet|       |       |       |
+  |           | above |       |       |       |
+  |           | High- |       |       |Date of|
+  |           | water | North |  West | first |
+  |   Name    | Spring| Lati- | Longi-| Exhi- |
+  | of Light. | Tides.| tude. | tude. |bition.|
+  +-----------+-------+-------+-------+-------+
+  |INCHKEITH  |  220  |56°  2′| 3°  8′|  1804 |
+  |           |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |ISLE OF MAY|  240  |56° 11′| 2° 33′|  1816 |
+  +-----------+-------+-------+-------+-------+
+  |DO. LEADING|  110  |       |       |  1844 |
+  |LIGHT      |       |       |       |       |
+  |           |       |       |       |       |
+  |           |       |       |       |       |
+  |           |       |       |       |       |
+  |           |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |BELL ROCK  |   90  |56° 26′| 2° 23′|  1811 |
+  |           |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |GIRDLENESS | 185 & |57°  8′| 2°  3′|  1833 |
+  |           |  115  |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |BUCHANNESS |  130  |57° 28′| 1° 46′|  1827 |
+  +-----------+-------+-------+-------+-------+
+  |KINNAIRD-  |  120  |57° 42′| 2°  0′|  1787 |
+  |HEAD       |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |COVESEA    |  160  |57° 43′| 3° 20′|  1846 |
+  |SKERRIES   |       |       |       |       |
+  |           |       |       |       |       |
+  |           |       |       |       |       |
+  |           |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |CHANONRY   |   40  |57° 35′| 4°  5′|  1846 |
+  |POINT      |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |CROMARTY   |   50  |57° 41′| 4°  2′|  1846 |
+  |POINT      |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |TARBETNESS |  175  |57° 51′| 8° 48′|  1830 |
+  |           |       |       |       |       |
+  |           |       |       |       |       |
+  |           |       |       |       |       |
+  |           |       |       |       |       |
+  |           |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |NOSSHEAD   |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |DUNNETHEAD |  346  |58° 40′| 3° 21′|  1831 |
+  |           |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |PENTLAND   | 140 & |58° 41′| 2° 55′|  1794 |
+  |SKERRIES   |  170  |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |START POINT|  100  |59° 17′| 2° 23′|  1806 |
+  |           |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |SUMBURGH-  |  300  |59° 51′| 1° 16′|  1821 |
+  |HEAD       |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |CAPE WRATH |  400  |58° 37′| 5°  0′|  1828 |
+  |           |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |ISLAND     |  130  |57° 52′| 6° 33′|  1789 |
+  |GLASS      |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |BARRAHEAD  |  680  |56° 48′| 7° 38′|  1833 |
+  |           |       |       |       |       |
+  |           |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |ARDNA-     |       |       |       |       |
+  |MURCHAN    |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |LISMORE    |  103  |56° 30′| 5° 38′|  1833 |
+  +-----------+-------+-------+-------+-------+
+  |SKERRY-    |  150  |56° 19′| 7°  7′|  1844 |
+  |VORE[89]   |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |RHINS OF   |  150  |55° 41′| 6° 29′|  1825 |
+  |ISLAY      |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |MULL OF    |  297  |55°  1′| 5° 49′|  1787 |
+  |KINTYRE    |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |PLADDA     |  77 & |55° 26′| 5°  7′|  1790 |
+  |           |  130  |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |CORSEWALL  |  112  |55°  1′| 5°  9′|  1817 |
+  |           |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |LOCH RYAN  |   30  |54° 58′| 5°  2′|  1847 |
+  +-----------+-------+-------+-------+-------+
+  |MULL OF    |  325  |54° 38′| 4° 51′|  1830 |
+  |GALLOWAY   |       |       |       |       |
+  |           |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |LITTLE ROSS|  175  |54° 46′| 4°  5′|  1843 |
+  +-----------+-------+-------+-------+-------+
+  |POINT OF   |  106  |54° 25′| 4° 22′|  1818 |
+  |AYRE       |       |       |       |       |
+  +-----------+-------+-------+-------+-------+
+  |CALF OF MAN| 275 & |54°  3′| 4° 49′|  1818 |
+  |           |  368  |       |       |       |
+  +-----------+-------+-------+-------+-------+
+
+  [89] At Hynish Point in Tyree Island, two fixed Lights are shewn from
+  the Pier, but ONLY when the Vessel which attends the Lighthouse is
+  expected to enter the Dock at Hynish. In the Trinity House Chart,
+  Skerryvore Light is erroneously described as “Intermittent.”
+
+BEACONS AND BUOYS.
+
+FRITH OF FORTH DISTRICT.
+
+  +------------+------------+--------+---------------------------------+
+  |            |            |  Depth |                                 |
+  |            |            | at Low |                                 |
+  |            |            |Water of| Bearings of Marks and of Lines  |
+  |  Name of   | Description| Spring |   of Intersection Meeting at    |
+  |  Station.  |  of Mark.  | Tides. |          the Station.           |
+  +------------+------------+--------+---------------------------------+
+  |MIDDLE BANK,|6 Feet Buoy,|3¹⁄₂    |ALLOA TOWER in line with the     |
+  |WEST END,   |Red.        |Feet.   |Centre of CLACKMANNAN PIER--     |
+  |BUOY.       |            |        |Bearing N. by E.                 |
+  |            |            |        |                                 |
+  |            |            |        |CLACKMANNAN CHURCH SPIRE in line |
+  |            |            |        |with HIGH CHIMNEY-STACK of       |
+  |            |            |        |PARK-FARM HOUSE--Bearing NE. ¹⁄₂ |
+  |            |            |        |E.                               |
+  |            |            |        |                                 |
+  |            |            |        |MIDDLE BANK BUOY, East End--     |
+  |            |            |        |Bearing SE. by S.                |
+  +------------+------------+--------+---------------------------------+
+  |MIDDLE BANK,|6 Feet Buoy,|4 Feet. |TULLYALLAN HOUSE in line with    |
+  |EAST END,   |Red.        |        |TULLYALLAN OLD CHURCH SPIRE, in  |
+  |BUOY.       |            |        |ruins--Bearing ESE. ¹⁄₂ S.       |
+  |            |            |        |                                 |
+  |            |            |        |Remarkable CLUMP of TREES on     |
+  |            |            |        |distant high land in line with   |
+  |            |            |        |AIRTH CHURCH SPIRE--Bearing W. by|
+  |            |            |        |N. ¹⁄₂ N.                        |
+  |            |            |        |                                 |
+  |            |            |        |BUOY off INCH BRAKE ROCK--Bearing|
+  |            |            |        |S. by E.                         |
+  +------------+------------+--------+---------------------------------+
+  |INCH BRAKE  |6 Feet Buoy,|5 Feet. |FLAGSTAFF on the FERRY PIER,     |
+  |BUOY.       |Black.      |        |KINCARDINE, clear outside of     |
+  |            |            |        |KINCARDINE STONE PIER--Bearing N.|
+  |            |            |        |by E.                            |
+  |            |            |        |                                 |
+  |            |            |        |ALLOA CHURCH SPIRE in line with  |
+  |            |            |        |South Corner of KENNET  PANS     |
+  |            |            |        |DISTILLERY GARDEN WALL--Bearing  |
+  |            |            |        |N. by W.                         |
+  |            |            |        |                                 |
+  |            |            |        |LONG ANNAT BUOY--Bearing SSE. ¹⁄₂|
+  |            |            |        |E.                               |
+  +------------+------------+--------+---------------------------------+
+  |LONG ANNAT  |6 Feet Buoy,|9 Feet. |SANDS HOUSE, West Wing, in line  |
+  |BUOY.       |Black.      |        |with WEST FACE of ANNAT QUARRY-- |
+  |            |            |        |Bearing NNE. ¹⁄₂ E.              |
+  |            |            |        |                                 |
+  |            |            |        |BINNS MONUMENT in line with the  |
+  |            |            |        |Middle of BO’NESS PIER--Bearing  |
+  |            |            |        |SE. by S.                        |
+  |            |            |        |                                 |
+  |            |            |        |HEN and CHICKEN’S BUOY--Bearing  |
+  |            |            |        |SE. by E. ¹⁄₄ S.                 |
+  +------------+------------+--------+---------------------------------+
+  |HEN AND     |6 Feet Buoy,|12 Feet.|The East Wing of CULROSS ABBEY in|
+  |CHICKEN’S   |Black.      |        |line with Eastmost House in      |
+  |BUOY.       |            |        |CULROSS VILLAGE--Bearing NNE. ¹⁄₂|
+  |            |            |        |E.                               |
+  |            |            |        |                                 |
+  |            |            |        |AIRTH CASTLE, in line with       |
+  |            |            |        |HIGH-WATER MARK on LONG ANNAT    |
+  |            |            |        |POINT--Bearing NW. ¹⁄₄ W.        |
+  |            |            |        |                                 |
+  |            |            |        |BUOY on East End of DODS’ BANK-- |
+  |            |            |        |Bearing SSE. ¹⁄₂ E.              |
+  +------------+------------+--------+---------------------------------+
+  |DODS’ BANK  |7 Feet Buoy,|15 Feet.|BERRY-LAW TREES in line with the |
+  |BUOY.       |Red.        |        |CHIMNEY-STACK of BUNYAN’S FARM-- |
+  |            |            |        |Bearing E. by N.                 |
+  |            |            |        |                                 |
+  |            |            |        |CHIMNEY STACK of the SNUB COAL   |
+  |            |            |        |PIT (the first Stack West of     |
+  |            |            |        |Kinneil New Iron Works), in line |
+  |            |            |        |with the WEST PIER WALL of       |
+  |            |            |        |BO’NESS--Bearing WSW. ³⁄₄ W.     |
+  |            |            |        |                                 |
+  |            |            |        |COMARY HOUSE, East Wing, in line |
+  |            |            |        |with the West Wing of the        |
+  |            |            |        |FACTOR’S HOUSE--Bearing N. by E. |
+  |            |            |        |³⁄₄ E.                           |
+  |            |            |        |                                 |
+  |            |            |        |VALLEYFIELD HOUSE, a little East |
+  |            |            |        |of the Eastern House on PRESTON  |
+  |            |            |        |ISLAND, about half-way between   |
+  |            |            |        |the house and where the Island   |
+  |            |            |        |dries at half-tide--Bearing N. by|
+  |            |            |        |E. ¹⁄₄ E.                        |
+  |            |            |        |                                 |
+  |            |            |        |The Buoy of HEN and CHICKEN’S    |
+  |            |            |        |ROCK--Bearing NNW. ¹⁄₂ W.        |
+  +------------+------------+--------+---------------------------------+
+  |BEAMER      |Painted     |Rock Dry|BO’NESS PIER--Bearing NW. by W.  |
+  |BEACON.     |Black, with |at Low  |                                 |
+  |            |Spherical   |Water.  |CHARLESTON PIER, Outer End--     |
+  |            |Ball at top.|        |Bearing NW. by N.                |
+  |            |            |        |                                 |
+  |            |            |        |South-West Extremity of the Point|
+  |            |            |        |at NORTH QUEENSFERRY--Bearing    |
+  |            |            |        |ESE. ¹⁄₄ E.                      |
+  |            |            |        |                                 |
+  |            |            |        |The HALLS, or principal SOUTH    |
+  |            |            |        |QUEENSFERRY PIER--Bearing SSE.   |
+  |            |            |        |¹⁄₄ E.                           |
+  +------------+------------+--------+---------------------------------+
+  |DRUM SAND   |7 Feet Buoy,|12 Feet.|NEWBIGGING HOUSE in line with    |
+  |EAST BUOY.  |Red.        |        |East Edge of CARCRAIG ROCK--     |
+  |            |            |        |Bearing NE. ¹⁄₂ E.               |
+  |            |            |        |                                 |
+  |            |            |        |OXSCARE BEACON--Bearing E. ³⁄₄ N.|
+  |            |            |        |                                 |
+  |            |            |        |INCHKEITH LIGHTHOUSE--Bearing    |
+  |            |            |        |ESE. ¹⁄₂ E.                      |
+  |            |            |        |                                 |
+  |            |            |        |Highest Point of ARTHUR’S SEAT in|
+  |            |            |        |line with                        |
+  |            |            |        |NELSON’S MONUMENT--Bearing S. by |
+  |            |            |        |E. ³⁄₄ E.                        |
+  +------------+------------+--------+---------------------------------+
+  |DRUM SAND   |8 Feet Buoy,|3¹⁄₄    |SOUTH POINT of INCHKEITH in line |
+  |WEST BUOY.  |Red, with   |Fathoms.|with CENTRE of OPENING of MICKERY|
+  |            |Fenders.    |        |STONE--Bearing ESE. ¹⁄₄ E.       |
+  |            |            |        |INCHKEITH LIGHTHOUSE--Bearing    |
+  |            |            |        |ESE. ¹⁄₂ E.                      |
+  |            |            |        |                                 |
+  |            |            |        |FORDEL HOUSE in line with CENTRE |
+  |            |            |        |of DONIBRISTLE HOUSE--Bearing N. |
+  |            |            |        |¹⁄₄ E.                           |
+  |            |            |        |                                 |
+  |            |            |        |CHIMNEY-STACK of CASTLE LANDHILL |
+  |            |            |        |FARM-HOUSE in line with END of   |
+  |            |            |        |LAZARETT PIER--Bearing NW. ³⁄₈ N.|
+  +------------+------------+--------+---------------------------------+
+  |OXSCARE     |Painted Red,|Rock Dry|South Point of CARLIN’S NOSE--   |
+  |BEACON.     |with Flat   |at Low  |Bearing W. ³⁄₄ N.                |
+  |            |Cone at top.|Water.  |                                 |
+  |            |            |        |BURNTISLAND PIER--Bearing ENE.   |
+  |            |            |        |                                 |
+  |            |            |        |Extremity of KINGHORNNESS--      |
+  |            |            |        |Bearing E. ¹⁄₂ N.                |
+  |            |            |        |                                 |
+  |            |            |        |INCHKEITH LIGHTHOUSE--Bearing    |
+  |            |            |        |ESE. ¹⁄₄ E.                      |
+  |            |            |        |                                 |
+  |            |            |        |MARTELLO TOWER--Bearing SSE. ³⁄₄ |
+  |            |            |        |E.                               |
+  |            |            |        |                                 |
+  |            |            |        |GRANTON PIER--Bearing S. by E.   |
+  |            |            |        |¹⁄₄ E.                           |
+  +------------+------------+--------+---------------------------------+
+  |WEST GUNNET |8 Feet Buoy,|3³⁄₄    |NELSON’S MONUMENT just clear East|
+  |BUOY.       |White.      |Fathoms.|of NORTH LEITH CHURCH SPIRE--    |
+  |            |            |        |Bearing SSW.                     |
+  |            |            |        |                                 |
+  |            |            |        |NORTH BERWICK LAW in line with   |
+  |            |            |        |North End of LONG CRAIG--Bearing |
+  |            |            |        |ESE. ¹⁄₄ E.                      |
+  |            |            |        |                                 |
+  |            |            |        |CLUMP of TREES East of GRANGE    |
+  |            |            |        |HOUSE in line with BURNTISLAND   |
+  |            |            |        |CHURCH SPIRE--Bearing N. ¹⁄₂ W.  |
+  |            |            |        |                                 |
+  |            |            |        |INCHKEITH LIGHTHOUSE--Bearing E. |
+  |            |            |        |¹⁄₂ S.                           |
+  +------------+------------+--------+---------------------------------+
+  |EAST GUNNET |8 Feet Buoy,|3¹⁄₂    |NOTCH at the foot of East Brow of|
+  |BUOY.       |White.      |Fathoms.|the PENTLAND HILLS in line with  |
+  |            |            |        |NORTH LEITH CHURCH SPIRE--Bearing|
+  |            |            |        |SSW. ³⁄₄ W.                      |
+  |            |            |        |                                 |
+  |            |            |        |CARLIN’S NOSE clear of the North |
+  |            |            |        |Side of MICKERY STONE--Bearing   |
+  |            |            |        |WNW. ³⁄₄ W.                      |
+  |            |            |        |                                 |
+  |            |            |        |KINGHORN NEW FREE CHURCH in line |
+  |            |            |        |with KINGHORNNESS--Bearing NE. by|
+  |            |            |        |N.                               |
+  |            |            |        |                                 |
+  |            |            |        |INCHKEITH LIGHTHOUSE--Bearing E. |
+  +------------+------------+--------+---------------------------------+
+  |PALLAS BUOY.|7 Feet Buoy,|3¹⁄₂    |KINGHORN FREE CHURCH in line with|
+  |            |striped     |Fathoms.|SWAN’S FACTORY--Bearing N. by E. |
+  |            |White and   |        |³⁄₄ E.                           |
+  |            |Black hori- |        |                                 |
+  |            |zontally.   |        |North Brow of INCHKEITH in line  |
+  |            |            |        |with the Centre of SILLY CARR    |
+  |            |            |        |ROCK--Bearing ENE. ¹⁄₄ N.        |
+  |            |            |        |                                 |
+  |            |            |        |ASSEMBLY HALL SPIRE, EDINBURGH,  |
+  |            |            |        |in line with MARTELLO TOWER--    |
+  |            |            |        |Bearing SW. ³⁄₄ S.               |
+  |            |            |        |                                 |
+  |            |            |        |INCHKEITH LIGHTHOUSE--Bearing    |
+  |            |            |        |ENE. ³⁄₄ E.                      |
+  +------------+------------+--------+---------------------------------+
+  |HERWIT BUOY.|8 Feet Buoy,|4³⁄₄    |East Brow of PENTLAND HILLS,     |
+  |            |Black.      |Fathoms.|touching West Brow of ARTHUR’S   |
+  |            |            |        |SEAT (half way up)--Bearing SW.  |
+  |            |            |        |¹⁄₂ W.                           |
+  |            |            |        |                                 |
+  |            |            |        |East Stables (Red-tiled House) of|
+  |            |            |        |PETTYCUR in line with East Brow  |
+  |            |            |        |of INCHKEITH--Bearing N. by W.   |
+  |            |            |        |                                 |
+  |            |            |        |INCHKEITH LIGHTHOUSE--Bearing N. |
+  |            |            |        |by W. ¹⁄₂ W.                     |
+  +------------+------------+--------+---------------------------------+
+  |CRAIG WAUGH |8 Feet Buoy,|4       |PETTYCUR PIER in line with       |
+  |BUOY.       |Red.        |Fathoms.|Eastern Brow of INCHKEITH--      |
+  |            |            |        |Bearing N. by W. ¹⁄₂ W.          |
+  |            |            |        |                                 |
+  |            |            |        |ASSEMBLY HALL SPIRE just clear,  |
+  |            |            |        |West of NELSON’S MONUMENT--      |
+  |            |            |        |Bearing W. ³⁄₄ S.                |
+  |            |            |        |                                 |
+  |            |            |        |INCHKEITH LIGHTHOUSE--Bearing N. |
+  |            |            |        |by W. ³⁄₄ W.                     |
+  +------------+------------+--------+---------------------------------+
+  |NORTH CRAIG |12 Feet Mast|3¹⁄₄    |NELSON’S MONUMENT in line with   |
+  |MAST BUOY.  |Buoy,       |Fathoms.|West Wing of LEITH BATHS--Bearing|
+  |            |Chequered   |        |WSW. ¹⁄₄ W.                      |
+  |            |Red and     |        |                                 |
+  |            |White.      |        |Summit of EAST LOMOND HILL in    |
+  |            |            |        |line with BIG HOUSE TREES--      |
+  |            |            |        |Bearing N. ¹⁄₂ E.                |
+  |            |            |        |                                 |
+  |            |            |        |CARLIN’S NOSE in line with Centre|
+  |            |            |        |of MICKERY STONE--Bearing WNW.   |
+  +------------+------------+--------+---------------------------------+
+  |WEST        |6 Feet Buoy,|3¹⁄₄    |DYSART COAL-PIT CHIMNEY-STACK in |
+  |ROCK-HEAD,  |Red.        |Fathoms.|line with MIDDLE of GABLE of PAN |
+  |OFF DYSART, |            |        |HALL HOUSE--Bearing N. ¹⁄₄ E.    |
+  |BUOY.       |            |        |                                 |
+  |            |            |        |NORTH END of PORTBRAE CHURCH,    |
+  |            |            |        |KIRKCALDY, just clear of the END |
+  |            |            |        |of KIRKCALDY PIER--Bearing WNW.  |
+  |            |            |        |³⁄₄ W.                           |
+  |            |            |        |                                 |
+  |            |            |        |INCHKEITH LIGHTHOUSE--Bearing SW.|
+  |            |            |        |by S.                            |
+  |            |            |        |                                 |
+  |            |            |        |N.B.--_The highest part of the   |
+  |            |            |        |Rock bearing N. ¹⁄₄ E. distant   |
+  |            |            |        |about one-half cable’s length    |
+  |            |            |        |from Buoy._                      |
+  +------------+------------+--------+---------------------------------+
+  |EAST        |6 Feet Buoy,|3¹⁄₂    |WEMYSS OLD CASTLE in line with   |
+  |ROCK-HEAD,  |Black.      |Fathoms.|SOUTHERN HOUSES of EAST WEMYSS-- |
+  |OFF DYSART, |            |        |Bearing NE. by E. ¹⁄₄ E.         |
+  |BUOY.       |            |        |                                 |
+  |            |            |        |EAST WING of DYSART CHURCH in    |
+  |            |            |        |line with TOWN-HOUSE STEEPLE--   |
+  |            |            |        |Bearing NNW. ³⁄₄ W.              |
+  |            |            |        |                                 |
+  |            |            |        |BUOY on WEST ROCK-HEAD--Bearing  |
+  |            |            |        |W. by N. ¹⁄₄ N.                  |
+  |            |            |        |                                 |
+  |            |            |        |INCHKEITH LIGHTHOUSE--Bearing SW.|
+  |            |            |        |¹⁄₂ S.                           |
+  |            |            |        |                                 |
+  |            |            |        |N.B.--_The highest part of Rock, |
+  |            |            |        |bearing NW. ¹⁄₄ W., distant about|
+  |            |            |        |two cables’ lengths._            |
+  +------------+------------+--------+---------------------------------+
+  |EAST VOWS   |Pyramid of  |Rock Dry|RUINS on CHAPELNESS--Bearing N.  |
+  |ROCK,       |Iron Pil-   |at Low  |³⁄₄ E.                           |
+  |BEACON, OFF |lars, with  |Water.  |                                 |
+  |ELIE.       |open Cylin- |        |NORTH END of ELIE PIER--Bearing  |
+  |            |dric Cage on|        |E. ³⁄₄ N.                        |
+  |            |top, painted|        |EXTREMITY of ELIENESS--Bearing E.|
+  |            |Red.        |        |by S. ¹⁄₂ S.                     |
+  |            |            |        |                                 |
+  |            |            |        |ISLE of MAY LIGHTHOUSE--Bearing  |
+  |            |            |        |ESE. ¹⁄₄ S.                      |
+  |            |            |        |                                 |
+  |            |            |        |WEST VOWS ROCK--Bearing WNW. ¹⁄₂ |
+  |            |            |        |N. distant ¹⁄₂ mile.             |
+  |            |            |        |                                 |
+  |            |            |        |BUOY on THILL ROCK--Bearing ESE. |
+  |            |            |        |¹⁄₈ S. distant two cables’       |
+  |            |            |        |lengths.                         |
+  +------------+------------+--------+---------------------------------+
+  |THILL ROCK  |7 Feet Buoy,|3³⁄₄    |WEST END of MILLHOUSE COTTAGE in |
+  |BUOY.       |Black.      |Fathoms.|line with NORTH END of ELIE PIER |
+  |            |            |        |--Bearing NE.                    |
+  |            |            |        |                                 |
+  |            |            |        |PETTIE LAW in line with WEST     |
+  |            |            |        |CHIMNEY-STACK of DAVID           |
+  |            |            |        |OVENSTONE’S HOUSE--Bearing N. ³⁄₈|
+  |            |            |        |W.                               |
+  |            |            |        |                                 |
+  |            |            |        |RUIN on CHAPELNESS--Bearing NNW. |
+  |            |            |        |¹⁄₂ W.                           |
+  |            |            |        |                                 |
+  |            |            |        |BEACON on EAST VOWS ROCK--Bearing|
+  |            |            |        |WNW. ¹⁄₈ N.                      |
+  |            |            |        |                                 |
+  |            |            |        |N.B.--_The Buoy lies about 35    |
+  |            |            |        |fathoms to the SSE. of the       |
+  |            |            |        |highest part of the Rock._       |
+  +------------+------------+--------+---------------------------------+
+  |SOUTH CARR  |Painted Red,|Rock Dry|CAIRN on BASS ROCK--Bearing N. by|
+  |BEACON.     |with Cross  |at Low  |E.                               |
+  |            |at top.     |Water.  |                                 |
+  |            |            |        |ISLE of MAY LIGHTHOUSE--Bearing  |
+  |            |            |        |NE.                              |
+  |            |            |        |                                 |
+  |            |            |        |DUNBAR CHURCH TOWER--Bearing SSE.|
+  |            |            |        |¹⁄₄ S.                           |
+  |            |            |        |                                 |
+  |            |            |        |OLDHAM FARM-HOUSE CHIMNEY-STACK--|
+  |            |            |        |Bearing W. ¹⁄₄ N.                |
+  +------------+------------+--------+---------------------------------+
+  |NORTH CARR  |Beacon of   |Rock Dry|1¹⁄₄ Mile from FIFENESS--Bearing |
+  |BEACON.     |Stone, with |at Low  |from ISLE of MAY LIGHT NNE.      |
+  |            |Iron Frame  |Water.  |distant 6 Nautic Miles.          |
+  |            |and Ball.   |        |                                 |
+  +------------+------------+--------+---------------------------------+
+
+BEACONS AND BUOYS.
+
+DISTRICT OF FRITHS OF MORAY, CROMARTY, INVERNESS, AND DORNOCH.
+
+  +------------+------------+--------+---------------------------------+
+  |            |            |  Depth |                                 |
+  |            |            | at Low |                                 |
+  |            |            |Water of| Magnetic Bearings of Marks and  |
+  |  Name of   | Description| Spring |    of Lines of Intersection     |
+  |  Station.  |  of Mark.  | Tides. |    Meeting at the Station.      |
+  +------------+------------+--------+---------------------------------+
+  |COVESEA     |Pyramid of  |Rock dry|COVESEA SKERRIES LIGHTHOUSE on   |
+  |SKERRIES    |Iron Pil-   |at Low  |the neighbouring land of         |
+  |BEACON.     |lars, with  |water.  |CRAIGHEAD--Bears WSW. ¹⁄₄ W.     |
+  |            |open cylin- |        |distant one mile.                |
+  |            |dric Cage,  |        |                                 |
+  |            |and a Cross,|        |                                 |
+  |            |rising to   |        |                                 |
+  |            |the height  |        |                                 |
+  |            |of about 50 |        |                                 |
+  |            |feet above  |        |                                 |
+  |            |High water. |        |                                 |
+  +------------+------------+--------+---------------------------------+
+  |LONGMAN     |Cone of Iron|Beach   |END of KESSOCK SOUTH PIER--      |
+  |POINT       |Plates      |Dry at  |Bearing W. by N. ¹⁄₄ N.          |
+  |BEACON.     |painted     |Low     |                                 |
+  |            |Black.      |water of|CRAIGTOWN POINT--Bearing NW. ¹⁄₂ |
+  |            |            |Spring  |W.                               |
+  |            |            |Tides.  |                                 |
+  |            |            |        |MEIKLEMEE, EAST END BUOY--Bearing|
+  |            |            |        |E. ¹⁄₂ N.                        |
+  |            |            |        |                                 |
+  |            |            |        |BOGBAIN HOUSE in line with       |
+  |            |            |        |RIGMORE HOUSE--Bearing S. ³⁄₄ E. |
+  |            |            |        |                                 |
+  |            |            |        |END of LONGMAN POINT--Bearing N. |
+  |            |            |        |¹⁄₄ W. distant 40 Fathoms.       |
+  +------------+------------+--------+---------------------------------+
+  |MEIKLEMEE   |6 Feet Buoy.|12 Feet.|PARK’S FARM-HOUSE in line with   |
+  |BANK BUOY.  |BLACK.      |        |RIGMORE HOUSE--Bearing SSW.      |
+  |East End.   |            |        |                                 |
+  |            |            |        |Middle of space between the      |
+  |            |            |        |Houses of SCORGUOY FARM-YARD in  |
+  |            |            |        |line with BLACK MILL CHIMNEY--   |
+  |            |            |        |Bearing W. ¹⁄₄ S.                |
+  |            |            |        |                                 |
+  |            |            |        |CHANONRY POINT LIGHTHOUSE--      |
+  |            |            |        |Bearing ENE. ¹⁄₄ E.              |
+  +------------+------------+--------+---------------------------------+
+  |MIDDLE BANK |6 Feet Buoy.|12 Feet.|SCORGUOY FARM-YARD (South End),  |
+  |BUOY.       |Black.      |        |in line with BLACK MILL CHIMNEY--|
+  |East End.   |            |        |Bearing W. ¹⁄₂ S.                |
+  |            |            |        |                                 |
+  |            |            |        |ROUND CLUMP of TREES, North of   |
+  |            |            |        |LEY’S HOUSE, in line with RIGMORE|
+  |            |            |        |HOUSE--Bearing SW. ³⁄₄ S.        |
+  |            |            |        |                                 |
+  |            |            |        |CHANONRY POINT LIGHTHOUSE--      |
+  |            |            |        |Bearing ENE.                     |
+  |            |            |        |                                 |
+  |            |            |        |MEIKLEMEE BANK BUOY--Bearing W.  |
+  |            |            |        |⁵⁄₈ S.                           |
+  +------------+------------+--------+---------------------------------+
+  |PETTY BANK  |6 Feet Buoy.|12 Feet.|DALCROSS CASTLE in line with     |
+  |BUOY.       |CHEQUERED   |        |FISHTOWN FARM-HOUSE--Bearing SE. |
+  |North or    |Black and   |        |³⁄₄ S.                           |
+  |Outer Edge. |White.      |        |                                 |
+  |            |            |        |EXTREMITY of EAST SUTER in line  |
+  |            |            |        |with STORE-HOUSE, CHANONRY POINT |
+  |            |            |        |--Bearing ENE. ³⁄₄ N.            |
+  |            |            |        |                                 |
+  |            |            |        |MUNLOCHY BUOY--Bearing N.        |
+  +------------+------------+--------+---------------------------------+
+  |MUNLOCHY    |6 Feet Buoy.|12 Feet.|WEST WING of AVOCH HOUSE, now in |
+  |BUOY.       |Black.      |        |ruins, in line with the most     |
+  |            |            |        |WESTERN SLATED HOUSE or COTTAGE  |
+  |            |            |        |in AVOCH--Bearing N. ¹⁄₄ W.      |
+  |            |            |        |                                 |
+  |            |            |        |NORTH END of FORT-GEORGE in line |
+  |            |            |        |with CHANONRY POINT--Bearing ENE.|
+  |            |            |        |¹⁄₄ E.                           |
+  +------------+------------+--------+---------------------------------+
+  |SKATE BANK  |6 Feet Buoy.|12¹⁄₂   |The EAST WING of KINCURDIE HOUSE |
+  |BUOY.       |Black.      |Feet.   |in line with SPIRE of ROSEMARKIE |
+  |East End.   |            |        |KIRK--Bearing NNE. ¹⁄₂ E.        |
+  |            |            |        |                                 |
+  |            |            |        |FLAGSTAFF of FORT-GEORGE in line |
+  |            |            |        |with the OUTER END of CHANONRY   |
+  |            |            |        |PIER--Bearing ENE. ¹⁄₄ E.        |
+  |            |            |        |                                 |
+  |            |            |        |DALCROSS CASTLE in line with     |
+  |            |            |        |COTTAGE on SEA-CLIFF--Bearing S. |
+  |            |            |        |³⁄₄ E.                           |
+  |            |            |        |                                 |
+  |            |            |        |MUNLOCHY BUOY--Bearing WSW. ¹⁄₈  |
+  |            |            |        |W.                               |
+  +------------+------------+--------+---------------------------------+
+  |CRAIGMEE OR |6 Feet Buoy.|2¹⁄₄     |HIGH PART, or WEST BROW of      |
+  |FORT-GEORGE |Chequered   |Fathoms. |ALTARLIE POINT, in line with    |
+  |BANK BUOY.  |Black and   |         |CHANONRY POINT LIGHTHOUSE--     |
+  |            |White.      |         |Bearing SW. ³⁄₄ W.              |
+  |            |            |         |                                |
+  |            |            |         |PATCH of TREES at West End of   |
+  |            |            |         |BROOMHILL WOOD, called BROOMHILL|
+  |            |            |         |BUSH, in line with PLATCOCK     |
+  |            |            |         |HOUSE--Bearing WNW. ¹⁄₄ W.      |
+  +------------+------------+---------+--------------------------------+
+  |RIFF BANK   |6 Feet Buoy.|3²⁄₃     |CRAIGHEAD FARM-HOUSE in line    |
+  |BUOY.       |Black.      |Fathoms. |with the most WESTERN of the    |
+  |West End.   |            |         |THREE BURNS--Bearing N. by E.   |
+  |            |            |         |¹⁄₄ E.                          |
+  |            |            |         |                                |
+  |            |            |         |BROOMHILL BUSH (East End) in    |
+  |            |            |         |line with the MANSE of          |
+  |            |            |         |ROSEMARKIE--Bearing W. ¹⁄₂ N.   |
+  |            |            |         |                                |
+  |            |            |         |CHANONRY POINT LIGHTHOUSE--     |
+  |            |            |         |Bearing WSW. ³⁄₄ S.             |
+  +------------+------------+---------+--------------------------------+
+  |RIFF BANK   |6 Feet Buoy.|3¹⁄₂     |THREE remarkable TREES at NORTH |
+  |BUOY.       |Black.      |Fathoms. |END of CRAIGIE WOOD, in line    |
+  |MIDDLE OR   |            |         |with ROSEMARKIE MANSE--Bearing  |
+  |North Angle.|            |         |W. ¹⁄₂ S.                       |
+  |            |            |         |                                |
+  |            |            |         |GAMEKEEPER’S HOUSE at End of    |
+  |            |            |         |WOOD in line with CAVE on       |
+  |            |            |         |SEA-SHORE, a little EAST of the |
+  |            |            |         |THREE BURNS--Bearing NW. ¹⁄₂ W. |
+  |            |            |         |                                |
+  |            |            |         |CHANONRY POINT LIGHTHOUSE--     |
+  |            |            |         |Bearing WSW. ¹⁄₂ S.             |
+  +------------+------------+---------+--------------------------------+
+  |RIFF BANK   |12 Feet     |4¹⁄₂     |CASTLE CRAIG ROCK in line with  |
+  |BUOY.       |Mast-Buoy.  |Fathoms. |STACK ROCK at foot of WEST SUTER|
+  |East End.   |Black.      |         |--Bearing N. by E. ¹⁄₄ E.       |
+  |            |            |         |                                |
+  |            |            |         |STORE-HOUSE on CHANONRY POINT,  |
+  |            |            |         |shut in by the NORTH corner of  |
+  |            |            |         |FORT-GEORGE, and in line with   |
+  |            |            |         |LOWER part of SOUTH BROW of ORD |
+  |            |            |         |HILL--Bearing W. ³⁄₄ S.         |
+  |            |            |         |                                |
+  |            |            |         |TOWRIE LUMB WOOD in line with   |
+  |            |            |         |CRAIGIE WOOD (South End)--      |
+  |            |            |         |Bearing W.                      |
+  +------------+------------+---------+--------------------------------+
+  |WHITENNESS  |     --     |   --    |  --                            |
+  |BEACON. (In |            |         |                                |
+  |prepara-    |            |         |                                |
+  |tion.)      |            |         |                                |
+  +------------+------------+---------+--------------------------------+
+  |NAVITY BANK |6 Feet Buoy.|2¹⁄₂     |TREES at end of NAVITY          |
+  |BUOY.       |Chequered   |Fathoms. |FARM-HOUSE in line with EAST    |
+  |South Edge. |Black and   |         |BANK or CLIFF of CRAIGHOUSE BURN|
+  |            |White.      |         |--Bearing N. ³⁄₄ E.             |
+  |            |            |         |                                |
+  |            |            |         |EXTREMITY of WOOD on BROW of    |
+  |            |            |         |EAST SUTER in line with Lower   |
+  |            |            |         |part of BROW of WEST SUTER--    |
+  |            |            |         |Bearing NE. by E.               |
+  |            |            |         |                                |
+  |            |            |         |CHANONRY POINT LIGHTHOUSE--     |
+  |            |            |         |Bearing SW. by W.               |
+  |            |            |         |                                |
+  |            |            |         |RIFF BANK MAST BUOY--Bearing SE.|
+  |            |            |         |⁵⁄₈ E.                          |
+  +------------+------------+---------+--------------------------------+
+  |NIGG SANDS  |6 Feet Buoy.|2        |CROMARTY GAELIC KIRK STEEPLE in |
+  |BUOY.       |Black.      |Fathoms. |line with EAST WING of HOTEL--  |
+  |East End.   |            |         |Bearing S. ³⁄₄ E.               |
+  |            |            |         |                                |
+  |            |            |         |FACE of EAST SUTER apparently on|
+  |            |            |         |a line halfway between          |
+  |            |            |         |FERRYHOUSE and STABLE--Bearing  |
+  |            |            |         |SE. by E.                       |
+  +------------+------------+---------+--------------------------------+
+  |NIGG SANDS  |6 Feet Buoy.|1²⁄₃     |FARM-HOUSE of DALNEY in line    |
+  |BUOY.       |Black.      |Fathoms. |with the PIGEON-HOUSE East of   |
+  |West End.   |            |         |BALLINTRADE--Bearing NNE. ¹⁄₈ E.|
+  |            |            |         |                                |
+  |            |            |         |EXTREMITY of WEST SUTER in line |
+  |            |            |         |with CROMARTY LIGHTHOUSE--      |
+  |            |            |         |Bearing SE. ⁵⁄₈ E.              |
+  +------------+------------+---------+--------------------------------+
+  |NEWHALL     |6 Feet Buoy.|2¹⁄₂     |PRIESTHILL FARM-HOUSE in line   |
+  |BANK BUOY.  |CHEQUERED   |FATHOMS. |with EASTERNMOST HOUSE in       |
+  |East End.   |Black and   |         |BALLINTRADE--Bearing NNE. ³⁄₄ E.|
+  |            |White.      |         |                                |
+  |            |            |         |EAST BROW of WEST SUTER in line |
+  |            |            |         |with CROMARTY GAELIC KIRK--     |
+  |            |            |         |Bearing ESE. ¹⁄₈ S.             |
+  |            |            |         |                                |
+  |            |            |         |NIGG SANDS WEST BUOY--Bearing   |
+  |            |            |         |ENE. ³⁄₈ N.                     |
+  +------------+------------+---------+--------------------------------+
+  |THREE KINGS |8 Feet Buoy.|7¹⁄₂     |EASTERN TREES upon Top of the   |
+  |ROCKS BUOY. |Red.        |Fathoms. |HIGH LAND, being the most       |
+  |            |            |         |projecting and highest part of  |
+  |            |            |         |SEA CLIFF, West of GILLIAM BURN,|
+  |            |            |         |in line with the HIGHEST EASTERN|
+  |            |            |         |part of THREE KINGS ROCK--      |
+  |            |            |         |Bearing WNW. ¹⁄₄ N.             |
+  |            |            |         |                                |
+  |            |            |         |DUKE of SUTHERLAND’S MONUMENT in|
+  |            |            |         |line with WEST END of LONG      |
+  |            |            |         |STOREHOUSE in SHANDWICK--Bearing|
+  |            |            |         |N. by E. ³⁄₈ E.                 |
+  +------------+------------+---------+--------------------------------+
+  |CULLODEN    |8 Feet Buoy.|8³⁄₄     |BRUCEFIELD FARM-HOUSE in line   |
+  |ROCK BUOY.  |BLACK.      |FATHOMS. |with TARBETNESS LIGHTHOUSE      |
+  |            |            |         |FLAG-STAFF--Bearing WSW. ³⁄₄ W. |
+  |            |            |         |                                |
+  |            |            |         |DUKE of SUTHERLAND’S MONUMENT in|
+  |            |            |         |line with Lower Corner of WOOD  |
+  |            |            |         |farthest West from DUNROBIN     |
+  |            |            |         |CASTLE--Bearing NNW.            |
+  +------------+------------+---------+--------------------------------+
+  |FAIRWAY     |12 Feet Mast|5        |WEST END of BENTAVIE HILL in    |
+  |BUOY OFF    |Buoy. Red.  |Fathoms. |line with TRENTHAM FARM-HOUSE-- |
+  |TAIN BAR.   |            |         |Bearing NNW. ⁷⁄₈ W.             |
+  |            |            |         |                                |
+  |            |            |         |WEST BROW of EAST SUTER in line |
+  |            |            |         |with MEIKLERENNIE FARM-HOUSE--  |
+  |            |            |         |Bearing SW. ³⁄₈ W.              |
+  |            |            |         |                                |
+  |            |            |         |TARBETNESS LIGHTHOUSE--Bearing  |
+  |            |            |         |SE. ³⁄₄ E.                      |
+  +------------+------------+---------+--------------------------------+
+  |TAIN BAR    |6 Feet Buoy.|2¹⁄₂     |REMARKABLE HOLLOW or NOTCH in   |
+  |INNER BUOY. |Black.      |Fathoms. |HIGH LAND East of EAST SUTER, in|
+  |NORTH SIDE. |            |         |line with LOCHSLAIN CASTLE--    |
+  |            |            |         |Bearing SSW. ¹⁄₄ W.             |
+  |            |            |         |                                |
+  |            |            |         |LOWER WEST BROW of CAMBUSMORE   |
+  |            |            |         |HILL in line with EAST END of   |
+  |            |            |         |WEST EMBO WOOD--Bearing N. by W.|
+  |            |            |         |³⁄₄ W.                          |
+  |            |            |         |                                |
+  |            |            |         |TARBETNESS LIGHTHOUSE--Bearing  |
+  |            |            |         |ESE. ¹⁄₂ S.                     |
+  |            |            |         |                                |
+  |            |            |         |FAIRWAY BUOY off TAIN BAR--     |
+  |            |            |         |Bearing E. ³⁄₄ S.               |
+  +------------+------------+---------+--------------------------------+
+  |TAIN BAR    |6 Feet Buoy.|4²⁄₃     |REMARKABLE HOLLOW or NOTCH in   |
+  |INNER BUOY. |Chequered   |Fathoms. |HIGH LAND EAST of EAST SUTER in |
+  |SOUTH SIDE. |BLACK AND   |         |line with MEIKLERENNIE FARMHOUSE|
+  |            |White.      |         |--Bearing SSW. ³⁄₈ W.           |
+  |            |            |         |                                |
+  |            |            |         |WEST END of EAST EMBO WOOD in   |
+  |            |            |         |line with EMBO FARMHOUSE--      |
+  |            |            |         |Bearing N. ¹⁄₂ W.               |
+  |            |            |         |                                |
+  |            |            |         |FAIRWAY BUOY off TAIN BAR--     |
+  |            |            |         |Bearing E. ¹⁄₄ N.               |
+  |            |            |         |                                |
+  |            |            |         |TAIN BAR INNER BUOY (North Side)|
+  |            |            |         |--Bearing ENE. ³⁄₈ N.           |
+  |            |            |         |                                |
+  |            |            |         |DORNOCH SPIRE--Bearing NNW. ³⁄₄ |
+  |            |            |         |W.                              |
+  +------------+------------+---------+--------------------------------+
+
+BEACONS AND BUOYS.
+
+FRITH OF CLYDE DISTRICT.
+
+  +------------+------------+--------+---------------------------------+
+  |            |            |  Depth |                                 |
+  |            |            | at Low |                                 |
+  |            |            |Water of| Bearings of Marks and of Lines  |
+  |  Name of   | Description| Spring |   of Intersection Meeting at    |
+  |  Station.  |  of Mark.  | Tides. |          the Station.           |
+  +------------+------------+--------+---------------------------------+
+  |FULLARTON   |7 Feet Buoy.|3¹⁄₂    |CLUMP of TREES at East side of   |
+  |ROCK BUOY.  |RED.        |FATHOMS.|CLACHLAN FARM, just opening from |
+  |            |            |        |the WEST BROW of HOLY ISLAND--   |
+  |            |            |        |Bearing N. by E.                 |
+  |            |            |        |                                 |
+  |            |            |        |Standing Stone upon KINROSS POINT|
+  |            |            |        |--Bearing W.                     |
+  |            |            |        |                                 |
+  |            |            |        |Buoy moored upon ESE. Tail of    |
+  |            |            |        |Rock. The shallowest part of Rock|
+  |            |            |        |has 8 Feet at Low water of Spring|
+  |            |            |        |Tides.                           |
+  +------------+------------+--------+---------------------------------+
+  |ARRANMAN’S  |8 Feet Buoy.|8¹⁄₂    |West End of ARRANMAN’S BARRELS   |
+  |BARRELS     |Red.        |Fathoms.|SHOAL--Bearing W. by N.          |
+  |ROCKS BUOY. |            |        |                                 |
+  |            |            |        |North-East Extremity of Shoal--  |
+  |            |            |        |Bearing N. ¹⁄₂ E.                |
+  |            |            |        |                                 |
+  |            |            |        |BALLYSHARE HOUSE in line with the|
+  |            |            |        |Lower East End of DUNACREEIN ROCK|
+  |            |            |        |--Bearing NW. ¹⁄₂ W.             |
+  |            |            |        |                                 |
+  |            |            |        |The Buoy is moored abreast of the|
+  |            |            |        |middle of the Shoal, and is      |
+  |            |            |        |distant from the Low water Rocks |
+  |            |            |        |about _half a cable’s length_.   |
+  +------------+------------+--------+---------------------------------+
+  |OTTERARD    |8 Feet Buoy.|3³⁄₄    |CLUMP of TREES at BALLAMINICH    |
+  |ROCK BUOY.  |Black.      |Fathoms.|FARM-HOUSE in line with the lower|
+  |            |            |        |part of the South-eastern Brow of|
+  |            |            |        |ISLAND DAVAAR--Bearing SW. ¹⁄₄ W.|
+  |            |            |        |                                 |
+  |            |            |        |The remarkable Notch in distant  |
+  |            |            |        |Hill called BALAVILAN, in line   |
+  |            |            |        |with North End of Green Patch on |
+  |            |            |        |the rising ground in Field south |
+  |            |            |        |of Long Dyke near SMERBY         |
+  |            |            |        |FARM-HOUSE--Bearing WNW. ³⁄₄ N.  |
+  |            |            |        |                                 |
+  |            |            |        |MACRINNAN’S POINT--Bearing WSW.  |
+  |            |            |        |¹⁄₂ W.                           |
+  |            |            |        |                                 |
+  |            |            |        |The Buoy is moored upon ESE. Tail|
+  |            |            |        |of Rock. The shallowest part of  |
+  |            |            |        |Rock at Low water of Springs has |
+  |            |            |        |12 Feet.                         |
+  +------------+------------+--------+---------------------------------+
+  |MILLBEG BANK|6 Feet Buoy.|2       |CAMPBELTON TOWN-HOUSE SPIRE in   |
+  |BUOY.       |Black.      |Fathoms.|line with House in ruins on      |
+  |            |            |        |TRENCH POINT--Bearing WNW.       |
+  |            |            |        |                                 |
+  |            |            |        |CROSSBEG FARM-HOUSE in line with |
+  |            |            |        |Lower part or Mouth of PORTER’S  |
+  |            |            |        |GLEN--Bearing N. ¹⁄₄ W.          |
+  +------------+------------+--------+---------------------------------+
+  |CAMPBELTON  |6 Feet Buoy.|2¹⁄₄    |West Corner of GAELIC CHURCH in  |
+  |HARBOUR     |Red.        |Fathoms.|line with TRENCH POINT--Bearing  |
+  |OUTER BUOY. |            |        |W. by N. ¹⁄₄ N.                  |
+  |            |            |        |                                 |
+  |            |            |        |West End of BARASKIE FARM-HOUSE  |
+  |            |            |        |(dwelling-house) in line with    |
+  |            |            |        |Angle of Plantation, and also    |
+  |            |            |        |with the Corner of the Second    |
+  |            |            |        |Field to the South of the House--|
+  |            |            |        |Bearing N. ³⁄₈ E.                |
+  +------------+------------+--------+---------------------------------+
+  |CAMPBELTON  |6 Feet Buoy.|1¹⁄₄    |CASTLE HILL CHURCH in line with  |
+  |HARBOUR     |Black.      |Fathoms.|high water-mark on TRENCH POINT  |
+  |INNER BUOY. |            |        |--Bearing WNW. ¹⁄₄ W.            |
+  |            |            |        |                                 |
+  |            |            |        |North End of Higher GLENREMISDIL |
+  |            |            |        |FARM-HOUSE in line with Cottage  |
+  |            |            |        |at East End of HETLY HOUSE--     |
+  |            |            |        |Bearing SW. ³⁄₄ S.               |
+  +------------+------------+--------+---------------------------------+
+  |MILLMORE    |Pyramid of  |Beach   |CAMPBELTON NORTH PIER-HEAD--     |
+  |BEACON.     |Iron Spars  |dry at  |Bearing NW. by W.                |
+  |            |with Wire   |Low     |                                 |
+  |            |Ball on top.|water.  |MACRINNAN’S POINT--Bearing ENE.  |
+  |            |            |        |¹⁄₄ N.                           |
+  +------------+------------+--------+---------------------------------+
+  |TRENCH POINT|Pyramid of  |Beach   |CAMPBELTON NORTH PIER-HEAD--     |
+  |BEACON.     |Iron Spars  |dry at  |Bearing NW. by W.                |
+  |            |with Wire   |Low     |                                 |
+  |            |Ball on top.|water.  |OUTER or RED BUOY (above         |
+  |            |            |        |described)--Bearing ESE. ¹⁄₄ E.  |
+  +------------+------------+--------+---------------------------------+
+  |LAPPOCK     |Tower with  |Rock dry|TROON HARBOUR LIGHT--Bearing S.  |
+  |BEACON.     |Stone Ball  |at Low  |by W. ¹⁄₄ W.                     |
+  |            |on top,     |water.  |                                 |
+  |            |painted Red.|        |BEACON on LADY ISLE--Bearing SW. |
+  |            |            |        |¹⁄₂ W.                           |
+  |            |            |        |                                 |
+  |            |            |        |EXTREMITY of ARDROSSAN PIER--    |
+  |            |            |        |Bearing NNW. ¹⁄₄ W.              |
+  +------------+------------+--------+---------------------------------+
+  |BREAST ROCK |Pyramid of  |Rock dry|TURNBERRY POINT--Bearing NE. by  |
+  |BEACON.     |Iron Pil-   |at Low  |N. ¹⁄₈ E.                        |
+  |            |lars, with  |water.  |                                 |
+  |            |cylindric   |        |PLADDA LIGHTHOUSE--Bearing NNW.  |
+  |            |open Cage,  |        |                                 |
+  |            |painted Red.|        |AILSA CRAIG (Highest Point)--    |
+  |            |            |        |Bearing W.                       |
+  +------------+------------+--------+---------------------------------+
+  |LOCH RYAN   |7 Feet Buoy.|3¹⁄₂    |Mr MOORE’S PIGEON-HOUSE in line  |
+  |INNER BUOY. |Red.        |Fathoms.|with Angle of Plantation lying to|
+  |            |            |        | the North of CORSEWALL HOUSE--  |
+  |            |            |        |Bearing N. by W. ³⁄₈ W.          |
+  |            |            |        |                                 |
+  |            |            |        |East End of CAIRN RYAN Hill      |
+  |            |            |        |Quarry, and East End of          |
+  |            |            |        |Plantation, at the foot of the   |
+  |            |            |        |same hill, in line with North    |
+  |            |            |        |Chimney of MRS BEGG’S INN, CAIRN |
+  |            |            |        |RYAN VILLAGE--Bearing NE. ³⁄₄ N. |
+  |            |            |        |                                 |
+  |            |            |        |NORTH END of STRANRAER PIER--    |
+  |            |            |        |Bearing SSW. ¹⁄₄ W.              |
+  +------------+------------+--------+---------------------------------+
+  |BEACON ON   |Cone of Iron|Dry at  |LOCH RYAN LIGHTHOUSE--Bearing    |
+  |THE SPIT OF |Plates,     |Low     |NNE. ¹⁄₄ E.                      |
+  |SCAR POINT, |painted Red.|water.  |                                 |
+  |OFF KIRKCOLM|            |        |LOCHNOLL HOUSES--Bearing SE. by  |
+  |POINT, IN   |            |        |E.                               |
+  |LOCH RYAN.  |            |        |                                 |
+  |            |            |        |STRANRAER PIER END--Bearing SSW. |
+  |            |            |        |¹⁄₂ W.                           |
+  |            |            |        |                                 |
+  |            |            |        |WAUKMILL HOUSES--Bearing SW. by  |
+  |            |            |        |W.                               |
+  |            |            |        |                                 |
+  |            |            |        |CORSEWALL HOUSE in line with THE |
+  |            |            |        |SCAR OFF KIRKCOLM POINT--Bearing |
+  |            |            |        |NNW. ¹⁄₄ N.                      |
+  +------------+------------+--------+---------------------------------+
+  |LOCH RYAN   |7 Feet Buoy,|3¹⁄₂    |PORTINCALLY FARM-HOUSE in line   |
+  |OUTER BUOY. |Black.      |Fathoms.|with the Brow of CLACHAN HEAD--  |
+  |            |            |        |Bearing NNW. ¹⁄₄ W.              |
+  |            |            |        |                                 |
+  |            |            |        |Mr CHARLES M‘DONALD’S HOUSE in   |
+  |            |            |        |line with the South End of       |
+  |            |            |        |GENERAL WALLACE’S PORTER’S LODGE |
+  |            |            |        |--Bearing SE.                    |
+  +------------+------------+--------+---------------------------------+
+  |LAGGAN, OR  |Pyramid of  |Rock dry|CORSEWALL LIGHTHOUSE--Bearing NE.|
+  |EBBSTONE    |IronPillars,|at Low  |by E.                            |
+  |ROCK BEACON.|with        |water.  |                                 |
+  |            |cylindric   |        |AILSA CRAIG (Highest Point)--    |
+  |            |Open Cage on|        |Bearing NE. ³⁄₄ N.               |
+  |            |top, painted|        |                                 |
+  |            |Red.        |        |LAGGAN POINT--Bearing SSE. ¹⁄₂ E.|
+  +------------+------------+--------+---------------------------------+
+
+BEACONS AND BUOYS.
+
+LOCH FYNE DISTRICT.
+
+  +------------+------------+--------+---------------------------------+
+  |            |            |  Depth |                                 |
+  |            |            | at Low |                                 |
+  |            |            |Water of| Magnetic Bearings of Marks and  |
+  |  Name of   | Description| Spring |     Lines of Intersection       |
+  |  Station.  |  of Mark.  | Tides. |    Meeting at the Station.      |
+  +------------+------------+--------+---------------------------------+
+  |OFF         |8 Feet Buoy.|2³⁄₄    |SOUTH-WEST EXTREMITY of WEST and |
+  |ARDLAMONT   |Red.        |Fathoms.|EASTERN HILLS upon ARDLAMONT     |
+  |POINT OR    |            |        |POINT in line with EXTREMITY of  |
+  |BRADEICH    |            |        |POINT--Bearing NW. ³⁄₄ W.        |
+  |ROCKS,      |            |        |                                 |
+  |ARGYLESHIRE,|            |        |HIGHEST PART of BRADEICH ROCKS-- |
+  |BUOY.       |            |        |Bearing NNW. ¹⁄₂ W.              |
+  |            |            |        |                                 |
+  |            |            |        |SOUTH END of INCHMARNOCK ISLAND--|
+  |            |            |        |Bearing S. ¹⁄₂ W.                |
+  |            |            |        |                                 |
+  |            |            |        |EXTREMITY of LAND SOUTH of       |
+  |            |            |        |ARDLAMONT POINT--Bearing N. by W.|
+  |            |            |        |                                 |
+  |            |            |        |The Buoy lies about 115 fathoms  |
+  |            |            |        |distant from High water-mark upon|
+  |            |            |        |the Point, and about 45 fathoms  |
+  |            |            |        |from the highest part of Bradeich|
+  |            |            |        |Rocks.                           |
+  |            |            |        |                                 |
+  |            |            |        |N.B.--_There is a small Rock     |
+  |            |            |        |which dries at Low Spring Tides, |
+  |            |            |        |about 10 or 12 fathoms outside of|
+  |            |            |        |the highest main Rock._          |
+  +------------+------------+--------+---------------------------------+
+  |SKERNA      |7 Feet Buoy.|2¹⁄₂    |SOUTH WING of Sir JOHN ORD’S     |
+  |SCALLAIG    |Red.        |Fathoms.|STABLES in line with NORTH       |
+  |ROCK, OFF   |            |        |EXTREMITY of DUNCHOAN ISLAND--   |
+  |ENTRANCE TO |            |        |Bearing NE. by E.                |
+  |CRINAN      |            |        |                                 |
+  |CANAL,      |            |        |SILVER CRAIG’S POINT, ISLAND     |
+  |ARGYLESHIRE,|            |        |MORE--Bearing SE. by S. ¹⁄₂ E.   |
+  |BUOY.       |            |        |                                 |
+  |            |            |        |WEST WING of ARDRISHAIG HOTEL in |
+  |            |            |        |line with LIGHTHOUSE upon END of |
+  |            |            |        |ARDRISHAIG PIER--Bearing N. ¹⁄₂  |
+  |            |            |        |E.                               |
+  |            |            |        |                                 |
+  |            |            |        |N.B.--_The Buoy lies upon the    |
+  |            |            |        |South-West tail of the Shoal or  |
+  |            |            |        |Rock._                           |
+  +------------+------------+--------+---------------------------------+
+  |OTTER BANK  |Conical Iron|Gravel  |AUCHABOLONABAITH HOUSE (East     |
+  |BEACON,     |Beacon.     |Beach.  |Wing) in line with CENTRE of     |
+  |OFF ENTRANCE|To be       |Dry at  |COTTAGE--Bearing N. by W. ¹⁄₄ W. |
+  |TO LOCH     |painted     |Low     |                                 |
+  |FYNE,       |Black.      |water.  |STRATHLACHLAN HILL in line with  |
+  |ARGYLLSHIRE.|            |        |SCHOOLHOUSE POINT--Bearing ENE.  |
+  |(Building.) |            |        |                                 |
+  |            |            |        |END OF LIATH ISLAND--Bearing W.  |
+  |            |            |        |¹⁄₄ S.                           |
+  +------------+------------+--------+---------------------------------+
+  |WEST OTTER  |Conical Iron|Gravel  |END of MINARD POINT--Bearing SW. |
+  |BEACON,     |Beacon.     |Beach.  |by W. ¹⁄₄ W.                     |
+  |OFF CASTLE  |To be       |Dry at  |                                 |
+  |LACHLAN,    |painted     |Low     |END of CHAPEL ISLAND--Bearing    |
+  |LOCH FYNE,  |Black.      |water.  |ENE. ³⁄₄ E.                      |
+  |ARGYLESHIRE.|            |        |                                 |
+  |(Building.) |            |        |BARNEYCARRY FARMHOUSE in line    |
+  |            |            |        |with NORTH-EAST END of HUGH      |
+  |            |            |        |ISLAND--Bearing SE. ¹⁄₄ E.       |
+  +------------+------------+--------+---------------------------------+
+
+BEACONS AND BUOYS.
+
+OBAN BAY, ARGYLESHIRE.
+
+  +------------+------------+--------+---------------------------------+
+  |            |            |  Depth |                                 |
+  |            |            | at Low |                                 |
+  |            |            |Water of| Magnetic Bearings of Marks and  |
+  |  Name of   | Description| Spring |     Lines of Intersection       |
+  |  Station.  |  of Mark.  | Tides. |    Meeting at the Station.      |
+  +------------+------------+--------+---------------------------------+
+  |SKERRAT     |10 Feet     |Dry at  |CENTRE of OBAN FREE CHURCH WINDOW|
+  |ROCK.       |Buoy, with  |Low-    |in line with NORTH-EASTERN       |
+  |S. W. End.  |Fenders.    |water of|CHIMNEY of FREEMASON’S HALL--    |
+  |            |RED.        |Spring  |Bearing SE. by E.                |
+  |            |            |Tides.  |                                 |
+  |            |            |        |CENTRE OF SKERRY DHU or BLACK    |
+  |            |            |        |ROCK (apparently in middle of    |
+  |            |            |        |Sound of Kerrera) in line with   |
+  |            |            |        |ARDINCAPLE POINT--Bearing WSW.   |
+  |            |            |        |                                 |
+  |            |            |        |BUOY on NORTH-EASTERN END of     |
+  |            |            |        |SKERRAT SHOAL--Bearing NE. ¹⁄₂ E.|
+  |            |            |        |distant 105 fathoms.             |
+  +------------+------------+--------+---------------------------------+
+  |SKERRAT     |6 Feet Buoy.|12 Feet |OBAN FREE CHURCH STEEPLE in line |
+  |SHOAL,      |Chequered   |at Low  |with SOUTH CHIMNEY TOP of SPRING |
+  |N. E. End.  |Black and   |water of|WELL COTTAGE--Bearing SE.        |
+  |            |White.      |Spring  |                                 |
+  |            |            |Tides.  |ARDINCAPLE POINT, a little West  |
+  |            |            |        |of the Western End of SKERRY DHU |
+  |            |            |        |or BLACK ROCK--Bearing WSW.      |
+  |            |            |        |                                 |
+  |            |            |        |BUOY ON SKERRAT ROCK--Bearing SW.|
+  |            |            |        |¹⁄₂ W. distant 105 fathoms.      |
+  |            |            |        |                                 |
+  |N.B.--_No Vessel should attempt to pass between those Buoys._       |
+  +------------+------------+--------+---------------------------------+
+
+BEACONS AND BUOYS.
+
+LINNHE LOCH DISTRICT, ARGYLESHIRE.
+
+  +------------+------------+--------+---------------------------------+
+  |            |            |  Depth |                                 |
+  |            |            | at Low |                                 |
+  |            |            |Water of| Magnetic Bearings of Marks and  |
+  |  Name of   | Description| Spring |     Lines of Intersection       |
+  |  Station.  |  of Mark.  | Tides. |    Meeting at the Station.      |
+  +------------+------------+--------+---------------------------------+
+  |CULCHENNA   |10 Feet Mast|4       |WEST END of ARDGOUR HOUSE in line|
+  |SPIT BUOY.  |Buoy, with  |Fathoms.|with EAST END of HUGH BOYD’S     |
+  |            |Red Ball.   |        |COTTAGE--Bearing N. ⁷⁄₈ E.       |
+  |            |            |        |                                 |
+  |            |            |        |JOHN CAMERON’S COTTAGE in line   |
+  |            |            |        |with END of CULCHENNA POINT--    |
+  |            |            |        |Bearing NE. ³⁄₄ E.               |
+  |            |            |        |                                 |
+  |            |            |        |SALLACHAN POINT--Bearing NNW. ¹⁄₄|
+  |            |            |        |W.                               |
+  |            |            |        |                                 |
+  |            |            |        |CHLAVOULIN SPIT BUOY--Bearing N. |
+  |            |            |        |³⁄₄ E.                           |
+  +------------+------------+--------+---------------------------------+
+  |CHLAVOULIN  |7 Feet Buoy.|2       |CENTRE of ARDGOUR HOUSE in line  |
+  |SPIT BUOY.  |Black.      |Fathoms.|with CENTRE of HUGH BOYD’S       |
+  |            |            |        |COTTAGE--Bearing N. by E.        |
+  |            |            |        |                                 |
+  |            |            |        |EAST END of SECOND WOOD from     |
+  |            |            |        |CORRAN POINT in line with BARN at|
+  |            |            |        |EAST END of HUGH CAMPBELL’S      |
+  |            |            |        |COTTAGE (Eastern House in Village|
+  |            |            |        |of Chlavoulin)--Bearing NE. ³⁄₄  |
+  |            |            |        |E.                               |
+  |            |            |        |                                 |
+  |            |            |        |CORRAN FLAT BUOY--Bearing ENE.   |
+  |            |            |        |³⁄₄ E.                           |
+  |            |            |        |                                 |
+  |            |            |        |END OF SALLACHAN POINT--Bearing  |
+  |            |            |        |W.                               |
+  +------------+------------+--------+---------------------------------+
+  |CORRAN FLAT |6 Feet Buoy.|3³⁄₄    |WEST END of BROW of SALLACHAN    |
+  |BUOY.       |Black.      |Fathoms.|HILL covered with Wood in line   |
+  |            |            |        |with DONALD M‘LEAN’S HOUSE--     |
+  |            |            |        |Bearing NW. by W. ¹⁄₄ W.         |
+  |            |            |        |                                 |
+  |            |            |        |WEST CHIMNEY-STACK of SOUTH      |
+  |            |            |        |CORRAN FERRY HOUSE in line with  |
+  |            |            |        |WHITE PART of ROCK near HIGH     |
+  |            |            |        |WATER MARK at the END of a DYKE--|
+  |            |            |        |Bearing E. ³⁄₄ N.                |
+  |            |            |        |                                 |
+  |            |            |        |SOUTH BROW of STRONCRIGAN HILL in|
+  |            |            |        |line with END of CORRAN CLIFF--  |
+  |            |            |        |Bearing NE. by E. ¹⁄₈ E.         |
+  +------------+------------+--------+---------------------------------+
+  |CORRAN BANK,|6 Feet Buoy.|2³⁄₄    |BUNRIE POINT in line with HIGH   |
+  |NORTH-WEST  |Chequered   |Fathoms.|WATER MARK on CORRAN POINT--     |
+  |END, BUOY.  |Black and   |        |Bearing S. by W. ¹⁄₂ W.          |
+  |            |White.      |        |                                 |
+  |            |            |        |BELFRY of CORRAN CHURCH--Bearing |
+  |            |            |        |W. by N.                         |
+  +------------+------------+--------+---------------------------------+
+  |CORRAN BANK,|6 Feet Buoy.|3¹⁄₂    |CULCHENNA POINT and KINTALLON    |
+  |SOUTH-EAST  |Black.      |Fathoms.|POINT, in line with END of CLIFF |
+  |END, BUOY.  |            |        |of CORRAN POINT--Bearing SW. by  |
+  |            |            |        |S. ¹⁄₈ W.                        |
+  |            |            |        |                                 |
+  |            |            |        |BELFRY of CORRAN CHURCH--Bearing |
+  |            |            |        |NW. by W. ⁵⁄₈ W.                 |
+  |            |            |        |                                 |
+  |            |            |        |SOUTH KEIL FARMHOUSE, in line    |
+  |            |            |        |with ARCH OF BRIDGE ON ROAD--    |
+  |            |            |        |Bearing NNW.                     |
+  |            |            |        |                                 |
+  |            |            |        |CORRAN BANK NORTH BUOY--Bearing  |
+  |            |            |        |NNW.                             |
+  +------------+------------+--------+---------------------------------+
+  |LOCHYFLAT   |6 Feet Buoy.|2³⁄₄    |SOUTH END of WOOD at STRONCRIGAN |
+  |EAST BUOY.  |Red.        |Fathoms.|POINT, just clear of CAMBUSNAGAUL|
+  |            |            |        |POINT--Bearing SW. by W. ³⁄₄ W.  |
+  |            |            |        |                                 |
+  |            |            |        |EAST END of DONALD CAMERON’S     |
+  |            |            |        |HOUSE in CORPACH, in line with   |
+  |            |            |        |NORTH END of OLD ENGINE HOUSE--  |
+  |            |            |        |Bearing N. by W. ¹⁄₄ W.          |
+  |            |            |        |                                 |
+  |            |            |        |SOUTH END of FREE CHURCH in line |
+  |            |            |        |with NORTH END of GREYHOUSE, or  |
+  |            |            |        |OLD CORPACH HOUSE--Bearing N. ⁷⁄₈|
+  |            |            |        |E.                               |
+  |            |            |        |                                 |
+  |            |            |        |ENTRANCE of CALEDONIAN CANAL--   |
+  |            |            |        |Bearing N. by W. ¹⁄₂ W.          |
+  +------------+------------+--------+---------------------------------+
+  |LOCHYFLAT   |6 Feet Buoy.|3¹⁄₂    |EAST END of HENDERSON’S HOUSE or |
+  |MIDDLE BUOY.|Red.        |Fathoms.|CROFT in line with EAST END of   |
+  |            |            |        |SCHOOLHOUSE near CAMBUSNAGAUL    |
+  |            |            |        |POINT--Bearing W. ¹⁄₂ S.         |
+  |            |            |        |                                 |
+  |            |            |        |FISH-HOUSE in line with END of   |
+  |            |            |        |DEARG POINT--Bearing N. by W. ³⁄₄|
+  |            |            |        |W.                               |
+  |            |            |        |                                 |
+  |            |            |        |ENTRANCE of CALEDONIAN CANAL--   |
+  |            |            |        |Bearing N.                       |
+  |            |            |        |                                 |
+  |            |            |        |NORTH END of WOOD at BANAVIE at  |
+  |            |            |        |SOUTH SIDE of CANAL in line with |
+  |            |            |        |CLUMP of TREES at EAST END of    |
+  |            |            |        |JOHN CAMERON’S COTTAGE in        |
+  |            |            |        |KILCORPACH--Bearing NE. by E. ¹⁄₄|
+  |            |            |        |E.                               |
+  |            |            |        |                                 |
+  |            |            |        |BUOY on EAST END of LOCHYFLAT--  |
+  |            |            |        |Bearing NE. ³⁄₄ N.               |
+  |            |            |        |                                 |
+  |            |            |        |M‘LEAN’S ROCK BUOY--Bearing NW.  |
+  |            |            |        |by N.                            |
+  +------------+------------+--------+---------------------------------+
+  |LOCHYFLAT   |6 Feet Buoy.|3       |CAMERON’S MONUMENT in line with  |
+  |WEST BUOY.  |Red.        |Fathoms.|END of DEARG POINT--Bearing N.   |
+  |            |            |        |¹⁄₄ E.                           |
+  |            |            |        |                                 |
+  |            |            |        |NORTH or STEEP FACE of DONNAY    |
+  |            |            |        |HILL in line with SOUTH WING of  |
+  |            |            |        |OLD CASTLE of INVERLOCHY--Bearing|
+  |            |            |        |E. ³⁄₈ S.                        |
+  |            |            |        |                                 |
+  |            |            |        |LOCHYFLAT MIDDLE BUOY--Bearing   |
+  |            |            |        |NE.                              |
+  |            |            |        |                                 |
+  |            |            |        |M‘LEAN’S ROCK BUOY--Bearing N. by|
+  |            |            |        |E. ¹⁄₄ E.                        |
+  |            |            |        |                                 |
+  |            |            |        |FORT-WILLIAM PIER--Bearing SSW.  |
+  |            |            |        |¹⁄₈ W.                           |
+  +------------+------------+--------+---------------------------------+
+  |MACLEAN’S   |6 Feet Buoy.|3³⁄₄    |OLD ENGINE-HOUSE in line with    |
+  |ROCK,       |Black.      |Fathoms.|HIGH WATER MARK on SOUTH END of  |
+  |LOCHEILHEAD,|            |        |ISLAND CREIAH--Bearing N. by E.  |
+  |BUOY.       |            |        |¹⁄₈ E.                           |
+  |            |            |        |                                 |
+  |            |            |        |NORTH BROW of DONNAY HILL in line|
+  |            |            |        |with ALAN KENNEDY’S BARN,        |
+  |            |            |        |SOUTHMOST HOUSE in KILCORPACH--  |
+  |            |            |        |Bearing E. ³⁄₄ S.                |
+  |            |            |        |                                 |
+  |            |            |        |LOCHYFLAT WEST BUOY--Bearing S.  |
+  |            |            |        |by W. ¹⁄₄ W.                     |
+  |            |            |        |                                 |
+  |            |            |        |FORT-WILLIAM PIER--Bearing S. by |
+  |            |            |        |W. ³⁄₄ W.                        |
+  +------------+------------+--------+---------------------------------+
+  |NEW ROCK,   |6 Feet Buoy.|3       |CAMERON’S MONUMENT in line with  |
+  |LOCHEILHEAD,|Chequered   |Fathoms.|END of DEARG POINT--Bearing N.   |
+  |BUOY.       |Black and   |        |¹⁄₄ E.                           |
+  |            |White.      |        |NORTH END of FREE CHURCH in line |
+  |            |            |        |with HIGH WATER MARK on EAST END |
+  |            |            |        |of ISLAND CREIAH--Bearing NE. ³⁄₄|
+  |            |            |        |N.                               |
+  |            |            |        |                                 |
+  |            |            |        |CENTRE of DONNAY HILL in line    |
+  |            |            |        |with ALAN KENNEDY’S BARN--Bearing|
+  |            |            |        |E. ⁷⁄₈ S.                        |
+  |            |            |        |                                 |
+  |            |            |        |N.B.--_Depth at Low Water of     |
+  |            |            |        |Spring Tides on Rock is 8 feet.  |
+  |            |            |        |The Buoy, moored in 3 fathoms,   |
+  |            |            |        |swings clear of the Rock on west |
+  |            |            |        |side of it._                     |
+  +------------+------------+--------+---------------------------------+
+
+  _By order of the Board_,
+
+  ALAN STEVENSON, _Engineer_.
+
+  _Edinburgh_, _1st January 1848_.
+
+NOTICE TO MARINERS.
+
+THE COMMISSIONERS OF NORTHERN LIGHTHOUSES _have resolved to publish, on
+1st January annually, for the use of Mariners, a Descriptive List of
+all the Lighthouses, Beacons, and Buoys under their charge, giving the
+characteristic appearance and correct bearings of each._
+
+MARINERS _are particularly requested to notice, that they should_ NEVER
+PURCHASE _any List_ EXCEPT THAT FOR THE YEAR CURRENT _at the time of
+purchase. As changes may have taken place, no reliance can be placed on
+any List which has been published for a preceding year._
+
+PUBLISHERS _are particularly cautioned not to sell any List which has
+been published on a preceding year. Arrangements have been made with
+the Publishers of the Board, that all copies remaining on hand with
+any Publisher, at the close of any year, will be exchanged for the New
+Issue; and all Publishers are_ MOST PARTICULARLY REQUESTED _not to
+retain on hand any copies of a past issue._
+
+  _By Order of the Board_,
+
+  ALEX. CUNINGHAM, _Secretary_.
+
+  NORTHERN LIGHTS OFFICE,        }
+  EDINBURGH, _1st January 1848_. }
+
+
+APPENDIX, No. IX.
+
+REPORT TO THE COMMISSIONERS OF NORTHERN LIGHTHOUSES, FOR THE YEAR 1846;
+WITH APPENDICES. BY ALEXANDER CUNINGHAM, W.S., SECRETARY TO THE BOARD.
+
+The gross amount of DUTIES received from Shipping in the year to 31st
+December 1846, as per detailed State appended hereto (No. I., p. 429),
+is £46,001 : 11 : 2⁶⁄₈.
+
+The COMMISSION paid to Collectors in the same period is £2401 : 7 :
+3⁴⁄₈, and Repayments of Duties erroneously charged, &c., £218 : 16 :
+10²⁄₈, making the nett amount of Duties for the year £43,381 : 7 : 1,
+as also appears from State, No. I., p. 429.
+
+  The nett amount of Duties in the year 1845 was           £52,391  8  4
+  While that received in 1846 is                            43,381  7  1
+                                                           -------------
+    Making a DEFICIENCY in the year of                      £9,010  1  3
+
+  Whereof--
+
+    Half-year to 30th June,                    £2350  9  1
+    Ditto to 31st December,                     6659 12  2
+                                               -----------   £9,010 1  3
+                                               =========================
+
+It is to be observed, however, that during the currency of this year,
+two reductions in the amount of Light-duties, resolved upon by the
+BOARD, have come into operation.
+
+1. The first of these reductions was one halfpenny per ton (or one-half
+of the amount leviable by Statute) for the Bell Rock Light; one
+farthing per ton (or one-half of the amount leviable) for each of the
+Lights of Corsewell and Mull of Galloway; and one-eighth of a penny
+per ton (or one-fourth of the amount leviable) for Pladda Light. These
+reductions were in operation during the first half of the year 1846.
+They were estimated to produce a deficiency in the annual Revenue of
+£5160, which, for the half-year, gives £2580. The actual deficiency in
+the amount levied for the first half of 1846, over that levied in the
+corresponding period of the preceding year, was £2350 : 9 : 1, being
+still £230 under the estimated amount.
+
+2. The BOARD came to the resolution of making such a further reduction
+as should, including the previous one, give an aggregate abatement
+to the Coasting Trade, for each of the Lighthouses, of 50 per cent.,
+that is, the amount leviable for each of the Lights being, previous
+to the first reduction, one halfpenny per ton, was reduced for the
+Coasting Trade to one farthing per ton; the amount for the Bell Rock
+and Skerryvore Lights, being one penny, was reduced to one halfpenny
+per ton. This reduction commenced on the 1st day of July 1846, and
+has consequently been in operation during the last half of that year.
+It was estimated to produce a deficiency in the annual revenue of the
+Board of £14,394 : 14 : 5, which, for the half-year, gives £7197 : 9 :
+2. The actual deficiency in the amount levied for the last half of
+1846, over that levied in the corresponding period of the preceding
+year, was £6659 : 12 : 2, being £540 under the estimated amount.
+
+  It is also proper to observe, that while there is the above
+  deficiency in Receipts of the year 1846, as contrasted with
+  1845, of                                                   £9010  1  3
+
+  There was a surplus Receipt of the year 1845, as
+  contrasted with 1844, amounting to                          6612 17  8
+                                                             -----------
+  Making the DEFICIENCY in 1846, as contrasted with the
+  RECEIPTS of 1844, upon which the calculations of the Board
+  were founded, only                                         £2397  3  7
+                                                             ===========
+
+On the other hand, the greater reduction having been in operation only
+during half the year, a greater deficiency in the Revenue must be
+looked for in future years.
+
+The Light-Duties in 1845 were contributed by 163,174 vessels in
+the Coasting Trade, giving an aggregate tonnage of 15,566,461, and
+by 45,612 vessels in Oversea Trade, giving an aggregate tonnage of
+9,300,983.
+
+The Light-Duties in 1846 have been contributed by 163,166 vessels in
+the Coasting Trade, giving an aggregate tonnage of 15,926,634, and by
+50,324 vessels in the Oversea Trade, giving an aggregate tonnage of
+9,577,478.
+
+A contrast of these statements shews an increase in the Coasting Trade
+of 1846 in tonnage of 360,173, with eight fewer vessels; and in the
+Oversea Trade an increase of 4712 vessels, with a tonnage of 276,495.
+
+These results (somewhat singular in their relative amounts) establish
+the important fact, that, though there is a deficiency in the revenue
+of the Board, it truly arises from the reductions in the Duties, and
+not from any reduction in the Shipping.
+
+For the information of the Board, there will be found appended (p. 433)
+a statement shewing the progressive increase of tonnage during the last
+four years.
+
+  The amount of Duties received in the year 1846, as
+  above, is                                             £46,001 11  2⁶⁄₈
+  While the Ordinary Expenditure of the Board has been   32,063  6  3
+                                                        ----------------
+    Giving a Surplus Receipt for the year to meet
+    Extraordinary Expenditure of (see State, No. II.,
+    p. 432)                                             £13,938  4 11⁶⁄₈
+                                                        ================
+  But the total Expenditure of the Board in the Year
+  has been                                              £60,374 15  9²⁄₈
+  From which if there be deducted the Gross Receipts,
+  per page 425,                                          47,895  8  8⁶⁄₈
+                                                        ----------------
+    It gives a Balance superexpended beyond the surplus
+    of the year of                                      £12,479  7  0⁴⁄₈
+
+  The Balance on hand at 31st March 1846
+  was                                  £42,069  6 10
+  While that on hand at 31st March 1847
+  is                                    29,589 19  9⁴⁄₈
+                                       ----------------
+    Difference equal to superexpenditure,               £12,479  7  0⁴⁄₈
+                                                        ================
+
+There has been expended on the various Works in progress, prior to the
+year 1846 and in that year, as follows:--
+
+  +----------------------+-------------+--------------+----------------+
+  |                      |    Prior    |              |                |
+  |                      |  to 1846.   |   In 1846.   |     TOTAL.     |
+  +----------------------+-------------+--------------+----------------+
+  |Skerryvore Lighthouse |             |              |                |
+  |Works                 |£93,576 10  0| £227  8  2   |£93,803 18  2   |
+  |  Add Bo-Pheg Beacon  |    416 10  7|   25 10  1   |    442  0  8   |
+  |                      +-------------+--------------+----------------+
+  |                      |£93,993  0  7| £252 18  3   |£94,245 18 10   |
+  |Covesea Lighthouse    |             |              |                |
+  |Works                 |  9,523 17  6|1,109  5  4   | 10,633  2 10   |
+  |Cromarty Ditto        |  2,895 18  8|  342  9  3   |  3,238  7 11   |
+  |Chanonry Ditto        |  2,832 16  1|  405  7  8   |  3,238  3  9   |
+  |Ardnamurchan Ditto    |    296  2  2|2,343 17  6   |  2,639 19  8   |
+  |Laggan Spur Beacon    |   ...   ... |  748 10  6   |    748 10  6   |
+  |Island Glass New      |             |              |                |
+  |Buildings and         |             |              |                |
+  |Inclosures            |  3,064 15  3|1,797  3  5¹⁄₂|  4,861 18  8¹⁄₂|
+  |Nosshead Lighthouse   |             |              |                |
+  |Works                 |   ...   ... |1,467  6  1   |  1,467  6  1   |
+  |Loch Ryan Ditto       |   ...   ... |  829 12  9¹⁄₂|    829 12  9¹⁄₂|
+  |Pentland Skerries New |             |              |                |
+  |Works                 |   ...   ... |3,135 17  5¹⁄₂|  3,135 17  5¹⁄₂|
+  |Ditto Dioptric Light  |   ...   ... |2,037 11  4   |  2,037 11  4   |
+  |Renewal of Fixed      |             |              |                |
+  |Lights                |   ...   ... |3,035 14  4   |  3,035 14  4   |
+  |Buoys, &c.            |   ...   ... |1,549 14 11¹⁄₂|  1,549 14 11¹⁄₂|
+  |Campbeltown Beacons   |   ...   ... |   17  4 10   |     17  4 10   |
+  |Lappock Beacon        |   ...   ... |    8 12  5   |      8 12  5   |
+  |Startpoint New Works  |   ...   ... |    5 19  4   |      5 19  4   |
+  |Elie or Vows Beacon   |   ...   ... |  205  5  8   |    205  5  8   |
+  |Whiteness Beacon      |   ...   ... |  152  5  8   |    152  5  8   |
+  |Longman’s Point Ditto |   ...   ... |  164 15  6   |    164 15  6   |
+  |Loch Ryan Ditto       |   ...   ... |  152  5  9   |    152  5  9   |
+  |Brist Beacon          |    734  2  9|    8 12  5   |    742 15  2   |
+  |Mull of Kintyre Dykes |             |              |                |
+  |and Road              |    586 14  4|  647 17  9   |  1,234 12  1   |
+  +----------------------+-------------+--------------+----------------+
+
+There has been expended on the new Steamer “Pharos,” £18,977 : 6 : 7.
+
+The COMMISSIONERS have purchased a House at Crail for £105 : 19 : 4 for
+the use of the Boatmen attending at the Isle of May.
+
+The attention of the COMMISSIONERS is called to the circumstance that
+a complete change has been made this year in the mode of stating the
+Accounts. The Accounts are now, for the first time, concentrated in the
+Secretary’s department, and for every item entered in the subjoined
+abstract, reference is now, and will hereafter, be made to a page of
+the Ledger containing a detailed account vouching the charge. Following
+out this arrangement, the account has been branched into three heads
+or divisions. The first head comprises the _ordinary_ expenses of
+the Lighthouses. In this branch it has been thought right to state
+separately, under the head of the Isle of May, the interest on the
+debt to Government, being the balance of the price of the Island.
+The second head comprises the ordinary expenses of the Board, not in
+the first instance chargeable against any particular Lighthouse, but
+falling to be afterwards allocated in the final view of the Receipt and
+Expenditure of each Lighthouse. This branch is again subdivided so as
+to shew--
+
+  1. The Expense of Collection.
+
+  2. Repayments, &c. of Light-Duties overcharged.
+
+  3. The Expense of the Establishment, including Salaries, Stationery,
+  &c.
+
+  4. The Shipping Establishment.
+
+  5. Beacons and Buoys--ordinary maintenance.
+
+  6. The Storehouse, Leith.
+
+  7. Charities and Superannuations.
+
+  8. Miscellaneous Payments.
+
+The last division of the abstract comprises what is termed the
+_extraordinary_ expenditure, that is, the expense of New Works and
+others not falling to be allocated upon the Lighthouses.
+
+       *       *       *       *       *
+
+In effecting this change, various payments which appeared in the former
+abstracts will not now be found in the present, such as Rents and
+Feu-duties, which are now charged to the respective Lighthouses for
+which they are paid; the Storekeeper’s Salary, which is stated in the
+Storehouse Account; the Office-Keeper’s, in the Office Account, &c.,
+and the Salaries of the Officers of the Board will be found under the
+head of Edinburgh Establishment.
+
+ABSTRACT _of the_ RECEIPTS _and_ PAYMENTS _on Account of the_ DUTIES
+_levied for the_ NORTHERN LIGHTHOUSES _for the year 1846._
+
+  +--------------------------------------------------------------------+
+  |                             RECEIPTS.                              |
+  |                                                   +----------------+
+  |I. GROSS AMOUNT of the Duties received for 1846,   |                |
+  |   per State, No. I. p. 429,                       |£46,001 11  2⁶⁄₈|
+  |                                                   |                |
+  |   Which has been received in the following        |                |
+  |   proportions for each Lighthouse, as appears from|                |
+  |   State, No. II., pp. 430-3, viz.:--              |                |
+  |                                  +----------------+                |
+  |        1. Inchkeith,             |  £2524  9  2²⁄₈|                |
+  |        2. Isle of May,           |   3825  8  5⁴⁄₈|                |
+  |        3. Bell Rock,             |   5342 15  5⁴⁄₈|                |
+  |        4. Girdleness,            |   2458  4  5⁴⁄₈|                |
+  |        5. Buchanness,            |   1880  1  3⁴⁄₈|                |
+  |        6. Kinnairdshead,         |   1744 11  3⁴⁄₈|                |
+  |        7. Tarbetness,            |    329 17  4⁶⁄₈|                |
+  |        8. Sumburghhead,          |    286 18  2⁶⁄₈|                |
+  |        9. Startpoint,            |   1154  5  4²⁄₈|                |
+  |       10. Pentland Skerries,     |   1370 10  5⁶⁄₈|                |
+  |       11. Dunnethead,            |   1311  1 10²⁄₈|                |
+  |       12. Capewrath,             |   1278  9  9   |                |
+  |       13. Island Glass,          |    679  1 10⁶⁄₈|                |
+  |       14. Barrahead,             |   1063  3  2⁶⁄₈|                |
+  |       15. Skerryvore,            |   2090 11  3⁴⁄₈|                |
+  |       16. Lismore,               |    239 11  4   |                |
+  |       17. Rhinns of Islay,       |   1414  5  8⁶⁄₈|                |
+  |       18. Mull of Kintyre,       |   1549  0  1   |                |
+  |       19. Pladda,                |   2762 14  3⁷⁄₈|                |
+  |       20. Corsewall,             |   2811  5  3⁶⁄₈|                |
+  |       21. Mull of Galloway,      |   2823 19  8⁶⁄₈|                |
+  |       22. Little Ross,           |   1187  7  9⁴⁄₈|                |
+  |       23. Point of Ayre,         |   1755 17  5⁴⁄₈|                |
+  |       24. Calf of Man (two       |                |                |
+  |           Lights),               |   3839  2 11²⁄₈|                |
+  |       25. Covesea Skerries,      |    193  7  0   |                |
+  |       26. Cromarty,              |     27 14 11   |                |
+  |       27. Chanonry,              |     57 15  1   |                |
+  |                                  +----------------+                |
+  |                                  |£46,001 11  3⁷⁄₈|                |
+  |       DEDUCT fractions short     |                |                |
+  |       credited by Bankers,       |      0  0  1¹⁄₈|                |
+  |                                  +----------------+                |
+  |                         As above,|£46,001 11  2⁶⁄₈|                |
+  |                                  +================+                |
+  |                                  |                |                |
+  |II. MISCELLANEOUS RECEIPTS--      |                |                |
+  |                                  |                |                |
+  +-------+                          |                |                |
+  | Folio |                          |                |                |
+  |   in  |                          |                |                |
+  |Ledger.|                          |                |                |
+  +-------+                          |                |                |
+  |32 & 73|Rent of Stable behind the |                |                |
+  |       |Office,                   |    £18  0  0   |                |
+  |  73   |Do. of Small Houses at    |                |                |
+  |       |Arbroath,                 |      5  5  0   |                |
+  |  33   |Proceeds sale of Regent   |                |                |
+  |       |Tender,                   |    485 14  3   |                |
+  |  32   |Composition of 1s. 6d. per|                |                |
+  |       |pound from the Trustee on |                |                |
+  |       |Andrew Greig’s Bankrupt   |                |                |
+  |       |Estate, on a claim of     |                |                |
+  |       |£340, 11s. 8d. and        |                |                |
+  |       |Expenses arising from an  |                |                |
+  |       |evasion of Light-dues,    |     27  0  9   |                |
+  |  30   |Price of Lighter sold to  |                |                |
+  |       |Kirkcaldy Harbour         |                |                |
+  |       |Commissioners,            |     60  0  0   |                |
+  |  74   |Do. do. to Leith Shipping |                |                |
+  |       |Company,                  |     45  0  0   |                |
+  |  40   |Do. of Horse sold at      |                |                |
+  |       |Barrahead,                |     10  0  0   |                |
+  |  ...  |Do. of an Ass sold at     |                |                |
+  |       |Inchkeith,                |      0  9  6   |                |
+  |  149  |Do. of Articles sold at   |                |                |
+  |       |Skerryvore,               |    126  5 10   |                |
+  | 73,75,|Fines imposed on Light-   |                |                |
+  | & 315 |keepers, received,        |     13  1  8   |                |
+  |   74  |Sum received from the     |                |                |
+  |       |General Post-Office, for  |                |                |
+  |       |the maintenance of the    |                |                |
+  |       |Harbour Light at          |                |                |
+  |       |Portpatrick for the year  |                |                |
+  |       |1845,                     |    136 10  9   |                |
+  |40 & 75|Interest received from    |                |                |
+  |       |the Royal Bank on money   |                |                |
+  |       |deposited,                |    966  9  9   |                |
+  |       |                          |                |                |
+  |       |                     SUM, +----------------+   1893 17  6   |
+  |       |                                           +----------------+
+  |       |             SUMS OF RECEIPTS carried to   |                |
+  |       |                     ABSTRACT, page 425,   |£47,895  8  8⁶⁄₈|
+  |       |                          =================+================+
+  |       |                                                            |
+  +-------+------------------------------------------------------------+
+  |                              PAYMENTS.                             |
+  +-------+------------------------------------------------------------+
+  | Folio |   BRANCH I.--ORDINARY EXPENSES of the BOARD, being the     |
+  |   in  |      Maintenance of the Lights for the year, viz:--        |
+  |Ledger.|                                                            |
+  +-------+                                           +----------------+
+  |       |1. LIGHTHOUSES--                           |                |
+  |  326  |   1. Inchkeith,                           |   £583  5 10¹⁄₂|
+  |       |                          +----------------+                |
+  |  327  |   2. Isle of May,        |   £702  3  9   |                |
+  |       |      Isle of May, Year’s |                |                |
+  |       |      Interest to         |                |                |
+  |       |      Government,         |    250  0  0   |                |
+  |       |                          +----------------+    952  3  9   |
+  |  355  |   3. Bell Rock,                           |    989  1  3¹⁄₄|
+  |  329  |   4. Girdleness,                          |    548 18  1   |
+  |  330  |   5. Buchanness,                          |    623  5  3   |
+  |  331  |   6. Kinnairdshead,                       |    578 10  0¹⁄₂|
+  |  332  |   7. Tarbetness,                          |    574 11 11   |
+  |  333  |   8. Sumburghhead,                        |    597  5  3³⁄₄|
+  |  334  |   9. Startpoint,                          |    347  0  8   |
+  |  335  |  10. Pentland Skerries (two Lights),      |    851  8 11   |
+  |  336  |  11. Dunnethead,                          |    470 19  7¹⁄₂|
+  |  337  |  12. Capewrath,                           |    587  6 11¹⁄₄|
+  |  338  |  13. Island Glass,                        |    515  2 10¹⁄₄|
+  |  339  |  14. Barrahead,                           |    594  3 10¹⁄₂|
+  |  357  |  15. Skerryvore,                          |   1122  0  7   |
+  |  340  |  16. Lismore,                             |    515 14  2¹⁄₄|
+  |  341  |  17. Rhinns of Islay,                     |    569 12  7³⁄₄|
+  |  342  |  18. Mull of Kintyre,                     |    554 17 10¹⁄₂|
+  |  343  |  19. Pladda,                              |    584 10 10   |
+  |  344  |  20. Corsewall,                           |    465 13  4   |
+  |  345  |  21. Mull of Galloway,                    |    517  0  5¹⁄₂|
+  |  346  |  22. Little Ross,                         |    516 18  6¹⁄₄|
+  |  347  |  23. Point of Ayre,                       |    409  1  4¹⁄₂|
+  |       |                          +----------------+                |
+  |  348  |  24. Calf of Man (High   |                |                |
+  |       |      Tower),             |   £394  4  7   |                |
+  |  354  |  25. Calf of Man (Low    |                |                |
+  |       |      Tower),             |    419 14 10   |                |
+  |       |                          +----------------+    813 19  5   |
+  |  351  |  26. Covesea Skerries,                    |    419 16  8¹⁄₂|
+  |  358  |  27. Cromarty,                            |    339 17  3   |
+  |  353  |  28. Chanonry,                            |    284  7  1   |
+  |  350  |  29. Loch Ryan,                           |    176  5  7   |
+  |       |                                           +----------------+
+  |       |        SUM,--Carried to ABSTRACT, p. 425, |£16,103  0  2³⁄₄|
+  |       |                         ==================+================+
+  |       |                                                            |
+  |       | BRANCH II.--ORDINARY EXPENSES falling to be allocated upon |
+  |       |                       each Lighthouse--                    |
+  |       |                                                            |
+  |       |1. EXPENSE of COLLECTION--                 +----------------+
+  |       |   To paid Commission to Collectors, per   |                |
+  |       |   State, No. I. p. 429,                   |  £2401  7  3⁴⁄₈|
+  |       |   To paid Commission to Bankers,          |    115  3  7   |
+  |       |                                           +----------------+
+  |       |                                           |  £2516 10 10⁴⁄₈|
+  |       |2. REPAYMENTS, &c., of LIGHT-DUTIES        |                |
+  |       |   OVERCHARGED,                            |    218 16 10²⁄₈|
+  |       |                                           |                |
+  |       |3. ESTABLISHMENT IN EDINBURGH--            |                |
+  |       |                +----------+---------------+                |
+  |       |   Engineer, ³⁄₄|          |               |                |
+  |       |   Salary at    |          |               |                |
+  |       |   £900,        |£675  0  0|               |                |
+  |       |   Engineer, ¹⁄₄|          |               |                |
+  |       |   Salary at    |          |               |                |
+  |       |   £1200,       | 300  0  0|               |                |
+  |       |                +----------+  £975  0  0   |                |
+  |       |   Secretary,              |   500  0  0   |                |
+  |       |   Accountant, Salary to   |               |                |
+  |       |   8th July, when he died, |    84 12  0   |                |
+  |       |                +----------+               |                |
+  |       |   Superinten-  |          |               |                |
+  |       |   dent of      |          |               |                |
+  |       |   Light-       |          |               |                |
+  |       |   keepers, ³⁄₄ |          |               |                |
+  |       |   Salary at    |          |               |                |
+  |       |   £145,        |£108 15  0|               |                |
+  |       |   Superinten-  |          |               |                |
+  |       |   dent of      |          |               |                |
+  |       |   Light-       |          |               |                |
+  |       |   keepers, ³⁄₄ |          |               |                |
+  |       |   Salary at    |          |               |                |
+  |       |   £210,        |  52 10  0|               |                |
+  |       |                +----------+   161  5  0   |                |
+  |       |                           |               |                |
+  |       |                +----------+               |                |
+  |       |   Foreman of   |          |               |                |
+  |       |   Lightroom    |          |               |                |
+  |       |   repairs, ³⁄₄ |          |               |                |
+  |       |   Salary at    |          |               |                |
+  |       |   £110,        | £82 10  0|               |                |
+  |       |   Foreman of   |          |               |                |
+  |       |   Lightroom    |          |               |                |
+  |       |   repairs, ¹⁄₄ |          |               |                |
+  |       |   Salary at    |          |               |                |
+  |       |   £140,        |  35  0  0|               |                |
+  |       |                +----------+   117 10  0   |                |
+  |       |   Engineer’s Clerk, ¹⁄₄   |               |                |
+  |       |   Salary (formerly paid by|               |                |
+  |       |   Engineer),              |    32 10  0   |                |
+  |       |   Examiner of Accounts,   |               |                |
+  |       |   from 8th January to     |               |                |
+  |       |   Candlemas,              |    17  2  6   |                |
+  |       |   First Clerk in          |               |                |
+  |       |   Secretary’s Department, |               |                |
+  |       |   ¹⁄₄ Salary,             |    25  0  0   |                |
+  |       |   Second Clerk in         |               |                |
+  |       |   Secretary’s Department, |               |                |
+  |       |   ¹⁄₄ Salary,             |    25  0  0   |                |
+  |       |   Officer (now conjoined  |               |                |
+  |       |   with  Housekeeper), ¹⁄₄ |               |                |
+  |       |   Salary,                 |    5  0  0    |                |
+  |       |   Payments to two Clerks  |               |                |
+  |       |   in Accountant’s         |               |                |
+  |       |   Department, to cease at |               |                |
+  |       |   Whitsunday in           |               |                |
+  |       |   consequence of the      |               |                |
+  |       |   appointments in         |               |                |
+  |       |   Secretary’s Department, |   174  6  0   |                |
+  |       |   Interim Accountant, per |               |                |
+  |       |   minute of the Board,    |               |                |
+  |       |   until Examiner of       |               |                |
+  |       |   Accounts was appointed, |   105  0  0   |                |
+  |       |   Office, including Porter|               |                |
+  |       |   and House-Servants’     |               |                |
+  |       |   Wages, House Expenses,  |               |                |
+  |       |   Taxes, Books for        |               |                |
+  |       |   Library, &c.,           |   910 10  3¹⁄₂|                |
+  |  279  |                           +---------------+   3132 15  9¹⁄₂|
+  |       |                                           |                |
+  |       |4. SHIPPING ESTABLISHMENT--+---------------+                |
+  |  132  |   Pharos Steam-Vessel,    | £3790  1 11³⁄₄|                |
+  |  133  |   Prince of Wales, Bell   |               |                |
+  |       |   Rock Tender,            |   954 10  2    |               |
+  |  135  |   Francis, Skerryvore     |               |                |
+  |       |   Tender,                 |   920 17  6¹⁄₂|                |
+  |  137  |   Regent Tender (now      |               |                |
+  |       |   sold),                  |   259  3  7   |                |
+  |       |                           +---------------+   5924 13  3³⁄₄|
+  |       |                                           |                |
+  |       |5. BEACONS and BUOYS--Expense of Ordinary  |                |
+  |       |   Maintenance,                            |     91  7  0   |
+  |       |                                           |                |
+  |       |6. STOREHOUSE, LEITH, including            |                |
+  |       |   Storekeeper’s Salary, Taxes, Freight of |                |
+  |       |   Stores, &c., viz:--                     |                |
+  |       |                +----------+---------------+                |
+  |       |   Salary, ³⁄₄, | £40 13  0|               |                |
+  |       |   Salary, ¹⁄₄, |          |               |                |
+  |       |   at £100 per  |          |               |                |
+  |       |   annum,       |  25  0  0|               |                |
+  |       |                +----------+   £65 13  0   |                |
+  |       |   Expenses of House,      |               |                |
+  |       |   Packing Stores, &c.,    |   145  9  7¹⁄₄|                |
+  |  184  |   Freight of Stores,      |   133  4  3¹⁄₂|                |
+  |       |                           +---------------+    344  6 10³⁄₄|
+  |       |                                           |                |
+  |       |7. CHARITIES and SUPERANNUATIONS to RETIRED|                |
+  |       |   SERVANTS of THE BOARD, viz.:--          |                |
+  |       |   1. Prior to the last Act of Parliament--|                |
+  |       |                           +---------------+                |
+  |       |      William Tweedy, one  |               |                |
+  |       |      year’s Annuity,      |   £20  0  0   |                |
+  |       |      Mrs Leask, one year’s|               |                |
+  |       |      Annuity,             |    10  0  0   |                |
+  |       |      Hugh Rose, one year’s|               |                |
+  |       |      Annuity,             |    20  0  0   |                |
+  |       |      Jane Walker, one     |               |                |
+  |       |      year’s Annuity, (died|               |                |
+  |       |      March 13, 1847),     |     6  6  0   |                |
+  |       |      Euphemia Poole, one  |               |                |
+  |       |      year’s Annuity,      |     5  0  0   |                |
+  |       |                           +---------------+     61  6  0   |
+  |       |   2. Since last Act, viz.:+---------------+                |
+  |       |      Robert Stevenson,    |               |                |
+  |       |      Esq., late Engineer, |  £580  0  0   |                |
+  |       |      Matthew Harvie,      |               |                |
+  |       |      Light-keeper,        |    69  7  6   |                |
+  |       |      John Bruce, late     |               |                |
+  |       |      Officer,             |    13  0  0   |                |
+  |       |      George Kirk, Light-  |               |                |
+  |       |      keeper,              |    40  0  0   |                |
+  |       |      John Watt, Light-    |               |                |
+  |       |      keeper (died Dec.    |               |                |
+  |       |      1846),               |    41 12  6   |                |
+  |       |      William Heddle,      |               |                |
+  |       |      Light-keeper,        |    17 15  0   |                |
+  |       |      Robert Selkirk,      |               |                |
+  |       |      Light-keeper (died   |               |                |
+  |       |      Jan. 1847),          |    20 16  4   |                |
+  |       |      Andrew Adamson,      |               |                |
+  |       |      Light-keeper         |    47  0  0   |                |
+  |       |      James Brown jun.,    |               |                |
+  |       |      Light-keeper         |    29 11  8   |                |
+  |       |      William Soutar,      |               |                |
+  |       |      Light-keeper         |    48 10  0   |                |
+  |       |      John Murray, late    |               |                |
+  |       |      Boatman, Isle of May,|    18  6  8   |                |
+  |       |      David Lyall, Light-  |               |                |
+  |       |      keeper,              |    43  0  0   |                |
+  |       |      Thomson Milne, Light-|               |                |
+  |       |      keeper               |    64  1  0   |                |
+  |       |      David Laughton,      |               |                |
+  |       |      Light-keeper         |    47 10  0   |                |
+  |       |      Alexander Burnett,   |               |                |
+  |       |      Light-keeper         |    45  0  0   |                |
+  |       |      James Wallace,       |    34  0  0   |                |
+  |       |      John Miller          |               |                |
+  |       |      (proportion till date|               |                |
+  |       |      of death),           |    11 12  0   |                |
+  |       |      Mrs Duncan, late     |               |                |
+  |       |      Housekeeper,         |               |                |
+  |       |      three-quarters,      |    10 10  0   |                |
+  |       |      John Scott, late     |               |                |
+  |       |      Mate, Prince of      |               |                |
+  |       |      Wales, quarter to    |               |                |
+  |       |      Martinmas last,      |    22 10  8   |                |
+  |       |      C. Cunningham, Esq., |               |                |
+  |       |      late Secretary, from |               |                |
+  |       |      21st December to     |               |                |
+  |       |      Candlemas,           |    45  7  3   |                |
+  |       |                           +---------------+   1249  9 11   |
+  |       |8. MISCELLANEOUS EXPENSES not appropriated |                |
+  |       |   to any Particular Head,                 |   2420 19  5   |
+  |       |           Being--                         |                |
+  |       |                           +---------------+                |
+  |       |    1. For Educating       |               |                |
+  |       |       Expectant Light-    |               |                |
+  |       |       keepers, being their|               |                |
+  |       |       Travelling Charges  |               |                |
+  |       |       and Subsistence,    |   £84 16  0   |                |
+  |       |    2. Travelling Expenses |               |                |
+  |       |       of the Board,       |   128 18 11   |                |
+  |       |    3. Travelling Expenses |               |                |
+  |       |       of Officers on the  |               |                |
+  |       |       Business of the     |               |                |
+  |       |       Board,              |   513  3  9   |                |
+  |       |    4. Half-yearly Dinner  |               |                |
+  |       |       Bills, £69, 5s., and|               |                |
+  |       |       £86 : 2 : 6,        |   155  7  6   |                |
+  |       |    5. Advertising         |               |                |
+  |       |       Reduction of Duties,|    90 10 10   |                |
+  |       |                +----------+---------------+                |
+  |       |    6. Printing |          |               |                |
+  |       |       Expenses,|          |               |                |
+  |       |       viz., New|          |               |                |
+  |       |       Tables,  |          |               |                |
+  |       |       Notices, |          |               |                |
+  |       |       Circu-   |          |               |                |
+  |       |       lars,    |          |               |                |
+  |       |       &c.,     |£173  5  7|               |                |
+  |       |       Printing |          |               |                |
+  |       |       Expenses,|          |               |                |
+  |       |       500 vols.|          |               |                |
+  |       |       Collec-  |          |               |                |
+  |       |       tor’s    |          |               |                |
+  |       |       Receipt  |          |               |                |
+  |       |       Books,   |          |               |                |
+  |       |       &c.,     | 146 19  6|               |                |
+  |       |       Printing |          |               |                |
+  |       |       Expenses,|          |               |                |
+  |       |       Annual   |          |               |                |
+  |       |       List of  |          |               |                |
+  |       |       Light-   |          |               |                |
+  |       |       houses,  |          |               |                |
+  |       |       &c.,     | 207 10 10|               |                |
+  |       |       Printing |          |               |                |
+  |       |       Expenses,|          |               |                |
+  |       |       “Steven- |          |               |                |
+  |       |       son on   |          |               |                |
+  |       |       Lenses,” |          |               |                |
+  |       |       and      |          |               |                |
+  |       |       Expenses |          |               |                |
+  |       |       connected|          |               |                |
+  |       |       with     |          |               |                |
+  |       |       Lenses,  |  31  1  5|               |                |
+  |       |                +----------+   558 17  4   |                |
+  |       |    7. Making Oil Casks,   |               |                |
+  |       |       and Cooperage of old|               |                |
+  |       |       do.                 |   145 11  2   |                |
+  |       |    8. Postages and        |               |                |
+  |       |       Carriage of Parcels,|   120 18 10   |                |
+  |       |    9. Messrs Cuningham and|               |                |
+  |       |       Bell, W.S., Law-    |               |                |
+  |       |       Agents, Account for |               |                |
+  |       |       Commissions to and  |               |                |
+  |       |       Bonds by Collectors,|               |                |
+  |       |       &c.,                |   136  4  0   |                |
+  |       |   10. Messrs Spottiswoode |               |                |
+  |       |       and Robertson,      |               |                |
+  |       |       Solicitors, London, |    57 11  8   |                |
+  |       |   11. Gratuity to Lewis   |               |                |
+  |       |       Proctor, an         |               |                |
+  |       |       occasional Light-   |               |                |
+  |       |       keeper, who met with|               |                |
+  |       |       a severe Accident by|               |                |
+  |       |       a fall from the     |               |                |
+  |       |       Lighthouse at       |               |                |
+  |       |       Kinnairdshead,      |    30  0  0   |                |
+  |       |   12. Medical Attendance  |               |                |
+  |       |       on Keepers’ Families|               |                |
+  |       |       at Insulated        |               |                |
+  |       |       Stations,           |    26 17  0   |                |
+  |       |   13. Paid for Nomination |               |                |
+  |       |       to Edinburgh Royal  |               |                |
+  |       |       Lunatic Asylum for  |               |                |
+  |       |       Keeper’s Wife at    |               |                |
+  |       |       Chanonry Lighthouse,|    12 10  0   |                |
+  |       |   14. Gratuities voted to |               |                |
+  |       |       aged Light-keepers  |               |                |
+  |       |       to meet Insurances  |               |                |
+  |       |       on their Lives,     |    38  7  1   |                |
+  |       |   15. Sundry small Sums   |               |                |
+  |       |       due by Light-       |               |                |
+  |       |       keepers, connected  |               |                |
+  |       |       with Insurances on  |               |                |
+  |       |       their Lives, and    |               |                |
+  |       |       Stamps for Premiums,|    37  2  8   |                |
+  |       |   16. R. W. Swinburne and |               |                |
+  |       |       Co., Newcastle,     |               |                |
+  |       |       Plate-Glass,        |    32  1  6   |                |
+  |       |   17. Paid for Temporary  |               |                |
+  |       |       Lanterns during     |               |                |
+  |       |       Repairs of          |               |                |
+  |       |       Lighthouses,        |    64 17  7   |                |
+  |       |   18. One Dozen Stamped   |               |                |
+  |       |       Receipt-Books for   |               |                |
+  |       |       Keepers’ Salaries,  |               |                |
+  |       |       and Fees getting    |               |                |
+  |       |       same Stamped in     |               |                |
+  |       |       London,             |     7  1  0   |                |
+  |       |   19. Expenses incurred by|               |                |
+  |       |       Henry Banks, tailor,|               |                |
+  |       |       in visiting the     |               |                |
+  |       |       different           |               |                |
+  |       |       Lighthouses, and    |               |                |
+  |       |       taking “measures”   |               |                |
+  |       |       for Clothing the    |               |                |
+  |       |       Keepers,            |    38  0  2   |                |
+  |       |   20. Periodicals         |               |                |
+  |       |       furnished to the    |               |                |
+  |       |       Keepers,            |     4 14  7   |                |
+  |       |   21. A Copper Buoy,      |     3 16 11   |                |
+  |       |   22. Repairs on Rankin   |               |                |
+  |       |       Lighter,            |     5  2  4   |                |
+  |       |   23. Account connected   |               |                |
+  |       |       with Skerryvore     |               |                |
+  |       |       Lighters,           |     6  7  0   |                |
+  |       |   24. Models of Dioptric  |               |                |
+  |       |       Light,              |    83 13  1   |                |
+  |       |   25. Freight to London,  |               |                |
+  |       |       Leith, Edinburgh,   |               |                |
+  |       |       and Glasgow Shipping|               |                |
+  |       |       Company,            |     3  1  5   |                |
+  |       |   26. Various small items |               |                |
+  |       |       for Lithographing,  |               |                |
+  |       |       &c. &c.,            |    35  7  1   |                |
+  |       |                           +---------------+                |
+  |       |  SUM as on preceding page,|  £2420 19  5  |                |
+  |       |                           +===============+----------------+
+  |       |                             Carry forward,|£15,960  6  0²⁄₈|
+  |       |                           ================+================+
+  |       |                                                            |
+  |       |                                           +----------------+
+  |       |    ORDINARY EXPENSES brought forward,     |£15,960  6  0²⁄₈|
+  |       |                                           |                |
+  |       |Which have been Allocated to each          |                |
+  |       |Lighthouse in the proportions following,   |                |
+  |       |as appears from State, No. II., pp. 430-3, |                |
+  |       |viz.--                                     |                |
+  |       |                           +---------------+                |
+  |       |   1. Inchkeith,           |  £577 15  9²⁄₈|                |
+  |       |   2. Isle of May,         |   941  8  6   |                |
+  |       |   3. Bell Rock,           |   977 17  9   |                |
+  |       |   4. Girdleness,          |   544  5  8   |                |
+  |       |   5. Buchanness,          |   617  4  1⁶⁄₈|                |
+  |       |   6. Kinnairdshead,       |   573 16 11²⁄₈|                |
+  |       |   7. Tarbetness,          |   569 18  1²⁄₈|                |
+  |       |   8. Sumburghhead,        |   591 11  8⁴⁄₈|                |
+  |       |   9. Startpoint,          |   345  4  4⁴⁄₈|                |
+  |       |  10. Pentland Skerries,   |   841 17 10⁴⁄₈|                |
+  |       |  11. Dunnethead,          |   467  8  4   |                |
+  |       |  12. Capewrath,           |   581 14  7²⁄₈|                |
+  |       |  13. Island Glass,        |   510 15  6⁴⁄₈|                |
+  |       |  14. Barrahead,           |   588 12  7   |                |
+  |       |  15. Skerryvore,          |  1108 19  1   |                |
+  |       |  16. Lismore,             |   511 15  4⁴⁄₈|                |
+  |       |  17. Rhinns of Islay,     |   564 19  6⁶⁄₈|                |
+  |       |  18. Mull of Kintyre,     |   550  3 10⁶⁄₈|                |
+  |       |  19. Pladda,              |   579 15  2²⁄₈|                |
+  |       |  20. Corsewall,           |   462  9  9⁴⁄₈|                |
+  |       |  21. Mull of Galloway,    |   512 14 11⁴⁄₈|                |
+  |       |  22. Little Ross,         |   512 14 11²⁄₈|                |
+  |       |  23. Point of Ayre,       |   406  6  4⁴⁄₈|                |
+  |       |  24. Calf of Man (two     |               |                |
+  |       |      Lights),             |   805  8  7⁴⁄₈|                |
+  |       |  25. Covesea Skerries,    |   417  3  1⁶⁄₈|                |
+  |       |  26. Cromarty,            |   338  6  4⁶⁄₈|                |
+  |       |  27. Chanonry,            |   283  2  8⁴⁄₈|                |
+  |       |  28. Loch Ryan,           |   176 14  1   |                |
+  |       |           As above,       +---------------+ 15,960  6  0²⁄₈|
+  |       |           =================================================+
+  |       |                                                            |
+  |       |  BRANCH III.--EXTRAORDINARY EXPENSES not Allocated to each |
+  |       |                        Lighthouse:--                       |
+  |       |                                                            |
+  |       |                                           +----------------+
+  |  189  |To paid for new Steamer Pharos,            |  £7548 13  7   |
+  |  310  |Expense of Harbour Light at Portpatrick,   |    129 17  4¹⁄₄|
+  |  182  |Expense connected with Skerryvore Book,    |    199 18  0   |
+  |   33  |To paid for House in Crail for use of Isle |                |
+  |       |of May Boatmen, and Fees connected with    |                |
+  |       |Purchase,                                  |    105 19  4   |
+  |       |                                           +----------------+
+  |       |                                           |  £7984  8  3¹⁄₄|
+  |       |EXPENSE OF NEW WORKS,                      |                |
+  |       |viz.:--                    +---------------+                |
+  |  150  |  Skerryvore,              |  £227  8  2   |                |
+  |  287  |  Bo Pheg Beacon,          |    25 10  1   |                |
+  |  284  |  Covesea,                 |  1109  5  4   |                |
+  |  296  |  Cromarty,                |   342  9  3   |                |
+  |  298  |  Chanonry,                |   405  7  8   |                |
+  |  300  |  Ardnamurchan,            |  2343 17  6   |                |
+  |  314  |  Laggan Spur Beacon,      |   748 10  6   |                |
+  |  316  |  Island Glass,            |  1797  3  5¹⁄₂|                |
+  |  319  |  Nosshead,                |  1467  6  1   |                |
+  |  322  |  Loch Ryan,               |   829 12  9¹⁄₂|                |
+  |  121  |  Loch Ryan, Beacon,       |   152  5  9   |                |
+  |  324  |  Pentland Skerries new    |               |                |
+  |       |  Works,                   |  3135 17  5¹⁄₂|                |
+  |  145  |  Pentland Skerries        |               |                |
+  |       |  Dioptric Light,          |  2037 11  4   |                |
+  |  308  |  Renewal of Fixed Lights, |  3035 14  4   |                |
+  |  106  |  Campbeltown Beacons,     |    17  4 10   |                |
+  |  ...  |  Lapock Beacon,           |     8 12  5   |                |
+  |  117  |  Startpoint New Works,    |     5 19  4   |                |
+  |  118  |  Elie or Vow’s Beacon,    |   205  5  8   |                |
+  |  119  |  Whiteness Beacon,        |   152  5  8   |                |
+  |  120  |  Longman’s Point Beacon,  |   164 15  6   |                |
+  |  184  |  Brist Beacon,            |     8 12  5   |                |
+  |  306  |  Mull of Kintyre Dykes    |               |                |
+  |       |  and Road,                |   647 17  9   |                |
+  |  286  |  Buoys,                   |  1458  7 11¹⁄₂|                |
+  |       |                      SUM, +---------------+ 20,327  1  3   |
+  |       |                                           +----------------+
+  |       |                Carried to ABSTRACT below, |£28,311  9  6¹⁄₄|
+  |       |               ===========================+=================+
+  |       |                                                            |
+  |       +------------------------------------------------------------+
+  |       |             ABSTRACT OF THE PRECEDING ACCOUNT.             |
+  |       +-------------------------------------------+----------------+
+  |       |  RECEIPTS:--                              |                |
+  |       |                                           |                |
+  |       |BRANCH  I.--Gross Amount of the Duties     |                |
+  |       |received for 1846, p. 418,                 |£46,001 11  2⁶⁄₈|
+  |       |       II.--Miscellaneous Receipts, p. 419,|  1,893 17  6   |
+  |       |                                           +----------------+
+  |       |                                           |£47,895  8  8⁶⁄₈|
+  |       |  PAYMENTS:--                              |                |
+  |       |                          +----------------+                |
+  |       |BRANCH  I.--Ordinary      |                |                |
+  |       |Expenses, being the       |                |                |
+  |       |Maintenance of Lights, &c.|                |                |
+  |       |p. 420,                   |£16,103  0  2³⁄₄|                |
+  |       |       II.--Ordinary      |                |                |
+  |       |Expenses, falling to be   |                |                |
+  |       |allocated upon each       |                |                |
+  |       |Lighthouse, p. 424,       | 15,960  6  0¹⁄₄|                |
+  |       |      III.--Extraordinary |                |                |
+  |       |Expenses not allocated to |                |                |
+  |       |each Lighthouse, as above,| 28,311  9  6¹⁄₄|                |
+  |       |                          +----------------+ 60,374 15  9²⁄₈|
+  |       |                                           |                |
+  |       |                                           +----------------+
+  |       |            BALANCE superexpended in 1846, |£12,479  7  0⁴⁄₈|
+  |       |       BALANCE on hand at 31st March 1846, | 42,069  6 10   |
+  |       |                                           +----------------+
+  |       |       BALANCE on hand at 31st March 1847, |£29,589 19  9¹⁄₂|
+  |       |                                           |                |
+  |       |  WHEREOF--               +----------------+                |
+  |       |                          |                |                |
+  |       |  In the Royal Bank,      |£28,944 16  8   |                |
+  |       |  In Secretary’s Account, |     40 16 11   |                |
+  |       |                          +----------------+                |
+  |       |                          |£28,985 13  7   |                |
+  |       |                          |                |                |
+  |   89  |  Balance due by Peter    |                |                |
+  |       |  Grant, Superintendent,  |                |                |
+  |       |  Nosshead,               |    203 10  2   |                |
+  |  157  |  Balance due by Master of|                |                |
+  |       |  Prince of Wales Tender, |     35  3  4   |                |
+  |  161  |  Balance due by Steward  |                |                |
+  |       |  of Pharos Steamer,      |     30 19  2   |                |
+  |  164  |  Balance due by Master of|                |                |
+  |       |  Francis, Skerryvore     |                |                |
+  |       |  Tender,                 |      2 12  5   |                |
+  |  166  |  Balance due by          |                |                |
+  |       |  Superintendent of Light-|                |                |
+  |       |  keepers,                |     11 11  2   |                |
+  |  168  |  Balance due by Foreman  |                |                |
+  |       |  of Light-room Repairs,  |      5  3  5   |                |
+  |  172  |  Balance due by          |                |                |
+  |       |  Buoymaster,             |      5  1  6   |                |
+  |  176  |  Balance due by Store-   |                |                |
+  |       |  keeper,                 |      7 17  0   |                |
+  |  180  |  Balance due by Thomas   |                |                |
+  |       |  Hope, Superintendent,   |                |                |
+  |       |  Island Glass,           |     87 17  7¹⁄₂|                |
+  |  307  |  Balance due by Master of|                |                |
+  |       |  Pharos,                 |      5 10  8   |                |
+  |  318  |  Balance due by James    |                |                |
+  |       |  Scott, Superintendent,  |                |                |
+  |       |  Pentland Skerries,      |    188 12  3   |                |
+  |       |                          |                |                |
+  +-------+                          |                |                |
+  | Folio |                          |                |                |
+  |   in  |                          |                |                |
+  | Small |                          |                |                |
+  |Ledger.|                          |                |                |
+  +-------+                          |                |                |
+  |    6  |  Sum due by Robert       |                |                |
+  |       |  Selkirk’s               |                |                |
+  |       |  Representatives, to be  |                |                |
+  |       |  paid when Insurance     |                |                |
+  |       |  money is received,      |     10  0  0   |                |
+  |    8  |  Balance due by Richard  |                |                |
+  |       |  Cumming, Light-keeper,  |      2 13  0   |                |
+  |    9  |  Balance due by James    |                |                |
+  |       |  Laughton, do.,          |      3  0  0   |                |
+  |   10  |  Balance due by William  |                |                |
+  |       |  Kirk, do.,              |      4 14  6   |                |
+  |       |                          |                |                |
+  |       |        Equal to BALANCE, +----------------+ 29,589 19  9¹⁄₂|
+  |       |                          ==================================+
+  |       |                                                            |
+  +-------+------------------------------------------------------------+
+
+  EDINBURGH, _5th May 1847_.--Prepared and Reported by
+
+  (Signed) ALEX. CUNINGHAM, _Secretary_.
+
+       *       *       *       *       *
+
+  84 George Street,
+  _Edinburgh, 25th May 1847_.
+
+In obedience to the Remit by the Honourable Board of Commissioners of
+Northern Lighthouses, I have carefully audited the Accounts of the
+Board for the year ending 31st March 1847; and I have to report, that
+the Accounts are clearly and accurately stated--that they are fully
+vouched--and that, in my humble opinion, the Report of the Secretary
+contains a very distinct statement of the Intromissions of the Board
+during the above period.
+
+  (Signed) KENNETH MACKENZIE, _Accountant_.
+
+STATEMENTS ANNEXED TO THE SECRETARY’S REPORT FOR 1846.
+
+No. I.--_Account of Northern Light-Duties received in the Year 1846._
+
+  +-----------------------+----------------+--------------+
+  |                       |      Gross     |  Commission  |
+  |                       |    Receipts.   |to Collectors.|
+  +-----------------------+----------------+--------------+
+  |  1. Aberdeen,         |  £2243  3  9⁴⁄₈| £121 11  8⁴⁄₈|
+  |  2. Alloa,            |    402  6  1⁴⁄₈|   23  6  8   |
+  |  3. Arbroath,         |    254  2 11⁶⁄₈|   12 17  2⁶⁄₈|
+  |  4. Ayr,              |    158 12 11   |    8  1 10   |
+  |  5. Aberystwith,      |      6 17  6⁴⁄₈|    0  6  9⁴⁄₈|
+  |  6. Arundel,          |       ...      |      ...     |
+  |  7. Banff,            |    467  7  5   |   28 17  6   |
+  |  8. Borrowstounness,  |    675  6  1⁴⁄₈|   48 11  9⁴⁄₈|
+  |  9. Barnstaple,       |      1  7  2⁴⁄₈|    0  1  4⁴⁄₈|
+  | 10. Beaumaris,        |    123 17  1⁴⁄₈|    6 12  7⁴⁄₈|
+  | 11. Berwick,          |    121  0  8⁴⁄₈|    6 11  9⁴⁄₈|
+  | 12. Bideford,         |      8 14 11   |    0  8  9   |
+  | 13. Boston,           |      9 15  0⁴⁄₈|    0 10  7⁴⁄₈|
+  | 14. Bridgewater,      |     12  0  7⁷⁄₈|    0 11 11⁷⁄₈|
+  | 15. Bridlington,      |     26  1  3⁴⁄₈|    1  6  1   |
+  | 16. Bridport,         |      2 18  0⁴⁄₈|    0  2 10⁴⁄₈|
+  | 17. Bristol,          |    124 12  7²⁄₈|    6  4  6⁶⁄₈|
+  | 18. Baltimore,        |       ...      |      ...     |
+  | 19. Belfast,          |   2446  1  4²⁄₈|  125  6  4²⁄₈|
+  | 20. Campbeltown,      |     82 14  9⁴⁄₈|    5  2  1⁴⁄₈|
+  | 21. Caernarvon,       |     25 13 10   |    1  7  7   |
+  | 22. Cardiff,          |    110 19  7   |    5 11  0   |
+  | 23. Cardigan,         |      1  7 11⁴⁄₈|    0  1  7⁴⁄₈|
+  | 24. Carlisle,         |     84  0  3²⁄₈|    4  7  9²⁄₈|
+  | 25. Chepstow,         |      0 14 11   |    0  0  9   |
+  | 26. Chester,          |    158  4  5¹⁄₈|    8  1  5³⁄₈|
+  | 27. Chichester,       |      2 15  6²⁄₈|    0  3  9²⁄₈|
+  | 28. Clay,             |      1  2  6   |    0  1  8⁴⁄₈|
+  | 29. Colchester,       |       ...      |      ...     |
+  | 30. Cowes,            |       ...      |      ...     |
+  | 31. Coleraine,        |    101  5  8⁴⁄₈|    5  1  7   |
+  | 32. Cork,             |     70 13  1   |    3 10  6   |
+  | 33. Dunbar,           |    115 11 11   |    7  1  2   |
+  | 34. Dundee,           |   2062  9 10   |  105  7  2   |
+  | 35. Dumfries,         |    351 10  6⁴⁄₈|   24 13  0⁴⁄₈|
+  | 36. Dartmouth,        |       ...      |      ...     |
+  | 37. Deal,             |       ...      |      ...     |
+  | 38. Dover,            |      0  8  0⁴⁄₈|    0  0  5   |
+  | 39. Dublin,           |   2256 17 10   |  114  0  9   |
+  | 40. Drogheda,         |    149  8  2⁴⁄₈|    7  9  5   |
+  | 41. Dundalk,          |    120  6  6⁴⁄₈|    6  0  3⁴⁄₈|
+  | 42. Exeter,           |      2 17  5⁴⁄₈|    0  3  0⁴⁄₈|
+  | 43. Fisherrow,        |    219  0  8⁶⁄₈|   13 12  4⁴⁄₈|
+  | 44. Falmouth,         |       ...      |      ...     |
+  | 45. Faversham,        |       ...      |      ...     |
+  | 46. Fowey,            |      2  4 11   |    0  3  0⁴⁄₈|
+  | 47. Glasgow,          |   3599 16 10   |  182 14  4⁴⁄₈|
+  | 48. Greenock,         |   2671  0  9   |  137 13  8   |
+  | 49. Grangemouth,      |   1251 12  5   |   62 11  6   |
+  | 50. Gainsborough,     |      5 19  8   |    0  6  9   |
+  | 51. Gloucester,       |     61 12 11²⁄₈|    3  1  8²⁄₈|
+  | 52. Goole,            |     31  2  4   |    1 12  2   |
+  | 53. Grimsby,          |     64 11  3⁴⁄₈|    3  4  7   |
+  | 54. Gweek,            |       ...      |      ...     |
+  | 55. Galway,           |     38  6  0   |    1 18  3⁴⁄₈|
+  | 56. Hartlepool,       |    153  4  0   |    7 13  2   |
+  | 57. Harwich,          |       ...      |      ...     |
+  | 58. Hull,             |   1532  8  2⁴⁄₈|   76 12  5⁴⁄₈|
+  | 59. Inverness,        |    920 17  1²⁄₈|   56 12 11⁴⁄₈|
+  | 60. Irvine,           |    915 10 10   |   63  8 11   |
+  | 61. Ipswich,          |     17  5  0   |    0 17  3   |
+  | 62. Isle of Man,      |    373 18  9¹⁄₈|   22 15  5⁶⁄₈|
+  | 63. Kirkcaldy,        |    745  5  5   |   42 16  2   |
+  | 64. Kirkwall,         |    131 15  6⁴⁄₈|    7  9  0⁴⁄₈|
+  | 65. Leith,            |   3224  7  3   |  161  4  4   |
+  | 66. Lerwick,          |    173  1  1   |    8 13  0   |
+  | 67. Lancaster,        |    107  0  5¹⁄₈|    6  3  6⁵⁄₈|
+  | 68. Leigh,            |       ...      |      ...     |
+  | 69. Liverpool,        |   6780 19  5   |  342  8  9   |
+  | 70. Llanelly,         |      8 12  3   |    0 11  9   |
+  | 71. London,           |   1943  8  9⁶⁄₈|   97  3  4⁶⁄₈|
+  | 72. Lyme,             |       ...      |      ...     |
+  | 73. Lynn,             |     79  7  7   |    4 15  2⁴⁄₈|
+  | 74. Limerick,         |    160  2  4⁴⁄₈|    8  3  2⁴⁄₈|
+  | 75. Londonderry,      |   1058  2  4   |   53  6  6   |
+  | 76. Montrose,         |    357 13  2²⁄₈|   18  6  0²⁄₈|
+  | 77. Maldon,           |       ...      |      ...     |
+  | 78. Milford,          |     14  4  6⁴⁄₈|    0 19  7   |
+  | 79. Maryport,         |     87 17  1⁴⁄₈|    4  5  7   |
+  | 80. Newcastle-on-Tyne,|   2118 16  8⁴⁄₈|   75  2  9   |
+  | 81. Newhaven,         |      1 14 10   |    0  1  9   |
+  | 82. Newport,          |     41  2  8   |    2  1  1⁴⁄₈|
+  | 83. Newry,            |    230 16  2   |   13  3  9   |
+  | 84. Perth,            |    275 14  3   |   14 13  6⁴⁄₈|
+  | 85. Port-Glasgow,     |    496  8  6   |   24 16  3   |
+  | 86. Padstow,          |      2 15  1³⁄₈|    0  2  8³⁄₈|
+  | 87. Penzance,         |      1  6 10   |    0  1  4   |
+  | 88. Plymouth,         |     25  4  9   |    1  6  2   |
+  | 89. Poole,            |      0 11  6   |    0  0  7   |
+  | 90. Portsmouth,       |     10 12  4⁴⁄₈|    0 10  6⁴⁄₈|
+  | 91. Preston,          |    562  1 11   |   41 14 10   |
+  | 92. Ramsgate,         |       ...      |      ...     |
+  | 93. Rochester,        |      1 15  1   |    0  1 10   |
+  | 94. Rye,              |      0 18  3⁴⁄₈|    0  0 10⁴⁄₈|
+  | 95. Ross,             |     12 17 10   |    0 12 11   |
+  | 96. Stranraer,        |     90 17  9   |    4 16  6   |
+  | 97. Stornoway,        |     56  6 11⁴⁄₈|    2 16  2⁴⁄₈|
+  | 98. Scarborough,      |      8 14 10⁴⁄₈|    0  8  8⁴⁄₈|
+  | 99. Seilly,           |       ...      |      ...     |
+  |100. Shoreham,         |      0 19  6⁷⁄₈|    0  0 11⁷⁄₈|
+  |101. Southampton,      |     30  0  9   |    1 10  1   |
+  |102. St Ives,          |      3  9  9¹⁄₈|    0  5  2¹⁄₈|
+  |103. Stockton,         |    226 19  2   |   12  0  2⁴⁄₈|
+  |104. Sunderland,       |    908 14  9⁶⁄₈|   47  1  4⁶⁄₈|
+  |105. Swansea,          |     28  4  9⁶⁄₈|    1 12  3   |
+  |106. Sligo,            |    355  0  4   |   19 15 10⁶⁄₈|
+  |107. Truro,            |      0 11  0   |    0  0  9   |
+  |108. Tralee,           |      9  7 10⁴⁄₈|    0  9  4²⁄₈|
+  |109. Wick,             |    356 17  9⁴⁄₈|   20 10  2⁴⁄₈|
+  |110. Wigton,           |     83  9  5   |    5  5  5   |
+  |111. Weymouth,         |      0 15 10²⁄₈|    0  0  9²⁄₈|
+  |112. Whitby,           |     31  5 10   |    1 11  4   |
+  |113. Whitehaven,       |    328  1  9   |   18  5  5   |
+  |114. Woodbridge,       |      3 18  9   |    0  3 11   |
+  |115. Waterford,        |     57 14  3⁴⁄₈|    2 17 10⁴⁄₈|
+  |116. Westport,         |     41  0  6⁴⁄₈|    2  1  0   |
+  |117. Wexford,          |     32 19  2   |    1 12 11⁶⁄₈|
+  |118. Yarmouth,         |     49  5  6   |    2  9  5   |
+  |                       +----------------+--------------+
+  |                       |£46,001 11  3⁷⁄₈|£2401  7  3⁴⁄₈|
+  |                       |                |              |
+  |    DEDUCT--Amount of  |                |              |
+  |    fractions short    |                |              |
+  |    credited by Bank,  |      0  0  1¹⁄₈|              |
+  |                       +----------------+--------------+
+  |                       |£46,001 11  2⁶⁄₈|£2401  7  3⁴⁄₈|
+  |                     ==+================+==============+
+  |
+  |                                                       +
+  |    GROSS RECEIPTS,                                    |
+  |                                                       |
+  |                                        +--------------+
+  |    DEDUCT--Commission,                 |£2401  7  3⁴⁄₈|
+  |            Repayments,                 |  218 16 10²⁄₈|
+  |            &c.,                        +--------------+
+  |                                                       |
+  |  NETT DUTIES received                                 +
+  |  in year to 31st
+  |  December 1846,
+  |                                        ================
+  |
+  +--------------------------------------------------------
+
+  +-----------------------+----------------+----------------+
+  |                       |   Repayments,  |  Nett Duties   |
+  |                       |       &c.      |    Received.   |
+  +-----------------------+----------------+----------------+
+  |  1. Aberdeen,         |     £5 14  5   |  £2115 17  8   |
+  |  2. Alloa,            |      6 17  9   |    372  1  8⁴⁄₈|
+  |  3. Arbroath,         |      3 17  7²⁄₈|    237  8  1⁶⁄₈|
+  |  4. Ayr,              |      1 15 10   |    148 15  3   |
+  |  5. Aberystwith,      |      0  1  0   |      6  9  9   |
+  |  6. Arundel,          |        ...     |                |
+  |  7. Banff,            |      2 19  3   |    435 10  8   |
+  |  8. Borrowstounness,  |      9  4  1   |    617 10  3   |
+  |  9. Barnstaple,       |        ...     |      1  5 10   |
+  | 10. Beaumaris,        |      0 15  1   |    116  9  5   |
+  | 11. Berwick,          |      0  1  8   |    114  7  3   |
+  | 12. Bideford,         |        ...     |      8  6  2   |
+  | 13. Boston,           |      0  5  6   |      8 18 11   |
+  | 14. Bridgewater,      |      0  2 10   |     11  5 10   |
+  | 15. Bridlington,      |        ...     |     24 15  2⁴⁄₈|
+  | 16. Bridport,         |        ...     |      2 15  2   |
+  | 17. Bristol,          |      0 14  0   |    117 14  0⁴⁄₈|
+  | 18. Baltimore,        |        ...     |                |
+  | 19. Belfast,          |     56 12 10   |   2264  2  2   |
+  | 20. Campbeltown,      |      1 12  8   |     76  0  0   |
+  | 21. Caernarvon,       |      0  8  0   |     23 18  3   |
+  | 22. Cardiff,          |        ...     |    105  8  7   |
+  | 23. Cardigan,         |        ...     |      1  6  4   |
+  | 24. Carlisle,         |      0 10  5   |     79  2  1   |
+  | 25. Chepstow,         |        ...     |      0 14  2   |
+  | 26. Chester,          |      1  0  0   |    149  2 11⁶⁄₈|
+  | 27. Chichester,       |        ...     |      2 11  9   |
+  | 28. Clay,             |        ...     |      1  0  9⁴⁄₈|
+  | 29. Colchester,       |        ...     |                |
+  | 30. Cowes,            |        ...     |                |
+  | 31. Coleraine,        |        ...     |     96  4  1⁴⁄₈|
+  | 32. Cork,             |      2  0  9   |     65  1 10   |
+  | 33. Dunbar,           |      0 11  4   |    107 19  5   |
+  | 34. Dundee,           |      7 15 10   |   1949  6 10   |
+  | 35. Dumfries,         |      2 10  8   |    324  6 10   |
+  | 36. Dartmouth,        |        ...     |                |
+  | 37. Deal,             |        ...     |                |
+  | 38. Dover,            |        ...     |      0  7  7⁴⁄₈|
+  | 39. Dublin,           |      9 16  9   |   2133  0  4   |
+  | 40. Drogheda,         |        ...     |    141 18  9⁴⁄₈|
+  | 41. Dundalk,          |      0  6  8   |    113 19  7   |
+  | 42. Exeter,           |        ...     |      2 14  5   |
+  | 43. Fisherrow,        |      0 15  3   |    204 13  1²⁄₈|
+  | 44. Falmouth,         |        ...     |                |
+  | 45. Faversham,        |        ...     |                |
+  | 46. Fowey,            |        ...     |      2  1 10⁴⁄₈|
+  | 47. Glasgow,          |     11 15 11⁴⁄₈|   3405  6  6   |
+  | 48. Greenock,         |      7 10  6   |   2525 16  7   |
+  | 49. Grangemouth,      |      2 16 10   |   1186  4  1   |
+  | 50. Gainsborough,     |        ...     |      5 12 11   |
+  | 51. Gloucester,       |      0  2  0   |     58  9  3   |
+  | 52. Goole,            |        ...     |     29 10  2   |
+  | 53. Grimsby,          |        ...     |     61  6  8⁴⁄₈|
+  | 54. Gweek,            |        ...     |                |
+  | 55. Galway,           |      0  6  0   |     36  1  8⁴⁄₈|
+  | 56. Hartlepool,       |        ...     |    145 10 10   |
+  | 57. Harwich,          |        ...     |                |
+  | 58. Hull,             |      0 10  0   |   1455  5  9   |
+  | 59. Inverness,        |      7  1 11   |    857  2  2⁶⁄₈|
+  | 60. Irvine,           |      3  8  8   |    848 13  3   |
+  | 61. Ipswich,          |      0  2  0   |     16  5  9   |
+  | 62. Isle of Man,      |      1 13  9   |    349  9  6³⁄₄|
+  | 63. Kirkcaldy,        |      1 16  2   |    700 13  1   |
+  | 64. Kirkwall,         |      0  9  9   |    123 16  9   |
+  | 65. Leith,            |     17 14  2   |   3045  8  9   |
+  | 66. Lerwick,          |      0 11  1   |    163 17  0   |
+  | 67. Lancaster,        |      0 18  8   |     99 18  2⁴⁄₈|
+  | 68. Leigh,            |        ...     |                |
+  | 69. Liverpool,        |      9 13 11   |   6428 16  9   |
+  | 70. Llanelly,         |        ...     |      8  0  6   |
+  | 71. London,           |        ...     |   1846  5  5   |
+  | 72. Lyme,             |        ...     |                |
+  | 73. Lynn,             |      0  7  2   |     74  5  2⁴⁄₈|
+  | 74. Limerick,         |      0  5  0   |    151 14  2   |
+  | 75. Londonderry,      |        ...     |   1004 15 10   |
+  | 76. Montrose,         |      0 10  3   |    338 16 11   |
+  | 77. Maldon,           |        ...     |                |
+  | 78. Milford,          |        ...     |     13  4 11⁴⁄₈|
+  | 79. Maryport,         |      2  6 11⁴⁄₈|     81  4  7   |
+  | 80. Newcastle-on-Tyne,|      0 14  8   |   2042 19  3⁴⁄₈|
+  | 81. Newhaven,         |        ...     |      1 13  1   |
+  | 82. Newport,          |        ...     |     39  1  6⁴⁄₈|
+  | 83. Newry,            |     14  6 11   |    203  5  6   |
+  | 84. Perth,            |      0 19 10   |    260  0 10⁴⁄₈|
+  | 85. Port-Glasgow,     |      0 15  7   |    470 16  8   |
+  | 86. Padstow,          |      0  5  0   |      2  7  5   |
+  | 87. Penzance,         |        ...     |      1  5  6   |
+  | 88. Plymouth,         |      0  1  0   |     23 17  7   |
+  | 89. Poole,            |        ...     |      0 10 11   |
+  | 90. Portsmouth,       |      0  4  9   |      9 17  1   |
+  | 91. Preston,          |        ...     |    520  7  1   |
+  | 92. Ramsgate,         |        ...     |                |
+  | 93. Rochester,        |        ...     |      1 13  3   |
+  | 94. Rye,              |        ...     |      0 17  5   |
+  | 95. Ross,             |      0  4  7   |     12  0  4   |
+  | 96. Stranraer,        |      1  9  3   |     84 12  0   |
+  | 97. Stornoway,        |      0  3  6   |     53  7  3   |
+  | 98. Scarborough,      |        ...     |      8  6  2   |
+  | 99. Seilly,           |        ...     |                |
+  |100. Shoreham,         |        ...     |      0 18  7   |
+  |101. Southampton,      |        ...     |     28 10  8   |
+  |102. St Ives,          |      0  0  1   |      3  4  6   |
+  |103. Stockton,         |      5 11  0   |    209  7 11⁴⁄₈|
+  |104. Sunderland,       |      0 14  9   |    860 18  8   |
+  |105. Swansea,          |        ...     |     26 12  6   |
+  |106. Sligo,            |      0 10  4   |    334 14  1⁶⁄₈|
+  |107. Truro,            |        ...     |      0 10  3   |
+  |108. Tralee,           |      0  2  8   |      8 15 10²⁄₈|
+  |109. Wick,             |      4  9  1   |    331 18  6   |
+  |110. Wigton,           |      1 12 11   |     76 11  1   |
+  |111. Weymouth,         |        ...     |      0 15  1   |
+  |112. Whitby,           |        ...     |     29 14  6   |
+  |113. Whitehaven,       |        ...     |    309 16  4   |
+  |114. Woodbridge,       |        ...     |      3 14 10   |
+  |115. Waterford,        |        ...     |     54 16  5   |
+  |116. Westport,         |        ...     |     38 19  6⁴⁄₈|
+  |117. Wexford,          |        ...     |     31  6  2²⁄₈|
+  |118. Yarmouth,         |        ...     |     46 16  1   |
+  |                       +----------------+----------------+
+  |                       |   £218 16 10²⁄₈|£43,381  7  2¹⁄₈|
+  |                       |                |                |
+  |    DEDUCT--Amount of  |                |                |
+  |    fractions short    |                |                |
+  |    credited by Bank,  |                |      0  0  1¹⁄₈|
+  |                       +----------------+----------------+
+  |                       |   £218 16 10²⁄₈|£43,381  7  1   |
+  |                       +================+                |
+  |                                        |                |
+  |                       +----------------+                |
+  |                       |£46,001 11  2⁶⁄₈|                |
+  |                       |                |                |
+  |                       +                |                |
+  |    DEDUCT--Commission,|                |                |
+  |            Repayments,|                |                |
+  |            &c.,       +   2620  4  1⁶⁄₈|                |
+  |                       |                |                |
+  |   NETT DUTIES received+----------------+ 43,381  7  1   |
+  |   in year to 31st                      |                |
+  |   December 1846,                       |                |
+  |                       =================+================+
+  |                                                         |
+  +---------------------------------------------------------+
+
+NO. II.--_State shewing the Gross Receipts on account of each of the
+Northern Lighthouses, the Number of Vessels, and amount of Tonnage
+passing them;--the Particular Expenses of the Lighthouses, and their
+Proportions of the General Expenses, embracing Commissions to, and
+Repayments by, the Collectors; Expenses of the Shipping Establishment,
+Salaries to Officers, Experiments, and other General Expenses; also the
+Ordinary Expenses of Beacons and Buoys, for the Year 1846._
+
+  +--------------+--------------------+-----------------------------+
+  |    NO. OF    |                    |                             |
+  |   VESSELS.   |      TONNAGE.      |                             |
+  +-------+------+----------+---------+                             |
+  | Coast-| Over-|  Coast-  |  Over-  |                             |
+  |  ing. | sea. |   ing.   |   sea.  |        LIGHTHOUSES.         |
+  +-------+------+----------+---------+-----------------------------+
+  | 15,872| 2,664| 1,238,057|  294,54 | 1. INCHKEITH,               |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  | 20,101| 3,349| 1,843,210|  383,516| 2. ISLE OF MAY,             |
+  |       |      |          |         |    Add for Leading Light,   |
+  |       |      |          |         |                             +
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  | 14,610| 4,485| 1,299,875|  632,328| 3. BELL ROCK,               |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  7,915| 3,978|   788,947|  587,977| 4. GIRDLENESS,              |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  5,293| 4,012|   419,988|  590,453| 5. BUCHANNESS,              |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  4,829| 2,819|   390,166|  546,856| 6. KINNAIRDSHEAD,           |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  2,256|   273|   191,345|   18,282| 7. TARBETNESS,              |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |    279|   644|    32,149|  113,598| 8. SUMBURGHHEAD,            |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |    307| 2,326|    33,710|  528,647| 9. STARTPOINT,              |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  2,434| 2,430|   181,284|  525,582|10. PENTLAND SKERRIES,       |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  1,911| 2,267|   139,379|  524,685|11. DUNNETHEAD,              |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  1,700| 2,231|   131,138|  517,333|12. CAPEWRATH,               |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  1,734| 1,153|   137,060|  226,941|13. ISLAND GLASS,            |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |    669| 1,821|     9,517|  466,010|14. BARRAHEAD,               |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |    555| 1,788|    52,541|  461,313|15. SKERRYVORE,              |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  2,430|    34|   159,719|    4,436|16. LISMORE,                 |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  3,152| 1,550|   385,786|  382,841|17. RHINNS OF ISLAY,         |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  5,023| 1,440|   509,914|  357,682|18. MULL OF KINTYRE,         |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  | 12,372| 1,937| 1,403,359|  450,849|19. PLADDA,                  |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  | 12,453| 2,776| 1,407,921|  645,447|20. CORSEWALL,               |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  | 12,884| 2,458| 1,648,915|  531,056|21. MULL OF GALLOWAY,        |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  9,195|    98|   729,918|   17,431|22. LITTLE ROSS,             |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  9,733| 1,034|   843,235|  209,237|23. POINT OF AYRE,           |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  | 13,867| 2,559| 1,769,475|  546,244|24. CALF OF MAN (2 Lights),  |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |  1,592|   198|   130,026|   14,288|25. COVESEA SKERRIES,[*]     |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |26. CROMARTY,[*]             |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |27. CHANONRY,[*]             |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |                             |
+  |       |      |          |         |28. LOCH RYAN,[*]            |
+  |       |      |          |         |    Particular Expense,      |
+  |       |      |          |         |    Share of General Expense,|
+  |       |      |          |         |      TOTAL EXPENDITURE,     +
+  |       |      |          |         |                             |
+  |       |      |          |         |* NOTE.--COVESEA SKERRIES,   |
+  |       |      |          |         |CROMARTY, and CHANONRY, were |
+  |       |      |          |         |not lighted till the 15th    |
+  |       |      |          |         |May, to which is owing the   |
+  |       |      |          |         |small amount of their        |
+  |       |      |          |         |Revenue; and LOCH RYAN was   |
+  |       |      |          |         |not lighted till the 3d of   |
+  |       |      |          |         |March subsequent to the      |
+  |       |      |          |         |period embraced in this      |
+  |       |      |          |         |STATE .                      |
+  +-------+------+----------+---------+                             |
+  |163,166|50,324|15,926,634|9,577,478|                       TOTAL,|
+  +-------+------+----------+---------+-----------------------------+
+  |
+  |
+  |
+  |
+  |The Surplus amounts as above to
+  |
+  |And the Deficiency to
+  |
+  |Actual Surplus,
+  |
+  |DEDUCT--Fractions short--credited
+  |by Bank, &c.,
+  |
+  |Surplus, as per p. 415,
+  |
+  |ADD--The Receipts derived from other
+  |sources besides
+  |Light-duties, per p. 419,
+  |
+  |
+  |But there has been expended, besides
+  |the amount allocated to the
+  |different Lighthouses above, as per
+  |p. 425,
+  |
+  |Amount superexpended, per p. 425,
+  |
+  |
+  +==================================================================
+
+  -----------------------------+--------------+--------------+
+                               |              |              |
+                               |              |              |
+                               |              |              |
+                               |              |    GROSS     |
+          LIGHTHOUSES.         |              |   RECEIPTS.  |
+  -----------------------------+--------------+--------------+
+   1. INCHKEITH,               |              |£2524  9  2²⁄₈|
+      Particular Expense,      | £583  5 10⁴⁄₈|              |
+      Share of General Expense,|  577 15  9²⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1161  1  7⁶⁄₈|
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+   2. ISLE OF MAY,             |£3676 18 11   |              |
+      Add for Leading Light,   |  148  9  6⁴⁄₈|              |
+                               +--------------+£3825  8  5⁴⁄₈|
+      Particular Expense,      | £952  3  9   |              |
+      Share of General Expense,|  941  8  6   |              |
+        TOTAL EXPENDITURE,     +--------------+ 1893 12  3   |
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+   3. BELL ROCK,               |              |£5342 15  5⁴⁄₈|
+      Particular Expense,      | £989  1  3²⁄₈|              |
+      Share of General Expense,|  977 17  9   |              |
+        TOTAL EXPENDITURE,     +--------------+ 1966 19  0²⁄₈|
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+   4. GIRDLENESS,              |              |£2458  4  5⁴⁄₈|
+      Particular Expense,      | £548 18  1   |              |
+      Share of General Expense,|  544  5  8   |              |
+        TOTAL EXPENDITURE,     +--------------+ 1093  3  9   |
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+   5. BUCHANNESS,              |              |£1880  1  3⁴⁄₈|
+      Particular Expense,      | £623  5  3   |              |
+      Share of General Expense,|  617  4  1⁶⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1240  9  4⁶⁄₈|
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+   6. KINNAIRDSHEAD,           |              |£1744 11  3⁴⁄₈|
+      Particular Expense,      | £578 10  0⁴⁄₈|              |
+      Share of General Expense,|  573 16 11²⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1152  6 11⁶⁄₈|
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+   7. TARBETNESS,              |              | £329 17  4⁶⁄₈|
+      Particular Expense,      | £574 11 11   |              |
+      Share of General Expense,|  569 18  1²⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1144 10  0²⁄₈|
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+   8. SUMBURGHHEAD,            |              | £286 18  2⁶⁄₈|
+      Particular Expense,      | £597  5  3⁶⁄₈|              |
+      Share of General Expense,|  591 11  8⁴⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1188 17  0²⁄₈|
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+   9. STARTPOINT,              |              |£1154  5  4²⁄₈|
+      Particular Expense,      | £347  0  8   |              |
+      Share of General Expense,|  345  4  4⁴⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+  692  5  0⁴⁄₈|
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+  10. PENTLAND SKERRIES,       |              |£1370 10  5⁶⁄₈|
+      Particular Expense,      | £851  8 11   |              |
+      Share of General Expense,|  841 17 10⁴⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1693  6  9⁴⁄₈|
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+  11. DUNNETHEAD,              |              |£1311  1 10²⁄₈|
+      Particular Expense,      | £470 19  7⁴⁄₈|              |
+      Share of General Expense,|  467  8  4   |              |
+        TOTAL EXPENDITURE,     +--------------+  938  7 11⁴⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  12. CAPEWRATH,               |              |£1278  9  9   |
+      Particular Expense,      | £587  6 11²⁄₈|              |
+      Share of General Expense,|  581 14  7²⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1169  1  6⁴⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  13. ISLAND GLASS,            |              | £679  1 10⁶⁄₈|
+      Particular Expense,      | £515  2 10²⁄₈|              |
+      Share of General Expense,|  510 15  6⁴⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1025 18  4⁶⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  14. BARRAHEAD,               |              |£1063  3  2⁴⁄₈|
+      Particular Expense,      | £594  3 10⁴⁄₈|              |
+      Share of General Expense,|  588 12  7   |              |
+        TOTAL EXPENDITURE,     +--------------+ 1182 16  5⁴⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  15. SKERRYVORE,              |              |£2090 11  3⁴⁄₈|
+      Particular Expense,      |£1122  0  7   |              |
+      Share of General Expense,| 1108 19  1   |              |
+        TOTAL EXPENDITURE,     +--------------+ 2239 19  8   |
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+  16. LISMORE,                 |              | £239 11  4   |
+      Particular Expense,      | £515 14  2²⁄₈|              |
+      Share of General Expense,|  511 15  4⁴⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1027  9  6⁶⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  17. RHINNS OF ISLAY,         |              |£1414  5  8⁶⁄₈|
+      Particular Expense,      | £569 12  7⁶⁄₈|              |
+      Share of General Expense,|  564 19  6⁶⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1134 12  2⁴⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+                               |              |              |
+  18. MULL OF KINTYRE,         |              |£1549  0  1   |
+      Particular Expense,      | £554 17 10⁴⁄₈|              |
+      Share of General Expense,|  550  3 10⁶⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1105  1  9²⁄₈|
+                               |              |              |
+                               |    BALANCE,  +--------------+
+                               |              |              |
+  19. PLADDA,                  |              |£2762 14  3⁷⁄₈|
+      Particular Expense,      | £584 10 10   |              |
+      Share of General Expense,|  579 15  2²⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1164  6  0²⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  20. CORSEWALL,               |              |£2811  5  3⁶⁄₈|
+      Particular Expense,      | £465 13  4   |              |
+      Share of General Expense,|  462  9  9⁴⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+  928  3  1⁴⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  21. MULL OF GALLOWAY,        |              |£2823 19  8⁶⁄₈|
+      Particular Expense,      | £517  0  5⁴⁄₈|              |
+      Share of General Expense,|  512 14 11⁴⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1029 15  5   |
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  22. LITTLE ROSS,             |              |£1187  7  9⁴⁄₈|
+      Particular Expense,      | £516 18  6²⁄₈|              |
+      Share of General Expense,|  512 14 11²⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1029 13  5⁴⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  23. POINT OF AYRE,           |              |£1755 17  5⁴⁄₈|
+      Particular Expense,      | £409  1  4⁴⁄₈|              |
+      Share of General Expense,|  406  6  4⁴⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+  815  7  9   |
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  24. CALF OF MAN (2 Lights),  |              |£3839  2 11²⁄₈|
+      Particular Expense,      | £813 19  5   |              |
+      Share of General Expense,|  805  8  7⁴⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+ 1619  8  0⁴⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  25. COVESEA SKERRIES,[*]     |              | £193  7  0   |
+      Particular Expense,      | £419 16  8⁴⁄₈|              |
+      Share of General Expense,|  417  3  1⁶⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+  836 19 10²⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  26. CROMARTY,[*]             |              |  £27 14 11   |
+      Particular Expense,      | £339 17  3   |              |
+      Share of General Expense,|  338  6  4⁶⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+  678  3  7⁶⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  27. CHANONRY,[*]             |              |  £57 15  1   |
+      Particular Expense,      | £284  7  1   |              |
+      Share of General Expense,|  283  2  8⁶⁄₈|              |
+        TOTAL EXPENDITURE,     +--------------+  567  9  9⁴⁄₈|
+                               |              |              |
+                               |   BALANCE,   +--------------+
+                               |              |              |
+  28. LOCH RYAN,[*]            |              |              |
+      Particular Expense,      | £176  5  7   |              |
+      Share of General Expense,|  176 14  1   |              |
+        TOTAL EXPENDITURE,     +--------------+              |
+                               |              |              |
+  * NOTE.--COVESEA SKERRIES,   |              |              |
+  CROMARTY, and CHANONRY, were |              |              |
+  not lighted till the 15th    |              |              |
+  May, to which is owing the   |              |              |
+  small amount of their        |              |              |
+  Revenue; and LOCH RYAN was   |              |              |
+  not lighted till the 3d of   |              |              |
+  March subsequent to the      |              |              |
+  period embraced in this      |              |              |
+  STATE .                      |              |              |
+                               |              |              +
+                         TOTAL,|              |              |
+  -----------------------------+--------------+--------------+
+
+
+                                RECONCILEMENT.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+  ============================================================
+
+  -----------------------------+----------------+--------------+
+                               |                |              |
+                               |                |              |
+                               |                |              |
+                               |                |              |
+          LIGHTHOUSES.         |    SURPLUS.    |  DEFICIENCY. |
+  -----------------------------+----------------+--------------+
+   1. INCHKEITH,               |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |  £1363  7  6⁴⁄₈|              |
+                               |                |              |
+   2. ISLE OF MAY,             |                |              |
+      Add for Leading Light,   |                |              |
+                               +                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |   1931 16  2⁴⁄₈|              |
+                               |                |              |
+   3. BELL ROCK,               |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |   3375 16  5²⁄₈|              |
+                               |                |              |
+   4. GIRDLENESS,              |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |   1365  0  8⁴⁄₈|              |
+                               |                |              |
+   5. BUCHANNESS,              |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |    639 11 10⁶⁄₈|              |
+                               |                |              |
+   6. KINNAIRDSHEAD,           |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |    592  4  6⁶⁄₈|              |
+                               |                |              |
+   7. TARBETNESS,              |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |                | £814 12  7⁴⁄₈|
+                               |                |              |
+   8. SUMBURGHHEAD,            |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |                | £901 18  9⁴⁄₈|
+                               |                |              |
+   9. STARTPOINT,              |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |    462  0  3⁶⁄₈|              |
+                               |                |              |
+  10. PENTLAND SKERRIES,       |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |                |  322 16  3⁶⁄₈|
+                               |                |              |
+  11. DUNNETHEAD,              |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |    372 13 10⁶⁄₈|              |
+                               |                |              |
+  12. CAPEWRATH,               |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |    109  8  2⁴⁄₈|              |
+                               |                |              |
+  13. ISLAND GLASS,            |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |                |  346 16  6   |
+                               |                |              |
+  14. BARRAHEAD,               |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |                |  119 13  2⁶⁄₈|
+                               |                |              |
+  15. SKERRYVORE,              |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |                |  140  8  4⁴⁄₈|
+                               |                |              |
+  16. LISMORE,                 |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |                |  787 18  2⁶⁄₈|
+                               |                |              |
+  17. RHINNS OF ISLAY,         |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |    279 13  6²⁄₈|              |
+                               |                |              |
+                               |                |              |
+  18. MULL OF KINTYRE,         |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |    443 18  3⁶⁄₈|              |
+                               |                |              |
+  19. PLADDA,                  |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |   1598  8  3⁵⁄₈|              |
+                               |                |              |
+  20. CORSEWALL,               |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |   1883  2  2²⁄₈|              |
+                               |                |              |
+  21. MULL OF GALLOWAY,        |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |   1794  4  3⁶⁄₈|              |
+                               |                |              |
+  22. LITTLE ROSS,             |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |    157 14  4   |              |
+                               |                |              |
+  23. POINT OF AYRE,           |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |    940  9  8⁴⁄₈|              |
+                               |                |              |
+  24. CALF OF MAN (2 Lights),  |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |   2219 14 10⁶⁄₈|              |
+                               |                |              |
+  25. COVESEA SKERRIES,[*]     |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |                |  643 12 10²⁄₈|
+                               |                |              |
+  26. CROMARTY,[*]             |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |                |  650  8  8⁶⁄₈|
+                               |                |              |
+  27. CHANONRY,[*]             |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |              |
+                               |                |              |
+                               |                |  509 14  8⁴⁄₈|
+                               |                |              |
+  28. LOCH RYAN,[*]            |                |              |
+      Particular Expense,      |                |              |
+      Share of General Expense,|                |              |
+        TOTAL EXPENDITURE,     +                |  352 19  8   |
+                               |                |              |
+  * NOTE.--COVESEA SKERRIES,   |                |              |
+  CROMARTY, and CHANONRY, were |                |              |
+  not lighted till the 15th    |                |              |
+  May, to which is owing the   |                |              |
+  small amount of their        |                |              |
+  Revenue; and LOCH RYAN was   |                |              |
+  not lighted till the 3d of   |                |              |
+  March subsequent to the      |                |              |
+  period embraced in this      |                |              |
+  STATE .                      |                |              |
+                               |----------------+--------------+
+                         TOTAL,|£19,529  5  1¹⁄₈|£5591  0  0²⁄₈|
+  -----------------------------+----------------+--------------+
+                                                               |
+                                                               |
+                                                               |
+                                              +----------------+
+                                              |£19,529  5  1¹⁄₈|
+                                              |                |
+                                              |  5,591  0  0²⁄₈|
+                                              +----------------+
+                                              |£13,938  5  0⁷⁄₈|
+                                              |                |
+                                              |                |
+                                              |      0  0  1¹⁄₈|
+                                              +----------------+
+                                              |£13,938  4 11⁶⁄₈|
+                                              |                |
+                                              |                |
+                                              |                |
+                                              |  1,893 17  6   |
+                                              +----------------+
+                                              |£15,832  2  5⁶⁄₈|
+                                              |                |
+                                              |                |
+                                              |                |
+                                              | 28,311  9  6²⁄₈|
+                                              +----------------+
+                                              |£12,479  7  0⁴⁄₈|
+                                              +================+
+                                                               |
+  =============================================================+
+
+  NOTE.--The General Expenses in the above STATE are allocated to each
+  Lighthouse in the same proportions as the Particular Expenses. The
+  expense of Beacons and Buoys is equally divided by the number of
+  Lighthouses, and the same amount allocated to each Lighthouse.
+
+No. III.--_Statement shewing the Increase in Tonnage during the Years
+1843-44-45-46, over 1842._
+
+  +------------------------------------------------------------------+
+  |                                                                  |
+  |                                                                  +
+  |The amount of the Tonnage in 1842 was                             |
+  |                          in 1843                                 |
+  |                                                                  +
+  |                                    INCREASE in 1843 over 1842    |
+  |                                                                  |
+  |                                  +----------+---------+----------+
+  |                                  | Coasting.| Oversea.|   Total. |
+  |                                  +----------+---------+----------+
+  |The amount of Tonnage in 1843 was |12,190,745|7,194,932|19,385,677|
+  |                      in 1844     |13,425,614|7,737,617|21,163,231|
+  |   INCREASE in 1844 over 1843     +----------+---------+----------+
+  |                                                                  |
+  |                                                                  +
+  |                                    INCREASE in 1844 over 1842    |
+  |                                  +----------+---------+----------+
+  |                                  | Coasting.| Oversea.|   Total. |
+  |                                  +----------+---------+----------+
+  |The amount of Tonnage in 1844 was |13,425,614|7,737,617|21,163,231|
+  |                      in 1845     |15,566,461|9,300,983|24,867,444|
+  |   INCREASE in 1845 over 1844     +----------+---------+----------+
+  |                                                                  |
+  |                                                                  +
+  |                                    INCREASE in 1845 over 1842    |
+  |                                  +----------+---------+----------+
+  |                                  | Coasting.| Oversea.|   Total. |
+  |                                  +----------+---------+----------+
+  |The amount of Tonnage in 1845 was |15,566,461|9,300,983|24,867,444|
+  |                      in 1846     |15,926,634|9,577,478|25,504,112|
+  |   INCREASE in 1846 over 1845     +----------+---------+----------+
+  |                                                                  +
+  |                                    INCREASE in 1846 over 1842    |
+  |                                  ================================+
+  |
+  +-------------------------------------------------------------------
+
+  +--------------------------------------------+---------+----------+
+  |                                   Coasting.| Oversea.|  Total.  |
+  |                                  ----------+---------+----------+
+  |The amount of the Tonnage in 1842 11,620,172|6,738,433|18,358,605|
+  |                          in 1843 12,190,745|7,194,932|19,385,677|
+  |                                  ----------+---------+----------+
+  |                                     570,573|  456,499| 1,027,072|
+  |                                            |         |          |
+  |                                            |         |          |
+  |                                            |         |          |
+  |                                            |         |          |
+  |The amount of Tonnage in 1843 was           |         |          |
+  |                      in 1844               |         |          |
+  |   INCREASE in 1844 over 1843      1,234,869|  542,685| 1,777,554|
+  |                                            |         |          |
+  |                                  ----------+---------+----------+
+  |                                   1,805,442|  999,184| 2,804,626|
+  |                                            |         |          |
+  |                                            |         |          |
+  |                                            |         |          |
+  |The amount of Tonnage in 1844 was           |         |          |
+  |                      in 1845               |         |          |
+  |   INCREASE in 1845 over 1844      2,140,847|1,563,366| 3,704,213|
+  |                                            |         |          |
+  |                                  ----------+---------+----------+
+  |                                   3,946,289|2,562,550| 6,508,839|
+  |                                            |         |          |
+  |                                            |         |          |
+  |                                            |         |          |
+  |The amount of Tonnage in 1845 was           |         |          |
+  |                      in 1846               |         |          |
+  |   INCREASE in 1846 over 1845        360,173|  276,495|   636,668|
+  |                                  ----------+---------+----------+
+  |                                   4,306,462|2,839,045| 7,145,507|
+  |                                  ==========+=========+==========+
+  |                                                                 |
+  +-----------------------------------------------------------------+
+
+
+APPENDIX, No. X.
+
+INSTRUCTIONS TO THE LIGHT-KEEPERS IN THE SERVICE OF THE COMMISSIONERS
+OF NORTHERN LIGHTHOUSES.
+
+1. The Lamps shall be kept burning bright and clear every night from
+sunset to sunrise; and in order that the greatest degree of light may
+be maintained throughout the night, the Wicks must be trimmed every
+four hours, or oftener if necessary; and the Keeper who has the first
+watch shall take care to turn the oil-valves so as to let the oil flow
+into the Burner a sufficient time before lighting.
+
+2. The Light-keepers shall keep a regular and constant Watch in the
+Light-room throughout the night. The First Watch shall begin at sunset.
+The Light-keepers are to take the watches alternately, in such manner
+that he who has the first watch one night, shall have the second watch
+next night. The length or duration of the watch shall not, in ordinary
+cases, exceed four hours; but during the period between the months of
+October and March, both inclusive, the first watch shall change at
+eight o’clock. The watches shall at all times be so arranged as to have
+a shift at midnight.
+
+3. At stations where there is only one Light-room, the daily duty shall
+be laid out in two departments, and the Light-keepers shall change from
+one department to the other every Saturday night.
+
+4. FIRST DEPARTMENT.--The Light-keeper who has this department, shall
+immediately after the morning Watch, polish or otherwise cleanse the
+Reflectors or Refractors till they are brought into a proper state of
+brilliancy; he shall also thoroughly cleanse the lamps, and carefully
+dust the Chandelier. He shall supply the Burners with cotton, the Lamps
+with oil, and shall have every thing connected with the Apparatus in a
+state of readiness for lighting in the evening.
+
+5. SECOND DEPARTMENT.--The Light-keeper who has this department shall
+cleanse the glass of the Lantern, lamp-glasses, copper and brass work
+and utensils, the walls, floors, and balcony of the Light-room, and the
+apparatus and machinery therewith connected; together with the Tower
+stair, passage, doors, and windows, from the Light-room to the Oil
+cellar.
+
+6. For the more effectual cleansing of the glass of the Lantern, and
+management of the Lamps at the time of lighting, both Light-keepers
+shall be upon watch throughout the first hour of the first watch every
+night, during the winter period, between the first day of October
+and last day of March, when they shall jointly do the duty of the
+Light-room during that hour. These changes to and from the double watch
+shall be intimated by the Keepers in the Monthly Returns for October
+and April.
+
+7. At those stations where there are two Light-rooms, each Light-keeper
+shall perform the entire duty of both departments in that Light-room
+to which he may be especially appointed. But after the first hour of
+the first Watch, the Light-keeper who has charge of this watch shall
+perform the whole duty of trimming and attending the Lights of both
+Light-rooms till the expiry of his watch; and in like manner, his
+successor on the watch shall perform the whole duty of both Light-rooms
+during his watch.
+
+8. The Light-keeper on duty shall on no pretence whatever, during his
+watch, leave the Light-room and balcony, or the passage leading from
+one Light-room to another, at stations where there are two Lights.
+Bells are provided at each Light-room to enable the Light-keeper
+on duty to summon the absent Light-keeper; and if at any time the
+Light-keeper on duty shall think the presence or assistance of the
+Light-keeper not on duty is necessary, he shall call him by ringing
+his bell, which should be immediately answered by the return signal,
+and the Keeper so called, should repair to the Light-room without
+delay. In like manner, when the watches come to be changed, the bell
+shall be rung to call the Light-keeper next in turn. After which the
+Light-keeper on duty shall, _at his peril_, remain on guard till he is
+relieved by the Light-keeper in person who has the next watch.
+
+9. Should the bell of the Light-keeper whose turn it is to mount guard,
+happen to be in an unserviceable state, the other house-bell shall be
+used, and some of the inmates of that house shall call the Light-keeper
+not on duty, so as by all means to avoid leaving the Light-room without
+a constant watch during the night.
+
+10. The Principal Light-keeper is held responsible for the safety and
+good order of the Stores, Utensils, and apparatus of what kind soever,
+and for every thing being put to its proper use, and kept in its proper
+place. He shall take care that none of the stores or materials are
+wasted, and shall observe the strictest economy, and the most careful
+management, yet so as to maintain in every respect the best possible
+light.
+
+11. The Principal Light-keeper shall daily serve out the allowance of
+Oil and other Stores for the use of the Light-room. The oil is to be
+measured by the Assistant, at the sight of the Principal Light-keeper.
+
+12. The Light-keepers shall keep a daily Journal of the quantity of
+Oil expended, the routine of their duty, and the state of the Weather,
+embodying any other remarks that may occur. These shall be written
+in the Journal-Books to be kept at each station for the purpose, at
+the periods of the day when they occur, as they must on no account be
+trusted to memory. On the first day of each month they shall make up
+and transmit to the Engineer a return, which shall be an accurate copy
+of the Journal for the preceding month.
+
+13. The Light-keepers are also required to take notice of any Shipwreck
+which shall happen within the district of the Lighthouse, and to
+enter an account thereof, according to the prescribed form, in a
+Book furnished to each Station for this purpose; and in such account
+he shall state whether the Light was seen by any one on board the
+shipwrecked Vessel and recognised by them, and how long it was seen
+before the vessel struck. A copy of this entry shall form the Shipwreck
+Return, to be forthwith forwarded to the Engineer.
+
+14. A book containing a Note of the Vessels passing each Lighthouse
+daily shall be kept; and an annual Schedule, shewing the number of
+vessels in each month, shall be sent to the Engineer in the month of
+January.
+
+15. The Monthly and Shipwreck Returns are to be written by the
+Assistant, and the accompanying letters by the Principal Light-keeper.
+The whole shall be carefully compared and signed by both Light-keepers,
+as directed by the printed form, and despatched by post to the Engineer
+as soon as possible.
+
+16. For the purpose of keeping up the practical knowledge of the
+“Occasional Keeper,” he shall be annually called in by the Principal
+Light-keeper to do duty for a fortnight in the month of January; and
+the same shall be stated in the Monthly Letter.
+
+17. The Principal Light-keeper is held responsible for the regularity
+of the Watches throughout the night, for the cleanliness and good order
+of the Reflecting or Refracting Apparatus, Machinery, and Utensils,
+and for the due performance of the whole duty of the Light-room or
+Light-rooms, as the case may be, whether performed by him personally,
+or by the Assistant.
+
+18. The Principal Light-keeper is also held responsible for the good
+order and condition of the Household Furniture belonging to the
+Lighthouse Board, as well in his own as in the Assistant’s house.
+This duty extends also to the cleanliness of the several apartments,
+passages, stairs, roofs, water-cisterns, store-rooms, work-shops,
+privies, ash-pits of the dwelling-houses, offices, court, and immediate
+access to the Lighthouse.
+
+19. The Light-keepers shall endeavour to keep in good order and repair
+the Dykes enclosing the Lighthouse grounds, the Landing-places, and
+Roads leading from thence to the Lighthouse and the Drains therewith
+connected, together with all other things placed under their charge.
+
+20. When stores of any kind are to be landed for the use of the
+Lighthouse, the Light-keepers shall attend and give their assistance.
+The Principal Light-keeper must, upon these occasions, satisfy himself,
+as far as possible, of the quantity and condition of the stores
+received, which must be duly entered in the Store-book and Monthly
+Return-book.
+
+21. The Light-keepers are to make a Report of the quality of the
+Stores, in the Monthly Return for March annually, or earlier should
+circumstances render this necessary; and this Report must proceed upon
+special trial of the several Cisterns of Oil and of the other Stores in
+detail, both at the time of receiving them and after the experience of
+the winter months.
+
+22. At all stations where Peat Fuel is in use, there must be such a
+quantity of Peats provided, that the Stock of the former year shall be
+a sufficient supply to the end of the current year.
+
+23. Should the supply of any of the Lighthouse Stores at any time
+appear to the Principal Light-keeper to be getting short, so as thereby
+to endanger the regular appearance of the Light, he shall immediately
+intimate the same to the Engineer, and he must be guided by prudence in
+reducing the stated number of Burners until a supply be received.
+
+24. The Light-keepers are prohibited from carrying on any trade or
+business whatever. They are also prohibited from having any boarders
+or lodgers in their dwelling-houses, and from keeping dogs at the
+Lighthouse establishments.
+
+25. The Light-keepers are also directed to take care that no smuggled
+goods are harboured or concealed in any way in or about the Lighthouse
+premises or grounds.
+
+26. The Light-keepers have permission to go from home to draw their
+salaries, and also to attend church. The Assistant Light-keeper, on all
+occasions of leave of absence, must consult the Principal Light-keeper
+as to the proper time for such leave, and obtain his consent; in like
+manner, the Principal Light-keeper shall duly intimate his intention
+of going from home to the Assistant Light-keeper;--it being expressly
+ordered that only one Light-keeper shall be absent from the Lighthouse
+at one and the same time.
+
+27. While the Principal Light-keeper is absent, or is incapacitated for
+duty by sickness, the full charge of the Light-room duty and of the
+premises shall devolve upon the Assistant, who shall in that case have
+access to the keys of the Light-room stores, and be held responsible
+in all respects as the Principal Light-keeper; and in the case of the
+incapacity of either Light-keeper, the assistance of the Occasional
+Light-keeper shall be immediately called in, and notice of the same
+given to the Engineer. Notice of any such occurrences to be taken
+in the Monthly Return, or by special letter to the Engineer, should
+circumstances render this necessary.
+
+28. The Light-keepers are required to be sober and industrious, cleanly
+in their persons and linens, and orderly in their families. They
+must conduct themselves with civility to strangers, by shewing the
+premises, at such hours as do not interfere with the proper duties of
+their office; it being expressly understood, that strangers shall not
+be admitted into the Light-room after sunset. But no money or other
+gratuity shall be taken from strangers on any pretence whatever.
+
+29. The Light-keepers are to appear in their Uniform-dress when any of
+the Commissioners or Principal Officers visit a station, and also on
+Sunday;--on which day, at noon, the weather permitting, the Lighthouse
+flag shall be hoisted by the Assistant Light-keeper, or in his absence
+by the Principal Light-keeper, when it shall remain displayed until
+sunset.
+
+30. These Instructions are to be read in the Light-room by the
+Principal Light-keeper, in the hearing of his Assistant, on the term
+days, before drawing his salary; and notice thereof taken in the
+Monthly Returns.
+
+31. In the event of any neglect occurring in the performance of any
+part of the duties required from a Light-keeper, the offending party
+shall, _jointly_ with the other Light-keeper or Light-keepers at the
+station, send immediate notice of the circumstance to the Engineer; and
+in the event of one party refusing or neglecting to concur in giving
+this intimation, the others (whether Principals or Assistants) shall
+proceed to give the notice in their own names.
+
+32. The breach of any of the foregoing Rules and Instructions shall
+subject the Light-keepers to dismissal, or to such other punishment as
+the nature of the offence may require.
+
+33. It is recommended that the Principal Light-keeper, or other
+Principal Officer at the respective Lighthouses for the time being,
+shall, every Sunday, perform the service pointed out for the inmates,
+by reading a portion of the Scriptures, and any other religious book
+furnished by the Board, and the Prayer composed for their use by the
+Rev. Dr Brunton, one of the Ministers of Edinburgh, or other Prayers
+in any work furnished by the Board. For this purpose, the Principal
+Light-keeper shall invite the families to assemble at noon in the
+Visiting Officer’s room.
+
+34. The Light-keepers are to observe that the above general Regulations
+are without prejudice to any more special Instructions which may be
+made applicable to any particular Lighthouse, or to such orders as may
+from time to time be issued by the Engineer.
+
+  _ALAN STEVENSON, Engineer
+  for Northern Lighthouses._
+
+  NORTHERN LIGHTS OFFICE, EDINBURGH,
+  _16th June 1847_.
+
+  EDINBURGH, _16th June 1847_.
+
+THE COMMISSIONERS having considered the preceding RULES and
+INSTRUCTIONS, approve of the same, direct them to be substituted for
+those now in use, appoint them to be signed by the Engineer, and copies
+of them and of this Minute to be issued to the present Light-keepers;
+direct a copy to be delivered in future to each Light-keeper at the
+time of his appointment, that they may understand that they are placed
+under the department and superintendence of the Engineer, who is held
+responsible for the strict observance of the Rules and Instructions,
+and for their general good conduct; that the Engineer has power, in
+case of neglect or disobedience, instantly to suspend and remove any
+of the Light-keepers, and to report the case to the Commissioners,
+by whom it will be considered, and the offending party subjected to
+dismissal, or such other punishment as the offence may merit. In case
+of a punishment less than dismissal, that circumstance, as well as
+the general conduct of the Light-keeper, will always be taken into
+consideration when any application may be made for superannuated
+allowance.
+
+  _Extracted from the Minutes by_
+
+  ALEX. CUNINGHAM, _Sec._
+
+
+
+
+EDINBURGH:
+
+PRINTED BY NEILL AND COMPANY, OLD FISHMARKET.
+
+
+
+
+[Illustration:
+
+  _PLATE_ I
+
+  _Eng^{d}. by W. & A. K. Johnston Edin^{r}._
+
+  CHART
+  Shewing the Situation of the
+  SKERRYVORE LIGHTHOUSE
+
+  Stevensons Account of Skerryvore Lighthouse]
+
+
+[Illustration:
+
+  _PLATE II._
+
+  _Engraved by W. & A. K. Johnston. Edinburgh._
+
+  CHART
+  of the POSITION of the
+  SKERRYVORE ROCKS
+  & FOULGROUND
+  _from a Survey made for the_
+  _COMMISSIONERS OF NORTHERN LIGHT HOUSES_
+  JAMES RITSON SURVEYOR
+  1846.
+
+  Stevenson’s Account of the Skerryvore Lighthouse.]
+
+
+[Illustration:
+
+  _PLATE_
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _James Andrews, Del^{t}._
+
+  _William Miller, Sculp^{t}._
+
+  PLAN OF SKERRYVORE ROCK
+  _AT LOW WATER OF SPRING TIDES._
+  _Shewing the site of the Lighthouse Tower, Barracks, Cranes, fresh
+  Water Tanks, Railway &c._]
+
+
+[Ilustration:
+
+  _N^{o}. III._
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _James Andrews, Del^{t}._
+
+  _William Miller, Sculp^{t}._
+
+  PLAN OF SKERRYVORE ROCK
+  _AT HIGH WATER OF SPRING TIDES._]
+
+
+[Illustration:
+
+  PLATE IV.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _James Andrews, Del^{t}._
+
+  _G. Aikman Sc_
+
+  CURVES FOR LIGHTHOUSE TOWERS
+
+  PARABOLA CONCHOID LOGARITHMIC HYPERBOLA]
+
+
+[Illustration:
+
+  _W. & A. K. Johnston Sculp^{t}._
+
+  MARINE DYNAMOMETER, SMALL SIZE, LENGTH 18 INCHES.]
+
+
+[Illustration:
+
+  PLATE V.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _Walter Ferrier Del^{t}._
+
+  _G. Aikman Sculp^{t}._
+
+  TEMPORARY BARRACK.
+
+  Barrack Room for Workmen
+  Engineer & Foreman’s Apartments
+  Kitchen & Provision Store
+  Store for Coals &c.]
+
+
+[Illustration:
+
+  PLATE VI.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _Walter Ferrier Del^{t}._
+
+  _G. Aikman Sculp^{t}._
+
+  Elevation
+
+  Fig. 1
+
+  TEMPORARY BARRACK.
+
+  TOP FIXTURES.
+
+  Plan
+
+  Fig. 2]
+
+
+[Illustration:
+
+  PLATE VII.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _James Andrews, Del^{t}._
+
+  _William Miller, Sculp^{t}._
+
+  ELEVATION.]
+
+
+[Illustration:
+
+  PLATE VIII.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _James Andrews, Del^{t}._
+
+  _William Miller, Sculp^{t}._
+
+  SECTION.
+
+  84th. Course
+
+  94th. Course
+
+  32d. Course
+
+  28th. Course
+
+  1st. Course
+
+  19th. Course]
+
+
+[Illustration:
+
+  PLATE IX.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _G. H. Slight Del^{t}._
+
+  _W. H. Lizars Sculp^{t}._
+
+  _BALANCE CRANE USED AT SKERRYVORE._
+
+  _Elevation_
+
+  _Plan_
+
+  _Section shewing Rollers_
+
+  _Plan of Rollers_
+
+  _Plan of Pedestal & Frame Circle_
+
+  _End view of Crane_]
+
+
+[Illustration:
+
+  _PLATE X._
+
+  _Engraved by W. & A. K. Johnston, Edinburgh._
+
+  PLAN
+  of ESTABLISHMENT at
+  HYNISH, ISLAND OF TYREE.
+  _SHEWING THE_
+  PIER, DOCK, RESERVOIR, LIGHTKEEPERS AND SEAMENS HOUSES &c.
+
+  NOTE
+  _The Soundings are marked in a fractional form thus ³²⁄₂₀ in which the
+  figures in the place of the Numerator indicate the depth at high
+  water of spring tides and those in the place of the Denominator the
+  depth at low water of spring tides, the rise of tide being 12 feet._
+
+  _Stevensons account of the Skerryvore Light House_]
+
+
+[Illustration:
+
+  PLATE XI.
+
+  _Walter Ferrier, Del^{t}._
+
+  _William Miller, Sculp^{t}._
+
+  HYNISH DOCK.
+
+  _Elevation._
+
+  _Section across Gates._
+
+  SINGLE BOOM]
+
+
+[Illustration:
+
+  _PLATE XII_
+
+  _J. L. Kerr, del^{t}._
+
+  _Eng^{d}. by W. & A. K. Johnston Edin^{r}._
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  ANNULAR LENS OF FIRST ORDER
+
+  SCALE ¹⁄₈^{th}.. FULL SIZE
+
+  PLAN
+
+  SECTION THROUGH A.B.
+
+  TABLE OF ELEMENTS OF LENS
+  IN MILLIMÈTRES
+
+  +-----+---------+---------+-----------------+
+  |     |         |         | CO-ORDINATES TO |
+  |     |         |         |    CENTRES OF   |
+  |     | RADIUS  | RADIUS  |    CURVATURE    |
+  |     |   OF    |   OF    +--------+--------+
+  |N^{o}|PERIPHERY|CURVATURE|  _x_   |   _y_  |
+  +-----+---------+---------+--------+--------+
+  |  1  | 140.00  |  483.50 | 454.79 |  00.00 |
+  |  2  | 208.15  |  543.60 | 488.55 |  13.08 |
+  |  3  | 262.40  |  598.62 | 513.38 |  31.72 |
+  |  4  | 309.20  |  659.77 | 540.71 |  57.00 |
+  |  5  | 350.50  |  719.84 | 565.27 |  84.86 |
+  |  6  | 387.44  |  779.48 | 588.00 | 114.93 |
+  |  7  | 422.23  |  846.45 | 614.35 | 151.50 |
+  |  8  | 456.23  |  911.30 | 636.90 | 189.55 |
+  |  9  | 490.00  |  980.30 | 660.11 | 250.17 |
+  | 10  | 523.33  | 1057.70 | 683.41 | 280.60 |
+  | 11  | 553.33  | 1136.01 | 712.79 | 328.00 |
+  +-----+---------+---------+--------+--------+]
+
+
+[Illustration:
+
+  _PLATE XIII_
+
+  _G. H. Slight Del^{t}._
+
+  _Eng^{d}. by W. & A. K. Johnston Edin^{r}._
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  REVOLVING
+  DIOPTRIC APPARATUS
+  FIRST ORDER.
+  ONE TWENTIETH OF FULL SIZE.]
+
+
+[Illustration:
+
+  PLATE XIV.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _G. Aikman, Sculp^{t}._
+
+  REVOLVING DIOPTRIC LIGHT OF THE FIRST ORDER.
+
+  _Plan_]
+
+
+[Illustration:
+
+  PLATE XV.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _G. Aikman, Sculp^{t}._
+
+  FIXED DIOPTRIC LIGHT OF THE FIRST ORDER.
+
+  _Vertical Section._]
+
+
+[Illustration:
+
+  PLATE. XVI.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _J. Andrews Del^{t}._
+
+  _W. H. Lizars Sculp^{t}._
+
+  1^{st}.
+  ORDER of LIGHTS.
+
+  _CONCAVE MIRRORS._]
+
+
+[Illustration:
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  PLATE XVII.
+
+  FIXED
+  CATADIOPTRIC LIGHT
+  OF 1^{st}. ORDER
+
+  ONE NINETEENTH OF FULL SIZE
+
+  REFERENCES.
+
+  A B C. CATADIOPTRIC ZONES.
+
+  D E F. COMPOUND DIOPTRIC BELT WITH DIAGONAL JOINTS C N M.
+
+  A′ B′ C′. LOWER CATADIOPTRIC ZONES ONE DIVISION BEING LEFT OUT FOR
+  FREE ACCESS TO THE LAMP.
+
+  F. FOCUS WITH FLAME OF LAMP.
+
+  REFERENCES.
+
+  X X X. DIAGONAL SUPPORTS FOR THE UPPER CATADIOPTRIC ZONES.
+
+  H H. SERVICE TABLE ON WHICH THE LAMP RESTS & WHERE THE KEEPER STANDS
+  TO TRIM THE BURNER.
+
+  R R. DIAGONAL FRAME FOR CARRYING THE APPARATUS.
+
+  _James Andrews, Del^{t}._
+
+  _William Miller, Sc._]
+
+
+[Illustration:
+
+  PLATE XVIII.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _G. H. Slight Del^{t}._
+
+  _W. H. Lizars Sculp^{t}._
+
+  1^{st}.
+  ORDER of LIGHTS.
+
+  _FIXED
+  CATADIOPTRIC
+  APPARATUS._]
+
+
+[Illustration:
+
+  PLATE XIX.
+
+  _Eng^{d}. by W. & A. K. Johnston Edin^{r}._
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  CATADIOPTRIC APPARATUS.
+
+  FOURTH ORDER]
+
+
+[Illustration:
+
+  PLATE XX
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _Walter H. Ferrier, del^{t}._
+
+  _Engraved by W. & A. K. Johnston Edin^{r}._
+
+  MECHANICAL LAMP
+  for
+  DIOPTRIC LIGHTS
+  of
+  FIRST ORDER.
+
+  A WICK HOLDERS
+  B GLASS HOLDER
+  C SCREW TO RACK D FOR RAISING WICK
+  D RACK FOR D^{o}.
+  E PIPE SUPPLYING OIL TO WICKS
+  F COLLAR SUPPORTING BURNERS
+  G DRIP CUP
+  H RETURN PIPE FOR OIL OVERFLOWING BURNER
+  I VALVE BOX
+  J CRANK RODS FOR WORKING LEATHER VALVES
+  K HINGE OF LID
+  L LID OF CISTERN
+  M OIL CISTERN
+  N SUCTION PIPE
+  O WINDING ARBOUR FOR MACHINE
+  P BOX FOR MACHINERY
+  Q SCREW FOR ADJUSTING LEVEL OF BURNER
+  R SERVICE TABLE
+  S COUPLING SCREW FOR OIL TUBE
+  T UNIVERSAL JOINTS FOR CONNECTING ROD
+  U CRANE FOR EMPTYING CISTERN
+  V CONNECTING ROD FOR CRANKS]
+
+
+[Illustration:
+
+  PLATE XXI
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _Walter H. Ferrier, del^{t}._
+
+  _Engraved by W. & A. K. Johnston Edin^{r}._
+
+  MECHANICAL LAMP.
+  ENLARGED VIEWS
+  OF OIL PUMPS.
+
+  ELEVATION
+
+  J   SUPPORTS OF BURNER
+  P   CRANK RODS FOR LEATHER VALVES
+  M N SUPPORTS FOR CRANK RODS
+  L   COUPLING
+  T   UNIVERSAL JOINT
+  P   CONNECTING ROD FOR CRANKS
+  S   SUCTION PIPE
+  O   SQUARE TRAY FOR OVERFLOWING OIL
+  Q   LID OF OIL CISTERN
+  I   OIL TUBE
+
+  PLANS AND SECTIONS IN REFERENCE TO OPPOSITE PLATE.
+
+  SECTION ON LINE A. B.
+
+  SECTION OF DISCHARGING CHEST E.
+
+  PLAN OF UPPER SIDE OF PUMP CHAMBER AT F. F.
+
+  PLAN OF VALVES AT F. F. AND H. H.
+
+  SECTION ON LINE C. D.
+
+  PLAN AND SECTION OF PLATE K.
+
+  PLAN OF LOWER SIDE OF PUMP CHAMBER AT H. H.]
+
+
+[Illustration:
+
+  _PLATE XXII_
+
+  _Walter H. Ferrier, del^{t}._
+
+  _Engraved by W. & A. K. Johnston, Edin^{r}._
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  MECHANICAL LAMP
+  ENLARGED VIEWS
+  OF OIL PUMPS.
+
+  ELEVATION
+
+  FRONT VIEW OF LEATHER PISTONS
+  AND LEVERS WORKING INTO PUMP
+
+  J   SUPPORTS OF BURNER
+  P   CRANK RODS FOR LEATHER VALVES
+  M N SUPPORTS FOR CRANK RODS
+  L   COUPLING
+  T   UNIVERSAL JOINT
+  R   CONNECTING ROD FOR CRANKS
+  S   SUCTION PIPE
+  O   SQUARE TRAY FOR OVERFLOWING OIL
+  Q   LID OF OIL CISTERN
+  I   OIL TUBE
+
+  PLAN]
+
+
+[Illustration:
+
+  _PLATE XXIII_
+
+  _Walter H. Ferrier Del^{t}._
+
+  _Eng^{d}. by W. & A. K. Johnston Edin^{r}._
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  CLOCKWORK MOVEMENT OF MECHANICAL LAMP
+
+  PLAN OF CLOCKWORK
+
+  SIDE VIEW OF CLOCKWORK]
+
+
+[Illustration:
+
+  _PLATE XXIV_
+
+  _James Andrews, del^{t}._
+
+  _Eng^{d}. by W. & A. K. Johnston Edin^{r}._
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  CLOCKWORK MOVEMENT AND BURNER OF MECHANICAL LAMP
+
+  SECTION OF BURNERS
+
+  ELEVATION OF WICKHOLDER
+
+  ELEVATION OF INNER TUBE OF GLASS GALLERY
+
+  PLAN OF BURNERS
+
+  PLAN OF THE LOWER SIDE OF BURNERS
+  SHEWING THE HANDLES OF THE RACKS FOR ELEVATING THE WICKS
+
+  A. UNIVERSAL JOINT OF PUMP ROD
+  B. REGULATOR
+  C. CHAIN BARREL
+  D. CHAIN
+  E. DRIVING WHEEL
+  F. BEVEL WHEELS FOR HORIZONTAL MOTION
+  G. WHEEL WITH COGS FOR LIFTING BELL-HAMMER
+  H. HAMMER FOR STRIKING ALARUM BELL
+  I. ALARUM BELL WHICH REPEATS WHILE THE PUMP IS WORKING
+  K. ENDLESS SCREW ON AXIS OF REGULATOR
+  L. WINDING ARBOUR
+
+  END VIEW OF CLOCKWORK]
+
+
+[Illustration:
+
+  PLATE XXV.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _G. Aikman, Sculp^{t}._
+
+  FLAME
+  FOR 1^{st}. ORDER OF
+  DIOPTRIC LIGHTS
+  at full size.]
+
+
+[Illustration:
+
+  _PLATE XXVI_
+
+  _James Andrews Del^{t}._
+
+  _Eng^{d}. by W. & A. K. Johnston Edin^{r}._
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  LANTERN
+  1^{ST}. ORDER OF LIGHTS.
+
+  PARAPET WALL
+
+  ELEVATION & SIDE VIEW OF UPPER PARTS OF
+  ASTRAGALS
+
+  ELEVATION & PLAN OF HORIZONTAL
+  PARTS OF ASTRAGALS
+
+  ENLARGED SECTIONS OF ASTRAGALS
+
+  ENLARGED SECTION OF CORNICE
+
+  ELEVATION & SIDE VIEW OF LOWER
+  PARTS OF ASTRAGALS
+
+  ENLARGED SECTION OF
+  SOLE PLATE & ASTRAGAL]
+
+
+[Illustration:
+
+  PLATE XXVII.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _James Andrews, Del^{t}._
+
+  _William Miller, Sculp^{t}._
+
+  ARDNAMURCHAN LIGHTHOUSE.]
+
+
+[Illustration:
+
+  PLATE XXVIII.
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  _H. G. Slight del^{t}._
+
+  _G. Aikman Sculp^{t}._
+
+  ARDNAMURCHAN LIGHTHOUSE.
+
+  PLAN]
+
+
+[Illustration:
+
+  _PLATE XXIX_
+
+  _James Andrews Del^{t}._
+
+  _Eng^{d}. by W. & A. K. Johnston Edin^{r}._
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  FLOATING LIGHT VESSEL
+
+  Reduced from Drawings in possession
+  of Honb^{le}. Corporation of Trinity House
+  Deptford Strond.
+
+  DIMENSIONS
+                                    F^{t}. In.
+  Length between the perpendiculars    80·0
+  Breadth moulded                      20·6
+  D^{o}. extreme                       21·0
+  Depth in hold                        10·8
+
+  Burthen in Tons 158⁹⁄₉₄]
+
+
+[Illustration:
+
+  _PLATE XXX_
+
+  _G. H. Slight Del^{t}._
+
+  _Engraved by W. & A. K. Johnston Edin^{r}._
+
+  ELEVATION OF COVESEA SKERRIES BEACON.
+
+  _N. B. The Letters refer to those in Plate XXXI._
+
+  _Stevenson’s Account of Skerryvore Lighthouse._]
+
+
+[Illustration:
+
+  _PLATE XXXI_
+
+  _G. H. Slight. Del^{t}._
+
+  _Engraved by W. & A. K. Johnston Edin^{r}._
+
+  COVESEA SKERRIES BEACON
+
+  _Plan on c d_
+
+  _Plan on a b_
+
+  _Section
+  showing
+  connection of
+  cage with
+  main Pillars_
+
+  _Plan on e f_
+
+  _Section
+  showing
+  connection
+  of Pillars_
+
+  _Section showing
+  attachment  of Pillars
+  to the      Sole plates
+  and its     connection
+  with        Rocks
+  by          Bats_
+
+  _Connecting Plate_
+
+  _Plan on g h_
+
+  _Stevenson’s Account of Skerryvore Lighthouse._]
+
+
+[Illustration:
+
+  _PLATE XXXII_
+
+  _James Andrews Del^{t}._
+
+  _Eng^{d}. by W. & A. K. Johnston Edin^{r}._
+
+  _Stevenson’s Account of Skerryvore Lighthouse_
+
+  STONE BEACON
+
+  ELEVATION
+
+  SECTION
+
+  IRON BEACON
+
+  ELEVATION
+
+  SECTION]
+
+
+[Illustration:
+
+  _PLATE XXXIII_
+
+  _James Andrews Del^{t}._
+
+  _Eng^{d}. by W. & A. K. Johnston Edin^{r}._
+
+  _Stevenson’s Account of Skerryvore Lighthouse._
+
+  BUOYS
+
+  MAST BUOY
+
+  CAN BUOY
+
+  CASK BUOY
+
+  NUN BUOY
+
+  _FOR WRECKS_
+
+  SPHERICAL BUOY
+
+  NELSON BUOY
+
+  _RIVER RIBBLE_
+
+  FAIRWAY BUOY
+
+  _RIVER TAY_]
+
+
+
+
+  Transcriber’s Notes
+
+
+  Inconsistent, archaic spelling, hyphenation, typography etc. have
+  been retained, also in proper and geographic names and in numbering
+  of illustrations and plates, except as listed under Changes below.
+  Depending on the hard- and software used and their settings not
+  all elements may display as intended.
+
+  The book regularly refers to a book published by the
+  author’s father: An Account of the Bell Rock Light-House by
+  Robert Stevenson, which is available at Project Gutenberg:
+  https://www.gutenberg.org/ebooks/48414.
+
+  Page xi: the errata have already been corrected in the text; see also
+  under Changes made below.
+
+  Page 149, ... the same mass of Mull stone would weigh 4252 tons ...:
+  possibly an error for 4152 tons (which would make the calculation
+  correct).
+
+  Page 174: ... somewhat on the same plan as that which is described
+  in the Appendix ...: it is not clear to which Appendix this refers;
+  possibly the reference is to Plate XXXI.
+
+  Page 252 ff.: Figures 59 and 60 are identical.
+
+  Page 271 ff.: Figures 71 and 72 are identical.
+
+  Page 276, See fig. 73 and the following paragraph: the description
+  appears to refer to Fig. 71/72 rather than to fig. 73.
+
+  Page 362, Conversely, n′ is the origin of the co-ordinates for the
+  grinding centre O of the interior convex refracting surface BC, ...:
+  in the illustration (Fig. 110) this appears to be a lower case o.
+
+  Page 389, entries for May 14 and 15, 1844: the order as given here is
+  the one printed in the source document; the reason for the inverse
+  order is not clear.
+
+  Page 422, item Charities &.c, number 2: Since last Act: there appears
+  to be a discrepancy between the individual amounts paid out and the
+  sub-total given.
+
+
+  Changes made:
+
+  Footnotes, illustrations and tables have been moved outside text
+  paragraphs; marginalia have been moved to directly above the
+  paragraphs they refer to. Some of the wider tables have been split
+  into chunks in order to fit the available width; such split tables
+  may be recombined into single tables (hence there are occasional
+  blank lines and columns in these split tables). In certain tables,
+  Do. or do. have been replaced with the dittoed text.
+
+  Some obvious minor typographical and punctuation errors have been
+  corrected silently. Some minor oddities in text lay-out have been
+  changed silently for easier readability.
+
+  Repeated table and column headers, carry/brought forward, subtotals
+  etc. on page transitions in lists and tables have been removed,
+  except partly on the transition from page 423 to 424.
+
+  Suter and Souter have been standardised to Suter.
+
+  Page xi: the errata listed have already been corrected in the text.
+  The amount L.93,306 : 8 : 10 does not occur on line 6 of page 178;
+  the amount L.90,268, 12 : 1 that does occur on line 7 of that page
+  has been replaced by L.86,977 : 17 : 7 as given in the Appendix (page
+  384).
+
+  Page 61, Footnote [13]:
+
+              G·M
+  ... will be ----, by which expression ...
+              G·M′
+
+  changed to
+
+               G·M
+  ... will be -----, by which expression ....
+              G′·M′
+
+  Page 231: In these figures, n n shews the reflector flame ... changed
+  to In these figures, n n shews the reflector frame ....
+
+  Page 267: François Soliel, whom I urged ... changed to François
+  Soleil, whom I urged ...; ... the light derived from the accessary
+  part ... changed to ... the light derived from the accessory part ....
+
+  Page 281: OA = ρ . cos . OAX. changed to OA = ρ . cos OAX.
+
+  Page 284: F is the small flame in the focus ... changed to E is the
+  small flame in the focus ....
+
+  Page 413, entry The Commission paid to Collectors ...: £2401 : 7 :
+  0⁴⁄₈ changed to £2401 : 7 : 3⁴⁄₈ cf. page 429.
+
+  Page 430, entry 9. Startpoint, Balance: 462 0 8⁶⁄₈ changed to 462 0
+  3⁶⁄₈.
+
+  Page 355: ... forming a flat parallelopepid ... changed to ...
+  forming a flat parallelopiped ....
+
+  Page 399, entry Drum Sand West Buoy, South Point: Bear changed to
+  Bearing.
+
+
+
+*** END OF THE PROJECT GUTENBERG EBOOK 75213 ***
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+</head>
+<body>
+<div style='text-align:center'>*** START OF THE PROJECT GUTENBERG EBOOK 75213 ***</div>
+
+<div class="tnbox">
+
+<p class="noindent">Please see the <a href="#TN">Transcriber’s Notes</a> at the end of this text.</p>
+
+<p class="noindent blankbefore75">Larger versions of illustrations and plates are available by opening them in a new tab or window.</p>
+
+<p class="noindent blankbefore75">New original cover art included with this eBook is granted to the public domain.</p>
+
+</div><!--tnbox-->
+
+<div class="x-ebookmaker-drop">
+
+<hr class="chap">
+
+<div class="container w30emmax" id="Cover">
+
+<img src="images/cover.jpg" alt="Cover image">
+
+</div><!--container-->
+
+</div><!--ebook drop-->
+
+<hr class="chap">
+
+<div class="container w30emmax" id="Fig0">
+
+<img src="images/illo001.jpg" alt="" class="bordered">
+
+<div class="illotext w15emmax">
+
+<p class="caption">SKERRYVORE LIGHTHOUSE.</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="titlepage">
+
+<h1><span class="fsize150 gesp2">ACCOUNT</span><br>
+<span class="fsize60">OF THE</span><br>
+<span class="fsize175"><span class="gesp2">SKERRYVORE LIGHTHOUSE</span>,</span><br>
+<span class="fsize60">WITH</span><br>
+<span class="fsize125">NOTES ON THE ILLUMINATION OF LIGHTHOUSES;</span></h1>
+
+<p class="center blankbefore15 highline15"><span class="fsize60">BY</span><br>
+<span class="fsize110">ALAN STEVENSON, LL.B., F.R.S.E., M.I.C.E.,</span><br>
+<span class="fsize80">ENGINEER TO THE NORTHERN LIGHTHOUSE BOARD.</span></p>
+
+<div class="container w10emmax">
+
+<img src="images/illo003.jpg" alt="Northern Lighthouses emblem" title=".NORTHERN LIGHTHOUSES. .IN SALUTEM OMNIUM." class="logo">
+
+</div><!--container-->
+
+<p class="center fsize125">“<span class="gesp2">ΥΠΕΡ · ΤΩΝ · ΠΛΩΙΖΟΜΕΝΩΝ</span>”<br>
+<span class="righttext fsize60"><i>Inscription on the Ancient Pharos of Alexandria.</i></span></p>
+
+<p class="center allclear fsize80 highline8">BY ORDER OF THE COMMISSIONERS OF NORTHERN LIGHTHOUSES.</p>
+
+<p class="center highline15">ADAM AND CHARLES BLACK, NORTH BRIDGE, EDINBURGH.<br>
+LONGMAN AND CO., LONDON.</p>
+
+<hr class="short">
+
+<p class="center fsize80">MDCCCXLVIII.</p>
+
+</div><!--titlepage-->
+
+<hr class="chap x-ebookmaker-drop">
+
+<p class="center highline8 fsize60">PRINTED BY NEILL AND COMPANY, EDINBURGH.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Pageiii">[iii]</span></p>
+
+<h2 class="nobreak">PREFACE.</h2>
+
+</div><!--chapter-->
+
+<p>I am unwilling to dismiss the following pages from my hands
+without saying a few words in extenuation of the defects which
+they contain. My chief plea in defence is, that the preparation of
+this <i>Account of the Skerryvore Lighthouse</i>, and the <i>Notes on the
+Illumination of Lighthouses</i> which follow it, was not chosen or
+assumed by me, but was a task imposed by the express desire of
+the Lighthouse Board, to whose enlightened and liberal views the
+Mariner owes the erection of the Lighthouse itself. My labours
+were also continually interrupted by the urgent calls of my official
+duties; and, on several occasions, I was forced to dismiss unfinished
+chapters from my mind for a period of several months—circumstances
+which, I hope, will in some measure account for the
+desultory character of the performance, the disproportion of some
+of its parts, and more especially for repetitions and perhaps omissions
+which would otherwise have been quite unpardonable.</p>
+
+<p>Having said thus much by way of apology for this Volume,
+I must acknowledge my many and great obligations to my Father
+who preceded me as Engineer to the Board of Northern Lighthouses,
+and of whose experience, as the Architect of no fewer than
+twenty-five Lighthouses, including that of the Bell Rock, I had<span class="pagenum" id="Pageiv">[iv]</span>
+the full benefit during the erection of the Skerryvore Lighthouse.
+To the generosity of my esteemed friend, <span class="smcap">M. Leonor Fresnel</span>, I
+owe all that I know of the Dioptric System of Illumination, invented
+by his late illustrious Brother; but this general acknowledgment
+will not supersede the necessity of frequent repetitions
+of my obligations to him, as occasion offers, in the course of these
+pages. I have also derived much assistance, as a careful reader
+will easily trace, from the valuable little work of <span class="smcap">M. Peclet</span>, entitled
+<i>Traité de l’Eclairage</i>. There are, besides, many other obligations,
+which I cannot attempt to acknowledge individually, but
+which those, who kindly conferred them, well know how much I
+value.</p>
+
+<p class="blankbefore75">In the <i>Account of the Skerryvore Lighthouse</i>, which forms the
+first part of this Volume, there is an important omission; and, in this
+short prefatory notice, I gladly embrace the only opportunity, which
+now remains, of supplying the defect. Although, in the course of
+the Narrative, I have occasionally noticed some special deliverances
+from danger, I have altogether neglected to record the remarkable
+fact, that, amidst our almost daily perils, during six seasons
+on the Skerryvore Rock, there was no loss of either life or
+limb amongst us. Those who best know the nature of the service
+in which we were engaged,—the daily jeopardy connected with
+landing weighty materials in a heavy surf and transporting the
+workmen in boats through a boisterous sea, the risks to so many
+men, involved in mining the foundations of the Tower in a space
+so limited, and above all, the destruction, in a single night by
+the violence of the waves, of our temporary barrack on the Rock,<span class="pagenum" id="Pagev">[v]</span>
+which had cost the toils of a whole season, will not wonder that
+I am anxious to express, what I know to have been a general
+feeling amongst those engaged in the work—that of heartfelt thankfulness
+to <span class="smcap">Almighty God</span> for merciful preservation in danger, and
+for the final success which terminated our arduous and protracted
+labours.</p>
+
+<p class="noindent blankbefore4 fsize80"><span class="smcap">Edinburgh</span>, <i>March 25, 1848</i>.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Pagevi">[vi-<br>vii]<a id="Pagevii"></a></span></p>
+
+<h2 class="nobreak">CONTENTS.</h2>
+
+</div><!--chapter-->
+
+<table class="toc">
+
+<tr>
+<td colspan="2" class="partno">PART I.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="partname">ACCOUNT OF SKERRYVORE LIGHTHOUSE.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="right">Page</td>
+</tr>
+
+<tr>
+<td class="subjects">Introduction — Constitution of the Lighthouse Board — Lights established since 1821 — Improvements in the mode of illumination — Dioptric
+Lights — Beacons and Buoys,</td>
+<td class="pagno"><a href="#Page9">9</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">CHAPTER I.</td>
+</tr>
+
+<tr>
+<td class="subjects">Topographic notice of the Skerryvore Rock,</td>
+<td class="pagno"><a href="#Page19">19</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">CHAPTER II.</td>
+</tr>
+
+<tr>
+<td class="subjects">Preliminary arrangements and works, including survey of the rocks, and opening of quarries from 1834 to 1837 — Survey of the Skerryvore
+rocks — Disadvantages of Tyree — Pier and workyard at Hynish, Tyree — Quarries at Hynish — Skerryvore Committee appointed,</td>
+<td class="pagno"><a href="#Page37">37</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">CHAPTER III.</td>
+</tr>
+
+<tr>
+<td class="subjects">On the construction of Lighthouse Towers,</td>
+<td class="pagno"><a href="#Page45">45</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">CHAPTER IV.<br><span class="chaptitle">OPERATIONS OF 1838.</span></td>
+</tr>
+
+<tr>
+<td class="subjects">Temporary Barrack on Rock — Tools and machinery — Steam Tender for the works —
+Employment and wages of workmen — Progress of the outfit for the
+season’s operations — Embark for Skerryvore — Lay down moorings, and try to land on the Rock —
+Driven to Mull — First day’s work on the Rock — Shipment of materials
+at Glasgow and Greenock — Reach Tyree — Driven to Mull — Return to Tyree — First good day’s work
+on the Rock — Sudden gale and great peril to the vessels — Reach Hynish
+in safety — Detained by bad weather four days at Hynish — Return to the Rock and have six days of
+good weather — Erection of the pyramid of the wooden barrack — Mode
+of determining the length of the beams, and the sites for their fixtures — Pyramid completed — Mode
+of living while erecting the barrack — Shoals of Medusæ
+seen — Driven by a gale to Mull — Return to Hynish and are driven to Coll — Return to the Rock —
+Driven to Tyree — Return to the Rock — Horizontal braces fixed — Driven
+to Mull — Heavy gale — Timber<span class="pagenum" id="Pageviii">[viii]</span> cast on Tyree —
+Return to Rock and further progress of barrack — Last day’s work on
+Rock this season — Precaution for the benefit of shipwrecked seamen — View from top of pyramid —
+Destruction of the barrack during a gale — Letter from Mr
+Hogben — Proceed to Skerryvore — State in which the Rock was found — Cause of the destruction of
+the barrack — Preparations for a new barrack — Works at Hynish — Hynish
+quarries,</td>
+<td class="pagno"><a href="#Page71">71</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">CHAPTER V.<br><span class="chaptitle">OPERATIONS OF 1839.</span></td>
+</tr>
+
+<tr>
+<td class="subjects">Shipping station and pier at Hynish — Granite quarries in Mull — Observations on the quarrying of granite — Dressing of the Lighthouse
+blocks — Excavation of foundation for the Lighthouse Tower on the Skerryvore Rock — Fitting up of the second barrack on the Rock — Sudden death of George
+Middlemiss — Wharf and landing-place on the Rock — Ring-bolts, water-tanks, and
+railways — Incidents of the season — Effects of a gale from the south-west — Mutiny of
+the crew — Near approach of the vessels to the Rock, and other circumstances shewing the importance of a Light on the Skerryvore,</td>
+<td class="pagno"><a href="#Page107">107</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">CHAPTER VI.<br><span class="chaptitle">OPERATIONS OF 1840.</span></td>
+</tr>
+
+<tr>
+<td class="subjects">Hynish workyard — Hynish pier — The Rock — Life in the barrack —
+Foundation-pit — Landing of the materials on the Rock — Laying the first stone,</td>
+<td class="pagno"><a href="#Page140">140</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">CHAPTER VII.<br><span class="chaptitle">OPERATIONS OF 1841.</span></td>
+</tr>
+
+<tr>
+<td class="subjects">Hynish workyard — The Rock — The waves — Colours of the breaking waves — The seals,</td>
+<td class="pagno"><a href="#Page151">151</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">CHAPTER VIII.<br><span class="chaptitle">OPERATIONS OF 1842.</span></td>
+</tr>
+
+<tr>
+<td class="subjects">State of the Rock in Spring of 1842 — Commencement of Rock operations — Last stone — The Lantern,</td>
+<td class="pagno"><a href="#Page163">163</a></td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">CHAPTER IX.<br><span class="chaptitle">CONCLUDING OPERATIONS AND EXHIBITION OF THE LIGHT.</span></td>
+</tr>
+
+<tr>
+<td class="subjects">Harbour works — Bo Pheg beacon — Light-keepers’ and seamen’s houses — Concluding works on the Rock, such as pointing, &amp;c. — Interior
+fittings of the Tower — Light-room apparatus, and first exhibition of the Light — Removal of the barrack from the Rock — Expense,</td>
+<td class="pagno"><a href="#Page169">169</a><span class="pagenum" id="Pageix">[ix]</span></td>
+</tr>
+
+<tr>
+<td colspan="2" class="partno">PART II.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="partname">NOTES ON THE ILLUMINATION OF LIGHTHOUSES, WITH SHORT NOTICES OF THEIR HISTORY, <a href="#Page181">181</a>.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="subjects">Early history, <a href="#Page181">181</a> — Colossus of Rhodes, <a href="#Page182">182</a> — Pharos of Alexandria,
+<a href="#Page183">183</a> — Coruna Tower, <a href="#Page187">187</a> — Lighthouse at the mouth of the Quadalquivir, <a href="#Page188">188</a> — Ancient
+Phari in Britain, <a href="#Page188">188</a> — Tour de Corduan, <a href="#Page189">189</a> — Eddystone, <a href="#Page189">189</a> — Bell Rock,
+<a href="#Page192">192</a> — Carlingford, <a href="#Page194">194</a> — Iron lighthouses, <a href="#Page194">194</a> — Early modes of illumination,
+<a href="#Page195">195</a> — Flame, <a href="#Page196">196</a> — Drummond and Voltaic Lights, <a href="#Page199">199</a> — Mr Gurney’s Lamp,
+<a href="#Page200">200</a> — Argand Burners, <a href="#Page200">200</a>.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">CATOPTRIC SYSTEM OF LIGHTS, <a href="#Page204">204</a>.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="subjects">Application of Paraboloidal Mirrors, <a href="#Page205">205</a> — Reflection, <a href="#Page207">207</a> — Paraboloidal Mirrors,
+<a href="#Page209">209</a> — Divergence of Paraboloidal Mirrors, <a href="#Page212">212</a> — Effect of Paraboloidal Mirrors, <a href="#Page217">217</a> — Power of
+ditto, <a href="#Page218">218</a> — Manufacture of reflectors, <a href="#Page218">218</a> — Testing of mirrors, <a href="#Page219">219</a> — Argand Lamps used in
+reflectors, <a href="#Page220">220</a> — Arrangements for raising or lowering the Argand wick, <a href="#Page222">222</a> — Flowing of the lamp,
+<a href="#Page223">223</a> — Placing the lamp in the focus, <a href="#Page226">226</a> — Distinctions of Catoptric Lights, <a href="#Page227">227</a> — Colour
+as a distinction for lights, <a href="#Page229">229</a> — Arrangement of reflectors on the frame, <a href="#Page230">230</a> — Bordier Marcet’s reflectors,
+<a href="#Page232">232</a> — Fanal sidéral, <a href="#Page232">232</a> — Fanal à double effet, <a href="#Page234">234</a> — Fanal à double face,
+<a href="#Page236">236</a> — Mr Barlow’s spherical mirrors, <a href="#Page237">237</a> — Captain Smith’s mirrors in the form of a parabolic spindle,
+<a href="#Page238">238</a>.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">DIOPTRIC SYSTEM OF LIGHTS, <a href="#Page239">239</a>.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="subjects">Early history of Lighthouse lenses, Condorcet, Buffon, Brewster, Fresnel, <a href="#Page239">239</a> — Refraction,
+<a href="#Page242">242</a> — Lenses, <a href="#Page245">245</a> — Spherical aberration, <a href="#Page248">248</a> — Fresnel’s formulæ for annular lenses,
+<a href="#Page249">249</a> — Testing lenses, <a href="#Page255">255</a> — Divergence of lenses, <a href="#Page256">256</a> — Illuminating power of lenses,
+<a href="#Page257">257</a> — Arrangement of lenses in a Lighthouse, <a href="#Page258">258</a> — Pyramidal lenses and mirrors, <a href="#Page259">259</a> — Curved
+mirrors, <a href="#Page260">260</a> — Cylindric refractors of fixed Lights, <a href="#Page263">263</a> — Application of crossed prisms to cause flashes,
+<a href="#Page264">264</a> — True cylindric form given to refractors, and other improvements in their construction, <a href="#Page264">264</a> — Catadioptric
+zones, the mode of computing their elements, &amp;c., <a href="#Page267">267</a> — Testing of zones, <a href="#Page282">282</a> — Framing of zones,
+<a href="#Page286">286</a> — Mechanical lamp, <a href="#Page286">286</a> — Height of flame of mechanical lamp, <a href="#Page289">289</a> — Position of flame
+in reference to focus, <a href="#Page290">290</a> — Working of the pumps, <a href="#Page291">291</a> — Choice of focal point for various parts of apparatus,
+<a href="#Page292">292</a> — Choice of a focal point for zones, <a href="#Page292">292</a> — Application of spherical mirrors to fixed Dioptric Lights,
+<a href="#Page293">293</a> — Arrangement of Dioptric apparatus, <a href="#Page293">293</a> — Arrangement of Dioptric apparatus in Lightroom,
+<a href="#Page294">294</a> — Power of Dioptric instruments, <a href="#Page298">298</a> — Orders of French Lights, <a href="#Page298">298</a> — Distinctions of
+Dioptric Lights, <a href="#Page299">299</a> — Comparison of Dioptric and Catoptric apparatus for revolving lights, <a href="#Page301">301</a> — Comparison for
+fixed lights, <a href="#Page303">303</a> — Summary<span class="pagenum" id="Pagex">[x]</span> of views as to two systems for revolving lights,
+<a href="#Page306">306</a> — Summary of views as to two systems for fixed lights, <a href="#Page306">306</a> — Advantages and disadvantages of both systems under
+certain circumstances, <a href="#Page308">308</a> — Distinctions of the Dioptric Lights and the application of coloured media, <a href="#Page311">311</a> — Captain
+Basil Hall’s proposal for fixed lights, <a href="#Page313">313</a> — Effects of rapid motion on the power of lights, <a href="#Page315">315</a> — Connection of
+experiments with irradiation, <a href="#Page320">320</a>.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="chaphead">VARIOUS GENERAL CONSIDERATIONS CONNECTED WITH LIGHTHOUSES, <a href="#Page320">320</a>.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="subjects">Masking Lights, <a href="#Page320">320</a> — Double Lights, <a href="#Page322">322</a> — Leading Lights,
+<a href="#Page323">323</a> — Distribution of Lights on a coast, <a href="#Page325">325</a> — Height of Lighthouse Tower, and its relation to range of light,
+<a href="#Page328">328</a> — Diagonal Lantern, <a href="#Page330">330</a> — Glazing of Lantern, <a href="#Page331">331</a> — Ventilation of Lanterns,
+<a href="#Page331">331</a> — Arrangements and Management of a Lighthouse, <a href="#Page334">334</a> — Cleansing of apparatus, <a href="#Page335">335</a> — Mode
+of measuring relative power of lights, <a href="#Page336">336</a> — More accurate comparison of intensity of lights, <a href="#Page338">338</a> — Floating Lights,
+<a href="#Page346">346</a> — Beacons and Buoys, <a href="#Page347">347</a>.</td>
+</tr>
+
+</table>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+
+<h2>APPENDIX.</h2>
+
+</div><!--chapter-->
+
+<table class="secondtoc">
+
+<tr>
+<td class="nr"><a href="#App1">1.</a></td>
+<td class="subj">Table of Co-ordinates of Hyperbolic Column.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#App2">2.</a></td>
+<td class="subj">Notes on the Making of Paraboloïdal Mirrors.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#App3">3.</a></td>
+<td class="subj">Notes on the Grinding and Polishing of Dioptric Instruments for Lighthouses.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#App4">4.</a></td>
+<td class="subj">Table of the Elements of the Catadioptric Zones for Lights of the first order in the system
+of Augustin Fresnel.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#App5">5.</a></td>
+<td class="subj">Notice to Mariners of the Exhibition of the Skerryvore Light.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#App6">6.</a></td>
+<td class="subj">Detailed Account of the Expense of the Skerryvore Lighthouse.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#App7">7.</a></td>
+<td class="subj">Excerpts from Account of Experiments on the Force of the Waves of the Atlantic and German
+Oceans, by Thomas Stevenson, F.R.S.E., Civil Engineer.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#App8">8.</a></td>
+<td class="subj">Annual List for 1848 of Lighthouses, Beacons, and Buoys, in the District of the Northern
+Lights Board.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#App9">9.</a></td>
+<td class="subj">Annual Report by the Secretary as to the Income and Expenditure of the Northern Lights
+Board for 1846.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#App10">10.</a></td>
+<td class="subj">Instructions to the Light-keepers in the Service of the Commissioners of the Northern
+Lighthouses.</td>
+</tr>
+
+</table>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Pagexi">[xi-<br>xii]<a id="Pagexii"></a></span></p>
+
+<h2 class="nobreak">PLATES.</h2>
+
+</div><!--chapter-->
+
+<table class="secondtoc">
+
+<tr>
+<td class="nr"><a href="#Plate1">I.</a></td>
+<td class="subj">Chart shewing the situation of the Skerryvore Lighthouse.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate2">II.</a></td>
+<td class="subj">Chart shewing the position of the Skerryvore Rocks and foul ground.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate3">III.</a></td>
+<td class="subj">Plans of the Skerryvore Rock at high and low water of spring tides.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate4">IV.</a></td>
+<td class="subj">Curves for Lighthouse Towers — Marine Dynamometer.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate5">V.</a></td>
+<td class="subj">Barrack of timber on the Skerryvore Rock.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate6">VI.</a></td>
+<td class="subj">Details of fixtures of timbers at the top of the Timber Barrack.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate7">VII.</a></td>
+<td class="subj">Elevation of Skerryvore Lighthouse.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate8">VIII.</a></td>
+<td class="subj">Section of Skerryvore Lighthouse.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate9">IX.</a></td>
+<td class="subj">Balance Crane used at Skerryvore.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate10">X.</a></td>
+<td class="subj">Plan shewing the Lighthouse Establishment of Barracks, Harbour, &amp;c., at Hynish, in the
+Island of Tyree.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate11">XI.</a></td>
+<td class="subj">Elevation and Section entrance to Dock at Hynish.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate12">XII.</a></td>
+<td class="subj">Plan and Section of Annular Lens.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate13">XIII.</a></td>
+<td class="subj">Perspective Elevation of Revolving Dioptric Apparatus of First Order.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate14">XIV.</a></td>
+<td class="subj">Plan of Revolving Dioptric Light of First Order, with Mirrors.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate15">XV.</a></td>
+<td class="subj">Vertical Section of fixed Dioptric Lights of First Order, with Mirrors.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate16">XVI.</a></td>
+<td class="subj">Elements of Concave Mirrors for Dioptric Lights of First Order, and arrangement on the
+Frame.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate17">XVII.</a></td>
+<td class="subj">Perspective View of Fixed Dioptric Light of First Order, with Catadioptric Zones.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate18">XVIII.</a></td>
+<td class="subj">Vertical Section of Fixed Dioptric Light of First Order, with Catadioptric Zones.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate19">XIX.</a></td>
+<td class="subj">Vertical Section of Catadioptric Light of Fourth Order, with Framing.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate20">XX.</a></td>
+<td class="subj">Elevation of Mechanical Lamp for Dioptric Lights of First Order.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate21">XXI.</a></td>
+<td class="subj">Enlarged Views of Oil-Pumps of Mechanical Lamp.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate22">XXII.</a></td>
+<td class="subj">Enlarged Views of Oil-Pumps of Mechanical Lamp.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate23">XXIII.</a></td>
+<td class="subj">Details of Clock-work of Mechanical Lamp.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate24">XXIV.</a></td>
+<td class="subj">Details of Clock-work of Mechanical Lamp.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate25">XXV.</a></td>
+<td class="subj">Flame of Mechanical Lamp of First Order at full size.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate26">XXVI.</a></td>
+<td class="subj">Elevation of Diagonal Lantern, and details of Astragals.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate27">XXVII.</a></td>
+<td class="subj">Elevation of Ardnamurchan Lighthouse.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate28">XXVIII.</a></td>
+<td class="subj">Plan of Ardnamurchan Lighthouse.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate29">XXIX.</a></td>
+<td class="subj">Lines of a Floating Light Vessel belonging to the Corporation of Trinity House of Deptford
+Strond.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate30">XXX.</a></td>
+<td class="subj">Elevation of Covesea Skerries Beacon.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate31">XXXI.</a></td>
+<td class="subj">Details of Covesea Skerries Beacon.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate32">XXXII.</a></td>
+<td class="subj">Elevations and Sections of Stone and Iron Beacons.</td>
+</tr>
+
+<tr>
+<td class="nr"><a href="#Plate33">XXXIII.</a></td>
+<td class="subj">Elevations of Buoys.</td>
+</tr>
+
+</table>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+
+<h2 class="nobreak">ERRATA.</h2>
+
+</div><!--chapter-->
+
+<table class="errata">
+
+<tr>
+<td>Page</td>
+<td>52,</td>
+<td>line 8, <i>for</i> Redelet <i>read</i> Rondelet</td>
+</tr>
+
+<tr>
+<td>...</td>
+<td>178,</td>
+<td>line 6, <i>for</i> L.93,306:8:10 <i>read</i> L.86,977:17:7</td>
+</tr>
+
+<tr>
+<td>...</td>
+<td>292,</td>
+<td>line 30, <i>for</i> radius rector <i>read</i> radius vector</td>
+</tr>
+
+<tr>
+<td>...</td>
+<td>294,</td>
+<td>line 13, <i>for</i> give <i>read</i> gives</td>
+</tr>
+
+<tr>
+<td>...</td>
+<td>329,</td>
+<td>line 3, <i>for</i> earth <i>read</i> sea</td>
+</tr>
+
+<tr>
+<td>...</td>
+<td>347,</td>
+<td>line 29, <i>for</i> Plate XXXII., <i>read</i> Plate XXX.,</td>
+</tr>
+
+</table>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page7">[7]</span></p>
+
+<h2 class="nobreak"><span class="partno">PART FIRST.</span><br>
+<span class="partname">ACCOUNT OF THE SKERRYVORE LIGHTHOUSE.</span></h2>
+
+</div><!--chapter-->
+
+<hr class="chap x-ebookmaker-drop">
+
+<p><span class="pagenum" id="Page8">[8-<br>9]<a id="Page9"></a></span></p>
+
+<h3>INTRODUCTION.</h3>
+
+<p>In the course of preparing the account of the building of the
+Skerryvore Lighthouse, it occurred to me, that a short Introduction
+should be prefixed, embracing a concise view of the constitution
+and acts of the Board of Commissioners of Northern Lights,
+more especially from 1824, when my Father’s work on the Bell
+Rock Lighthouse was published, up to the present time. This
+object will be best accomplished, by presenting to the reader, in
+the first place, an account of the constitution and powers of the
+Lighthouse Board, chiefly drawn from the “Introduction to the
+Bye-Laws, Rules, and Regulations of the Commissioners of Northern
+Lighthouses,” prepared by a Committee of their number; and
+by afterwards briefly noticing the principal works of the Board
+since 1824, and stating generally the nature of the changes
+and improvements made within that period on the mode of illumination,
+of which I propose, in a subsequent part of this volume, to
+give a somewhat detailed account.</p>
+
+<p class="blankbefore75">The trade of Scotland had begun to increase very soon after
+the settlement of the civil war in 1745; but it was not till the year
+<span class="sidenote">Constitution of
+the Lighthouse
+Board.</span>
+1784 that the general establishment of Sea Lights upon the Coast
+appears to have been brought under the notice of the Legislature.
+In that year, the subject was first mentioned at a meeting of the
+Convention of the Royal Burghs of Scotland, by Mr <span class="smcap">Dempster</span> of
+Dunichen, M.P., the Provost of the burgh of Forfar; and, in the
+year 1786, that gentleman brought a bill into Parliament, and an
+Act was obtained establishing the present Board of Northern
+Lights.</p>
+
+<p><span class="pagenum" id="Page10">[10]</span></p>
+
+<p>This Act sets forth, that “it would conduce greatly to the
+security of navigation and the fisheries, if four Lighthouses were
+erected in the Northern parts of Great Britain, one on Kinnaird’s
+Head, Aberdeenshire, one in the North Isles of Orkney, one
+on the point of Scalpa, in the Island of Harris, and a fourth on
+the Mull of Kintyre, Argyllshire;” and it accordingly authorises
+the erection of those four Lighthouses. The Commissioners appointed
+for carrying this Act into execution were, the Lord Advocate
+and Solicitor-General of Scotland, the Lord Provost and first
+Bailie of Edinburgh, the Lord Provost and first Bailie of Glasgow,
+the Provosts of Aberdeen, Inverness, and Campbeltown, the Sheriffs
+of the counties of Edinburgh, Lanark, Renfrew, Bute, Argyll,
+Inverness, Ross, Orkney and Zetland, Caithness, and Aberdeen.
+An Act was subsequently passed, which authorised the Commissioners,
+when any new Lighthouse was established on any part of
+the coast of Scotland, to add to their number the Provost or Chief
+Magistrate of the nearest Royal Burgh, and also the Sheriff-Depute
+of the nearest county; and, by the exercise of this power of assumption,
+the board now includes the Sheriffs of the counties of
+Ayr, Fife, Forfar, Wigtown, Sutherland, Kincardine, and Kirkcudbright.
+To enable the Board to carry on the intended works
+and to provide the means of maintaining the Lights, those Acts gave
+power to the Commissioners to levy a duty of 1d. per ton on British
+vessels, and 2d. per ton on foreign vessels; and liability to pay
+this duty was incurred by all vessels passing any of the Lighthouses
+in the course of a voyage; but this single payment freed them from
+any farther exaction, although they should pass more than one
+Lighthouse in the course of the voyage. The Board held its first
+meeting at Edinburgh on 1st August 1786. A Secretary and
+Engineer were appointed, and a resolution was adopted to borrow
+L.1200. For this sum the Magistrates of the five Royal Burghs
+named in the Act interposed their security; and, at the same time,
+assigned, in farther security, the duties under the Act of Parliament.
+After appointing a Committee to prepare matters for a general<span class="pagenum" id="Page11">[11]</span>
+meeting, they adjourned till the 23d of January 1787. Some inconvenience
+having been felt in conducting the business of the
+Board, particularly in the holding of stock and other property, by
+reason of its not being an incorporated body, an Act was obtained
+for erecting the Commissioners into a body politic, by the name of
+the “Commissioners of the Northern Lighthouses.” Several Acts
+have been subsequently passed, in order to facilitate the erection
+of particular Lighthouses, and for the purpose of granting duties
+for their support. All those duties, however, are now abolished,
+and others have been substituted, the collection of which is regulated
+by an Act, 6th and 7th William IV., cap. 79, intituled, “An
+Act for vesting Lighthouses, Lights, and Sea-marks on the Coasts
+of England, in the Corporation of Trinity-House of Deptford
+Strond, and for making provision respecting Lighthouses, Lights,
+Buoys, Beacons, and Sea-marks, and the Tolls and Duties payable
+in respect thereof.” This Act declares, “That from the first day
+of January one thousand eight hundred and thirty-seven, the tolls
+now payable by or in respect of vessels for or towards the maintenance
+of the several lighthouses at present under the management
+of the Commissioners of Northern Lighthouses shall cease to
+be payable, and that, in lieu thereof, there shall thenceforth for
+ever be paid to the said Commissioners of the Northern Lighthouses,
+for every vessel belonging to the United Kingdom of Great
+Britain and Ireland (the same not belonging to his Majesty, his
+heirs or successors, or being navigated wholly in ballast), and for
+every foreign vessel which, by any Act of Parliament, order in
+Council, convention, or treaty, shall be privileged to enter the
+ports of the said United Kingdom, upon paying the same duties of
+tonnage as are paid by British vessels (the same not being vessels
+navigated wholly in ballast), which shall pass any of the said
+lighthouses, or derive benefit thereby, the toll of one halfpenny
+per ton of the burden of every such vessel for each time of passing
+every such lighthouse, or deriving benefit thereby, and of one
+penny per ton for each time of passing the Bell Rock Lighthouse,<span class="pagenum" id="Page12">[12]</span>
+and double the said tolls for every foreign vessel not so privileged.”
+And with regard to any new Lighthouses to be hereafter erected,
+it is provided, that there “shall be paid to the Commissioners by
+the owner, or other person having the command of any vessel not
+belonging to His Majesty, which shall pass such lighthouse, or
+derive benefit thereby, such reasonable toll as shall have been first
+approved in that behalf by His Majesty in Council.” Before the
+passing of this Act, the Commissioners had been uncontrolled in
+the selection of stations for Lighthouses, or in choosing the characteristic
+appearance for the Lights; but it being considered desirable
+to have a systematic arrangement in the three kingdoms,
+the Irish Lighthouse Board, as well as the Commissioners, are
+now required to give notice to the Corporation of the Trinity-House
+of Deptford Strond, before altering the character of any
+Light, or erecting any new Lighthouse; and that Corporation
+must, within the period of six months after receiving such notice,
+signify their opinion as to the propriety of the change, or
+the utility of any new Lighthouses submitted for their consideration.
+The Act, however, provides, that, if the Commissioners are
+dissatisfied with the opinion of the Trinity-House, they may appeal
+to the Privy Council, whose determination is final. By this
+Act, also, an important power is given to the Commissioners to
+control the exhibition of all harbour and local Lights, or other
+sea-marks, and to prevent the exhibition of any Lights or fires on
+the sea-coast, which might be mistaken for the regular Lights exhibited
+by the Board. In the Appendix I have given a copy of the
+<a href="#App9">Annual Statement</a> of the Income and Expenditure of the Board
+for the year 1846, prepared by Mr <span class="smcap">Alexander Cuningham</span>, the
+Secretary to the Commissioners.</p>
+
+<p class="blankbefore75">Since the Sumburghhead Lighthouse in Zetland was lighted
+in the year <span class="sidenote">Lights established
+since 1821.</span>
+1821, with a notice of which the account of the Bell
+Rock Lighthouse concludes, the Commissioners have been engaged
+in the establishment of seventeen new Lighthouses, and the remodelling
+of several old ones; and they have, more particularly,<span class="pagenum" id="Page13">[13]</span>
+effected important changes in the mode of illumination, and have
+begun to place Beacons and Buoys on the coast. They have, besides,
+executed several considerable improvements, for the purpose
+of facilitating the communication with the Lighthouses at Kintyre
+in Argyllshire, Cape Wrath in Sutherlandshire, and Dunnethead
+in the county of Caithness, by the establishment of landing-piers
+and the formation of roads, varying in length from three to ten
+miles, in connection with those Stations. Of those works, many
+interesting details might be given, were it not desirable that the
+introduction to an account of a single Lighthouse should be restricted
+within a very moderate compass; and I have, therefore,
+thought it sufficient to lay before the reader the most important
+circumstances of each Lighthouse Station belonging to the Board
+in a tabular form in the Appendix.</p>
+
+<p>I shall not, in this place, enter on any exposition of the general
+principles which regulate the illumination of Lighthouses, and still
+less will it be proper to discuss the advantages of the different methods
+of illumination by Reflection and Refraction, as I shall, in
+the <a href="#Page181">sequel</a>, find a more convenient opportunity for speaking somewhat
+in detail on those subjects. It will be enough to present a
+very brief notice of the <span class="sidenote">Improvements in
+the mode of illumination.</span>improvements in the mode of illuminating
+Lighthouses, which the Northern Lights Board have introduced
+since 1824, up to which time, as already mentioned, a sketch of
+their works is already before the public. One of the most important
+changes in Lighthouse apparatus was, unquestionably, the introduction
+of Revolving Lights at the Tour de Corduan about the
+year 1780, by which the means of distinguishing one light from
+another were greatly extended, and a marked difference in the appearance
+of contiguous lights was at once simply obtained. The
+mere variation of the velocity of the revolution is so simple as to
+afford an obvious source of distinction among lights; and yet it is
+remarkable, that it was only lately that one of its principal advantages
+was perceived by my Father, who first applied it in the year
+1827 as a means of distinction for the Light of Buchanness. This
+distinction consists in giving the frame a greater number of sides or<span class="pagenum" id="Page14">[14]</span>
+faces, and a more rapid revolution, so as to cause a flash in every
+five seconds of time, which produces an effect so marked and characteristic
+as to afford by far the most effective distinction which
+has been exhibited since the introduction of Revolving Lights.
+Under the auspices of the Board, this distinction has been since
+applied at the Rhinns of Islay Lighthouse, and has given much
+satisfaction wherever it has been tried. The late King of the
+Netherlands, a great patron of the useful arts, was so much pleased
+with this device that he presented the author of it with a splendid
+gold medal, in token of his approbation. The only other improvement
+on the Reflecting Lights, which I shall notice in this
+place, is that called the <i>intermittent light</i>, which is due to the
+same officer, and was by him introduced at the stations of Mull of
+Galloway, Tarbetness, and Barrahead. It consists of the apparatus
+of a fixed Light, in front of which two cylindric shades are
+alternately shut and opened by a vertical movement, so as to produce
+a sudden extinction and exhibition of the light, in a manner
+very difference from the gradual decline and growth of the flash,
+which is produced in revolving Lights by the attenuating effects
+of divergence on the penumbral portions of the light reflected from
+the mirror.</p>
+
+<p><span class="sidenote">Dioptric Lights.</span>
+The introduction of lenticular apparatus into Lighthouses has
+been the last great improvement effected in their illumination.
+So far back as the year 1823, the attention of the Commissioners was
+first called by their Engineer to the invention of the late <span class="smcap">Augustin
+Fresnel</span>, who had succeeded in building polyzonal lenses of large
+dimensions, and in adapting to them a lamp of great power, having
+four concentric wicks supplied with oil by a clock-work movement
+like that of the Carcel lamp. A committee was appointed to consider
+this subject; and under its direction a long train of experiments
+was made with those instruments and with the paraboloidal
+mirrors which are generally used in British Lighthouses. The
+results of the experiments led the Board, in the summer of 1834,
+to send me on a mission to France, with instructions to report
+my opinion as to the comparative merits of the dioptric and catoptric<span class="pagenum" id="Page15">[15]</span>
+apparatus for the illumination of Lighthouses. Through the
+kindness of my friend <span class="smcap">M. Leonor Fresnel</span>, Secretary of the
+<i>Commission des Phares</i>, who in the most liberal manner put me in
+possession of all the information which I required, and afforded me
+an opportunity of visiting the most important Lighthouses on the
+French coast, I was enabled on my return to report very fully my
+views on the various topics whose investigation had been committed
+to me by the Lighthouse Board.</p>
+
+<p>The characteristics of the two systems of illumination by Reflection
+and Refraction may be briefly described as follows: In the
+reflecting apparatus, the lamp is placed in <i>front</i> of the mirror,
+whose surface is so formed that the rays which fall upon it, and
+are reflected from it, must afterwards move in lines parallel to the
+axis of the mirror; while in using Refracting instruments, the
+flame is placed <i>behind</i> the lens, whose action is simply to bend the
+rays in their passage through it, in such a manner that they come
+out from its face parallel to a line drawn from the focus to the centre
+of the lens. In Revolving Lights, on the reflecting principle, the
+mirrors containing the lamps are placed on a frame which revolves
+on its centre, and carries them round in succession to the different
+points of the horizon, so that each mirror produces a bright flash
+when it crosses the line drawn from an observer’s eye to the centre
+of the Lighthouse; but in Refracting Lights, a single lamp of great
+power is fixed in the centre of the lightroom, while the lenses,
+placed on a revolving frame, intercept and modify the rays which
+fall upon them from the Lamp, as they pass in front of it, and thus
+produce successive flashes whenever the centre of the lens crosses
+the imaginary line already noticed, as joining the observer’s eye
+and the lightroom.</p>
+
+<p>In Fixed Lights, on the Reflecting plan, the mirrors are ranged
+around a fixed chandelier in tiers, one above another, their centres
+being placed in spiral lines, so that each shall subtend an equal arc
+of the horizon, and thus distribute the light with as little inequality
+as is consistent with the application of such an instrument as the<span class="pagenum" id="Page16">[16]</span>
+paraboloidal mirror to this purpose. This object of distributing
+the light equally over the horizon, which, next to intensity, is the
+main object of a fixed light, and ought, indeed, to be strictly co-ordinate
+with it, is much better effected by using dioptric instruments.
+That apparatus consists of successive rings or bent prisms
+arranged in the form of a hoop or belt, which may be described as
+a cylinder, generated by the revolution of the central section of a
+polyzonal lens about its focus as a vertical axis, and which consequently
+acts only in a vertical direction, leaving the natural horizontal
+divergence of the light unchanged, and thus distributing
+it with perfect equality in every direction.</p>
+
+<p>Those two systems of illumination possess advantages and defects
+peculiar to each. The lenticular instruments insure greater
+intensity when applied to revolving lights; but this advantage is
+in part counterbalanced by the greater duration of the flash caused
+by the reflectors, whose divergence is greater; while in fixed lights,
+the refracting instruments not only produce at least an equal intensity
+of light, but, what is of the greatest importance, afford the
+same quantity of light in all directions, a property which fixed
+Lights on the reflecting principle employed in Britain cannot
+possess.</p>
+
+<p>On my return from France I made a Report, which was printed
+by order of the Commissioners; and the views which I gave of
+the superiority of the refracting apparatus, led the Board to adopt
+the resolution of at once converting the revolving light of Inchkeith
+from the catoptric to the dioptric system, as its nearness to
+Edinburgh offered good opportunity of observation as to the effect
+of the change. In October 1835, the new light was exhibited to
+the public, and I was forthwith instructed to make a similar change
+on the fixed light of the Isle of May; but in carrying this into
+effect, I introduced an important modification of the form of the
+refracting part of the apparatus, with the view of obtaining a still
+nearer approach to the equal distribution of the light. The only
+other considerable change in the lightroom apparatus which has<span class="pagenum" id="Page17">[17]</span>
+since been effected, is the substitution of catadioptric zones in room
+of the mirrors hitherto used in the subsidiary parts of the larger
+French lights, which, as will appear in the sequel, was suggested
+by me in 1841, and finally carried into effect in 1843, agreeably
+to the computations of <span class="smcap">M. Leonor Fresnel</span>. A Table of the
+Elements of those zones computed by myself, and closely verifying
+<span class="smcap">M. Fresnel’s</span> results, will be found in the Appendix. The
+lenticular apparatus has been applied at the new Lighthouse stations
+of the Little Ross and the Skerryvore, and, still more recently,
+at Covesea Skerries, Cromarty Point, Chanonry Point,
+Loch Ryan, and Girdleness.</p>
+
+<p>The establishment of a system of <span class="sidenote">Beacons and
+Buoys.</span>
+Beacons and Buoys on the
+coast of Scotland for the purpose of affording additional facilities
+to navigation, had long been looked upon as a desirable extension
+of the operations of the Northern Lights Board; and the increase
+of the trade and shipping of the kingdom having, some years ago,
+directed particular attention to the subject, a committee was
+named, on the 12th January 1839, to take special superintendence
+of that department. In 1840, the Engineer reported to the committee
+upwards of fifty stations for Beacons, and nearly a hundred
+for Buoys, as auxiliaries to the navigation in situations where the
+establishment of a Lighthouse was either too expensive or not
+warranted by the wants of the district; and means were immediately
+taken for erecting three Beacons in the Frith of Forth, two
+in the Clyde, one in Loch Ryan, and two in Cambeltown Loch.
+Beacons were also erected on the Iron Rock or Skervuile in the
+Sound of Jura, and on the Covesea Skerries in Morayshire, in connection
+with the Lighthouse of that name. Those works, notwithstanding
+many obstacles arising from doubts as to the powers of
+the Board, have been carried on with great vigour. In the Appendix,
+I have given <a href="#Plate32">drawings</a> of three of those Beacons, one being
+of masonry, and the other two of iron; and also <a href="#App8">Tables</a> which
+shew the positions of the various Beacons and Buoys at present
+belonging to the Board.</p>
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page18">[18-<br>19]<a id="Page19"></a></span></p>
+
+<h3 class="nobreak"><span class="chapno">CHAPTER I.</span><br>
+<span class="chapname">TOPOGRAPHIC NOTICE OF THE SKERRYVORE ROCK.</span></h3>
+
+</div><!--chapter-->
+
+<p>From the great difficulty of access to the inhospitable rock of
+Skerryvore, which is exposed to the full fury of the Atlantic, and
+is surrounded by an almost perpetual surf, the erection of a Light
+Tower on its small and rugged surface has always been regarded
+as an undertaking of the most formidable kind. So discouraging
+was the consideration of expense, and the uncertainty of the final
+success of such a work, that the Commissioners of the Northern
+Lighthouses, after successfully completing the arduous and somewhat
+similar work on the Bell Rock, were induced to proceed with
+other operations of less magnitude, but probably, in some respects,
+of no less utility; and to delay the construction of the Skerryvore
+Lighthouse till the present time, although the Act of Parliament
+authorising its erection was obtained so long ago as 1814.</p>
+
+<p>The cluster of Rocks, of which that called the Skerryvore is
+the largest, has ever been a just cause of terror to the mariner. Its
+dangers have long been known, and the means of removing these
+dangers, by converting its dark horrors into a cheering guide for
+the benighted mariner, have often occupied the attention of the
+Lighthouse Board, and especially of my predecessor in the office
+of their Engineer, with whom it was a constant subject of interest,
+from its similarity to his own work on the Bell Rock.</p>
+
+<p>The first landing that my Father, in the course of his annual
+voyages round the coast, as Engineer of the Northern Lighthouse
+Board, effected on Skerryvore, was in the year 1804. In 1814,
+he visited it a second time, while accompanying a committee of
+the Commissioners on a tour of inspection to the Lighthouses<span class="pagenum" id="Page20">[20]</span>
+all round the coast, from the Frith of Forth to the Clyde. On
+that occasion, Sir Walter Scott was of the party, and we find in
+his diary the following record of his impressions at the time,
+expressed in the terse and humorous language by which this
+interesting relic of the poet is characterised; and as the hasty
+observations of that great man seem worthy of a place in a work
+descriptive of the means which have been taken to obviate the
+dangers to which he refers, no apology seems necessary for introducing
+it in this place.</p>
+
+<p class="blankbefore75">“Having crept upon deck about four in the morning,” says Sir
+Walter, “I find we are beating to windward off the Isle of Tyree,
+with the determination, on the part of Mr Stevenson, that his constituents
+should visit a reef of rocks called <i>Skerry Vhor</i>, where he
+thought it would be essential to have a Lighthouse. Loud remonstrances,
+on the part of the Commissioners, who, one and all,
+declare they will subscribe to his opinion, whatever it may be,
+rather than continue the infernal buffeting. Quiet perseverance
+on the part of Mr S., and great kicking, bouncing, and squabbling,
+upon that of the yacht, who seems to like the idea of Skerryvore
+as little as the Commissioners. At length, by dint of exertion,
+come in sight of this long ridge of rocks (chiefly under water) on
+which the tide breaks in a most tremendous style. There appear
+a few low broad rocks at one end of the reef, which is about a
+mile in length. These are never entirely under water, though the
+surf dashes over them. To go through all the forms, Hamilton,
+Duff,<a id="FNanchor1" href="#Footnote1" class="fnanchor">[1]</a> and I, resolve to land upon these bare rocks, in company with
+Mr Stevenson. Pull through a very heavy swell with great difficulty,
+and approach a tremendous surf dashing over black pointed
+rocks. Our rowers, however, get the boat into a quiet creek
+between two rocks, where we contrive to land well wetted. I
+saw nothing remarkable in my way excepting several seals, which<span class="pagenum" id="Page21">[21]</span>
+we might have shot, but, in the doubtful circumstances of the
+landing, we did not care to bring guns. We took possession of the
+rock in name of the Commissioners, and generously bestowed our
+own great names on its crags and creeks. The rock was carefully
+measured by Mr S. It will be a most desolate position for a
+Lighthouse—the Bell Rock and Eddystone a joke to it, for the
+nearest land is the wild island of Tyree, at fourteen miles distance.
+So much for the Skerry Vhor.”</p>
+
+<div class="footnote">
+
+<p><a id="Footnote1" href="#FNanchor1" class="label">[1]</a> The Sheriffs-Depute of Lanark and Edinburgh.</p>
+
+</div><!--footnote-->
+
+<p class="blankbefore75">Notwithstanding those occasional visits, however, it was not
+till the year 1834, that the Commissioners directed their Engineer
+to make a survey of the whole of this extensive reef, preparatory
+to taking measures for the erection of a Lighthouse on that part of
+it which might be found, after careful inspection, to afford the
+most suitable site; and, at the same time, the shores of part of the
+Island of Tyree were surveyed, with the view of establishing a
+Signal Tower for communicating with the Lighthouse, and of
+forming a small harbour, of shelter for the vessels to be employed
+in attending it. From these surveys the general view of the Reef
+which is given in <a href="#Plate2">Plate II.</a>, and the enlarged plan shewn in <a href="#Plate3">Plate
+III.</a> of the Skerryvore or principal Rock, on which the Lighthouse
+has been built, were constructed.</p>
+
+<p class="blankbefore75">The Skerryvore or principal Rock of this remarkable group,
+is situated in North Lat. 56° 19′ 22″, and West Long. 7° 6′ 32″.<a id="FNanchor2" href="#Footnote2" class="fnanchor">[2]</a>
+It is about 11 Nautic miles W.S.W ¹⁄₄ W. of the island of Tyree,
+which is the nearest land, 20 miles W.N.W ³⁄₄ N. of the island of
+Iona, 33 miles S. ¹⁄₄ E. of the Lighthouse of Barrahead, the most
+southern of the Hebrides, and 53¹⁄₂ miles N.E. by N. of Mallinhead,
+in the county of Donegal in Ireland. It may also be added, that
+the principal rock is about 50 miles from the nearest point of<span class="pagenum" id="Page22">[22]</span>
+the main land of Scotland. The extent of the Reef, and its
+situation in reference to the general position of the coast, will be
+best understood by referring to <a href="#Plate1">Plate I.</a>, which is a small Map
+of the British Isles. From this it will be seen that it lies in an
+irregular semicircular sea, inclosed by the southern extremity of the
+Hebrides, the rugged shores of Argyllshire, and the northern coast
+of Ireland on the one side, but open on the other to the Atlantic.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote2" href="#FNanchor2" class="label">[2]</a> According to information for which I am indebted to Captain Yolland, R.E., of the
+Ordnance Survey.</p>
+
+</div><!--footnote-->
+
+<p class="blankbefore75">The importance of the Skerryvore as a station for a Lighthouse
+is so evident as to require but little comment. Although the
+smaller class of coasting vessels almost invariably sail through the
+sheltered Sounds of Mull, Loing, and Islay, to avoid the difficulties
+and dangers (Skerryvore among the number) of the rough navigation
+of the outward passage, yet these rocks lie much in the track
+of the larger vessels bound over seas round the North of Ireland
+from the Clyde and the Mersey. Government Cruisers and Ships
+of War are also necessarily often within a short distance of its
+dangers. But for homeward-bound vessels sailing for the Clyde, or
+for any of the Ports in the Irish sea, and directing their course for
+the North Irish Channel, the establishment of a light at this place is
+of the last importance. When such vessels happened to encounter
+bad weather before making land, and so had difficulty in ascertaining
+their true position in relation to the coast, they often, in the
+event of being driven so far north from their course, as to miss
+the lights of Ireland or that of Barrahead, continued their progress
+onwards in the direction of the Skerryvore Rocks; and
+thus, while running in apparent safety, and probably, from the state
+of the weather, not within sight of Tyree, which it is often difficult
+to see, they were very liable to encounter some of the many
+detached rocks and shoals which form this broken reef of nearly
+seven miles in extent.</p>
+
+<p class="blankbefore75">In estimating the risks to which vessels were exposed from
+this cause, the peculiarly insidious nature of the danger must be<span class="pagenum" id="Page23">[23]</span>
+kept in view. A headland, or line of coast, which rises to some
+height above the surface of the sea can be seen in most states of
+the weather, at a sufficient distance, even during the night, to enable
+the seaman to avoid danger; but, in approaching a sunken reef
+or a low rock, in the dark, there is no object to warn the crew of
+their position, until their vessel gets unexpectedly among breakers,
+after which it is generally too late to bring her round again. And
+even the very knowledge of the existence of a reef, such as this,
+often causes the seaman, in ignorance of its exact position, to give
+it too wide a berth; in which case his ship is liable to be carried
+away by the force of tides or winds, perhaps on a lee shore, where,
+although the crew may be saved, the vessel generally goes to
+pieces.</p>
+
+<p class="blankbefore75">The exhibition of a Light, however, altogether changes the
+case. Instead of shunning as a danger those dreaded rocks, vessels
+will steer boldly on their course, until checked by the Light,
+availing themselves of which they will be enabled to <i>lie off-and-on</i>
+during the night, and so wait the return of daylight, in perfect
+confidence as to their position, and without the necessity of endeavouring
+to avoid hidden dangers. Thus, that which was formerly
+an obstruction and a danger, is rendered an aid and a safety,
+to the navigation of the western coasts of our country.</p>
+
+<p class="blankbefore75">That this source of danger to shipping was by no means imaginary,
+and the consequent terror of mariners far from being ill
+founded, there is a too melancholy proof in the following list of
+disasters caused by the Skerryvore Rock, and the neighbouring
+dangers off the coast of <span class="nowrap">Tyree:—</span></p>
+
+<table class="wrecks">
+
+<tr>
+<td rowspan="31" class="in">In</td>
+<td class="year">1790.</td>
+<td class="text">The Ship Rebecca of 700 tons lost; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1804.</td>
+<td class="text">Ship Brigand of Nova Scotia, Wright, master, of 600 tons, lost off Hough, in Tyree; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1804.</td>
+<td class="text"><i>A Brig</i>, M‘Iver, master, lost off Hough; crew saved.<span class="pagenum" id="Page24">[24]</span></td>
+</tr>
+
+<tr>
+<td class="year">1806.</td>
+<td class="text">Ellen of Bath, Paterson, master, of 90 tons, lost off Balaphuil, in Tyree; one man drowned.</td>
+</tr>
+
+<tr>
+<td class="year">1809.</td>
+<td class="text">Brig Mary, Sanders, master, lost off Balaphuil; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1813.</td>
+<td class="text">Sloop, Penelope of Wick, 60 tons, lost at Gott Bay, Tyree; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1810.</td>
+<td class="text">A Brig from New York, Greenlees, master, lost off Hynish Point, Tyree; crew all drowned.</td>
+</tr>
+
+<tr>
+<td class="year">1813.</td>
+<td class="text"><i>A Sloop</i>, Eugene M‘Intyre, master, lost off Balaphuil; one man drowned.</td>
+</tr>
+
+<tr>
+<td class="year">1814.</td>
+<td class="text">Brig, Betsey of Leith, Ross, master, lost off Hough; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1817.</td>
+<td class="text"><i>A Brig</i>, of 400 tons, foundered off Kennavarah, Tyree; crew all drowned. Numerous casks of butter came ashore.</td>
+</tr>
+
+<tr>
+<td class="year">1818.</td>
+<td class="text">Sloop, Benlomond of Greenock, M‘Lauchlan, master, lost off Balaphuil; crew all drowned.</td>
+</tr>
+
+<tr>
+<td class="year">1819.</td>
+<td class="text">Sloop, Bee, Coice, master, of 60 tons, lost off Hough; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1820.</td>
+<td class="text"><i>A Sloop</i>, M‘Donald, master, of 50 tons, lost in Reef Bay, Tyree; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1820.</td>
+<td class="text">Ship, Masters, of Port-Glasgow, Martin, master, of 700 tons, foundered off Skerryvore Rocks, and came ashore at Clate
+Hynish, in Tyree; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1821.</td>
+<td class="text">Sloop, Catharine, M‘Rae, master lost; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1821.</td>
+<td class="text"><i>A Sloop</i>, of 60 tons, lost off Hough; master and three men drowned.</td>
+</tr>
+
+<tr>
+<td class="year">1825.</td>
+<td class="text">Sloop, Dan of Campbelltown, M‘Innes, master, of 50 tons, lost; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1828.</td>
+<td class="text">Sloop, Delight, of 70 tons, Stevenson, Master, lost.</td>
+</tr>
+
+<tr>
+<td class="year">1828.</td>
+<td class="text"><i>An Irish Schooner</i> of 100 tons, Montgomery, master, lost off Hough; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1828.</td>
+<td class="text">Jane of Sligo, Collins, master, lost off Balaphuil.</td>
+</tr>
+
+<tr>
+<td class="year">1829.</td>
+<td class="text">Van Scapan of Stockholm, Fisherton, master, of 700 tons, lost off Hough; fourteen people
+drowned.<span class="pagenum" id="Page25">[25]</span></td>
+</tr>
+
+<tr>
+<td class="year">1834.</td>
+<td class="text">Confidence of Dundee, Wesley, master, lost off Hough; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1834.</td>
+<td class="text"><i>A Schooner</i> of 70 tons, lost; three men drowned.</td>
+</tr>
+
+<tr>
+<td class="year">1835.</td>
+<td class="text">Peggy, Bitters, master, of 500 tons, lost off Beist, Tyree; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1841.</td>
+<td class="text">April 2. Majestic of North Shields, Tait, master, of 400 tons, foundered <i>by a sea</i> off Boinshly Rock, and came
+ashore at Gott Bay; captain and four men washed overboard and drowned, and the mate and one seaman had their legs broken when the vessel
+was struck by the sea.</td>
+</tr>
+
+<tr>
+<td class="year">1842.</td>
+<td class="text">Fleurs of Liverpool, Thomson, master, of 300 tons, lost off Kennavarah; crew saved.</td>
+</tr>
+
+<tr>
+<td class="year">1842.</td>
+<td class="text">March 14. Two deck beams, a knee, and some pieces of deck-plank of a <i>North American built vessel</i>, came ashore at Clate Hynish.</td>
+</tr>
+
+<tr>
+<td class="year">1842.</td>
+<td class="text"><i>A Barra Boat</i> wrecked, and four corpses washed ashore; two men, a woman and a child.</td>
+</tr>
+
+<tr>
+<td class="year">1842.</td>
+<td class="text">Pieces of wreck were seen in the Sound of Coll, and at the same time the shores of Tyree were strewed with candles, mostly of wax,
+supposed to be altar candles for the West Indies.</td>
+</tr>
+
+<tr>
+<td class="year">1843.</td>
+<td class="text">September 2. The Prussian Barque Formosa, of 326 tons, P. R. Reick, master, lost off Hough; two seamen drowned.</td>
+</tr>
+
+<tr>
+<td class="year">1844.</td>
+<td class="text">December 1. The Hull of <i>a Sloop</i> of about 70 tons, was washed ashore off Clate Hynish. The Hull was very much broken up by
+being in contact with the rocks; and one of the planks, apparently off the taffrail, had the words “Port of Dundee” lettered upon it; the crew
+supposed to be all drowned.</td>
+</tr>
+
+</table>
+
+<p class="blankbefore75">This list is made up chiefly from data kindly furnished to me
+by the Rev. Neil Maclean, the Minister of Tyree and Coll, whose
+long residence on the former island has afforded him ample opportunity<span class="pagenum" id="Page26">[26]</span>
+for making observations on the subject. It is not to be
+imagined, however, that Mr Maclean’s list, which is made up from
+recollection, contains a full catalogue of the disasters caused by the
+Skerryvore, within the dates which it cites. Very many vessels were
+wrecked on this dangerous reef whose names could never be learned,
+and of which nothing but portions of the drift wood or cargo came
+ashore; and there have, no doubt, been many shipwrecks of which
+not a single trace has been left. Nothing, indeed, is more probable
+than that many of the foreign vessels whose course lay through the
+North Irish Channel, and whose fate has been briefly and vaguely
+described, as “foundered at sea,” have met their fate on the <i>infames
+scopuli</i> of the Skerryvore. It is also well known that the Tyree
+Fishermen were in the constant practice of visiting the Skerryvore,
+after gales, in quest of wrecks and their produce, in finding which
+they were but too often successful.</p>
+
+<p class="blankbefore75">The natives of Tyree have many traditions of vessels having
+struck on the Skerryvore and gone to pieces; but, as might have
+been anticipated, few traces of this were to be found on the Rocks
+themselves, the breach of sea which sweeps over them during
+storms being sufficient to remove any heavy bodies which might be
+left there after a shipwreck. Some relics, however, were found
+during the progress of the works, and among the rest an anchor
+which was fished up close to the Rock, and which appeared to have
+belonged to a vessel of about 150 tons burden. It had been wasted
+to a perfect shadow by the action of the sea, and was covered with
+a thick coating of seaweed and barnacles. Although, however,
+the Rocks themselves do not retain the proofs of the disasters of
+which they have been the cause, the shores of the neighbouring
+Islands, during the progress of the works, were frequently strewed
+with drift wreck in such a manner as clearly to indicate what had
+taken place on the shoals round the Skerryvore.</p>
+
+<p class="blankbefore75">On examining <a href="#Plate2">Plate II.</a>, it will be seen that what I have
+hitherto denominated the Skerryvore Reef, is a tract of foul ground,<span class="pagenum" id="Page27">[27]</span>
+consisting of various small rocks, some always above the level of
+the sea, others covered at high water, and exposed only at low
+water, and others, again, constantly under the surface, but on which
+the sea is often seen to break after heavy gales from the westward.
+This cluster of rocks extends from Tyree in a south-westerly direction,
+leaving, however, between that island and the rock called
+Boinshly, the first of the great Skerryvore cluster, a passage of
+about five miles in breadth, and having a depth of thirteen fathoms
+at low water of spring tides, but not without hidden dangers, which
+line the rugged shores of Tyree from Kennavarah to Ben Hynish,
+and some of which lie farther off than might be expected. This
+passage is called the passage of Tyree; but it is by no means safe
+during strong and long continued gales, as the sea which rises between
+Tyree and Skerryvore, is such that no vessel can <i>live</i> in
+it. I have myself often seen it one field of white broken water,
+the whole way from Tyree to the Rock; and we know that the
+wreck of the Majestic, which occurred in 1841, during the progress
+of the works, was entirely caused by the heavy seas which she
+encountered off Boinshly.</p>
+
+<p class="blankbefore75">The principal rocks of the group, are called Boinshly, Bo-rhua,
+and Skerryvore, while those lying to the westward, which have
+been more recently laid down, have received the names of Mackenzie,
+Fresnel, and Stevenson.</p>
+
+<p class="blankbefore75">The rock called Boinshly lies about 3³⁄₄ miles from Skerryvore,
+and is of considerable extent. The origin of the names of the different
+rocks in the vicinity of Tyree is by no means clear, and very
+little assistance or information is to be obtained in this matter from
+the natives. The name of Boinshly is probably derived from the
+Gaelic words <i>boun</i>, signifying <i>bottom</i>, and <i>slighe</i>, <i>deceitful</i>, as indicative
+of the dangers of the place; but other interpretations have
+been put on it, and that which has been now given is by no means
+certain. In the course of the survey, several soundings were<span class="pagenum" id="Page28">[28]</span>
+at considerable risk obtained, both upon this Rock itself, and in its
+immediate vicinity. The sea in that exposed situation is seldom
+so tranquil as to warrant an attempt to approach very near this
+Rock. The swell, which, in a greater or less degree, almost
+constantly prevails, is apt to impel, or seemingly draw the boat
+as by a kind of suction, upon the rock; and sometimes such accidents
+cannot be prevented, even although the greatest caution
+is used. Sudden <i>lifts</i> of the sea, during an apparent calm, are
+common in all the more exposed parts of the coast, more especially
+in the Orkney and Zetland Isles, and on the shores of the
+most western of the Hebrides; and any one much accustomed to
+the use of boats on these shores, must have experienced the hazard
+of encountering such unexpected risings of the sea, more especially
+near shelving rocks, or in rapid tide-ways. In some places the
+boatmen apply the name of <i>lumps</i> to these sudden waves. This
+effect is not felt to the same extent in attempting to reach a
+rock which is partially uncovered at low water, as a landing
+can, in such a case, often be effected on one side, at a time when
+the same rock on the opposite side, or a sunk rock just topping
+with the water, would, on every side, be quite unapproachable.
+From the soundings marked on the plan, it will be seen that
+shoal water extends all round Boinshly to distances varying
+from a quarter to half a mile. The sea breaks on the rock with
+great violence, and its position can easily be discovered from the
+island of Tyree by the white foam with which it is almost constantly
+surrounded, and which, in the heavy swells which sometimes
+accompany a dead calm, before or after a heavy gale of
+wind, rises to a prodigious height in a column or jet, resembling,
+at a distance, the play of a gigantic fountain. So high, indeed,
+does the sea rise on this shoal after heavy gales, that it often quite
+obscures the larger and more distant object of the Rock and
+Tower of the Skerryvore, even when viewed from the top of Ben
+Hynish in Tyree. The wooden barrack erected on the Skerryvore
+for the use of the workmen during the progress of the operations,<span class="pagenum" id="Page29">[29]</span>
+although about sixty feet in height, was often lost sight of at
+Tyree by the uprising of the sea on Boinshly, and could be seen
+only during the calm that intervenes between returning waves.</p>
+
+<p class="blankbefore75">The next Rock that occurs is Bo-rhua, a name derived from
+the Celtic, and signifying, according to the natives, Red Rock. It
+lies about 2³⁄₄ miles from Boinshly, and about one mile from the
+Skerryvore. The passage between it and Boinshly is clear, and
+has a depth of about fourteen fathoms; but it is too narrow to be
+safely navigated except by daylight, even under the most favourable
+circumstances, and then no mariner would run the risk of taking
+such a passage, but would prefer, even at some sacrifice of time, the
+fairway of the passage of Tyree. Bo-rhua is completely covered at
+high, but is dry at low water. The extent of rock uncovered is
+about forty feet by twenty feet, and the highest point of it is about
+six feet above low water level of spring tides. A small outlying
+pinnacle, about ten feet square, is also uncovered at low water. The
+depth immediately round Bo-rhua is considerable, from three to
+seven fathoms being found within fifty feet of it; and in this respect
+it differs from Boinshly, which, as already mentioned, is
+surrounded by shoal water for some distance. Between Bo-rhua
+and Skerryvore, however, which is a distance of about a mile,
+there cannot properly be said to be any clear navigable channel, as
+will be distinctly seen by referring to the plan. The whole of this
+tract may, in fact, be termed <i>foul ground</i>.</p>
+
+<p class="blankbefore75">The Skerryvore or chief rock, and the detached rocks immediately
+surrounding it, were surveyed with greater minuteness than
+the others, as it was at once apparent, that on this part of the reef
+alone could a suitable site for a lighthouse be found. The name is
+derived from the Gaelic, and signifies the Great Rock. It is very
+much wasted and cut up; the number of detached rocks, sunk and
+exposed, in its immediate neighbourhood, whose positions were determined
+during the survey, amounting to no fewer than 130. The<span class="pagenum" id="Page30">[30]</span>
+depth of water between those different detached fragments, which
+extend over a surface of about a mile in length, by half a mile in
+breadth, is considerable, varying from 2¹⁄₂ to 8¹⁄₂ fathoms at low
+water of spring tides.</p>
+
+<p class="blankbefore75">The surface of the main or principal rock, on which the Lighthouse
+has been placed, measures, at the lowest tides, about 280 feet
+square. It is extremely irregular, and is intersected by many gullies
+or fissures, of considerable breadth, and of unlooked for depth,
+and which leave it solid only to the extent of 160 feet by 70 feet.
+The extremity of one of these gullies, at the south-east corner of
+the rock, forms the landing-creek, which is a narrow track of 30
+feet wide, having deep water; and, with the help of some artificial
+clearing and dressing, which was executed with much difficulty, by
+blasting under water, while the other works were in progress, its
+sides and bottom are now comparatively smooth. At this place a
+landing can often be effected when the rock is unapproachable from
+any other quarter, although great inconvenience is felt from the
+surge, which finds its way from the opposite side of the rock,
+through the westward opening of the gulley in which the landing-place
+is situated.</p>
+
+<p class="blankbefore75">Another of the gullies, immediately to the south-east of the
+Lighthouse, was found, on examination, to undermine the rock to
+the extent of eight or ten feet, and to terminate in a hollow submarine
+chamber, which threw up a spout or jet of water about
+twenty feet high, resembling in appearance the Geyser of Iceland,
+and accompanied by a loud sound like the snorting of some sea
+monster. The effect of this marine <i>jet d’eau</i> was at times extremely
+beautiful, the water being so much broken as to form a
+snow-white and opaque pillar, surrounded by a fine vapour, in
+which, during sunshine, beautiful rainbows were observed. But
+its beauties by no means reconciled us to the inconvenience and
+discomfort it occasioned, by drenching us whenever our work carried<span class="pagenum" id="Page31">[31]</span>
+us near it. One calm day I contrived, at a very low tide,
+by means of ropes and a ladder, to explore the interior of the
+cavern, from which this fountain rose, and found it to terminate
+in a polished spherical chamber, about seven feet in diameter, its
+floor filled with boulders, whose incessant play had hollowed it
+out of the veined rock, and rendered its interior beautifully
+smooth and glassy. As I considered that this curious cavern
+penetrated too far, and came too close to what I had selected as the
+best foundation, I changed the site of the tower, so as to avoid any
+chance of its being undermined. I also deemed it prudent to fill
+up the cavity, to prevent its further extension, and at the same
+time to rid ourselves of the discomfort of being drenched by
+the column of water which spouted up from it, even during fine
+weather, when the sea was apparently calm. This gulley affords a
+good example of the power of pebbles kept constantly in play by
+the waves to wear down the hardest rock, and shews what extensive
+effects so insignificant an agent may effect in the course of
+time.</p>
+
+<p class="blankbefore75">Before the excavation for the foundation of the tower was made,
+a single conical loaf of rock, about five feet in diameter, rose to the
+height of eighteen feet above the level of high water, the greater
+part of the rest of its surface being about six feet above the tide
+mark.</p>
+
+<p class="blankbefore75">In addition to its shattered and disjointed appearance, the
+Skerryvore Rock presents, in another respect, a striking example
+of the action of the sea, which no one, on first landing on the rock,
+can fail to perceive. I allude to the glassy smoothness of its surface,
+a feature that existed to so remarkable an extent as to have
+proved throughout the whole duration of the work, but more especially
+at its commencement, a serious obstacle and hindrance to the
+operations. It may, at first sight, appear strange that this grievance
+should have been so much felt; but, when I mention that the landings<span class="pagenum" id="Page32">[32]</span>
+were often made in very bad weather, it will be obvious that
+there was considerable danger in springing ashore from a boat in
+a heavy surf upon an irregular mass of rock as smooth and slippery
+as ice. The workmen were, in that respect, often sorely tried, and
+many inconvenient accidents occurred from falls. It was after one
+of these trials of patience, that the foreman of the masons was
+heard very graphically to describe a landing on the rock as “like
+climbing up the side of a bottle.” Instead of a weather-beaten
+rock, whitened by the dung of sea-fowls, and with marine crustacea
+adhering to it, the surface of the Skerryvore is smoothly polished
+by the action of the waves, every projecting angle or point is
+worn down, and the whole presents more the appearance of a mass
+of dark-coloured glass than a reef of gneiss-rock. Excepting in
+some of the more sheltered crevices, no marine crustacea find shelter;
+but different kinds of sea-plants grow upon it, in great abundance,
+at and below the low water mark. These plants are, doubtless,
+enabled to resist the action of the waves in the same way as
+the sapling, yielding to the blast, is preserved during the storm that
+uproots the aged and more stubborn oak.</p>
+
+<p class="blankbefore75">The rocks of Skerryvore have the same characteristics as those
+of the neighbourhood of Tyree, being what we may, perhaps, call
+a syenitic gneiss, as it consists of quartz, felspar, hornblende, and
+also mica. It will be seen, from the narrative of the progress of
+the works, that this rock was, from its hardness, exceedingly difficult
+and tedious to excavate. The only variation in the geology of
+the Skerryvore, is the presence of a trap rock, in the form of a
+dyke of basalt, which intersects the strata, and exhibits a fine specimen
+of the intrusion of igneous rocks. It is shewn in <a href="#Plate3">Plate,
+No. III.</a>, by a thick black line.</p>
+
+<p class="blankbefore75">Connected with this general view of the appearance and geology
+of the rock, it may be interesting also to notice, that a considerable
+mass of foreign matter, somewhat resembling, in its<span class="pagenum" id="Page33">[33]</span>
+structure, a deposit of lime, was found in different places resting in
+horizontal layers of various thickness and size. This substance
+was found in pools or sheltered parts of the rock, about the level
+of high water mark, and, in some cases, even a little below it. It
+was so hard as to admit of a pretty high degree of polish; and
+emitted an offensive odour on being burned in the fire, or rubbed
+on a stone with water. It gave other clear indications of containing
+animal matter, and in other respects resembled the bergmeal
+and guano. To account for its presence in such a situation, seems
+rather a difficult problem. On sending a specimen of this material
+to my friend the Rev. Dr Fleming, Professor of Natural Philosophy
+in King’s College, Aberdeen, I received from him an analysis
+of the substance, and a concurrence in the opinion I had
+formed as to its containing animal matter; and Dr Fleming, indeed,
+expressed his belief that the matter in question is the indurated
+soil of birds, and had been deposited when the reef was more
+extensive, and the resort, and probably the breeding-place of sea-fowls.<a id="FNanchor3" href="#Footnote3" class="fnanchor">[3]</a>
+How this singular formation should be found on the verge
+of the ocean, and even within the high water mark, in spite of
+winds and waves, or how it should have assumed the stratified
+structure which seems to indicate the depositation of successive
+layers in still water, are matters very difficult to be explained, without
+coming to the conclusion, that the uncovered surface of Skerryvore
+Rock must at some distant period have been much more extensive
+than at present, so as to permit the deposit to go on in an interior
+basin or lagoon, sheltered from the waves, and somewhat similar
+to those which Dr Darwin has described as characteristic of the
+Coral Isles of the Pacific. This supposition seems not at all improbable,
+as it does not require a great stretch of fancy to conceive, that
+at some period, the whole of the rocks in the immediate vicinity
+of Skerryvore, and extending perhaps even so far as Bo-rhua, may
+have been connected by a matrix of softer materials, which have<span class="pagenum" id="Page34">[34]</span>
+gradually yielded to the action of the sea, leaving the harder portions
+to be smoothed and polished by the waves, and to assume the
+characteristic features of permanent rocks and sunk reefs which
+they now possess. There is also some countenance to such a view
+to be derived from the features of the neighbouring Island of Tyree,
+which contains numerous small lagoons, in which such deposits
+might be formed by the flocks of sea fowl which frequent them.
+Some of these pools are so near the shore, as to make it no difficult
+matter to conceive that their walls might be broken by the sea,
+and that they might eventually become part of it, and thus exhibit
+the phenomenon of deposits apparently lacustrine within the verge
+of the ocean.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote3" href="#FNanchor3" class="label">[3]</a> Dr Fleming has since obtained from Ichaboe indurated bird-soil or guano, closely resembling
+that from the Skerryvore.</p>
+
+</div><!--footnote-->
+
+<p class="blankbefore75">Another remarkable feature which I observed in the Skerryvore
+Rock, was a deposit of gravel in the narrow crevices of the
+rock, which run nearly from north-east to south-west, dipping at an
+angle of 80° to the westward. In almost all of the fissures we found
+great quantities of small water worn boulders, less in size than a horsebean,
+and generally of the same materials as the rock itself. The
+boulders bore the appearance of having been forced into the fissures
+of the rock by some very powerful pressure, and were wedged hard
+into the crevices. In some cases a considerable quantity of softer
+matter containing iron was found, and in it the pebbles were imbedded.
+In the upper parts of the rock the crevices swarmed
+with centipedes of a reddish-brown colour. The rock was covered
+with sea fowl when first visited, and during heavy gales seals resorted
+to it.</p>
+
+<p class="blankbefore75">About three miles to the westward of Skerryvore lie Mackenzie’s
+Rock, Fresnel’s Rock, and Stevenson’s Rock, which, as will be
+seen from <a href="#Plate2">Plate II.</a>, are connected by a tract of foul ground of
+about a mile and a quarter in length. Those rocks are the western
+limit of what we have already denominated the Skerryvore Reef.
+The passage between them and the Skerryvore or main rock is clear,<span class="pagenum" id="Page35">[35]</span>
+and has a depth of water varying from eleven to twenty-eight
+fathoms.</p>
+
+<p class="blankbefore75">Mackenzie’s Rock, which derives its name from the celebrated
+Marine Surveyor, is uncovered, at low water, to the extent of about
+forty yards, and consists of scattered patches of rock, one of which,
+at its highest part, rises about ten feet above high water mark of
+spring-tides. Fresnel’s and Stevenson’s Rocks are always under
+water; but the sea is often seen to break violently over them, as
+well as over the whole stretch of the sunken reefs which extend
+between them. The first of those rocks is indebted for its name
+to the great optical philosopher, who so greatly improved lighthouses;
+and the second bears the name of the surveyor who first
+laid down the rock,—the late Engineer of the Northern Lights
+Board.</p>
+
+<p class="blankbefore75">During the progress of the survey, a register of the rise and fall
+of the tides was regularly kept at Hynish on the neighbouring
+Island of Tyree; and from those observations it was determined,
+that the rise at that place is between twelve and thirteen feet at
+high spring tides, and three feet at dead low neap tides; and observations
+subsequently made while the works were in progress,
+gave the same results at the Rock of Skerryvore. It is high
+water at the Rock at full and change of the moon, at five hours
+and twenty-five minutes. The tides round the Skerryvore are not
+remarkable for their rapidity. In spring-tides the velocity is between
+four and five miles, and in neap-tides between two and
+three miles an hour. The flood sets to the N.N.E., and the ebb to
+the S.S.W.</p>
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page36">[36-<br>37]<a id="Page37"></a></span></p>
+
+<h3 class="nobreak"><span class="chapno">CHAPTER II.</span><br>
+<span class="chapname">PRELIMINARY ARRANGEMENTS AND WORKS, INCLUDING SURVEY
+OF THE ROCKS, AND OPENING OF QUARRIES, FROM 1834 to 1837.</span></h3>
+
+</div><!--chapter-->
+
+<p>In this chapter I shall very briefly notice those preliminary arrangements
+which may be said to have been in a great measure preparatory
+to the commencement of the work itself. It has been already
+stated, that the erection of the Lighthouse was provided for
+in the Act of 1814; but so formidable did this work appear,
+that although it was repeatedly under consideration, it was not
+until the General Meeting of the Board, on the 8th July 1834,
+that any measures were taken to carry into effect the provisions
+of the Act. On that occasion it was moved by the late Mr
+<span class="smcap">Maconochie</span>, Sheriff of Orkney and Zetland, that the Engineer
+should be instructed to make the <span class="sidenote">Survey of the
+Skerryvore
+Rocks.</span>
+necessary survey, and to report
+as to the expense of erecting the Lighthouse. In terms of
+this remit, the survey of the Rocks was commenced in the autumn
+of 1834; but from the broken state of the weather, little was
+effected at that time beyond making the triangulation; and it was
+not until the summer of 1835 that the survey was completed from
+which the Chart, <a href="#Plate2">Plate No. II.</a> was constructed. This survey was
+attended with much more labour than its extent would lead one
+to suppose, in consequence of its embracing the entire range of
+operations required in a more extensive nautical survey, and combining
+with the ordinary details required for a Chart, the minute
+accuracy in regard to surface and levels, which are always necessary
+for the purposes of the Engineer.</p>
+
+<p><span class="pagenum" id="Page38">[38]</span></p>
+
+<p class="blankbefore75">The first step was the measurement of a base line in the low
+lands of the adjoining Island of Tyree, which, owing to the distance
+and disadvantageous position of that island, could not be
+satisfactorily extended to the Rock without fixing stations in some
+of the more distant islands; and in the course of the work not fewer
+than twenty land triangles were measured. The calculations of the
+distances founded on this triangulation agreed with those afterwards
+obtained from the data of the Trigonometrical Survey, which were
+kindly furnished to me by Captain Yolland of the Royal Engineers,
+in 1843. For the purpose of making the soundings and laying
+down the sunken rocks, an entirely separate triangulation, based
+upon and connected with that which has already been noticed, became
+necessary, as the land objects were too distant, and their relative
+positions were such as to render it difficult by observations from
+them alone to determine any stations on the sea. Buoys were therefore
+moored at convenient points, and their positions determined
+by a subsidiary triangulation, so as to form a net-work of triangles
+between the shore and the Skerryvore Rock. The distances between
+these buoys were afterwards used as the bases of imaginary
+triangles, having points of sounding or shoals in their apex;
+and the angles subtended by those distances being measured by
+the sextant, the positions of the shoals or soundings were thence
+easily deduced and protracted on the <a href="#Plate2">Chart</a>.<a id="FNanchor4" href="#Footnote4" class="fnanchor">[4]</a> In connection also
+with the soundings whose positions were determined in the way
+above described, a complete set of tide observations was made,
+extending over a period of about six weeks. Those tide observations
+were connected in point of time, with the soundings, and
+were employed as the means of correcting the observed depths
+taken with the sounding-line, so as to give the true depth in reference
+to the high or low water of a given tide. Accurate measurements,
+and minute sections, were also made of the rocks in reference
+to the tide-level, and more especially of the main rock, on which<span class="pagenum" id="Page39">[39]</span>
+alone it was obvious, from the first inspection, that the Lighthouse
+Tower could be erected. In the course of this survey, the positions
+of upwards of 140 rocks were determined, and laid down on the
+<a href="#Plate2">Chart</a>, and 500 soundings were taken, and their positions protracted.
+An interesting fact was also noticed regarding the mean level of all
+the tides which had been watched during the period of about six
+weeks, as above noticed, viz., that the point half way between the
+high and low water of every tide is on <i>one and the same level</i>. This
+fact regarding the tides was, it is believed, first detected by my
+Father, in the course of some tidal observations which he made in
+the Dornoch Frith in 1830, and has since been observed in the
+Frith of Forth in 1833, and again on the shores of the Isle of Man,
+and at Liverpool. The agreement of so many observations by various
+persons at places on the opposite shores of the Kingdom, seems to
+imply the universality of this phenomenon in the British Seas; and
+the position of Skerryvore would lead to the belief, that it is
+not confined to narrow seas, but that it exists in the ocean. I
+cannot dismiss the subject of the survey, without mentioning the
+late Mr James Ritson, who acted as principal assistant surveyor,
+and to whose zeal and intelligence so much of its accuracy is
+to be attributed. The deep gulley which intersects the main
+Rock from N.E. to S.W., and across which he one day sprang while
+it was filled with a breaking wave, bears his name, as a memorial
+of his activity and perseverance. At the close of the survey in
+1835, the station-pole was left wedged and batted into one of the
+fissures or crevices of the Rock, and a cask of water was firmly
+<i>lashed</i> to ring-bolts in a cleft of the highest part of the Rock, in
+the hope that it might possibly prove useful to some shipwrecked
+seamen.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote4" href="#FNanchor4" class="label">[4]</a> <i>Vide</i> Stevenson’s Marine Surveying and Hydrometry. Edinburgh, 1842, p. 144.</p>
+
+</div><!--footnote-->
+
+<p class="blankbefore75">For the purposes of navigation generally, a survey merely
+indicating the position and extent of the foul ground would have
+been sufficient. But in connection with the work which was about
+to be commenced, it was particularly desirable to have exact details
+of the depths, rocks, and shallows of the surrounding sea, with the<span class="pagenum" id="Page40">[40]</span>
+nature of the bottom, accurately laid down; and our experience
+during the course of the work, more than once shewed how essential
+was the possession of minute topographic information to
+the safety of the shipping attending the works; more especially as
+some of the vessels lay very near the rocks, and were frequently
+driven, by a sudden change of wind, to seek shelter, during the
+darkest nights, among the neighbouring islands.</p>
+
+<p class="blankbefore75">Until this time the greatest ignorance prevailed amongst seamen
+as to the extent of the Reef, which had never before been minutely
+surveyed. Of this some proofs occurred even during the
+progress of the survey; for several vessels came so near the Rocks
+as to cause, in the minds of the surveyors, who witnessed their
+temerity, serious fears for their safety. On one occasion, in particular,
+a large vessel belonging to Yarmouth, with a cargo of timber,
+was actually boarded between Mackenzie’s Rock and the main Rock
+of Skerryvore by the surveyors, who warned the master of his
+danger in having so nearly approached these rocks, of the existence
+of which his chart gave no indication. On another occasion,
+a vessel belonging to Newcastle was boarded while passing between
+Bo-Rhua and the main Rock; and so little, indeed, had the master
+(whose chart terminated with the main Rock, and shewed nothing of
+Bo-Rhua) been dreaming of danger, or fancying that he was within
+a cable’s length of the reef, that he was found lying at ease on the
+companion, enjoying his pipe, with his wife sitting beside him knitting
+stockings.</p>
+
+<p class="blankbefore75">Much preliminary investigation was necessarily occasioned by
+the difficulties and disadvantages arising from the remote situation
+of the island in which a great part of the works was to be carried
+on. Not only is the Rock itself often inaccessible and dangerous,
+being surrounded by numerous shoals, and visited by the heaviest
+seas of the Atlantic; but what gave rise to no small part of the
+difficulties which attended this work, was the nature of the neighbouring
+Island of Tyree. <span class="sidenote">Disadvantages of
+Tyree.</span>
+This island is unhappily destitute of any<span class="pagenum" id="Page41">[41]</span>
+shelter for shipping, a fact which was noticed as a hinderance to its
+improvement, upwards of 140 years ago, by Martin, in his well-known
+description of the Western Islands.<a id="FNanchor5" href="#Footnote5" class="fnanchor">[5]</a> Nor is its interior
+more attractive; for although some parts of the soil when cultivated
+are excellent, the greater part of its surface is composed of
+sand. It was therefore obvious, at a glance, that Tyree was one
+of those places to which every thing must be brought; and this is
+not much to be wondered at, as the population, who, on a surface
+not exceeding 27 square miles, amounted in 1841 to 4687 souls,
+labour under all the disadvantages of remoteness from markets,
+inaccessible shores and stormy seas, and the oft-recurring toil of
+seeking fuel (of which Tyree itself is destitute) from the Island
+of Mull, nearly 30 miles distant, through a stormy sea. It is
+said that this total absence of fuel in Tyree is the result of the
+reckless manner in which it was wasted, in former days, in the preparation
+of whisky; but, however this may be, certain it is that
+the want of fuel greatly depresses the condition of the people. For
+our works, therefore, craftsmen of every sort were to be transported,
+houses were to be built for their reception, provisions and
+fuel were to be imported, and tools and implements of every kind
+were to be made.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote5" href="#FNanchor5" class="label">[5]</a> A Description of the Western Islands of Scotland, &amp;c., by M. Martin, Gent. London,
+1703. <i>Vide</i> 2d Edition of 1716, p. 267.</p>
+
+</div><!--footnote-->
+
+<p class="blankbefore75">In the course of the survey, much attention had been bestowed
+upon the selection of a convenient place for a workyard in Tyree
+for the preparation of materials, and in examining its rugged
+shores in quest of the best site for a Harbour, for the shipment
+of the building materials for the Rock, and for the all-important
+purpose of enabling the future attending vessel to lie in safety
+within sight of signals from the Rock, when the Light should
+come to be exhibited to the public. The point chosen for this
+establishment was <span class="sidenote">Pier and workyard
+at Hynish
+Tyree.</span>
+Hynish, which, though twelve miles distant, is,
+nevertheless, the nearest creek to the Skerryvore Rock, and which,<span class="pagenum" id="Page42">[42]</span>
+however exposed it may be, if compared with creeks elsewhere
+dignified with the name of Harbour, certainly affords as good prospect
+of shelter as any other part of the Island of Tyree, and is, in this
+respect, greatly to be preferred to any other place within sight of
+the Rock. A deputation of the Commissioners visited the Skerryvore
+in the month of July 1836, and concurred with the Engineer
+in regard to his choice of Hynish as a site for the Harbour and
+establishment.</p>
+
+<p class="blankbefore75">Another most important point of inquiry was regarding the
+materials for building the Lighthouse; and on this subject the suggestions
+in a Report by the Engineer, of the 31st December 1835, were
+followed, which proposed the opening of quarries among the gneiss
+rocks around <span class="sidenote">Quarries at
+Hynish.</span>
+Hynish.  Much facility was afforded by the liberality
+of the late Duke of Argyll, the proprietor of Tyree, who granted
+to the Commissioners free permission “to quarry materials for
+the purpose of the Lighthouse, on any part of the Argyll estates.”
+This freedom was generously continued by the present Duke, who
+has all along taken a lively interest in the success of the works.
+In terms, therefore, of the Engineer’s recommendations contained
+in the above noticed Report, Mr James Scott and fourteen
+quarriers were employed, during the summers of 1836 and 1837,
+in opening quarries, with very promising appearances of final success,
+among the gneiss rocks near Hynish Point. In the summer
+of 1837, Mr Scott and his party turned out about 3800 cubic
+feet of rock, capable of being applied to the purposes of squared
+masonry, and a very large quantity of stones fit for rubble work.
+This produce, although small, if contrasted with that of established
+quarries, is by no means despicable, when the <i>force</i> employed
+and all the disadvantages of the situation are considered; and if
+the nature of the material, which is full of rents and fissures (technically
+called <i>dries</i> and <i>cutters</i>), the frequent deceptions attending
+the opening of new quarries, the excessive hardness and unworkable
+nature of the rock, the quality and size of the blocks required
+to entitle them to claim a place in a marine tower, and the great<span class="pagenum" id="Page43">[43]</span>
+loss of time, caused by the badness of the weather, be considered,
+it will not appear that Mr Scott and his party had been eating the
+bread of idleness.</p>
+
+<p class="blankbefore75">In the mean time, measures had been taken for obtaining from
+his Grace the Duke of Argyll a feu of fifteen acres of ground at
+Hynish, for carrying on the works, with a view to its being finally
+occupied as an establishment for the crew of the vessel which was
+to attend the Lighthouse, and the families of the four lightkeepers,
+as well as for the site of the harbour. To this was added a lease
+of thirty acres, for the various purposes connected with a workyard,
+and such an establishment as seemed necessary for carrying
+on the work. A subject of anxious deliberation with the Board,
+was the construction of the harbour at Hynish for the vessels
+engaged in the service of the work; and the Commissioners, on
+the 24th May 1837, authorized the Engineer to make arrangements
+for commencing the formation of the Pier. The work
+was, accordingly, undertaken, in terms of his Reports of the 31st
+December 1835, and 27th February 1836; and the summer of
+1837 was chiefly occupied in preparing a wharf, mostly composed
+of <i>pierres-perdues</i>,<a id="FNanchor6" href="#Footnote6" class="fnanchor">[6]</a> and in the opening of the quarry already
+noticed. Such may serve as a brief and somewhat desultory
+notice of the work during the seasons of 1836 and 1837, after
+which it appeared to the Board that the operations must soon
+assume such an aspect as to require the superintendence of a committee
+of their number, as well as that of an Engineer specially
+entrusted with the management of the work.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote6" href="#FNanchor6" class="label">[6]</a> Blocks rough from the quarry, which are dropt or thrown promiscuously into the sea.</p>
+
+</div><!--footnote-->
+
+<p class="blankbefore75">At the meeting of the Board, on the 8th December 1837, a
+Committee of their number was accordingly named, to superintend
+the erection of the Lighthouse. <span class="sidenote">Skerryvore Committee
+appointed.</span>
+This Committee consisted of—<span class="smcap">Robert
+Bruce</span>, Esq., Sheriff of Argyllshire; <span class="smcap">Andrew Murray</span>,<span class="pagenum" id="Page44">[44]</span>
+Esq., Sheriff of Aberdeenshire; <span class="smcap">Robert Thomson</span>, Esq., Sheriff of
+Caithness; and the late <span class="smcap">James Maconochie</span>, Esq., Sheriff of
+Orkney and Zetland; and, shortly after its appointment, the Committee,
+on the motion of Mr <span class="smcap">Bruce</span>, the Chairman, appointed me
+Engineer for the work.</p>
+
+<p class="blankbefore75">Among the first matters which engaged the attention of this
+Committee, was a Report from the Engineer, dated the 30th
+January 1838, in which the necessity of erecting a wooden
+barrack, as a place of shelter for the workmen on the Rock,
+was pointed out; the general arrangements for carrying on the
+operations were described; and the building of a steam-tender,
+to act as a towing vessel for the stone lighters between the
+workyard in Tyree and the Rock, was also recommended.
+The Report was accompanied by a detailed requisition or estimate
+for the operations of the ensuing season, amounting to
+L.15,000&#160;: 3&#160;: 3; of which sum it was proposed to expend about
+one-third in building a steam-tender, and the rest in erecting the
+wooden barrack on the Rock, and in providing tools and materials
+for the work, as well as in the wages of men to be employed in
+preparing the foundation of the Lighthouse Tower, and in building
+the Pier, and dressing stones at Hynish.</p>
+
+<p class="blankbefore75">The Committee, after considerable deliberation, sanctioned the
+various items of the estimate, but hesitated to embark in the expense
+of building a steamer, until a fruitless correspondence with
+various ports of the kingdom, with the view of purchasing an
+old vessel, satisfied them of the necessity of building a tender
+expressly for the purpose.</p>
+
+<p class="blankbefore75">Offers were immediately received from various parties at
+Greenock for the preparation of the wooden barrack, which was
+soon afterwards commenced by the late Mr John Fleming, house-carpenter,
+who was the successful competitor.</p>
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page45">[45]</span></p>
+
+<h3><span class="chapno">CHAPTER III.</span><br>
+<span class="chapname">ON THE CONSTRUCTION OF LIGHTHOUSE TOWERS.</span></h3>
+
+</div><!--chapter-->
+
+<p>In this chapter I purpose, in the first place, to make a few observations
+regarding the construction of Lighthouse Towers in
+situations which are exposed to the assault of the waves, and
+afterwards to give a short notice of the design which I adopted
+for the Tower on the Skerryvore Rock. In making a design
+for a Lighthouse Tower in an exposed situation, numerous considerations
+at once present themselves to the Engineer; and it
+is difficult to assign to any one of them a priority in the train
+of thought which eventually conducts him to the formation of
+his plan. These considerations, however, may be conveniently
+divided into two classes:—<i>1st</i>, Those which refer to elements
+common to Lighthouses in all situations, and differ only in
+amount, such as the height of the Tower necessary for commanding
+a given visible horizon, and the accommodation required
+for the Lightkeepers and the Stores; and, <i>2d</i>, Those which are
+peculiar to Towers in exposed situations, and which refer solely
+to their fitness to resist the force of the waves which tend to
+destroy them. The first class of considerations is so extremely
+simple, as to require few remarks in this place. The distance at
+which it is desirable that a light should be visible being ascertained,
+with reference to the nature of the surrounding seas and
+the extent to which any dangerous or foul ground lies seaward of
+the proposed Lighthouse, the height of the Tower is at once determined<span class="pagenum" id="Page46">[46]</span>
+by means of the known relations which subsist between
+the spheroidicity of the earth, the effects of atmospheric refraction,
+and the height required for an object which is to be seen from a
+given distance. The question regarding the space to be provided
+in the interior of the Tower, can only be properly answered
+by a person who has a minute practical acquaintance with the
+peculiar wants and the internal economy of Lighthouses. The
+accommodation required for Lighthouses in exposed situations
+must, in a considerable degree, depend upon the greater or less
+facility of access to them, and the opportunities for replenishing
+the stores of all kinds which are in daily consumption. In such
+places, also, the risk of accidents naturally leads to the precaution
+of retaining additional Lightkeepers, and of having duplicates
+or even triplets of those parts of the apparatus that are
+liable to be injured. Of such circumstances, corresponding extension
+of the space devoted to the reception of Stores and the
+accommodation of the Lightkeepers, is the necessary consequence.
+In the long nights of a Scotch winter, when the lamps are kept
+burning for about seventeen hours, during which time they are
+never left for a moment without the superintendence of at least
+one Keeper, the care of the light, even in the most favourable
+situations, necessarily occupies at least two persons; but in places
+like the Eddystone, the Bell Rock, and the Skerryvore, where it
+sometimes happens that six or eight weeks elapse without its being
+possible to effect a landing, it has been thought necessary that
+there should never be fewer than three Keepers on duty. This
+addition to the ordinary establishment of a Lighthouse calls for
+a greater number of sleeping-cabins, and, at the same time, involves
+a corresponding increase in the supply of water, fuel and
+other provisions, requiring much additional stowage. So far, therefore,
+a Light Tower in an exposed situation, differs from one on
+shore only in the extent of its internal accommodation.</p>
+
+<p>The second class of considerations, which must guide the Engineer
+in framing a design for a Light Tower which is exposed<span class="pagenum" id="Page47">[47]</span>
+to the force of the waves, refers solely to the stability of the
+building.</p>
+
+<p>The first observation which must occur to any one who considers
+the subject is, that we know little of the nature, amount and
+modifications of the forces, on the proper investigation of which the
+application of the principle which regulates the construction must
+be based. When it is recollected, that, so far from possessing any
+accurate information regarding the momentum of the waves, we
+have little more than conjecture to guide us, it will be obvious,
+that we are not in a situation to estimate the power or intensity
+of those shocks to which Sea Towers are subject; and much less
+can we pretend to deal with the variations of these forces which
+shoals and obstructing rocks produce, or to determine the power
+of the waves as destructive agents. No systematic or intelligible
+attempt has been made practically to measure the force of the
+waves, so as to furnish the Engineer with a <i>constant</i> to guide him
+in his attempts to oppose the inroads of the ocean. The only
+experiments, indeed, on the subject, with which I am acquainted,
+are those of Mr Thomas Stevenson, Civil-Engineer, who had long
+entertained the idea of registering the force of the impulse of the
+waves, and lately contrived an instrument for the purpose, which
+he has applied at various parts of the coast. I therefore gladly
+avail myself of the present opportunity, to give a brief statement
+of the results indicated by it, as contained in a paper by the inventor,
+which appeared in the Transactions of the Royal Society
+of Edinburgh of 20th January 1845, and of which a <a href="#App7">digest</a> will
+be found in the Appendix, as any attempt to throw light upon
+this most obscure, but highly important subject, cannot fail to be
+interesting, not merely to the philosopher, but to the Marine
+Architect. It would naturally be expected, that the force of the
+waves should vary according to the season of the year, and the
+nature of the exposure, and this expectation is fully justified by
+the indications of the Marine Dynamometer. Thus it appears,<span class="pagenum" id="Page48">[48]</span>
+that during five summer months of 1843 and 1844, the average
+indications registered at different places near Tyree and
+Skerryvore, gave 611 lb. of pressure per square foot of surface
+exposed to the waves; while the average for the winter months
+for the same places during those two years, gave 2086 lb.
+per square foot, or upwards of <i>three times</i> that of the summer
+months. It also appears, that the greatest result as yet obtained
+at Skerryvore Rock was 4335 lb. per square foot; while that observed
+on the Bell Rock was 3013 lb., or <i>one-fourth part</i> less than
+that of Skerryvore. But these experiments have not been continued
+long enough as yet to render them available for the Engineer.
+In the present state of our information, therefore, we
+cannot be said to possess the elements of exact investigation, and
+must consequently be guided chiefly by the results of those numerous
+cases which observation collects, and which reason arranges,
+in the form which constitutes what is called <i>professional
+experience</i>. This kind of experience can only be acquired by
+long habit in carefully observing the appearance and effects of
+waves in different situations, and under various circumstances. We
+must attend to their magnitude and velocity, their level in regard
+to the rocks on which they break, the height of the spray caused by
+their collision against the shore, the masses of rock which they
+have been able to move, and those which have successfully resisted
+their assault; as also, where such exist, the slopes of the shores
+produced by the waves, viewed in connection with the nature of the
+materials composing the beach, with many other transient features
+which an experienced eye seizes and fixes in the mind as elements
+of primary importance in determining the power of the sea to produce
+certain effects. Such phenomena, with all their features and circumstances,
+we may carry in our recollection; and by comparing them
+with what has been observed at places where we know that artificial
+works have resisted the shocks of the waves, we may in some
+cases successfully arrive at a conclusion as to what works will, at all<span class="pagenum" id="Page49">[49]</span>
+events, be within the bounds of safety. We must not, however,
+in any case, venture to approach too near the limit of stability, so
+long as we continue to labour under our present disadvantages of
+defective information on some of the most important elements
+in the inquiry. If it be asked, therefore, how the size and form
+of buildings exposed to the shock of the waves are to be determined,
+the answer must be, that, in any given case, the problem is
+to be solved chiefly by the union of an extensive knowledge of
+what the sea has done against man, and how, and to what extent,
+man has succeeded in controlling the sea; together with a cautious
+comparison of the circumstances which modify and affect <i>any given
+case</i> which has not been the object of direct experience; nor does
+it seem possible as yet to found the art of Engineering, in so far
+as it refers to this class of works, upon any more exact basis.
+The uncertainty which must ever attend such reasoning can only,
+it is obvious, be dispelled by actual experience of the result; and
+time only can test the success of our schemes in cases of difficulty.</p>
+
+<p class="blankbefore75">A primary inquiry, in regard to Towers in an exposed situation,
+is the question, whether their stability should depend upon their
+<i>strength</i> or their <i>weight</i>; or, in other words, on their <i>cohesion</i>, or
+their <i>inertia</i>? In preferring <i>weight</i> to <i>strength</i>, we more closely
+follow the course pointed out by the analogy of nature; and
+this must not be regarded as a mere notional advantage, for the
+more close the analogy between nature and our works, the less
+difficulty we shall experience in passing from nature to art, and
+the more directly will our observations on natural phenomena bear
+upon the artificial project. If, for example, we make a series of
+observations on the force of the sea, as exerted on masses of rock,
+and endeavour to draw from these observations some conclusions
+as to the amount and direction of that force, as exhibited by the
+masses of rock which resist it successfully and the forms which
+these masses assume, we shall pass naturally to the determination
+of the <i>mass</i> and <i>form</i> of a building which may be capable of opposing
+similar forces, as we conclude, with some reason, that the mass and<span class="pagenum" id="Page50">[50]</span>
+form of the natural rock are exponents of the amount and direction
+of the forces they have so long continued to resist. It will readily
+be perceived, that we are in a very different and less advantageous
+position when we attempt, from such observations of natural phenomena,
+in which <i>weight</i> is solely concerned, to deduce the <i>strength</i> of
+an artificial fabric capable of resisting the same forces; for we must
+at once pass from one category to another, and endeavour to determine
+the <i>strength</i> of a comparatively <i>light</i> object which shall be
+able to sustain the same shock, which we know, by direct experience,
+may be resisted by a given <i>weight</i>. Another very obvious
+reason why we should prefer <i>mass</i> and <i>weight</i> to <i>strength</i>, as a source
+of stability, is, that the effect of mere <i>inertia</i> is constant and unchangeable
+in its nature; while the <i>strength</i> which results, even
+from the most judiciously disposed and well executed fixtures of a
+comparatively light fabric, is constantly subject to be impaired by
+the loosening of such fixtures, occasioned by the almost incessant
+tremor to which structures of this kind must be subject, from the
+beating of the waves.<a id="FNanchor7" href="#Footnote7" class="fnanchor">[7]</a> Mass, therefore, seems to be a source of
+stability, the effect of which is at once apprehended by the mind, as
+more in harmony with the conservative principles of nature, and
+unquestionably less liable to be deteriorated than the <i>strength</i>,
+which depends upon the careful proportion and adjustment of
+parts.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote7" href="#FNanchor7" class="label">[7]</a> It was chiefly on these grounds that the Commissioners of Northern Lights, after consulting
+a Committee of the Royal Society of Edinburgh, and Messrs Cubitt and Rennie, Civil
+Engineers, rejected the design of Captain Sir Samuel Brown, R. N., who volunteered a proposal
+to build an Iron Pillar at the time that the erection of the Skerryvore Lighthouse was
+determined on in 1835.</p>
+
+</div><!--footnote-->
+
+<p class="blankbefore75">Having satisfied himself that <i>weight</i> is the most eligible source
+of stability, the next step of the Engineer is to inquire what
+quantity of matter is necessary to produce stability, and what is
+the most advantageous form for its arrangement in a tower. The
+first question, which respects the mass to be employed, is, as already
+stated, one of the utmost difficulty, and can be solved by experience<span class="pagenum" id="Page51">[51]</span>
+alone, directed by that natural sagacity which Smeaton, in
+his account of his own thoughts on the subject, with much <i>naïveté</i>,
+terms ‘<i>feelings</i>,’ in contradistinction to that more accurate process
+of deduction which he calls ‘<i>calculation</i>.’ It is very difficult, for
+example, to conceive that the waves could displace a cylindric
+block of granite, 25 feet in diameter and 10 feet high, which would
+contain about 380 tons, and we almost <i>feel</i> that they could not do
+so. If, in order to test the soundness of this expectation, we appeal
+to such experience as we possess, and apply to the <i>largest vertical
+section</i> of such a solid, the greatest force yet indicated by my
+brother’s Marine Dynamometer, which, as already stated, is 4335
+lb. per square foot, we shall obtain a pressure of 484 tons, which,
+being reduced by <i>one-half</i><a id="FNanchor8" href="#Footnote8" class="fnanchor">[8]</a> for the loss of force occasioned by the
+convexity of the opposing cylindric surface, gives 242 tons, as
+the greatest force of the waves tending to displace the cylinder.
+But in the extreme case we have now supposed the solid will
+be entirely immersed in the water, and its efficient weight will thus
+be reduced by 140 tons, or the weight of an equal bulk of sea-water;
+and the remaining weight of 240 tons, by which it will resist
+the force of the waves, will be almost exactly equal to the pressure
+which they exert. This imaginary cylinder may, however,
+be regarded as still within the limits of safety, because the waves
+could not overturn it, unless their pressure exceeded the weight of
+the block in a ratio greater than that of its diameter to its height,
+which in this case is that of 25 to 10, or 2¹⁄₂ times. In order, therefore,
+to endanger the stability of the solid by overturning it, the pressure,
+instead of being 240 tons, must be 600 tons.<a id="FNanchor9" href="#Footnote9" class="fnanchor">[9]</a> We have thus
+seen, that the cylinder is secure from the chance of being overturned;
+but we have yet to consider how far it is exempt from the risk of being
+displaced by the pressure of the waves, causing it to slide along
+the surface of the Rock, owing to deficiency of friction between<span class="pagenum" id="Page52">[52]</span>
+the two surfaces in contact. The block, for our present purposes,
+may be regarded as <i>monolithic</i>, either being really so or as a mass
+composed of parts so united by joggles, treenails and mortar, as to
+be free from any tendency to disintegration by the force of the
+waves; and in this case the stability of the cylinder will depend
+upon the amount of friction opposing the pressure of the waves
+which tends to produce a sliding movement. It appears, by some
+experiments of M. Rondelet,<a id="FNanchor10" href="#Footnote10" class="fnanchor">[10]</a> that the friction of a block of stone
+sliding on a chiselled floor of rock is equal to ⁷⁄₁₀ths of its own weight;
+and we should thus obtain in the present instance 168 tons, as the
+amount of friction tending to resist the pressure of the waves, which
+would therefore exert a power superior to that resistance by 74
+tons.<a id="FNanchor11" href="#Footnote11" class="fnanchor">[11]</a> But this excess of force would be easily neutralized by the
+adhesion of the mortar and the abutment of the block against the
+sides of the foundation pit into which Lighthouse Towers in such
+exposed places are generally sunk in the solid rock. When, in
+addition to these considerations, we learn that the solid frustum,
+or lower part of the Eddystone Tower, which has weathered so
+many storms for the last ninety years, does not greatly exceed in
+mass the imaginary cylindric block which I have spoken of, our
+confidence in the stability of the cylinder is greatly increased.
+Our belief receives a still farther confirmation from the fact,
+that the strongest instance recorded of the power of the waves,
+falls considerably short of the case which we have just imagined.
+The instance alluded to is given in Mr Lyell’s Geology, on the
+authority of the Reverend George Low, of Fetlar, in Zetland,
+who mentions, that a block, whose dimensions seem to give
+us reason to estimate its weight at nearly 300 tons (or about
+<i>one-fifth</i> less than that of the cylinder), was moved over a point,<span class="pagenum" id="Page53">[53]</span>
+and thrown into the sea; and it must be remembered, that the
+form of this block, which was only 5 feet thick and about 40 feet
+long, rendered it very susceptible of a sliding motion, and must
+have greatly aided its transport. We may therefore not unreasonably
+conclude, that, in designing such a tower, it is safe to assume
+a mass which our own judgment and recorded facts seem to concur
+in pronouncing beyond the power of the greatest waves, as
+fixing the <i>lowest</i> limit to which the contents of the proposed edifice
+may be reduced.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote8" href="#FNanchor8" class="label">&#8199;[8]</a> This reduction seems to be warranted by the results of some experiments of Bossut.</p>
+
+<p><a id="Footnote9" href="#FNanchor9" class="label">&#8199;[9]</a> This is the product of 240 tons, by the ratio of 2·5.</p>
+
+<p><a id="Footnote10" href="#FNanchor10" class="label">[10]</a> L’art de bâtir.</p>
+
+<p><a id="Footnote11" href="#FNanchor11" class="label">[11]</a> The number 168 is ⁷⁄₁₀ths of 240, which is the weight of the cylinder, reduced by the
+weight of an equal bulk of salt water; and 74 is the excess of 242 tons, the pressure of the
+waves, above 168, the amount of friction.</p>
+
+</div><!--footnote-->
+
+<p class="blankbefore75">There are several circumstances, however, which tend to increase
+or diminish the stability of the same mass exposed to the
+same forces. Of these a very prominent one is the <i>form</i> of the
+mass, which may be so modified as to offer more or less resistance
+to the forces which assault the building. Thus a parallelopiped
+would be a much less suitable form for a sea tower than
+a cylinder, and so proportionally of all the polygonal prisms
+which may occur between these two extremes. I remember having
+heard it proposed, in the course of conversation, by a non-professional
+friend, that Lighthouse Towers might be formed in
+such a manner, that each horizontal section should be a wedge
+with its narrow end directed to the greatest assaulting force.
+This notion is in itself not destitute of ingenuity; for, if the circumstances
+to which it is to be adapted were constant, we should
+thereby present the form of least resistance, and, at the same time,
+the greatest depth and strength of the building to the line of
+greatest impulse. But the notion is wholly impracticable, because
+the direction of the winds and waves is so variable, as
+to render it almost certain that a Tower so constructed would,
+on some occasion, be assaulted in the line of its thinnest section;
+and thus, what might in one case be an advantage, would, in
+the event of such a change in the point of attack, become a
+great source of weakness, as the flat side of the wedge would
+then be opposed to the force, thereby presenting to the direct<span class="pagenum" id="Page54">[54]</span>
+assault of the waves the largest surface, with, at the same time, the
+most disadvantageous disposition of the resisting matter. There
+seems little reason, therefore, for any doubt as to the circular section
+being practically the most suitable for a Tower exposed in
+every direction to the force of the waves.</p>
+
+<p class="blankbefore75">Next to this, and hardly to be separated from it, inasmuch as it
+involves the question regarding the form of the Tower, is the
+position of the centre of gravity. The stability of any solid will,
+in general, greatly depend upon its centre of gravity being placed
+as low as possible; and the general sectional form which this
+notion of stability indicates is that of a triangle. This figure revolving
+on its vertical axis, must, of course, generate a cone as the
+solid, which has its centre of gravity most advantageously placed,
+while its rounded contour would oppose the <i>least</i> resistance which
+is attainable in <i>every</i> direction. Whether, therefore, we make
+<i>strength</i> or <i>weight</i> the source of stability, the conic frustum seems,
+abstractly speaking, the most advantageous form for a high
+Tower. But there are various considerations which concur to
+modify this general conclusion, and, in practice, to render the conical
+form less eligible than might at first be imagined. Of these considerations,
+the most prominent theoretically, although, I must
+confess, not the most influential in guiding our practice, is, that
+the base of the cone must in many cases meet the foundation on
+which the Tower is to stand, in such a manner, as to form an
+angular space in which the waves may break with violence. The
+second objection is more considerable in practice, and is founded
+on the disadvantageous arrangement of the materials, which would
+take place in a conic frustum carried to the great height which
+Lighthouse Towers must generally attain, in order to render them
+useful as sea-marks. Towards its top, the Tower cannot be assaulted
+with so great a force as at the base, or, rather, its top
+is entirely above the shock of heavy waves; and, as the conoidal
+solid should be prolate in proportion to the intensity of the shock<span class="pagenum" id="Page55">[55]</span>
+which it must resist, it follows that, if the base be constructed
+as a frustum of a given cone, the top part ought to be formed
+of successive frusta of other cones, gradually less prolate than
+that of the base. But it is obvious, that the union of frusta of
+different cones, independently of the objection which might be
+urged against the <i>sudden</i> change of direction at their junction,
+as affording the waves a point for advantageous assault, would form
+a figure of inharmonious and unpleasing contour, circumstances
+which necessarily lead to the adoption of a curve osculating the outline
+of the successive frusta composing the Tower; and hence, we
+can hardly doubt, has really arisen in the mind of Smeaton the beautiful
+form which his genius invented for the Lighthouse Tower of
+the Eddystone, and which subsequent Engineers have contented
+themselves to copy, as the general outline which meets all the conditions
+of the problem which they have to solve. And here I
+cannot help observing, as an interesting, and by no means unusual,
+psychological fact, that men sometimes appear to be conducted to
+a right conclusion by an erroneous train of reasoning; and such,
+from his “Narrative,” we are led to believe, must have been the
+case with Smeaton in his own conception of the form most suitable
+for his great work. In that “Narrative” (§ 81), he seems
+to imply, that the trunk of an oak was the counterpart or antitype
+of that form which his (§ 246) “feelings, rather than <i>calculations</i>,”
+led him to prefer. Now, there is no analogy between
+the case of the tree and that of the Lighthouse, the tree being
+assaulted at the top, and the Lighthouse at the base; and although
+Smeaton goes on, in the course of the paragraph above
+alluded to, to suppose the branches to be cut off, and water to
+wash round the base of the oak, it is to be feared the analogy
+is not thereby strengthened; as the <i>materials</i> composing the tree
+and the tower are so different, that it is impossible to imagine
+that the same opposing forces can be resisted by similar properties
+in both. It is obvious, indeed, that Smeaton has unconsciously
+contrived to obscure his own clear conceptions in his attempt<span class="pagenum" id="Page56">[56]</span>
+to connect them with a fancied natural analogy between a
+tree which is shaken by the <i>wind</i> acting on its <i>bushy top</i>, and which
+resists its enemy by the <i>strength</i> of its fibrous texture and wide-spreading
+ligamentous roots, and a tower of masonry, whose
+<i>weight</i> and <i>friction</i> alone enable it to meet the assault of the <i>waves</i>
+which wash round its <i>base</i>; and it is very singular, that, throughout
+his reasonings on this subject, he does not appear to have regarded
+those properties of the tree which he has most fitly characterized
+as “its elasticity,” and the “coherence of its parts.” One
+is tempted to conclude that Smeaton had, in the first place, reasoned
+quite soundly, and arrived by a perfectly legitimate process
+at his true conclusion; and that it was only in the vain attempt
+to justify these conclusions to others, and convey to them conceptions
+which a large class of minds can never receive, that he has
+misrepresented his own mode of reasoning. In the paragraph preceding
+that which refers to the tree (§ 80), he has, in point of fact,
+clearly developed the true views of the subject; and, with the
+single exception of the allusion to the oak, he has discussed the question
+throughout in a masterly style.</p>
+
+<p class="blankbefore75">In a word, then, the sum of our knowledge appears to be contained
+in this proposition—<i>That, as the stability of a sea-tower
+depends</i>, cæteris paribus, <i>on the lowness of its centre of gravity, the
+general notion of its form is that of a cone; but that, as the forces to
+which its several horizontal sections are opposed decrease towards its
+top in a rapid ratio, the solid should be generated by the revolution
+of some curve line convex to the axis of the tower, and gradually approaching
+to parallelism with it</i>. And this is, in fact, a general description
+of the Eddystone Tower devised by Smeaton.</p>
+
+<div class="container left w05emmax" id="Fig1">
+
+<p class="caption">No. 1.</p>
+
+<img src="images/illo057.jpg" alt="Figure of Pthah">
+
+</div><!--container-->
+
+<p class="blankbefore75">It is deserving of notice, as one of the many proofs which the
+records of antiquity afford of the similarity of the results of human
+thought in all ages, and of the truth of the Wise Man’s saying, that
+“there is nothing new under the sun,” that the ancient Egyptians<span class="pagenum" id="Page57">[57]</span>
+appear to have had the same conceptions of the solid of stability
+that were present to the mind of the modern Engineer of the Eddystone
+Lighthouse. In the admirable work recently published by
+Sir J. Gardner Wilkinson on the Manners and Customs of the
+Ancient Egyptians, he gives, in the first volume of his
+second series, at page 253, a wood-cut, shewing the figure
+of the deity Pthah, under the symbol of stability, according
+to Egyptian conceptions. This symbol so closely and
+strikingly resembles the general appearance of the Eddystone,
+that I willingly give it a place in the text, (<a href="#Fig1">No. 1</a>)
+denuded, however, of the arms and head-dress of the deity whom
+it shrouds.</p>
+
+<p class="blankbefore75">In applying these general notions to the design of a Tower for
+the Skerryvore Rock, I was, of course, guided by numerous circumstances,
+which modified my views and produced the individual form
+of Tower which I have adopted. Since the days of Smeaton, when
+his magnificent Tower was lighted by common candles, the application
+of optical apparatus to Lighthouses has greatly altered the state
+of the case; and the improvement of the system in modern times
+has, in most instances, rendered a greater altitude of Tower desirable,
+in order to extend, as much as possible, the benefit of a system
+capable of illuminating the visible horizon of any Tower which
+human art can reasonably hope to construct. In the particular
+case of the Skerryvore, also, the great distance of the outlying rocks
+(some of which, as will be seen from the <a href="#Plate2">chart</a>, are 3 miles right
+seaward of the Lighthouse) concurs with the improvement of the
+Lights, in making it desirable that the Tower should be of considerable
+height, and that the light should command an extensive range.
+It was, therefore, from the first consideration of the subject, determined
+that the Light should be elevated about 150 feet above high
+water of spring tides, so as to illuminate a visible horizon of not
+less than 18 miles of radius; and, after much deliberation, and a full
+consideration of the infrequency of communication with the proposed<span class="pagenum" id="Page58">[58]</span>
+Lighthouse from the great difficulty of landing on the Rock,
+and the consequent uncertainty of keeping up the supplies, I found
+that, for the convenient accommodation of the Lightkeepers and
+the suitable stowage of the stores, a void space of about 13,000
+cubic feet would be required. These elements being fixed, the
+general proportions of the Tower came next to be considered.</p>
+
+<p class="blankbefore75">In the Eddystone the radius of the base, at the level of high water
+of spring tides, is somewhat less than <i>one-fifth</i> of the height of the
+Tower above that level; while in the Bell Rock, at the same level,
+it is little more than <i>one-seventh</i> of the height. If, again, we suppose
+the curve of the Eddystone to be continued downwards to
+the level of low water, the radius (in so far as we may judge from
+sketching the continuation of a curve undefined by any geometrical
+property) would be rather more than <i>one-fourth</i> of the whole
+height above that level; while in the Bell Rock the proportion, in
+reference to the same level, is a little more than <i>one-fifth</i>. Viewing
+the whole height of the Skerryvore Tower above <i>high water</i> of
+spring tides as equal to 142 feet, and finding that, in the cases
+of the Eddystone and the Bell Rock, the radius of the horizontal
+section at that level is respectively <i>one-fifth</i> and <i>one-seventh</i>
+of the whole height; and again, viewing the extreme height of
+the Skerryvore Tower above <i>low water</i> of spring tides as equal
+to about 155 feet, and considering the proportionate radii of the
+Bell Rock and Eddystone (in so far as the latter is ascertainable)
+as respectively <i>one-fifth</i> and <i>one-fourth</i> of the heights of the top of
+the masonry above the level of low water, I finally decided upon
+giving the Tower at the Skerryvore such dimensions as would
+not be widely discordant with these general proportions. In
+this view, I determined that the radius of the base should not
+exceed 22 feet, on the level of about 4 feet above the high water
+mark, where I expected to obtain a solid foundation—a base
+which bears to the whole height of the Tower a proportion
+somewhat <i>less</i> than that of the Bell Rock, which is <i>one-fifth</i>.<span class="pagenum" id="Page59">[59]</span>
+It so happens, that the diameter adopted is nearly the greatest
+which the Rock affords; for, although a glance at the accompanying
+plan of the Rock at high water (<a href="#Plate3">Plate, No. III.</a>) would lead
+one to suppose that a more extended base might have been obtained,
+I found, after many careful examinations of the gullies and
+fissures which intersect it, that some of the concealed fissures run
+much farther into the Rock than might at first be imagined. The
+adoption of a much larger base, even had it been otherwise advisable,
+would therefore have involved some risk of the external ring of stones
+of the lowest course giving way by the yielding of an unsound part
+of the outer portion of the Rock to the pressure of the superincumbent
+mass, and might eventually have led to the destruction of the
+Tower.</p>
+
+<div class="container right w08emmax" id="Fig2">
+
+<p class="caption">No. 2.</p>
+
+<img src="images/illo060.jpg" alt="Dimensions of pillar">
+
+</div><!--container-->
+
+<p>The height of the Pillar having been finally fixed at 138·5 feet,
+and the radius of the base, at the level of about 4 feet above high
+water, at 21 feet, I next proceeded to consider the details of its
+proportions. Of the whole height of 138·5 feet, 18 were to be
+absorbed in a suitable capital for the Pillar, consisting of a parapet
+for the Lantern, an abacus, a cavetto, and a belt separating these
+from the shaft. The internal void I determined should be 12
+feet in diameter, as the size most suitable for the reception of
+the lantern and apparatus; and this, combined with the choice
+of about 13,000 cubic feet of void already mentioned, fixed the
+height of the solid frustum at the base of the Tower at about
+26 feet above the foundation. Having farther decided that the
+thinnest part of the walls, immediately under the belt-course
+which separates the capital from the shaft, should not be less than
+2 feet thick, as necessary to give due solidity and strength to the
+walls, and prevent, by the breadth of the joints, the percolation
+through the walls of the water which might be furiously dashed
+against them in storms, I had nothing farther to do but to determine
+the nature of the line which should connect the extremities
+of the top and bottom radii of the Pillar. As I had already concluded
+that this line must, as in the Eddystone and Bell Rock, be<span class="pagenum" id="Page60">[60]</span>
+a curve line, concave to the sea, I next proceeded to try the effects
+of various curves traced between these points, in giving a convenient
+and advantageous disposition of the materials, with regard to both
+the thickness of the walls and the mass of the solid frustum at the
+base of the Tower. These two points, as will be better
+understood by means of the accompanying diagram
+(<a href="#Fig2">No. 2</a>), are separated from each other vertically 120·25
+feet, and are horizontally distant from each other 13
+feet, which is the excess of the bottom radius over that
+of the top of the shaft, or the consequent amount of
+what may be called the <i>aggregate slope</i> of the wall.
+The solid generated by the revolution of some curve
+line about the vertical axis of the building then becomes
+the shaft of the pillar. For this purpose I tried four different
+curves, the Parabola, Logarithmic, Hyperbola, and Conchoid, figures
+of which, upon the same scale, will be found in <a href="#Plate4">Plate, No. IV.</a>,
+with the position of the centre of gravity, which was carefully
+calculated, marked on each. The logarithmic curve I at once rejected,
+from its too near approach to a conic frustum, and the excessive
+thickness of the walls which such a figure would produce,
+where the hollow cylindric space for the internal accommodation
+commences at the level of 26 feet above the base. The parabolic
+form displeased my eye by the too rapid change of its slope near
+the base; and I had some difficulty in reconciling myself to the condition
+of the exterior ring of stones at the base, too much of the
+outer portion of each stone being left without the advantage of direct
+pressure from the superincumbent mass of the wall above. The
+two remaining pillars, derived from the hyperbolic and
+conchoidal<a id="FNanchor12" href="#Footnote12" class="fnanchor">[12]</a><span class="pagenum" id="Page61">[61]</span>
+frusta, are nearly identical in form; and of these two curves I preferred
+the former, which gives the most advantageous arrangement
+of materials, in regard to stability, of all the four forms. This
+quality of advantageous proportion exists in these forms, in the
+ratio of the numbers in the last column of the following table:<a id="FNanchor13" href="#Footnote13" class="fnanchor">[13]</a>
+which shews a slight superiority of the Hyperbolic over any of
+the other forms.</p>
+
+<table class="standard">
+
+<tr class="bt">
+<th rowspan="2" class="bl br">Hypothetical<br>Towers.</th>
+<th rowspan="2" class="br">Height<br>of the<br>Tower<br>in feet.<br>(H.)</th>
+<th colspan="2" class="br">Diameter</th>
+<th rowspan="2" class="br">Volume of<br>solid Tower<br>in cubic<br>feet.<br>M.</th>
+<th rowspan="2" class="br">Distance of<br>centre of<br>Gravity<br>from Base.<br>G.</th>
+<th rowspan="2" class="br"><span class="divide"><span class="num">H</span><span class="denom">G</span></span></th>
+<th rowspan="2" class="br">Economic<br>Advantage.<br><span class="divide"><span class="num">G.M.</span><span class="denom">G′·M′.</span></span></th>
+</tr>
+
+<tr class="bb">
+<th class="br">at<br>Base<br>in feet.</th>
+<th class="br">at<br>Top<br>in feet.</th>
+</tr>
+
+<tr>
+<td class="left bl br">Hyperbolic,</td>
+<td class="center br">120</td>
+<td class="center br">42</td>
+<td class="center br">16</td>
+<td class="center br">62,915</td>
+<td class="center br">41·227</td>
+<td class="center br">2·911</td>
+<td class="center br">1·00000</td>
+</tr>
+
+<tr>
+<td class="left bl br">Conchoidal,</td>
+<td class="center br">120</td>
+<td class="center br">42</td>
+<td class="center br">16</td>
+<td class="center br">62,984</td>
+<td class="center br">41·336</td>
+<td class="center br">2·903</td>
+<td class="center br">0·99627</td>
+</tr>
+
+<tr>
+<td class="left bl br">Parabolic,</td>
+<td class="center br">120</td>
+<td class="center br">42</td>
+<td class="center br">16</td>
+<td class="center br">63,605</td>
+<td class="center br">43·400</td>
+<td class="center br">2·765</td>
+<td class="center br">0·93963</td>
+</tr>
+
+<tr>
+<td class="left bl br">Logarithmic,</td>
+<td class="center br">120</td>
+<td class="center br">42</td>
+<td class="center br">16</td>
+<td class="center br">74,742</td>
+<td class="center br">42·460</td>
+<td class="center br">2·826</td>
+<td class="center br">0·81608</td>
+</tr>
+
+<tr class="bb">
+<td class="left bl br">Conical,</td>
+<td class="center br">120</td>
+<td class="center br">42</td>
+<td class="center br">16</td>
+<td class="center br">84,737</td>
+<td class="center br">43·280</td>
+<td class="center br">2·773</td>
+<td class="center br">0·70725</td>
+</tr>
+
+</table>
+
+<div class="footnote">
+
+<p><a id="Footnote12" href="#FNanchor12" class="label">[12]</a> The solid, in this case, would have been formed by the revolution of the interior conchoid
+of Nicomedes about its directrix; and its co-ordinates were kindly calculated for me by my
+late revered preceptor, Dr <span class="smcap">Wallace</span>, Professor of Mathematics in the University of Edinburgh,
+who employed so many hours of his latter years in labours of kindness among his friends.
+This act of the Professor was the result of a conversation I had with him on the subject.
+Before I received his friendly communication, however, I had resolved to adopt the rectangular
+hyperbola, whose co-ordinates I had myself determined with this view some time before;
+and when I found that the conchoid and the hyperbola, traced between the two fixed points
+by means of the calculated co-ordinates, were so nearly coincident, that it was difficult to
+prevent their running into each other, even when drawn out on a large scale, I determined
+to adhere to my original purpose of adopting the latter curve as my guide.</p>
+
+<p><a id="Footnote13" href="#FNanchor13" class="label">[13]</a> The last column of this table is derived as follows:—Assuming that the economic advantage
+of any proposed tower of given height and diameter at base and top, is <i>inversely</i> as the mass
+and the height of the centre of gravity above the base, and denoting these quantities by M and G
+respectively, the fraction <span class="divide"><span class="num">1</span><span class="denom">G·M</span></span>
+may be taken as an indication of the economic advantage of
+the proposed tower. Let <span class="divide"><span class="num">1</span><span class="denom">G′·M′</span></span>
+express the economic advantage of another tower; then the
+advantage of the second tower, compared to that of the first, taken as unity, will be
+<span class="divide"><span class="num">G·M</span><span class="denom">G′·M′</span></span>, by
+which expression, the last column in the table was calculated.</p>
+
+</div><!--footnote-->
+
+<p>The shaft of the Skerryvore Pillar, accordingly, is a solid, generated
+by the revolution of a rectangular hyperbola about its asymptote
+as a vertical axis. Its exact height is 120·25 feet, and<span class="pagenum" id="Page62">[62]</span>
+its diameter at the base 42 feet, and at the top 16 feet. The ordinates
+of the curve, at every foot of the height of the column,
+were carefully determined in feet to three places of decimals; and
+the Appendix contains a tabular view of the co-ordinates from
+which the working drawings were made at full size. The first 26
+feet of height is a solid frustum, containing about 27,110 cubic feet,
+and weighing about 1990 tons.<a id="FNanchor14" href="#Footnote14" class="fnanchor">[14]</a> Immediately above this level the
+walls are 9·58 feet thick, whence they gradually decrease throughout
+the whole height of the shaft, until at the belt they are reduced
+to 2 feet in thickness. Above the shaft rests a cylindric belt 18
+inches deep; and this is surmounted by a cavetto 6 feet high, and
+having 3 feet of projection. The contour of this cavetto is that
+resulting from a quadrant of an ellipse revolving about the centre
+of the tower, with a radius of 8 feet on the level of its transverse
+axis; and the moulds for this curve were drawn at full size from
+co-ordinates calculated for the purpose. The cavetto supports an
+abacus 3 feet deep, the upper surface of which forms the balcony
+of the tower, and above it rest the parapet-wall and lantern.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote14" href="#FNanchor14" class="label">[14]</a> At the rate of 13·62 cubic feet of granite to a ton.</p>
+
+</div><!--footnote-->
+
+<p>It may, perhaps, be not uninteresting to the reader to examine
+the woodcuts (<a href="#Fig3">No. 3</a>), which shew, on one scale, the elevations of
+the Lighthouses of the Eddystone, the Bell Rock, and the Skerryvore,
+and exhibit the level of their foundations in relation to high
+water. They will also serve to give some idea of the proportionate
+masses of the three buildings. The position of the centre of gravity,
+as calculated from measurements of the solids, is also marked by a
+round black dot on each tower; and in the table following, I have
+given the cubic contents of each of these towers, the height of the
+centre of gravity above the base and the ratio of that quantity
+to the height of the tower.</p>
+
+<p><span class="pagenum" id="Page63">[63]</span></p>
+
+<div class="container w60emmax" id="Fig3">
+
+<p class="caption">No. 3.</p>
+
+<img src="images/illo063.jpg" alt="Three lighthouses">
+
+<div class="split3070">
+
+<div class="left3070">
+
+<p class="caption sstype"><span class="fsize90"><b>EDDYSTONE.</b></span></p>
+
+</div><!--left3070-->
+
+<div class="right3070">
+
+<div class="split5545">
+
+<div class="left5545">
+
+<p class="caption sstype"><span class="fsize90"><b>SKERRYVORE.</b></span></p>
+
+</div><!--left5545-->
+
+<div class="right5545">
+
+<p class="caption sstype"><span class="fsize90"><b>BELL ROCK.</b></span></p>
+
+</div><!--right5545-->
+
+</div><!--split5545-->
+
+</div><!--right3070-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split3070-->
+
+</div><!--container-->
+
+<table class="standard">
+
+<tr class="bt">
+<th rowspan="2" class="bl br">Lighthouse.</th>
+<th rowspan="2" class="br">Height of<br>Tower above<br>first entire<br>course.<br>(H)</th>
+<th rowspan="2" class="br">Contents<br>of<br>Tower.</th>
+<th colspan="2" class="br">Diameter</th>
+<th rowspan="2" class="br">Distance of<br>centre of<br>gravity in feet<br>from Base.<br>(G)</th>
+<th rowspan="2" class="br"><span class="divide"><span class="num">H</span><span class="denom">G</span></span></th>
+</tr>
+
+<tr class="bb">
+<th class="br">at Base.</th>
+<th class="br">at Top.</th>
+</tr>
+
+<tr>
+<td class="left bl br">Eddystone,</td>
+<td class="center br">&#8199;68&#8200;&#8199;</td>
+<td class="center br">13,343</td>
+<td class="center br">26</td>
+<td class="center br">15</td>
+<td class="center br">15·92</td>
+<td class="center br">4·27</td>
+</tr>
+
+<tr>
+<td class="left bl br">Bell Rock,</td>
+<td class="center br">100&#8200;&#8199;</td>
+<td class="center br">28,530</td>
+<td class="center br">42</td>
+<td class="center br">15</td>
+<td class="center br">23·59</td>
+<td class="center br">4·24</td>
+</tr>
+
+<tr class="bb">
+<td class="left bl br">Skerryvore,</td>
+<td class="center br">138·5</td>
+<td class="center br">58,580</td>
+<td class="center br">42</td>
+<td class="center br">16</td>
+<td class="center br">34·95</td>
+<td class="center br">3·96</td>
+</tr>
+
+</table>
+
+<p>I come now to notice the few subordinate points in which the
+design of the Skerryvore Tower may be regarded as differing from
+those of the Eddystone and the Bell Rock. In glancing at the<span class="pagenum" id="Page64">[64]</span>
+contrasted figures of the three buildings, it will be at once observed
+that the outline of the Skerryvore approaches more nearly
+to that of a conic frustum than the other two. To the adoption
+of this form, various considerations induced me; and these I shall
+very briefly detail. In the first place, it seemed to me that, in
+both the Bell Rock and the Eddystone, the thickness of the walls
+had been reduced to the lowest limits of safety towards the top;
+and the effects of the sea and wind acting upon a heavy cornice,
+cause a degree of tremor which I felt satisfied would not occur
+in a building with thicker walls. The effect of thickening the
+walls at the top, is, of course, <i>cæteris paribus</i>, to diminish the
+projection of the base, and thus to produce less concavity of
+figure, and consequently a nearer approximation to the contour of
+a conic frustum. I have already stated, that this excess of the
+bottom radius over that of the top, is in the Skerryvore Tower
+13 feet, and that the height of the shaft is 120·25 feet. The
+quotient resulting from the division of the height by the excess of
+bottom radius over that at the top is 9·27; and, if the figure had been
+conical, this number would have given a measure of the slope of the
+walls throughout. There can be little doubt that the more nearly
+we approach to the perpendicular, the more fully do the stones at
+the base receive the effect of the pressure of the superincumbent
+mass as a means of retaining them in their places, and the more perfectly
+does this pressure act as a bond of union among the parts of
+the Tower. This consideration materially weighed with me in
+making a more near approach to the conic frustum, which, next to
+the perpendicular wall, must, other circumstances being equal, possess
+the property of pressing the mass below with a greater weight,
+and in a more advantageous manner, than a curved outline in
+which the stones at the base are necessarily farther removed from
+the line of the vertical pressure of the mass at the top.<a id="FNanchor15" href="#Footnote15" class="fnanchor">[15]</a>
+This vertical<span class="pagenum" id="Page65">[65]</span>
+pressure operates in preventing any stone being withdrawn
+from the wall in a manner which, to my mind, is much more satisfactory
+than an excessive refinement in <i>dovetailing</i> and <i>joggling</i>,
+which I consider as chiefly useful in the early stages of the progress
+of a work, when it is exposed to storms, and before the superstructure
+is raised to such a height as to prevent seas from
+breaking right over it.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote15" href="#FNanchor15" class="label">[15]</a> It is most satisfactory to find that the views expressed above, regarding the eligibility
+of the conical form, seem to have the sanction of the late Dr Thomas Young, who appears to
+have connected his preference of this form with its greater efficiency as a source of friction
+among the parts of a building. In his syllabus of Lectures, under the section “Architecture,”
+he thus speaks: “For a Lighthouse where a great force of wind and water was to be resisted,
+Mr Smeaton chose a curve convex to the axis. In such a case, the strength depends more
+on weight than on cohesion, and also in a considerable degree on the friction which is the effect
+of that weight. Perhaps a cone would be an eligible form.”</p>
+
+</div><!--footnote-->
+
+<p>If these views be substantially correct, it may not, perhaps, be
+altogether inadmissible (without, however, venturing to enunciate
+any general law) to conclude, that, in the three Lighthouses of the
+Eddystone, the Bell Rock, and the Skerryvore, this source of union
+among the outer stones of the lower courses must bear some proportion
+to the numbers 753, 659, and 927, which are the quotients of
+the height of the column, divided by the difference of the top and
+bottom radii of the shaft in each case respectively. This consideration
+seems too important to be entirely overlooked; and I conceive
+that, by following out this view, I have been enabled to depart with
+perfect safety from the intricate and elaborate work required for the
+connection of the materials by means of dovetailing and joggling,
+which the adoption of a more concave outline (in which the vertical
+pressure could not have been so advantageously transmitted
+to the outer stones of the base), would perhaps have rendered advisable.
+In the case of the Bell Rock, however, whose construction,
+in regard to this property, is the least advantageous
+of the three buildings, it must be borne in mind that the Tower
+is covered to the depth of 15 feet at spring tides, and that this
+principle of vertical pressure could not have been safely appealed
+to during the whole time which intervened between the commencement<span class="pagenum" id="Page66">[66]</span>
+of the building and the attainment of a height sufficient
+to render it available, which, in a Tower having so great
+a part submerged, was of necessity much prolonged. The stones
+were thus exposed to the full effect of heavy seas, at all levels,
+during two entire winters, and could not therefore have been safely
+left, without being kept together by numerous ties and dovetails.
+It also seemed important, in designing that Tower, with reference
+to the rise of tide, to give its lower part a sloping form, as the least
+likely to obstruct the free passage of the waves. The outer stones
+of the lower courses were also selected of unusual length <i>inwards</i>, so
+as to bring them more under the influence of the vertical pressure
+of the upper wall.</p>
+
+<p>Before leaving this subject, I may remark, that it is quite possible
+to construct a Tower of a curved form, in such a manner,
+that the pressure of the upper part of the pillar shall be distributed
+to the greatest advantage on every stone, by building the outer
+walls as inverted arches, so that the section of each stone shall
+be that of a voussoir, with joints perpendicular to the successive
+tangents of the curve. This arrangement of the stones is,
+in fact, practised in sea walls of various kinds, and has even
+been recommended for circular Towers in an ingenious paper
+in the Transactions of the Royal Scottish Society of Arts. But
+in many situations, and at Skerryvore in particular, this mode
+of transmitting the pressure, so as to throw it perpendicular
+to the beds of the stones, is inadmissible, as conducing to or involving
+a greater evil. The evil has already been noticed, and
+consists in the thrust of the lowest stone (which is of course inclined
+to the horizon) having a tendency to push out the sides
+of the Rock on which the Tower is built. This fear, where the
+Towers are to be placed on small steep rocks or pinnacles, and more
+especially when these Rocks are traversed by veins nearly vertical,
+is by no means visionary; and there is good reason to apprehend,
+that the pressure thus resulting in a line considerably inclined to
+the plane of <i>cleavage</i>, might throw outwards a thin portion of<span class="pagenum" id="Page67">[67]</span>
+rock, which, under the more conservative influence of a vertical
+pressure, might continue to retain its connection with the rest of
+the Rock unimpaired for ages.</p>
+
+<p>Another method of, in some degree, increasing the resistance of
+a Sea Tower to a horizontal thrust, if such aid be required, is to
+give the line of courses a continuous spiral form, instead of building
+them in successive horizontal layers. Were there reason to fear
+that the entire dislocation of the building might take place in a plane
+nearly horizontal, this method seems more calculated to counteract
+the danger than the use of dowels or joggles passing from
+the course below to the course above; but, as this is one of the
+accidents least to be apprehended, there does not seem any good
+ground for resorting to a mode of structure which would lead
+to considerable intricacy of workmanship, and would, in practice,
+be attended with difficulty in obtaining a proper vertical bond
+or union among the several stones.</p>
+
+<p>The only remaining point, in which the example furnished by
+the Eddystone and Bell Rock Lighthouses has been at all materially
+departed from, is (as has already been hinted at by an unavoidable
+anticipation) the mode of uniting the different parts of the masonry
+together. In both these Towers the stones were dovetailed
+throughout the buildings, chiefly (at least in the case of the Bell
+Rock where the foundation was so much below the tide) with
+the view of preventing the sea from washing away the courses
+which might be left exposed to the winter storms before the weight
+of the superstructure had been brought to bear upon them. In the
+upper part of the Bell Rock my father also introduced a kind of
+band joggle, which consists of a flat ribband of stone raised upon
+the upper bed of one course, and fitting into a corresponding
+groove cut in the under bed of the course above; and this system
+of tying the adjoining courses together also forms a chief feature
+in his design for a Lighthouse on the Wolf Rock.<a id="FNanchor16" href="#Footnote16" class="fnanchor">[16]</a>
+When the<span class="pagenum" id="Page68">[68]</span>
+great pressure of the superstructure of these Towers, however, and
+the effect of the mortar are considered, there seems little probability
+of one course being dislocated, in defiance of the friction resulting
+from the weight of the column. An impulse sufficient to
+produce such an effect would tend to overset the whole superstructure
+from mere deficiency in weight, and in this case the
+joggle would have little effect. But if joggles be thought necessary
+for this purpose, the ribband form certainly produces a better
+arrangement than that of the cubic joggles employed by Smeaton
+for connecting the adjoining courses of his building together, as the
+sectional strength of these scattered square joggles is very small
+compared to the effect of a shock which could be supposed capable
+of moving the whole mass of a Tower. In the lower parts of the
+Skerryvore Tower, I entirely dispensed with dovetailing and
+<i>joggles between the courses</i>, and thus avoided much expensive dressing
+of materials. The stones were retained in their places during
+the early progress of the work, chiefly by common diamond joggles,
+and the courses were temporarily united to each other by wooden
+treenails, like those used in the Eddystone and Bell Rock. These
+treenails had split ends, with small wedges of hardwood loosely inserted,
+which being forced against the bottom of the holes in the
+course below, into which the treenails were driven, expanded their
+lower ends until they pressed against the sides of the holes; while
+their tops were made tight by similar wedges driven into them with
+a mallet. I have, however, adopted the ribband-joggle in the higher
+part of the Tower, where the walls begin to get thin in the very
+same manner as at the Bell Rock, where it was used, partly that it
+might counteract any tendency to a <i>spreading</i> outwards of the stones,
+and partly that it might operate as a kind of <i>false joint</i> to exclude
+the water which, when pressed with great violence against
+the Tower, is apt to be forced through a straight or plain joint.
+The stones in the higher courses throughout each ring are also
+connected at the ends by double dovetailed joggles, which unite
+the two adjoining stones; and the walls are, besides, tied together<span class="pagenum" id="Page69">[69]</span>
+at various points by means of the floor stones, which are all
+connected by dovetails let into large circular stones which form
+the centres of the floors. I also ventured to leave out the metallic
+ties at the cornice, which consisted, at the Eddystone, of chains,
+and, at the Bell Rock, of copper rings. The reasons which induced
+me to adopt this change I need not here enlarge upon.
+It is sufficient to state, that I believe I have nearly balanced the
+forces which would have tended to throw the cornice outwards,
+had a greater disproportion existed in the weight of the outer and
+inner parts of the cavetto, and to point out (<a href="#Plate7">Plate VII.</a>) that the
+Lightroom or highest floor occurs, at such a level, as of itself to
+answer all the ends which metallic ties could have served.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote16" href="#FNanchor16" class="label">[16]</a> Account of the Bell Rock Lighthouse, Plate XXI.</p>
+
+</div><!--footnote-->
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page70">[70-<br>71]<a id="Page71"></a></span></p>
+
+<h3 class="nobreak"><span class="chapno">CHAPTER IV.</span><br>
+<span class="chapname">OPERATIONS OF 1838.</span></h3>
+
+</div><!--chapter-->
+
+<p>The hazardous nature of the anchorage, and the consequent
+difficulty of mooring a vessel in the neighbourhood of the Skerryvore
+Rock, induced me, from the first, to consider it as a matter of great
+importance, even at a large expenditure of time and money, to
+erect <span class="sidenote">Temporary Barrack
+on Rock.</span>
+some temporary dwelling on the Rock for the accommodation
+of the people engaged in the work, with the view of rendering
+the operations less dependent on the state of the sea, which
+varied with every wind. So important, indeed, did this object appear
+to me, that I was at times apt to look upon it as an indispensable
+step towards ultimate success. That opinion was amply
+confirmed during our first season’s operations, by the experience of
+the oft-recurring difficulty of returning to the moorings when driven
+away by stress of weather, together with the daily risk and loss of
+time in landing the workmen in small boats, even in weather when
+they could be profitably occupied if once placed on this small <i>terra
+firma</i>. With this view, I naturally turned to the same plan which
+had been adopted at the Bell Rock, where the temporary barrack
+stood the test of five winters. That structure, which is represented
+in <a href="#Plate5">Plate No. V.</a>, and is particularly described in the Appendix
+to my father’s Account of the Bell Rock Lighthouse, consisted
+of an open framework of six logs, about 47 feet long and 13 inches
+square, assembled in such a manner as to form by their union a
+hexagonal pyramid, on the top of which rested a wooden turret;
+the whole erection rising to the height of about 60 feet above the
+rock. This pyramidal framework was strongly trussed and tied;
+and, being open at the lower part, offered little resistance to the
+waves. The upper part contained a gallery for keeping various<span class="pagenum" id="Page72">[72]</span>
+stores and such materials as could not be safely left on the Rock,
+even in the finest weather; but it was framed of lighter materials,
+so as to admit of its yielding easily to any extraordinary waves,
+without involving injury to the principal part of the structure,
+by offering great resistance to the sea. The turret on the top was
+in the form of a twelve-sided prism, 12 feet in diameter, and 30
+feet high, and was securely attached, by means of the ties and
+braces shewn in the <a href="#Plate5">drawing</a>, to the apex of the pyramid, which
+entered into the lower part of it. The small space which the turret
+afforded was, with the utmost economy of room, divided into three
+storeys, of which the lower was entirely taken up by the kitchen
+and the bread-store, a great deal of room being occupied by the
+main beams of the pyramid which passed through its centre. The
+next storey was subdivided into two chambers, of which one was
+appropriated to the foreman of the works and the landing-master,
+while the other was set apart for myself; and the top storey, which
+was surmounted by a small lantern and ventilator, formed a barrack
+room, capable of containing 30 people. Of the comforts and discomforts
+of this habitation I shall at some future time have occasion
+to speak. I merely draw attention to its erection at present,
+as an operation, which it was most desirable should precede every
+other work on the Rock. One of the first proceedings, therefore,
+was to obtain estimates for the preparation of this log-house, which,
+in order to avoid loss of time in making adjustments on the Rock,
+was to be carefully fitted up in the workyard of the contractor
+before being shipped. Drawings and a specification were accordingly
+prepared, and submitted to several carpenters in Greenock,
+who gave in offers for the work; and it was finally commenced in
+the month of March, by the late Mr John Fleming, who was the
+successful offerer.</p>
+
+<p><span class="sidenote">Tools and Machinery.</span>
+It was also necessary to provide a large assortment of quarriers’
+and masons’ tools of every kind; and many cranes, crabs,
+anchors, mooring buoys and other implements were ordered, according
+to detailed specifications and drawings. These preparations
+necessarily occupied the early part of the year 1838.</p>
+
+<p><span class="pagenum" id="Page73">[73]</span></p>
+
+<p>From the extent of the foul ground round the Skerryvore, and
+the absence of good harbours in the neighbourhood, it was foreseen
+at the outset that the operation of landing about 6000 tons of
+materials on the Rock could not be accomplished by means of sailing
+vessels with that degree of certainty or regularity which was
+desirable, in order to obtain the full benefit of the short working
+season which the climate of the Western Hebrides affords; and
+the necessity for providing a <span class="sidenote">Steam Tender for
+the Works.</span>
+steam tender was, therefore, generally
+admitted. It has already been stated, that, in order to avoid the
+expense attending the building of a vessel for this purpose, application
+was made at the principal ports of the kingdom, with the
+view of purchasing a suitable vessel; but, although twenty-four
+vessels of nearly the required dimensions were offered for sale, not
+one of them was considered fit for such a service, the great majority
+being light craft, such as are generally used in river and port navigation.
+It was therefore found necessary to build a steamer; for
+which purpose, specifications and drawings were prepared, and after
+receiving various tenders from respectable parties, a contract was
+entered into with Messrs Menzies and Sons, shipbuilders, and
+Messrs J. B. Maxton and Co., engineers, both of Leith, for building
+a steamer of 150 tons, with two engines of 30 horse power
+each.</p>
+
+<p>The use of a steamer, at the very outset of the works, would
+doubtless have proved of the greatest service in the erection of the
+barrack on the Rock, and would have materially lightened our
+cares and toils; but I am not sure that I should have acquired so
+thorough an acquaintance with the difficulties and dangers of the
+Skerryvore, or that I should have been so well prepared for all the
+obstacles that presented themselves in the after parts of the work,
+had the first season’s operations been conducted under those advantages
+which are always derived from the use of steam-power.
+As it was, we had much to bear from the smallness of the Lighthouse
+Tender, named the <i>Pharos</i>, a vessel of 36 tons, new register,
+which was all the regular shipping attendance we possessed during
+this first season; and the inconvenience arising from her heavy<span class="pagenum" id="Page74">[74]</span>
+pitching, was, to landsmen, by no means the least evil to be endured.
+But the frequent loss of opportunities, of which we might
+easily have availed ourselves, if we had possessed the command of
+steam-power, and the danger and difficulty of managing a sailing
+vessel in the foul ground near the Rock, and between it and Tyree,
+were, perhaps, even more felt by the seamen than by the landsmen;
+and if the experience of a single year’s work can form any
+ground for an estimate of the length of time required for building
+the Skerryvore Lighthouse, with a sailing vessel, I should say,
+we must still (even in 1845) have been engaged in the masonry
+part of the work, which was finished on the 25th July 1842.</p>
+
+<p>About the middle of April, arrangements were made with Mr
+Charles Neilson, a builder in Aberdeen, to select granite masons
+for the works at the Skerryvore, as it was expected that the operation
+of dressing stones for the Tower would be begun in the ensuing
+summer; and it was also obvious, that their services would be
+required in excavating seats for the supports of the Barrack-house
+on the Rock. <span class="sidenote">Employment and
+Wages of Workmen.</span>
+Masons were accordingly selected, and engaged on
+the terms stated in the following letter to Mr James Scott, the
+Foreman, who was sent to Aberdeen to assist in choosing the
+men:—“Although it is difficult to fix the precise number of men
+who may be required, during the progress of the works, as this
+must, in some measure, depend upon the produce of the quarries at
+Hynish, and of those to be opened in Mull, you may, in the mean
+time, engage thirty masons or stone-cutters, twelve quarriers, and
+three or four smiths, for two years of certain employment. With
+regard to the rate of wages to be paid to the men, this will, in
+some measure, depend upon the demand for the season at Aberdeen;
+it is, at all events, expected, that they will on no account
+exceed the rate of 3s. 10d. per day for masons, and 2s. 6d. per
+day for quarriers, as paid last season during the long day, or from
+the 1st of February till 31st of October; and for the short day
+during the remaining three months, 3s. for the masons, and 2s. for
+the quarriers, from 1st November till 31st January.</p>
+
+<p>“It is intended that subsistence money shall be paid to such of<span class="pagenum" id="Page75">[75]</span>
+the families or relatives of the workmen as may require it; and
+that their wages shall be fully settled monthly, deducting the subsistence
+money advanced to their relatives. A Store will be kept
+at the works by the Lighthouse Board, from which provisions will
+be served out at stated periods, to be fixed by the storekeeper; and
+these provisions shall be sold to the workmen at the cost prices at
+which such stores are laid in. Barrack accommodation or lodgings,
+with cooking, will also, as formerly, be allowed to the men free
+of expense.”</p>
+
+<p><span class="sidenote">Progress of the
+outfit for the season’s
+operations.</span>
+Early in the month of May the preparation of the wooden barrack
+for the Rock had been completed, and the whole had been set
+up in the workyard at Greenock; and when I visited it for the
+last time about the 5th of that month, I found it all ready for shipment,
+excepting some additional iron ties, which I ordered for
+securing the turret to the top of the pyramid, which were to be
+applied at the level of the floor of the upper or barrack-room
+storey. I also found that the moorings, including the mushroom
+anchors and chains, and the workyard materials, consisting of
+several cranes, trucks, a janker for the transport of timber, and a
+Woolwich sling-cart for carrying stones to the various sheds, were
+in the course of preparation. A large assortment of masons’ and
+quarriers’ tools was at the same time ready for shipment at Aberdeen.
+Early in June, a vessel called the Duke of Montrose was
+chartered to carry coals to Tyree, both for household purposes and
+for the work; and two small portable smiths’ forges were prepared
+for use on the Rock.</p>
+
+<p>In providing the means of efficiently carrying on so many complicated
+operations in a situation so difficult and remote, it is impossible,
+even with the greatest foresight, to avoid omissions;
+while delay of a most injurious kind may result from very trivial
+wants. Even the omission of a handful of sand, or a piece of clay,
+might effectually stop for a season the progress of plans, in the
+maturing of which hundreds of pounds had been expended. Accordingly,
+although I had bestowed all the forethought which I
+could give to the various details of the preparation for the season (of<span class="pagenum" id="Page76">[76]</span>
+which I found it absolutely indispensable to be personally aware,
+even to the extent of the cooking dishes), new wants were continually
+springing up, and new delays occasioned, so that it was not until
+the evening of the 23d of June that I could <span class="sidenote">Embark for
+Skerryvore.</span>
+embark at Tobermory
+in the <i>Pharos</i> Lighthouse Tender, commanded by Mr Thomas
+Macurich, with all the requisites on board for commencing the season’s
+operations. Next morning we moored off Hynish Point about
+three o’clock, and, from the roughness of the passage, were not unwilling
+to land at that early hour. Here I found that Mr Scott,
+the foreman of the workyard, had, notwithstanding the unworkable
+nature of the Rock, more particularly afterwards noticed, procured
+about sixty fine blocks of gneiss, as the produce of the Tyree
+quarries, which had been wrought for upwards of 15 months; and
+had at the same time completed the masonry of a range of buildings
+for stores and barracks, capable of containing upwards of 100
+men, and had built about 100 feet in length of a landing-pier,
+reaching nearly to low-water mark. A magazine for gunpowder,
+of which a considerable stock was required for quarrying purposes,
+had also been built; and a piece of garden ground had been inclosed
+and stocked for the use of the people to be employed at the
+works. Measures had also been taken for inclosing the ground,
+which had been feued by the Board from the Duke of Argyll. This
+day being Sunday, nothing was done at Hynish, and we waited
+until next morning before sailing for the Rock.</p>
+
+<p><i>25th June.</i>—Sailed in the <i>Pharos</i> from Hynish Bay this morning
+about six, with Mr Scott, the foreman of the workyard, and
+one or two masons on board; but, having a foul wind during the
+early part of the day, and the weather falling afterwards calm, it
+was not until three in the morning of the 26th that we reached the
+Rock.</p>
+
+<p><i>26th June.</i>—Our first step was to <span class="sidenote">Lay down Moorings,
+and try to
+land on the Rock.</span>lay down moorings for the
+tender as near the Rock as seemed to be consistent with safety. The
+position chosen by Mr Macurich, who commanded the vessel, was
+to the S.S.E. of the Rock, about a quarter of a mile off, and in
+13 fathoms water, on an irregular rocky bottom. About half-past<span class="pagenum" id="Page77">[77]</span>
+five I attempted a landing on the Rock, but there was a great deal
+too much sea. The vessel was pitching the bowsprit under at her
+moorings, and the surf broke into the creek where landings are
+generally made, in such a manner as to render it quite impossible
+to get near the Rock. After hanging on our oars in the boat for
+nearly an hour, in the hope of a smooth lull between the heavy
+seas, we returned to the vessel, and, as the wind still freshened
+from the S.E., we reefed the mainsail and set the first jib, and
+steered for the Mull shores, where, about ten at night, we came to
+an anchor in Loch Loich, not far from the Island of Iona.</p>
+
+<p><i>27th June.</i>—Next day also being unsuitable for attempting to
+reach the Skerryvore, the vessel lay in North Bay, and the early part
+of the day was spent in a careful examination of the granite Rocks
+of the district called <span class="sidenote">Driven to Mull.</span>
+<i>Ross of Mull</i>, with the view of establishing quarries
+there; as our experience of the unsatisfactoriness of working
+the Tyree quarries during fifteen months had frequently led me
+to anticipate the necessity of soon seeking a supply of materials in
+some other quarter. In this district an almost inexhaustible supply
+of flesh-coloured granite was found, not certainly of the hardest
+description, but singularly equal and homogeneous in its texture.
+I therefore made a general survey of the neighbouring localities,
+with a view to select the best position for opening quarries and
+establishing a landing place or wharf for shipping the materials, as
+well as for erecting barracks for the workmen. In the afternoon,
+I embarked at the call of Mr Macurich, to attempt another landing
+on the Skerryvore; but as the wind soon fell calm, we did very
+little good until evening, when some progress was made in stretching
+across towards the Rock.</p>
+
+<p><i>28th June.</i>—At nine this morning, we reached our moorings at
+the Rock, but there was still so much surf that a landing could not
+be attempted till mid-day, when I went with Mr Macurich in the
+boat, and with some difficulty contrived to spring on the Rock,
+after which the boat returned to the vessel for the rest of the
+party. While left alone on this sea-beaten Rock, on which I had<span class="pagenum" id="Page78">[78]</span>
+landed with so much difficulty, and as I watched the waves, of
+which every succeeding one seemed to rise higher than the last,
+the idea was for a few minutes forcibly impressed on my mind,
+that it might, probably, be found impracticable to remove me
+from the Rock, and I could not avoid indulging in those unaccountable
+fancies which lead men to speculate with something like
+pleasure upon the horrors of their seemingly impending fate. These
+reflections were rendered more impressive by the thought that many
+human beings must have perished amongst those rocks. A consideration,
+however, of the rarity of an opportunity of landing on
+the Rock, and the necessary shortness of our stay, soon recalled
+me to my duty, and before the boat returned with a few of the
+workmen, I had projected some arrangements as to the first step
+to be taken in erecting the framework of the barrack-house. The
+second landing was more easily effected, as the tide had fallen, and
+the landing-place was more sheltered, <span class="sidenote">First day’s work
+on the Rock.</span>
+so that we were the more
+emboldened to make a fair commencement of operations. It was a
+day of great bustle and interest, the work consisting in chalking out
+and marking on the Rock with paint, the sites of the Lighthouse-Tower,
+and the wooden barrack, and the positions for cranes, crabs,
+and ring-bolts for guys and other tackling, as well as ascertaining
+such dimensions as would enable me at once to proceed to fit up
+the log-house, or barrack, at our next landing. In that way, we
+spent four hours on the Rock, much to the annoyance of the
+seals and the innumerable sea-fowl, which we drove from their
+favourite haunts. During the whole day, the sun had great power;
+and the smell from the cast-away feathers and the soil of the sea-fowl
+was extremely disagreeable. I was amazed to find that those
+animals should select, as their place of repose, a rock in the
+Atlantic, intersected by deep gullies which are never dry, with only
+one pinnacle, about 5 feet in diameter, raised about 16 feet above
+the sea. while the greater part is only 5 feet above high water.
+Yet, in a crevice of this Rock, I found an egg resting on a few
+downy feathers, which the first wave must have infallibly washed<span class="pagenum" id="Page79">[79]</span>
+away! After the day’s work on the Rock, we sailed for Tyree,
+but did not reach the workyard till next morning at nine; and
+a long day of bustle and hurry was spent there in preparing provisions,
+timber, ring-bolts, chains and all sorts of tackling for the
+operations connected with the erection of the barrack on the Rock.
+On the evening of the 30th June, I sailed for Greenock, whence I
+trusted soon to return to the Skerryvore with the whole of the
+materials, to commence operations.</p>
+
+<p>It seldom happens that human expectations are fully realised,
+especially in matters which excite a strong interest in the mind,
+and thus lead one to desire a more rapid progress than usual.
+But this is peculiarly true in all arrangements which depend on
+the co-operation of many persons; and so I experienced on my visit
+to Greenock and Glasgow, where I had given orders for <span class="sidenote">Shipment of all
+the materials at
+Glasgow and
+Greenock.</span>
+shipping all
+the machinery and apparatus required for carrying on the works,
+such as cranes, trucks, boats, blocks and tackle, anchors, coals,
+grindstones, stucco, pavement, mats and fascines for blasting, clay
+for puddling, shear-poles, and innumerable small utensils, some of
+no great value, but all necessary to the success of the work. The
+great bulk of those materials were despatched by a vessel called the
+<i>New Leven</i>, and part by the <i>Mary Clark</i>, on the 24th July; but it
+was not until the 30th that the <i>Pharos</i> Lighthouse tender was
+fully loaded, on the morning of which day I again embarked at
+Greenock for the Skerryvore Rock. The weather proving somewhat
+unfavourable, we were forced (being very heavily laden) to
+pass through the Crinan Canal, instead of going round the Mull of
+Kintyre, so that it was not till the morning of the 4th August that
+we landed at <span class="sidenote">Reach Tyree.</span>
+Hynish, in Tyree. Here I found some farther progress
+had been made in building the barracks for the men, some of
+the houses being already roofed and slated. The quarries, too, had
+turned out stones sufficient for about four of the lowest courses of
+the Tower, a quantity which might be estimated at about 7920
+cubic feet. Next day (August 5th), the wind blowing strong from
+the S.S.W., we were forced to leave Hynish Bay, <span class="sidenote">Driven to Mull.</span>
+and retreat before
+a very heavy sea to Tobermory. We immediately sailed again,<span class="pagenum" id="Page80">[80]</span>
+and made for Loch Erin, a small creek in the Island of Coll, as
+being nearer to Hynish and better adapted for enabling us to take
+advantage of any sudden improvement in the weather. On our arrival
+at this singular natural haven, at nine in the evening, I was
+glad to find the <i>New Leven</i>, before mentioned as having loaded
+materials at Greenock lying already there, waiting a favourable
+change of wind. Next morning we weighed anchor, <span class="sidenote">Return to Tyree.</span>
+and sailed
+along with that vessel for Hynish, where she was immediately discharged
+of her cargo, which was chiefly intended for the workyard
+there, and took in materials for the erection of the barrack on the
+Skerryvore Rock.</p>
+
+<p><i>7th August.</i>—We this morning took on board various tools
+and implements for the Rock, together with workmen to the number
+of four carpenters, sixteen masons and quarriers, and a smith,
+along with Mr George Middlemiss, as foreman. Having sailed with
+a northerly wind, we made a landing about noon, <span class="sidenote">First good day’s
+work on the Rock.</span>
+and had what
+may be called our first entire day of work on the Rock. Our
+work was by no means easy, as we had to erect <i>shear-poles</i> and
+fix <i>crabs</i> for landing the materials, and to lash every article that
+was landed, with great care down to ring-bolts on the Rock, which
+a few of the masons were fixing, while the rest of the people were
+discharging the vessel. All this was attended with a good deal of
+trouble, and it required my constant attention to keep everything
+going on in a fair train, so as to prevent one party of workmen
+requiring to wait for another; but, after eight hours of very hard
+work, I had the satisfaction of seeing all the materials which had
+been landed left in a secure state. The extreme smoothness of
+the surface of the Rock greatly impeded the landing of materials;
+for as yet we had no tramways on which wheeled trucks
+could be moved, and the transport by hand of heavy materials
+over so irregular and slippery a surface was attended with considerable
+danger. A short trial was this day made of boring one
+of the holes for the stancheons or bats, by which the timbers of the
+Barrack were to be secured to the Rock; and I found, that with a
+jumper of 3¹⁄₂ inches diameter, a depth of about 3 inches was bored<span class="pagenum" id="Page81">[81]</span>
+in one hour. The commencement of the operations involved much
+labour and considerable discomfort; but it invariably happened
+throughout the work, that in spite of all the fatigue and privation
+attending a day’s work on this unsheltered Rock, the landsmen were
+for the most part sorry to exchange it for the ship, which rolled
+so heavily as to leave few free from sea-sickness, and to deprive
+most of the workmen of sleep at night, even after their unusually
+great exertions during the day.</p>
+
+<p>On leaving the Rock at night we had the greatest difficulty in
+boarding the <i>Pharos</i> with two boats containing upwards of thirty-two
+persons, as the vessel rolled so heavily, that there was great
+danger of the boats being thrown right upon her deck. Next
+morning (8th August) we landed, with some sea running, about
+nine o’clock, before which hour it was impracticable, owing to the
+surf in the landing creek. Our first work was to prepare the
+tackling for landing the heavy materials from the <i>New Leven</i>,
+which came up about eleven o’clock, and was made fast by a warp
+to the <i>Pharos</i>. We next took means for fixing the smith’s forge
+on the Rock and preparing the fixtures for the crab, which stood
+on the point of rock to the westward (see <a href="#Plate3">Plate III.</a>), and served
+chiefly for raising the beams of the log-house into their places.
+The greater part of the day, till half-past eight in the evening
+(when it became dark), was spent in lining off with accuracy the
+site of the supports of the wooden barrack, and in landing and
+fixing by strong lashings to the Rock, all the principal timbers and
+iron fixtures. The spot in which the framework of the first
+barrack was placed, will be seen by reference to <a href="#Plate3">Plate III.</a> The
+Rock was at this place a good deal lower than the site afterwards
+adopted for the barrack. The high water of spring-tides rose 2¹⁄₂
+feet upon the legs or main beams; but this site had many advantages,
+as it left more room for operations at or near the Tower
+itself than could have been obtained in any other position.</p>
+
+<p>We also made some progress in erecting a wooden shed round
+the smith’s forge, to protect him and his fire from the wind and<span class="pagenum" id="Page82">[82]</span>
+the spray of the sea. As we left the Rock in the boats, speculating
+on the prospect of getting the whole of the materials discharged in
+the course of next day, it was remarked that the northern sky
+was very clear, and that the wind had entirely fallen. The great
+and sudden stillness of the air, which permitted every ripple on the
+ocean to be heard, was regarded by Mr Macurich and the seamen
+generally, as the forerunner of a change; and the moon, which rose
+red and fiery, confirmed their fears of a gale. Nor were they
+wrong in their forebodings. <span class="sidenote">Sudden gale, and
+great peril to the
+vessels.</span>About midnight there was a stiff
+breeze from the S.E., which induced the master of the <i>New
+Leven</i> to hoist sail, cast loose from us, and run; and had not the
+seaman on watch on the deck of the <i>Pharos</i> fallen asleep in consequence
+of excessive fatigue, there can be little doubt we should
+have been at once called to follow her example, if, indeed, we
+had not led the way. No sooner, however, did Mr Macurich
+become aware of the state of the wind, which was blowing very
+strong at S.S.E. right into the landing place, than he roused
+me about two o’clock. At this time there was a very heavy sea;
+the little vessel was pitching her forecastle under, and we had
+to contend with a strong tide combined with the wind against
+us in working clear of the Rock, from which our moorings were
+not more than a quarter of a mile to windward; while from the
+place where we lay, half of the horizon was foul ground, all lying
+to our leeward. We soon set sail, but in vain tried to weather
+the sunk rock Bo-Rhua, whose large black mass (after having
+imagined ourselves past it) we discovered encircled by a wreath of
+white foam within less than a cable’s length of us. The heavy seas
+we encountered had greatly deceived us as to our progress, and thick
+blinding showers of rain made it difficult to see far beyond the
+vessel’s head. Such was the precarious and dangerous position of
+the vessel, that had an attempt been made to <i>tack</i> her amidst the
+surf which came rolling off the Rock, she would most probably have
+missed stays, the consequence of which would have been the inevitable
+loss of the vessel and of every soul on board. In this dilemma<span class="pagenum" id="Page83">[83]</span>
+we were obliged to resort to a less dangerous expedient, by <i>wearing</i>
+the ship and running her through the narrow passage between Bo-Rhua
+and the sunk rocks, about 300 yards to the W.N.W. of it,
+although this was a most hazardous attempt, as we had then little
+or no knowledge of that dangerous and intricate passage. A more
+anxious night I never spent; there being upwards of thirty people
+on board, with the prospect, during several hours, of the vessel
+striking every minute. And here I must award due praise to Mr
+Macurich for the coolness and intrepidity which he on this occasion
+displayed, and the calmness with which he gave his orders
+to the crew; and as I stood in the companion, telling him the
+time at intervals of five minutes, so as to enable him the better
+to judge of the vessel’s way through the water, I could not but
+remark the necessity for silence on the part of the master of a
+vessel in cases of difficulty. The workmen were told to be getting
+ready for landing, but we did not make them aware of the full extent
+of the danger; and to avoid confusion, they were not permitted
+to come on deck. We had no sooner cleared the sunk
+rocks already alluded to, than we were in fear of the great reef of
+Boinshly, and the heavy seas which were breaking over the foul
+ground all round it. In this way we spent a night of almost
+uninterrupted anxiety until daylight, and at eight in the morning
+<span class="sidenote">Reach Hynish in
+safety.</span>
+we came to the moorings in Hynish Bay, after a hard struggle
+against wind and tide and a very heavy sea, which made us hang
+<i>dead</i> a long time off Hynish Point. At one time I feared we
+should have been forced, as I had been, when returning from my
+first unsuccessful and discouraging attempt to land on the Skerryvore
+in 1836, to go round the west side of Tyree and Coll, which
+is a very foul coast; and when we did round Hynish Point, it was
+almost at the expense of our boat, which the heavy sea had nearly
+swept away from us. After all this anxiety about our safety and
+discomfort from rain, wind, and spray, during five or six hours, we
+were not sorry to set foot even on the wild shores of Tyree; and I
+trust there were none who did not gratefully acknowledge the protecting
+care of Almighty God, in preserving us through such peril.</p>
+
+<p><span class="pagenum" id="Page84">[84]</span></p>
+
+<p><span class="sidenote">Detained by bad
+weather four days
+at Hynish.</span>
+It was not until Monday the 13th that a landing was again
+effected on the rock, as the wind continued to blow strongly from
+the south; and the intervening four days were spent in Hynish
+Bay, landing in the morning, and again returning to the vessel in
+the evening. During this time I was engaged in making drawings
+of some of the lower courses of the Lighthouse Tower, with a
+view to fix finally upon dimensions, from which working drawings
+and wooden moulds for cutting the stones could be made. The
+only alleviation of my impatience at being detained at Hynish was
+the satisfaction of seeing some 20 feet of the pier founded at low
+water. Late in the evening of the 13th August we again landed on
+the Rock, when we found time, before dark, to complete the fixture
+of the smith’s forge, which I had been forced to leave unfinished.
+Even the short period of work this evening was curtailed by a
+very heavy shower, which drenched us to the skin—a great evil,
+where there are many people to be accommodated in a small vessel,
+without room for much spare clothing, or the means of getting any
+thing quickly dried. <span class="sidenote">Return to the
+Rock, and have
+six days of good
+weather.</span>
+After this we had an uninterrupted tract of
+good weather for six days; and as we landed every morning at
+four o’clock, and remained on the Rock until eight, taking only
+half an hour for breakfast, and the same time for dinner, we had
+thus the work of twenty-eight persons for about ninety hours.</p>
+
+<p><span class="sidenote">Erection of the
+Pyramid of the
+wooden Barrack.</span>
+After carefully setting out the radial directions in which the
+six legs, or main beams were to stand, our next step was to lay
+off their approximate distances from the centre of the Barrack, and
+to clear a space in the solid Rock of sufficient extent to admit of
+adjusting the exact positions of the bats before boring the holes.
+This operation involved the necessity of blasting parts of the Rock
+by very small shots, the bores being about 1¹⁄₂ inch diameter, and 15
+inches in depth, and so directed as to have the effect of throwing
+off a thin superficial crust without shaking the solid part below.
+The materials thus quarried in forming the seats for each post were
+thrown, by means of tackle, into the deepest pools, to prevent their
+being driven by the sea against the timbers of the barrack, and so
+injuring them.</p>
+
+<p><span class="pagenum" id="Page85">[85]</span></p>
+
+<div class="container w60emmax" id="Fig4">
+
+<p class="caption">No. 4.</p>
+
+<img src="images/illo085.jpg" alt="Method of determining length of Beams">
+
+</div><!--container-->
+
+<div class="container left w10emmax" id="Fig5">
+
+<p class="caption">No. 5.</p>
+
+<img src="images/illo086a.jpg" alt="Knobs on board">
+
+</div><!--container-->
+
+<p><span class="sidenote">Mode of determining
+the
+length of the
+Beams, and the
+sites for their
+fixtures.</span>
+For ascertaining the exact length of each of the six beams,
+which formed by their union a pyramid of about 21° 30′ of inclination,
+and, at the same time, for determining its exact place,
+in reference to the centre of the hexagon, both of which elements
+necessarily varied with the level of the irregular surface of the
+Rock, I used the following simple arrangement:—Each beam
+being of the greatest length that could be required, the level and
+distance from the centre were ascertained for the longest beam,
+which, of course, had the lowest seat or rest, by means of a
+wooden frame, shewn in the diagram (<a href="#Fig4">No. 4</a>), in which <i>a&#160;a</i> is
+a vertical rod of iron firmly batted into the rock, so as to coincide
+with the centre of the pyramid to be formed by the main
+beams, and of sufficient length to exceed the greatest variation of
+level between the different points where the beams are likely to
+stand; <i>c&#160;c</i> is a horizontal board which can be freely turned about
+<i>a&#160;a</i> horizontally, and resting upon a small shoulder <i>d</i>, and which
+is equal in length to the radius of the hexagon, on the horizontal
+plane at the level of the lowest beam. On this board is a spirit-level
+<i>s</i>, which regulates its horizontality; <i>e&#160;e</i> is the approximate
+position of the lower end of the beam; <i>f&#160;f</i> is a <i>pitched board</i>,
+representing the section of the permanent beam, on a vertical
+plane passing through the axis of the pyramid, and also shewing
+its inclination towards the centre of the pyramid. As this <i>pitched
+board</i> is capable of being moved up or down by sliding through a
+groove at <i>g</i>, it may be successively applied to the rough surface at
+<i>e&#160;e</i> in the course of cutting it down, and thus be made truly to represent
+the position of the beam, and, at the same time, give the<span class="pagenum" id="Page86">[86]</span>
+inclination of the surface <i>e&#160;e</i>, which must be at right angles to the
+axis of the beam <i>f&#160;f</i>. In this way, by repeated trials, the surface
+was truly dressed to its proper inclination, and the length ascertained
+which required to be cut from the beam, so as to make
+it rest on that surface when in its true position. Hence, also,
+in the case of all the other beams, the length which the pitch-board
+<i>f&#160;f</i> was moved upwards through the groove <i>g</i>, beyond the
+level <i>c&#160;c</i>, indicated the quantity to be cut from the end of any
+given beam.<a id="FNanchor17" href="#Footnote17" class="fnanchor">[17]</a> The surface of the Rock, dressed for the seat of the
+beam, being thus brought to its proper inclination, the sliding-board
+correctly set and the centre line <i>a&#160;a</i> of the beam carefully
+marked on the Rock, a square board (see <a href="#Fig5">fig. No. 5</a>) representing
+the cross section of one of the beams, was then put
+down at the proper distance, so as to cover the
+space indicated by the <i>pitch-board</i> as the site of
+the beam, and with its centre coinciding with the
+radius already traced on the dressed seat or bed.
+When so placed, the small round knobs, or ears,
+<i>d</i>&#160;<i>d</i> (<a href="#Fig5">No. 5</a>) on this board, shewed the position of the holes to be
+bored for the bats or side fixtures, which, as afterwards shewn in
+figure (<a href="#Fig8">No. 8</a>, p. 88), spread outwards from the axis of the beam,
+and thus formed a kind of dovetail. In order to make the holes
+capable of receiving the bats and, at the same time, embracing the
+timbers of the barrack, a quoin of wood (<a href="#Fig6">Nos. 6</a> and <a href="#Fig7">7</a>) <i>e</i>, was
+put down, with bevelled faces or grooves <i>g</i>, cut in it for directing
+the motion of the jumper or boring iron <i>i</i>, <span class="nowrap">thus:—</span></p>
+
+<div class="container w40emmax">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<div class="container notopbot" id="Fig6">
+
+<p class="caption">No. 6.</p>
+
+<img src="images/illo086b.jpg" alt="Wooden quoin">
+
+</div><!--container-->
+
+</div><!--left5050-->
+
+<div class="right5050">
+
+<div class="container notopbot" id="Fig7">
+
+<p class="caption">No. 7.</p>
+
+<img src="images/illo086c.jpg" alt="Wooden quoin">
+
+</div><!--container-->
+
+</div><!--right5050-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+</div><!--container-->
+
+<p><span class="pagenum" id="Page87">[87]</span></p>
+
+<p class="noindent">These holes were bored with jumpers, 3¹⁄₂ inches in diameter, and
+were sunk 2 feet deep in the rock. The boring of each hole took
+upwards of eight hours, in consequence of the hardness of the material,
+which is gneiss, a stone considerably more difficult to bore
+than even the granite of Aberdeenshire. The bats or stancheons,
+although very accurately forged, were occasionally found not to
+fit truly, owing to unavoidable twists in the holes, which arose
+from <i>dries</i> or veins in the Rock crossing the line of the hole,
+and thus disturbing the motion of the jumper. This gave us
+much trouble, and shewed that, had we determined, as I at
+first contemplated, to cut a lewis-hole, swelling towards the base,
+the work would have been almost impracticable. The mode which
+I had proposed for executing this operation was to bore a number
+of very small holes, inclined at the proper angle, all round the outside
+of this lewis chamber, and then to cut out between them; but
+this, as our after experience in cutting the foundation of the Tower
+proved, would have occupied an extent of time which we should
+have been very unwilling to bestow upon a merely temporary erection
+like the wooden barrack. Even as it was, and with all the
+retrenchments that could be safely adopted, the preparation of the
+seats for the six outer or main beams, and those for the six inner
+braces, employed twelve men for four days.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote17" href="#FNanchor17" class="label">[17]</a> The accented letters <i>e′</i>, <i>c′</i>, <i>f′</i>, <i>g′</i>, <i>o′</i>, <i>s′</i>,
+in the figure (<a href="#Fig4">No. 4</a>), page 85, denote the various
+parts of the gauging-rule, when applied to the beam, opposite that to which the letters
+<i>e</i>, <i>c</i>, <i>f</i>, <i>g</i>, <i>o</i>, <i>s</i>, in the text, refer.</p>
+
+</div><!--footnote-->
+
+<div class="container w60emmax" id="Fig8">
+
+<p class="caption">No. 8.</p>
+
+<img src="images/illo088a.jpg" alt="Anchoring of pyramid feet">
+
+</div><!--container-->
+
+<p>After the seats for the timbers had been dressed in this manner,
+the carpenters were employed cutting the beams to their respective
+lengths, the piece to be cut off being measured, as already stated,
+by the length through which the sliding-board <i>f&#160;f</i> (<a href="#Fig4">No. 4</a>, p. 85) had
+been raised above its position on the level platform on which the
+pyramid had been erected in the workyard at Greenock. At the
+same time, the stancheons (<i>k&#160;k</i>) in the figure (<a href="#Fig8">No. 8</a>, p. 88), and the
+glands or collars <i>e</i>&#160;<i>e</i> (in <a href="#Fig8">figure No. 8</a>), were let into grooves in the
+beam, and the holes admitting the screwed bolts <i>a</i>&#160;<i>a</i>, to pass through
+the two stancheons and the beam between them, were bored with
+an auger, and widened with a red hot iron. The tops of the beams
+<i>b</i>&#160;<i>b</i> (see <a href="#Fig9">fig. No. 9</a>), having been already fitted in the workyard at<span class="pagenum" id="Page88">[88]</span>
+Greenock, so as to meet a hexagonal quoin of hardwood <i>e</i>, round
+which they were assembled as shewn in the figure (<a href="#Fig9">No. 9</a>), straps of
+iron <i>d&#160;d</i>, were made to pass over the top of the whole, and were
+secured to the beams with bolts, and a spike at <i>a</i> was driven into
+the centre to wedge the timbers tightly up, so as to fill a ring which
+embraced the exterior of the whole. It was obvious, that if the
+sliding-board (described on <a href="#Page85">p. 85</a>) had indicated the true inclination
+of the seat on the Rock for the end of the beam to rest on,<span class="pagenum" id="Page89">[89]</span>
+as well as its radial distance from the centre of the pyramid and
+the corresponding length of the beams, the top of each beam must
+necessarily meet in its exact place around the central hexagonal
+quoin. The operation of determining the positions and lengths of
+such beams on a rugged rock, and placing them with the accuracy
+requisite, to insure their <i>mitering</i> truly at the top, was attended
+with a good deal of trouble; and I have judged it advisable to give
+these details, as they may prove useful to others who may have a
+similar work in hand.</p>
+
+<div class="container w30emmax" id="Fig9">
+
+<p class="caption">No. 9.</p>
+
+<img src="images/illo088b.jpg" alt="Detail of pyramid construction">
+
+</div><!--container-->
+
+<p>After a good deal of trouble, owing to the lowness of the Rock
+and the smallness of its surface, the six main beams, each nearly 50
+feet long, were raised on end by means of shear-poles, and the iron
+straps which passed over the top of them, and the ring which
+embraced the whole so as to secure them at the top, were fixed
+with much care. The temporary guys were removed on the afternoon
+of the 18th August. A plummet suspended from the centre
+of the quoin, after all the six beams were in their places and the
+stancheons had been run up with lead, came within half-an-inch of
+the centre bar, which was about 40 feet below the point of suspension,
+thus indicating an angular deviation of less than 4′. This is a
+very good approximation, under all the circumstances with which
+we had to contend; and it is chiefly to be imputed to the very
+accurate measures pursued in the workyard of the contractor at
+Greenock, by Mr George Middlemiss, foreman of the carpenters
+(who then acted as superintendent of the contract works), and
+whose intelligence and zeal made him, at all times, able and ready
+to do full justice to all my suggestions for incurring as little loss
+of time on the Rock as possible. The operation of fixing these
+six beams, which formed, by their union, a hexagonal pyramid of
+about 44 feet high, and about 34 feet in diameter at the base,
+occupied only six days, including the cutting of the seats and the
+boring of the holes in the Rock. Much labour and time were
+consumed in the mere moving of beams, each weighing about 13
+cwt., over the rugged surface of the Rock, for which purpose we<span class="pagenum" id="Page90">[90]</span>
+could only use a small set of shear-poles, with crabs and blocks,
+and tackle purchase; and it sometimes happened, that merely for
+the purpose of moving a beam, it was necessary to place a special
+ring-bolt for holding a <i>snatch-block</i> for a few minutes, in spite of
+all the care and forethought which had been bestowed, in selecting
+the most advantageous positions for placing them, before the work
+of raising the beam was begun. Nor was the necessity for securing
+every loose material by means of lashings to the Rock, before
+leaving for the night, an insignificant source of delay; for we
+were sometimes forced by the waves or the darkness, which drove
+us from our work, to lower a beam which was just ready for being
+fixed and to replace it in a safe situation.</p>
+
+<p><span class="sidenote">Pyramid completed.</span>
+On Saturday the 18th August, the pyramid having been successfully
+erected, the men were busied for two hours, before embarking
+for the vessel, in collecting and lashing all the loose materials
+to the Rock, for the sky gave some indications of a change.
+As we took to the boats, I looked at the result of our labours with
+some satisfaction, not unmingled with gratitude.</p>
+
+<p>During the week, while we had been engaged in fitting up the
+main timbers of the barrack, the weather had been very fine; and
+except the long hours of toil and the sea-sickness on board the
+vessel, there was nothing to complain of; <span class="sidenote">Mode of living
+while erecting
+the Barrack.</span>
+but the economy of
+our life while moored for days off the Rock, was somewhat singular.
+We landed at four o’clock every morning to commence
+work, and generally breakfasted on the Rock at eight, at which
+time the boat arrived with large pitchers of tea, bags of biscuit,
+and <i>canteens</i> of beef. Breakfast was despatched in half an hour
+and work again resumed, till about two o’clock, which hour
+brought the dinner, differing in its materials from breakfast only
+in the addition of a thick pottage of vegetables, and the substitution
+of beer for tea. Dinner occupied no longer time than breakfast,
+and like it, was succeeded by another season of toil, which
+lasted until eight and sometimes till nine o’clock, when it was so
+dark that we could scarcely scramble to the boats, and were often<span class="pagenum" id="Page91">[91]</span>
+glad to avail ourselves of all the assistance we could obtain from an
+occasional flash of a lantern and from following the voices. Once
+on the deck of the little tender and the boats hoisted in, the materials
+of breakfast were again produced under the name of supper;
+but the heaving of the vessel damped the animation which attended
+the meals on the Rock, and destroyed the appetite of the
+men, who, with few exceptions, were so little <i>sea-worthy</i> as to
+prefer messing on the Rock even during rain, to facing the closeness
+of the forecastle. As I generally retired to the cabin to write
+up my notes, when that was practicable, and to wait the arrival
+of my own refection, I was sometimes considerably amused by
+the regularity with which the men chose their mess-masters,
+and the desire which some displayed for the important duties of
+carving and distributing the rations. Even the short time that
+could be snatched from the half-hour’s interval at dinner, was
+generally devoted to a nap; and the amount of hard labour and
+long exposure to the sun, which could hardly be reckoned at less
+than 16 hours a-day, prevented much conversation over supper:
+yet, in many, the love of controversy is so deeply rooted, that I
+have often, from my small cabin, overheard the political topics of
+the day, with regard to Church and State, very gravely discussed
+on deck, over a pipe of tobacco. Perhaps the great heat below,
+where upwards of twenty people were confined, might in some
+measure account for this wakefulness on board the Tender.</p>
+
+<p>One beautiful morning, during our stay of six days at the
+Rock, we had a visit from <span class="sidenote">Shoals of Medusæ
+seen.</span>
+a shoal of small fish, whose novel appearance
+made me take them for a fleet of some species of Nautilus.
+Those animals came in such numbers, that the pale blue silky
+membranes or sails, which wafted them before a gentle breeze
+over the glassy surface of the ocean, literally covered the water as
+far as we could see. One of those animals I sent in a small phial
+to my friend, Professor Fleming, then of King’s College, Aberdeen,
+who assigns to it the Linnean name of <i>Medusa velilla</i>, and says it
+is noticed by Dr Walker and Mr Pennant, as a native of Scotland.</p>
+
+<p><span class="pagenum" id="Page92">[92]</span></p>
+
+<p>The threatening of the previous night was fully verified by the
+succeeding Sunday morning, as a strong southerly wind with heavy
+showers, forced us to part from our moorings at the Rock at break
+of day, and make sail for Hynish Bay, where we anchored at seven.
+On Monday I landed at Hynish; but as the wind, which had increased
+to a strong gale, was still rising and inclining more to E., Mr
+Macurich summoned me to the boat, when, with much difficulty, and
+at the expense of shipping several seas, we reached the vessel which
+was pitching the bowsprit under. <span class="sidenote">Driven by a gale
+to Mull.</span>
+This soon forced us to run for the
+Sound of Mull, where we were detained until Saturday the 25th,
+on the morning of which day we again made Hynish Bay; but the
+wind, which had been less violent when we started from Tobermory
+the night before, again commencing to blow strong from the
+same unpropitious quarter, <span class="sidenote">Return to Hynish,
+and are driven to
+Coll.</span>
+we had only time to land at Hynish,
+and take on board a salted sheep (which proved a rather unpalatable
+addition to our provisions), when we were forced to seek
+shelter in our old quarters at Loch Erin in Coll. As we entered
+Loch Erin, we saw the <i>Regent</i> (the General Lighthouse Tender)
+leave the Sound of Mull, and again put back to Tobermory. Next
+day (the 26th August) we left Loch Erin, and boarded the Regent;
+but the weather proving boisterous, we were again forced into our
+old anchorage, while the <i>Regent</i> proceeded with the Engineer, who
+was then on his annual voyage, to Barrahead Lighthouse, without
+attempting to go near the Skerryvore. From this date the weather
+did not prove favourable for a landing until the 30th, when the
+wind being N.W., we sailed from Loch Erin at daybreak, <span class="sidenote">Return to the
+Rock.</span>
+and
+reached the Skerryvore at ten. We now discharged all the remaining
+materials which had been shipped for the Rock with a
+view to complete the pyramid of the barrack, which it was intended
+should stand the test of a winter, deferring the fixing of the habitable
+part till next spring.</p>
+
+<p><i>31st August.</i>—The last day of August was one of considerable
+discomfort. Our landing at four in the morning was attended with
+great difficulty and some danger; and throughout the day we were<span class="pagenum" id="Page93">[93]</span>
+a good deal incommoded by a thick drizzling rain, which continued
+without intermission. About mid-day the sea rose so much as to
+render it no longer prudent to delay leaving the Rock, and we
+therefore embarked. After lying at our moorings until half-past
+two, in what, to landsmen, was a most distressing sea, <span class="sidenote">Driven to Tyree.</span>
+we slipped
+and ran for Hynish Bay, which we reached at 5¹⁄₂ <span class="allsmcap">P.M.</span> The weather
+continued boisterous until next evening (1st September), when
+the wind went round to the north, and at eight all the men were
+summoned on board; but although we sailed at daybreak, we could
+not reach the moorings with daylight; <span class="sidenote">Return to the
+Rock.</span>
+and it was not till the
+morning of the 4th September, about four o’clock, that we could
+again land on the Rock. We succeeded, in spite of a very unfavourable
+day, in remaining till three o’clock, <span class="sidenote">Horizontal braces
+fixed.</span>
+during which time
+we fixed the whole of the horizontal braces, and got everything
+which we had not been able to secure in its place firmly lashed
+to the ring-bolts on the Rock, after which <span class="sidenote">Driven to Mull.</span>
+we were forced to leave
+it for Mull. <span class="sidenote">Heavy gale.</span>
+The gale continued to blow very hard, without any
+intermission, for some days; and on the 6th, <span class="sidenote">Timber cast on
+Tyree.</span>
+some wreck-timber,
+covered with goose-barnacles, came ashore among the surf at the
+beach at Hynish, but no trace of its history was ever found, nor
+did any rumour reach us of a shipwreck having occurred on this
+coast. It was not till the 8th that we could again attempt to
+reach the Skerryvore; when, sailing from Mull with a fair wind,
+and taking on board at Hynish nine masons, and Mr C. Barclay,
+foreman of the quarriers, we again landed on it at 2¹⁄₂ <span class="allsmcap">P.M.</span> <span class="sidenote">Return to Rock,
+and farther progress
+of barrack.</span> We
+succeeded in getting up the mortar gallery (see <a href="#Plate5">Plate V.</a>), and in
+fixing some of the diagonal braces, and left the Rock about eight.
+A marrot perched on the vessel’s side this afternoon, much fatigued
+and evidently desirous to get on board; but the sailors, from some
+superstitious dread, would not admit the poor bird.</p>
+
+<p><i>10th September.</i>—We landed at four o’clock, and had a long
+and good day’s work until daylight left us. We were now within
+twenty-four hours at most of completing all that could be expected
+to be done this season; and it was with no small anxiety that I observed<span class="pagenum" id="Page94">[94]</span>
+a change of wind from N.E. to S.S.W., accompanied by a
+fall of the sympiesometer; as in the event of a change of weather
+at that season, it seemed very uncertain when we might again land,
+and still more uncertain whether our work, in its incomplete
+state, could resist the winter’s seas.</p>
+
+<p><i>11th September.</i>—<span class="sidenote">Last day’s work
+on Rock this
+season.</span>
+This was our last day’s work on the Rock
+this season. We landed at four o’clock with very great difficulty,
+and some danger of having our boats swamped; and we were
+forced, owing to the heavy sea which broke upon it, to leave the
+Rock at high water; but, about one o’clock, we were enabled to
+return, as the sea fell a little. By dint of great exertions, we got
+the last of the diagonal braces fixed, and the bats run up with lead
+and painted, for their protection against corrosion. We also contrived
+to remove the greater part of the tools from the Rock, but
+some we were forced to leave to their fate. To the upper part of
+the pyramid we lashed a water-tight chest, containing biscuits and
+a cask of water, <span class="sidenote">Precaution for
+the benefit of
+shipwrecked
+seamen.</span>to serve as a means of support to any shipwrecked
+mariners who might chance to reach the Rock. I also caused some
+spars to be lashed at various levels, by way of testing the effects of
+the sea; but to how little purpose, the sequel will shew. Before leaving
+the Rock, I climbed to the top of the pyramid, <span class="sidenote">View from top of
+pyramid.</span>
+from which I
+now, for the first time, got a bird’s eye view of the various shoals
+which the stormy state of the sea so well disclosed; and my elevation
+above the Rock itself decreased the apparent elevation of the
+rugged ledge so much, that it seemed to me as if each successive
+wave must sweep right over its surface, and carry us all before it
+into the wide Atlantic. So loud was the roaring of the wind among
+the timbers of the barrack, and so hoarse the clamour of the waves,
+that I could not hear the voices of the men below; and I, with
+difficulty, occasionally caught the sharp tinkle of the hammers on
+the Rock. When I looked back upon the works of the season,
+upon our difficulties, and, I must add, dangers, and the small result
+of our exertions—for we had only been 165 hours at work on the
+Rock between the 7th August and the 11th September—I could<span class="pagenum" id="Page95">[95]</span>
+see that, in good truth, there were many difficulties before us; but
+there was also much cause for thankfulness, in the many escapes
+we had made.</p>
+
+<p>After a somewhat precarious embarkation in the boats, and
+shipping several seas in our way, we reached the vessel, and immediately
+set sail with three cheers, rejoicing to have thus concluded
+our season’s work.</p>
+
+<p>After spending a few days at Hynish in making various arrangements
+for the operations of the next season, which were to
+embrace the extension of the pier, the completion of the barracks
+and the erection of sheds and workshops for carrying on the dressing
+of the materials for the Lighthouse Tower, I left Tyree with
+the pleasing belief that the successful termination of our first season’s
+labours might be taken as an omen of future success. But
+how uncertain are even the most rational sources of satisfaction
+which Time can furnish! On the 12th November, I received from
+Mr Hogben, the clerk and store-keeper at Tyree, the unwelcome
+intelligence <span class="sidenote">Destruction of
+the barrack
+during a gale.</span>
+that the Barrack-house had been destroyed, as was supposed,
+by the heavy sea of the 3d November; and as his letters contain
+all the facts of the case in so far as they could be collected at
+the time, I cannot do better than quote them at full length:—<span class="sidenote">Letter from
+Mr Hogben.</span>
+“<i>Skerryvore
+Lighthouse Works, Tyree, 5th November 1838.</i>—Dear Sir,—I
+am extremely sorry to inform you, that the barrack erected on
+Skerryvore Rock has totally disappeared. It was seen on the 31st
+of October, when I observed no change in its appearance. On the
+two following days the weather was showery, with haze, so that the
+Rock was not seen; and on the 3d it rained almost all day, with
+strong breezes. In the evening the wind increased to a gale, with
+a great swell, and an extraordinary high tide. Yesterday (Sunday
+the 4th) the weather was moderate, but the swell prevented the
+Rock being seen from the low ground. Mr Scott and Charles Barclay,
+however, having gone to the top of Ben Hynish, got a momentary
+glimpse of the Rock through the spray, and both were of
+opinion that the barrack was gone. This was not credited by the<span class="pagenum" id="Page96">[96]</span>
+workmen who had been employed at it, but this morning we found
+it to be the case; the Rock was pretty clearly seen, but no trace of
+the barrack. From the circumstance of the yard of a large vessel,
+and also a piece of a boom, having come ashore in the direction of
+the Rock, we think it is not improbable that some wreck has happened,
+and that some part of it has been thrown upon the barrack
+by the force of the sea. Should any opportunity occur for going
+out to the Rock, we shall take advantage of it, in order to give
+you farther information on the subject. I remain, &amp;c. (Signed)
+<span class="smcap">Wm. S. Hogben</span>.” A subsequent letter from Mr Hogben is of the
+following tenor:—“<i>Skerryvore Lighthouse Works, Tyree, 10th
+November 1838.</i>—Dear Sir,—This morning, Charles Barclay, with
+a boat and four men, went out to the Rock to view the site of the
+barrack; and, the weather being moderate, he got a good landing.
+The following is the state in which he found everything:—The
+whole barrack timbers had been carried away, excepting the long
+beam next the place where the crab stood which drew up the
+beams, and about seven feet of the long beam opposite the place
+where the other crab stood. The former of these beams had fallen
+in the direction of the highest part of the Rock, and had drawn
+one of the iron stancheons 16 inches. The latter was all in
+splinters, with one of the iron stancheons broken, and the other
+bent. The rest of the stancheons were broken at the point between
+the round and the flat, and some of them were drawn about
+9 inches. The iron hoop which bound the top of the beams was
+lying at the distance of about the length of the beams to the
+eastward of the centre of the barrack, having one of its screws
+broken. Five large wooden knees were remaining, a ladder partly
+broken, some moulds for taking the angle of the beams, and most
+of the quarry and masons’ tools. The grindstone was thrown from
+the top of the Rock into a deep hole on the side next Tyree, a distance
+of about 12 yards, apparently whole. The smith’s forge had
+disappeared, and the anvil had been thrown about 8 yards to the
+N.E. of the place, where it was left; it was brought ashore, along<span class="pagenum" id="Page97">[97]</span>
+with the hoop which encircled the top of the barrack. The iron
+posts which supported the bellows were standing. The crab on the
+S.W. side was thrown from its place to the east side of the site of
+the barrack, a distance of about 15 or 20 yards, and was dashed to
+pieces, excepting the axle, handles, pinion, and the trunk of the
+barrel. The other crab was thrown from its place to the N.E.,
+over a part of the rock 5 or 6 feet high, to a distance of about 6
+yards, and was found in a similar state to the former. A stone
+measuring three-fourths of a ton was found near the seat of one of
+the beams; it had been thrown up from the hole where it had been
+deposited while cutting the seats for the barrack timbers. One of
+the ring-bolts near the top of the Rock to which the chain binding
+the wood had been made fast, was broken close by the surface of
+the Rock, and the wood was all gone. The mooring buoy has
+also disappeared. The barrack was seen from the top of Ben Keen-na-vara,
+by some men on Saturday, 3d November, so that the
+succeeding night, which was truly awful, must have done the
+damage. I may mention, that many of the islanders say that they
+have not seen such a swell as on that evening for about sixteen
+years. I am happy to say that no damage has been done to the
+works on shore here, as on that evening the wind was about S.W.,
+and we are pretty much sheltered from the wind in that direction.
+The shore on the S.W. side of the island is strewed with sea-weed,
+which has been carried up far beyond the usual reach of the tide.
+Hoping that the above information will suffice, I remain, &amp;c.
+<span class="righttext"><span class="padr4">(Signed)</span> “<span class="smcap">Wm. S. Hogben</span>.”</span></p>
+
+<p class="thinline allclear">&#160;</p>
+
+<p class="blankbefore75">On the day on which I received this discouraging intelligence,
+I requested a special meeting of the Committee, for the purpose of
+deliberating as to the best course to be pursued, when I received
+instructions to proceed to the Rock, and for that purpose to hire a
+steamer at Glasgow. <span class="sidenote">Proceed to
+Skerryvore.</span>
+I accordingly started that very evening for
+Skerryvore, with the intention at the same time of removing such
+of the men from Tyree as were not to be employed during the
+winter. I left Greenock in the steamer <i>Tobermory</i>, accompanied<span class="pagenum" id="Page98">[98]</span>
+by Mr Macurich of the Lighthouse tender, at midnight of the
+14th November, after some delay in repairing a leak in the boiler,
+which was discovered in time before starting, and reached Hynish
+at 11 on the forenoon of the 16th, having got a good passage
+round the Mull of Kintyre. The weather was, however, in every
+other respect most unfavourable for the purpose; and having
+merely touched, in passing Tyree, at the workyard at Hynish, to
+inquire whether any thing farther had transpired, and to take
+on board Mr Charles Barclay, who had visited the Rock after
+the loss of the barrack, we at once proceeded and reached Skerryvore
+about 4 o’clock in the afternoon. The sea ran very high,
+and there was not the most remote chance of landing, but, having
+got into the boat, I approached near enough to the Rock
+to enable me to survey <span class="sidenote">State in which
+the Rock was
+found.</span>
+the melancholy remains of our labours,
+which seemed to be in the same state in which they were described
+by Mr Hogben. The beam which lay back on the inclined
+ledge still kept its place, having been firmly lashed by Mr
+Charles Barclay to a ring which was near it when he landed on
+the 10th November; and I could see the remains of some of the
+stancheons and of the crabs which the sea had left. After waiting,
+in the hope of a change in the state of the sea, until it was nearly
+dark, we again turned towards Tyree, in all the gloom of a stormy
+night, and depressed by mingled disappointment and sad forebodings,
+occasioned by the fate of our intended asylum from the waves.
+Owing to the heavy sea, and a strong gale against us, we hung for
+a long time off Hynish Point, and did not reach the Bay till midnight.
+Next morning about 7, we came off Hynish, in order to
+take in the men who were to go home for the winter. The ground
+was deeply covered with snow, which made the embarkation of
+so many persons and so much baggage a tedious and uncomfortable
+operation; and when we sailed, we experienced all the inconveniences
+of a strong gale and a heavy sea, with the concomitant of a
+deck covered with passengers, all very sick and much dispirited.
+Many of the men, indeed, seemed to be as deeply concerned for the
+loss we had sustained as I myself was. To add to our difficulties,<span class="pagenum" id="Page99">[99]</span>
+the vessel, under the care of a native pilot, had touched slightly on
+a rock off Hynish Point, and gave some indications of leaking.
+We, however, reached Oban in safety.</p>
+
+<div class="container w35emmax" id="Fig10">
+
+<p class="caption">No. 10.</p>
+
+<img src="images/illo099.jpg" alt="Top of barrack">
+
+</div><!--container-->
+
+<p>Various conjectures were made as to the cause of the destruction
+of the barrack. Those who saw it erected were so confident
+of its stability, that they could not avoid connecting its failure with
+some injury received from the wreck-timber, which had come ashore
+on the island of Tyree, two days after the supposed date of the accident.
+In this opinion they were strengthened by the total destruction
+of the cranes and other objects on the rock, forgetting that the
+timber of the barrack itself, when once let loose, must of necessity
+have proved even a more powerful agent of destruction than the
+driftwood of the wreck. But whatever doubt may exist as to the
+<span class="sidenote">Cause of the
+destruction of
+the barrack.</span>
+first cause of the injury, there seems good reason to suppose that
+the dismemberment of the parts of the structure had commenced
+with the removal of the horizontal braces, and that the beams,
+having thus more liberty for play and tremor, had gradually shaken
+loose the fixtures at the top, which consisted of straps <i>c</i>&#160;<i>c</i>, passing
+right over the tops <i>a</i>&#160;<i>a</i>, of the beams and <i>b&#160;b</i>, the hexagonal
+quoin of hardwood already noticed at <a href="#Page88">p. 88</a>, which were secured
+by means of a central bolt <i>d</i>, and finally girt outside by a ring,
+<i>e</i>&#160;<i>e</i>, as shewn in the annexed woodcut (<a href="#Fig10">No. 10</a>.) The moment
+this dismemberment occurred, the
+beams would be free to work their
+own destruction; and the enormous
+leverage which they exerted,
+when dashed to and fro by the
+breakers, would soon snap the iron
+stancheons at the base, and throw
+all loose to the waves. The only
+remaining beam was that which
+was supported against a ledge of
+rock, and which had received the
+sea from the opposite direction<span class="pagenum" id="Page100">[100]</span>
+to that in which it was found lying. That beam, however, although
+firmly lashed to the rock by the men who first visited it
+after the accident, along with Mr Charles Barclay, also disappeared
+in the course of the winter. As a proof how severely these beams
+had been dashed by the waves, I may state, that the only remaining
+part of a beam which I saw attached to the iron stancheons, when
+I landed in the following spring, was so thoroughly riven and
+<i>shaken</i> as to be quite like a bundle of lathwood.</p>
+
+<div class="container w50emmax" id="Fig11">
+
+<p class="caption">No. 11.</p>
+
+<img src="images/illo101.jpg" alt="">
+
+</div><!--container-->
+
+<p>These circumstances by no means shook my belief in the suitableness
+of the plan adopted for obtaining a temporary dwelling
+on the rock; but they induced me, as soon as I received authority
+from the Commissioners, whose confident expectation of final success
+was not damped by the unhappy issue of our season’s labours,
+to examine very carefully the whole details of the ties and fastenings.<span class="sidenote">Preparations for
+a new barrack.</span>
+In preparing a similar structure for next season, I resolved
+to strengthen the ties at the top, where I imagined the former
+failure to have occurred, by adding six strong stancheons <i>a</i>, <i>a</i>
+(<a href="#Plate5">Plate V.</a>), one to each beam, with heads passing through a centre-plate
+(H), which united them in one as a cap and to which they
+were secured by strong screws and keys. The nature of those
+fixtures will be more easily understood by a reference to the figures
+(1) and (2) in <a href="#Plate6">Plate VI.</a>, which shew an elevation and plan of the
+upper part of the beams. In the elevation only the beams A, B, C,
+are shewn; but in the plan, all the six beams appear <i>mitering</i> at
+their heads <i>n</i>, <i>n</i>, to the central beam or tie <i>o</i>, <i>o</i> (see also <a href="#Plate5">Plate V.</a>),
+which was introduced to counteract the tendency of the heavy seas
+that might burst inside the pyramid, and by exerting a powerful
+force in the vertical direction, might separate the beams at the top.
+In the <a href="#Plate6">Plate (VI.)</a>, <i>a</i>, <i>a</i>, are strong stancheons of iron attached to
+the outside of the beams by bolts, and also by collars <i>r</i>, <i>r</i>, attached
+to ears <i>g</i>, <i>g</i>. These stancheons being bent into the vertical direction
+and rounded at the top, passed through the malleable iron plate H,
+which was held down, and, as already stated, bound the beams
+together by nuts <i>c</i>, <i>c</i>, and wedges <i>b</i>, <i>b</i>. Through a hole in the centre<span class="pagenum" id="Page101">[101]</span>
+of this plate, a large spike <i>p</i> was driven, which produced an expansion
+of the central beam, and thus wedged up or tightened all the
+joints formed by the <i>mitering</i> of the seven timbers. On each of those
+stancheons, <i>snugs</i> were formed at <i>e</i>, capable of receiving and retaining
+in its place against any tendency to move upwards, a strong
+metallic ring <i>g</i>, which was tightly keyed by wedges at <i>k</i>. Additional
+ties of iron D, E, F, were also provided, which connected
+the six beams together in pairs. Each end of those ties was attached
+to the timbers by three spikes; one tie, D, is shewn a little
+fore-shortened; another, E, is seen only on the end; while the third
+F, is shewn as cut off at the middle. Lastly, an important change
+was made, by the substitution of malleable iron for wooden braces
+(see <a href="#Plate5">Plate V.</a>) <i>b</i>, <i>b</i>, <i>b</i>, <i>b</i>, in the horizontal direction. Fixtures of this
+kind held the whole more firmly together; and their construction was
+such that they might firmly embrace each beam, without requiring
+any means of attachment beyond wedging tightly up; and thus the
+entire strength of the timbers was unimpaired by the driving of
+spikes or bolts. Those braces (<a href="#Fig11">No. 11</a>), <i>a</i>, <i>a</i>, had, at each end, double
+knobs, and were pushed up along the beams, until they squeezed the
+timbers <i>x</i>, <i>x</i>, <i>x</i> between them; plates <i>p</i>, <i>p</i> (having holes in them
+through which the double knobs of the braces were made to pass),
+were then put on and keyed and screwed, as shewn in the figure, so<span class="pagenum" id="Page102">[102]</span>
+that each beam was quite enclosed by fixtures, which were thus independent
+of spikes or bolts. Thin hardwood wedges were afterwards
+driven in, wherever they could be inserted between the iron
+and the timber; and those wedges were “<i>stitched</i>” to the beams
+with common nails, merely to prevent their dropping downward,
+after any temporary contraction of the timber from the state of the
+atmosphere. In all this, I have anticipated what more properly
+belongs to the works of the season 1839; but I consider it best,
+for the sake of clearness, to connect this account of the new with
+the destruction of the old Barrack.</p>
+
+<p class="blankbefore75">While the operations already described were in progress at the
+Rock, <span class="sidenote">Works at Hynish.</span>
+various works were going forward at the workyard in Tyree.
+About 16 masons, 12 quarriers, and 4 carpenters, were employed
+in building the barracks for the workmen and in erecting smiths’
+and carpenters’ shops. A large room, paved with a stone floor,
+for drawing out at full size the courses of the Tower and making
+the moulds for dressing the stones, was also provided; and a platform
+of squared masonry was set in the workyard, on which the
+courses were to be laid, before being shipped for the Rock. During
+the season, the pier had also been carried out 256 feet, to a point
+15 feet within the low-water mark. It was also necessary to
+provide depositories for the security of tools and other implements,
+as well as a large coal-shed for the supply of the Steamer which was
+then in the course of being built. It had, as already noticed, been
+determined that the stores were to be served out at the cost prices
+of the Greenock market, to be paid for once a month, at the same
+time that the wages of the men were paid. That arrangement had
+been carried into effect on a small scale, from the very beginning
+of the works; but this season it became necessary, owing to the
+increased number of men, to conduct it on a more extended and
+systematic plan; and, for that purpose, a person was required to act
+as storekeeper and clerk. In order also to preserve the provisions<span class="pagenum" id="Page103">[103]</span>
+from injury by damp and to secure them from the inroads of
+the needy Celts and from innumerable rats which overrun that
+part of Tyree, it was found necessary to set apart, as a storehouse,
+a large room on the second storey of one of the workshops.
+The chief articles served out in the store were meal, molasses,
+sugar, coffee, tea, tobacco and butter. The establishment of the
+store entailed a great deal of trouble, and led to some expense
+for carriage and packages, as well as to occasional trifling losses
+in serving out the allowances or from injury sustained in the
+transport of the goods; but the inhospitable nature of the country,
+and the remoteness of Tyree from the ordinary steam-boat traffic,
+made the adoption of some such plan unavoidable. Amongst other
+inconveniences which attended the store, not the least may be
+reckoned the frequent importunities, on the part of the native labourers
+whom we employed, to be permitted to purchase provisions
+at the workyard; but that was never acceded to, except
+in cases where dearths (which are of frequent occurrence in the
+island) rendered the call irresistible. Had their entreaties easily
+prevailed, we should soon have had the whole population of Tyree
+as our regular customers at the Store.</p>
+
+<p><span class="sidenote">Hynish Quarries.</span>
+The quarries at Hynish, as already stated, were by no means
+productive. The great proportion of the materials which had been
+quarried, was found to be applicable only to the building of the
+pier and the inclosing walls, and to the various erections in the
+workyard; and not more than <i>one-tenth</i> of the whole could be
+dressed as blocks for the Tower.</p>
+
+<p>During the numerous occasions on which I had been driven by
+stress of weather to the neighbouring coasts, I had visited the
+quarries around Oban and in various parts of Morven and Mull.
+When so forced to leave what I might more especially call my <i>post</i>,
+I had an opportunity of seeing the quarries at Ardentallen near
+Oban, which contain the old red sandstone strongly impregnated
+with clay. That stone is by no means suitable for the<span class="pagenum" id="Page104">[104]</span>
+<i>face-work</i> of a marine building, in such a situation as the
+Skerryvore; while the comparatively small quantity of <i>hearting</i>
+which could be admitted into such a work, made it inexpedient
+to seek such materials at so great a distance. In this way, the
+Ardentallen quarry seemed completely excluded from the field.
+At another time, in passing through Inverary, I devoted a day to
+the examination of the quarries which had lately been opened at
+that place and in which a beautiful porphyry is wrought; but I
+saw no appearance of very large blocks, or, at all events, nothing
+that could favour the expectation of a considerable supply. But
+after carefully weighing the matter, the great masses of granite at
+the Ross of Mull finally determined my choice in favour of that
+locality; and the Duke of Argyll having, with the greatest liberality,
+ratified his predecessor’s grant of liberty to the Lighthouse
+Board to quarry stones from any part of the Argyll estates, it was
+resolved to take measures early in the spring of 1839 for opening
+quarries at North Bay, in Mull, where an excellent station for
+shipping had been discovered, close to the place where we saw the
+most promising appearance of rock. This measure seemed the
+more indispensable, as the last part of the quarry <i>terred</i><a id="FNanchor18" href="#Footnote18" class="fnanchor">[18]</a> or laid
+bare at Hynish, had greatly disappointed our expectations. The
+unworkable nature of gneiss rock also and its extreme uncertainty
+with regard to quality, farther concurred to make a change
+most desirable. Granite, indeed, is a material in many respects
+superior to sandstone, gneiss, or porphyry. The first it greatly
+excels in durability and weight; and, as a stone for the workyard,
+it is superior to the other two, from its property of being <i>fissile</i>,
+or easily split in any direction. In this respect it resembles certain
+parts of some sandstone strata which are commonly called <i>liver<span class="pagenum" id="Page105">[105]</span>
+rock</i>, of which Craigleith quarry, near Edinburgh, furnishes an excellent
+example. Porphyry, and, I think, all other igneous rocks
+(excepting granite), gneiss also, and most of the other primary
+rocks, have not this property, being <i>fissile</i> only in one plane, so that
+quarries of those rocks generally turn out very uncouth or irregular
+stones, which, though they may in some favourable cases possess
+good natural <i>beds</i>, will always be found to have ragged and irregular
+<i>joints</i>, which, for the most part, are incapable of being properly
+dressed.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote18" href="#FNanchor18" class="label">[18]</a> This term in Scotland denotes the removal of the soil and unsolid material, in order to
+lay bare the rock previous to working the quarry, and seems obviously to be derived from the
+Latin “terra,” perhaps through the medium of some old charter. The quantity of terring
+very much affects the profitable working of a quarry.</p>
+
+</div><!--footnote-->
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page106">[106-<br>107]<a id="Page107"></a></span></p>
+
+<h3 class="nobreak"><span class="chapno">CHAPTER V.</span><br>
+<span class="chapname">OPERATIONS OF 1839.</span></h3>
+
+</div><!--chapter-->
+
+<p>During the winter months which intervened between November
+1838 and March 1839, a small detachment of men, consisting of
+three masons, nine quarriers, and one smith, were left at Hynish
+under the superintendence of Mr Charles Barclay, to clear the
+landing-place of several patches of rock which encumbered the
+entrance. <span class="sidenote">Shipping Station
+and Pier at
+Hynish.</span>
+They were also to build some walls of inclosure, and
+to quarry and dress stones for the pier and other buildings at Hynish.
+The provision of accommodation for shipping at that place
+was now naturally regarded as of more urgent necessity than formerly,
+because the importation of stones from Mull, which the
+failure of the Tyree stone had rendered unavoidable, led to the
+necessity of a reshipment of all the materials at Hynish, where
+they were dressed before being sent to the Rock. It may, perhaps,
+be naturally enough imagined, that instead of importing the materials
+to be dressed at Tyree and there reshipped in order to be
+carried to the Rock, they might have been prepared in Mull, and
+sent directly to the Skerryvore; but many things concurred to
+render this inexpedient, if not altogether impracticable. The advantage
+of being able, by means of a good telescope, in some measure
+to ascertain the state of the sea at the Rock, the comparative
+shortness of the passage, which gave the prospect of several cargoes
+being landed on it in one day during fine weather, and the convenience
+of communicating with the Rock by signal, were circumstances
+in themselves quite sufficient to determine my choice in<span class="pagenum" id="Page108">[108]</span>
+favour of Hynish, as the place from which the materials must be
+shipped for the Rock, even if there had been no other considerations
+leading to the same conclusion. But in addition to all
+this, I could not fail to perceive that Hynish was the only place
+for the permanent station of the vessel attending on the future
+Lighthouse; and that on that account alone the construction of a
+Harbour there was unavoidable. That the arrangement, by which
+the future station for the Tender was used as the workyard for
+the operations, was the most judicious that could have been
+adopted, was fully proved by my subsequent experience of the
+advantage of assembling all our materials and all our force at a
+point as near to the Rock as possible, so that we might be at all
+times ready to supply defects or omissions, and take advantage of
+every favourable change of the sea or sky.</p>
+
+<p>In the middle of March the <i>Regent</i> conveyed from Aberdeen
+a detachment of twenty-nine masons and quarriers and five smiths,
+and the foreman of the workyard, who, together with the men
+already at Hynish and the native labourers, were to be employed
+during the season of 1839, in the various departments of the work.
+On their arrival the men were separated into two small bands, of
+which the one, consisting of six masons, twelve quarriers, one
+smith and a foreman, was stationed at North Bay in Mull, where
+the new quarries were to be opened; while the other had its head
+quarters at Hynish, and, when not engaged in the work on the
+Rock itself, was subdivided into smaller parties, varying in number
+with the nature of the particular operations in which the men
+were occupied.</p>
+
+<p>On the afternoon of the <i>19th April</i> I sailed from Greenock in
+the <i>Regent</i>, for North Bay in Mull, <span class="sidenote">Granite quarries
+in Mull.</span>
+where the quarries were to be
+opened. We had on board the whole materials of the new Barrack,
+which was to supply the place of that which had been destroyed
+in the preceding month of November; and we had also a
+party of carpenters who came to fit up the Barrack in a temporary
+manner at North Bay, as a residence for the masons who were to<span class="pagenum" id="Page109">[109]</span>
+be engaged in preparing more permanent dwellings for the quarriers
+and in forming a landing-wharf for the shipment of the stones
+for Tyree. It was not till the 25th, after a tedious passage of six
+days, that we anchored at North Bay; and next morning we had
+the satisfaction of seeing the steamer, the <i>Skerryvore</i> (by which
+name she was specially set apart for the service of the works), arrive
+in the Bay with a party of masons and quarriers, who had
+been appointed to meet us in order to begin the work.</p>
+
+<p>The necessary arrangements with the Duke of Argyll’s tenants
+at the <i>Ross</i> of Mull (in which district North Bay is situated) having
+been already made, no time was lost in erecting the wooden Barrack;
+and, in seven days after our arrival, the masons and quarriers
+entered their new habitation under the charge of Mr Charles
+Stewart, whom I left as foreman of the North Bay works. Mr
+Stewart and his party, following the example of diligence thus set
+to them, were not less expeditious in proceeding with the work
+which had been assigned to them; and by the beginning of August
+a range of barracks, capable of accommodating forty persons, had
+been erected, a landing wharf had been built, and various storehouses
+had been provided, although the quarry had to be opened,
+and the blocks of stone required for those various works were still
+<i>in situ</i> at the time of our landing at North Bay three months before.</p>
+
+<p>The landing wharf is placed on a small projecting face of
+rock in a depth of 12 feet at high water of ordinary spring tides.
+It presents a face of 40 feet in length, and was provided with
+wooden fenders for the protection of the vessels loading stones.
+Landward of it a considerable space was levelled, by cutting and
+filling, to serve as a yard for storing the quarried materials, so as
+to be ready for shipment. The quarry itself was opened in the
+face of a hill, so steep as almost to deserve the name of a cliff; but
+advantage was taken of a deep gully which intersected it and in
+it an inclined plane was formed communicating directly with the
+landing-place. This gully was partly cleared by excavation of the<span class="pagenum" id="Page110">[110]</span>
+rock and partly, where necessary, its inequalities were smoothed
+down by filling it with stone shivers; and along its bed thus prepared,
+longitudinal sleepers of timber were laid, to which <i>edge-rails</i>
+were attached.</p>
+
+<p>At the top of the incline two iron drums or barrels were set,
+and round them were wound, in opposite directions, the chains by
+which the trucks or wagons, loaded with stones from the quarry,
+were lowered to the wharf below. A powerful break apparatus
+was attached to those barrels, to check the velocity of the descending
+wagons, which was also in part counteracted, by making
+their gravity act as a power to raise the empty wagons in the same
+manner as is usually practised in coal-mines.</p>
+
+<p>The quarry itself, as already stated, was opened in the face of
+the cliff, at a point where the successive beds of solid rock seemed
+to promise the fairest prospect of success. The preliminary operation
+was to remove a very thin alluvial cover which scarcely
+concealed from view a large mass of most beautiful granite, whose
+reddish colour is said to have given the name of <i>Ross</i><a id="FNanchor19" href="#Footnote19" class="fnanchor">[19]</a> to that part
+of Mull, the shores of which everywhere exhibit massive slopes of
+that fine rock. The granite is separated very abruptly from the
+basalts of the surrounding district, so as to leave the Ross purely
+granitic; but in no part of the whole coast, which abounds with
+creeks and bays, does the rock appear to be of equal quality, or so
+conveniently situated for shipping, and so easily accessible to quarriers,
+as at the spot we had chosen. I know of no instance of a
+quarry so fully answering the most sanguine expectations as that
+of the Ross of Mull; and I have never seen a granite quarry of
+equally great resources, as regards both the quantity and the quality
+of the material produced. The rock in general yielded easily
+before well-directed shots, and was separated into large masses,
+capable of being advantageously cut, with little loss of material, into<span class="pagenum" id="Page111">[111]</span>
+shapely blocks, by means of wedges, which work remarkably
+well in that rock. A few weeks after the quarrying operations
+had been commenced, a single shot detached 150 tons of excellent
+stone, in the cutting of which into blocks for the Lighthouse Tower
+little loss of material occurred; and in the course of the season of
+1839, although the summer was chiefly spent in the preliminary
+works above noticed, the Mull quarries produced nearly as much
+workable material for the Lighthouse Tower as the Hynish quarries
+had done in three years. In the course of the future working
+of the quarry, when it came to be more fully opened, its resources
+were so great, that on one occasion a single shot shook about 570
+tons, while another shot detached a mass of 460 tons. In that
+way, between April 1839 and June 1840, material had been quarried
+in that single spot, sufficient to supply 4300 selected blocks,
+varying in weight from ³⁄₄ ton to 2¹⁄₂ tons each. The average
+monthly produce of the quarries was about 400 tons, and there
+were generally employed in them 26 quarriers, 3 labourers, and
+2 smiths. The quantity of gunpowder consumed in the quarry
+was small, as it was almost exclusively employed in great bores
+about 11 feet deep, for the purpose of detaching large masses
+which had no <i>open side</i> and could not be removed by means of
+the <i>pinch</i> or <i>crow-bar</i>. When a mass of rock had been thus removed,
+it was cut up into various portions by means of wedges,
+and finally subdivided into blocks, <i>hammer</i> (or as it is called
+<i>quarry</i>) <i>dressed</i>, according to rough moulds, whose dimensions
+exceeded those of the stones of the various courses of the building
+by a quantity which was considered sufficient to cover any
+casualty in the final dressing of the block by the masons at Hynish,
+and which allowance was generally equal to a film of rock
+about 1¹⁄₂ inch in depth. The blocks thus roughly formed were
+shipped for Hynish, distant about 26 miles, through a tempestuous
+sea, open to the full reach of the Atlantic towards the south-west,
+sometimes in a small vessel called the “Queen,” belonging to the<span class="pagenum" id="Page112">[112]</span>
+Commissioners, and sometimes in undecked boats of 16 tons, belonging
+to the adventurous men of Tyree. The freight usually
+paid was 5s. a ton, and yet the whole of the blocks for the Lighthouse
+Tower, and many of those used in the pier at Hynish, were
+laid down to the number of about 5000, at the rate of 2s. 1¹⁄₂d. per
+cubic foot, including all the expense of building barracks, opening
+quarries, freight of stones, and the expense of building and maintaining
+the small vessel called the “Queen,” above noticed. The
+stone of the Mull quarries is a reddish or flesh-coloured granite, in
+which felspar predominates. About 13·66 cubic feet weigh a ton,
+and it is not quite so hard as the granite of Aberdeen.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote19" href="#FNanchor19" class="label">[19]</a> Whether from any inflection
+of the Celtic <i>Rhua</i>, or <i>Roy</i>, or directly from the Italian
+<i>Rosso</i>, it would, perhaps, be impossible to determine.</p>
+
+</div><!--footnote-->
+
+<p>As I am not aware that any professional work contains a detailed
+description of the quarrying of granite, some observations
+on that subject may not be unacceptable in this place; <span class="sidenote">Observations on
+the quarrying
+of granite.</span>
+and I therefore
+propose, at the risk of appearing somewhat prolix, to give a
+pretty minute account of the mode of opening and working a granite
+quarry, more especially as practised by us at North Bay.</p>
+
+<p>Having laid bare the rock of earth, gravel, or other loose matter
+(which operation, as I have elsewhere mentioned, is in Scotland
+technically called <i>terring</i>), and having swept or washed clean
+the surface of the rock so as to have a good view of the natural
+seams or joints which traverse it, the next step is to fix the best
+place for putting in a bore or mine.</p>
+
+<p>In selecting the position of the bore, the direction of the seams
+and veins of the rock must be duly considered, with a view to
+employ the force of the explosion to the greatest advantage in
+separating the natural joints or beds of the rock, instead of shattering
+the solid <i>masses</i> or <i>posts</i> (as they are called in the language
+of the quarry) into shivers or fragments.</p>
+
+<p>One thing to be strictly borne in mind is, that the bore should
+never be in the centre of a fine or large block, but should be placed
+within a few inches of its back so as not to break the finer rock
+into small and useless fragments; and care must, at the same time,<span class="pagenum" id="Page113">[113]</span>
+be taken to keep the bore clear of cracked or unsound rock, as the
+jumper, in passing through such material, is liable to be jammed
+by the cracks and fissures before it can be driven to the proposed
+depth. It is not possible to lay down precise rules for guiding the
+quarrier in choosing the place of the bore, as his plan must be regulated
+chiefly by the circumstances of each case; but it may be
+observed, that having first determined the depth of the hole, it will
+seldom be found advantageous to keep the bore farther back from
+the face of the rock than about <i>four-fifths</i> of that depth. The
+depth itself, also, to which the mine should be carried, is a point
+for deliberation with the skilful and experienced quarrier, who
+will take great care not to go so deep as to pass through the solid
+rock in which he is boring and thus to touch a bed, unless indeed
+he shall think it advisable to attempt to raise more than one <i>post</i> of
+rock by a single mine, in which case he will carry the bore through
+the first post into the second or third as the case may be. But in
+all cases the boring must be stopt at two inches before coming to
+the bed or seam of the post in which the mine is to terminate, lest
+the exploding powder should escape by the bottom of the bore, and
+thus leave the top of the rock altogether undisturbed. In endeavouring
+to procure large materials, the bores should in general be
+as deep as possible. It is only experience, however, which teaches
+the quarrier to form a sound <i>prognosis</i> as to the direction and
+level of the beds of the rock at any particular spot, and enables
+him to choose the most advantageous position and depth for the
+mines.</p>
+
+<p>In the blasting of granite there are a few general rules which
+(although it may not be necessary to follow them in every case)
+may be considered as constituting the best practice. If the bore
+be a vertical one of the depth of 6 feet, 2¹⁄₂ inches diameter at the
+top, diminishing to 2 inches at the bottom, may be considered a proportionate
+caliber. If the bore be a deep one (perhaps of 14 feet),
+its diameter will require to be 3¹⁄₂ inches at the top, and should diminish
+to 2³⁄₄ inches at the bottom; and the quantity of powder<span class="pagenum" id="Page114">[114]</span>
+required for the charge will in most cases be about as much as is
+required to fill ²⁄₅ths of the hole.<a id="FNanchor20" href="#Footnote20" class="fnanchor">[20]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote20" href="#FNanchor20" class="label">[20]</a> Miners and quarriers, who always work by empirical rules, disregard entirely the <i>line
+of least resistance</i> as a measure for the <i>charge</i>, and invariably refer to the <i>depth</i> of the bore.</p>
+
+</div><!--footnote-->
+
+<p>The patent <i>fusee</i> having been inserted among the powder, with
+its end about the centre of the charge, and the upper part of the
+bore having been filled up with dried clay, well forced down with a
+wooden rammer faced with copper, a length of 3 or 4 inches of the
+<i>fusee</i> should be left outside the bore, to which the match is to be
+attached. Having cleared away every thing near the blast which
+can receive any injury and covered up the machinery of the cranes
+with strong planks, the mine may be said to be ready for being
+fired; and, on a signal given, by blowing a horn, all hands retreat
+to a safe distance, with the exception of the fireman, who then lights
+the match, and follows the others as fast as possible.</p>
+
+<p>If, as already stated, the object in quarrying be to obtain large
+materials, the bores should, if possible, be deep; and, in that case,
+the rock will seldom be thrown down in fragments by the blast,
+but will merely be cracked, and intersected by rents about one
+inch in width. Recourse must therefore be had to what, in quarry
+language, is called a <i>Bull</i>, which consists in running a quantity of
+loose powder into the crack which has been made by the blast, at
+that part where its explosion seems most likely to throw out the
+cracked or broken mass in various fragments and disengage them
+from their place in the rock. In <i>bulling</i>, perhaps twice as much
+powder as was used in the bore is loosely poured into the crack,
+care being at the same time taken to get as much of it to go under
+the bottom of the rock as possible. After enough of powder has
+been poured into the crack, a quantity of dried smithy ashes, or
+dry sand, is run in over the powder, so as completely to cover
+it, except so much as is required to fire it by; and that coating,
+which is merely superficial, is employed partly to keep down
+the powder, and partly for security against its being accidentally
+fired before all things are ready. The fireman having seen every<span class="pagenum" id="Page115">[115]</span>
+thing cleared away, gives notice to sound the alarm, when all hands
+escape to a distance in the direction which is supposed to be the
+safest. The match is then applied, and the fireman retires, as fast
+and as far as he can, yet so as if possible to keep in view, during
+his retreat, the progress of the match. The operation of <i>bulling</i> is
+far more dangerous than the firing of a bore, as the charge is much
+greater, and not so well confined, so that many splinters are thrown
+off, and the direction in which they fly varies continually with the
+direction of the cracks which the original bore may have produced.
+As might be expected, by far the greater part of the accidents which
+occur to firemen in granite quarries, arise from that practice.</p>
+
+<div class="container right w15emmax" id="Fig12">
+
+<p class="caption">No. 12</p>
+
+<img src="images/illo115.jpg" alt="Plug and feathers">
+
+</div><!--container-->
+
+<p>Should it happen, as it sometimes does, that after having gone
+through those operations, the quarrier fails in getting the cracked
+mass thrown down to the bottom of the quarry, he varies his mode
+of attack, and proceeds to bore a row of <i>plug-holes</i> on the face of
+the rock in such a line as to cut off a part from one end of the
+shaken mass; and for that purpose he is often obliged to hang a
+scaffold over the face of the rock on which to stand while boring
+the holes. Those plug-holes should be slightly inclined, so that,
+when the wedges, called <i>plugs</i><a id="FNanchor21" href="#Footnote21" class="fnanchor">[21]</a> and <i>feathers</i>, are driven into them,
+they may rend the rock in such a direction that
+the piece intended to be cut off may be a little
+narrower on the inner than the outer face, so
+that, thus resting on an incline it may be more
+easily taken out. The plug-holes should be cut
+at one foot asunder, and bored with a jumper 1¹⁄₂
+inch diameter to the depth of 9 inches; and if the
+plug-holes be deep, and some difficulty in driving
+be expected, the plugs should be carefully
+greased or oiled previously to being driven. Having cut off a
+block as above described, an attempt may be made, if the mass<span class="pagenum" id="Page116">[116]</span>
+be great, to throw it down by means of <i>bulling</i>; but if it be of
+lesser dimensions, and there be reason to expect that it may be
+removed in the ordinary way, the power of the crane may be
+applied to draw it down. For that purpose, the quarrier employs
+an instrument called a <i>Dog</i>, which is a strong short hook,
+armed like a pick on the point with steel, and having a ring in
+the end of it for the hook of the crane-chain to pass through. Having
+cut a small hole with a pick, on the upper part of the block which
+is meant to be removed, the <i>steeled</i> point of the dog is inserted
+into it, in such a manner that the weight of the crane-chain may retain
+it steadily in its place. Five or six men then heave on the crane a
+strain just as much as they suppose it may bear, without danger of
+carrying away any of its fixtures; and as many men as can find
+room are, at the same time, employed at the top of the rock, working
+with crow-bars behind the block, so as to shake it and loosen
+its hold. The two parties continue their work reciprocally, leading
+and following,—the men at the crane, still keeping up the strain,
+and taking care not to heave so much as to break any of the chains,
+while those on the top continue to shake the block by means of the
+crow-bars, or throw in stones into the opening, which is always
+getting wider between the block and the cliff, so as to prevent the
+loosened mass from falling back into its old place. When the block
+has been drawn as far forward as to appear just ready to fall over the
+cliff, one of the most expert men at the crane stands carefully watching
+the movement of the block; and whenever the stone begins to
+fall, he instantly throws the crane <i>out of the gear</i>, so as to prevent
+the wheelwork being pulled to pieces by the tumbling mass getting
+entangled in the chains, on which it frequently falls and breaks
+them to pieces. The operation of taking down large blocks from a
+great height is very tedious, and is often attended with much danger,
+as the stone, when it falls on the bottom of the quarries, makes the
+shivers among which it alights fly in all directions with a force
+which nothing can withstand.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote21" href="#FNanchor21" class="label">[21]</a> The <i>plug</i> (<a href="#Fig12">fig. 12</a>,
+<i>c</i>&#160;<i>c′</i>), and <i>feathers</i> (<a href="#Fig12">fig. 12</a>, <i>d</i>&#160;<i>d′</i>), are flat pieces of malleable iron,
+slightly tapered, and forming together a kind of compound wedge, the two feathers being
+first inserted into the hole, and the plug being driven between them by a series of gentle
+blows, from malls of the weight of from 30 lb. to 35 lb.</p>
+
+</div><!--footnote-->
+
+<p>An opening being made in the manner above described, by
+getting one piece brought down, the same process is continued by<span class="pagenum" id="Page117">[117]</span>
+cutting off and taking down pieces of eight or ten tons weight, until
+there be as many blocks in the floor of the quarry as can be easily
+managed at one time. Those masses are then arranged by means
+of the crane in convenient positions for being cut up into blocks of
+the requisite sizes; and as all of them are within range of the crane,
+they can with its assistance be easily turned over or set in any position.
+While some of the men are employed in cutting up those
+blocks, others are clearing away the rubbish, and others are boring
+holes or making ready for a fresh blast.</p>
+
+<div class="container left w08emmax" id="Fig13">
+
+<p class="caption">No. 13.</p>
+
+<img src="images/illo118a.jpg" alt="30 lb. mall">
+
+</div><!--container-->
+
+<p>If those blocks, which we have supposed to be brought down
+to the quarry floor and to be ready for cutting, exceed seven feet
+in depth of cut, their farther subdivision will require the use of the
+plugs and feathers already described; but if their depth or thickness
+fall short of that, the ordinary iron wedges will answer. If
+the cut be of the depth of about 6 feet, the wedges must be placed
+about 3 inches apart from side to side; but if the depth of cut be
+less, they may be set 4 or 5 inches asunder. The method of setting
+in those wedges is as follows:—The person who cuts the wedge-holes
+generally works in a sitting posture, and if the block will
+admit of it, he prefers to bestride it, with a stone, as a stool, under
+each foot. He works with a pick of 16 lb. weight, having a handle
+only 16 inches long, with which he cuts the first hole generally
+about 3 inches from the end of the block. The holes are for the
+most part about 2¹⁄₂ inches deep, and 3¹⁄₂ inches long, and must be well
+cleared out at the bottom with a sharp pick; and the wedges must
+be set in a line as fair and straight as possible. Cutting wedges of
+that kind are of iron, from 7 to 9 inches long, and 2¹⁄₂ inches broad,
+and weigh about 7 lb. weight each. When in good order they must
+not be sharp in the mouth, but about ³⁄₈ of an inch thick, to prevent
+their <i>grounding</i> in the bottom of the hole; for if they but touch
+the bottom of the hole, they fly out at the first touch of the mall.
+When the wedges have been all properly arranged for a cut, the
+workman proceeds to give each of them in succession a gentle tap,
+so as to make them all fast; and for that purpose he uses a mall<span class="pagenum" id="Page118">[118]</span>
+about 30 lb. weight (<a href="#Fig13">fig. No. 13</a>), and having a handle 2 feet 9 inches
+long. He then goes over all the wedges, giving each
+of them a smart blow in regular, yet not too rapid
+succession, but allowing a little time for the parts of
+the stone to separate gradually. If the wedges be
+forced too quickly, there is great danger of the cut
+being spoiled by its flying out obliquely at one side,
+and thus not reaching throughout the whole depth
+of the block. The blocks, when thus subdivided
+by means of the wedges, are generally nearly of the
+size required by the rough moulds sent from the
+workyard, and are fit to be carried to the stone-cutter’s
+shed.</p>
+
+<div class="container right w05emmax" id="Fig14">
+
+<p class="caption">Fig. 14.</p>
+
+<img src="images/illo118b.jpg" alt="Hand mall">
+
+</div><!--container-->
+
+<p>As a conclusion to the above account of quarrying,
+it may perhaps be thought desirable to
+give some notion of the probable time required to
+perform certain parts of that sort of work. In boring holes of
+1 inch to 1¹⁄₄ inch in diameter, it may be observed that they
+are generally done with the <i>hand mall</i> (<a href="#Fig14">fig. No. 14</a>), one and
+the same person striking with the mall with one hand, and
+turning the boring tool for himself with the other; and in
+most cases a man will bore 9 or 10 inches an hour in granite
+rock. If the bore be 1¹⁄₂ inch diameter, as for plugs, three
+men will generally bore two plug holes in one hour, each hole
+being about 9 inches deep. If the bore be for blasting and
+of 2 or 2¹⁄₂ inches diameter, three men will bore, at the rate of one foot
+per hour, to the depth of 6 or 7 feet; but if the bore be for a large
+blast of 13 or 14 feet deep, the hole must be 3¹⁄₂ inches in diameter at
+the top (diminishing to 2³⁄₄ inches at bottom), and will employ three
+men working hard between two and three days. Bores of that sort,
+indeed, cannot be made (at least by hand) to a greater depth than
+14 or 15 feet, as the weight of a rod of iron, 17 feet in length, and
+2 inches in diameter, makes it quite unmanageable for one man either
+to turn or to lift; while, from its great mass, the strokes of the mall<span class="pagenum" id="Page119">[119]</span>
+produce little effect on it. The malls used in boring holes, which
+require three men, are 7 or 8 lb. weight, having handles
+3 feet long (fig. No. 15), and are swung over the shoulder,
+while striking for <i>down bores</i>, in the same manner as a
+smith’s forehammer is used. An expert cutter with the
+wedges will make good wages by cutting holes at the rate
+of 2¹⁄₂d. for a dozen of holes, taking light and heavy cuts
+as they come to hand.</p>
+
+<div class="container left w08emmax" id="Fig15">
+
+<p class="caption">No. 15.</p>
+
+<img src="images/illo119.jpg" alt="Three-men mall">
+
+</div><!--container-->
+
+<p>What has been said above of boring and blasting
+refers only to <i>downright</i> or vertical bores; but, in the
+lower parts of a quarry, it is often necessary to have recourse
+to what are called <i>breast-bores</i>, from their running
+in a nearly horizontal direction and piercing the front
+or breast of the rock. Those bores are not so easily
+made as the <i>downright</i> bores and, in general, are only used where
+the rock is low, or in taking up bottom rock. They can seldom be
+carried to a greater depth than about 9 or 10 feet, owing to the
+difficulty of turning the jumper, and can never be bored quite horizontally,
+but require as much dip as will retain a little water in the
+hole to keep the jumper moving. Instead of throwing the mass
+outward, as is done by <i>down-bores</i>, those <i>breast-bores</i> generally only
+cut or break the stone in the direction or line of the bore, so that
+the block always requires to be afterwards removed by <i>bulling</i>, in
+the manner already described.</p>
+
+<p><span class="sidenote">Dressing of the
+Lighthouse blocks.</span>
+The dressing of the blocks for the Lighthouse Tower, as already
+mentioned, was one of the most important operations in the
+workyard at Hynish; and as no writer with whom I am acquainted
+has given any account of the mode now practised of dressing
+granite, I hope I shall be excused for attempting, in this place, to
+give some idea of the method employed by the masons of Aberdeenshire,
+whose skill in that department of workmanship is well
+known both in our own and in other countries. As the whole
+of the materials for the Tower were to be dressed in such a
+manner as to avoid the necessity of any fitting on the Rock, by<span class="pagenum" id="Page120">[120]</span>
+the introduction of what are technically called <i>closers</i>, the greatest
+accuracy in the formation of the moulds from which the stones
+were to be shaped became necessary. With that view, I had a
+<i>trainer</i> or <i>radius</i> made with a moveable <i>vernier</i>, capable of sliding
+along it, so as to give the differences between the <i>readings</i> of
+the feet, as far as to the <i>thirtieth</i> part of an inch; and I was thus
+enabled to lay off the <i>batter</i> or slope on each course (according to
+the quantities in the <a href="#Page354">Table of Co-ordinates</a> in the <a href="#App1">Appendix</a>) with
+great nicety, and so to trace very distinctly the contour of the
+intended column.<a id="FNanchor22" href="#Footnote22" class="fnanchor">[22]</a> On the stone floor of an apartment in one of
+the workshops, the <i>quadrant</i> of each course of the building was
+carefully drawn out, at full size, and divided into the sectors which
+were required for preserving a due <i>bond</i> among the joints of the
+adjoining courses. The form of each stone in the tower having
+been thus determined by those full-sized draughts, moulds, representing
+the <i>beds</i> and <i>sides</i> of each stone, were prepared according to
+them, of seasoned timber, well shielded at the angles with sheet-iron,
+to prevent their being injured. Those moulds having been
+marked with reference to the number of the course, and the position
+of the stones in the wall, were given to the foreman of the workyard,
+who regulated the work of each of the stone-cutters, often to
+the number of 70 men. A proper block having been selected for
+each stone, leaving about 1¹⁄₂ inch all round the extremity of the
+moulds when applied to its several faces, it was conveyed, by means
+of the sling-cart, to the shed where it was to be dressed. The
+shed for dressing granite stones differs in no respect from an ordinary
+mason’s shed, except in its greater height; but, as the stone
+cutter, in order to wield his tools to advantage, must, at certain
+parts of the work, stand on the top of the block, it has been found,
+that a height of about 15 feet is required for the back-wall of a<span class="pagenum" id="Page121">[121]</span>
+granite mason’s shed. Each man also requires, for large blocks, a
+space of about 10 feet (measured along the front of the shed), as
+his peculiar territory.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote22" href="#FNanchor22" class="label">[22]</a> Such nicety, I would observe, was by no means superfluous, because the arrangements of
+the Tower precluded the possibility of using a trainer in building; and as the whole was done
+by means of <i>plumb-templets</i>, the greatest accuracy in tracing the curve of the Tower became
+necessary, as the only true basis of good workmanship on the Rock.</p>
+
+</div><!--footnote-->
+
+<p>When a block has been brought to the shed, the first thing to
+be done, if it is a large stone of 1¹⁄₂ or 2 tons weight, is to lay it
+nearly level on the ground, with the side which is to be first dressed
+uppermost. The form or <i>plan</i> is then sketched upon it according
+to the mould, and the stone is <i>blocked</i> out with a large hammer
+weighing 30 or 35 lb. (<a href="#Fig16">fig. No. 16</a>), which is the most
+suitable weight for ordinary men, although a stout
+man will manage one of 40 lb. well enough, if the
+block be lying in an advantageous position. When
+the stone has been thus rudely <i>blocked</i> out, it is set
+upon its edge with a gentle inclination to one side,
+so that the mason, who mounts on the top of it, may
+conveniently use a pick of 18 lb. weight, having a
+handle three feet long, to dress off very roughly the
+most prominent parts of its irregular surface. In
+doing that he makes a great many deep ruts in a
+downward direction, at the same time taking care
+that none of them shall be so deep as to fall below
+the general surface of the stone when finished.
+When he has in that style dressed as far down the surface of the
+stone as he can conveniently reach, (and that is generally about
+half way,) the stone is then thrown over and set up on the opposite
+edge, when he again mounts upon it, and goes over the rest of the
+surface in the same manner, until the whole shall be reduced to one
+rough plane, so that in spite of numerous partial inequalities, the
+general face may be straight, or what is technically termed <i>out of
+winding</i>. A stone in that state is also said to be <i>well opened</i>.</p>
+
+<div class="container w25emmax">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<div class="container notopbot" id="Fig16">
+
+<p class="caption">No. 16.</p>
+
+<img src="images/illo121.jpg" alt="Heavy hammer">
+
+</div><!--container-->
+
+</div><!--left5050-->
+
+<div class="right5050">
+
+<div class="container notopbot" id="Fig17">
+
+<p class="caption">No. 17.</p>
+
+<img src="images/illo122a.jpg" alt="two feet pick">
+
+</div><!--container-->
+
+</div><!--right5050-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split5050-->
+
+</div><!--container-->
+
+<div class="container right w05emmax" id="Fig18">
+
+<p class="caption">No. 18.</p>
+
+<img src="images/illo122b.jpg" alt="Chisel or punch">
+
+</div><!--container-->
+
+<p>The next step is to raise the stone so that it may incline at
+about 30° or 40° with the horizon; after which the mason, standing
+at the higher side, commences to put on the <i>draughts</i> or
+<i>guide-lines</i> all round the edge of the face which he has just<span class="pagenum" id="Page122">[122]</span>
+<i>opened</i>. For that purpose he first employs a pick of about 12 lb.
+weight, having a handle about 2 feet in length
+(<a href="#Fig17">fig. No. 17</a>), with which he dresses a band of
+about 3 inches broad, taking care that this band
+or draught be straight and <i>out of winding</i>. He
+then, with the pick, goes over the whole face between
+the draughts, dressing off all the ridges
+which still remain between the ruts which he had
+made while the stone was standing on edge, as
+before noticed, so that the whole surface will present
+the appearance of a pretty regularly <i>dabbed</i>
+face. Having arrived at that stage, he next proceeds
+to put on the <i>true draughts</i> (as round the
+edges of the stone, as in the case of the <i>guide-lines</i>),
+with the cast-steel chisel or <i>punch</i> (<i>a</i>, <i>a′</i>, <a href="#Fig18">fig. No. 18</a>), and a
+small iron-mall of 3¹⁄₂ lb. weight; and afterwards with the axe, he
+carefully <i>axes</i> a band about 2¹⁄₂ inches broad, so as to be
+quite out of winding, and as straight as possible all round.
+The dressing is then completed between those bands. If the
+block be a broad one, the mason will probably be able to
+take in only one half of the face at a time; and, in that case,
+the stone must be let down at the high side, and the other
+one raised as high as may be necessary to enable him to
+work to advantage. If the surface thus dressed, which is in this
+case supposed to be the largest side, be intended for the <i>bed</i> of a
+stone, the knobs or high points between the <i>pick-dabs</i> are merely
+roughly dressed down with a blunt axe, so as to be all as low as
+the axed lines or draughts round the extremities, and thus to present
+no convexity on which the stone, when laid, could rock; but if
+the surface should be meant for a fine <i>face</i>, the dressing must be
+commenced with a bluntish axe, taking care that all the axe marks
+be made quite across the stone, at right angles to the side where the
+workman stands. The whole face having been once gone over in
+that manner with a blunt axe, a sharper and well ground axe is<span class="pagenum" id="Page123">[123]</span>
+next used for crossing the first axing in such a manner that all the
+second axe-marks may be inclined at an angle of 45°, or thereby,
+with the first. The whole face having been thus brought to a
+smoother and more uniform surface, the third and last axing follows;
+and then the mason uses his shortest and lightest axe, which
+must, for that work, be well ground and sharp. That
+axing must be done right across the block, or in the
+same direction as the first axing had been done, and in
+that state the surface of the stone may be supposed to be
+fine enough for most kinds of work used in housebuilding
+or in public works; but for very fine work, such
+as some sepulchral monuments, or for surfaces which
+are afterwards to be polished, it is not unusual to axe
+four or even five times, care being always taken that how
+often soever that operation may be performed, the axing
+should never be made twice consecutively in the same
+direction, for by that precaution alone can a true and even
+surface be obtained. (The form of the axe is shewn in <a href="#Fig19">fig. No. 19</a>.)</p>
+
+<div class="container w12emmax" id="Fig19">
+
+<p class="caption">No. 19.</p>
+
+<img src="images/illo123a.jpg" alt="Mason's axe">
+
+</div><!--container-->
+
+<div class="container left w08emmax" id="Fig20">
+
+<p class="caption">No. 20.</p>
+
+<img src="images/illo123b.jpg" alt="Chipper or pincher">
+
+</div><!--container-->
+
+<p>The dressing of the first face being finished in the manner described,
+the block is laid flat on the ground, and the plan or form
+of the stone is then accurately drawn on it, according to the
+mould, with some substance that makes a bright or good mark,
+such as a piece of tile ground sharp, or a thin splinter of logwood.
+If there be much <i>waste</i> to be taken off beyond the lines so drawn,
+a hammer, whose weight must be in proportion to the piece to
+be struck off, is applied; but care must be taken not to come too
+near the lines with the hammer, and it is generally safe
+to leave at least an inch outside of them. The piece
+which is left gives a good hold for the <i>chipper</i> or <i>pincher</i>
+(<a href="#Fig20">fig. No. 20</a>), which is next carefully applied along the
+line, being steadily held within one hand, and with the
+other sharply struck with a small iron mall of 3¹⁄₂ lb.
+weight, having a short handle about 8 inches in length. While
+the <i>chipper</i> receives sharp strokes in succession with the mall,<span class="pagenum" id="Page124">[124]</span>
+it must be slowly moved several times along the line from one
+end of the stone to the other, till the piece projecting beyond the
+line, or a part of it, breaks off. Such is the power of this small instrument,
+that it not infrequently cuts down to a depth of 9 or even
+12 inches, thereby doing more execution and to greater purpose, than
+a heavy hammer can generally accomplish, even in the hands of a
+skilful workman. The <i>chipper</i> is a tool lately introduced; but has
+now become a most important article in every hewer’s <i>kit</i>. It makes
+a regular and clean cut, and leaves little to be done by the punches
+and chisels (<a href="#Fig18">fig. No. 18</a>, in p. 122), in preparing the <i>arris</i> of the next
+face of the stone. The block is now raised a little from the ground,
+and the workman standing at its higher side, the axing of which he
+has just finished, puts on with the punches and chisel a fine band or
+draught along the side next to that just dressed. He then applies to
+the finished face the <i>square</i> or <i>bevel</i>, according to the inclination of
+the faces, and dresses a band across the stone at each end of the block;
+and, finally, joins those two cross bands by means of another band
+along the back. In that way the external draughts on the second side
+are completed. He then with the pick and axe dresses away the material
+between those draughts until the second face is finished; and
+the same process is repeated for each side of the block which requires
+to be dressed. If the block be a large one, and it require to
+be dressed on all its sides, it will, lastly, be cut to the proper thickness
+or height, which is regulated by means of a gauge,
+known, in the technical language of the shed, as “<i>a
+grippers</i>” (<a href="#Fig21">fig. No. 21</a>),<a id="FNanchor23" href="#Footnote23" class="fnanchor">[23]</a> from its embracing the stone
+on three sides. It is simply a three-sided iron templet,
+having one long and one short tail (at right angles
+to the connecting piece), the space between the two
+tails shewing the thickness of the stone.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote23" href="#FNanchor23" class="label">[23]</a> The figure shews “<i>a grippers</i>” for a stone 14 inches thick.</p>
+
+</div><!--footnote-->
+
+<div class="container w10emmax" id="Fig21">
+
+<p class="caption">No. 21.</p>
+
+<img src="images/illo124.jpg" alt="Grippers">
+
+</div><!--container-->
+
+<p>The practical reader will readily see, that what has been said
+above about the hewing of granite, is chiefly applicable to the dressing<span class="pagenum" id="Page125">[125]</span>
+of the large stones used in public works, such as docks, bridges, or
+marine towers; and it may be proper to add, that such heavy materials
+are always dressed on the ground, and that a piece of wood is
+placed under each end of the stone as a necessary precaution to prevent
+its being split by the blows of the mall. In dressing the lighter
+materials for house building, where a good deal of fine work is generally
+required, the stones are laid on what is called a <i>banker</i>, similar
+to that which is used in hewing freestone. The banker is a bench
+of stone 2¹⁄₂ or 3 feet long, and 2 feet broad, and is raised about
+2 feet above the ground, so as to suit the workman’s convenience.</p>
+
+<p>In dressing one of the outside stones of the first or lowest
+courses of the Skerryvore Tower, a mason was occupied <i>eighty-five</i>
+hours (see Plans of courses, <a href="#Plate8">Plate VIII.</a>); and in dressing one of
+the largest of the hearting or inner stones of the same courses, <i>fifty-five</i>
+hours. But as the work proceeded, owing to the greater readiness
+which the men had acquired in the application of the moulds,
+gauges and bevels, the time occupied, gradually decreased to the
+extent of about <i>ten hours</i> for each stone, until the work had been
+carried on as far as to the thirteenth course, where the number of
+outside stones was reduced to twenty-four, at which stage of the
+work, the time required for dressing increased to about <i>one hundred
+and twenty hours</i> for each outside stone. From that point upwards,
+the time again gradually decreased till we reached the sixty-fourth
+course, where it may be stated, that, on an average, a man was employed
+<i>sixty-three</i> hours in dressing each stone; but the time gained
+in the last instance seemed to depend less on the readier application
+of the implements, than on the gradual diminution in the size of
+the stones, which, from that level upwards, decreased along with the
+thickness of the wall. But above the sixty-fourth course, a very
+marked increase in the time of dressing took place, owing to the
+introduction of the <i>ribband or ring joggles</i> (shewn in the Plans of
+the 84th and 94th courses, <a href="#Plate8">Plate VIII.</a>); and to the substitution of
+the <i>dovetailed joggles</i> in the place of the <i>square</i> or <i>diamond joggles</i>,
+which were used in the lower parts of the building. The time<span class="pagenum" id="Page126">[126]</span>
+required for dressing a stone of the sixty-fifth course was <i>ninety-three</i>
+hours of one man, a circumstance which strikingly shews,
+that a small, and, apparently, trifling alteration in the style of
+workmanship may sometimes increase to a considerable extent,
+the expense of a great work. Each radiating stone of the <i>eighty-fourth</i>
+course, which forms the floor that goes quite through the
+wall, required <i>one hundred and sixty-one hours</i> for its completion;
+and the other radiating floor-stones, which did not pass quite
+through the wall to the outside, occupied one man about <i>one hundred
+and twenty hours</i>. Each centre stone of the floors into which
+the others were dovetailed, required about <i>three hundred and twenty
+hours</i> of one man’s time. The time of a labourer occupied in cutting
+a hole for the dovetailed Lewis bats, by which the stones were
+raised, was about <i>three hours</i>.</p>
+
+<p>The tools necessary fully to equip a granite mason are as follows:—One
+dressing hammer about 16 or 18 lb. weight; 6 dressing
+picks, from 12 to 20 lb. weight; one small hand-mall, or
+mash-hammer, about 4 lb. weight; 3 stone axes about 7 lb.; 16
+or 18 cast-steel punches and chisels, with one or two chippers or
+pinchers of 2¹⁄₂ lb. weight. One large blocking-hammer of 30 or
+32 lb., may very well serve for eight men. The value of a granite
+mason’s <i>kit</i> may be estimated, when in good working order, at
+about L.7. A very great revolution has taken place during a
+few years in the method of working granite. The most important
+change is the substitution of the hand-mall and chisel in the operation
+of putting the <i>drafts</i> or bands on the stones, in place of <i>arris-picks</i>,
+which made the workmanship clumsy, tedious and imperfect,
+by slowly grinding down the stone at a great expense of labour
+to the hewer, who was forced to remain bent forward in an irksome
+posture, without the relief which is obtained by occasionally shifting
+his position, a change, which, every one who has been long employed
+in any laborious occupation, knows well how to value. The
+introduction of the <i>chipper</i> may also be regarded as one of the most
+important modern improvements in the art of working granite; and<span class="pagenum" id="Page127">[127]</span>
+had it not been for those changes, the actual expense of dressing the
+blocks for the Skerryvore Tower, as ascertained from the journals
+of the works, would have been exceeded by a sum of between
+L.4000 and L.5000; and it may even be questioned whether it
+would have been at all practicable with such tools to cut the dovetailed
+spaces of the floors out of the solid stone.</p>
+
+<p><span class="sidenote">Excavation of
+Foundation for the
+Lighthouse Tower
+on the Skerryvore
+Rock.</span>
+The excavation of the foundation of the Lighthouse Tower was
+the first operation which engaged my attention at Skerryvore Rock,
+at the beginning of the season of 1839. It was commenced on the
+6th of May, and was continued up to the last hour of our remaining
+on the Rock, on the 3d of September. A more unpromising prospect
+of success in any work than that which presented itself at the
+commencement of our labours, I can scarcely conceive. The great
+irregularity of the surface, and the extraordinary hardness and unworkable
+nature of the material, together with the want of room on
+the Rock, greatly added to the other difficulties and delays, which
+could not fail, even under the most favourable circumstances, to
+attend the excavation of a foundation-pit on a rock at the distance
+of 12 miles from the land. The Rock, as already noticed, is a hard
+and tough gneiss, and required the expenditure of about <i>four times</i>
+as much labour and steel for boring as are generally consumed in
+boring the Aberdeenshire granite.</p>
+
+<p>After a careful survey of the Rock, and having fully weighed all
+the risks of injuring the foundation, I determined at once to enter
+upon a horizontal cut, so as to lay bare a level floor of extent sufficient
+to contain the foundation pit for the Tower. The very rugged
+and uneven form of the Rock made this an almost necessary precaution,
+in order to prevent any misconception as to its real state,
+for it was traversed by numerous veins and bands inclined at various
+angles, on the position and extent of which the stability of
+the foundation in no small degree depended. That operation occupied
+30 men for 102 days, and required the firing of no fewer than
+246 shots, chiefly horizontal, while the quantity of material removed
+did not greatly exceed 2000 tons. It was a work of some<span class="pagenum" id="Page128">[128]</span>
+hazard; for the small surface of the Rock confined us within 30, and
+sometimes within a dozen yards of the mines, while its form afforded
+us no cover from the flying splinters. The only precautions we
+could adopt were to cover the mines with mats and with coarse nets,
+which I had caused to be made during the previous winter, of the
+old ropes of one of the Lighthouse Tenders, and in each blast to
+apportion very carefully the charge of powder to the work that was
+to be done. That was managed with great skill by Charles Barclay,
+the foreman of the quarriers, who charged all the bores, and,
+along with myself, fired all the shots. So completely did the simple
+expedient of covering the bores with nets and mats check the flight
+of the stones, that, except on one or two occasions, none of the splinters
+reached us, and all the damage done was a slight injury to one
+of the cranes. Perhaps, also, our safety may, in some measure, be
+attributed to a change which I introduced into the mode of charging
+the horizontal shots, by which all the risk of pushing home the
+powder in the ordinary mode with the <i>tamping rod</i> is avoided.
+That change consisted in using a kind of shovel, formed of a rod,
+armed with a hollow half-cylinder of sheet copper, which contained
+the powder, and being inverted by giving the rod half a turn round
+its axis, made the powder drop out when the cylinder reached the
+bottom of the bore. It was, in all respects, excepting size, the same
+as the charging-rod used for great guns. The amount of materials
+removed by blasting, as nearly as I could ascertain, was only about
+1000 cubic yards; and, taking all the circumstances into account,
+it may be doubted whether there be any instance in modern engineering
+of an operation <i>of so small an extent</i> occupying so much time,
+and involving so great risk. The blasting of the Rock, however,
+was not the only difficulty with which we had to contend, for it
+also became necessary to remove the quarried materials, amounting
+to about 2000 tons, into the deep water round us, to prevent
+their being thrown by the waves upon the Rock, and so endangering
+the future temporary Barrack. That was rather a laborious
+work, and occupied two cranes, with temporary runs and trucks,<span class="pagenum" id="Page129">[129]</span>
+during the greater part of the time we spent on the Rock. I am
+well aware that the quantity of materials which I have just mentioned,
+will be apt to produce a smile from those who have been
+chiefly conversant with the gigantic but simple operations which
+generally characterize the great railways of this country; but if it
+be remembered that we were at the mercy of the winds and waves
+of the wide Atlantic, and were every day in the expectation of a
+sudden call to leave the Rock, and betake ourselves to the vessel,
+and on several occasions had our cranes and other tools swept into
+the sea, the slowness of our progress will excite less surprise; and
+still less will those who duly weigh the dangers of our daily life,
+both in our little vessel and on the Rock, and who, at the same
+time, reflect on the many striking proofs which we almost every
+hour experienced of the care of an Almighty hand, be disposed to
+withhold their sympathy from the heartfelt expressions of gratitude
+which often went round our little circle in the boats, as we rowed
+in the twilight from the Rock to the ship. Isolation from the
+world, in a situation of common danger, produces amongst most
+men a freer interchange of the feelings of dependence on the Almighty,
+than is common in the more chilly intercourse of ordinary
+life.</p>
+
+<p>With a view to lessen the dangers of blasting in such a situation,
+I had provided a galvanic battery on the plan proposed by Mr
+Martyn Roberts, but I used it less frequently than I intended. The
+attachments of the wires were very liable to be broken from various
+causes, where there were many men congregated in a small space;
+and as we could not venture to leave the apparatus on the Rock,
+the frequent re-shipment of it in a heavy sea was another cause of
+the derangement of its parts. I soon, therefore, laid it aside, and
+only had recourse to it when any work was to be done under
+water, or in cases where the simultaneous firing of several mines
+(for which it is admirably adapted) was of importance in effecting
+any special purpose.</p>
+
+<p><span class="pagenum" id="Page130">[130]</span></p>
+
+<p>When the floor had been roughly levelled I again carefully surveyed
+the Rock, with the view of fixing precisely the site of the
+foundation-pit, and of taking advantage of its form and structure
+to adopt the largest diameter for the Tower of which the Rock
+would admit. In some places I found that parts of the Rock, apparently
+solid, had been undermined by the constant action of the
+waves, to the distance of 13 feet inward from its face; but none
+of those cavernous excavations reached the main nucleus, so that,
+after much deliberation and repeated examinations of all the veins
+and fissures, I was enabled to mark out a foundation-pit 42 feet in
+diameter, on one level throughout. That was a point of no small
+importance; and although it had cost great labour at the very outset,
+much time was saved by it in the subsequent stages of the work.
+Not only was the labour thereby avoided of cutting the rock into separate
+terraces, and fitting the blocks to each successive step, as was
+done by Smeaton at the Eddystone; but the certainty that we had
+a level foundation to start from, enabled us at once to commence the
+dressing of stones without regard to any irregularities in the surface
+of the Rock; and the building operations, when once commenced,
+continued unimpeded by the necessity for accommodating the
+courses to their places in the foundation-pit, so that the Tower soon
+rose above the level, at which there was the greatest risk of the
+stones being removed by the waves before the pressure of the superincumbent
+building had become great enough to retain them in
+their places.</p>
+
+<p>The outline of the circular foundation pit, 42 feet in diameter,
+having been traced with a trainer on the rock, numerous jumper-holes
+were bored in various places, having their bottoms all terminating
+in one level plane, so as to serve as guides for the depth to
+which the basin was to be excavated. The depth did not exceed 15
+inches below the average level, already laid bare by the cutting of
+the rough horizontal floor which has just been described; and before
+the close of the season of 1839, about <i>one-third</i> of the area of<span class="pagenum" id="Page131">[131]</span>
+the circle had been cleared, and was ready for the final pick-dressing
+which prepared it for the reception of the first course. The
+excavation of this circular basin was conducted with the greatest
+caution, and few shots were permitted to be fired lest the foundation
+should in any place be shaken by the action of the gunpowder
+on any of the natural fissures of the Rock. The work was chiefly
+done by means of what are called <i>plugs and feathers</i>, the form
+of which has already been shewn in the woodcuts (<a href="#Fig12">No. 12</a>, p. 115).
+In that part of the work the bores were nearly horizontal, and the
+action of the <i>plug and feathers</i> was to throw up a thin superficial
+shelf or paring of rock of from 6 to 12 inches in depth, and not
+more than 2 feet square. By that painful process an area of about
+1400 superficial feet was cleared. The chief trouble connected
+with that operation was cutting, by means of the pick, a vertical
+face for the entrance of the horizontal <i>jumpers</i> or boring rods;
+and wherever advantage could be taken of natural fissures it was
+gladly done. Another considerable source of labour was the dressing
+of the vertical edges of the basin, as that implied cutting a
+<i>square check</i>, 15 inches deep and about 130 feet long, in the
+hardest gneiss rock; and the labour attending which, can only be
+fully estimated by a practical stone-cutter who has wrought in
+such a material. The plan employed was to bore all around the
+periphery of the circle, 1⁵⁄₈ inch vertical jumper-holes, 6 inches apart,
+to the required depth, and to cut out the stone between them. The
+surface thus left was afterwards carefully dressed, so as to admit
+vertical and horizontal moulds, representing truly the form of the
+masonry which the check was intended to receive. The experience
+of the labour attending that operation gave me great reason
+for congratulation on having adopted a foundation on one level
+throughout, instead of cutting the rock into several terraces, at each
+of which the same labour of cutting angular checks must necessarily
+have been encountered. The cutting of the foundation occupied
+20 men for 217 days in all, whereof 168 days were in the season of
+1839, and the rest in the summer of 1840.</p>
+
+<p><span class="pagenum" id="Page132">[132]</span></p>
+
+<p>The minute details given in my account of the destruction
+of the first Barrack, have entirely superseded the need for any
+particular description of the fitting up of the second Barrack on the
+Rock; and I shall therefore confine myself to a brief notice of the
+work in the chronological order in which it occurred. <span class="sidenote">Fitting up of the
+Second Barrack
+on the Rock.</span>
+On the 1st
+of July, after the level floor for the foundation of the Tower had
+been roughly cleared, and all risk of injury from the firing of mines
+was past, the boring of holes for the fixtures of the second Barrack
+was begun; and so great were our exertions, that in the short
+period of fourteen days, the pyramidal frame-work on which the
+Barrack-house was to stand (see <a href="#Plate5">Plate V.</a>), consisting of 13 beams,
+of about 50 feet in length, with all their braces, ties and stancheons,
+and the malleable iron cap which secured their union at the top,
+was firmly fixed on the Rock. After the pyramid was completed,
+the Barrack-house (which had previously been removed from
+North Bay, where, as already noticed, it had served as a temporary
+abode for the men who opened the quarries there), was
+transported, piece-meal, from Hynish to the Rock as required; for
+it was not considered prudent, after the experience of last year,
+to trust, even in the finest part of the season, a great quantity of
+timber to <i>lashings</i> on the Rock. The fitting-up of the Barrack-house
+was completed on the 3d September and occupied only
+eleven days; so that the whole work extended to only twenty-five
+days, a remarkably short time for such a work, in such a situation.
+That despatch, indeed, was only obtained by working (as
+we did both during the excavation of the foundation and the erection
+of the Barrack), at all times when the weather would permit,
+from four o’clock in the morning till eight, and even nine in the
+evening, with an interval of only half-an-hour for breakfast and
+the same for dinner. The erection of the Barrack was a work of
+great difficulty and anxiety; for, as every thing depended on the
+exact union of all its parts, the slightest error in any dimension
+would have stopped the work until it could be remedied, a delay
+which, in such a situation, would, at certain stages of its progress,<span class="pagenum" id="Page133">[133]</span>
+have proved fatal to the whole structure. <span class="sidenote">Sudden death of
+George Middlemiss.</span>
+I cannot, therefore, omit
+this opportunity of paying a tribute, in passing, to the memory of
+the late Mr George Middlemiss, the foreman of the carpenters who
+fitted up the Barrack, whose zeal for the completion of the work
+was very conspicuous. Poor Middlemiss died very suddenly at
+Hynish, about a fortnight after the completion of his labours on
+the Rock. He had received some instructions from me, so late as
+11 o’clock, on the night of the 20th September; and when one of
+the men went to call him next morning at 6 o’clock, he was found
+dead, and in such a state as led Mr Moxey, the surgeon attached
+to the works, after a careful examination, to conclude, that he had
+died of paralysis of the heart, about three hours before he was
+found, or not more than four hours after I had seen him, to all
+appearance, in perfect health!</p>
+
+<p><span class="sidenote">Wharf and Landing-place
+on the
+Rock.</span>
+No inconsiderable part of the labour of this season was devoted
+to the clearing of the landing-place, which was formed in
+a natural creek (see <a href="#Plate3">Plate III.</a>) and in excavating the rocks in
+front of the line of wharf, so as to admit the vessels carrying
+the building materials to come alongside of it. That work
+could only be done at certain times of tide and during very
+fine weather, and was, therefore, tedious as well as hazardous.
+After two entire days spent in cutting with a sickle, mounted
+on a long pole, the thick cover of gigantic sea-weed, which hid
+the true form of the Rock from view, we were able to mark
+out the line of the wharf; and after all the mines were bored
+and charged and the tide had risen, and every one had retired
+from the spot, the whole were fired at the same instant, by
+means of the galvanic battery, to the great amazement and
+even terror of some of the native boatmen, who were obviously
+much puzzled to trace the mysterious links which connected the
+drawing of a string at the distance of about 100 yards, with a low
+murmur, like distant thunder, and a sudden commotion of the
+waters in the landing-place, which boiled up, and then belched
+forth a dense cloud of smoke; nor was their surprise lessened,<span class="pagenum" id="Page134">[134]</span>
+when they saw that it had been followed by a large rent in the
+rock; for so effectually had the simultaneous firing of the mines
+done its work, that a flat face for a quay had been cleared in a
+moment, and little remained to be done, to give the appearance of
+a regular wharf and to fit it for the approach of a stone lighter,
+except attaching wooden fenders and a trap ladder.</p>
+
+<p><span class="sidenote">Ring-bolts, Water-Tanks,
+and Railways.</span>
+A good deal of time was also spent in fixing a great many ring-bolts
+on various parts of the Rock and its <i>outlyers</i>, for the use of the
+shipping, which we expected to carry stones to the Rock the next
+season and in clearing a line for a permanent iron railway, about
+50 yards long, from the landing wharf to the Tower, the position
+of which is shewn in <a href="#Plate3">Plate III.</a> The railway was used for the
+conveyance of materials from the stone-lighters to the building, and
+is now the <i>highway</i> for all the stores which pass from the wharf to
+the Tower. Means were also taken for laying down two cast-iron
+water-tanks on the Rock in tolerably sheltered positions, as
+shewn in <a href="#Plate3">Plate III.</a> One of those tanks was completed and filled
+with water, but the sole-plate only of the other was fixed, as unfortunately
+one of the plates dropped from the vessel’s side into
+the water, while the seamen were lowering it into one of the boats,
+a loss which prevented the second tank from being finished till the
+next year. Those tanks, together, held about 900 gallons, and
+contained our chief supply of water during the whole subsequent
+progress of the works, when there were often about fifty men on
+the Rock.</p>
+
+<p><span class="sidenote">Incidents of the
+Season.</span>
+I shall conclude this Chapter, by noticing a few incidents which
+occurred during the season of 1839, serving, in some degree to
+throw light upon the peculiar difficulties we had to encounter, or
+tending to shew the importance of the work in which the Commissioners
+had engaged.</p>
+
+<p><span class="sidenote">Effects of a gale
+from the S.W.</span>
+On the 9th of August a strong gale suddenly sprang up from
+the S.W., which, while it lasted, caused us much alarm and anxiety
+at Hynish, whither we had been driven from our station at the
+Rock to seek shelter at the commencement of the storm. Several<span class="pagenum" id="Page135">[135]</span>
+small pieces of timber, which we had left on the Rock when we
+were forced to leave it, came ashore in Balaphuil Bay; and it was
+generally reported in the Island that the Barrack had, for the
+second time, been destroyed. That report I did not credit, as I
+had great confidence in the fixtures which attached it to the Rock;
+but my anxiety to ascertain the true state of the case, led me to
+examine the south-eastern shore of Tyree, when all that could be
+discovered was a few pieces of loose timber, and one of the smith’s
+cooling tubs, which had been washed from the Rock. Next day,
+however, the smith’s bellows came ashore in the same Bay, and
+so little injured, that we had them repaired and put in use again
+on the Rock. On the 12th of August, when the weather permitted
+us to return to our station at the Skerryvore, we found all the
+timbers which had been lashed down with chains to the Rock
+scattered in every direction around the beams of the Barrack,
+the smith’s forge overturned, the bellows of course gone; one of
+the cranes also which had been used for the removal of the excavated
+materials had been swept away, and not a vestige of it
+left, except a small piece of one of the wooden stays, which the
+force of the waves had broken. But that which most of all
+surprised us, and gave us the greatest concern, as an alarming
+proof of the force of the sea and a source of great inconvenience
+and hazard during the rest of the season, was the disappearance
+of our moorings, which had been lost by the <i>foundering</i> of the
+cask buoy in the heavy surf which the gale had raised. During all
+the rest of our stay at the Rock that season, we were forced to
+ride at anchor in foul rocky ground of the worst and most irregular
+description, over which the vessel frequently drifted to a considerable
+distance, occasioning us no small fear for our safety.
+That was the second set of moorings which had disappeared at
+Skerryvore; and a stronger proof of the very great power of the
+western swell can hardly be imagined, as nothing of the kind had
+happened during the whole time the Bell Rock works were in progress.
+That circumstance also convinced us of the necessity of<span class="pagenum" id="Page136">[136]</span>
+adopting vessels of small burden for landing the materials. So
+great, indeed, was the difficulty of <i>hanging</i> even the boats at the
+Rock, that on two occasions (on the nights of the 4th May and 12th
+July) we had both the boats half filled by the sea, and nine or ten
+men thrown out on the Rock by the <i>kanting</i> of one of the boats
+at the recoil of the wave. The landing department was indeed,
+throughout the whole season, attended with great difficulty, and
+was to me a source of constant anxiety; for, in the daily transport
+to and from the vessel and the Rock of 30 men, unaccustomed to
+boating, during a period of four months, it was more than could
+have been expected that we should have been preserved from the
+loss of either life or limb. On the night of the 3d September,
+when we left our anchorage at the Skerryvore for the season, every
+heart was full of rejoicing, and many cordial expressions of gratitude
+to our Almighty Protector were uttered in deep whispers by
+the more seriously disposed men, whose number bore a goodly
+proportion to our whole band. I cannot omit saying, in this place,
+that both Mr Macurich, who acted as landing-master on the Rock,
+and the late Mr Heddle, the master of the steam-tender, conducted
+the boating department in a most masterly style.</p>
+
+<p>As an aggravation of our difficulties, we were occasionally
+much annoyed by the unprincipled and cowardly conduct of a few
+of the seamen, who, despite the contempt of their comrades, fearing
+or pretending to fear the risk of lying all night so near the face of
+the Rock, spared no pains to spread alarm, and made several
+attempts, <span class="sidenote">Mutiny of the
+Crew.</span>
+by threatening desertion, to extort a rise of wages.
+They even spoke of leaving the vessel at the Rock, which they
+could easily have done by some of the native boats which called
+in passing to see the progress of the works; and Mr Heddle, the
+master of the steamer, was forced to dismiss the mutineers on the
+first occasion when the vessel was driven for shelter to the land,
+and to rely during the rest of the season on the native boatmen
+to supply their place. That firm conduct had, for some time afterwards,
+the desired effect on those who remained; but the spirit of<span class="pagenum" id="Page137">[137]</span>
+disaffection having spread pretty widely, we had subsequently
+several other instances of sudden desertion from the service.</p>
+
+<p>In the course of my residence for four months on board the
+tender moored off the Rock, I had opportunities of witnessing
+many proofs of the great necessity which existed for a Light on
+the Skerryvore; and if I had ever entertained any doubt as to
+the beneficial effects of such an establishment, the experience of the
+season of 1839 must have entirely removed it. <span class="sidenote">Near approach of
+Vessels to the
+Rock, and other
+circumstances
+shewing the importance
+of a Light
+on the Skerryvore.</span>
+It often happened
+that for several days successively, not fewer than five or six vessels
+of large size, both outward and homeward bound, were visible at
+distances varying from 3 to 6 miles from the Rock; and much
+anxiety was often felt by us for the safety of those vessels, several
+of which approached so near the outlying rocks as to keep us for
+some time in the most painful suspense. On two occasions, more
+especially, I was about to direct the steam to be raised, in order that
+the Skerryvore tender might be sent to warn the masters of vessels
+of their danger, or if too late for that, to afford them assistance in
+case of accident. On the 29th of May a large schooner, and on the
+13th of June a large brig ran right down upon the western <i>outlyers</i>,
+called <span class="smcap">Fresnel’s</span> Rocks (which were covered at the time), and just
+<i>put about</i> in time to avoid striking; and on the 12th June, a fine
+foreign barque (apparently a Prussian) passed so close to Bo-Rhua
+as to leave us for a short time in doubt whether or not she had
+struck on it. On the 21st of June, also, a large brig came very
+near the rocks which lie off Tyree, at the base of Ben-Hynish, in
+trying to avoid Boinshley Rock, which lies about 5 miles to the
+N.W. of the Skerryvore. Those circumstances, together with the
+list of shipwrecks already given at page 23, afford strong proofs
+that the Skerryvore Rock occupies a most fatal position in a great
+fairway much frequented by large vessels bound to or from ports
+in the Irish Sea and in the Clyde.</p>
+
+<p>There cannot be a doubt that many vessels have been wrecked
+on the Skerryvore and its numerous <i>outlyers</i>, being borne down
+upon the reef by the strong tide which runs at the rate of between<span class="pagenum" id="Page138">[138]</span>
+four and five miles an hour at the height of spring tides; and the
+natives of Tyree have many stories about chains and anchors and
+hidden treasures, with which their fancy has filled every nook of
+the Rocks. To what extent those stories, which are often most
+circumstantially told, may be true, it is not easy to determine;
+but in the end of July 1839, we succeeded, under the guidance of
+a native boatman, in raising from a creek in one of the detached
+shelves to the south-west of the main Rock, an anchor worn by the
+action of the sea to a mere skeleton, a circumstance which so far
+corroborates the truth of their traditions.</p>
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page139">[139]</span></p>
+
+<h3 class="nobreak"><span class="chapno">CHAPTER VI.</span><br>
+<span class="chapname">OPERATIONS OF 1840.</span></h3>
+
+</div><!--chapter-->
+
+<p>In describing the progress of the works during the season of
+1840, I shall speak of the various departments separately, as in the
+last chapter, beginning with the workyard at Hynish.</p>
+
+<p><span class="sidenote">Hynish Workyard.</span>
+During the preceding winter months, the establishment at Hynish
+was reduced to about fifty persons, of whom twenty-seven were
+masons employed chiefly in dressing blocks for the Lighthouse, in
+laying the stone platform in the workyard (on which each course was
+adjusted previously to its being shipped for the Rock, to prevent the
+occurrence of mistakes which might not be easily remedied there),
+and in building some additional barracks, masons’ sheds and a limekiln
+for the summer of 1840. The quarriers and labourers formed
+a party of about eighteen, and were engaged in cutting blocks in the
+Tyree quarries, which, although unfit for the Lighthouse Tower,
+were very suitable for the completion of the Pier at Hynish; while
+nine carpenters had full occupation in making moulds for dressing
+the Lighthouse blocks, preparing oaken treenails to be used in the
+lower courses of the Lighthouse Tower, and in dressing handles
+for the masons’ and quarriers’ tools. In the month of April, a reinforcement
+of thirty-seven masons from Aberdeen arrived at
+Hynish; and the greater number of them were at once employed
+in the dressing of stones for the Tower; while a few assisted in
+building the dressed materials in a temporary manner on the stone
+platform in the workyard already mentioned. The number of
+masons in the workyard, during the summer months, varied considerably,<span class="pagenum" id="Page140">[140]</span>
+according to the state of the works on the Rock, where
+seldom fewer than thirty men were stationed throughout the whole
+working season. But the dressing of the stones for the Tower
+proceeded with considerable vigour; and notwithstanding the inroads
+necessarily made upon the men’s time, by their being frequently
+required to assist in the landing of materials from Mull, a
+work for which few of the Tyree men were fit, from their awkwardness
+in the management of cranes and all kinds of machinery
+or tackling, and also by the constant detachment of a considerable
+number both of men and of tools for the laborious work of dressing
+the foundation-pit at the Rock, upwards of 20,000 cubic feet of
+granite had been dressed and fitted on the platform, when I left
+Hynish in the end of October 1840.</p>
+
+<p><span class="sidenote">Hynish Pier.</span>
+During the whole of the summer, the traffic at the pier at
+Hynish was so great in landing materials from the Mull quarries,
+and in shipping stones for the Rock, that much inconvenience was
+felt from want of room. Nearly 4000 tons were shipped and discharged
+at the quay, independently altogether of the ballasting of
+each vessel which discharged at the pier, and the receiving, storing,
+and finally supplying coals to the steamer, which formed no
+inconsiderable item of the labour. Every exertion was made to
+extend the pier, so soon as the works at the Rock were closed for
+the season and the stone trade with Mull had ceased; and by
+great perseverance on the part of Mr James Scott, the foreman of
+the workyard, whom I always found ready, night and day, to
+second and even to anticipate my wishes in regard to the progress
+of the works, an additional length of 36 feet was added to the
+berthage of the quay before the winter had set in.</p>
+
+<p><span class="sidenote">The Rock.</span>
+The first landing on the Rock, for the purpose of resuming the
+work in 1840, was on the 30th April, when all things connected
+with the Barrack were found in nearly the same state in which we
+had left them seven months before. The red paint with which
+we had coated it had become nearly white, partly by a covering
+of sea-salt, and by blanching of the paint itself, but chiefly towards<span class="pagenum" id="Page141">[141]</span>
+the top by the soil of the numerous sea-fowl which had perched on
+the roof. The timbers, also, bore the signs of being wave-washed,
+and in the more sheltered parts were tufted with the finer kinds
+of seaweed; the iron-work was much rusted and entirely divested
+of paint. The door had been firmly secured with lashings and
+bolts, and some difficulty was experienced in forcing an entrance
+into the interior, about the state of which, as our future abode,
+much curiosity was naturally felt by the men, who were desirous
+to know how it had weathered a seven months’ exposure to the
+waves of the Atlantic. It was with no small pleasure, therefore,
+that, when the door was opened and the windows unbarred and
+the sunshine admitted to dispel its gloom and chilly damp, we
+found, that although the water had forced its way through some
+of the imperfect seams in the window-frames, the interior shewed
+evident signs of the stability of the fabric, and was in some places
+so dry, that the greater part of the biscuits which we had left the
+year before, as a store for shipwrecked seamen who might find
+their way to the Rock, although some of them were wet and pulpy
+on the side nearest the outer walls, admitted of being dried, and
+when a little toasted at the fire, were palatable enough to hungry
+men, so that, in fact, we consumed the greater part of that stock
+before we entered on our new supply.</p>
+
+<p>The most important change which had occurred during the
+winter, was the removal of a mass of rock in the neighbourhood of
+the foundation-pit, which had been shaken by the effects of the
+blasting operations of the previous year. That mass, the moving of
+which shewed that a great weight of water had passed over the
+Rock, weighed about five tons, and had been detached from its bed
+during a heavy gale from the N.W., in the month of March, and
+carried right across the foundation-pit to the Barrack, against one
+of the beams of which it had rested, and had partially injured
+the iron <i>collars</i> or <i>glands</i> by which the beam was secured. The
+stone was broken into small fragments by a party of men, who
+had been appointed to visit the Rock after heavy gales, and had<span class="pagenum" id="Page142">[142]</span>
+landed on the 27th of March, to see the state of the Barrack. The
+men, in their anxiety to break down the block, which they
+feared might injure the Barrack, if thrown against it by the waves,
+and allured by the smoothness of the sea, most imprudently remained
+all night, mooring their boat in the landing creek, and
+trusting to the scanty stock of provisions which they had brought
+out, with the intention of at once returning to Hynish. The risk
+involved in such a proceeding, we afterwards had many opportunities
+of knowing during our stay on the Rock, as we were often
+forced to make fast all our materials, to prevent their being washed
+away by the sudden rising of the waves, especially about the time
+of high-water in spring-tides. The discomforts, however, experienced
+by the men on that occasion while in the Barrack, without
+fire, light or bedding, in a cold dark night of spring were such,
+that several of them did not afterwards much affect the Rock as a
+residence even in summer.</p>
+
+<p>Owing to the great difficulty of landing on the Rock in the
+early part of May, few opportunities occurred of preparing the
+Barrack as a habitation; <span class="sidenote">Life in the
+Barrack.</span>
+and it was not until the 14th of that
+month that we were enabled to take up our quarters in it; and
+even then we were most uncomfortably lodged, as many of the
+smaller fittings which are essential to a <i>wind-and-water-tight</i> habitation
+had not been completed. During the first month we suffered
+much from the flooding of our apartments with water, at
+times when heavy sprays lashed the walls of the Barrack with
+great violence and also during rainy weather; and in northerly
+gales we had much difficulty in keeping ourselves warm. On one
+occasion, also, we were fourteen days without communication with
+the shore or the steamer; and during the greater part of that time
+we saw nothing but white fields of foam as far as the eye could
+reach, and heard nothing but the whistling of the wind and the
+thunder of the waves, which were at times so loud as to make
+it almost impossible to hear any one speak. For several days,
+the seas rose so high as to prevent our attempting to go down to<span class="pagenum" id="Page143">[143]</span>
+the Rock; and the cold and comfortless nature of our abode reduced
+all hands to the necessity of seeking warmth in bed, where
+(rising only to our meals) we generally spent the greater part of the
+day listening to the howling of the winds and the beating of the
+waves, which occasionally made the house tremble in a startling
+manner. Such a scene, with the ruins of the former barrack not
+20 yards from us, was calculated only to inspire the most desponding
+anticipations; and I well remember the undefined sense of
+dread that flashed across my mind, on being awakened one night by
+a heavy sea which struck the Barrack, and made my cot or hammock
+swing inwards from the wall, and was immediately followed
+by a cry of terror from the men in the apartment above me, most
+of whom, startled by the sound and tremour, immediately sprang
+from their berths to the floor, impressed with the idea that the
+whole fabric had been washed into the sea. The alarm, however,
+was very short and the solemn pause, which succeeded the cry, was
+soon followed by words of reassurance and congratulation. Towards
+the end of the fourteen days I began to grow very uneasy,
+as our provisions were drawing to a close; and when we were at
+length justified, by the state of the sea on the rock, in making the
+signal to those on shore (at the hour fixed for pointing the telescope
+at Hynish on the Barrack), that a landing could be effected,
+we had not more than twenty-four hours’ provision on the Rock,
+so that when the steamer came in sight she was hailed by all hands
+with the greatest joy!</p>
+
+<p>The construction of the Barrack has already been very fully
+described, and a glance at <a href="#Plate5">Plate V.</a> will be sufficient to give a
+pretty correct idea of the nature of our singular dwelling. Immediately
+under the wooden tower was an open gallery, the floor of
+which was removed at the end of each season, so as to allow free
+space for the passage of the sea during the storms of winter, but on
+which, during the summer, we kept the stock of coals, the tool-chests,
+the beef and beer casks, and other smaller materials which
+we could not, even at that season, safely leave on the Rock itself.<span class="pagenum" id="Page144">[144]</span>
+Next came the kitchen and provision store, a six-sided apartment
+about 12 feet in diameter and somewhat more than 7 feet high, in
+which small space, curtailed as it was by the seven beams which
+passed through it, stood a <i>caboose</i>, capable of cooking for forty
+men, and various cupboards and lockers, lined with tin, for holding
+the biscuits, meal, flour, barley and other things needful for the
+sustenance of the human frame. That apartment, for protection
+against fire, was coated, partly with tin and partly with sheet-lead,
+which latter, although not in all respects the most desirable material
+to come in contact with that element, was found to be the only one
+which we could in some parts conveniently apply. The next storey
+was divided into two apartments, whereof one was shared by Mr
+Thomas Macurich, who superintended the landing of all the materials
+and Mr Charles Stewart, the foreman of the builders, and the
+other was allotted to myself. The apartments thus occupied consisted
+of a twelve-sided narrow space twisted around a centre
+pyramid, whose bevelled faces formed, as will in part be seen by
+inspecting <a href="#Plate5">Plate V.</a>, their sloping walls on one side. The half of
+that space constituted my apartment, which, I think, would be generally
+pronounced not over commodious; and when it is added that
+it contained my bed, desk, chair and table, and a stock of groceries,
+it will readily be imagined I had little room to spare for myself.
+So much attention was paid to economy of space, that the recesses of
+the pyramid formed by the meeting of the beams were boarded over
+and made into cupboards; while my <i>cot</i>, or framed hammock (which,
+during the night, rested upon brackets which could be folded close
+to the wall when not required), was, during the day, hoisted by
+pullies to the roof of the apartment, so as to leave me as much
+space to move about in as a prisoner could expect. The cornice of
+the apartment consisted of a narrow shelf adorned with books,
+which I found very needful helps to solitary life. The highest
+apartment was also twelve-sided, surmounted by a pyramidal roof
+and a small six-sided lantern or ventilator, and was lined round
+the sides with four tiers of berths, capable of accommodating thirty<span class="pagenum" id="Page145">[145]</span>
+people. The closeness of that room was most intolerable, especially
+during the heat of fine weather in summer, at which time several of
+the men preferred taking a nap on the rock, with the clear blue sky
+for a canopy. The economy of our life on the Rock was strange
+enough. At half-past three in the morning we were called, and at
+four the work commenced, continuing till eight, when half-an-hour
+was given for breakfast: after which it was carried on till two, when
+another half-hour was given for dinner; and the work was again
+resumed and continued till seven, eight, and even nine o’clock,
+when anything urgent was in hand. Supper was then produced
+and eaten with more leisure and comfort in the cool of the evening.
+Such protracted exertion produced a continual drowsiness,
+and almost every one who sat down fell fast asleep. I have myself
+repeatedly fallen asleep in the middle of breakfast or dinner;
+and have not unfrequently awakened, pen in hand, with a half-written
+word on the paper! Yet life on the Skerryvore Rock
+was by no means destitute of its peculiar pleasures. The grandeur
+of the ocean’s rage, the deep murmur of the waves, the hoarse
+cry of the sea-birds, which wheeled continually over us, especially
+at our meals, the low moaning of the wind, or the gorgeous brightness
+of a glassy sea and a cloudless sky, and the solemn stillness of
+a deep blue vault, studded with stars, or cheered by the splendours
+of the full moon, were the phases of external things that often arrested
+our thoughts in a situation where, with all the bustle that
+sometimes prevailed, there was necessarily so much time for reflection.
+Those changes, together with the continual succession of
+hopes and fears connected with the important work in which we
+were engaged, and the oft-recurring calls for advice or direction,
+as well as occasional hours devoted to reading and correspondence,
+and the pleasures of news from home, were more than sufficient to
+reconcile me to, nay, to make me really enjoy, an uninterrupted residence,
+on one occasion, of not less than five weeks on that desert
+Rock.</p>
+
+<p>During the first half of the season 30 men were engaged 14 hours<span class="pagenum" id="Page146">[146]</span>
+a day in the preparation of <span class="sidenote">Foundation-pit.</span>
+the foundation-pit, which, as already
+said, was a work of the greatest labour. The Rock, indeed, was
+in many places so hard as often to make it seem hopeless that tools
+could make any impression on it. The time employed in the excavation
+and the number of tools expended on it, were very great, as
+a pick seldom stood more than three strokes in the harder quartzose
+veins; but our perseverance was at length amply rewarded by
+obtaining a foundation so level and so fairly wrought throughout
+the whole area of a circle 42 feet in diameter, as to present to the
+view the appearance of a gigantic basin of variegated marble; and
+so much pleased were the workmen themselves with the result of
+their protracted toil, that many of them expressed serious regret
+that the foundation must soon be covered up so, as (we trusted),
+never to be seen again. In the dressing of the Rock much inconvenience
+arose from the small splinters which flew out before
+the tools, sometimes rising to the height of 40 feet, and coming
+in at the windows of the Barrack; and after several injuries had
+been sustained, I at length found it necessary to send to Glasgow
+for fencing masks to protect the men’s faces. In all our work, nothing
+was more grudged than the occasional loss of half a day in
+<i>baling</i> out the water from the foundation-pit after it had been filled
+by a heavy sea.</p>
+
+<p><span class="sidenote">Landing of materials
+on the Rock.</span>
+Before we had made an actual trial of landing stones on a
+Rock at the distance of 12 miles from the nearest shore, exposed
+to the incessant beating of Atlantic waves, there was much room
+for doubt as to the measure of success to be expected; and, as
+the time approached, I naturally looked to the attempt with increasing
+anxiety, as to an experiment in a great measure decisive
+of the future complexion of our operations. Four small vessels,
+carrying from 16 to 19 tons, had been built at Leith and Dumbarton,
+for the purpose of carrying the stones on their decks, so as
+to admit of their being easily lifted by the crane, and so to avoid
+the risk which would have been incurred by any attempt to raise
+stones by a crane from the hold of a vessel moored to a rock<span class="pagenum" id="Page147">[147]</span>
+in the open sea and moving about with every wave. Had that
+been attempted, the crane would, on many occasions, have been
+pulled down before the stone could be cleared from the hold. The
+vessels were very similar to those which were used for the same
+purpose at the Bell Rock; and I therefore beg leave to refer the
+reader to page 509, and to Plate XI. of my Father’s account of
+that work, for a description of them. Being decked all over, to
+give room for cargo (for they carried nothing in the hold but
+empty casks for the purpose of floating them in the event of their
+sustaining any injury), they were towed between Hynish and the
+Rock by the steamer, and being <i>cast off</i> as near the landing-place
+as possible, were taken by the boats to the creek, and moored with
+warps to the fenders at the quay.</p>
+
+<p>The first trial of the lighters in landing stones on the Rock
+was made on the 20th of June, on which occasion both the steamer
+and the stone craft were decorated with flags; and due honour
+was done to the occasion of landing the first stone, by firing a
+salvo shot and drinking success to the works. The landing service
+throughout the whole progress of the works was one of much difficulty
+and anxiety and many narrow escapes were made; but it
+was managed with great prudence, and at the same time with unremitting
+energy, by Messrs Macurich and Heddle, in their several
+departments, both ashore and afloat. On many occasions the men
+who steered the lighters ran great risks; and it was often found
+necessary to lash them to the rails, to prevent their being thrown
+overboard by the sudden bounds of the vessels, or being carried
+away by the weight of water which swept their decks as they were
+towed through a heavy sea. Sometimes, also, we were forced,
+owing to the rush of the sea into the creek, which threatened
+to lift the vessels on the top of the Rock, to draw out the loaded
+lighters from the wharf without landing a single stone, after they
+had been towed through a stormy passage of 13 miles; and one day,
+during the very best part of the season, so sudden was the bounding
+of the vessel before the sea, that eight large warps were snapped<span class="pagenum" id="Page148">[148]</span>
+like threads as the lighter was carried violently before a crested
+wave which rolled unexpectedly into the creek, while those who
+stood on her deck were thrown flat on their faces and imagined
+that the vessel had been laid <i>high and dry</i> on the top of the Rock.
+During the whole season, however, in the course of landing 800
+tons of masonry on the Rock, too often in that dangerous manner,
+none of the dressed stones received any great damage, nor was any
+other injury of importance sustained.</p>
+
+<p>The building of the Tower was commenced on the 4th July;
+<span class="sidenote">Building the
+first stone.</span>
+but it was not till the 7th that the ceremony of laying the foundation-stone
+was performed by His Grace the Duke of Argyll, who,
+as proprietor of the adjacent Island of Tyree, took a great interest
+in the success of the works, and on that day visited the Skerryvore
+with the Duchess of Argyll, the Marquis of Lorne, Lady
+Emma Campbell, and a party of friends, in the Toward Castle
+steamer. On that occasion His Grace expressed himself much
+pleased with the works and kindly left with me a donation of L.10
+for the workmen.</p>
+
+<p>The building operations in 1840 were entirely carried on by
+means of two cranes with moveable jibs, of which one was fixed
+just beyond the foundation, at the place shewn in <a href="#Plate3">Plate III.</a>, between
+the landing quay and the Tower, and was chiefly used in
+bringing forward the materials; and the other, placed in the centre
+of the Tower, served for laying the stones, and was raised along
+with the rise of the building. So perfectly had the stones been
+dressed in the workyard at Tyree, that no alteration or paring of
+the beds or joints was required; and such was the facility afforded
+by the building apparatus, that by working 14 hours, we occasionally
+<i>set</i>, through the activity of Mr Charles Stewart, the foreman
+builder, so many as 85 blocks in a day. The first course of
+masonry was laid by means of a wooden trainer; but the place
+of all the subsequent stones was, as already noticed, regulated by
+the use of <i>plumb-templets</i>, whose inner faces were arcs of the generating
+hyperbola. By those means we succeeded in <i>setting</i>, in a<span class="pagenum" id="Page149">[149]</span>
+most perfect manner, six courses, which carried the building to the
+height of 8 feet 2 inches, and contained a mass equal to 10,780 cubic
+feet. That quantity is not greatly less than the whole materials
+of the Eddystone Lighthouse Tower, which, according to my computations
+from the drawings of <span class="smcap">Smeaton</span>, do not exceed 13,300
+cubic feet, and is somewhat more than <i>one-third</i> of the contents of
+the Bell Rock Tower, which are about 28,500 cubic feet. That
+frustum was also nearly equal to <i>one-fifth</i> part of the whole mass
+of the proposed building, which is about 56,000 cubic feet. Of the
+six courses, the first three are of Hynish gneiss, and the rest are of
+granite from the Ross of Mull. The comparative merits of those
+two materials may be stated as follows:—The Hynish stone is
+harder, and susceptible of finer workmanship, and perhaps its most
+perfect blocks are more durable; but it requires much more labour
+in dressing than the Mull granite, which is more homogeneous
+in its structure and is not intersected by hard veins, like those
+which occur in the gneiss of Tyree. There is good reason also
+for concluding that the Mull stone is sufficiently durable, because
+it contains but a small proportion of micaceous matter, and in its
+texture closely resembles some of the blocks of St Oran’s chapel
+in the neighbouring Island of Iona, which have resisted the action
+of the weather, it is believed, for more than 600 years and still retain
+the marks left by the tools of the workmen. I had also carefully
+compared the density of the Hynish and Mull stones, by
+weighing blocks of known dimensions, and found that it requires
+13·16 cubic feet of the former, and 13·66 cubic feet of the latter
+to weigh one ton, a difference much less than the appearance of
+the stone would lead one to expect. A Tower of the dimensions
+of that at Skerryvore, built entirely of Hynish stone, would have
+weighed about 4308 tons, while the same mass of Mull stone would
+weigh 4252 tons, leaving a difference of not more than 156 tons in
+favour of the Hynish stone.</p>
+
+<p>The mortar employed in the building was composed of equal
+parts of Aberdda lime and Pozzolano earth, and was therefore<span class="pagenum" id="Page150">[150]</span>
+identical, in its composition, with that used by Smeaton at the
+Eddystone. Not having been able, after searching the neighbouring
+islands, to obtain good sand, I found it inexpedient to adopt the
+proportion of equal parts of lime, sand, and Pozzolano, which were
+so successfully used at the Bell Rock; but so perfect was the adhesion
+of the mortar used at the Skerryvore, that in that mass
+of 800 tons only two small leaks were discernible, which being
+<i>ripped</i> or opened with an <i>iron</i>, and allowed to run dry, were afterwards
+carefully repointed, and have never since shewn the slightest
+symptoms of leaking.</p>
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page151">[151]</span></p>
+
+<h3 class="nobreak"><span class="chapno">CHAPTER VII.</span><br>
+<span class="chapname">OPERATIONS OF 1841.</span></h3>
+
+</div><!--chapter-->
+
+<p><span class="sidenote">Hynish workyard.</span>
+The workyard at Hynish presented a very busy scene during the
+summer and winter of 1840; and the desolation and misery of the
+surrounding hamlets of Tyree seemed to enhance the satisfaction
+of looking on our small colony, where about 150 souls were collected
+in a neat quadrangle of cleanly houses, conspicuous by their
+chimnies and windows amongst the hovels of the poor Hebrideans,
+who generally make no outlet for the smoke in their gloomy
+dwellings, but permit it to escape by the doors. The regular
+meals and comfortable lodgings and the cleanly and energetic
+habits of the Lowland workmen, whose days were spent in toil and
+their evenings, most generally, in the sober recreations of reading
+and singing, formed a cheering contrast to the listless, dispirited,
+and squalid look of the poor Celts, who have none of the comforts
+of civilized life and are equally ignorant of the value of time and
+the pleasures of activity.</p>
+
+<p>The number of masons employed in 1841, varied from 60 to
+84 and they were chiefly engaged in dressing blocks for the Lighthouse-Tower,
+in discharging the cargoes of vessels loaded with
+stone from Mull and also in shipping stones for the Rock, in which
+operation, their acquaintance with the handling of dressed materials
+and their readiness in working the cranes, made them very
+useful in directing and also in working along with the native labourers,
+who, partly from incapacity and partly from excessive indolence,
+could not be trusted for a moment to themselves. During<span class="pagenum" id="Page152">[152]</span>
+that year, upwards of 38,000 cubic feet of granite were dressed
+into blocks with straight beds and joints, and with faces of double
+curvature, so as to suit the contour of the Tower, when arranged
+in the wall. The blocks were also fitted with stone joggles, for
+retaining them in their places, and with lewis-holes for raising
+them in the manner usually practised in building materials of that
+description. Of those materials upwards of 70 blocks were floor-stones
+(see Plans of 84th and 85th courses, <a href="#Plate8">Plate VIII.</a>), <i>dovetailed</i>
+on the heads, <i>checked</i> on the joints and having a plain surface on
+the upper and a concave one on the under bed. The necessity of
+preserving throughout their entire joints a perfect uniformity of
+bearing, made the dressing of those materials a work of great
+nicety; and each stone, as before noticed, being cut according to
+moulds, was fitted temporarily in its place on the platform at
+Hynish, previously to its being laid aside as ready for transport to
+the Rock. Those various operations were conducted with great
+care; and the stones, which were regularly arranged and numbered
+according to a schedule, formed, at the time I left the workyard
+in the end of October, a considerable pile, bearing ample testimony
+to the diligence and zeal of Mr James Scott, the foreman of
+the workyard and leader of the party ashore.</p>
+
+<p>Owing to the uncertain and stormy weather in spring, it was
+not till the 13th of May, that the first landing was effected on the
+Rock. <span class="sidenote">The Rock.</span>
+The result of our visit, however, was most satisfactory.
+We found the Barrack quite as we had last seen it six months before;
+and not one joint of the pile of masonry, which we had left
+exposed to the waves, had been shaken or <i>started</i>. The Railway
+and Landing Wharf, although much exposed to the breach of the
+sea, had survived the winter’s storms with no greater damage than
+the loss of one of the sleepers or beams, on which the rails rested,
+which had been torn by the waves from its fixtures to the rock.
+It was not till a week after our first landing that we were enabled
+again to take up our quarters on the Rock; for we had few landings
+in the mean time, and some of them, owing to the heavy surf<span class="pagenum" id="Page153">[153]</span>
+which played round the Rock, were of no very satisfactory kind.
+Our first experience of this season was indeed far from inviting. So
+difficult was the first landing, that we were forced to direct all our
+endeavours to laying in a small stock of provisions in the Barrack,
+before being left on the Rock; and, considering the scanty nature
+of the supplies which the weather permitted us to secure, it was
+thought prudent to restrict the number of men to eight masons and
+myself, with as many tools as we could land, to enable them to
+make the necessary repairs and arrangements before fairly commencing
+for the season the works of a more strictly progressive
+character. The vessel then returned to Tyree with the rest of the
+men and all the heavy apparatus which we could not land; and,
+to add to the unpleasantness of being left in such a position, with
+the improbability of a visit from the vessel for several days, one of
+the masons took alarmingly ill soon after the steamer was too far
+off for a signal, and suffered so acutely during the whole night,
+that his piercing cries in the spasms which accompanied his disorder,
+combined with the howling of a strong <i>north-wester</i> and the
+incessant lash of the waves, deprived the whole party of sleep
+during the first night. In this uncomfortable predicament, until
+the steamer returned on the 22d, we spent two days exposed to
+winds piercingly cold and in apartments soaked with spray, which
+found its way through inlets which had been made by the winter’s
+storms. We were not sorry, at the same time, to have an opportunity
+of removing the poor man to the care of Dr Campbell,
+the surgeon who was attached to the workyard at Hynish and of
+reinforcing our stock of provisions and the detachment of men.
+We also succeeded in landing the cranes and other building apparatus,
+which, owing to the heavy surf on the 20th, we had not
+been able to accomplish.</p>
+
+<p>The few first days after getting fairly established in our habitation
+for the season, were occupied in extending the railway to a
+point on the northern part of the Rock, somewhat sheltered during
+certain seas (see <a href="#Plate3">Plate III.</a>), where a crane for stowing the materials<span class="pagenum" id="Page154">[154]</span>
+previously to building them had been erected; and thus it was
+not till the 25th of May that the first cargo of stones was landed.
+Next day a crane (then thirty-four years old), which had been
+used in the building of the Bell Rock Lighthouse, was placed on
+the top of the masonry, and the more cheering operations of mixing
+the mortar and of <i>setting</i> stones were begun.</p>
+
+<p>In spite of the unfavourable state of the weather and the continual
+distraction of our exertions, occasioned by storms and the
+landing of materials, we continued our operations with such vigour
+as to complete the solid part of the masonry of the Tower on the
+8th July. Until the building had reached to the level of 15 feet,
+the work was carried on by the use of two jib-cranes, one on the
+Rock and the other on the Tower, by means of which latter the
+stones were <i>set</i>, after being <i>brought to hand</i> by the first. But above
+that level, <i>shear-legs</i> similar to those used at the Eddystone, were
+employed. Those shear-legs were about 50 feet high, and were
+erected in the situation, at the side of the Tower, shewn in <a href="#Plate3">Plate
+III.</a> They consisted of two spars attached at the base to <i>jointed</i>
+sockets <i>batted</i> into the Rock, and connected at the top by means of
+a crosshead of timber. The jointed sockets permitted the shears
+to hang forward at any angle suited to the level and distance of
+the part of the Tower to be reached; and chain guys both in front
+and behind, secured them from falling either backwards or forwards.
+At the crosshead hung an iron sheave with a chain, one
+end of which was provided with a hook for raising stones, while
+the other was wound around the barrel of a <i>crab machine</i> well
+batted down to the rock, by working which the blocks were raised
+to such a level as to be within reach of the building crane on the
+top of the masonry. The <i>shear-poles</i> were used, until the building
+of the Tower was completed, to raise the stones the first lift of
+forty feet above the Rock. In the later stages of the work, the
+stones, instead of being taken by the building cranes directly from
+the <i>shear-poles</i>, were raised from storey to storey by means of crabs
+placed inside the Tower, which worked chains, <i>reeved</i> through<span class="pagenum" id="Page155">[155]</span>
+sheaves hanging from the end of beams projecting from the windows.
+Such beams are called <i>needles</i>, and are described at page
+504, and shewn in Plate IX., fig. 3, of my Father’s Account of
+the Bell Rock Lighthouse, where they were used for the same
+purpose.</p>
+
+<p>During the early part of the season the weather was intensely
+cold, with showers of sleet and heavier showers of spray, which
+dashed round us in all directions, to the great discomfort of the
+poor masons, whose apartments did not admit of a large wardrobe,
+while they had not the benefit of much room for drying their
+clothes at the small <i>coboose</i> or cooking-stove in the Barrack. For
+days together, also, the men were left without building materials,
+owing to the impossibility of landing them, or, what was worse,
+without the power of building what we had on hand in consequence
+of the violence of the winds. During such times we often felt much
+anxiety about the safety of the stones which we had piled on the
+rock ready for being built; and it took no small trouble, by the occasional
+application of the crane, to save them from being swept into
+the sea by the surf. <span class="sidenote">The Waves.</span>
+Nothing struck me more than the illusive
+effect produced on the mind by the great waves which rolled past
+the rock. The rapidity of their movements, and the noise which
+accompanied their passage through the gullies and rents of the
+rugged reef, seemed to give them the appearance of being much
+larger than they really were; and, even when viewed from the
+Tower, after it had risen to the height of 30 feet, they seemed, on
+approaching the rock, to be on the eve of washing right over the top
+of the building and sweeping all before them into the sea. It was
+a long time before, by continually watching the waves and comparing
+their apparent height with the results of their impact on
+the rock, we were enabled to correct our notions of their magnitude,
+so as to mark the approach of their crested curling heads
+with composure; and some of the party never became sufficiently
+familiarized with those visitors, to avoid suddenly looking round<span class="pagenum" id="Page156">[156]</span>
+when the rush of a breaker was heard behind them, or recoiling a
+few paces when they saw its towering crest apparently about to
+burst in a torrent over their heads. It was only after a long residence
+on the rock and continual experimental observation, that I
+acquired confidence to approach within a few feet of the point
+which I expected the breakers to reach. I occasionally suffered for
+my temerity, by being thoroughly drenched with spray; but by
+long perseverance, I attained considerable skill in predicting the
+limits of their influence, though ever and anon an extraordinary
+wave overthrew all our confidence, by bursting far above the
+boundaries which we had assigned in our minds. That, however,
+did not generally occur in calm weather, but after strong gales from
+the N.W., when the waves had assumed the larger and more flattened
+form known by the name of the <i>ground-swell</i>. To gauge
+the height of those waves by means of a vertical rod, graduated
+with large divisions, so as to be read at a little distance, as the
+waves washed it in passing, was an object I had long in view; but
+I found it utterly impossible to apply any fixture in the deep water,
+in a situation fitted for the purpose. By making numerous comparisons,
+however, of the waves, with various known points of
+rock near the main Rock, and by availing myself of the observations
+of some of the more intelligent of the masons, I was led to
+conclude, that the greatest elevation of an unbroken wave, measuring
+from the hollow to the crest, does not, in the sea around the
+Skerryvore, exceed 15 feet; but the sailors, perhaps from their
+being less accustomed to accurate measurement, generally estimated
+it at 30 or even 40 feet. <span class="sidenote">Colours of breaking
+Waves.</span>
+I was often much interested,
+while I sat watching the waves that boiled round us on every side,
+to observe the peculiar tints which they assumed at the moment
+of breaking, passing as they did from the bluish-green colour of
+solid water by very rapid changes, to a delicate and very evanescent
+<i>blush</i> of rose colour, which invariably accompanied their greatest
+state of comminution or disintegration. Those appearances I have<span class="pagenum" id="Page157">[157]</span>
+often observed in other places, and I supposed them to be produced
+by <i>reflection from the thin plates of water</i>; and took them for indications
+of the perfect homogeneousness of the sea-water, in regard
+to density, and also of the similarity of its condition at the <i>moment</i>
+of breaking.</p>
+
+<p><span class="sidenote">The Seals.</span>
+Amongst the many wonders of the “great deep,” which we
+witnessed at the Skerryvore, not the least is the agility and power
+displayed by the unshapely seal. I have often seen half a dozen
+of those animals round the Rock, playing on the surface or riding
+on the crests of curling waves, come so close as to permit us to see
+their eyes and head, and lead us to expect that they would be
+thrown <i>high and dry</i> at the foot of the Tower; when suddenly they
+performed a somersault within a few feet of the Rock, and diving
+into the flaky and wreathing foam, disappeared and as suddenly
+reappeared a hundred yards off, uttering a strange low cry, as we
+supposed, of satisfaction at having caught a fish. At such times
+the surf often drove among the crevices of the Rock a bleeding
+cod, from whose back a seal had taken a single moderate bite,
+leaving the rest to some less fastidious fisher.</p>
+
+<p>The latter part of the season, although not so stormy as the
+first, was far from being favourable for the building operations
+which, on one occasion, even during the month of July, were suspended
+for five days by a violent gale, which made it unsafe to attempt
+standing on the Tower. Happily the wind was from the
+N.E., a quarter from which it has comparatively little power in
+raising heavy seas, otherwise we should infallibly have lost a large
+part of the dressed materials which lay piled on the Rock, and, in
+all probability, should have had our work thus prematurely cut
+short in the middle of summer.</p>
+
+<p>After building a few courses above the level of the solid part
+of the Tower, the jib-crane could no longer be conveniently used,
+and recourse was had to a <i>balance-crane</i>, which, during the previous
+winter, I had caused to be constructed at Edinburgh, in the
+workshop of Mr James Dove. That apparatus, which, except as<span class="pagenum" id="Page158">[158]</span>
+to its greater size and strength, in order to suit the greater dimensions
+of the Tower, was almost identical with that which was
+used at the Bell Rock, is shewn in <a href="#Plate9">Plate IX.</a>; and it is only
+necessary, in this place, to notice its general construction and
+mode of working, which is also shewn in Plate XVII. of my
+Father’s Account of the Bell Rock Lighthouse. In the hollow
+of the Tower, a cast-iron pipe or pillar was erected, susceptible
+of being lengthened as the Tower rose, by means of additional
+pieces of pillar let in by <i>spigot and faucet joints</i>; and on the
+pillar a frame of iron was placed capable of revolving freely
+round it, and carrying two trussed arms and a double train of barrels
+and gearing. On the one arm hung a cylindric weight of
+cast-iron, which could be moved along it by means of the gearing,
+so as to increase or diminish by leverage its effect as a counterpoise;
+and on the other was a roller. The roller was so connected
+with the weight on the opposite arm, as to move along with it, receding
+from, or approaching to, the centre pillar of iron in the same
+manner as the weight did. From the roller hung a sheave, over
+which a chain moved, with a hook at the end for raising the stones.
+When a stone was to be raised, the weight and the sheave were
+drawn out to the end of the arms of the crane, which projected
+over the outside of the walls of the Tower, and they were held in
+their places by simply locking the gearing which moved them.
+The second train of gearing was then brought into play to work
+the chain which hung over the sheave, and so to raise the stone to
+a height sufficient to clear the top of the wall. When in that position,
+the first train of gearing was slowly unlocked and the slight
+declivity inwards from the end of the arms formed an <i>inclined
+plane</i>, along which the roller carrying the sheave was allowed
+slowly to move (one man using a break on the gearing to prevent
+a rapid run), while the first train of gearing was slowly wound by
+the others, so as to take up the chain which passed over the sheave,
+and thus to keep the stone from descending too low in proportion
+as it approached the centre of the Tower. When the stone so<span class="pagenum" id="Page159">[159]</span>
+raised had reached such a position as to hang right over the wall,
+the crane was made to turn round the centre column in any direction
+that was necessary, in order to bring it exactly above the place
+where it was to be <i>set</i>; and by working either train of gearing, it
+could be moved horizontally or vertically in any way that was
+required. The men who wrought the crane, stood on two small
+stages of planks attached to either side of the framework, and
+moving round the shaft along with it.</p>
+
+<p>The balance-crane was safely landed on the Rock on the 20th
+July and on the 25th it was erected in working order on the top
+of the masonry. On the afternoon of that day, I had the satisfaction
+of seeing it put to a severe trial in raising a stone of nearly
+two tons weight and drawing it from the <i>shear-poles</i> already noticed
+to the top of the building. As that trial was made at an earlier
+stage of the works than was originally intended, the Tower was
+of larger diameter than was quite suited to the arrangements of
+the crane, which was consequently subjected to the weight of the
+stone at the very point of the jib. I felt no small anxiety as to
+the result, and had taken the precaution to relieve the centre pillar
+or shaft, on which the crane swung, from part of its burden, by
+means of a guy attached to a lewis-bat on the top of the building;
+yet even with that aid, the point of the jib was depressed 6 or 8
+inches on a length of 14 feet. That test, however, having been
+successfully passed and not the slightest trace of any injury having
+been discoverable in any part of the crane, we continued to work
+it with perfect confidence and in the most satisfactory manner
+throughout the whole season until the close of the Rock operations
+for the year on the 17th of August.</p>
+
+<p>The mass of masonry built during the season was 30,300 cubic
+feet, a quantity considerably more than double that contained in
+the Eddystone and somewhat more than the mass of the Bell Rock.
+The whole was very carefully <i>set</i> and when gauged at the upper
+bed of each course was found to preserve the diameter due to the<span class="pagenum" id="Page160">[160]</span>
+height, according to the calculated dimensions, within a fraction
+rarely exceeding ¹⁄₁₆th of an inch. The height of the mass also,
+when measured, exceeded the specified height only by <i>half an inch</i>.
+The mortar employed was composed of equal parts of lime from
+the Halkin Mountain in North Wales and Pozzolano; and I consider
+it if possible superior to that produced from the lime of
+Aberdda. When we left the Rock this season, two apartments
+were covered in and the third was nearly completed, as will appear
+from the section (<a href="#Plate3">Plate III.</a>) (on which the progress of the
+several seasons is marked), and only about <i>one-third</i> of the whole
+Tower remained to be built.</p>
+
+<p>Our last work on the Rock before leaving it for the season on
+the 17th August, was to cover the balance-crane with a strong
+tarpaulin in order to protect it as much as possible from the weather
+and also to make a temporary lightning-conductor from the top of
+the building to the sea.</p>
+
+<p>The extent of work done during the season of 1841 at the Rock,
+must in a great measure be attributed to the advantage of steam
+attendance, without which numerous favourable opportunities of
+landing materials must necessarily have been lost, from the uncertainty
+which pervades all the movements of sailing craft. The
+number of lighters towed out and discharged at the Rock was 120;
+and it is remarkable that no accident of importance occurred, although
+many risks were run, from the breaking of warps while the
+craft lay moored to the landing quay during heavy seas. I cannot
+omit in this place to record my sense of the services rendered
+to the works by the late Mr James Heddle, who commanded the
+steamer and who died from some consumptive disease soon after
+the close of the season’s operations. Mr Heddle’s health had been
+somewhat enfeebled towards the latter part of the autumn; and
+his excessive exertions and continued exposure during his arduous
+service, in some measure, I fear, hastened the crisis of his disease,
+which at length terminated suddenly by the rupture of an abscess<span class="pagenum" id="Page161">[161]</span>
+in the lungs. Of his anxiety to forward the work, and his unwearied
+exertion in the discharge of his harassing duty at Skerryvore,
+which frequently allowed him less than twenty hours sleep
+in a week, I cannot speak too highly, as I consider his intrepidity
+and zeal to have been one of the most efficient causes of our success
+ever since the commencement of the works on the Rock in
+1839. Mr Heddle possessed attainments superior to those generally
+found among persons in his walk of life and was in every respect
+a most estimable man.</p>
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page162">[162-<br>163]<a id="Page163"></a></span></p>
+
+<h3 class="nobreak"><span class="chapno">CHAPTER VIII.</span><br>
+<span class="chapname">OPERATIONS OF 1842.</span></h3>
+
+</div><!--chapter-->
+
+<p>On the 17th of April 1842, I made my first landing on the Skerryvore,
+for the season, <span class="sidenote">State of the
+Rock in Spring
+of 1842.</span>
+and found traces of very heavy seas having
+passed over the Rock during the preceding winter. Its surface was
+washed quite clean from all the scattered materials which were
+left lying on it at the end of the last season; and the building, to
+the height of 6 or 8 feet from the foundation, was covered with a
+thick coating of green sea-weed. The railway had suffered considerably
+from large stones having been thrown upon it; and several
+blocks of about half a ton in weight were found wedged into
+the deep fissures of the Rock, and lying among the main timbers
+of the Barrack. Heavy sprays had been playing over the Tower,
+in the upper uncovered apartment of which a great number of
+water-worn pebbles or boulders were found. Those stones had
+been raised by the heavy surf and deposited on the floor of the
+apartment and on the top of the wall at a height of no less than
+60 feet above high watermark; but the balance-crane, which had
+stood all winter on the top of the Tower, had sustained no damage,
+although the canvass cover was torn to shreds by the action of the
+weather. In the Barrack every thing was in good order except
+the smoke-funnel, which, from the effects of the sea-water, was
+riddled full of holes and required to be completely renewed.</p>
+
+<p>As I had resolved to keep, during the summer of 1842, a complement
+of about eighteen or twenty seamen on the Rock, in addition
+to the usual detachment of masons, in order to work the crabs<span class="pagenum" id="Page164">[164]</span>
+for raising the materials to the top of the Tower by successive
+stages; <span class="sidenote">Commencement
+of Rock operations.</span>
+my first step was to set about preparing additional accommodation
+in the Barrack, by converting the open gallery
+(called <i>store for coals</i>, &amp;c., in <a href="#Plate5">Plate V.</a>), immediately below the
+cook-house, into a covered apartment for lodgings for the additional
+hands. I accordingly landed on the 20th of April, with
+a stock of provisions, water and fuel and a party of joiners and
+a smith, to prepare that apartment by simply flooring over the
+joists of the gallery and closing the <i>triangular</i>, or rather <i>trapezoïdal</i>,
+spaces between the uprights of the Barrack, with double
+planking, protected on the seams with painted canvass, so as to
+render them impervious to the heavy sprays which, even in summer,
+dashed forcibly on the lower parts of the Barrack. Windows
+were formed on the sides least exposed to the intrusion
+of the sea; but, with all our precautions, we could not succeed in
+keeping dry even the cots or hammocks, which were suspended
+there; and it must be admitted that the addition to the Barrack
+proved, in bad weather, but a comfortless retreat, the inconveniences
+of which few but seamen would have patiently endured.
+Those discomforts, however, were to a certain extent, counterbalanced
+by some advantages which that singular abode possessed
+in hot weather; for, at such times, its inhabitants enjoyed more
+room, freer air, and more tolerable temperature, than any of their
+neighbours in the highest storey could obtain, owing to the greater
+number of persons in that part of the Barrack and its exposure to
+the heat of the cook’s stove.</p>
+
+<p>During the remainder of the month of April and the commencement
+of May we had frequent stiff gales; and it often happened
+that the men could not venture out of the Barrack, owing
+to the heavy sea which swept over the Rock. The crane, too,
+which had been erected at the wharf for unloading the stones, although
+its top stood about 8 feet above the Rock, was often buried
+in the breakers and seemed in hourly danger of being carried away,
+an event which we were the more ready to fear from our experience<span class="pagenum" id="Page165">[165]</span>
+in a former season, when the crane disappeared during a heavy
+westerly gale. The sea on those occasions also broke so heavily
+on the Barrack, that the windows of my apartment, which were
+about 55 feet above the sea, were often darkened by the sheet of
+water which flowed over them after the house had been struck by
+a wave. From those causes it was not till the 18th May that we
+were enabled to occupy the Rock in full force; and on the day following
+we commenced building the 38th course on the top of the
+last year’s work.</p>
+
+<p>After that period we had a long continuance of north-easterly
+winds, which always brought both smooth water for landing materials
+and dry weather for building; so that by the 23d of May
+our work had made such progress and the Tower had risen so
+high, that the chain of the balance-crane, which had been raised
+along with the building, by sliding it upwards on the cast-iron
+pillar or shaft placed in the centre of the Tower, could not reach
+the top of the <i>shear-poles</i>, by which the stones were raised to the
+level of about 40 feet above the Rock; and it was found necessary
+to rig from the lowest window a beam or <i>needle</i> (in the manner
+described at <a href="#Page155">page 155</a>, and as also shewn in Plate IX. of my
+Father’s <i>Account of the Bell-Rock Lighthouse</i>), as an intermediate
+stage between the top of the Tower and the shear-poles on the
+Rock. The needle, as already noticed, projected horizontally from
+the window and the stones were raised by a chain which passed
+over the sheave at its outer end and was wrought by means of a
+crab placed in the interior of the Tower. In that manner we continued
+for about six weeks, with little interruption from the weather,
+to raise the blocks of stone to the top of the Tower by successive
+needles from storey to storey; while the mortar, lewis-bats
+and other lighter materials were raised at once by means of a line
+wrought by a windlass placed on the Rock.</p>
+
+<p>On the night of Saturday the 9th of July, however, a heavy
+sea, caused by a combination of high tides and strong gales, threw
+down some of the stones of the belt course which lay piled up<span class="pagenum" id="Page166">[166]</span>
+round the base of the Tower ready to be raised for building; and
+they were with great difficulty, but most happily, saved from the
+insatiable deep. The loss of any of the stones of that course would
+have been a serious obstacle to the progress of the works and
+might have prevented our completing the erection of the lantern
+until next year; and indeed, as that course formed a prominent feature
+of the Tower, any slight injury even to the arris or corners of
+the outer face would have been much to be regretted. It was with
+great satisfaction, therefore, that it was found on examination
+next morning that none of the stones had sustained the slightest
+damage.</p>
+
+<p><span class="sidenote">Last Stone.</span>
+On the 21st July the last stones of the Tower were safely landed
+on the Rock, under a salute from the steamer, as an expression, no
+doubt, of the satisfaction which the commander Mr Kerr and his
+crew naturally felt at having successfully brought out not fewer
+than 75 lighter loads, or about 1500 tons, of stone during the season,
+as well as in some measure of their joy at the prospect of a
+speedy and happy termination of our arduous labours. The process
+of landing, indeed, owing to the fine weather that prevailed
+throughout the season, was very easy, compared with that of former
+years; in proof of which, I may state, that in 1841, there were
+often as many as five warps broken at a single landing, while in
+1842, not a single rope was broken in the discharging of the stones.
+On the 25th July the last stone of the parapet or top-course was
+built; and immediately thereafter we proceeded to remove from the
+Tower, the balance-crane and the cast-iron pillar on which it was
+swung, and to make way for the erection of the Lantern.</p>
+
+<p>In looking back upon the works we found great cause for
+thankfulness for the successful conclusion of the building operations,
+without loss of life, or even the occurrence of any serious
+accident, excepting the destruction of the first Barrack in November
+1839. It also gave me great satisfaction to reflect that, however
+difficult a rigid adherence to scrupulous accuracy of workmanship
+may be in such a situation as the Skerryvore, it had nevertheless,<span class="pagenum" id="Page167">[167]</span>
+from the exactness with which the stones were dressed,
+on no occasion been necessary, throughout the execution of the
+whole work, to deviate from the rule which I had laid down of
+carefully gauging the diameter of each course and of admitting no
+variation from the true form materially exceeding ¹⁄₈ inch. Every
+part of the stone work, indeed, was fitted in an accurate manner
+and the floor stones, in particular, which serve as <i>ties</i> across the
+building, were finely dressed and carefully set. All opportunities
+were also embraced, whenever it was practicable, to grout each
+course over night that the recent masonry might be in a state fit
+for building upon in the morning; and by those precautions and
+the peculiar properties of the mortar used, any disadvantages from
+very rapid building were entirely avoided. Even the elliptic
+cavetto which forms the cornice and which projects no less than
+three feet from the face of the wall, although bearing a very heavy
+<i>entablature</i> or <i>plinth</i>, never gave any signs of <i>settling</i> outwards; and
+when I examined it from a stage hung from the end of the balance-crane
+just before it was removed, there was no appearance of any
+change in the thickness of the joints, although the outer heads of
+the stones had been purposely kept a little high to allow for any
+tendency to settlement. The effect of the cornice is very bold
+and striking and is quite in accordance with the simple and almost
+severe style of the pillar itself. The masonry of the Tower is 137
+feet 11 inches in height and it contains 58,580 cubic feet or about
+4308 tons.</p>
+
+<p>The day after landing the last stone of the parapet, the steamer
+started from Tyree for Greenock, with two lighters in tow, for
+the transport of <span class="sidenote">The Lantern.</span>
+the Lantern; and by the 10th of August the whole
+was landed on the Rock. No time was lost in preparing the beds
+for the sole-plates of the Lantern, and that operation had been
+nearly completed when my Father, in the course of his annual
+tour of inspection, as Engineer for the Northern Lights, visited the
+Rock, two days after the iron work had been landed. By the
+16th the whole of the sashes and the frame of the roof were to<span class="pagenum" id="Page168">[168]</span>
+their places; and on the same day the fixtures of the lightning-conductor
+were completed. On the 18th of August Mr Bruce, the
+Sheriff of Argyll, and some gentlemen who accompanied him and
+had spent the preceding night at Hynish, visited the Rock; and,
+after breakfasting at the base of the Tower, ascended to the top
+and minutely inspected every part of the work. They afterwards
+returned to Hynish, whither I accompanied them and had an opportunity
+of pointing out to Mr Bruce the various works in progress
+there. The party sailed for Oban in the afternoon of the
+same day.</p>
+
+<p>From want of room on the Rock it was found necessary to
+build the roof of the Lantern in separate pieces instead of rivetting
+together the sheets of which it was composed on the ground, and
+raising the whole to the top in one mass, as is usually done; but, in
+spite of that disadvantage, the work was brought to a close for the
+season on the 14th September, on which day the glazing of the
+Lantern was completed and the glass was covered with a framework
+of timber to protect it from the sea-fowls which frequent in
+myriads the Rock and the Tower. The workmen were, on the
+same day, removed from the Rock, although with much difficulty,
+owing to the heavy surf which broke over the landing-place and
+rendered the embarkation more perilous than almost any I had
+before experienced at the Skerryvore.</p>
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page169">[169]</span></p>
+
+<h3 class="nobreak"><span class="chapno">CHAPTER IX.</span><br>
+<span class="chapname">CONCLUDING OPERATIONS AND EXHIBITION OF THE LIGHT.</span></h3>
+
+</div><!--chapter-->
+
+<p>The shores of Tyree, as already often noticed in these pages,
+and as deplored by Martin 140 years ago, in his Account of the
+Hebrides, afford few places of safety fit even for boats. It had
+therefore been determined, by the Commissioners, that any attempt
+at <span class="sidenote">Harbour Works.</span>
+the construction of a harbour should be strictly confined
+to the provision of a place of shelter for the vessel which was to
+attend the Lighthouse. Much attention had been bestowed on
+the subject, not merely by myself during my five years’ acquaintance
+with Tyree, but also by Mr Thomas Stevenson, who succeeded
+me in the charge of the works at Hynish, at the time
+when I was appointed Engineer to the Lighthouse Board in January
+1843, after the completion of the masonry of the Tower. A
+small sandy beach at Hynish, which lies embayed between rugged
+rocks, had been selected as the fittest place for the pier; and all
+the materials had been landed and shipped there, so that we naturally
+looked to it as the site for the projected harbour, not
+only as presenting works already finished, which might be made
+available as part of a more extended plan, but as a place which,
+during an experience of some years, had justified our anticipations
+as to its being less frequently disturbed during stormy weather
+than most of the neighbouring creeks. All that was contemplated
+in the proposed plan, was to form a small basin in which the vessel
+could lie sheltered in all states of the weather, and from which
+she could find an easy departure in any condition of the sea which<span class="pagenum" id="Page170">[170]</span>
+would permit a landing to be made on the Rock. The Skerryvore
+Steamer having been sold and a small vessel of 35 tons, named the
+“Francis,” having been purchased at Deal, the dock accommodation
+at Hynish was, for the sake of economy, laid out with reference
+to the shelter of that vessel. It was calculated that a basin
+100 feet in length and 50 feet wide, would afford sufficient room
+for such a vessel; and as her draught of water is between 7 and 8
+feet, it was thought sufficient to provide for a depth of about 12
+feet at high water of spring-tides, which, it was expected, would
+render the dock accessible during good springs at about <i>three
+quarters flood</i>.</p>
+
+<p>The exposure of the shore at Hynish, to the effects of heavy
+westerly swells, made it desirable to avoid carrying the entrance of
+the basin so far seaward, as, under more favourable circumstances,
+would undoubtedly have been done; and it was accordingly determined
+that the landing pier should be extended to about 40 feet
+seaward of low-water mark, and terminated in a round head, as
+shewn in <a href="#Plate10">Plate X.</a>, having a talus wall on its seaward face, composed
+of rough blocks, arranged in courses regularly receding, so
+as to form a slope of 45° of inclination, as shewn in <a href="#Plate11">Plate XI.</a>
+The inner face of that pier, being nearly vertical and guarded by
+fenders of timber, had served as the quay for landing and shipping
+stones and other stores and it now forms one side of the basin or
+dock. The other side consists of a shorter talus wall, built about
+60 feet to the westward of the first, and, together with the crossheads
+projecting from each wall and containing the gateway,
+completes the inclosure of the basin. In the gateway, <i>booms</i>
+are employed, as the shifting nature of the sand and the heavy
+seas render <i>gates</i> inadmissible. The space contained between
+those walls was left completely dry at low water of spring-tides,
+and was chiefly composed of rock, covered with a thin layer of
+shifting sand, which varied in depth with the state of the wind
+and sea. The rocky matter, consisting of decomposed gneiss,
+was excavated to the extent of about 5000 tons, in three separate<span class="pagenum" id="Page171">[171]</span>
+compartments, protected by successive dams of rubble masonry,
+built with Pozzolano mortar, and presenting an aggregate
+area of 7339 square feet. Those dams, two feet thick, proved
+so water-tight, that by the aid of a small hand-pump, the excavation
+and the building of the entrance heads of the booms went regularly
+forward without any delay, although the men worked in the
+bottom of the pit, surrounded on all sides by the sea, which, at
+high water of spring-tides, rose 17 feet above them. The dams
+were sheltered from the action of the swell by a temporary breakwater
+of heavy blocks, which formed a convenient roadway for the
+transport of the materials during the progress of the works, and
+which were removed at the close of the operations.</p>
+
+<p>The talus wall for protecting the seaward side of the harbour,
+has about 60 feet of its foundation laid in a depth of water
+varying at low spring-tides from 18 inches to 3¹⁄₂ feet. The mode
+of its construction, as already stated, is shewn in <a href="#Plate11">Plate XI.</a> It is
+surmounted by a strong parapet of rustic masonry of Mull granite,
+and is altogether a most substantial piece of work.</p>
+
+<p>The idea of a tide-basin with boom-gates facing the breach of
+Atlantic waves is somewhat novel and was not very hastily entertained
+by me at first; but the most complete success has attended
+the plan. During my occasional visits to the works in the
+course of the summer 1843, our attention had been often occupied
+with considering the probability of the sand shutting up the basin;
+and as a single tide during heavy winds from the N.W., made
+great changes on the appearance of the beach, we feared that the
+vessel might often be imprisoned within the boomgates by a bank
+of sand heaped against them by the sea. To such an extent did
+the accumulation go before the harbour was fully opened, that on
+many occasions there was not water for a rowboat to pass between
+the boom-heads even at the highest spring-tides. The only
+remedy for such an evil, was obviously to attempt some mode of
+artificial scouring; and for that purpose, it was proposed to divert
+several small streams which run from Ben Hynish and the neighbouring<span class="pagenum" id="Page172">[172]</span>
+hills through the grounds at Hynish, into one feeder, and
+pen them up in a pond, so as to afford the means of scouring the entrance
+to the basin from the incumbrance of the loose sand which
+might choke it. Those streams were repeatedly gauged during the
+summer and were found to deliver from 13 to 50 cubic feet of water
+per minute, according to the state of the weather,—a supply which
+seemed ample for the purpose in view. The sand at Hynish is
+of a light nature and is easily acted on by currents of very feeble
+power. It consists of comminuted shells and requires about 25¹⁄₂
+cubic feet to make a ton, instead of 24 feet, which is the common
+allowance for silicious sand. The leave of the Duke of Argyll and
+also of the Farmer at Hynish, having been obtained, various cuts
+were made and the stream was diverted into a pond capable of
+containing about 175,000 cubic feet and provided with a waste-weir
+and with sluices for opening the communication between the
+pond and the scouring tunnel, from which the water flows in a
+stream of about 9 square feet of area, at the rate of about 260 feet
+per minute for a period of 1¹⁄₄ hour. The operation of scouring is
+performed at low water and is generally found quite sufficient for
+the purpose of clearing a passage down to the bare rock in a single
+tide. Nothing can be more satisfactory than to witness the effect
+of that process in opening the entrance to a basin apparently inaccessible;
+and but for such an arrangement, the dock must have
+remained permanently choked with sand and sea-weed. The position
+of the various works is marked in <a href="#Plate10">Plate X.</a>, which shews the
+ground at Hynish.</p>
+
+<p>On the side of the dock stands a crane, which is used for various
+purposes connected with the shipment and discharging of
+materials. It also serves for raising the booms, by means of a
+double hook, which can be attached to the chain and which embraces
+the pegs in the centre of each boom, shewn in <a href="#Plate11">Plate XI.</a>
+The two tiers of booms are firmly lashed down by means of chains
+passing through ring-bolts in the manner shewn in the section
+(<a href="#Plate11">Plate XI.</a>), so as to prevent their rising with the tide.</p>
+
+<p><span class="pagenum" id="Page173">[173]</span></p>
+
+<p>The necessity of providing somewhere in the neighbouring
+island of Tyree for the proper accommodation of the vessel which
+was to wait upon the Lighthouse (if it could ever have been a matter
+of doubt), was abundantly demonstrated by the experience of
+1843, and more especially by that of the months of November and
+December. Owing to the shortness of the day and the distance
+of any place of shelter from the Skerryvore, together with the difficulty
+of landing on the Rock and the extreme variableness and
+uncertainty of the climate, the Regent Tender, although constantly
+waiting on the coast and making trials on every occasion that
+seemed to offer any prospect of success, could not effect any communication
+with the people who had been left on the Rock, during
+a period of no less than seven <i>long</i> weeks. The poor seamen
+who were living in the Barrack passed that time most drearily, for
+not only had their clothes been literally worn to rags, but they
+suffered the want of many things dearer to them than clothes, and
+amongst others of tobacco, the failure of the supply of which they
+had despondingly recorded in chalk on the walls of their prison-house,
+with the date of the occurrence! Unless, therefore, the
+vessel had been stationed near the rock, the few casual and uncertain
+opportunities which occur at intervals, during the short days
+of winter, would often have been lost, and the future maintenance
+of the Light rendered excessively precarious. The experience of
+subsequent years, during which the relief of the Light-keepers has
+been kept up with considerable regularity, shews that the small
+Harbour at Hynish forms a most important integral part of the
+Establishment of Skerryvore, than which I believe no Lighthouse
+on the coast is more comfortable as a residence.</p>
+
+<p>In connection with the Harbour at Hynish, I naturally notice
+the erection of a <span class="sidenote">Bo Pheg Beacon.</span>
+Beacon on a rock called Bo Pheg, which
+is dry only at low water of spring tides. It lies about one mile
+NE. from Hynish Point, (See <a href="#Plate2">Plates II.</a> and <a href="#Plate10">X.</a>) right in
+the track of the Tender in its passage to and from the Lighthouse.
+From the great difficulty of landing on that small rock,<span class="pagenum" id="Page174">[174]</span>
+over which the sea almost continually breaks, even in very
+fine weather, the shortness of the time during which the men
+could remain at work, and the want of room on its irregular surface
+of about 16 yards square, the erection of a beacon proved to
+be a work of great difficulty. The Beacon consisted of an open
+frame-work of iron, (somewhat on the same plan as that which
+is described in the Appendix) and calculated to offer little
+opposition to the free passage of the waves; but before all
+the fixtures could be completed, the heavy storms of the winter of
+1844, acting on its unfinished base (the bats of which were only
+partially secured), destroyed it piecemeal, at a season when no
+landing could be effected, nor any effort made to save almost any
+part of it from the sea. In the ensuing summer, a second Beacon,
+consisting of a hollow cone, composed of iron plates, united together
+by strong flanges and attached to the rock by <i>webbed flanges</i>
+round its base with strong bats passing through them, was fixed
+down to the rock; and in order to increase its weight, the interior
+was filled with concrete gravel. That structure also has since
+yielded to the force of the waves, after giving slight indications of
+movement, an effect which I attribute chiefly to the smallness of
+the base, which the narrow limits of the rock unhappily prescribe.</p>
+
+<p>Another necessary part of the Establishment at Hynish, was
+the provision of <span class="sidenote">Lightkeepers’ and
+Seamen’s House.</span>
+dwelling-houses for the families of the Lightkeepers
+and Seamen and of Storehouses of various kinds. Those
+were partly built on purpose and partly consisted of altered forms
+of the buildings which had been found necessary as barracks for
+workmen and stores for materials, during the progress of the works.</p>
+
+<p>On landing on the Rock, on the 29th of March 1843, the
+Resident Engineer had the satisfaction of finding the whole building
+perfectly water-tight and saw not the slightest trace of a defective
+joint. <span class="sidenote">Concluding works
+on the Rock, such
+as pointing, &amp;c.</span>
+The outside joints of the building were therefore
+carefully “ripped,” and repointed with mortar, composed of
+equal parts of Halkin lime and Pozzolano. That operation, from
+the difficulty of employing many men, where suspended scaffolds<span class="pagenum" id="Page175">[175]</span>
+were necessary and from the care with which it requires to be
+executed, occupied a great deal of time.</p>
+
+<p>Another tedious operation was the <span class="sidenote">Interior fittings of
+the Tower.</span>
+fitting up of the interior of
+the Tower with wainscot lining and forming the various stories
+into apartments separate from the staircase. Much work was also
+expended in providing the fire-places with proper flues, in fitting
+up water tanks, coal stores, and oil tanks, and also in conveying
+the air-tubes between the Lightroom and the several apartments
+by which the signal bells are rung for summoning the keepers to
+mount guard. The keeper on duty is, by the rules of the Service,
+forbidden, under penalty of instant dismissal, to leave the Light-room,
+on any pretext, until relieved by the next who mounts
+guard, and who is summoned by means of a bell placed inside his
+cot or sleeping berth, which is rung by means of a small piston,
+propelled by simply blowing into a mouth-piece in the Light-room.
+The keeper in bed answers this signal by a “<i>counter-blast</i>,” which
+rings another bell in the Light-room, and informs the keeper there
+that his signal has been heard and will be obeyed.</p>
+
+<p><span class="sidenote">Arrangement of
+the several apartments.</span>
+The general arrangement of the Tower, may be seen in the
+Section <a href="#Plate8">Plate VIII.</a>; and the details of its subdivision are very
+similar to those shewn in Plate XVI. of my Father’s Account of
+the Bell Rock Lighthouse. The ascent to the outside door is by
+a ladder or trap of gun metal, 26 feet high. The first apartment
+on the level of the entrance door, is chiefly appropriated to
+the reception of iron water-tanks, capable of holding a supply of
+1251 gallons. The next story is set aside for coals, which are
+stowed in large iron boxes. The third apartment is a workshop;
+the fourth is the provision store; and the fifth is the kitchen.
+Above are two stories, each divided into two sleeping apartments,
+for the four Light-keepers. Over them is the room for
+the Visiting Officers; then follows the oil store, and lastly comes the
+Lightroom, making in all twelve apartments. The nearness of the
+oil store to the Lightroom is a great convenience to the Keepers,
+who are thus saved the trouble of carrying the daily supply of oil<span class="pagenum" id="Page176">[176]</span>
+to the Lightroom, up a long flight of steps. The passage from
+story to story is by oaken trap ladders, passing through hatches
+in each floor and partitioned off from each apartment in order to
+prevent accidents and to check cold draughts.</p>
+
+<p><span class="sidenote">Lightroom Apparatus,
+and first exhibition
+of the
+Light.</span>
+The light of Skerryvore was exhibited to the mariner on the
+night of the 1st February 1844, in terms of the <a href="#App5">Statutory Notice</a>,
+which will be found in the Appendix. The light is revolving,
+appearing in its brightest state once in every minute of time. It
+is elevated 150 feet above the sea, and is well seen as far as the
+curvature of the earth permits; it is also frequently seen as a
+brilliant light from the high land of Barra, a distance of 38 miles.
+The apparatus consists of eight annular lenses (of the first order, in
+the system of <span class="smcap">Augustin Fresnel</span>), of 36·22 inches focal distance,
+revolving round a lamp with four concentric wicks, and producing
+a bright blaze when each lens passes between the lamp and the
+eye of a distant observer. Above those lenses are placed eight
+pyramidal lenses of 19·68 inches focal distance, inclined at 50°
+with the horizon and combined with eight plane mirrors, inclined
+in the opposite direction at 50° with the horizon. By this arrangement,
+that part of the light from the lamp which would
+otherwise escape uselessly beyond the great lenses, upwards into
+the sky, being parallelized in its passage through the smaller
+lenses and falling on the mirrors, is finally projected forwards
+in horizontal beams, so as to aid the effect of the light. Those
+lenses and mirrors, however, instead of having their axes in the
+same vertical plane with the axes of the principal lenses, are inclined
+about 7° horizontally to the right hand, and by that deviation
+produce small premonitory blazes, which, blending with the
+beams of the larger lenses, tend in some measure to lengthen the
+duration of the impression on the eye. So far the apparatus of the
+Skerryvore Lighthouse is identical in its general arrangements
+with that of the Tour de Corduan, and differs only in the superior
+workmanship of the lenses and the machinery, which the experience
+of more than twenty years has brought about, since <span class="smcap">Fresnel<span class="pagenum" id="Page177">[177]</span></span>
+designed that light in 1822. Instead, however, of employing
+curved mirrors, as has been done at Corduan, to collect the
+light which would otherwise escape below the lenses and, at the
+same time, to send it to the horizon, I determined to put in
+practice a plan which I had long contemplated, of placing totally
+reflecting zones below the lenses, similar in construction
+to the zones of the small Harbour Light Apparatus of the fourth
+order, which was also invented by <span class="smcap">Fresnel</span>. This was finally
+carried into effect, agreeably to the design of <span class="smcap">M. Leonor Fresnel</span>,
+his brother, with whom I had corresponded on the subject. In the
+subsequent pages of this volume, I intend to make some observations
+explanatory of the principles and arrangement of the various optical
+instruments employed in Lighthouses; and as that will afford
+me a more convenient opportunity of describing the nature and properties
+of the <i>totally reflecting zones</i>, I shall forbear in this place to
+enter into further details as to the construction or action of the
+apparatus at the Skerryvore. It is right, however, that I should
+mention here that the lenses, mirrors and zones are from the works
+of <span class="smcap">M. François</span> of Paris, whose name I shall afterwards have
+occasion to notice; and that the machinery was constructed to my
+entire satisfaction, and in a manner worthy of his reputation as a
+mechanician, by Mr <span class="smcap">John Milne</span> of Edinburgh.</p>
+
+<p>In such a situation as the Skerryvore, new wants were discovered
+every day; and each summer brought its round of smaller
+works, which the experience of the preceding winter had suggested.
+The Barrack was found very useful as a place of residence
+for the workmen, who were engaged in such needful works;
+and it was not until the summer of 1846, <span class="sidenote">Removal of the
+Barrack from the
+Rock.</span>
+that it was taken to
+pieces and removed from the Rock, after having kept its place for
+six years. Its removal, however, was then thought advisable, as
+some of its fixtures, by the continual action of the weather, had
+become very loose and precarious; and, although a very small outlay
+would have made it almost as stable as at first, it was considered
+inexpedient to attempt to perpetuate a structure confessedly<span class="pagenum" id="Page178">[178]</span>
+temporary in its nature, and the sudden destruction of which
+by the waves, seemed to involve some risk of injury to the Tower
+itself.</p>
+
+<p><span class="sidenote">Expense.</span>
+The expense of erecting the Skerryvore Lighthouse, including
+the opening of quarries and forming wharfs at the quarries in Mull
+and also the Harbour in Tyree, was, as appears from the <a href="#App6">Account</a>
+in the Appendix, L.86,977&#160;: 17&#160;: 7.</p>
+
+<p>In the course of the Summer of 1844, a marble tablet, bearing an
+inscription in letters of gold, was, by order of the Commissioners,
+placed over one of the windows in the Visiting Officers’ Room.
+With a <a href="#Fig21a">representation</a> of the Tablet and the Inscription, which,
+after acknowledging the hand of Almighty God in the success
+which attended the work, briefly sets forth the beneficent purposes
+for which the Lighthouse was erected and records the laying
+of the foundation-stone by his Grace the Duke of Argyll, I willingly
+close this most defective narrative of the work.</p>
+
+<div class="container w25emmax" id="Fig21a">
+
+<img src="images/illo178.jpg" alt="Tablet with inscription">
+
+<p class="center fsize80"><i>Engraved by W. &amp; A.K. Johnston</i></p>
+
+<div class="illotext sstype">
+
+<p class="center">IN SALUTEM OMNIUM<br>
+NORTHERN LIGHTHOUSES</p>
+
+<p class="center blankbefore75">A. D. O. M.</p>
+
+<p class="center blankbefore75">AUCTORITATE . ET . CONCILIIS<br>
+PHARORUM . SCOTIAE . COLLEGII<br>
+HAEC . STRUCTA . FUIT . PHAROS<br>
+CUJUS . DIRECTI . FLAMMA<br>
+NAUTAE<br>
+INFAMIBUS . HIS . SCOPULIS . ADHUC . MERITO . DETERRITI<br>
+OPTATUM . PORTUM . RECTIUS . ADVENIRENT.</p>
+
+<p class="center blankbefore75">JOANNES . DUX . DE . ARGYLL<br>
+INSULARUM . ADJACENTIUM . DOMINUS<br>
+LAPIDEM . AUSPICALEM . RITE . STATUIT<br>
+DIE . IV . MENSIS . JULII . ANNO . IV . VICT. REG.<br>
+M . D . C . C . C . X . L .<br>
+OPERUM . MAGISTRO . ALANO . STEVENSON . L.L.B.</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page179">[179]</span></p>
+
+<p class="center highline4 gesp1"><span class="fsize125">PART SECOND.<br>
+<span class="gesp1">NOTES</span></span><br>
+<span class="fsize60">ON THE</span><br>
+<span class="fsize125"><span class="gesp1">ILLUMINATION OF LIGHTHOUSES</span>.</span></p>
+
+<hr class="chap x-ebookmaker-drop">
+
+</div><!--chapter-->
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page180">[180-<br>181]<a id="Page181"></a></span></p>
+
+<h2 class="nobreak"><span class="partno">PART SECOND.</span><br>
+<span class="chapname">NOTES ON THE ILLUMINATION OF LIGHTHOUSES, WITH SHORT
+NOTICES OF THEIR EARLY HISTORY.</span></h2>
+
+</div><!--chapter-->
+
+<p><span class="sidenote">Early History.</span>
+The early history of Lighthouses is very uncertain; and some
+ingenious antiquaries, finding the want of authentic records, have
+been anxious to supply the deficiency by conjectures based upon
+casual and obscure allusions in ancient writers, and by vague hypotheses
+drawn from the heathen mythology. Some writers have gone
+so far as to imagine, that the Cyclopes were the keepers of lighthouses;
+whilst others have actually maintained that Cyclops was intended,
+by a bold prosopopœia, to represent a lighthouse itself.<a id="FNanchor24" href="#Footnote24" class="fnanchor">[24]</a>
+A notion so fanciful deserves little consideration; and accords very
+ill with that mythology of which it is intended to be an exposition,
+as seems sufficiently plain from a passage in the ninth Odyssey,
+where Homer (who flourished about 907 B. C.), after describing
+the darkness of the night, informs us that the fleet of Ulysses actually
+struck the shore of the Cyclopean island, before it could be seen.<a id="FNanchor25" href="#Footnote25" class="fnanchor">[25]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote24" href="#FNanchor24" class="label">[24]</a> This spirit of etymological
+conjecture has converted <i>Cyclops</i>, <i>Proteus</i>, <i>Cneph</i>, <i>Phanes</i>,
+<i>Canobus</i>, <i>Chiron</i>, <i>Tithonus</i>, <i>Thetis</i>, <i>Amphitrite</i>, <i>Minotaurus</i>, <i>Chronus</i>, <i>Phrontis</i>, and other
+demigods, into celebrated lighthouses, or, at all events, has imagined that those mythological
+personages were worshipped under the emblem of fire or light in buildings, which, at
+the same time, served as guides to the benighted mariner. On the faith, also, of similar
+obscure and finely drawn etymologies, various places, such as <i>Calpe</i> and <i>Abyla</i>, the opposite
+points of Africa and Europe, at the Straits of the Mediterranean, have been unhesitatingly
+recognized as the sites of celebrated light-towers; and the Latin words <i>turris</i> and
+<i>columna</i> have been supposed primarily to signify a lighthouse, the first being written <i>Tor-is</i>,
+the <i>Tower of fire</i>, and the <i>Col-on</i>, the <i>Pillar of the Sun</i>.</p>
+
+<p><a id="Footnote25" href="#FNanchor25" class="label">[25]</a></p>
+
+<div class="poetry-container">
+
+<div class="poetry">
+
+<div class="stanza">
+
+<div class="verse indent0">Ἔνθ’ ὄυτις τὴν νῆσον ἐσέδρακεν ὀφθαλμοῒσιν</div>
+<div class="verse indent0">Ὅυτ’ οὖν κύματα μακρὰ κυλινδόμενα ποτὶ χέρσον</div>
+<div class="verse indent0">Ἐισίδομεν πρὶν νῆας ἐϋσσέλμους ἐπικελσαι.</div>
+
+</div><!--stanza-->
+
+</div><!--poetry-->
+
+<p class="poemcredit"><i>Odyss.</i>, ix., 146.</p>
+
+</div><!--poetry-container-->
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page182">[182]</span></p>
+
+<p>Nor does there appear any better reason for supposing, that
+under the history of Tithonus, Chiron, or any other personage of
+antiquity, the idea of a lighthouse was conveyed; for such suppositions,
+however reconcileable they may appear with some parts
+of mythology, involve obvious inconsistencies with others. It
+seems, indeed, most improbable, that, in those early times, when
+navigation was so little practised, the advantages of beacon lights
+were so generally known and acknowledged as to render them the
+objects of mythological allegory.</p>
+
+<p>It must not, however, be imagined, that ancient writings are
+entirely destitute of allusions to the subject of Beacon Lights for
+the guidance of the Mariner. The venerable poet, already noticed,
+in speaking of the shield of Achilles, has beautifully described the
+flash of a beacon-light in some solitary place, as seen by seamen
+leaving their friends, in those lines, which contain ample proof of
+the existence of such a provision for the safety of the mariner in
+Homer’s <span class="nowrap">time:—</span></p>
+
+<div class="poetry-container">
+
+<div class="poetry">
+
+<div class="stanza">
+
+<div class="verse indent0">Ὣς δ’ ὅταν ἐκ πόντοιο σέλας ναύτῃσι φανείη</div>
+<div class="verse indent0">Καιομένοιο πυρὸς, τὸ δὲ καίεται ὑψόθ’ ὄρεσφι,</div>
+<div class="verse indent0">Σταθμῷ ἐν οἰοπόλῳ· τοὺς δ’ οὐκ ἐθέλοντας ἄελλαι</div>
+<div class="verse indent0">Πόντον ἐπ’ ἰχθυόεντα φίλων ἀπάνευθε φέρουσιν.</div>
+
+</div><!--stanza-->
+
+</div><!--poetry-->
+
+<p class="poemcredit"><i>Il.</i>, xix., 375.</p>
+
+</div><!--poetry-container-->
+
+<p>In the Holy Scriptures the word <i>Beacon</i> occurs but once, and
+that in Prophecies of Isaiah (xxx. 17.), who lived above 200
+years later than Homer; but it is obvious that the original term,
+which the Septuagint translate by the word ἱστος, merely imports
+a flagstaff or perch and does not at all imply the knowledge
+of beacon-lights among the Hebrews, who were not a maritime
+people.</p>
+
+<p><span class="sidenote">Colossus of
+Rhodes.</span>
+About 300 years before the Christian era, Chares, the disciple
+of Lysippus, constructed the celebrated brazen statue, called
+the Colossus of Rhodes. It was of such dimensions as to allow
+vessels to sail into the harbour between its legs, which spanned<span class="pagenum" id="Page183">[183]</span>
+the entrance. There is considerable probability in the idea that
+this figure served the purposes of a lighthouse; but there is no
+passage in any ancient writer, where this use of the Colossus is
+expressly mentioned. Many inconsistencies occur in the account
+of this fabric by early writers, who, in describing the distant objects
+which could be seen from it, appear to have forgotten the
+height which they assign to the figure. It was partly demolished
+by an earthquake, about eighty years after its completion; and so
+late as the year 672 of our era, the brass of which it was composed
+was sold by the Saracens to a Jewish merchant of Edessa, for a
+sum, it is said, equal to L.36,000.</p>
+
+<p><span class="sidenote">Pharos of Alexandria.</span>
+Little is known with certainty regarding the Pharos of Alexandria,
+which was regarded by the ancients as one of the seven
+wonders of the world. It was built in the reign of Ptolemy Philadelphus,
+about 300 years before the Christian era; and Strabo
+relates that Sostratus, a friend of the royal family, was the architect.
+He describes it as built in a wonderful manner in many stories
+of white stone, on a rock forming the promontory of the island
+Pharos (whence the Tower derived its name), and says that
+the building bore the inscription—<a id="Ref1"></a>“Sostratus of Cnidos, the son of
+Dexiphanes, to the Gods, the Saviours, for the benefit of seamen.”
+He concludes his brief notice of it by describing the neighbouring
+shores as low and encumbered with shoals and snares, and as calling
+for the establishment of a lofty and bright beacon, a sign to
+guide sailors arriving from the ocean into the entrance to the
+haven.<a id="FNanchor26" href="#Footnote26" class="fnanchor">[26]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote26" href="#FNanchor26" class="label">[26]</a> The passage from which the above description is drawn will be found in the Oxford
+edition of Strabo, 1807, page 1123. It is as follows: Ἔστι δε και ἀυτο τὸ τῆς νησίδος ἄχρον
+πετρα πολυκλύστος, ἔχουσα πῦργον θαυμαστῶς κατεσκευασμένον λευκου λιθου, πολυοροφον, ὁμωνυμον τῇ
+νὴσῳ· τουτον δε ἄνέθηκε Σωστρατος Κνὶδιος φιλος τῶν βασιλεων, της των πλωϊζομενων σωτηριας χαριν, ὥς
+φησιν ἥ ἐπιγραφη Επιγραμμα, ΣΩΣΤΡΑΤΟΣ ΚΝΙΔΙΟΣ ΔΕΧΙΦΑΝΟΥΣ, ΘΕΟΙΣ ΣΩΤΗΡΣΙΝ
+ΥΠΕΡ ΤΩΝ ΠΑΩΙΖΟΜΕΝΩΝ. Ἀλιμένου γαρ ὄυσης και ταπεινῆς της ἕκατέρωθεν παραλίας, ἐχουσης
+δε και χοιράδας και βράχη τινὰ, ἔδει σημεὶου τινος ὑψηλου και λαμπρου, τοις ἀπὸ του πελάγους προσπλέουσιν,
+ὥστ’ ἐυστοχειν της ἐισβολης του λιμενος. Strabo’s account of the position of the island of
+Pharos at once leads to the conclusion of its having formed part of the harbour of Alexandria
+(as is abundantly testified by Josephus, Pliny, and other writers), and cannot be easily
+reconciled with that of Homer (fourth Odyssey, l. 354), who describes the island as a day’s
+sail with a fair wind from the mainland. His words are as <span class="nowrap">follows:—</span></p>
+
+<div class="poetry-container">
+
+<div class="poetry">
+
+<div class="stanza">
+
+<div class="verse indent0">Νῆσος ἔπειτά τις ἐστὶ πολυκλύστῳ ἐνὶ πόντῳ</div>
+<div class="verse indent0">Αἰγύπτου προπάροιθε (Φάρον δέ ἑ κικλήσkουσι)</div>
+<div class="verse indent0">Τοσσον δ’ ἂνευθ’ ὄσσον τεπανημέριη γλαφυρὴ νηῦς</div>
+<div class="verse indent0">Ἤνυσεν, ᾗ λιγὺς οὖρος ἐπιπνέιῃσιν ὂπισθεν.</div>
+
+</div><!--stanza-->
+
+</div><!--poetry-->
+
+<p class="poemcredit"><i>Odyssey</i>, iv., l. 354.</p>
+
+</div><!--poetry-container-->
+
+<p class="noindent">Pliny, however, does not scruple to identify the Pharos of Homer’s time with that of his
+own day. “Pharos,” says he, “quondam diei navigatione distans ab Ægypto, nunc è turri
+nocturnis ignibus cursum navium regens.” Hist. Nat., v. 31; see also Hist. Nat., ii. 87,
+and xiii. 21.</p>
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page184">[184]</span></p>
+
+<p>The accounts which have come down to us of the dimensions
+of this remarkable edifice are exceedingly various; and the statements
+of the distance at which it could be seen are clearly fabulous.
+That of Josephus (who likens it to the second of Herod’s
+three Towers at Jerusalem, called Phasael, in honour of his brother)
+is the least removed from probability; yet even he informs us, that
+the fire which burnt on the top to enable seamen to anchor in sight
+of it, before coming near the shore, and so to avoid the difficulty of
+the navigation by night, was visible at a distance equal to about
+thirty-four English miles. Such a range for a lighthouse on the low
+shores of Egypt, would require a tower about 550 feet in height!<a id="FNanchor27" href="#Footnote27" class="fnanchor">[27]</a>
+Ammianus Marcellinus<a id="FNanchor28" href="#Footnote28" class="fnanchor">[28]</a> and Pliny<a id="FNanchor29" href="#Footnote29" class="fnanchor">[29]</a>
+are both very circumstantial<span class="pagenum" id="Page185">[185]</span>
+in their notices of the Pharos as a beacon-light to guide seamen in
+approaching the coast of Egypt and port of Alexandria. The latter
+adds the interesting fact, that the cost of the Tower was
+reckoned at a sum equal to about L.390,000 of our money;<a id="FNanchor30" href="#Footnote30" class="fnanchor">[30]</a> and
+both of them agree in stating that a light was shewn from it at night.
+Ammianus Marcellinus differs from all the other writers, in attributing
+the erection of the Tower to Queen Cleopatra. Pliny mentions
+in passing, that there were also lighthouses at Ostia and Ravenna.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote27" href="#FNanchor27" class="label">[27]</a> Bell. Judaic. iv., cap. 10, sec. 5. (Havercamp’s Josephus, tom. ii., p. 309. Amsterdam,
+1726.) ἐν δεξιᾳ δε ἡ προσαγορευομενη Φαρος νησις προκειται, πῦργον ανἐχουσα μεγιστον,
+εκπυρσευοντα τοις καταπλὲουσιν, ἐπι τριακοσιους σταδιους, ὤς ἐν νυκτὶ πὂρρωθεν ὁρμιζοιντο προς την δυσχέρειαν
+του καταπλοῦ. And again, in the sixth Book of the same History (v. 4, sec. 3, tom. ii.,
+p. 330), he says, και τὸ μεν σχημα παρεῴκει τῳ κατα τὴν Φαρον ἐκπυρσεὐοντι τοις επ’ Αλεξανδρείας
+πλέουσι. The height of the Tower in the text proceeds on the idea of the observer’s eye
+being ten feet above the sea.</p>
+
+<p><a id="Footnote28" href="#FNanchor28" class="label">[28]</a> Ammianus Marcellinus, l. xxii., c. 16. (Leipsic 1807, tom. i., p. 306.) Hoc littus
+cum fallacibus et insidiosis accessibus affligeret antehac navigantes discriminibus plurimis,
+excogitavit in portu Cleopatra turrim excelsam, quae Pharos a loco ipso cognominatur,
+praelucendi navibus nocturna suggerens ministeria; cum, quondam ex Parthenio
+pelago venientes aut Libyco, per pandas oras et patulas, montium nullas speculas vel
+collium signa cernentes, harenarum inlisae glutinosae mollitiae frangerentur.</p>
+
+<p><a id="Footnote29" href="#FNanchor29" class="label">[29]</a> Plinii Hist. Nat., xxxvi. 18. (Paris, 1723, p. 739.) Magnificatur et alia turris
+a rege facta in insula Pharo portum obtinente Alexandriae, quam constitisse octingentis
+talentis tradunt; magno animo (nequid omittamus) Ptolemai regis, quod in ea permiserit
+Sostrati Guidii Architecti structuræ ipsius nomen inscribi. Usus ejus, nocturno navium
+cursu ignes ostendere ad praenuncianda vada portûsque introïtum: quales, jam compluribus
+locis flagrant, ut Ostiae ac Ravennae. Periculum in continuatione ignium, ne sidus
+existimetur, quoniam è longinquo similis flammarum aspectus est.</p>
+
+<p><a id="Footnote30" href="#FNanchor30" class="label">[30]</a> Supposing, as is most probable, that Pliny means the <i>Egyptian</i> talent; the <i>Attic</i>
+talent was about one-half the value of the other.</p>
+
+</div><!--footnote-->
+
+<p>If the reports of some writers are to be believed, this Tower
+must have far exceeded in size the great Pyramid itself; but the
+fact that a building of comparatively so late a date should have so
+completely disappeared, whilst the Pyramid remains almost unchanged,
+is a sufficient reason for rejecting, as erroneous, the dimensions
+which have been assigned by most writers to the Pharos
+of Alexandria. Some have pretended that large mirrors were employed
+to direct the rays of the beacon-light on its top, in the
+most advantageous direction; but, in so far as I know, there is no
+definite evidence in favour of this supposition. Others, with
+greater probability, have imagined that this celebrated beacon was
+known to mariners, simply by the uncertain and rude light afforded
+by a common fire. In speaking of the Pharos, the poet Lucian, on
+most occasions sufficiently fond of the marvellous, takes no notice
+of the gigantic mirrors which it is said to have contained. He thus
+speaks of this celebrated lighthouse as having indicated to Julius
+Cæsar his approach to the Pharos of Egypt on the seventh night
+after he sailed from Troy:</p>
+
+<div class="poetry-container">
+
+<div class="poetry">
+
+<div class="stanza">
+
+<div class="verse indent0">Septima nox, Zephyro nunquam laxante rudentes,</div>
+<div class="verse indent0">Ostendit Phariis Ægyptia littora <i>flammis</i>.</div>
+<div class="verse indent0">Sed prius orta dies nocturna <i>lampada</i> texit,</div>
+<div class="verse indent0">Quam tutas intraret aquas.</div>
+
+</div><!--stanza-->
+
+</div><!--poetry-->
+
+<p class="poemcredit"><i>Pharsal.</i>, ix., 1004.</p>
+
+</div><!--poetry-container-->
+
+<p><span class="pagenum" id="Page186">[186]</span></p>
+
+<p class="noindent">It is true that, by using the word “<i>lampada</i>,” which can only
+with propriety be applied to a more perfect mode of illumination
+than an open fire, he appears to indicate that the “<i>flammis</i>” of
+which he speaks, were not so produced. The word <i>lampada</i> may
+however, be used metaphorically; and <i>flammis</i> would, in this case,
+not improperly describe the irregular appearance of a common fire.</p>
+
+<p>Perhaps, also, the opinion that some kind of lamp was used in
+the Pharos, may seem to receive countenance from the remarkable
+words of Pliny, in the passage above cited—“Periculum in continuatione
+ignium, ne sidus existimetur, quoniam è longinquo similis
+flammarum aspectus est.” The fear he expresses lest the light
+viewed from a distance should be mistaken for a star, could hardly
+be applicable to the diffuse, oscillating, lambent light derived from
+an open fire, and certainly gives some reason for imagining that,
+even at that remote time, the art of illuminating lighthouses was
+better understood than in the early part of the present century.</p>
+
+<p>Before leaving the subject of the Pharos of Alexandria, I wish
+to vindicate the memory of its architect Sostratus from the calumny
+of Lucian, who, in his Treatise on the art of writing history, with
+his usual acrimony, accuses the builder of the Pharos of a fraud, in
+cutting his own name on the solid walls of the Tower, and covering
+the inscription with plaster, on which he carved the name of
+his royal master Ptolemy.<a id="FNanchor31" href="#Footnote31" class="fnanchor">[31]</a> Against this assertion I would oppose
+the testimony of Strabo, who calls Sostratus the “friend of the
+Kings” (see the <a href="#Ref1">quotation</a> at the foot of page 183), and the direct
+evidence of Pliny, who, in the passage above cited, expressly states,
+as a proof of Ptolemy’s magnanimity, his giving the architect liberty<span class="pagenum" id="Page187">[187]</span>
+to inscribe his own name on the Tower. The only other notices
+of the Pharos which I have been able to find in ancient writers
+are from Cæsar’s Commentaries, Valerius Flaccus, and Pomponius
+Mela.<a id="FNanchor32" href="#Footnote32" class="fnanchor">[32]</a> At Alexandria, there is a modern lighthouse called the
+Pharos, which is maintained by the Pacha of Egypt.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote31" href="#FNanchor31" class="label">[31]</a> Lucian, in his Treatise (Amsterdam, 1743, vol. ii., p. 68.) Πως δει ἱστοριαν συγγραφειν, thus
+details the merit and fraud of Sostratus. Ορᾷς τον Κνίδιον ἐκεῖνον ἀρχιτεκτονα, οἶον ἐποίησεν;
+οἰκοδομὴσας γαρ τον ἐπὶ τῇ Φαρῳ πῦργον, μεγιστον και καλλιστον ἔργων ἀπαντων, ὡς πυρσεύοιτο ἀπ’ αὐτου
+τοις ναυτιλλομενοις, ἐπὶ πολὺ της θαλασσης, και μὴ καταφέροιντο εἰς την Παραιτονίαν, παγχάλεπον, ὣς
+φασιν, οὖσαν και ἄφυκτον, εἴ τις ἐμπεσοι εἴς τα, ἕρματα. Οἰκοδομήσας οὐν το ἔργον, ἔνδοθεν μεν, κατα
+των λιθων, το αὐτου ὄνομα ἐπέγραψεν. Ἐπιχρίσας δὲ τιτάνῳ και ἐπικαλύψας, ἐπέγραψε το ὀνομα του
+τότε βασιλέυοντος, εἰδὼς, ὃσπερ και ἐγενετο, πάνυ ὀλιγου χρονου, συνεκπεσουμενα μεν τῳ χρισματι τα γραμματα,
+εκφανησόμενον δε ΣΩΣΤΡΑΤΟΣ ΔΕΧΙΦΑΝΟΥΣ Κνιδιος. θεοις σωτηρσιν ὑπερ των πλωΐζομεων, κ.τ.λ.</p>
+
+<p><a id="Footnote32" href="#FNanchor32" class="label">[32]</a> Cæsar de Bell. Civil., iii. 98 (Lond. 1712, p. 355). Pharus est in insula turris,
+magna altitudine, mirificis operibus extructa, quae nomen ab insula accepit.</p>
+
+<p>Valerius Flaccus very distinctly sets forth the great advantage of lighthouses to the
+seaman, and especially speaks of those at Alexandria and Ostia in these <span class="nowrap">lines—</span></p>
+
+<div class="poetry-container">
+
+<div class="poetry">
+
+<div class="stanza">
+
+<div class="verse indent0">Non ita Tyrrhenus stupet Ioniusve magister,</div>
+<div class="verse indent0">Qui portus, Tyberine, tuos, claramque serenâ</div>
+<div class="verse indent0">Arce Pharon præceps subiit:</div>
+
+</div><!--stanza-->
+
+</div><!--poetry-->
+
+<p class="poemcredit"><i>Argonaut</i>, vii., v. 84.</p>
+
+</div><!--poetry-container-->
+
+<p>Pompon. Mela, ii. cap. 7.</p>
+
+</div><!--footnote-->
+
+<p><span class="sidenote">Coruña Tower</span>
+Mr Moore, in his <i>History of Ireland</i>, vol. i., p. 16, speaks of
+the Tower of Coruña, which he says is mentioned in the traditionary
+history of that country, as a lighthouse erected for the use of
+the Irish in their frequent early intercourse with Spain. In confirmation
+of this opinion, he cites a somewhat obscure passage from
+Æthicus, the cosmographer. This in all probability is the tower
+which Humboldt mentions in his Narrative under the name of the
+<i>Iron Tower</i>, which was built as a lighthouse by Caius Saevius Lupus,
+an architect of the city of Aqua Flavia, the modern Chaves.<a id="FNanchor33" href="#Footnote33" class="fnanchor">[33]</a>
+<span class="pagenum" id="Page188">[188]</span>
+A Lighthouse has lately been established on this headland, for
+which Dioptric apparatus was supplied from the workshop of M.
+<span class="smcap">Letourneau</span> of Paris.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote33" href="#FNanchor33" class="label">[33]</a> “The traditionary history,” says Mr Moore, “of the latter country (Ireland) gives
+an account of an ancient Pharos or lighthouse erected in the neighbourhood of the port now
+called Coruña, for the use of navigators on their passage between that coast and Ireland.
+There is a remarkable coincidence between this tradition and an account given by Æthicus,
+the cosmographer, of a lofty Pharos or lighthouse standing formerly on the sea-coast of
+Gallicia, and serving as a beacon in the direction of Britain. <i>Secundus Angulus intendit
+ubi Brigantia civitas sita est Galliciae, et altissimum Pharum et inter pauca memorandi
+operis ad speculum Britanniae.</i> Whether the translation I have given of the last three
+words of this passage convey their real meaning, I know not; but they have been hitherto
+pronounced unintelligible. The passage is thus noticed by Casaubon, in a note on Strabo,
+lib. iii. ‘Æthicus in Hispaniae descriptione altissimi cujusdam Fari meminit.’” The passage
+in Strabo above referred to is on page 179 of the first volume of the Oxford folio edition
+of 1807, where the geographer speaks of Cape Νεριον, which Casaubon distinctly identifies
+with the <i>Cabo de Finisterra</i> of modern seamen.</p>
+
+</div><!--footnote-->
+
+<p>There is also a record in Strabo of a magnificent lighthouse of
+stone at <span class="sidenote">Lighthouse at the
+mouth of the Guadalquivir.</span>
+Capio, or Apio, near the Harbour of Menestheus (the modern
+Mesa Asta, or Puerto de Sta. Maria), which he describes as
+built on a rock nearly surrounded by the sea, as a guide for the
+shallows at the mouth of the Guadalquivir, in terms almost identical
+with those used by him in speaking of the Pharos of Alexandria.
+I am not aware of any other notice of this great work, for
+such it seems to have been, to have deserved the praises of Strabo.<a id="FNanchor34" href="#Footnote34" class="fnanchor">[34]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote34" href="#FNanchor34" class="label">[34]</a> The words of Strabo are (Oxon. 1807, p. 184), Και ὁ του Καπὶωνος (vel Ἀπιωνος)
+πὺργος ἵδρυται ἐπι πέτρας ἀμφκλυστου, θαυμασιως κατεσκευασμένος, ὥσπερ ό Φαρος τῆς των πλωϊζομενων
+σωτηριας χαριν, ῃ τε γαρ ἐκβαλλομενη χους ὕπο του ποταμου βραχεα ποιει και χοιραδωδης ἐστὶν
+ὁ πρὸ ἀυτου τοπος ὥστε δει σημειου τινος ἐπιφανοῦς.</p>
+
+</div><!--footnote-->
+
+<p><span class="sidenote">Ancient Phari in
+Britain.</span>
+In Camden’s Britannia, a passing notice is taken of the ruins
+called <i>Cæsar’s Altar</i>, at Dover, and of the <i>Tour d’Ordre</i>, at Boulogne,
+on the opposite coast; both of which are conjectured to
+have been ancient lighthouses. Pennant describes the remains of
+a Roman Pharos near Holywell, but cites no authorities for his
+opinion as to its use. There were likewise remains of a similar
+structure at Flamborough-head. A very meagre and unintelligible
+account is also given of a lighthouse at St Edmund’s Chapel, on
+the coast of Norfolk, in Gough’s additions to Camden, by which it
+might seem that the lighthouse was erected in 1272.<a id="FNanchor35" href="#Footnote35" class="fnanchor">[35]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote35" href="#FNanchor35" class="label">[35]</a> Gough’s Camden’s Britannia, vol. i., 318, and vol. ii., p. 198; Batcheller, in his
+Dover Guide (1845, p. 111), says, that the Dover Pharos was built “during the lieutenancy
+of Aulus Plautius and Ostorius Scapula, the latter of whom left Britain, <span class="allsmcap">A. D.</span> 53.”—Pennant’s
+History of Whiteford and Holywell, p. 112.</p>
+
+</div><!--footnote-->
+
+<p>Such seems to be the sum of our knowledge of the ancient history
+of lighthouses, which, it must be admitted, is neither accurate
+nor extensive. Our information regarding modern lighthouses is
+of course more minute in its details and more worthy of credit.
+The greater part of it is drawn from authentic sources; and much<span class="pagenum" id="Page189">[189]</span>
+of what is afterwards stated is the result of my own observation,
+during my visits to the most important lighthouses of Europe.</p>
+
+<p>The first lighthouse of modern days that merits attention, is
+the <span class="sidenote">Tour de Corduan.</span>
+<i>Tour de Corduan</i>, which, in point of architectural grandeur, is
+unquestionably the noblest edifice of the kind in the world. It is
+situated on an extensive reef at the mouth of the river Garonne,
+and serves as a guide to the shipping of Bordeaux and the Languedoc
+Canal, and indeed of all that part of the Bay of Biscay. It
+was founded in the year 1584, but was not completed till 1610,
+under Henri IV. It is minutely described in Belidor’s <i>Architecture
+Hydraulique</i>. The building is 197 feet in height, and consists
+of a pile of masonry, forming successive galleries, enriched with
+pilasters and friezes, and rising above each other with gradually
+diminished diameters. Those galleries are surmounted by a conical
+tower, which terminates in the lantern. Round the base is a
+wall of circumvallation, 134 feet in diameter, in which the light-keepers’
+apartments are formed, somewhat in the style of casemates.
+This wall is an outwork of defence, and receives the chief
+shock of the waves. The tower itself contains a chapel, and various
+apartments; and the ascent is by a spacious staircase. The
+first light exhibited in the Tour de Corduan was obtained by burning
+billets of oak-wood, in a chauffer at the top of the tower; and
+the use of coal instead of wood, was the first improvement which
+the light received. A rude reflector, in the form of an inverted cone,
+was afterwards added, to prevent the loss of light which escaped
+upwards. About the year 1780, M. <span class="smcap">Lenoir</span> was employed to substitute
+paraboloïdal reflectors and lamps; and in 1822, the light
+received its last improvement, by the introduction of the dioptric
+instruments of <span class="smcap">Augustin Fresnel</span>, the celebrated French Academician.</p>
+
+<p><span class="sidenote">Eddystone.</span>
+The history of the famous Lighthouse on the Eddystone Rocks
+is well known to the general reader, from the narrative of
+<span class="smcap">Smeaton</span> the Engineer. Those Rocks are 9¹⁄₂ miles from the Ram-Head,
+on the coast of Cornwall; and from the small extent of the<span class="pagenum" id="Page190">[190]</span>
+surface of the chief Rock and its exposed situation, the construction
+of the Lighthouse was a work of very great difficulty. The
+first erection was of timber, designed by Mr <span class="smcap">Winstanley</span>; and was
+commenced in 1696. The light was exhibited in November 1698.
+It was soon found, however, that the sea rose upon that tower to
+a much greater height than had been anticipated; so much so, it is
+said, as to “<i>bury under the water</i>” the lantern, which was sixty
+feet above the Rock; and the Engineer was therefore afterwards
+under the necessity of enlarging the Tower, and carrying it to the
+height of 120 feet. In November 1703, some considerable repairs
+were required, and Mr <span class="smcap">Winstanley</span>, accompanied by his workmen,
+went to the Lighthouse to attend to their execution; but the
+storm of the 26th of that month, carried away the whole erection,
+when the Engineer and all his assistants unhappily perished!</p>
+
+<p>The want of a light on the Eddystone, soon led to a fatal accident;
+for not long after the destruction of Mr <span class="smcap">Winstanley’s</span> lighthouse,
+the Winchilsea man-of-war was wrecked on the Eddystone
+Rocks, and most of her crew were lost. Three years, however,
+elapsed, after this melancholy proof of the necessity for a light, before
+the Trinity-House of London could obtain a new Act of Parliament,
+to extend their powers; and it was not till the month of
+July 1706, that the construction of a new lighthouse was begun
+under the direction of Mr <span class="smcap">John Rudyerd</span> of London. On the 28th
+of July 1708, the new light was first shewn, and it continued to be
+regularly exhibited till the year 1755, when the whole fabric was
+destroyed by accidental fire, after it had stood forty-seven years.
+But for this circumstance, it is impossible to tell how long the
+lighthouse might, with occasional repair, have lasted, as Mr
+<span class="smcap">Rudyerd</span> seems to have executed his task with much judgment,
+carefully rejecting all architectural decoration, as unsuitable for
+such a situation, and directing his attention to the formation of a
+tower which should offer the least resistance to the waves. The
+height of the tower, which was of a conical form and constructed
+of timber, was 92 feet, including the lantern; and the diameter at<span class="pagenum" id="Page191">[191]</span>
+the base, which was a little above the level of high water, was 23
+feet.</p>
+
+<p>The advantages of a light on the Eddystone having been so
+long known and acknowledged by seamen, no time was permitted
+to elapse before active measures were taken for its restoration;
+and <span class="smcap">Smeaton</span>, to whom application was made for advice on the
+subject, recommended the exclusive use of stone as the material,
+which, both from its weight and other qualities, he considered
+most suitable for the situation. On the 5th of April 1756,
+<span class="smcap">Smeaton</span> first landed on the Rock and made arrangements for
+erecting a Lighthouse of stone and preparing the foundations, by
+cutting the surface of the rock into regular horizontal benches,
+into which the stones were carefully dovetailed or notched. The
+first stone was laid on 12th June 1757 and the last on the 24th of
+August 1759. The Tower measures 68 feet in height and 26 feet
+in diameter at the level of the first entire course; and the diameter
+under the cornice is 15 feet. The first 12 feet of the Tower
+form a solid mass of masonry; and the stones of which it is composed
+are united by means of stone joggles, dovetailed joints, and
+oaken treenails. It is remarkable that <span class="smcap">Smeaton</span> should have
+adopted an arched form for the floors of his building, instead of employing
+the floors as tie-walls formed of dovetailed stones. To
+counteract the injurious tendency of the outward thrust of those
+arched floors, he had recourse to the ingenious expedient of laying,
+in circular trenches or grooves cut in the stones which
+form the outside casing, tie-belts of chain, which were heated before
+being set in the grooves by means of an application of hot lead
+and became tight in cooling, after they were fixed in the wall.
+The light was exhibited on the 16th October 1759; but such was
+the state of lighthouse apparatus in Britain at that period, that
+a feeble light from tallow candles was all that decorated this noble
+structure. In 1807, when the property of this lighthouse again
+came into the hands of the Trinity-House, at the expiry of a long
+lease, Argand burners, and paraboloïdal reflectors of silvered copper,
+were substituted for the chandelier of candles.</p>
+
+<p><span class="pagenum" id="Page192">[192]</span></p>
+
+<p><span class="sidenote">Bell Rock.</span>
+The dangerous reef called the Inch Cape, or Bell Rock, so long
+a terror to mariners, was well known to the earliest navigators of
+Scotland. Its dangers were so generally acknowledged, that the
+Abbots of Aberbrothwick, from which the Rock is distant about
+twelve miles, caused a float to be fixed upon the Rock with a bell
+attached to it, which being swung by the motion of the waves,
+served by its tolling to warn the mariner of his approach to the
+reef. From this circumstance, which formed the groundwork of
+<span class="smcap">Southey’s</span> striking ballad of Sir Ralph the Rover, the Rock
+is said to have derived its name. Amongst the many losses which
+occurred on the Bell Rock in modern times, one of the most remarkable
+is that of the <i>York</i>, <i>seventy-four</i>, with all her crew,
+part of the wreck having been afterwards found on the Rock and
+part having come ashore on the neighbouring coast. During the
+survey of the Rock also, several instances were discovered of the
+extent of loss which this reef had occasioned; and many articles
+of ships’ furnishings were picked up on it, as well as various
+coins, a bayonet, a silver shoe-buckle, and many other small objects.
+Impressed with the great importance of some guide for
+the Bell Rock, Captain Brodie, R.N., set a small subscription
+on foot and erected a beacon of spars on the Rock, which, however,
+was soon destroyed by the sea. He afterwards constructed
+a second beacon, which soon shared the same fate. It was not,
+therefore, until 1802, when the Commissioners of Northern Lights
+brought a bill into Parliament for power to erect a lighthouse on
+it, that any efficient measures were contemplated for the protection
+of seamen from this Rock, which, being covered at every spring-tide
+to the depth of from twelve to sixteen feet, and lying right in the
+fairway to the Friths of Forth and Tay, had been the occasion of
+much loss both of property and life. In 1806, the bill passed into
+a law; and various ingenious plans were suggested for overcoming
+the difficulties which were apprehended, in erecting a lighthouse
+on a rock twelve miles from land, and covered to the depth of
+twelve feet by the tide. But the suggestion of Mr <span class="smcap">Robert Stevenson</span>,<span class="pagenum" id="Page193">[193]</span>
+the Engineer to the Lighthouse Board, after being submitted
+to the late Mr <span class="smcap">Rennie</span>, was at length adopted; and it was determined
+to construct a tower of masonry, on the principle of the
+Eddystone. On the 17th of August 1807, Mr <span class="smcap">Stevenson</span> accordingly
+landed with his workmen and commenced the work
+by preparing the Rock to receive the supports of a temporary
+pyramid of timber, on which a barrack-house for the reception of
+the workmen (similar to that which has already been described
+in a preceding part of this volume) was to be placed; and
+during this operation, much hazard was often incurred in transporting
+the men from the Rock, which was only dry for a few
+hours at spring-tides, to the vessel which lay moored off it. The
+lowest floor of this temporary erection, in which the mortar for the
+building was prepared, was often broken up and removed by the
+force of the sea. The foundation for the tower having been excavated,
+the first stone was laid on the 10th July 1808, at the depth
+of sixteen feet below the high water of spring-tides; and at the
+end of the second season, the building was five feet six inches
+above the lowest part of the foundation. The third season’s
+operations terminated by finishing the solid part of the structure,
+which is thirty feet in height; and the whole of the masonry was
+completed in October 1810. The light was first exhibited to the
+public on the night of the 1st of February 1811. The difficulties
+and hazards of this work were chiefly caused by the short time
+during which the Rock was accessible between the ebbing and
+flowing tides; and amongst the many eventful incidents which
+render the history of this work interesting, was the narrow escape
+which the Engineer and thirty-one persons made from being
+drowned, by the rising of the tide upon the Rock, before a boat
+came to their assistance, at a time when the attending vessel had
+broken adrift. This circumstance occurred before the Barrack-house
+was erected, and is narrated by Mr <span class="smcap">Stevenson</span>, in his Account
+of the work, published at the expense of the Lighthouse
+Board in 1824, to which I would refer for more minute information<span class="pagenum" id="Page194">[194]</span>
+on the subject of this work and the other lighthouses on the coast of
+Scotland.</p>
+
+<p>The Bell Rock Tower is 100 feet in height, 42 feet in diameter
+at the base, and 15 at the top. The door is 30 feet from
+the base and the ascent is by a massive copper ladder. The apartments,
+including the light-room, are six in number. The light is a
+<i>revolving red and white light</i>; and is produced by the revolution
+of a frame containing sixteen Argand lamps, placed in the foci of
+paraboloïdal mirrors, arranged on a quadrangular frame, whose alternate
+faces have shades of red glass placed before the reflectors, so
+that a red and white light is shewn successively. The machinery,
+which causes the revolution of the frame containing the lamps, is
+also applied to tolling two large bells, to give warning to the
+mariner of his approach to the Rock in foggy weather. The
+erection of the Bell Rock Lighthouse cost L.61,331&#160;: 9&#160;: 2.</p>
+
+<p><span class="sidenote">Carlingford.</span>
+The most remarkable Lighthouse on the coast of Ireland is that
+of Carlingford, near Cranfield Point, at the entrance of Carlingford
+Lough. It was built according to the design of Mr <span class="smcap">George Halpin</span>,
+the Inspector of the Irish Lights; and was a work of an arduous
+nature, being founded 12 feet below the level of high-water, on the
+Hawlbowling Rock, which lies about two miles off Cranfield Point.
+The figure of the Tower is that of a frustum of a cone, 111 feet in
+height, and 48 in diameter at the base. The light, which is fixed, is
+from oil burned in Argand lamps, placed in the foci of paraboloïdal
+mirrors. It was first exhibited on the night of December 20, 1830.</p>
+
+<p>There are various other Lighthouses, which, in themselves, are
+sufficiently deserving of a separate notice, were it not that they
+have more or less something in common with those already described,
+which are unquestionably the most remarkable edifices of
+the kind. The first design for an <span class="sidenote">Iron Lighthouses.</span>
+Iron Lighthouse, is that by my
+Father for the Bell Rock, in the year 1800. The invention of
+Mr <span class="smcap">Mitchell</span> of Belfast, for applying the principle of the screw
+to the erection of Lighthouses on soft foundations, deserves a
+longer notice than is consistent with the nature of these notes.<span class="pagenum" id="Page195">[195]</span>
+It must therefore be sufficient to say, that the principal Lighthouses
+on this plan (those of the Maplin, Fleetwood, and Belfast
+Lough) consist of piles or of hollow pillars of cast-iron, grouped together
+in the form of a truncated pyramid, and closely resembling,
+in the general arrangement of their parts, the Beacon shewn in <a href="#Plate30">Plate
+XXX.</a>, and that erected on the Carr Rock in 1821. The lower
+end of each pillar is furnished with a flat screw or worm and a
+sharp point, which is screwed into the sand, clay, or gravel, or
+other soft subsoil. Mr <span class="smcap">Alexander Gordon</span> of London also fitted
+up a Lighthouse, composed of cast-iron plates, which was erected
+at Morant, in the West Indies, a style of building in itself by
+no means eligible, and which seems suitable only where stone
+cannot be easily obtained, or conveniently applied. Both those
+plans (except in so far as the screw is concerned, which is indeed
+the distinguishing feature of Mr <span class="smcap">Mitchell’s</span> ingenious plan) are
+to be found in one of my Father’s designs for the Bell Rock Lighthouse
+(see his Account, at Plate VII., figs. 2, 3, 4, and 5, and
+pp. 499, 500). Dr <span class="smcap">Potts</span> has also invented a method of driving
+piles by means of atmospheric pressure, which has been used at the
+South Galliper Beacon, on the Goodwin Sands.</p>
+
+<p>Having thus hastily described the most interesting and celebrated
+Lighthouses, I proceed to the proper object of these Notes,
+which are chiefly intended to make known the various methods
+now in use for the illumination of Lighthouses. There can be
+little doubt, that down to a very late period, <span class="sidenote">Early modes of
+Illumination.</span>
+the only mode of
+illumination adopted in the Lighthouses, even of the most civilized
+nations of Europe, was the combustion of wood or coal in <i>chauffers</i>,
+on the tops of high towers or hills. It consists with the personal
+knowledge of many persons now living, that the Isle of May Light,
+in the Frith of Forth, previous to its being assumed by the Commissioners
+of the Northern Lights in 1786, was of that kind; and,
+even in England, the art of illumination had made so little progress,
+that the magnificent Tower of the Eddystone, for about forty
+years after it came from the hands of <span class="smcap">Smeaton</span>, could boast of no<span class="pagenum" id="Page196">[196]</span>
+better Light than that derived from a few miserable tallow candles.
+Such methods were most imperfect, not only in point of efficiency
+and power, but also as respects the distinction of one light from another,
+an object which, on a difficult and rugged coast, may be considered
+as of almost equal importance with the distance at which
+the Light can be seen.</p>
+
+<p>Solid substances which remain so throughout their combustion,
+are only luminous at their own surface, and exhibit phenomena,
+such as the dull red heat of iron, or of most kinds of pit-coal, and
+are therefore more suited for the purpose of producing heat than
+light. But by using substances which are formed into inflammable
+vapours, at a temperature below that which is required for the
+ignition of the substances themselves, gas is obtained and <span class="sidenote">Flame.</span>
+<i>flame</i> is
+produced. Much light is thus evolved at a comparatively low
+temperature. The gas necessarily rises <i>above</i> the combustible substance
+from which it is evolved, owing to its being formed at a
+temperature considerably higher than that of the surrounding air,
+than which it is necessarily rarer. Of this description are the flames
+obtained by the burning of the various oils, which are generally
+employed in the illumination of lighthouses. In the combustion
+of oil, wicks of some fibrous substance, such as cotton, are used,
+into which the oil ascends by capillary action, and being supplied
+in very thin films, is easily volatilized into vapour or gas
+by the heat of the burning wick. The gas of pit-coal has been
+occasionally used in lighthouses; it is conveyed in tubes to the
+burners, in the same manner as when employed for domestic
+purposes. There are certain advantages, more especially in dioptric
+lights, where there is only one large central flame, which
+would render the use of gas desirable. The form of the flame,
+which is an object of considerable importance, would thus be rendered
+less variable, and could be more easily regulated, and the inconvenience
+of the clock-work of the lamp would be wholly avoided.
+But it is obvious, that gas is by no means suitable for the majority
+of lighthouses, their distant situation and generally difficult access<span class="pagenum" id="Page197">[197]</span>
+rendering the transport of large quantities of coal expensive and
+uncertain; whilst in many of them there is no means of erecting
+the apparatus necessary for manufacturing gas. There are other
+considerations which must induce us to pause before adopting gas as
+the fuel of lighthouses; for, however much the risk of accident may
+be diminished in the present day, it still forms a question, which
+ought not to be hastily decided, how far we should be justified in
+running even the most remote risk of explosion in establishments
+such as lighthouses, whose sudden failure might involve consequences
+of the most fatal description, and whose situation is often
+such, that their re-establishment must be a work of great expense
+and time. Gas is, besides, far from being suitable in catoptric lights,
+to which, in many cases (especially when the frame is moveable,
+as in revolving lights), it could not be easily applied. The oil most
+generally employed in the Lighthouses of England is the sperm oil
+of commerce, which is obtained from the South Sea whale (<i>Physeter
+macrocephalus</i>). In France, the colza oil, which is expressed from
+the seed of a species of wild cabbage (<i>Brassica oleracea colza</i>), and
+the olive oil are chiefly used; and a species of the former has lately
+been successfully introduced into the Lighthouses of Great Britain.
+Of all these oils, the purified sperm oil has hitherto been generally
+considered the most advantageous for lighthouse purposes; but there
+is every reason for anticipating that the late adoption of the colza
+oil in many of the British Lights, on the suggestion of Mr <span class="smcap">Joseph
+Hume</span>, M.P., while chairman of a select committee of the House of
+Commons on Lighthouses, will lead to an important saving, as its
+combustion produces an equal quantity of light at somewhat more
+than one-half of the expense for spermaceti oil. Careful trials have
+been made of this oil; and on the 10th of March 1847, I was enabled
+to report the results to the Commissioners of Northern Lighthouses
+in the following terms:</p>
+
+<p>“1. The colza oil possesses the advantage of remaining fluid at
+temperatures which thicken the spermaceti oil so that it requires
+the application of the frost lamp.</p>
+
+<p><span class="pagenum" id="Page198">[198]</span></p>
+
+<p>“2. It appears, from pretty careful photometrical measurements
+of various kinds, that the light derived from the colza oil is, in
+point of intensity, a little superior to that derived from the spermaceti
+oil, being in the ratio of 1·056 to 1.</p>
+
+<p>“3. The colza oil burns both in the Fresnel lamp and the single
+Argand burner with a thick wick during seventeen hours without
+requiring any coaling of the wick or any adjustment of the damper;
+and the flame seems to be more steady and free from flickering
+than that from spermaceti oil.</p>
+
+<p>“4. There seems (most probably owing to the greater steadiness
+of the flame) to be less breakage of glass chimneys with the
+colza than with the spermaceti oil.</p>
+
+<p>“5. The consumption of oil, in so far as that can be ascertained
+during so short a period of trial, seems in the Fresnel lamp to be
+121 for colza, and 114 for spermaceti; while in the common Argand,
+the consumption appears to be 910 for colza, and 902 for
+spermaceti.</p>
+
+<p>“6. If we assume the means of these numbers, 515 for colza,
+and 508 for spermaceti, as representing the relative expenditure of
+these oils, and if the price of colza be 3s. 9d., while that of spermaceti
+is 6s. 9d. per imperial gallon, we shall have a saving in the
+ratio of 1 to 1·755, which, at the present rate of supply for the
+Northern Lights, would give a saving of about L.3266 per annum.</p>
+
+<p>“Of these conclusions, the three last may be considered as
+more or less conjectural, being founded on data derived from too
+short a trial; but the striking agreement of the results obtained at
+the six lights in which the experiments were made, tends in some
+measure to supply the place of a longer period of trial; and I have
+no hesitation, therefore, in recommending the Board at once to introduce
+the use of the colza oil into all the dioptric lights, except
+that of Skerryvore, where some special reasons induce me to defer
+the change for another season. In the catoptric lights, the only
+reason for not making an equally extensive trial is the necessity
+for renewing all the burners, which require to be so constructed as<span class="pagenum" id="Page199">[199]</span>
+to receive thick wicks of brown cotton; and it may perhaps be
+considered prudent to proceed with some caution in changing the
+apparatus, so as to suit it for burning a patent oil, the circumstances
+attending the regular and extensive supply of which are
+not yet fully known. I may remark, that I have burnt the colza
+oil in the solar lamp alluded to in my last report; but I disapprove
+of it as tending to elongate the flame vertically, and thus to decrease
+its horizontal volume. The elongated form of flame increases
+the divergence vertically where the light is lost, and so far
+circumscribes its horizontal range where it is most required. I
+have therefore substituted the thick wick burner for the solar lamp,
+whereby an equally complete combustion is obtained, and the
+proper form of the flame is at the same time preserved.”<a id="FNanchor36" href="#Footnote36" class="fnanchor">[36]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote36" href="#FNanchor36" class="label">[36]</a> Since the above report was written, the price of colza oil has risen; and other circumstances
+have occurred to justify the caution as to the universal adoption of that oil.</p>
+
+</div><!--footnote-->
+
+<p class="blankbefore75"><span class="sidenote">Drummond and
+Voltaic Lights.</span>
+The application of the Drummond and Voltaic lights<a id="FNanchor37" href="#Footnote37" class="fnanchor">[37]</a> to lighthouse
+purposes is, owing to their prodigious intensity, a very desirable
+consummation; but it is surrounded by so many practical
+difficulties that, in the present state of our knowledge, it may safely
+be pronounced unattainable. The uncertainty which attends
+the exhibition of both these lights, is of itself a sufficient reason
+for coming to this conclusion. But other reasons unhappily are
+not wanting. The smallness of the flame renders them wholly<span class="pagenum" id="Page200">[200]</span>
+inapplicable to dioptric instruments, which require a great body
+of flame in order to produce a degree of divergence sufficient to
+render the duration of the flash in revolving lights long enough to
+answer the purpose of the mariner. M. <span class="smcap">Fresnel</span> made some experiments
+on the application of the Drummond light to dioptric
+instruments, which completely demonstrate their unfitness for
+this combination. He found that the light obtained by placing it
+in the focus of a great annular lens was much more intense than
+that produced by the great lamp and lens; but the divergence
+did not exceed 30′; so that, in a revolution like that of the Corduan
+Light, the flashes would last only 1¹⁄₃ second, and would not,
+therefore, be seen in such a manner as to suit the practical purposes
+of a revolving light. The great cylindric refractor used in
+fixed lights of the first order, was also tried with the Drummond
+light in its focus; but it gave coloured spectra at the top and bottom,
+and only a small bar of white light was transmitted from the centre
+of the instrument. The same deficiency of divergence completely
+unfits the combination of the Drummond light with the reflector
+for the purposes of a fixed light, and even if this cause did not
+operate against its application in revolving lights on the catoptric
+plan, the supply of the gases, which is attended with almost insurmountable
+difficulties, would, in any case, render the maintenance
+of the light precarious and uncertain in the last degree.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote37" href="#FNanchor37" class="label">[37]</a> The Drummond light is produced by the ignition or combustion of a ball of lime
+(³⁄₈ inch diameter) in the united flames of hydrogen and oxygen gases, and is equal to about
+264 flames of an ordinary Argand Lamp with the best Spermaceti oil. It derives its name
+from the late <span class="smcap">Lieut. Drummond</span>, R. E., who first applied it in the focus of a paraboloïd
+for geodetical purposes, and afterwards proposed it for Lighthouses. (See his Account of
+the Light in the Phil. Trans. for 1826, p. 324, and for 1830, p. 383.) The Voltaic light
+is obtained by passing a stream of Voltaic electricity from a powerful battery between two
+<i>charcoal points</i>, the distance between which requires great nicety of adjustment, and is the
+chief circumstance which influences the stability and the permanency of the light. The
+Voltaic light greatly exceeds the Drummond light in intensity, as ascertained by actual
+comparison of their effects; but the ratio of their power has not been accurately determined.
+It was first exhibited in the focus of a reflector by Mr <span class="smcap">James Gardner</span>, formerly engaged
+in the Ordnance Survey of Great Britain.</p>
+
+</div><!--footnote-->
+
+<p><span class="sidenote">Mr Gurney’s
+Lamp.</span>
+In 1835, Mr <span class="smcap">Gurney</span> proposed the combination of a current of
+oxygen with the flame of oil, in order to obtain a powerful light
+of sufficient size to produce the divergence required for the illumination
+of lighthouses. The Trinity-House of London entertained
+the proposal, and made some experiments on this important subject;
+but the plan was finally rejected as disadvantageous in practice.</p>
+
+<p><span class="sidenote">Argand Burners.</span>
+Until the invention by <span class="smcap">Argand</span> (about the year 1784), of the
+lamp with a double current of air, the art of illumination seems to
+have received no improvement, and to have occupied very little
+attention from the time of <span class="smcap">Cardan</span>, or at all events of
+Dr <span class="smcap">Hook</span>,<span class="pagenum" id="Page201">[201]</span>
+who, about the year 1677, in a monograph entitled “Lampas,”
+made some important observations on the constitution of <i>flame</i>, so
+as to make one wonder that he should have stopped short of the
+discoveries of later inventors. Before <span class="smcap">Argand’s</span> time, every wick
+consisted of a solid cord, whose flame was fed only by the current
+of air on its outside; and the consequence of this arrangement is,
+that the stream of vapour or smoke, especially from the centre
+of thick wicks, escapes unburnt, because, before it reaches the
+height at which the combustion of the central stream can take
+place, its temperature has become too low to admit of its
+ignition.<a id="FNanchor38" href="#Footnote38" class="fnanchor">[38]</a><span class="pagenum" id="Page202">[202]</span>
+The chief improvements which had been made, consisted in
+varying the level of the oil in the cistern, or in attempts to
+render that level constant, by mechanical means, and in lessening
+the thickness of the wick, by spreading its substance into a flat
+form, thus reducing the stream of gas which escapes from the
+centre of a thick cylindric wick without being burnt, and thereby
+causing a more complete combustion, and producing less smoke
+and a whiter flame. To <span class="smcap">Argand</span> belongs the great merit of having
+first formed the wick into a hollow cylinder, thus supplying the
+flame with two currents of air, one of which, as in the case of the
+solid wick, envelopes the flame, and the other, passing through
+the centre of the wick, is enveloped by the flame itself. He also
+added a chimney, which served to defend the flame from irregular
+draughts of air, and to regulate the proportion between the velocities
+of the currents of air and the stream of gas. This was indeed
+a most important step in the art of illumination, and causes the
+great difference between the incomplete combustion, which, owing
+chiefly, as we have seen, to a defect in the supply of air, always
+takes place with a solid wick (from which much unburnt gas
+escapes in the form of smoke), and that more perfect combustion
+in which passage is given for a free current of air through the centre
+of the wick. The invention of <span class="smcap">Argand</span> came nearly perfect from
+his hands; and but a few slight modifications of his original arrangement
+have been introduced. The Argand burner consists
+of two concentric tubes or cylinders, separated by a small annular
+space, which is shut at the bottom, and communicates by a pipe
+with the oil fountain, whose level ought to be a little <i>below</i> the
+level of the upper edge of the cylinders. In this annular space,
+partly filled with oil from the fountain, stands a cylindric wick of
+cotton, loosely wove, into which the oil rises freely by capillary action.<span class="pagenum" id="Page203">[203]</span>
+The wick has its lower edge fixed to a metallic ferule or
+ring, called a wickholder, which (by means of a peculiar arrangement,
+to be afterwards described) gives the power of raising or depressing
+the wick to any convenient level with regard to the burner.
+A cylinder of glass, of greater diameter than the burner, rests on a
+gallery or ring which hangs from the burner and surrounds it. This
+glass cylinder, or chimney as it is generally called, should stand
+vertically with its axis coincident with that of the burner itself.
+The effect of this arrangement is obvious, and has already in part
+been indicated. The flame is thus necessarily bounded on all sides
+by two conical concentric surfaces, one external and concave, and
+the other internal and convex, both of which receive a free current
+of air. The flame is therefore very thin in every direction;
+and, as a consequence of the mutual radiation of its different parts
+on each other, it is throughout its entire surface of more equal temperature
+than can ever be attained in the thick solid wick or the narrow
+flat one. The glass cylinder also increases the force of the two
+currents which pass outside and inside of the flame; and the union
+of so many favourable circumstances produces a greater amount of
+pure light than has yet been obtained by any other method. The
+contraction of the glass chimney (known by the technical name
+of the <i>shoulder</i>) at a point a little above the level of the wick,
+tends to direct the current of air inwards on the flame, thereby
+causing a more perfect combustion and the evolution of more light.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote38" href="#FNanchor38" class="label">[38]</a> That the form of a flame is necessarily conoidal, and that its height is determined by
+the relation subsisting between its diameter and the continually varying velocities of the
+currents of gas and air, may be easily shewn; and the combustion of each annular film of the
+stream of gas from the wick can take place only at a level determined by, and continually
+varying with, the ratio of the velocities of the streams of gas and air. I am unwilling to
+offer this explanation in my own words, when those of M. Peclet, in his excellent work,
+Traité de l’Eclairage, are at hand,—“Let us conceive,” says he, “a very thin film or layer
+of inflammable gas placed horizontally, and which rises into the air parallel to itself, with
+a uniform motion. We shall suppose that it cannot be burnt, except at its circumference,
+and that the top and bottom of the film are, by some means, preserved from combustion
+(they are so preserved in ordinary flames, by the films which precede and follow them). If
+the circumference is at a high enough temperature it will burn; at each instant the
+film or layer of air, which has assisted the combustion and also the products of
+that combustion, being very hot, will rise very rapidly, and will make room for other
+layers or films of air, which will rise in their turn; and as the diameter of the film
+of gas is continually diminishing, it is obvious that its combustion will offer the appearance
+of a series of circles continually growing smaller, and terminating at length in
+a point. If we trace in thought the series of circles which the combustion has successively
+developed, we shall form a cone whose length will depend on the ratio of the velocities
+of the films of gas and of air which escape after combustion. If, for example, the
+velocity of the current of air were very great, compared to the velocity of the cylinder of
+gas, the entire combustion would take place, while the film of gas passes over a very small
+space; and the cone formed by the succession of luminous circles would, consequently, be
+very short. If, on the contrary, there were but a very small difference between these velocities,
+the luminous circles would only appear at considerable intervals from each other;
+for the air which had served for combustion, being unable to feed it longer, the surface of the
+cylinder could not become luminous until the difference of velocity had freed it from the
+air which had served for the preceding combustion. If, then, we imagine a set of similar
+films succeeding each other, each of them would give rise to the same series of coloured
+rings; and as there would be a film in each section of the cone in a state of combustion
+at the same instant of time, the cone would, of course, appear luminous throughout its
+height.”—Peclet, <i>Traité de l’Eclairage</i>, p. 51.</p>
+
+</div><!--footnote-->
+
+<p>Great as the improvement of <span class="smcap">Argand</span> undoubtedly was, the
+value of the lamp alone as a means for the illumination of lighthouses
+must be regarded as comparatively small. The primary
+object of a lighthouse is to give early notice to the mariner of
+his approach to the coast, and it is therefore necessary that the
+light be of such a kind that it may be seen at a great distance.
+Every one is practically acquainted with the fact that the rays
+proceed in all directions from a luminous body in straight lines;
+and if we could obtain a ball equally luminous in every part of its
+surface, it would give an equal share of light to every part of<span class="pagenum" id="Page204">[204]</span>
+the inner surface of a hollow sphere, whose centre coincided
+with the centre of the ball. Again, if an opaque body were
+placed between the luminous ball and the hollow sphere, the part
+opposite that body would be deprived of the light by the interception
+of the rays, and no light would emerge from a hole bored in
+that part of the surface of the hollow sphere. The bearing of
+these facts is obvious; and no one can fail to perceive that in the
+case of a lighthouse illuminated by a single unassisted burner, a
+seaman could only receive the benefit of that small portion of light
+which emerges from the lamp in a line joining his eye and the
+centre of the flame. The other rays would be occupied partly
+in making the light visible in other parts of the horizon, and
+but a very small portion of them would be usefully employed
+for that purpose, while all the rest would be lost by escaping upwards
+into the sky, or downwards below the plane in which seamen
+can see a lighthouse. This state of matters would be little
+improved by increasing the number of burners, as the effective part
+of the light would only be augmented by the addition of an equally
+trifling portion of light from each burner. The small pencils of rays
+thus meeting at the eye of a distant observer, would form a very
+minute fraction of the whole quantity of light uselessly escaping
+above and below the horizon, and also at the back of each flame;
+and the wasteful expenditure of light would be enormous. By
+such a method no practically efficient sea-light could ever be obtained.</p>
+
+<div class="chapter">
+
+<h3 class="nobreak"><span class="chapname">CATOPTRIC<a id="FNanchor39" href="#Footnote39" class="fnanchor">[39]</a> SYSTEM OF LIGHTS.</span></h3>
+
+<div class="footnote">
+
+<p><a id="Footnote39" href="#FNanchor39" class="label">[39]</a> From the Greek κατοπτρον, a <i>mirror</i>; a compound of κατα, <i>opposite to</i>, and ὂπτομαι,
+<i>I see</i>.</p>
+
+</div><!--footnote-->
+
+</div><!--chapter-->
+
+<p>For those defects a simple remedy is found in the well known
+power possessed by most bodies, of <i>reflecting</i> or throwing back
+from them the light which falls upon them. This property is not
+possessed by all reflecting bodies in an equal degree, some absorbing
+more and some less of the incident light. Perhaps the earliest<span class="pagenum" id="Page205">[205]</span>
+attempts to apply this property as a corrective for the direction of
+the rays from a Lighthouse, would be confined to placing plane
+mirrors behind each lamp; yet this would prove but a partial remedy,
+as it would still leave the greater part of the light to stray above and
+below the proper direction. Hollow mirrors of a spherical form
+might next be tried; and if properly placed with reference to the
+flame, would constitute a very great improvement in lighthouse illumination.
+But those steps in the march of improvement are more
+imaginary than real; and I am not aware of any well authenticated
+records of such gradual attempts having preceded the adoption of
+the right mode of applying reflection as a means of rectifying the
+direction of the rays emerging from a lighthouse. There is, on the
+contrary, distinct evidence that the impulse given by <span class="smcap">Argand’s</span>
+invention, led to an immediate adoption of the most perfect form
+of reflecting instruments.</p>
+
+<p><span class="sidenote">Application of
+Paraboloïdal Mirrors
+into Lighthouses.</span>
+The name of the inventor of paraboloïdal mirrors and the date
+of their first application to Lighthouses, have not been accurately
+ascertained. The earliest notice which I have been able to find, is
+that by Mr <span class="smcap">William Hutchinson</span>, the pious and intelligent author
+of a quarto volume on “Practical Seamanship” (published at Liverpool
+in 1791), who notices (at p. 93) the erection of the four lights at
+Bidstone and Hoylake, in the year 1763, and describes large parabolic
+moulds, fashioned of wood and lined with mirror-glass, and
+smaller ones of polished tin-plate, as in use in those Lighthouses.
+Mr <span class="smcap">Hutchinson</span> seems to have understood the nature, properties,
+and defects of the instruments which he describes, and has shewn
+a good acquaintance with many of the most important circumstances
+to be attended to in the illumination of Lighthouses. Many claims
+to inventions rest on more slender grounds than might be found
+in Mr <span class="smcap">Hutchinson’s</span> book for concluding him to have first invented
+the paraboloïdal mirror and applied it to use in a Lighthouse;<a id="FNanchor40" href="#Footnote40" class="fnanchor">[40]</a>
+but, in the absence of any statement as to the date when<span class="pagenum" id="Page206">[206]</span>
+the mirrors were really adopted, the merit of the improvement
+must, in justice, be awarded to others.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote40" href="#FNanchor40" class="label">[40]</a> Mr <span class="smcap">Hutchinson</span>
+seems also (“Practical Seamanship,” p. 198) to have tried speculum
+metal as a material for Lighthouse reflectors.</p>
+
+</div><!--footnote-->
+
+<p>M. <span class="smcap">Teulere</span>, a member of the Royal Corps of Engineers of
+Bridges and Roads in France, is, by some, considered the first who
+hinted at the advantages of paraboloïdal reflectors; and he is said, in
+a memoir dated the 26th June 1783, to have proposed their combination
+with Argand lamps, ranged on a revolving frame, for the
+Corduan Lighthouse. Whatever foundation there may be for the
+claim of M. <span class="smcap">Teulere</span>, certain it is that this plan was actually carried
+into effect at Corduan, under the directions of the <span class="smcap">Chevalier
+Borda</span>; and to him is generally awarded the merit of having conceived
+the idea of applying paraboloïdal mirrors to lighthouses.
+These were most important steps in the improvement of lighthouses,
+as not only the power of the lights was thus greatly increased, but
+the introduction of a revolving frame proved a valuable source of
+differences in the appearance of lights, and, in this way, has since
+been the means of greatly extending their utility. The exact date
+of the change on the light of the Corduan is not known; but as it
+was made by <span class="smcap">Lenoir</span>, the same young artist to whom <span class="smcap">Borda</span>, about
+the year 1780, entrusted the construction of his reflecting circle, it
+has been conjectured by some that the improvement of the light
+was made about the same time. The reflectors were formed of
+sheet-copper, plated with silver, and had a double ordinate of 31
+French inches. It was not long before these improvements were
+adopted in England, by the Trinity-House of London, who sent
+a deputation to France to inquire into their nature. In Scotland,
+one of the first acts of the Northern Lights Board in
+1786, was to substitute reflectors in the room of the coal-light
+then in use at the Isle of May in the Frith of Forth, which, along
+with the light on the Cumbrae Isle in the Frith of Clyde, had,
+till that period, been the only beacons on the Scotch coast. The
+first reflectors employed in Scotland were formed of <i>facets</i> of mirror
+glass, placed in hollow paraboloïdal moulds of plaster, according to
+the designs of the late Mr <span class="smcap">Thomas Smith</span>, the Engineer of the Board,<span class="pagenum" id="Page207">[207]</span>
+who (as appears from the article <i>Reflector</i>, in the Supplement to the
+third edition of the Encyclopædia Britannica) was not aware of
+what had been done in France, and had himself conceived the
+idea of this combination. The same system was also adopted in
+Ireland; and in time, variously modified, it became general wherever
+lighthouses are known.</p>
+
+<p>To enable us to enter on the subject of the proper forms of reflectors,
+we must glance very briefly at the <span class="sidenote">Reflection.</span>
+<i>laws of reflection</i>. Those
+laws are two in number. <i>1st</i>, The ray which falls on a reflecting
+surface, called the <i>incident</i> ray, and the ray which leaves the
+reflector, called the <i>reflected</i> ray, are always in one <i>plane</i>, which
+plane is perpendicular to the <i>reflecting surface</i>. <i>2d</i>, The angle
+which the <i>reflected</i> ray makes with the reflector is always equal
+to the angle which the <i>incident</i> ray makes with it, or, in other words,
+the angle of <i>incidence</i> is equal to the angle of <i>reflection</i>.<a id="FNanchor41" href="#Footnote41" class="fnanchor">[41]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote41" href="#FNanchor41" class="label">[41]</a> This will be more readily
+understood by referring to the accompanying figure (<a href="#Fig22">No. 22</a>),
+in which CDEF is the reflecting surface; GHOKI the plane of reflection perpendicular
+to that surface; BO a line perpendicular or <i>normal</i> to the surface CDEF; and AO the
+incident ray. Then if in the plane GHOKI,
+the angle BOI be made equal to AOB, OA′
+is the reflected ray; BOG is then the angle of
+incidence; and BOI the angle of reflection.
+GOH and IOK, which are the complements
+of those angles, are, indeed, more strictly
+speaking, the angles of incidence and reflection;
+but in cases where the reflecting surface
+is curved, it is more convenient to refer
+the angles to the normal BO.</p>
+
+<div class="container w25emmax" id="Fig22">
+
+<p class="caption">Fig. 22.</p>
+
+<img src="images/illo207.jpg" alt="Reflecting light">
+
+</div><!--container-->
+
+</div><!--footnote-->
+
+<p>It would lead to prolixity altogether superfluous in this place,
+to explain, in a rigorous manner, the effects produced by various
+reflecting surfaces on the direction of the rays incident on them;
+as any one who comprehends the laws of reflection just enumerated,
+may easily satisfy himself of the following truths: <i>1st</i>, That
+a plane mirror makes no change on the divergence of the rays, but
+merely causes them to emerge from its surface in the same direction
+as if they had come from a point as much behind the mirror<span class="pagenum" id="Page208">[208]</span>
+as the luminous body lies in front of it. <i>2d</i>, A convex reflecting
+surface increases divergence, and disperses the rays in the same
+manner as if they had come directly from a point behind it, whose
+distance from the mirror increases with the distance of the luminous
+body from its surface, and diminishes with the degree of convexity
+of the mirror. <i>3d</i>, A concave surface diminishes the divergence
+of the rays incident upon it from a point between the surface
+and its centre of curvature; the distance of the point in which the
+reflected rays converge diminishing as the distance of the radiant
+point or the concavity of the mirror is increased. It is obvious,
+therefore, that concave mirrors are those which are required to produce
+a correction of the path of the rays, so as to apply them to
+most advantage in a lighthouse, the object to be attained being that
+of throwing the greatest amount of light towards given points in
+the horizon, and collecting the divergent rays, which, as we have
+already seen, are scattered above and below it.</p>
+
+<p>To simplify our view of this matter, I shall, in the first place,
+suppose that the object to be attained is to throw the whole rays
+of a single lamp, with an infinitely small flame, to a given mathematical
+point at a moderate distance; and, as this is a case which
+can hardly occur in the practice of Lighthouse illumination, I content
+myself with observing that this object may be attained <i>approximately</i>
+by placing the lamp in front of a spherical mirror at
+any distance greater than half the radius of the curve surface, or <i>accurately</i>
+by placing it in one focus of an elliptical mirror; in all
+those cases the rays would meet in the opposite, or, as they are
+termed, <i>conjugate foci</i>. Let us next suppose that our object is to
+illuminate, by means of a mathematical point of light, a small circular
+space on the horizon equal in diameter to the mirror employed;
+this object will be rigorously attained only by placing the
+light in the focus of a paraboloïdal reflector. The same object
+may be approximately attained by placing the light in a spherical
+mirror, at a point <i>half-way</i> between the centre of curvature and
+the surface of the mirror, provided the surface of the mirror shall<span class="pagenum" id="Page209">[209]</span>
+subtend only a small angle at the centre of curvature. The paraboloïdal
+mirror, on the contrary, has the property of converging to
+the focus parallel rays falling upon every point of its surface, however
+extended it may be.</p>
+
+<p><span class="sidenote">Paraboloïdal
+Mirrors.</span>
+Any one practically acquainted with this subject, must at once
+perceive that the paraboloïdal mirror completely fulfils one great
+object required in a lighthouse; and to render this more obvious
+to the general reader, I shall, for the present, confine my remarks
+to the case of those lighthouses which exhibit to the mariner in
+every part of the horizon, pencils of light at certain intervals of
+time, separated by periods of darkness, reserving the consideration
+of Lights which are continually in sight all round the horizon or
+over a given portion of it, for a subsequent part of these Notes. In
+doing this, I am aware that I may appear to be departing from the
+strict order of investigation, by suddenly introducing the idea of motion;
+but a little consideration will, I think, satisfy the reader that
+this is, in reality, the more convenient mode of treating the subject.
+Let us suppose, then, that our object is to give occasional flashes of
+light, separated by intervals of darkness, to seamen in various azimuths
+and at various distances from a lighthouse. It is obvious that
+this may be most efficiently done by causing concave mirrors, which
+collect the rays from lamps placed in them and thereby increase the
+light in front of the mirror, to revolve round a vertical axis with a
+velocity suited to produce the required number of flashes in a given
+time. The paraboloïdal mirror is best adapted for producing this
+effect, for the following reasons: <i>1st</i>, Because it alone produces a
+rigorous parallelism of all rays proceeding from its focus, and falling
+upon any point of its surface, however distant the point of reflection
+from that focus, or however far <i>in front</i> of it. <i>2d</i>, Because it therefore
+embraces in its action the greatest number of the whole rays
+coming from the focus, and, <i>cæteris paribus</i>, will produce the strongest
+light. <i>3d</i>, Because the <i>theoretical</i> object to be attained is to make
+those flashes equally powerful at any distance, an effect which would<span class="pagenum" id="Page210">[210]</span>
+be rigorously fulfilled by placing an infinitely small flame in a perfect
+paraboloïdal mirror. And, <i>4th</i>, Because, although absolute
+equality of luminousness at any distance is not attainable, and, in
+practice, is inconsistent with other conditions required in a useful
+light, we still, by using the parabolic mirror, make the nearest
+approach to parallelism of the reflected rays, and consequently obtain
+the strongest light which is consistent with a due regard to a
+certain duration of the flash on the eye of a distant observer, which
+is measured by the angle of the luminous cone projected to the
+horizon.</p>
+
+<p>Having thus so far anticipated what some might think would
+more naturally have occurred in a subsequent part of these Notes,
+I return to a more detailed consideration of the parabola itself, and
+its product, the paraboloïdal mirror. I content myself, however,
+with describing the parabola, by that property which peculiarly
+adapts it to the purposes of a lighthouse. The parabola, then, is
+a curve of the second order, obtained by cutting a cone in a plane
+parallel to one side, which possesses this remarkable property, <i>that
+a line drawn from the focus to any point in the curve, makes, with a
+tangent at that point, an angle equal to that which a line parallel to
+the axis of the curve makes with that tangent</i>.<a id="FNanchor42" href="#Footnote42" class="fnanchor">[42]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote42" href="#FNanchor42" class="label">[42]</a> See third corollary to Proposition III. of Wallace’s Conic Sections, which shews
+that a tangent to the parabola makes equal angles with the diameter which passes through
+the point of contact and a straight line drawn from that point to the focus. The curve
+may be traced in two different ways, both dependent on the property, <i>that the distance of
+any point in the parabola from the focus is equal to its distance from the directrix</i>.</p>
+
+<p>To draw the curve mechanically (<a href="#Fig23">fig. 23</a>), let F be the focus, MF the focal distance
+(chosen at pleasure according to rules which I shall afterwards notice), KMX is the axis,
+and AB the directrix (the dotted line <i>f</i>&#160;F&#160;<i>e</i>, bounded by the curve at either end, would then
+be the <i>parameter</i> or <i>latus rectum</i>). Place the edge of the straight ruler AKHB along the
+directrix; and let LHB be a square ruler
+which may slide along the fixed ruler AKHB,
+so that the edge HL may be constantly perpendicular
+to AB, or parallel to MX, the
+axis; let LDF be a string equal in length
+to HL, and having one end fixed in F, and
+the other at L, a point in the sliding square.
+Then if the string be stretched by a pencil D,
+so as to keep the part DL close to the edge
+of the square, and if at the same time the
+square be gently pushed along the line AB,
+the point D will be forced to move along the
+edge LH of the square, and will trace out a curve which will be the required parabola.
+This is obvious from the consideration, that the string LDF being equal in length to LH,
+and LD being common to both, the remainder DF must be equal to the remainder DH, so
+that the point which traces the curve being equidistant from the directrix and the focus
+must, in terms of the above definition, describe a parabola.</p>
+
+<div class="container w25emmax" id="Fig23">
+
+<p class="caption">Fig. 23.</p>
+
+<img src="images/illo211a.jpg" alt="Mechanical construction of curve">
+
+</div><!--container-->
+
+<p>In the second place, the same property, as already stated, furnishes us with the means
+of tracing the curve by finding successive points
+therein. Draw a line <i>a&#160;b</i> perpendicular to the axis
+OX, and the position in this line, of a point <i>p</i>
+through which the curve passes, is easily found thus:
+Describe from F the focus as a centre with a radius
+equal to the perpendicular distance O <i>d</i> of the line
+<i>a&#160;b</i> from the directrix AB, a circle cutting the line
+<i>a&#160;b</i> in two points <i>p</i> and <i>p′</i>; then both these points
+are in the curve. By repeating the same process,
+any number of points in the curve may be obtained.</p>
+
+<div class="container w25emmax" id="Fig24">
+
+<p class="caption">Fig. 24.</p>
+
+<img src="images/illo211b.jpg" alt="Tracing of curve">
+
+</div><!--container-->
+
+<p>Lastly, from the equation to the curve, the length <i>y</i> of any ordinate may be computed,
+in terms of <i>m</i> its principal focal distance, and x its abscissa, by the simple <span class="nowrap">expression,—</span></p>
+
+<p class="center highline2"><i>y</i> = √<span class="bt">4 <i>m&#160;x</i></span>.</p>
+
+</div><!--footnote-->
+
+<p>It is easy to see, that if this curve revolve about its axis, it will
+generate a parabolic conoid, which we may conceive to be concave
+or convex, as we please. If the surface be concave, we obtain the
+mirror of which we are in search; for every principal section, or
+that passing through the axis of such a mirror, will necessarily<span class="pagenum" id="Page211">[211]</span>
+possess the same properties as that of the plane curve, and will
+each have a focus meeting in one and the same point; the union of
+all these sections will therefore form a mirror capable of reflecting,
+in a direction parallel to the axis and to each other, all the rays of
+light which fall on its surface.</p>
+
+<p><span class="pagenum" id="Page212">[212]</span></p>
+
+<p>We have already seen that a perfect paraboloïdal mirror, with
+a point of light infinitely small placed in the focus, would project
+a beam equally intense at any distance, every transverse section
+of which would be of the same superficial extent. <span class="sidenote">Divergence of
+Paraboloïdal
+Mirrors.</span>
+In practice,
+these conditions can never be rigorously fulfilled. No perfect instrument
+can come from the hands of man, and every mirror must
+of necessity possess many defects. To obtain a true mathematical
+point of light is also impossible; and for the purposes of a lighthouse,
+it would be completely useless, as will appear from the following
+simple considerations. Let us suppose that a true paraboloïdal
+mirror, having a double ordinate or space of two feet, and
+illuminated by a point of light, projects a truly cylindric beam of
+light to the horizon, and that it revolves horizontally round a vertical
+axis, with such a velocity as to cause the beam to pass over
+the eye of an observer stationed at the distance of 100 feet in one
+second of time, and we shall find that another observer, at a distance
+of 15 miles from the mirror, would not see the light at all,
+although of equal size, because its velocity at that distance would
+be so great as only to be present to his eye for ¹⁄₇₉₂d of a second,
+a space of time far too short to make a perceptible impression
+on the eye of a distant observer. This is no mere hypothesis
+unsupported by facts; for I shall have occasion, in another part of
+these Notes, to describe certain experiments, by which it was ascertained
+that a beam of light emerging from a lens, and passing over
+the eye of an observer at 14 miles distance, in a space of time equal
+to ¹⁄₁₆₆th of a second, became altogether invisible at that distance.</p>
+
+<p>For this evil, happily a very simple and efficient remedy may
+be found in what may be said to constitute a <i>theoretical</i> defect in
+the combination of the Argand burner with the reflector. The
+burner, instead of being a mathematical point, has generally a diameter
+of about one inch, and a ray proceeding from the edge of
+the flame to any point on the surface of the mirror, makes with the
+line joining that point and the principal focus an angle which,<span class="pagenum" id="Page213">[213]</span>
+being repeated by reflection, gives the effective divergence of <i>each</i>
+side of the mirror at that point.<a id="FNanchor43" href="#Footnote43" class="fnanchor">[43]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote43" href="#FNanchor43" class="label">[43]</a> This is easily understood by
+reference to the accompanying figure (<a href="#Fig25">No. 25.</a>), in which
+AOB is a central section of a paraboloïdal mirror.</p>
+
+<div class="container w20emmax" id="Fig25">
+
+<p class="caption">Fig. 25.</p>
+
+<img src="images/illo213.jpg" alt="Divergence of light">
+
+</div><!--container-->
+
+<p>PF = distance from the focus F to a point in the
+curve P, and PG a tangent drawn from P to the surface
+of the flame at G;</p>
+
+<p>FG = radius of the wick or flame;</p>
+
+<p class="blankafter75">and GPF = G′PF′ = divergence of one side of mirror,
+and consequently 2 GPF = the whole effective divergence
+of the mirror at that cross section.</p>
+
+<p>Now sin&#160;GPF = <span class="divide"><span class="num">GF</span><span class="denom">PF</span></span>
+or the sine of the divergence from each point
+= <span class="divide"><span class="num">Radius of flame.</span><span class="denom">Distance
+from focus to point of reflection.</span></span></p>
+
+<div class="container w30emmax" id="Fig26">
+
+<p class="caption">Fig. 26.</p>
+
+<img src="images/illo214.jpg" alt="Divergence of light">
+
+</div><!--container-->
+
+<p>It is obvious that this quantity which varies <i>inversely</i>
+with the distance of the reflecting surface from
+the focus, is greatest at the vertex of the curve, and
+least at the sides or edges of the paraboloïd. The
+most useful part of the light, or that which conduces to the strongest part of the flash in a
+revolving light, is that which is derived from the cone of rays which is bounded by the limits
+of this <i>minimum</i> divergence; for the faint light which first reaches the eye of a distant
+observer, in the revolution of a reflector, is not that which is reflected by the sides or edges,
+as might at first be supposed, but proceeds from the centre. The light, in fact, gradually
+increases in power in proportion as additional rays of reflected light are brought to bear
+on the observer’s eye, until, last of all, the extreme edge of the mirror adds its effect. The
+light continues in its best state until the opposite limit of minimum divergence has been
+reached, when it begins gradually to decline, receding from the margin of the mirror towards
+the centre, and, having at length reached the limit of its maximum divergence, it finally
+disappears at the centre. The increase and decline of the power of a mirror in the course
+of its movement round the circle of the lantern, as seen by a distant observer, will, therefore,
+in all its different states, be measured by the areas of a series of circles described from
+its focus, with radii equal to the distance of the focus from the point of the mirror which
+reflects to the observer’s eye the extreme ray which can reach him in any given position of the
+mirror. This will be more easily understood by referring to the accompanying diagram, <a href="#Fig26">Fig. 26</a>,
+in which <i>e a e′</i> is the principal section of a paraboloïdal mirror, F its focus, αFA its axis, and
+FK the radius of the flame. If the reflector revolve round a vertical axis at O, an observer
+placed in front of it (at a distance so great that the subtense of the mirror’s width would be
+small enough to allow us safely to
+consider the lines drawn from <i>e</i> and
+<i>e′</i> to his eye as parallel), would receive
+the first ray of light in the direction
+<i>a</i> D, as reflected at <i>a</i>, from a
+single point on the edge of the flame
+(where a tangent to the flame would
+pass through <i>a</i>); and conversely he
+would lose the last ray at D′, as reflected
+at <i>a</i>, from a single point on
+the opposite margin of the flame;
+and hence, as above, the greatest divergence
+is measured by the angle
+which the flame subtends at the
+vertex a of the mirror, being the sum
+of the angles <i>α</i> and <i>α′</i>. We shall
+next suppose the mirror to move a
+little, so that the observer may receive
+at G a ray of light from some
+other point in the flame which is reflected
+at <i>b</i>; while another ray from
+an opposite point reflected at <i>b′</i> would be seen in the parallel direction <i>b′</i> G′, thus indicating
+the boundary of a circular portion of the mirror <i>b a b′</i>, the whole of which would reflect
+light to the distant observer’s eye. Again, let us suppose a ray to come from another
+part of the flame, and be reflected at the mirror’s edge <i>e</i> into the direction <i>e</i> H, and another
+from the opposite side of the flame to be reflected at its opposite edge <i>e′</i>, into the direction
+<i>e′</i> G″, and we obtain the full effect of the whole reflecting surface, which will continue unabated
+until the mirror in the course of its revolution shall reflect at <i>e′</i> to the observer’s eye, a
+ray from a point in the margin of the flame (through which a tangent drawn from <i>e′</i> to
+the flame would pass) in such a direction, that the angle which it makes with the axis of
+the mirror is equal to that subtended by the radius of the flame at the distance F <i>e</i> or F <i>e′</i>.
+After this the light would recede from the edges of the mirror in the same gradual manner,
+until it should vanish in the direction <i>a</i> D′, which is the opposite limit of the extreme divergence
+of the instrument. In the above explanation, I have confined myself simply to the
+effects of the outer ring of the flame, which is the source of divergence; but I need not remind
+the reader that every portion of the flame radiates light, which, being reflected, conduces
+to the effect. Some rays also are passing from the opposite sides of the flame through the
+true focus, so as to be normally reflected in lines parallel to its axis. The solid lines in
+the diagram shew the theoretical reflection of rays proceeding from F to <i>b</i>, <i>b′</i>, <i>e</i>, <i>e′</i>, where
+they are diverted into the directions <i>b</i> B, <i>b′</i> B′, <i>e</i> E, and <i>e′</i> E′; and by contrast with the
+dotted lines, serve to render more perceptible the path of the divergent rays which come
+from the edge of the flame. The Greek letters indicate the angles of divergence, and point
+out their relations to each other on either side of the mirror. The arcs of greatest and
+least divergence are marked in the diagram. This subject will be found treated less directly,
+but, certainly, more concisely and neatly, by Mr <span class="smcap">W. H. Barlow</span>, in a paper on the Illumination
+of Lighthouses in the London Transactions for 1837, p. 218.</p>
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page214">[214-<br>215]<a id="Page215"></a></span></p>
+
+<p>It is still more obvious that a perfect paraboloïdal figure, and
+a luminous <i>point</i> mathematically true, would render the illumination
+of the whole horizon by means of a fixed light <i>impossible</i>; and
+it is only from the divergence caused by the size of the flame which
+is substituted for the <i>point</i>, that we are enabled to render even
+revolving lights practically useful. But for this aberration, the
+slowest revolution in a revolving light would be inconsistent with
+a continued observable series, such as the practical seamen could follow,
+and would, as we have seen, render the flashes of a revolving
+light too transient for any useful purpose; whilst fixed lights, being
+visible in the azimuths only in which the mirrors are placed, would,
+over the greater part of the distant horizon, be altogether invisible.
+The size of the flame, therefore, which is placed in the focus of a
+paraboloïdal mirror, when taken in connexion with the form of the
+mirror itself, leads to those important modifications in the paths of
+the rays and the form of the resultant beam of light, which have
+rendered the catoptric system of lights so great a benefit to the benighted
+seamen.</p>
+
+<p>In order to obtain a mirror capable of producing a given divergence
+of the reflected beam, therefore, we must proportion its focal
+distance to the diameter of the flame in such a manner, that the
+sine of <i>one-half</i> of the whole effective divergence of the mirror, may
+be equal to the <i>quotient of the radius of the flame, divided by the distance
+of a given point on the surface of the mirror from the focus</i>.
+The best proportions for paraboloïdal mirrors depend on the objects
+which they are meant to attain. Those which are intended
+to give great divergence to the resultant beams, as in fixed lights,
+capable of illuminating the whole horizon at one time, should<span class="pagenum" id="Page216">[216]</span>
+have a short focal distance; while those mirrors which are designed
+to produce a nearer approach to parallelism (as in the case
+of revolving lights which illuminate but a few degrees of the horizon
+at any one instant of time), will have the opposite form.
+Those two objects may, no doubt, be attained with the same mirror,
+by increasing or diminishing the size of the burner; but that is
+by no means desirable, as any change on the size of a burner, which
+is found to be the best in other respects, must be considered as to
+some extent disadvantageous.</p>
+
+<p>What I have stated above as to the use of mirrors with a short
+focal distance for lights of great divergence, proceeds on the assumption,
+that the penumbral portion of the light on each side of the
+strongest beam (which is confined within the limits of the least divergence,
+due to that portion of the mirror where the focal distance
+is the greatest) is to be pressed into service in the illumination of
+the horizon; and it is the chief inconvenience which attends the
+application of paraboloïdal mirrors to fixed lights, that because it is
+impracticable to apply a number of mirrors sufficient to light the
+whole horizon with an equally strong light, spaces occur on either
+side of each reflector in which the mariner has a light sensibly
+inferior to that which illuminates the sector near the axis of each
+mirror. This will be best explained by stating the numerical results
+of the computations of the divergence of the mirrors used in the
+Northern Lights for this purpose, both at the vertex and the sides.
+In a mirror whose focal distance is 4 inches, and its greatest double
+ordinate 21 inches, illuminated by a flame 1 inch in diameter,
+we find by computation, that the greatest divergence is 14° 22′,
+and that the strongest arc of light is only 5° 16′; a difference so
+great, that while the one may admit of the horizon being imperfectly
+illuminated by means of 26 reflectors, the superior light
+which would result from confining the duty of each instrument
+within the range of its best effect, could only be obtained by the
+use of 68 reflectors, and the expenditure of a proportionately great
+quantity of oil, not to speak of the great practical difficulty which<span class="pagenum" id="Page217">[217]</span>
+would attend the arrangement of so many lamps in a lantern of
+moderate size. In revolving lights, the mirrors are not, as in fixed
+lights, inconveniently taxed for horizontal divergence, because each
+portion of the divergent beam visits successively each point of
+the horizon. In this view of the merits of <i>fixed</i> and <i>revolving</i>
+lights, I should be disposed to recommend, in any new organisation
+of lights with parabolic reflectors, the adoption, in fixed lights, of
+reflectors with a short focal distance and small span, so as to admit
+of many being ranged around the frame; while in revolving
+lights, it would be my aim to approach the largest size of reflector
+that could be made, so as if possible to illuminate each face of the
+revolving frame by means of a large lamp in a single mirror, with
+a great focal distance, thereby diminishing the difference between
+the divergence of the powerful cone of rays reflected from the more
+distant parts of the mirror and that of the feebler and more diffuse
+light from its apex.</p>
+
+<p><span class="sidenote">Effect of Paraboloïdal
+mirrors.</span>
+The maximum luminous effect of the reflectors ordinarily employed
+in fixed lights, as determined by observation, is generally
+equal to about 350 times the effect of the unassisted flame which
+is placed in the focus; while for those employed in revolving lights,
+which are of larger size, it is valued at 450. This estimate, however,
+is strictly applicable only at the distances at which the observations
+have been made, as the proportional value of the reflected beam
+must necessarily vary with the distance of the observer, agreeably
+to some law dependent upon the unequal distribution of the
+light in the illuminous cone which proceeds from it. The effect
+also varies very much in particular instruments. The ordinary
+burners used in lighthouses are one inch in diameter, and the focal
+distance generally adopted is 4 inches, so that the extreme divergence
+of the mirror in the horizontal plane may be estimated at about
+14° 22′; while the divergence of the most luminous cone is 5° 16′
+for the small reflectors, and 4° 25′ for the larger size. In arranging
+reflectors on the frame of a fixed light, however, it is advisable<span class="pagenum" id="Page218">[218]</span>
+to calculate upon a less amount of effective divergence, for beyond
+11° the light is very feeble; but the difficulty of placing
+many mirrors on one frame, and the great expense of oil required
+for so many lamps, have generally led to the adoption of the first
+valuation of the <i>effective</i> divergence.</p>
+
+<p><span class="sidenote">Power of Paraboloïdal
+Mirrors.</span>
+The measure of the illuminating power of a paraboloïdal mirror
+may be estimated as the <i>quotient of the</i> <span class="allsmcap">SURFACE</span> <i>of the circle which
+cuts it in the plane of its greatest double ordinate, divided by the surface
+of the largest vertical section of the flame, and diminished by the
+loss of light in the process of reflection</i>. This estimate will be found
+near enough for all practical purposes; but it is obviously inaccurate,
+inasmuch as it overlooks the circumstance of the focal distance
+of each portion of the mirror being different, and the consequent
+increase in the length of the various trajectories at each point of
+the surface as you recede from the axis; and the only correct rule,
+therefore, is, to find an imaginary focal distance which must be the
+radius of a spherical segment which shall answer the double condition
+of having its surface equal to that of the greatest cross section
+of the mirror, and of including, at the same time, a number of
+degrees equal to those which are brought under the influence of the
+reflecting action of the paraboloïd. This subject, however, as I
+have already hinted, is not of great practical importance; and I
+shall not therefore dilate on it farther, but content myself with saying,
+that such a line will be found to be a <i>mean proportional</i> between
+the <i>greatest</i> and <i>least</i> focal distances of the mirror.<a id="FNanchor44" href="#Footnote44" class="fnanchor">[44]</a> The large
+mirrors used in the Northern Lights have about ¹²⁄₁₇ths of the whole
+light of the lamp incident on their surface; the rest escapes in the
+comparatively useless state of naturally radiating light.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote44" href="#FNanchor44" class="label">[44]</a> This subject is treated in
+detail in M. <span class="smcap">Barlow’s</span> Paper already noticed. (London
+Transactions for 1837, p. 212.)</p>
+
+</div><!--footnote-->
+
+<p><span class="sidenote">Manufacture of
+Reflectors.</span>
+The reflectors used in the best lighthouses, are made of sheet-copper
+plated in the proportion of six ounces of silver to sixteen
+ounces of copper. They are moulded to the paraboloïdal form, by<span class="pagenum" id="Page219">[219]</span>
+a delicate and laborious process of beating with mallets and hammers
+of various forms and materials, and are frequently tested during
+the operation by the application of a mould carefully formed.
+After being brought to the curve, they are stiffened round the
+edge by means of a strong bizzle, and a strap of brass which is
+attached to it for the purpose of preventing any accidental alteration
+of the figure of the reflector. Polishing powders are then applied,
+and the instrument receives its last finish. The <a href="#App2">details</a> of
+this manufacture are given in the Appendix.</p>
+
+<p><span class="sidenote">Testing of
+Mirrors.</span>
+Two gauges of brass are employed to test the form of the reflector.
+One is for the back, and is used by the workmen during the
+process of hammering, and the other is applied to the concave face
+as a test, while the mirror is receiving its final polish. It is then
+tested, by trying a burner in the focus, and measuring the intensity
+of the light at various points of the reflected conical beam.
+Another test may also be applied successively to various points in
+the surface, by masking the rest of the mirror; but as it proceeds
+upon the assumption that the surface of the reflector is perfect,
+and that we can measure accurately the distance from a radiant coincident
+with the focus to the point of the mirror to be tried, it is
+in practice almost useless. For such a trial we must place a screen
+in the line of the axis of the mirror at some given distance from
+it, and ascertain whether the image of a very small object placed
+in the conjugate focus, which is due to the distance of the screen
+in front of the focus, be reflected to any point considerably distant
+from the centre of the screen through which the prolongation of
+the axis of the mirror should pass. We thus obtain a measure of
+the error of the instrument. For this purpose, we must find
+the position of the conjugate focus, which corresponds to the
+distance of the screen. If <i>b</i> be the distance to which the object
+should be removed outwards from the principal focus of the mirror,
+<i>d</i> the distance from the focus to the screen, and <i>r</i> the distance
+from the focus to that point of the mirror which is to be tested,<span class="pagenum" id="Page220">[220]</span>
+we shall have <i>b</i> = <span class="divide"><span class="num"><i>r</i>²</span><span class="denom"><i>d</i></span> </span>
+as the distance to which the object must be
+removed outwards from the true focus on the line of the axis.<a id="FNanchor45" href="#Footnote45" class="fnanchor">[45]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote45" href="#FNanchor45" class="label">[45]</a> The truth of this equation may
+be easily ascertained as follows (See <a href="#Fig27">fig. 27</a>):—Let
+AP be the mirror, F its principal
+focus, and PH the line of reflection of the
+ray FP; then an object at I will be reflected
+at P to the conjugate focus O,
+where the screen is supposed to be placed.
+But by construction, FPI = HPO = POF,
+and the angle at F being common, the
+triangle FPI is similar to FPO, and hence
+FO&#160;∶ PF&#160;∷ PF&#160;∶ FI, and FI = <span class="divide"><span class="num">PF²</span><span class="denom">FO</span></span>; and
+substituting the letters in the text, we get
+<i>d</i>&#160;∶ <i>r</i>&#160;∷ <i>r</i>&#160;∶ <i>b</i>, and <i>b</i> =
+<span class="divide"><span class="num"><i>r</i>²</span><span class="denom"><i>d</i></span></span>.</p>
+
+<div class="container w30emmax" id="Fig27">
+
+<p class="caption">Fig. 27.</p>
+
+<img src="images/illo220.jpg" alt="Reflection of parabolic mirror">
+
+</div><!--container-->
+
+</div><!--footnote-->
+
+<div class="split3367">
+
+<div class="left3367">
+
+<div class="container w20emmax" id="Fig28">
+
+<p class="caption">Fig. 28.</p>
+
+<img src="images/illo221a.jpg" alt="Details of lamp assembly">
+
+</div><!--container-->
+
+</div><!--left3367-->
+
+<div class="right3367">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<div class="container w20emmax" id="Fig29">
+
+<p class="caption">Fig. 29.</p>
+
+<img src="images/illo221b.jpg" alt="Details of lamp assembly">
+
+</div><!--container-->
+
+</div><!--left5050-->
+
+<div class="right5050">
+
+<div class="container w20emmax" id="Fig30">
+
+<p class="caption">Fig. 30.</p>
+
+<img src="images/illo221c.jpg" alt="Details of lamp assembly">
+
+</div><!--container-->
+
+</div><!--right5050-->
+
+</div><!--split5050-->
+
+</div><!--right3367-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split3367-->
+
+<div class="container left w08emmax" id="Fig31">
+
+<p class="caption">Fig. 31.</p>
+
+<img src="images/illo222.jpg" alt="Oil cup">
+
+</div><!--container-->
+
+<p><span class="sidenote">Argand Lamps
+used in Reflectors.</span>
+The flame generally used in reflectors, is from an Argand fountain-lamp,
+whose wick is an inch in diameter. Much care is bestowed
+upon the manufacture of the lamps for the Northern Lighthouses,
+which sometimes have their burners tipped with silver to
+prevent wasting by the great heat which is evolved. The burners
+are also fitted with a sliding apparatus, accurately formed, by
+which they may be removed from the interior of the mirror at the
+time of cleaning them, and returned exactly to the same place, and
+locked by means of a key. This arrangement, which is shewn in
+<a href="#Fig28">figs. 28</a>, <a href="#Fig29">29</a>, and <a href="#Fig30">30</a>, is very important, as it insures the burner always
+being in the focus, and does not require that the reflector be lifted
+out of its place every time it is cleaned; so that, when once
+carefully set and screwed down to the frame, it is never altered.
+In these figs. <i>a a a</i> represents one of the reflectors, <i>b</i> is the burner,
+and <i>c</i> a cylindric fountain, which contains 24 ounces of oil. The
+oil-pipe, the fountain <i>c</i> for supplying oil, and the burner <i>b</i>, are
+connected with the rectangular frame <i>d</i>, which is moveable in a
+vertical direction upon the guide-rods <i>e</i> and <i>f</i>, by which it can be<span class="pagenum" id="Page221">[221]</span>
+let down, so that the burner may be lowered out of the reflector, by
+simply turning the handle <i>g</i> (as will be more fully understood by
+examining <a href="#Fig28">figs. 28</a> and <a href="#Fig29">29</a>), which has the effect of forcing a <i>thread</i>
+(like that of a screw) on the outside of the guide into a groove in
+the frame, or withdrawing it, and thus allows it to slide down or
+locks it at pleasure. An aperture of an elliptical form, measuring
+about two inches by three, is cut in the upper and lower part of
+the reflector, the lower serving for the free egress and ingress of
+the burner, and the upper, to which the copper tube <i>h</i> is attached,
+serving for ventilation; <i>i</i> shews a cross section and a back view of
+the main bar of the chandelier or frame on which the reflectors are
+ranged, each being made to rest on knobs of brass, one of which, as
+seen at <i>k&#160;k</i>, is soldered to the brass band <i>l</i>, that clasps the exterior
+of the reflector. <a href="#Fig28">Fig. 28</a> is a section of the reflector <i>a&#160;a</i>, shewing
+the position of the burner <i>b</i>, with the glass chimney <i>b′</i>, and oil-cup <i>l</i>,
+which receives any oil that may drop from the lamp. <a href="#Fig30">Fig. 30</a> shews
+the apparatus for moving the lamp up and down, so as to remove it
+from the reflector at the time of cleaning it. In the diagram (<a href="#Fig30">fig. 30</a>)
+the fountain <i>c</i> is moved partly down; <i>d&#160;d</i> shews the rectangular
+frame on which the burner is mounted, <i>e&#160;e</i> the elongated socket-guides
+through which the guide-rods slide, and <i>f</i> the guide-rod, connected<span class="pagenum" id="Page222">[222]</span>
+with the perforated sockets on which the <i>checking-handle g</i>
+slides. The oil-cup <i>l</i> (covered with a lid and wick-holder, as shewn
+in <a href="#Fig31">fig. 31</a>) also serves as a <i>frost-lamp</i> during the long
+nights of winter, when the oil is apt to turn thick. It is
+attached to the lower part of the oil-tube by the arm <i>h</i>;
+and is lighted about an hour before sunset, so as to prepare
+the reflector lamp for lighting at the proper time.
+The communication between the burner and the fountain is easily
+opened or shut in the burners used in the Scotch Lighthouses,
+by simply giving the fountain a turn of one quadrant of the horizon
+round its own vertical axis by means of the round knob at its top,
+and thereby moving a simple slide-valve, which shuts off the communication
+between the fountain-tube and lamp-tube. By this
+mode, the oil is cut off about fifteen minutes before extinguishing
+the lights, so that when that is done, the burner is quite free of oil.</p>
+
+<div class="container w30emmax" id="Fig32">
+
+<p class="caption">Fig. 32.</p>
+
+<img src="images/illo223a.jpg" alt="Argand burner details">
+
+</div><!--container-->
+
+<p>It would needlessly occupy much time and space to describe the
+various means (many of them sufficiently clumsy) which have been
+employed, and in many places are still in use, for raising and depressing
+the wick; it will be enough to say, that they all involve
+some application of the rack and pinion. <span class="sidenote">Arrangements for
+Raising or lowering
+the Argand
+Wick.</span>
+I shall, therefore, only describe
+the method (invented, it is believed, by M. <span class="smcap">Verzy</span>) which is
+adopted in all the Lighthouses in the district of the Commissioners
+of Northern Lights. The arrangement is as follows (see <a href="#Fig32">figs. 32</a>,
+<a href="#Fig33">33</a>, <a href="#Fig34">34</a>, <a href="#Fig35">35</a>, <a href="#Fig36">36</a>):—The inner tube <i>t</i> of the burner is enclosed by a
+strong tube <i>s</i>, which fits to it tightly, so as not to be easily moved.
+This strong tube has a spiral groove cut on its outer or convex surface.
+The wick-holder has two small pegs projecting from it, the
+one on the inside (not seen), and the other on the outside at <i>a</i>
+(<a href="#Fig33">fig. 33</a>). That on the inside works in the spiral groove of the
+tube S (<a href="#Fig32">figs. 32</a> and <a href="#Fig33">33</a>), already described as embracing the inner
+tube <i>t</i>; and all that is required for raising the wick is to make the
+wick-holder turn round on its vertical axis. This is effected by
+means of the small external peg <i>a</i> of the wick-holder (<a href="#Fig33">fig. 33</a>), which
+moves in a vertical slit <i>a</i> (<a href="#Fig32">figs. 32</a> and <a href="#Fig34">34</a>),
+cut in a tube standing<span class="pagenum" id="Page223">[223]</span>
+in the burner, and concentric with it, and which also moves freely
+round its axis. Small knobs <i>n</i>&#160;<i>n</i> (<a href="#Fig32">figs. 32</a>, <a href="#Fig34">34</a>, and <a href="#Fig36">36</a>), at the top
+of this tube, fit into a notch in the upper ring of the gallery, which
+supports the glass chimney. By turning this gallery <i>g</i> (see <a href="#Fig33">figs. 33</a>
+and <a href="#Fig36">36</a>), therefore, motion is given to the tube, with its knobs <i>n</i>&#160;<i>n</i>,
+whose vertical slit <i>a</i> (while it holds the external peg of the wick-holder,
+and also turns it round along with it) permits that peg <i>a</i> to
+slide upwards or downwards, and thus the wick-holder rises or falls,
+according as its own internal peg moves up or down the spiral groove
+in the tube S. In <a href="#Fig32">fig. 32</a>, C shews the glass chimney resting on
+the gallery <i>g&#160;g</i>.</p>
+
+<div class="split3367">
+
+<div class="left3367">
+
+<div class="container w10emmax" id="Fig33">
+
+<p class="caption">Fig. 33.</p>
+
+<img src="images/illo223b.jpg" alt="Argand burner details">
+
+</div><!--container-->
+
+</div><!--left3367-->
+
+<div class="right3367">
+
+<div class="container w20emmax" id="Fig34">
+
+<p class="caption">Fig. 34.</p>
+
+<img src="images/illo223c.jpg" alt="Argand burner details">
+
+</div><!--container-->
+
+</div><!--right3367-->
+
+</div><!--split3367-->
+
+<div class="split3367">
+
+<div class="left3367">
+
+<div class="container w10emmax" id="Fig35">
+
+<p class="caption">Fig. 35.</p>
+
+<img src="images/illo223d.jpg" alt="Argand burner details">
+
+</div><!--container-->
+
+</div><!--left3367-->
+
+<div class="right3367">
+
+<div class="container w20emmax" id="Fig36">
+
+<p class="caption">Fig. 36.</p>
+
+<img src="images/illo223e.jpg" alt="Argand burner details">
+
+</div><!--container-->
+
+</div><!--right3367-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split3367-->
+
+<p>An important point in the economy of the Argand lamp, is the
+level at which the outlet for the oil, in its passage from the fountain to
+the burner, should be cut. The cutting of this hole (generally called<span class="pagenum" id="Page224">[224]</span>
+the <i>flow-hole</i>) in the pipe is termed the <span class="sidenote">Flowing of the
+Lamp.</span>
+<i>flowing</i> of the lamp, and is
+commonly done by successive trials, until the oil stands at the proper
+level of the burner, before the wick is put in. A more ready
+and accurate method of accomplishing this object and at once determining
+the level at which the <i>flow-hole</i> should be cut, was introduced
+by Mr <span class="smcap">James Murdoch</span>, the Foreman of Lightroom Repairs to the
+Scotch Board, and is generally employed in the Northern Lighthouses.
+Its nature will be readily understood by a reference to the
+accompanying diagram, <a href="#Fig37">No. 37</a>:</p>
+
+<div class="container w30emmax" id="Fig37">
+
+<p class="caption">Fig. 37.</p>
+
+<img src="images/illo224.jpg" alt="Working of oil outlet">
+
+</div><!--container-->
+
+<p>The <i>hatched</i> surface represents
+a metallic ruler, with a spirit-level
+at L; C is the cup in which the bottom
+of the fountain <i>f</i> (shewn in
+dotted lines) rests. When the
+fountain is removed, and the ruler
+rests on the edge of the cup C, the
+screw at A is used to adjust the
+level at L; and a gauge GG is allowed
+to fall until a notch in it at
+<i>x′</i> rests on the outer tube of the
+burner F; the pinching-screw B
+retains this ruler in its place, and
+the point <i>x′</i> indicates the level at
+which the oil should stand in the
+burner. The level line <i>x′ x</i> indicates
+the level on which the top
+of the <i>flow-hole</i> H should be cut
+in the fountain-tube, which is shewn in dotted lines within the
+outer tube, or <i>body</i> of the lamp. In other words, <i>y′&#160;x′</i> measures
+the level at which the oil should stand in the burner <i>below</i> the
+lower edge of the metallic ruler, while the corresponding line <i>y&#160;x</i>,
+at the opposite end, shews the level of the top of the <i>flow-hole</i> H,
+below the edge of the cup C. The gauge GG applied to that point
+of the fountain which coincides with the edge of the cup (so that <i>y′</i><span class="pagenum" id="Page225">[225]</span>
+coincides with <i>y</i>) measures the length <i>yx</i> = <i>y′&#160;x′</i>; and a <i>set-square</i>
+applied at <i>x</i> gives the position of H on the fountain-tube. The
+round dot at <i>a</i> shews the position of the air-hole in the body of the
+lamp, which establishes a connection between the external air and
+the surface of the oil. The rods SS′ shew the sliding gear (described
+as <i>d</i> and <i>f</i>, <a href="#Page221">page 221</a>), and are only introduced to identify
+this diagram with those of the fountain and burner which have
+preceded it.</p>
+
+<p>The most advantageous level of the flow-hole depends on many
+circumstances too obscure and complicated to admit of any systematic
+elucidation; and it is enough for all practical purposes, to
+know that the capillary powers of the wick, and the greater or less
+viscidity of the oil, are the chief circumstances which determine
+that level. Actual experience is the only sure guide to the best
+practice in this respect; and I therefore content myself with stating,
+that it is generally found that the sperm oil should stand in
+the empty burner at about ³⁄₈ inch below its top. For colza oil ²⁄₈
+inch is sufficient. In summer, owing to the oil being more fluid,
+there is sometimes a tendency to overflow the burner; but any
+inconvenience arising from it is avoided by the plan adopted in the
+Northern Lights, of shutting off the oil (by means of the apparatus
+already alluded to on <a href="#Page222">p. 222</a>) about fifteen minutes before
+extinguishing the lights in the morning.</p>
+
+<div class="container w10emmax" id="Fig38">
+
+<p class="caption">Fig. 38.</p>
+
+<img src="images/illo225.jpg" alt="Oil cut-off">
+
+</div><!--container-->
+
+<p>The arrangement for cutting off the oil is very simple,
+as will be seen from the annexed diagram (fig. 38),
+in which F is the fountain, T the oil-tube leading to
+the burner, and V the <i>flow-hole</i>, with its sliding valve.
+By turning the handle H one quadrant of the circle,
+the whole fountain F and tube T turn round their vertical
+axis, while the valve V, which rests in a notch
+in the cup of the lamp, remains still, and sliding over
+T, opens the <i>flow-hole</i>. S is the screw-plug which retains
+the oil in the fountain, and which is unscrewed
+and removed when the fountain is to be filled.</p>
+
+<p><span class="pagenum" id="Page226">[226]</span></p>
+
+<div class="container w40emmax" id="Fig39">
+
+<p class="caption">Fig. 39.</p>
+
+<img src="images/illo226a.jpg" alt="Burner adjustment apparatus">
+
+</div><!--container-->
+
+<div class="container w30emmax" id="Fig40">
+
+<p class="caption">Fig. 40.</p>
+
+<img src="images/illo226b.jpg" alt="Burner adjustment apparatus">
+
+</div><!--container-->
+
+<p><span class="sidenote">Placing the Lamp
+in the Focus.</span>
+In the reflecting apparatus of the Northern Lighthouses, the focal
+position of
+the lamp is not,
+as we have already
+seen, liable
+to derangement,
+by the removal
+of the
+burner for the
+purpose of cleaning,
+as the sliding
+gear described
+at <a href="#Page221">p. 221</a> insures
+the return
+of the lamp to its
+true place. The burner is originally set by means of a gauge, which
+touches four points of the mirror’s surface (one of them being its vertex,
+and the other three in the
+vertical plane of its greatest
+double ordinate). This gauge
+being provided with a short
+tube or collar properly placed
+for the purpose of receiving
+the burner, at once verifies its
+true position, both vertical and
+horizontal. The <a href="#Fig39">diagrams 39</a>
+and <a href="#Fig40">40</a> shew the nature of the
+apparatus for adjusting the
+burners, the one being a plan
+and the other a section. The
+four points which touch the
+curve are one <i>g</i> at the vertex,
+two in the same horizontal
+plane with the focus, and near the edge of the mirror at PP, and<span class="pagenum" id="Page227">[227]</span>
+the fourth, also near the edge, and in the same vertical plane with
+the focus. F is the focus. The horizontal arms are graduated, and
+fitted with sliding pieces and clamping screws at R, so as to admit
+of being varied with the width of the mirror; but each gauge applies
+only to curves of the same focal distance; the distance F <i>g</i> being
+fixed. The gauge, when applied to the mirror, is properly secured
+by the screws at R, R, and R′; and the burner which is attached
+to the oil-tube in a temporary manner at A, is raised into the interior
+of the mirror. If the tube of the burner ascends into the circular
+tube at F until (when fixed by the checking handle already
+noticed at <a href="#Page221">p. 221</a>) its upper edge just touches a narrow projection
+inside the tube F (so placed that the rim of the burner should just
+touch it when it is on the level required for putting the brightest
+part of the flame in the focus), then the burner is in the proper position;
+but if, on the one hand, the axis of the burner stands beyond
+F, at some point between it and N (which lies in the plane of the
+mirror’s edge), the bent tube O from the fountain must be shortened
+at A; and if it rise too high, that tube must be bent down (and <i>vice
+versa</i>), until, by successive trials, it shall exactly fit into the tube F,
+and stand at the proper level. A skilful workman soon comes to
+guess those quantities very accurately; and, almost at the first trial,
+curtails the tube to the proper length, and bends it to the suitable
+level. All that is needful is to proceed cautiously, so as not to cut
+the tube too short, for this leads to some trouble.</p>
+
+<p>The great advantage derived by seamen from the establishment
+of lights on a coast, soon makes the calls for additional lights
+so frequent, that their very number itself produces a new evil, in
+the difficulty of distinguishing the lights from each other. As the
+object of a light is to make known to the benighted mariner the
+land he has made, with as much certainty as the sight of a hill or
+tower would shew him his position during the day, it becomes an
+object of the first importance to <span class="sidenote">Distinctions of
+Catoptric Lights.</span>
+impress upon each light a distinctive
+character, which shall effectually prevent the possibility of its
+being mistaken for any other.</p>
+
+<p><span class="pagenum" id="Page228">[228]</span></p>
+
+<p>Catoptric lights are susceptible of nine separate distinctions,
+which are called <i>fixed</i>, <i>revolving white</i>, <i>revolving red and white</i>, <i>revolving
+red with two whites</i>, <i>revolving white with two reds</i>, <i>flashing</i>,
+<i>intermittent</i>, <i>double fixed lights</i>, and <i>double revolving white lights</i>.
+The first exhibits a steady and uniform appearance, which is not
+subject to any change; and the reflectors used for it (as already
+noticed) are of smaller dimensions than those employed in revolving
+lights. This is necessary, in order to permit them to be ranged
+round the circular frame, with their axes inclined at such an angle,
+as shall enable them to illuminate every point of the horizon. The
+revolving light is produced by the revolution of a frame with three
+or four sides, having reflectors of a larger size grouped on each side,
+with their axes parallel; and as the revolution exhibits once in
+two minutes, or once in a minute, as may be required, a light gradually
+increasing to <i>full strength</i>, and in the same gradual manner
+decreasing to total darkness, its appearance is extremely well
+marked. The succession of <i>red</i> and <i>white</i> lights is caused by the
+revolution of a frame whose different sides present red and white
+lights; and these, as already mentioned, afford three separate distinctions,
+namely, alternate red and white; the succession of two
+white lights after one red, and the succession of two red lights
+after one white light. The <i>flashing</i> light is produced in the same
+manner as the <i>revolving</i> light; but owing to a different construction
+of the frame, the reflectors on each of eight sides are arranged
+with their rims or faces in one vertical plane, and their axes in
+a line inclined to the perpendicular, a disposition of the mirrors
+which, together with the greater quickness of the revolution, which
+shews a flash once in five seconds of time, produces a very striking
+effect, totally different from that of a revolving light, and presenting
+the appearance of the flash alternately rising and sinking.
+The brightest and darkest periods being but momentary, this light
+is farther characterised by a rapid succession of bright flashes,
+from which it gets its name. The <i>intermittent</i> light is distinguished
+by bursting suddenly into view and continuing steady<span class="pagenum" id="Page229">[229]</span>
+for a short time, after which it is suddenly eclipsed for half a
+minute. Its striking appearance is produced by the perpendicular
+motion of circular shades in front of the reflectors, by which
+the light is alternately hid and displayed. This distinction, as
+well as that called the <i>flashing light</i>, is peculiar to the Scotch
+coast, having been first introduced by the late Engineer of the
+Northern Lights Board. The double lights (which are seldom
+used except where there is a necessity for a <i>leading</i> line, as a guide
+for taking some channel or avoiding some danger) are generally
+exhibited from two Towers, one of which is higher than the other.
+At the Calf of Man, a striking variety has been introduced into the
+character of leading lights, by substituting, for two <i>fixed</i> lights,
+two lights which revolve in the same periods, and exhibit their
+flashes at the same instant; and these lights are, of course, susceptible
+of the other variety enumerated above, that of two revolving
+red and white lights, or flashing lights, coming into view at equal
+intervals of time. The utility of all these distinctions is to be
+valued with reference to their property of at once striking the eye
+of an observer and being instantaneously obvious to strangers.</p>
+
+<p>The introduction of colour, as a source of distinction, is necessary,
+in order to obtain a sufficient number of distinctions; but it
+is in itself an evil of no small magnitude; as the effect is produced
+by interposing coloured media between the burner and the observer’s
+eye, and much light is thus lost by the absorption of those rays,
+which are held back in order to cause the appearance which is desired.
+Trial has been made of various colours; but red, blue, and
+green alone have been found useful, and the two latter only at
+distances so short as to render them altogether unfit for sea-lights.
+Owing to the depth of tint which is required to produce a marked
+effect, the red shades generally used absorb from ⁴⁄₇ths to ⁵⁄₆ths of
+the whole light, an enormous loss, and sufficient to discourage the
+adoption of that mode of distinction in every situation where it
+can possibly be avoided. The red glass used in France absorbs<span class="pagenum" id="Page230">[230]</span>
+only ⁴⁄₇ths of the light; but its colour produces, as might be expected,
+a much less marked distinction to the seaman’s eye. In the
+Lighthouses of Scotland, a simple and convenient arrangement
+exists for colouring the lights, which consists in using chimneys of
+red glass, instead of placing large discs in front of the reflectors.</p>
+
+<div class="container w40emmax" id="Fig41">
+
+<p class="caption">Fig. 41.</p>
+
+<img src="images/illo230.jpg" alt="Gauge for reflector alignment">
+
+</div><!--container-->
+
+<p>After what has been already said on the subject of divergence,
+it will at once be seen, that in revolving lights the reflectors
+are placed with their axes parallel to each other, so as to concentrate
+their power in one direction; whilst in fixed lights it is
+necessary, in order to approach as near as possible to an equal distribution
+of the light over the horizon, <span class="sidenote">Arrangement of
+Reflectors on the
+Frame.</span>
+to place the reflectors, with
+their axes inclined to each other, at an angle somewhat less than
+that of the divergence of the reflected cone. For this purpose, a
+brass gauge (see <a href="#Fig41">fig. 41</a>), composed of two long arms, AM, AM,
+somewhat in the form of a pair of common dividers, connected
+by a means of a graduated limb A, is employed. The arms
+having been first placed at the angle, which is supplemental to
+that of the inclination of the axes of the two adjacent mirrors at
+O, are made to span the faces of the reflectors, one of which is<span class="pagenum" id="Page231">[231]</span>
+moved about till its edges are in close contact with the flat surface
+of one of the arms of the gauge.</p>
+
+<div class="container w25emmax" id="Fig42">
+
+<p class="caption">Fig. 42.</p>
+
+<img src="images/illo231a.jpg" alt="Elevation of revolving apparatus">
+
+</div><!--container-->
+
+<div class="container w35emmax" id="Fig43">
+
+<p class="caption">Fig. 43.</p>
+
+<img src="images/illo231b.jpg" alt="Plan of revolving apparatus">
+
+</div><!--container-->
+
+<p><a href="#Fig42">Figs. 42</a> and <a href="#Fig43">43</a> shew an elevation and plan of a revolving
+apparatus on the catoptric principle. In these figures, <i>n&#160;n</i> shews
+the reflector frame or chandelier; <i>o&#160;o</i>, the reflectors with their oil-fountains
+<i>p</i>&#160;<i>p</i>. The whole is attached to the revolving axis or shaft
+<i>q</i>. The copper tubes <i>r</i>&#160;<i>r</i> convey the smoke from the lamps; <i>s</i>&#160;<i>s</i> are
+cross bars which support the shaft at <i>t&#160;t</i>; <i>u&#160;u</i> is a copper pan for
+receiving any moisture which may accidentally enter at the central
+ventilator in the roof of the light-room; <i>l</i> is a cast-iron bracket,
+supporting the cup in which the pivot of the shaft turns; <i>m</i>&#160;<i>m</i>
+are bevelled wheels, which convey motion from the machine to the
+shaft. The machinery does not require any particular notice, being
+that of common clock-work, moved by the descent of a weight.</p>
+
+<p><span class="pagenum" id="Page232">[232]</span></p>
+
+<div class="container w40emmax" id="Fig44">
+
+<p class="caption">Fig. 44.</p>
+
+<img src="images/illo232.jpg" alt="Reflector arrangement">
+
+</div><!--container-->
+
+<p><a href="#Fig44">Fig. 44</a> shews a plan of one tier of reflectors arranged in the
+manner employed in a fixed catoptric light; <i>n</i>&#160;<i>n</i> shews the chandelier,
+<i>q</i> the fixed shaft in the
+centre, which supports the whole,
+<i>o</i>&#160;<i>o</i> the reflectors, and <i>p</i>&#160;<i>p</i> the fountains
+of their lamps. In this
+figure (in order to prevent confusion)
+only one tier of reflectors
+is shewn; the other tiers are so
+arranged, that their axes divide
+into equal angles the arcs intercepted
+between the axes of the
+adjoining reflectors on the first tier,
+thereby producing the nearest approach
+to an equal distribution of the light, which is attainable by
+this arrangement.</p>
+
+<p>In lighthouses of moderate height, the proper position for the reflector
+itself is perfect horizontality of its axis, which may be ascertained
+with sufficient accuracy, by trying with a plummet, whether
+the lips of the instrument, which we may conclude to be at right
+angles to the plane of its axis, be truly vertical. In lightrooms very
+much elevated above the sea, however, the dip of the horizon becomes
+notable; and a slight inclination forwards should be given to
+the face of the reflectors, so that their axes produced may be tangents
+to the earth at the visible horizon of the light-room. This, however,
+must not be permitted to interfere with the perfect horizontality of
+the top of the burner, which is indispensable to its proper burning.</p>
+
+<p><span class="sidenote">Bordier Marcet’s
+Reflectors.</span>
+Various forms of the parabolic mirror were invented by M.
+<span class="smcap">Bordier Marcet</span>, the pupil and successor of <span class="smcap">Argand</span>, who has
+laboured with much enthusiasm in perfecting catoptric instruments,
+more especially with a view to their application in the illumination
+of lighthouses and the streets of towns. Amongst many other
+ingenious combinations, he has invented and constructed an apparatus
+which is much used in harbour-lights on the French coast,<span class="pagenum" id="Page233">[233]</span>
+where it is known by the fanciful name of <span class="sidenote">Fanal Sidéral.</span>
+<i>Fanal<a id="FNanchor46" href="#Footnote46" class="fnanchor">[46]</a> sidéral</i>.
+The object is to fulfil, as economically as possible, the conditions
+required in a fixed light, by illuminating, with perfect equality,
+every part of the horizon, by means of a single burner; and M.
+<span class="smcap">Bordier Marcet</span> has in his work-shop an instrument of this kind,
+eight feet in diameter, which he constructed on speculation. The
+apparatus used in harbour-lights, on the French coast, is of much
+smaller dimensions, and does not exceed fifteen inches in diameter.
+A perfect idea of the construction and effect of this instrument
+may be formed, by conceiving a parabola to revolve about
+its parameter as a vertical axis, so that its upper and lower limbs
+would become the generating lines of two surfaces possessing the
+property of reflecting, in lines parallel to the axis of the parabola,
+all the rays incident upon them, from a light placed in the point
+where the parameter and axis of the generating parabola intersect
+each other. This point being the focus of each parabolic section
+of this apparatus, light is equally dispersed in every point of the
+horizon, when the axis of the parabolic section is in a plane perpendicular
+to a vertical line. But however perfectly this apparatus may
+attain its important object, it necessarily produces a feeble effect;
+because as its action is entirely confined to the vertical direction,
+the light distributed by it decreases directly as the distance of the
+observer. This beautiful little instrument is shewn at <a href="#Fig45">fig. 45</a>, in
+which <i>b</i> shews the burner, <i>p&#160;p</i> the
+upper reflecting surface, and <i>p′&#160;p′</i> the
+lower reflecting surface, both generated
+in the manner above described
+by the revolution of a parabola about
+its parameter <i>x&#160;b</i>; F is the focus of
+the generating parabola; and <i>l</i>&#160;<i>l</i> are
+small pillars, which connect the two
+reflecting plates, and give strength to the apparatus.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote46" href="#FNanchor46" class="label">[46]</a> Fanal, from φανεν, a lantern.</p>
+
+</div><!--footnote-->
+
+<div class="container w40emmax" id="Fig45">
+
+<p class="caption">Fig. 45.</p>
+
+<img src="images/illo233.jpg" alt="Fanal sidéral">
+
+</div><!--container-->
+
+<p><span class="pagenum" id="Page234">[234]</span></p>
+
+<p>M. <span class="smcap">Bordier Marcet</span> has also prepared an ingenious modification
+of the paraboloïdal mirror, which he has described under the
+name of <span class="sidenote">Fanal à double
+effet.</span>
+<i>fanal à double effet</i>; and the object of which is to obtain a
+convenient degree of divergence from parabolic mirrors, by the
+use of two flames and two reflecting surfaces, each of which is
+acted upon by its own flame, and also by that of the other.
+This modification consists in the union of two portions of hollow
+paraboloïdal mirrors, generated by the revolution of two parabolas
+about a common horizontal axis, and illuminated by two
+lamps placed in the focus of each. The first surface is generated
+by the revolution on its axis of a segment of a paraboloid intercepted
+between the parameter and some double ordinate greater
+than it, and may, from its form, be called the ribbon-shaped mirror.
+The second surface is that of a parabolic conoid, which is cut off by
+a vertical plane passing through a double ordinate, which is equal to
+the parameter of the parabolic ribbon, which is placed in front of
+it. The elements of the curve which forms the conoïdal mirror,
+must be so chosen as to have its focus at a convenient distance in
+<i>front</i> of that of the ribbon-shaped mirror, so as to admit of placing
+the two lamps separate from each other, as well as to produce the
+necessary degree of divergence, which is to be obtained by the action
+of these mirrors respectively on the flame placed in the focus of
+the other. These two mirrors are joined together in the line of the
+parametric section of the ribbon, which coincides with the lips of the
+conoid at some double ordinate <i>behind</i> its parameter. Each mirror
+produces, by means of the lamp placed in its focus, an approach
+to parallelism of the reflected rays, which M. <span class="smcap">Bordier Marcet</span>
+has not inaptly termed the <i>principal effect</i>; whilst the action of
+each surface on the lamp which is placed in the focus of the other,
+causes what the inventor calls the <i>secondary</i> or <i>lateral effect</i>.
+Their secondary action may be described thus: The lamp, which
+is in the focus of the ribbon, is much nearer the vertex of the
+conoid than its own focus; so that its rays making, with normals
+to the surface of the conoid, angles greater than those which are
+formed by the rays proceeding from its focus, are of necessity reflected<span class="pagenum" id="Page235">[235]</span>
+in lines diverging from the axis of the mirror. Those, on
+the contrary, which proceed from the focus of the conoid, meet the
+ribbon-shaped surface, so as to make angles with its normals more
+acute than those which the rays from its own focus could do, and
+which are, therefore, reflected in lines converging to the axis of
+the mirror. Those reflected rays must therefore cut the axis, and
+diverge from it on the other side. This apparatus has been used
+at La Hève and some other lights on the French coast; but it is
+impossible not to perceive the great loss of light which results
+from the use of two flames in one mirror; and it must not be forgotten,
+that the divergence which is obtained by means of it is
+not confined to the horizontal direction in which only it is wanted;
+but that the light is at the same time scattered in every
+direction round the edge of the mirror.</p>
+
+<p>Arrangements of a similar kind were proposed and executed for
+the same purpose of uniting greater divergence with considerable
+power in the central parts of the resultant beam, by <span class="smcap">Argand</span> himself,
+in 1806, and also in 1808, by M. <span class="smcap">Haudry</span>, <i>Ingénieur des Ponts
+et Chaussées</i>. <span class="smcap">Argand</span> proposed the union of a paraboloid, and an
+ellipsoid having their foci coincident in one point, which being the
+posterior focus of the latter curve, was illuminated by the rays reflected
+to it by means of the ellipsoïdal surface from the lamp placed
+in the anterior focus. From the <i>optical focus</i> thus obtained, some
+rays would fall on the paraboloïdal surface and produce, by reflection,
+a cylinder of parallel rays, while the rest would diverge from
+the axis, and form a zone of spreading rays. M. <span class="smcap">Haudry’s</span> plan
+consisted of a combination of a conical with a paraboloïdal mirror,
+so placed, that the rays from the front part of the hollow cone
+might be nearly parallel to those sent out by the paraboloid; while
+the rays from its base diverging from the axis might produce a ring
+of divergent rays, similar to that obtained from the ellipsoid of <span class="smcap">Argand’s</span>
+apparatus.</p>
+
+<p>It would occupy much time to exhibit all the disadvantages of
+the arrangements in the <i>fanal à double effet</i> of M. <span class="smcap">Bordier Marcet</span>,<span class="pagenum" id="Page236">[236]</span>
+and also in those of <span class="smcap">Argand</span> and <span class="smcap">Haudry</span>; and I shall therefore dismiss
+the subject by observing, that the loss of light due to the position
+of the flame in the apparatus of <span class="smcap">Argand</span>, is so great as to induce
+one to wonder that such combinations should ever have been
+attempted. There can be no doubt, that the most efficient mode
+of obtaining due divergence from mirrors, is to adopt the paraboloid,
+with a short focal distance, which has the double advantage of
+increasing the divergence which is due inversely to the focal distance,
+and, at the same time, subjecting to the action of the mirror
+a larger portion of the luminous sphere proceeding from the flame.</p>
+
+<div class="container w45emmax" id="Fig46">
+
+<p class="caption">Fig. 46.</p>
+
+<img src="images/illo236.jpg" alt="Fanal à double face">
+
+</div><!--container-->
+
+<p><span class="sidenote">Fanal à double
+face.</span>
+Lastly, I shall notice M. <span class="smcap">Bordier Marcet’s</span> <i>fanal à double face</i>,
+which consists of two paraboloïdal mirrors, truncated in the vertical
+plane of the parameter, and united together back to back, so as to be
+illuminated by the same lamp placed in their common focus. To
+save the light which would otherwise escape the catoptric action, he
+adds a parabolic conoid of greater focal distance, and so placed, that
+while its focus may coincide with the common focus of the other
+mirrors, its size may be so restricted, that it shall not interfere
+with the effect of the truncated mirror opposite which it is placed.
+The obvious consequence of such an arrangement is, that the rays
+(see <a href="#Fig46">fig. 46</a>) produced from a lamp in the common focus of the
+three mirrors, will produce in opposite directions a luminous ring
+from each of the truncated mirrors AC, BC, and A′C′, B′C′, while
+the central or conoïdal mirror MN will fill the interior of one of those
+luminous rings with a cone of rays, whose intensity will be in the inverse<span class="pagenum" id="Page237">[237]</span>
+ratio of MN² to <i>a</i>&#160;<i>b</i>² (or FM² to F <i>a</i>²), which latter surface represents
+the whole amount of naturally divergent rays, which strike
+on <i>a</i>&#160;<i>b</i>, and which are spread over MN. Two sets of reflectors of
+this form facing in opposite directions (each set arranged in one
+plane, and fixed on a frame which could be made to revolve round
+a vertical axis), would thus present their brightest effect after considerable
+intervals of darkness; but, by arranging them with their
+axes slightly inclined, they were made to prolong the light periods
+and curtail the dark ones. M. <span class="smcap">Bordier Marcet</span> speaks of this apparatus
+with all the satisfaction generally felt by inventors; but it
+is no difficult matter to identify its effect with that of the common
+paraboloïdal mirrors. It is obvious, that all the rays which fall
+from a true focal point on the three reflectors AC, BC, A′C′, B′C′,
+and MN, are merely those which would fall on a single reflector,
+whose double ordinate and the portion of the abscissa between that
+ordinate and the focus, are equal to those of the first reflector of
+the compound system, so that the quantity of light reflected by
+the three reflectors is neither more nor less than that which would
+be projected by one. All the difference that can exist is, that in the
+case of a flame which has a notable size, the surface MN being
+farther distant than <i>a</i>&#160;<i>b</i>, would produce less aberration and, consequently,
+a very slight increase of intensity in the small portion of the
+reflected beam of parallel rays due to that part of the compound
+mirror. We cannot, therefore, sensibly err in rejecting any advantage
+to be derived from this arrangement as insignificant.<a id="FNanchor47" href="#Footnote47" class="fnanchor">[47]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote47" href="#FNanchor47" class="label">[47]</a> See Peclet′s Traité de l′Eclairage, p. 302, from which fig. 46 is copied.</p>
+
+</div><!--footnote-->
+
+
+<p>Spherical mirrors have been employed in Lighthouses chiefly
+when they can be introduced to aid the effect of refracting apparatus:
+and it will not be necessary to say much of them in this
+place. I must, however, notice an ingenious proposal of <span class="sidenote">Mr Barlow′s
+Spherical Mirrors.</span>
+Mr <span class="smcap">W. H.
+Barlow</span>,<a id="FNanchor48" href="#Footnote48" class="fnanchor">[48]</a> who suggests placing in front of the flame a small spherical
+reflector, whose centre is coincident with the focus of a paraboloïd,<span class="pagenum" id="Page238">[238]</span>
+and whose subtense is the parameter of the generating curve. The
+small mirror, being somewhat less than a hemisphere, would cause
+the light falling upon it to be returned through the focus so as to
+reach the paraboloïdal surface and to be finally reflected from that
+portion of it which is embraced between the limits of its extreme
+divergence. If there were no loss of light at the surface of the
+small mirror, its effect would be to increase the power of the beam
+of parallel rays by an amount equal to the sum of the rays incident
+on the spherical surface, but at the same time to diminish it
+by intercepting a portion of the light reflected from the paraboloïd.
+I am not aware that such a combination has been tried, as it applies
+most advantageously to reflectors whose span does not exceed the
+parameter of the generating curve, a form rarely adopted in lighthouses;
+but it might also be adapted to reflectors which intercept
+a larger portion of light, by making the spherical reflector some
+segment less than the hemisphere.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote48" href="#FNanchor48" class="label">[48]</a> In an excellent paper above noticed, on the Illumination of Lighthouses, in the London
+Transactions, for 1837.</p>
+
+</div><!--footnote-->
+
+<p><span class="sidenote">Captain Smith’s
+Mirrors in the form
+of a parabolic
+spindle.</span>
+<span class="smcap">Captain Smith</span> of the Madras Engineers, has described in the
+“Professional papers of the ‘Corps of Royal Engineers,’<a id="FNanchor49" href="#Footnote49" class="fnanchor">[49]</a> a new
+system of fixed lights,” which consists in placing a flat wick in the
+focus of one-half of a hollow parabolic spindle generated by the rotation
+of a parabola about its parameter as a vertical axis. The action
+of the instrument is obvious, for each vertical section being parabolic,
+effects a change only in the <i>vertical</i> divergence of the rays incident
+on it from the focus, and suffers their horizontal direction to remain
+unaltered; thus each vertical plate of reflected rays passes through
+the parameter of the curve and illuminates the opposite point of
+the horizon by means of a narrow strip or line of light. Two
+hollow spindles of that form, each lighting 180° and facing opposite
+azimuths, would, therefore, be sufficient to illuminate the
+whole horizon. The author of the paper, however, appears to contemplate
+the employment of a series of those mirrors ranged one
+above another and <i>breaking joint</i> vertically, somewhat in the manner
+already described in speaking of the arrangement of the paraboloïdal<span class="pagenum" id="Page239">[239]</span>
+mirrors used in fixed lights. The advantages of this mode
+of illumination are much overrated by <span class="smcap">Captain Smith</span>, who seems
+to magnify beyond its real importance the risk attending the
+use, in the dioptric apparatus, of a single lamp, whose sudden extinction
+would deprive at once the whole horizon of the benefit of
+the light; while, on the contrary, he reckons the security obtained
+by his arrangement as an advantage of the highest value. In certain
+situations, where no regular establishment of trained light-keepers
+is maintained, that security may be an object of more importance
+and may warrant a greater sacrifice, than is necessary in
+Great Britain; but I have no hesitation in saying, that I know of
+no situation in which the plan proposed by <span class="smcap">Captain Smith</span> could
+bear comparison with the mode of illumination for fixed lights by
+means of the catadioptric instruments of <span class="smcap">Fresnel</span>.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote49" href="#FNanchor49" class="label">[49]</a> Vol. v., p. 56.</p>
+
+</div><!--footnote-->
+
+<div class="chapter">
+
+<h3 class="nobreak"><span class="chapname">DIOPTRIC<a id="FNanchor50" href="#Footnote50" class="fnanchor">[50]</a> SYSTEM OF LIGHTS.</span></h3>
+
+<div class="footnote">
+
+<p><a id="Footnote50" href="#FNanchor50" class="label">[50]</a> Most probably directly derived from the Greek διόπτρον, an optical instrument with holes
+for looking through, whose name is a compound of διὰ, through, and ὄπτομαι, <i>I see</i>.</p>
+
+</div><!--footnote-->
+
+</div><!--chapter-->
+
+<p>One of the earliest notices of the application of lenses to lighthouses
+is that recorded by <span class="smcap">Smeaton</span> in his Narrative of the Eddystone
+Lighthouse, where he mentions a London optician, who, in
+1759, proposed grinding the glass of the lantern to a radius of seven
+feet six inches; but the description is too vague to admit of even a
+conjecture regarding the proposed arrangement of the apparatus.
+About the middle of the last century, however, lenses were actually
+tried in several lighthouses in the south of England, and in particular
+at the South Foreland in the year 1752; but their imperfect
+figure and the quantity of light absorbed by the glass, which was of
+impure quality and of considerable thickness, rendered their effect
+so much inferior to that of the parabolic reflectors then in use, that
+after trying some strange combinations of lenses and reflectors, the
+former were finally abandoned. Lenses were also tried at the lights<span class="pagenum" id="Page240">[240]</span>
+of Portland, Hill of Howth, and Waterford, by Mr Thomas Rogers,
+a glass manufacturer in London; who possessed, it is said, the art of
+blowing mirrors of glass, “and by a new method silvered over the
+convex side without quicksilver.”<a id="FNanchor51" href="#Footnote51" class="fnanchor">[51]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote51" href="#FNanchor51" class="label">[51]</a> Hutchinson’s Practical
+Seamanship, p. 200. See also the <a href="#App3">notice</a> of the spherical mirrors
+made by Messrs François and Letourneau of Paris in a subsequent part of this volume.</p>
+
+</div><!--footnote-->
+
+<p>The object to be attained by the use of lenses in a Lighthouse
+is, of course, identical with that which is answered by employing
+reflectors; and both instruments effect the same end by different
+means, collecting the rays which diverge from a point called the
+<i>focus</i>, and projecting them forward in a beam, whose axis coincides
+with the produced axis of the instrument. We have already seen
+that, in the case of <i>reflection</i>, this result is produced by the light
+being <i>thrown back</i> from a surface so formed as to make all the rays
+to proceed in one and the same required direction. In the case
+of <i>refraction</i>, on the other hand, the rays pass through the refracting
+medium, and are <i>bent</i> or <i>refracted</i> from their natural course
+into that which is desired.</p>
+
+<p>The celebrated <span class="smcap">Buffon</span>, to prevent the great absorption of light
+by the thickness of the material, which would necessarily result
+from giving to a lens of great dimensions a figure continuously
+spherical, proposed to grind out of a solid piece of glass, a lens in
+steps or concentric zones. This suggestion of <span class="smcap">Buffon</span> regarding the
+construction of large burning glasses, was first executed, with tolerable
+success, about the year 1780, by the Abbé <span class="smcap">Rochon</span>; but such
+are the difficulties attending the process of working a solid piece of
+glass into the necessary form, that it is believed the only other instrument
+ever constructed in this manner, is that which was made
+by Messrs <span class="smcap">Cookson</span> of Newcastle-upon-Tyne, for the Commissioners
+of Northern Lighthouses.</p>
+
+<p>The merit of having first suggested the building of lenses in separate
+pieces, seems to be due to <span class="smcap">Condorcet</span>, who, in his <i>Eloge de
+Buffon</i>, published so far back as 1773, enumerates the advantages
+to be derived from this method. Sir <span class="smcap">David Brewster</span> also described<span class="pagenum" id="Page241">[241]</span>
+this mode of building lenses in 1811, in the <i>Edinburgh
+Encyclopædia</i>; and in 1822, the late eminent <span class="smcap">Fresnel</span>, unacquainted
+with the suggestions of <span class="smcap">Condorcet</span> or the description by
+Sir <span class="smcap">David Brewster</span>, explained, with many ingenious and interesting
+details, the same mode of constructing those instruments.
+To <span class="smcap">Fresnel</span> belongs the additional merit of having first followed
+up his invention, by the construction of a lens and, in conjunction
+with MM. <span class="smcap">Arago</span> and <span class="smcap">Mathieu</span>, of placing a powerful lamp in its
+focus, and indeed of finally applying it to the practical purposes of
+a Lighthouse.</p>
+
+<p>The great advantages which attend the mode of construction
+proposed by <span class="smcap">Condorcet</span> are,—the ease of execution, by which a
+more perfect figure may be given to each zone and spherical aberration
+in a great measure corrected, and the power of forming a lens
+of larger dimensions than could easily be made from a solid piece.
+Both <span class="smcap">Buffon</span> and <span class="smcap">Condorcet</span>, however, chiefly speak of reducing
+the thickness of the material, and do not seem to have thought of determining
+the radius and centre of the curvature of the generating
+arcs of each zone, having contented themselves with simply depressing
+the spherical surface in separate portions. <span class="smcap">Fresnel</span>, on the
+other hand, determined those centres, which constantly recede from
+the vertex of the lens in proportion as the zones to which they refer
+are removed from its centre; and the surfaces of the zones of the
+annular lens, consequently, are not parts of concentric spheres, as in
+<span class="smcap">Buffon’s</span> lens. It deserves notice, that the first lenses constructed
+for <span class="smcap">Fresnel</span> by M. <span class="smcap">Soleil</span> had their zones polygonal, so that the
+surfaces were not annular, a form which <span class="smcap">Fresnel</span> considered less
+accommodated to the ordinary resources of the optician. He also,
+with his habitual penetration, preferred the plano-convex to the
+double-convex form, as more easily executed.<a id="FNanchor52" href="#Footnote52" class="fnanchor">[52]</a> After mature consideration,
+he finally adopted crown glass, which, notwithstanding its
+greenish colour, he preferred to flint glass, as being more free from<span class="pagenum" id="Page242">[242]</span>
+<i>striæ</i>. All his calculations were made in reference to an index of
+refraction of 1·51, which he had verified by repeated experiments,
+conducted with that patience and accuracy for which, amidst his
+higher qualities, he was so remarkably distinguished.<a id="FNanchor53" href="#Footnote53" class="fnanchor">[53]</a> The instruments
+have received the name of <i>annular</i> lenses, from the figure
+of the surface of the zones.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote52" href="#FNanchor52" class="label">[52]</a> The plano-convex lens, with its curved side towards the parallel rays, is also a form
+producing small spherical aberration, a circumstance which may also have influenced his
+choice.</p>
+
+<p><a id="Footnote53" href="#FNanchor53" class="label">[53]</a> My friend, Mr
+<span class="smcap">William Swan</span>, carefully examined, by his new and ingenious method,
+described in the Edinburgh New Philosophical Journal, January 1844, several specimens of
+the St Gobain glass (which is now used in the manufacture of the lenses), and found its
+refractive index to be 1·51793, the <i>difference</i> between the greatest and least values being
+only 0·00109.</p>
+
+</div><!--footnote-->
+
+
+<p>A ray of light, in passing <i>obliquely</i> from one transparent body
+into another of different density, experiences at the point of the intersection
+of the common surface of the two planes, a sudden change
+of direction, to which the name of <span class="sidenote">Refraction.</span>
+<i>refraction</i> has naturally been
+given, in connection with the most familiar instance of the phenomenon,
+which is exhibited by a straight ruler with one half plunged
+into a basin of water while the other remains in the air. The ruler
+no longer appears straight, but seems to be <i>bent</i> or <i>broken</i> at the point
+where it enters the water. It may not be out of place to call attention
+to the laws which regulate the change of direction in the incident
+light, which are <i>three</i> in number.</p>
+
+<p>1. Incidence and refraction, in uncrystallized media of homogeneous
+structure such as glass, always occur in a plane perpendicular
+to that of the refracting surface.</p>
+
+<p>2. In the same substances, the angle formed with the perpendicular
+by the ray at its entering the surface of the second medium,
+has to the angle which it makes with the normal after it
+has entered the surface, such a relation, that their sines have a fixed
+ratio, which is called the <i>refractive index</i>. When a ray falls normally
+on the surface of any substance, it suffers no refraction.</p>
+
+<p>3. The effect of passing from a rare to a dense medium, as from
+air into water or glass, is to make the angle of <i>refraction</i> less than
+the angle of <i>incidence</i>; and those angles are measured with reference<span class="pagenum" id="Page243">[243]</span>
+to a normal to the plane which separates the media at the
+point of incidence. The converse phenomenon, of course, takes
+place in the passage from a dense to a rare medium, in which case
+the angle of <i>incidence</i> is less than the angle of <i>refraction</i>. To this
+rule there are a few exceptions; for there are certain combustible
+bodies, such as diamond, whose refractive powers are much greater
+than other substances of equal density.</p>
+
+<div class="container w30emmax" id="Fig47">
+
+<p class="caption">Fig. 47.</p>
+
+<img src="images/illo243.jpg" alt="Refraction explained">
+
+</div><!--container-->
+
+<p>The diagram (<a href="#Fig47">fig. 47</a>) will serve to render those laws more intelligible.
+Let a ray of light <i>a</i> O meet a
+surface of water <i>n&#160;m</i> at O, it will be immediately
+bent into the direction O <i>a′</i>; and if,
+from the centre O, we describe any circle,
+and draw a line <i>b</i> O <i>b′</i>, perpendicular to
+<i>nm</i>; then <i>ab</i> and <i>a′&#160;b′</i>, perpendiculars drawn
+to the normal <i>bb′</i>, from the points <i>a</i> and
+<i>a′</i> where the circle cuts the incident and
+refracted rays, will be the sines of the angle
+of incidence <i>b</i> O <i>a</i>, and of the angle of refraction <i>b′</i> O <i>a′</i>, and the
+ratio of those sines to each other, or
+<span class="divide"><span class="num"><i>b&#160;a</i></span><span class="denom"><i>b′&#160;a′</i></span></span> will be the relative index of
+<i>refraction</i> for the two media.</p>
+
+<p>4. It may perhaps be added, for convenience, as a <i>fourth</i> law,
+deducible from the others, that since rays passing from a dense
+into a rare medium, have their angle of refraction greater than the
+angle of incidence, there must be some angle of incidence whose
+corresponding angle of refraction is a right angle; beyond which
+no refraction can take place, because there is no angle whose sine
+can be greater than the radius. In such circumstances, <i>total reflection</i>
+ensues. For common glass, whose index of refraction is 1·5, we have
+(in the case of emergent rays) sine of incidence =
+<span class="divide"><span class="num">sine of refraction</span><span class="denom">1·5</span></span>;
+but, as no sine can exceed radius or unity, the angle of incidence
+must be limited to 41° 49′; beyond which total reflection will take
+place, and the light will return <i>inwards</i> into the glass, being <i>reflected</i>
+at its surface.</p>
+
+<p><span class="pagenum" id="Page244">[244]</span></p>
+
+<p>Thus, if a ray proceed from a point O (<a href="#Fig48">fig. 48</a>), within a piece
+of glass, to a point C, at its surface
+A B; and if O C <i>b</i>, its incidence, be
+less than 41° 49′, it will be <i>refracted</i>
+in some direction C <i>f</i>; but if
+this angle be greater than 41° 49′,
+as O C′ <i>b′</i>, the ray will be <i>reflected</i>
+back into the glass in the direction
+C′ O′.</p>
+
+<div class="container w25emmax" id="Fig48">
+
+<p class="caption">Fig. 48.</p>
+
+<img src="images/illo244a.jpg" alt="Refraction and reflection">
+
+</div><!--container-->
+
+<p>The material hitherto employed in the construction of lighthouse
+apparatus is crown glass, which, although it possesses a lower refractive
+power than flint glass and has, besides, a slightly greenish tinge,
+offers the great practical advantages of being more easily obtained of
+homogeneous quality; and, being less subject to deterioration from
+atmospheric influences, it is peculiarly suitable for use in the exposed
+situations generally occupied by Lighthouses. The refractive
+index of crown glass, as already noticed, is about 1·5.</p>
+
+<p>Any one may easily satisfy himself by a careful protraction of
+the angles of <i>incidence</i> and <i>refraction</i>, in the manner above described,
+as to the truth of the following general propositions resulting
+from those <span class="nowrap">laws:—</span></p>
+
+<p>1. A ray of light passing through a plate of some diaphanous
+substance such as glass, with parallel surfaces, suffers no change of
+<i>direction</i>, but emerges in a line parallel to its original path, merely
+suffering a <i>displacement</i>, depending on the obliquity of the incident
+ray, and the refractive power and thickness
+of the plate. The effect of this displacement
+is merely to give the ray an apparent
+point of origin different from the true one.
+This will be easily understood by the diagram
+(<a href="#Fig49">fig. 49</a>), in which <i>a&#160;b</i> is a normal to the
+plate, whose surfaces <i>x&#160;x</i> and <i>x′&#160;x′</i> are parallel,
+<i>r r r r</i> shews the path of the ray, <i>r&#160;r</i> the displacement,
+and <i>r′</i> the apparent point of origin
+resulting from its altered <i>direction</i>.</p>
+
+<div class="container w25emmax" id="Fig49">
+
+<p class="caption">Fig. 49.</p>
+
+<img src="images/illo244b.jpg" alt="Refraction and displacement">
+
+</div><!--container-->
+
+<p><span class="pagenum" id="Page245">[245]</span></p>
+
+<p>2. When a ray passes through a triangular prism <i>a b c</i>, the inclination
+of the faces <i>a&#160;c</i> and <i>c&#160;b</i> causes
+the emergent ray <i>r′</i> to be bent towards
+<i>a&#160;b</i>, the base of the prism, in a measure
+depending on the inclination of the
+sides of the prism and the obliquity
+of the incident ray to the first surface.</p>
+
+<div class="container w25emmax" id="Fig50">
+
+<p class="caption">Fig. 50.</p>
+
+<img src="images/illo245a.jpg" alt="Prism">
+
+</div><!--container-->
+
+<p>3. When parallel rays fall on a concave lens, they will, at their
+emergence, be divergent. The section
+of the diaphanous body <i>a b c d</i>
+may be regarded as composed of innumerable
+frusta of prisms, having
+their apices directed towards the
+centre line <i>x&#160;r</i>; and the rays which
+pass through the centre, being normal
+to the surface, will be unchanged
+in their direction, while all the others will (as shewn in
+the <a href="#Fig51">figure</a>) suffer a change of direction, increasing with their distance
+from the centre, owing to the increasing inclination of the surfaces
+of the lens as they recede from its axis.</p>
+
+<div class="container w25emmax" id="Fig51">
+
+<p class="caption">Fig. 51.</p>
+
+<img src="images/illo245b.jpg" alt="Concave lens">
+
+</div><!--container-->
+
+<p>4. Lastly, when divergent rays fall on a convex lens <i>a&#160;b</i>, from
+a point <i>f</i>, called the principal
+focus, they are made parallel
+at their emergence; while,
+<i>conversely</i>, parallel rays
+which fall on the lens are
+united in that point.<a id="FNanchor54" href="#Footnote54" class="fnanchor">[54]</a> This
+effect, which is the opposite
+of that caused by the concave
+lens, may be explained in a similar manner, by conceiving the section
+<i>a&#160;b</i> of the convex lens to be composed of innumerable frusta of
+prisms, arranged with their <i>bases</i> towards the centre of the lens.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote54" href="#FNanchor54" class="label">[54]</a> It is, of course, to be understood that only rays incident near the axis of the lens
+are refracted accurately to a focus.</p>
+
+</div><!--footnote-->
+
+<div class="container w25emmax" id="Fig52">
+
+<p class="caption">Fig. 52.</p>
+
+<img src="images/illo245c.jpg" alt="Convex lens">
+
+</div><!--container-->
+
+<p><span class="pagenum" id="Page246">[246]</span></p>
+
+<p>Now, it is obvious, that we can derive no assistance, in economising
+the rays of a lamp for Lighthouse purposes, from concave
+lenses, whose property is to increase the dispersion of the rays incident
+on them. With concave lenses, therefore, we have no concern;
+and we shall confine ourselves to the consideration of the
+convex or converging lenses.</p>
+
+<p>The lens always used in Lighthouses is (for reasons already
+noticed) plano-convex, and differs from the last only by having a
+plane and a curve surface, instead of two curve surfaces, whose
+radii are on opposite sides of the lens. The plano-convex is generally
+regarded, by writers on optics, as a <i>case</i> of the double convex
+having one side of an <i>infinite</i> radius. Both forms cause parallel
+rays to converge to a focus.</p>
+
+<p>We commence with a general view of the relations which exist
+between the position of the <i>radiant</i> and the focus.</p>
+
+<div class="container w25emmax" id="Fig53">
+
+<p class="caption">Fig. 53.</p>
+
+<img src="images/illo246.jpg" alt="Plano-convex lens">
+
+</div><!--container-->
+
+<p>Let Q <i>q</i> be a section of a lens, and <i>f</i> A <i>r</i> its optical axis, or the
+line in which a ray of light passes unchanged in its direction through
+the lens, from its being normal to both surfaces, whether the lens
+be double-convex as above, or
+plano-convex (see <a href="#Fig53">fig. 53</a>), then
+the <i>principal focus f</i> is that point
+where the rays from <i>r r r</i>, which
+fall parallel to the optic axis on the
+outer face of the lens, meet after
+refraction at the two faces,—or,
+to speak more in the language of
+the art which is under consideration, the <i>principal focus f</i> is the
+point whence the rays of light, proceeding in their naturally divergent
+course, fall on the inner surface Q A <i>q</i> of the lens, and are so
+changed by refraction there and at the outer face, that they finally
+emerge parallel to the <i>optic axis</i> in the directions Q <i>r</i>, <i>q&#160;r</i>. The position
+of this point depends partly on the refractive power of the
+substance of which the lens is composed and partly on the curvature
+of the surface or surfaces which bound it.</p>
+
+<p><span class="pagenum" id="Page247">[247]</span></p>
+
+<p>It would be quite beyond the scope of these Notes to attempt to
+present the subject of refraction at spherical surfaces before the
+reader’s view in a rigorous or systematic manner, and thus to advance,
+step by step, to the practical application of refracting instruments,
+as a means of directing and economising the light in a Pharos.
+This would involve the repetition, in a less elegant form, of what is
+to be found in all the works on optics; and instead of this, I am content
+to refer, where needful, to those works, and shall confine myself
+simply to what concerns Lighthouse lenses and their use. It
+would also be superfluous to determine the position of the principal
+focus of a plano-convex lens, in terms of the refractive index
+and radius of curvature,<a id="FNanchor55" href="#Footnote55" class="fnanchor">[55]</a> as it can be very accurately found in
+practice by exposing the instrument to the sun, in such a manner
+that his rays may fall upon it in a direction parallel to its axis.
+The point of union between the converging and diverging cones of
+rays (where the spectrum is smallest and brightest), which is the
+<i>principal focus</i>, is easily found by moving a screen behind the lens,
+farther from or nearer to it as may be required. The path of the
+Lighthouse optician, moreover, generally lies in the opposite direction;
+and his duty is not so much to find the focal distance of a
+ready-made lens, as to find the best form of a lens for the various
+circumstances of a particular Pharos, whose diameter, in some
+measure, determines the focal distance of the instruments to be
+employed. All, however, that I shall really have to do is to give
+an account of what has been done by the late illustrious <span class="smcap">Fresnel</span>,
+who seems to have devoted such minute attention to every detail<span class="pagenum" id="Page248">[248]</span>
+of the Dioptric apparatus, that he has foreseen and provided for
+every case that occurs in the practice of Lighthouse illumination.
+His brother, Mons. <span class="smcap">Leonor Fresnel</span>, who succeeded him in the
+charge of the Lighthouses of France, has, with the greatest liberality,
+put me in possession of the various formulæ used by his lamented
+predecessor, in determining the elements of those instruments which
+have so greatly improved the lighthouses of modern days.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote55" href="#FNanchor55" class="label">[55]</a> F =
+<span class="divide"><span class="num"><i>r</i></span><span class="denom"><i>m</i> - 1</span></span>
+in which <i>r</i> is the radius of curvature, and <i>m</i> is the refractive index.—<i>Coddington’s
+Optics</i>, Chap. VIII. If the radiant be brought near the lens, so as to cast
+divergent rays on its surface, then the conjugate focus will recede behind the <i>principal focus</i>;
+and when the luminous body reaches the <i>principal</i> focus <i>in front</i> of the lens, the rays will
+emerge from its posterior surface in a direction parallel to its axis. If it be brought still
+nearer the lens, the rays would emerge as a divergent cone. Hence converging lenses can
+only collect rays into a focus, when they proceed from some point <i>more</i> distant than the
+principal focus.</p>
+
+</div><!--footnote-->
+
+<p>Spherical lenses, like spherical mirrors, collect truly into the focus
+those rays only which are incident near the axis; and it is, therefore,
+of the greatest importance to employ only a small segment of
+any sphere as a lens. The experience of this fact, among other considerations,
+led <span class="smcap">Condorcet</span>, as already noticed, to suggest the building
+of lenses in separate pieces. <span class="smcap">Fresnel</span>, however, was the first
+who actually constructed a lens on that principle; and he has subdivided,
+with such judgment, the surface of the lens into a centre
+lens and concentric annular bands and has so carefully determined
+the elements of curvature for each, that no farther improvement is
+likely to be made in their construction. For the drawings of the
+great lens, I have to refer to <a href="#Plate12">Plate XII.</a>, which also contains a tabular
+view of the elements of its various parts. The central disc of the
+lens, which is employed in lights of the first order, and whose focal
+distance is 920 millimètres, or 36·22 inches, is about 11 inches in
+diameter; and the annular rings which surround it vary slightly in
+breadth from 2³⁄₄ to 1¹⁄₄ inches. The breadth of any zone or ring is,
+within certain limits, a matter of choice, it being desirable, however,
+that no part of the lens should be much thicker than the rest, as well
+for the purpose of avoiding inconvenient projections on its surface,
+as to permit the rays to pass through the whole of the lens with
+nearly equal loss by absorption. The objects to be attained in the
+polyzonal or compound lens, are chiefly, as above noticed, to correct
+the excessive aberration produced by refraction through a
+hemisphere or great segment, whose edge would make the parallel
+rays falling on its curve surface converge to a point much nearer
+the lens than the principal focus, as determined for rays near the<span class="pagenum" id="Page249">[249]</span>
+optical axis, and to avoid the increase of material, which would not
+only add to the weight of the instrument and the expense of its
+construction, but would greatly diminish by absorption the amount
+of transmitted light. Various modes of removing similar inconveniences
+in telescopic lenses have been devised; and the suggestions
+of <span class="smcap">Descartes</span>, as to combinations of hyperbolic and elliptic
+surfaces with plane and spherical ones, more especially fulfil the
+whole conditions of the case; but the excessive difficulty which
+must attend grinding and polishing those surfaces, has hitherto deprived
+us of the advantages which would result from the use of
+telescopic lenses entirely free from spherical aberration. In Lighthouse
+lenses, where so near an approach to accurate convergence
+to a single focus is unnecessary, every purpose is answered by the
+partial correction of aberration which may be obtained, by determining
+an average radius of curvature for the central disc, and
+for each successive belt or ring, as you recede from the vertex of
+the lens. In the lenses originally constructed for <span class="smcap">Fresnel</span> by
+<span class="smcap">Soleil</span>, the zones were united by means of small <i>dowels</i> or <i>joggles</i>
+of copper, passing from the one zone into the other; but the greater
+exactness of the workmanship now attained, has rendered it safe to
+dispense with those fixtures; and the compound lens is now held
+together solely by a metallic frame and the close union between the
+concentric faces of the rings, which, however, are in contact with
+each other at surfaces of only ¹⁄₄ inch in depth, as shewn in <a href="#Plate12">Plate
+XII.</a> It is remarkable, that an instrument, having about 1300
+square inches of surface, and weighing 109 lb., and which is composed
+of so many parts, should be held together by so slender a
+bond as two narrow strips of polished glass, united by a thin film
+of cement.</p>
+
+<p>I now proceed to the formulæ employed by <span class="smcap">Fresnel</span>, to determine
+the elements of the compound lens,<a id="FNanchor56" href="#Footnote56" class="fnanchor">[56]</a> in the calculation of<span class="pagenum" id="Page250">[250]</span>
+which two cases occur, viz., the central disc and a concentric ring.
+The focal distance of the lens and the refractive index of the glass
+are the principal data from which we start.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote56" href="#FNanchor56" class="label">[56]</a> It may be proper to mention that, while the formulæ given in the text are those of
+M. <span class="smcap">Fresnel</span>, I am responsible for the investigations in the Notes; I have, at the same
+time, much pleasure in acknowledging my obligations, at various times (about ten years
+ago), to Mr <span class="smcap">Edward Sang</span>, and (more recently) to Mr <span class="smcap">William Swan</span>, for their kind advice
+on this part of the subject.</p>
+
+</div><!--footnote-->
+
+<div class="container w15emmax" id="Fig54">
+
+<p class="caption">Fig. 54.</p>
+
+<img src="images/illo250a.jpg" alt="Central disc">
+
+</div><!--container-->
+
+<p>I begin with the case of the central disc or lens round which
+the annular rings are arranged. Its principal section is a mixtilinear
+figure (<a href="#Fig54">fig. 54</a>) composed of a segment
+<i>b</i>&#160;<i>a</i>&#160;<i>c</i>, resting on a parallelogram <i>b</i>&#160;<i>c</i>&#160;<i>d</i>&#160;<i>e</i>, whose
+depth <i>b</i>&#160;<i>d</i> or <i>c</i>&#160;<i>e</i> is determined by the strength
+which is required for the joints which unite
+the various portions of the lens. Those particulars
+have, as I already stated, been determined with so much
+judgment by <span class="smcap">Fresnel</span> and the dimensions of the lenses so varied
+to suit the case of various lights, that nothing in this respect remains
+to be done by others.</p>
+
+<div class="container w30emmax" id="Fig55">
+
+<p class="caption">Fig. 55.</p>
+
+<img src="images/illo250b.jpg" alt="Refraction by central disc">
+
+</div><!--container-->
+
+<p>Referring to <a href="#Fig55">fig. 55</a>, we have, for obtaining the radius of the
+central disc, the following formulæ, in which</p>
+
+<div class="varlist">
+
+<p class="hind04"><i>r</i> = AB, half the aperture of the lens</p>
+
+<p class="hind04"><i>r′</i> = AB′</p>
+
+<p class="hind04">φ = AF, the focal distance</p>
+
+<p class="hind04"><i>t′</i> = A&#160;<i>a</i>, the thickness of the lens at the
+vertex</p>
+
+<p class="hind04"><i>t″</i> = B&#160;<i>b</i>, the thickness of the joint</p>
+
+<p class="hind04">μ = the index of refraction</p>
+
+<p class="hind04">ρ = the radius of curvature.</p>
+
+</div><!--fsize90-->
+
+<p>Then for the radius of curvature
+near the axis we have:</p>
+
+<div class="formula">
+
+<p>ρ′ = (μ - 1)<span class="fsize175">(</span>φ +
+<span class="divide"><span class="num"><i>t′</i></span><span class="denom">μ</span></span><span class="fsize175">)</span></p>
+
+</div><!--formula-->
+
+<p class="noindent">and for that near the margin we
+have:</p>
+
+<p><span class="pagenum" id="Page251">[251]</span></p>
+
+<div class="centerblock fsize90">
+
+<p class="frml">tan&#160;<i>i′</i> = <span class="divide"><span class="num">r</span><span class="denom">φ</span></span><br>
+
+sin&#160;<i>e</i> = <span class="divide"><span class="num">sin&#160;<i>i′</i></span><span class="denom">μ</span></span><br>
+
+<i>r′</i> = <i>r</i> - <i>t″</i> . tan&#160;<i>e</i><br>
+
+tan&#160;<i>i</i> = <span class="divide"><span class="num"><i>r′</i></span><span class="denom">φ</span></span><br>
+
+sin&#160;ε = <span class="divide"><span class="num">sin&#160;<i>i</i></span><span class="denom">μ</span></span></p>
+
+</div><!--centerblock-->
+
+<div class="formula">
+
+<p>ρ″ = <span class="divide"><span class="num"><i>r</i></span><span class="denom">μ&#160;sin&#160;<i>e</i></span></span>
+√<span class="bt">μ² - 2&#160;μ&#160;cos&#160;<i>e</i> + 1</span></p>
+
+<p>and, finally ρ = <span class="divide"><span class="num">ρ′ + ρ″</span>
+<span class="denom">2</span></span><a id="FNanchor57" href="#Footnote57" class="fnanchor">[57]</a></p>
+
+</div><!--formula-->
+
+<div class="footnote">
+
+<p><a id="Footnote57" href="#FNanchor57" class="label">[57]</a> The following steps lead to the formulæ
+given in the text. Let APQB (<a href="#Fig56">fig. 56</a>) represent
+a section of the central lens by a plane
+passing through its axis AF; F the focus for
+incident rays; and FQPH the path of a ray
+refracted finally in the direction PH, parallel
+to the axis. Let C be the centre of curvature,
+then PC is a normal to the curve at P;
+and, producing PQ to meet the axis in G, we have G the focus of the rays, after refraction
+at the surface BQ.</p>
+
+<div class="container w25emmax" id="Fig56">
+
+<p class="caption">Fig. 56.</p>
+
+<img src="images/illo251.jpg" alt="Refraction of central lens">
+
+</div><!--container-->
+
+<div class="formula">
+
+<p>Then μ = <span class="divide"><span class="num">sin&#160;PCG</span><span class="denom">sin&#160;GPC</span></span>
+= <span class="divide"><span class="num">PG</span><span class="denom">CG</span></span>; and also μ =
+<span class="divide"><span class="num">sin&#160;QFG</span><span class="denom">sin&#160;QGF</span></span> =
+<span class="divide"><span class="num">QG</span><span class="denom">QF</span></span></p>
+
+</div><!--formula-->
+
+<p>Now, as P approaches A, we have ultimately PG = AG, QG = BG, and QF = BF;</p>
+
+<div class="formula">
+
+<p>Therefore, putting AG = θ and AC = ρ′</p>
+
+<p>μ = <span class="divide"><span class="num">AG</span><span class="denom">CG</span></span> =
+<span class="divide"><span class="num">θ</span><span class="denom">θ - ρ′</span></span>; μ =
+<span class="divide"><span class="num">BG</span><span class="denom">BF</span></span> =
+<span class="divide"><span class="num">θ - <i>t′</i></span><span class="denom">φ</span></span>,</p>
+
+</div><!--formula-->
+
+<p class="noindent">from which μ&#160;θ - μ&#160;ρ′ = θ; and μ&#160;φ = θ - <i>t′</i> and eliminating θ, we have μ²&#160;φ + μ&#160;ρ′ =
+μ&#160;φ + <i>t′</i>, whence, as above, ρ′ = (μ - 1)<span class="fsize200 downpoint2">(</span>φ +
+<span class="divide"><span class="num"><i>t′</i></span><span class="denom">μ</span></span>.<span class="fsize200 downpoint2">)</span></p>
+
+<p>But as this value of the radius of curvature, as already stated, is calculated for rays
+near the axis, it would produce a notable aberration for rays incident on the margin of
+the lens. In order, therefore, to avoid the effects of aberration as much as possible, a
+second radius of curvature must be calculated, so that rays incident on the margin of the
+lens may be refracted in a direction parallel to the axis. This second value of the radius
+is called ρ″ in the text, and is found as follows (referring to <a href="#Fig57">fig. 57</a>):</p>
+
+<p>Let FB′ <i>b</i>&#160;<i>x</i> be the course of a ray refracted in the direction <i>b</i>&#160;<i>x</i> parallel to the axis A <i>x′</i>.
+This ray meets the surface AB in the point B′, whose position may be found approximately
+by tracing the path of the ray FB, on the supposition that the surface of the refracting medium
+is produced in the directions AB, <i>a′</i>&#160;<i>b′</i>.</p>
+
+<div class="container w25emmax" id="Fig57">
+
+<p class="caption">Fig. 57.</p>
+
+<img src="images/illo252.jpg" alt="Refraction in central lens">
+
+</div><!--container-->
+
+<p class="noindent">Let C be the centre of curvature (see <a href="#Fig57">fig. 57</a>)</p>
+
+<p>α = AC&#160;<i>b</i> the angle of emergence</p>
+
+<p>η = B′&#160;<i>b</i>&#160;C the second angle of refraction</p>
+
+<p>ε = B&#160;b&#160;B′ the first angle of refraction</p>
+
+<p><i>i</i> = B′FA the first angle of incidence</p>
+
+<p><i>i′</i> = BFA</p>
+
+<p><i>e</i> = <i>b′</i>&#160;B&#160;<i>b</i></p>
+
+<p class="noindent">AB = <i>r</i></p>
+
+<p class="noindent">AB′ = <i>r′</i></p>
+
+<p class="noindent">B&#160;<i>b</i> = <i>t″</i> the thickness of the lens at the edge</p>
+
+<p class="noindent">AF = φ the focal distance.</p>
+
+<p class="noindent">Then tan&#160;<i>i′</i> = <span class="divide"><span class="num"><i>r</i></span><span class="denom">φ</span></span>;
+sin&#160;<i>e</i> = <span class="divide"><span class="num">sin&#160;<i>i′</i></span><span class="denom">μ</span></span>
+whence <i>b</i>&#160;<i>b′</i> = <i>t″</i>&#160;tan&#160;<i>e</i> becomes known.</p>
+
+<p class="noindent">Now, since BB′ = <i>b</i>&#160;<i>b′</i> nearly, AB′ = AB - <i>b</i>&#160;<i>b′</i>
+or <i>r′</i> = <i>r</i> - <i>t″</i>&#160;tan&#160;<i>e</i>.</p>
+
+<p>From this is obtained the angle of incidence
+<i>i</i>, and the first angle of refraction ε;
+for tan&#160;<i>i</i> = <span class="divide"><span class="num"><i>r′</i></span><span class="denom">φ</span></span>
+and sin&#160;ε = <span class="divide"><span class="num">sin&#160;<i>i</i></span><span class="denom">μ</span></span>.</p>
+
+<table class="formulas">
+
+<tr>
+<td class="rightpart">Next B′&#160;<i>b</i>&#160;C = B&#160;<i>b</i>&#160;C - B&#160;<i>b</i>&#160;B′ or η = α - ε<br>
+<span class="padl4">and</span> sin&#160;α = μ&#160;sin&#160;η = μ&#160;sin&#160;(α - ε)</td>
+</tr>
+
+<tr>
+<td class="rightpart">from which, sin&#160;α&#160;cos&#160;ε - cos&#160;α&#160;sin&#160;ε = <span class="divide"><span class="num">sin&#160;α</span>
+<span class="denom">μ</span></span></td>
+</tr>
+
+<tr>
+<td class="rightpart">whence sin&#160;α&#160;<span class="fsize200 downpoint2">(</span>cos&#160;ε -
+<span class="divide"><span class="num">1</span>
+<span class="denom">μ</span></span><span class="fsize200 downpoint2">)</span> = cos&#160;α&#160;sin&#160;ε; and</td>
+</tr>
+
+<tr>
+<td class="rightpart">sin²&#160;α&#160;<span class="fsize200 downpoint2">(</span>cos²&#160;ε -
+<span class="divide"><span class="num">2&#160;cos&#160;ε</span><span class="denom">μ</span></span> +
+<span class="divide"><span class="num">1</span><span class="denom">μ²</span></span><span class="fsize200 downpoint2">)</span>
+= cos²&#160;α&#160;sin²&#160;ε = (1 - sin²&#160;α)&#160;sin²&#160;ε = sin²&#160;ε - sin²&#160;α&#160;sin²&#160;ε</td>
+</tr>
+
+</table>
+
+<p>Then transposing we have</p>
+
+<p class="center">sin²&#160;α&#160;<span class="fsize200 downpoint2">{</span>(cos²&#160;ε + sin²&#160;ε) -
+<span class="divide"><span class="num">2&#160;cos&#160;ε</span><span class="denom">μ</span></span> +
+<span class="divide"><span class="num">1</span><span class="denom">μ²</span></span><span class="fsize200 downpoint2">}</span> = sin²&#160;ε</p>
+
+<p class="center highline2">and because (cos²&#160;ε + sin²&#160;ε) = 1 we have, by dividing,</p>
+
+<p class="center"><span class="tripleline1">sin²&#160;α =</span> <span class="divide"><span class="num">sin²&#160;ε</span>
+<span class="denom"><span class="fsize200 downpoint2">{</span>1 -
+<span class="divide"><span class="num">2&#160;cos&#160;ε</span><span class="denom">μ</span></span> +
+<span class="divide"><span class="num">1</span><span class="denom">μ²</span></span><span class="fsize200 downpoint2">}</span></span></span>
+<span class="tripleline1">= <span class="divide"><span class="num">μ²&#160;sin²&#160;ε</span>
+<span class="denom">μ² - 2&#160;μ&#160;cos&#160;ε + 1</span></span></span></p>
+
+<p class="center">and sin&#160;α =
+<span class="divide"><span class="num">μ&#160;sin&#160;ε</span>
+<span class="denom paddedtop">√<span class="bt">1 - 2&#160;μ&#160;cos&#160;ε + μ²</span></span></span></p>
+
+<p>Next, since <i>b</i>&#160;C = <span class="divide"><span class="num"><i>a′</i>&#160;<i>b</i></span>
+<span class="denom">sin&#160;AC&#160;<i>b</i></span></span>
+= <span class="divide"><span class="num"><i>r</i></span><span class="denom">sin&#160;α</span></span>,
+putting C&#160;<i>b</i> = <i>ρ″</i>, and substituting
+we have <i>ρ″</i> = <span class="divide"><span class="num"><i>r</i></span><span class="denom">μ&#160;sin&#160;ε</span></span>
+√<span class="bt">μ² - 2&#160;μ&#160;cos&#160;ε + 1</span><br>
+and, taking for the radius of curvature, the mean of <i>ρ′</i> and <i>ρ″</i> the values calculated for the
+central and marginal rays, we have finally ρ = <span class="divide"><span class="num">ρ′ + ρ″</span>
+<span class="denom">2</span></span></p>
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page252">[252-<br>253]</span><a id="Page253"></a></p>
+
+<div class="container w15emmax" id="Fig58">
+
+<p class="caption">Fig. 58.</p>
+
+<img src="images/illo253a.jpg" alt="Refraction of ring">
+
+</div><!--container-->
+
+<p>I come next to the <i>second</i> case, which concerns the calculation
+of the elements of a concentric ring. The section <i>a</i>&#160;<i>b</i>&#160;<i>c</i>&#160;<i>d</i>&#160;<i>e</i>
+(<a href="#Fig58">fig. 58</a>) of one of those rings includes a mixtilinear
+triangle <i>a</i>&#160;<i>b</i>&#160;<i>e</i>, and a rectangle <i>b</i>&#160;<i>c</i>&#160;<i>e</i>&#160;<i>d</i>, the
+thickness <i>b</i>&#160;<i>c</i> being the same as that of the edge
+of the central disc; and the elements to be determined
+are the radius of the curve surface, and
+the position of the centre of curvature, with reference
+to the vertex of the lens.</p>
+
+<div class="container w35emmax" id="Fig59">
+
+<p class="caption">Fig. 59.</p>
+
+<img src="images/illo253b.jpg" alt="Refraction of ring">
+
+</div><!--container-->
+
+<p>The radius of curvature of the zone may be calculated by
+the following formulæ, in which
+(see <a href="#Fig59">fig. 59</a>)</p>
+
+<div class="varlist notop">
+
+<p class="noindent"><i>r</i>₁ = AB the distance of the outer margin
+of the zone from the axis of the lens</p>
+
+<p class="noindent"><i>r</i>₂ = AE the distance of the inner margin
+from the axis</p>
+
+<p class="noindent"><i>l</i> = BE the breadth of the zone = <i>r</i>₁ - <i>r</i>₂</p>
+
+<p class="noindent">ρ = the radius of curvature = <i>b</i>&#160;C = <i>m</i>&#160;C</p>
+
+<p class="noindent">φ = focal distance AF</p>
+
+<p class="noindent"><i>t</i> = thickness of the joint B&#160;<i>b</i></p>
+
+<p class="noindent"><i>t″</i> = B&#160;<i>b</i></p>
+
+<p class="noindent">μ = refractive index of the glass</p>
+
+<p class="noindent"><i>i</i>₁ = BFA</p>
+
+<p class="noindent"><i>i</i>₂ = EFA</p>
+
+</div><!--varlist-->
+
+<div class="formula">
+
+<p>Then tan&#160;<i>i′</i>₁ = <span class="divide"><span class="num"><i>r</i>₁</span><span class="denom">φ</span></span>;
+tan&#160;<i>i′</i>₂ = <span class="divide"><span class="num"><i>r</i>₂</span><span class="denom">φ</span></span></p>
+
+<p>sin&#160;<i>e</i>₁ = <span class="divide"><span class="num">sin&#160;<i>i′</i>₁</span><span class="denom"><i>μ</i></span></span>;
+sin&#160;<i>e</i>₂ = <span class="divide"><span class="num">sin&#160;<i>i′</i>₂</span><span class="denom"><i>μ</i></span></span></p>
+
+<p><i>r′</i>₁ = <i>r</i>₁ - <i>t″</i>&#160;sin&#160;<i>e</i>₁; <i>r′</i>₂ = <i>r</i>₂ - <i>t″</i>&#160;sin&#160;<i>e</i>₂</p>
+
+<p>tan&#160;<i>i</i>₁ = <span class="divide"><span class="num"><i>r′</i>₁</span><span class="denom">φ</span></span>;
+tan&#160;<i>i</i>₂ = <span class="divide"><span class="num"><i>r′</i>₂</span><span class="denom">φ</span></span></p>
+
+<p>sin&#160;ε = <span class="divide"><span class="num">sin&#160;<i>i</i>₁</span><span class="denom">μ</span></span>;
+sin&#160;ε′ = <span class="divide"><span class="num">sin&#160;<i>i</i>₂</span><span class="denom">μ</span></span></p>
+
+<p>sin&#160;α = <span class="divide"><span class="num">μ&#160;sin&#160;ε</span>
+<span class="denom paddedtop">√<span class="bt">μ² - 2&#160;μ&#160;cos&#160;ε + 1</span></span></span>;</p>
+
+<p>sin&#160;α′ = <span class="divide"><span class="num">μ&#160;sin&#160;ε′</span>
+<span class="denom paddedtop">√<span class="bt">μ² - 2&#160;μ&#160;cos&#160;ε′ + 1</span></span></span>; η = α′ - ε′</p>
+
+<p>and lastly ρ = <span class="divide"><span class="num">2&#160;cos&#160;ε′</span>
+<span class="denom">2&#160;cos&#160;{η + ¹⁄₂(α - α′)}&#160;sin&#160;¹⁄₂&#160;(α - α′)</span></span></p>
+
+</div><!--formula-->
+
+<p>which is <span class="smcap">Fresnel’s</span> value of the radius of
+curvature.<a id="FNanchor58" href="#Footnote58" class="fnanchor">[58]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote58" href="#FNanchor58" class="label">[58]</a> The following steps will conduct us to this expression:</p>
+
+<div class="container w35emmax" id="Fig60">
+
+<p class="caption">Fig. 60.</p>
+
+<img src="images/illo254.jpg" alt="Refraction of ring">
+
+</div><!--container-->
+
+<p>Let B&#160;<i>b</i>&#160;<i>f</i>&#160;E (<a href="#Fig60">fig. 60</a>) represent the section of a zone by a plane passing through the
+axis of the lens AF, C the centre of curvature, F the radiant point, and FB′&#160;<i>b</i>&#160;<i>x</i>, FE′<i>m</i>&#160;<i>x′</i>
+the course of the extreme rays which are transmitted through the zone (and the latter of
+which passes from E′ to <i>e</i> through a portion of the zone or lens in contact with that under
+consideration). Then putting</p>
+
+<div class="varlist notop">
+
+<p class="noindent">AB = <i>r</i>₁; AB′ = <i>r′</i>₁; C&#160;<i>b</i> = ρ</p>
+
+<p class="noindent">AE = <i>r</i>₂; AE′ = <i>r′</i>₂; B&#160;<i>b</i> = <i>t″</i>; BE = <i>r</i>₁ - <i>r</i>₂ = <i>l</i></p>
+
+<p class="noindent">ε = the first angle of refraction <i>b</i>&#160;B′&#160;<i>k</i></p>
+
+<p class="noindent">η = the second angle of refraction B′&#160;<i>b</i>&#160;C</p>
+
+<p class="noindent">ε′ = the first angle of refraction <i>e</i>&#160;E&#160;<i>k′</i></p>
+
+<p class="noindent">η′ = the second angle of refraction <i>e</i>&#160;<i>m</i>&#160;C</p>
+
+<p class="noindent">α = the angle of emergence <i>b</i>&#160;C&#160;<i>q</i></p>
+
+<p class="noindent">α′ = the angle of emergence <i>m</i>&#160;C&#160;<i>q</i></p>
+
+<p class="noindent"><i>i′</i>₁ = BFA; <i>i′</i>₂ = EFA; <i>i</i>₁ = B′FA; <i>i</i>₂ = E′FA</p>
+
+<p class="noindent"><i>e</i>₁ = B&#160;<i>b</i>&#160;B′; <i>e</i>₂ = E&#160;<i>e</i>&#160;E′.</p>
+
+</div><!--varlist-->
+
+<p>Proceeding exactly as in the case of the central
+lens we shall have</p>
+
+<div class="formula">
+
+<p>tan&#160;<i>i′</i>₁ = <span class="divide"><span class="num">BA</span><span class="denom">AF</span></span> =
+<span class="divide"><span class="num"><i>r</i>₁</span><span class="denom">φ</span></span>;
+tan&#160;<i>i′</i>₂ = <span class="divide"><span class="num">EA</span><span class="denom">AF</span></span> =
+<span class="divide"><span class="num"><i>r</i>₂</span><span class="denom">φ</span></span></p>
+
+<p>sin&#160;<i>e</i>₁ = <span class="divide"><span class="num">sin&#160;<i>i′</i>₁</span><span class="denom">μ</span></span>;
+sin&#160;<i>e</i>₂ = <span class="divide"><span class="num">sin&#160;<i>i′</i>₂</span><span class="denom">μ</span></span></p>
+
+<p><i>r′</i>₁ = <i>r</i>₁ - <i>t″</i>&#160;sin&#160;<i>e</i>₁; <i>r′</i>₂ = <i>r</i>₂ - <i>t″</i>&#160;sin&#160;<i>e</i>₂</p>
+
+<p>tan&#160;<i>i</i>₁ = <span class="divide"><span class="num"><i>r′</i>₁</span><span class="denom">φ</span></span>;
+tan&#160;<i>i</i>₂ = <span class="divide"><span class="num"><i>r′</i>₂</span><span class="denom">φ</span></span></p>
+
+<p>sin&#160;ε = <span class="divide"><span class="num">sin&#160;<i>i</i>₁</span><span class="denom">μ</span></span>;
+sin&#160;ε′ = <span class="divide"><span class="num">sin&#160;<i>i′</i>₂</span><span class="denom">μ</span></span></p>
+
+<p>sin&#160;α = <span class="divide"><span class="num">μ&#160;sin&#160;ε</span>
+<span class="denom paddedtop">√<span class="bt">μ² - 2&#160;μ&#160;cos&#160;ε - 1</span></span></span>;
+and sin&#160;α′ =  <span class="divide"><span class="num">μ&#160;sin&#160;ε′</span>
+<span class="denom paddedtop">√<span class="bt">μ² - 2&#160;μ&#160;cos&#160;ε′ + 1</span></span></span></p>
+
+</div><!--formula-->
+
+<p>Now, the angle <i>b</i>&#160;C&#160;<i>m</i> = α - α′ from which (since the triangle <i>b</i>&#160;<i>m</i>&#160;C is
+isosceles) <i>b</i>&#160;<i>m</i>&#160;C = 90° - ¹⁄₂&#160;(α - α′); also, in the triangle <i>b</i>&#160;<i>m</i>&#160;<i>e</i>, the angle
+<i>b</i>&#160;<i>m</i>&#160;<i>e</i> = <i>b</i>&#160;<i>m</i>&#160;C - <i>e</i>&#160;<i>m</i>&#160;C = 90° - ¹⁄₂&#160;(α - α′) - η
+and <i>b</i>&#160;<i>e</i>&#160;<i>m</i> = <i>k′</i>&#160;<i>e</i>&#160;E′ = 90° - ε′</p>
+
+<p>We have therefore in the triangle <i>b</i>&#160;<i>m</i>&#160;<i>e</i></p>
+
+<div class="formula">
+
+<p><i>b</i>&#160;<i>m</i> = <span class="divide"><span class="num"><i>b</i>&#160;<i>e</i>&#160;sin&#160;<i>b</i>&#160;<i>e</i>&#160;<i>m</i></span>
+<span class="denom">sin&#160;<i>b</i>&#160;<i>m</i>&#160;<i>e</i></span></span> =
+<span class="divide"><span class="num"><i>l</i>&#160;cos&#160;ε′</span><span class="denom">cos&#160;{η + ¹⁄₂&#160;(α - α′)}</span></span></p>
+
+</div><!--formula-->
+
+<p>and in <i>b</i>&#160;<i>m</i>&#160;C</p>
+
+<table class="formulas">
+
+<tr>
+<td class="leftpart mid"><i>b</i>&#160;C</td>
+<td class="midpart mid">=</td>
+<td class="rightpart"><span class="divide"><span class="num"><i>b</i>&#160;<i>m</i>&#160;sin&#160;<i>b</i>&#160;<i>m</i>&#160;C</span>
+<span class="denom">sin&#160;<i>b</i>&#160;C&#160;<i>m</i></span></span> =
+<span class="divide"><span class="num"><i>l</i>&#160;cos&#160;ε′&#160;cos&#160;¹⁄₂&#160;(α - α′)</span>
+<span class="denom">(cos&#160;(η + ¹⁄₂&#160;(α - α′))&#160;sin&#160;(α - α′)</span></span></td>
+</tr>
+
+<tr>
+<td colspan="3" class="center">= <span class="divide"><span class="num"><i>l</i>&#160;cos&#160;ε′&#160;cos&#160;¹⁄₂&#160;(α - α′)</span>
+<span class="denom">cos&#160;{η + ¹⁄₂&#160;(α - α′)}&#160;2&#160;sin&#160;¹⁄₂&#160;(α - α′)&#160;cos&#160;¹⁄₂&#160;(α - α′)</span></span></td>
+</tr>
+
+</table>
+
+<p>from which, putting <i>b</i>&#160;C = ρ</p>
+
+<div class="formula">
+
+<p>ρ = <span class="divide"><span class="num"><i>l</i>&#160;cos&#160;ε′</span>
+<span class="denom">2&#160;cos&#160;{η + ¹⁄₂&#160;(α - α′)}&#160;sin&#160;¹⁄₂&#160;(α - α′)</span></span></p>
+
+</div><!--formula-->
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page254">[254]</span></p>
+
+<p>Lastly, the position of C the centre of curvature for a ring is easily
+determined by two co-ordinates in reference to their origin, A,
+which is the vertex of the lens (see <a href="#Fig60">fig. 60</a> below), by the equations:</p>
+
+<table class="formulas">
+
+<tr>
+<td class="leftpart">CG</td>
+<td class="midpart">=</td>
+<td class="midpart">ρ . sin&#160;α - <i>a</i>&#160;<i>b</i></td>
+<td class="midpart">=</td>
+<td class="rightpart">ρ . sin&#160;α - <i>r</i>₁</td>
+</tr>
+
+<tr>
+<td class="leftpart">CQ</td>
+<td class="midpart">=</td>
+<td class="midpart">ρ . cos&#160;α - <i>q</i>&#160;Q</td>
+<td class="midpart">=</td>
+<td class="rightpart">ρ . cos&#160;α - <i>t″</i></td>
+</tr>
+
+</table>
+
+<p><span class="pagenum" id="Page255">[255]</span></p>
+
+<p>The elements of each successive zone are determined in the same
+manner. The annular lens of the first order of lights in <span class="smcap">Fresnel’s</span>
+system consists, as already stated, of a central disc 11 inches in diameter,
+and 10 concentric rings, all of which have a common principal
+focus, where the rays of the sun meet after passing through the
+lens. With such accuracy are those rings and the disc ground and
+placed relatively to each other, that the position of the actual conjugate
+focus of the entire surface of the compound lens, differs in
+a very small degree from that obtained by calculation in the manner
+described below.<a id="FNanchor59" href="#Footnote59" class="fnanchor">[59]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote59" href="#FNanchor59" class="label">[59]</a></p>
+
+<p><span class="sidenote">Testing Lenses.</span>
+The tests generally applied for examining the lenses used in Lighthouses, is to find the
+position of the conjugate focus <i>behind</i> the lens, due to a given position of a lamp in <i>front</i>
+of it. This test depends on the following considerations:—Draw a line from an object
+O in front of a lens, to any point Q
+in the lens; and from A, the centre of
+the lens, draw AR parallel to OQ, and
+cutting a line RF&#160;<i>r</i> which passes through
+the principal focus F, at right angles to
+the axis of the lens; then join the points
+Q and R, and produce the line joining them: I, the image of O must be in that line. In
+the same way, draw a line from O to <i>q</i>, another point in the lens on the other side of its
+axis, and parallel to it draw A&#160;<i>r</i> from the centre of the lens, cutting the plane of the principal
+focus in <i>r</i>. Join <i>q</i>&#160;<i>r</i>, in which line the image will lie; and hence the intersection of
+OR and <i>q</i>&#160;<i>r</i>, in I, will be the point in which the image of O is formed, or will be the conjugate
+focus of the lens due to the distance OA. This mode will serve to give the distance
+of the conjugate focus of a lens (<i>neglecting its thickness</i>) for rays falling on its surface at
+any angle.</p>
+
+<div class="container w30emmax" id="Fig61">
+
+<p class="caption">Fig. 61.</p>
+
+<img src="images/illo255.jpg" alt="Testing a lens">
+
+</div><!--container-->
+
+<p>We shall suppose QA (<a href="#Fig61">fig. 61</a>) to represent the half of a lens, and remembering the
+conditions described in reference to the last figure, we shall at once perceive the truth of the
+following analogy <span class="nowrap">(<a href="#Fig62">fig. 62</a>):—</span></p>
+
+<div class="container w35emmax" id="Fig62">
+
+<p class="caption">Fig. 62.</p>
+
+<img src="images/illo256a.jpg" alt="Lens testing">
+
+</div><!--container-->
+
+<p>OA&#160;∶ AF&#160;∷ AQ&#160;∶ FR&#160;∷ AI&#160;∶ FI,
+and putting OA = δ, AI = φ′, and
+AF = φ, we have δ&#160;∶ φ&#160;∷ φ′&#160;∶ φ′ - φ,
+and, consequently, δ&#160;φ′ - δ&#160;φ = φ&#160;φ′;
+and hence the following equations, which express the relations subsisting between the
+principal focus of the lens and the distance of any object and its corresponding image:</p>
+
+<p>1<i>st</i>, To find the principal focal distance of a lens from the measured position of its object
+and its image refracted through it, we have, φ = <span class="divide"><span class="num">δ&#160;φ′</span>
+<span class="denom">δ + φ′</span></span>.</p>
+
+<p>2<i>d</i>, For the distance of the object, when that of the image is known, we have, δ =
+<span class="divide"><span class="num">φ&#160;φ′</span><span class="denom">φ′ - φ</span></span>.</p>
+
+<p>3<i>d</i>, For the position of the image, when that of the object is known, we have, φ′ =
+<span class="divide"><span class="num">δ&#160;φ</span><span class="denom">δ - φ</span></span>.</p>
+
+<div class="container w40emmax" id="Fig63">
+
+<p class="caption">Fig. 63.</p>
+
+<img src="images/illo256b.jpg" alt="Lens testing">
+
+</div><!--container-->
+
+<p>In testing lenses, of course, it is this last equation which we use, because the value of φ or
+the principal focus is always known, and is that whose accuracy we wish to try, while δ may
+be chosen within certain limits at will. I have found that the best mode of proceeding is the
+following:—In front of the lens Q<i>&#160;q</i> (see <a href="#Fig63">fig. 63</a>) firmly fixed on a frame, place a lamp at O
+at the distance of about 50 yards.
+Calculate the value of φ′ due to
+50 yards, which in this case is
+equal to AF′, OA being equal
+to δ; and move a screen of white
+paper backwards and forwards
+until you receive on it the smallest
+image that can be formed, which is at the point where the cones of converging and
+diverging rays meet. The image will always increase in size whether you approach nearer
+to the lens or recede farther from it, according as you pass from the converging into the
+diverging cone of rays, or <i>vice versa</i>; and hence the intermediate point is easily found by a
+very little practice. The distance from the centre of the lens to the face of the screen, which
+must be adjusted so as to be at right angles to a line joining the centre of the lens and the
+lamp, is then measured; and its agreement with the calculated length of φ′, is an indication
+of the accuracy of the workmanship of the lens. When the measured distance is greater
+than the calculated φ′, we know that the lens is too flat; and it is on this side the error
+generally falls. On the other hand, when φ′ is greater than the measured distance, we
+know that the lens has too great convexity. I have only to add, that an error of ¹⁄₆₀ on
+the value of φ′ may be safely admitted in Lighthouse lenses; but I have had many instruments
+made by M. <span class="smcap">François Soleil</span>, whose error fell below ¹⁄₈₀ of φ′. Owing probably
+to the mode of grinding, the surfaces of all the lenses I have yet examined are somewhat
+too flat.</p>
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page256">[256-<br>257]</span>
+<a id="Page257"></a></p>
+
+<p>In the combination of lenses with the flame of a lamp, similar
+considerations must influence us in making the necessary arrangements,
+as in the case of reflectors. We have already seen that the
+size of the flame and its distance from the surface of reflecting instruments
+have an important practical bearing on the utility of
+the instrument, <span class="sidenote">Divergence of Annular
+Lenses.</span>
+and that the divergence of the resultant beam materially
+affects its fitness for the purpose of a Lighthouse. So also,
+in the case of the lens, unless the diameter of the flame of the lamp
+has to the focal distance of the instrument a relation such as may
+cause an appreciable divergence of the rays refracted through it, it
+could not be usefully applied to a Lighthouse; for, without this, the
+light would be in sight during so short a time, that the seaman
+would have much difficulty in observing it. To determine the
+amount of this divergence of the refracted beam, therefore, is a
+matter of great practical importance, and I shall briefly point out
+the conditions which regulate its amount, as they are nearly identical
+with those which determine the divergence of a paraboloïdal
+mirror illuminated by a lamp in its focus. The divergence, in the
+case of lenses, may be described as <i>the angle which the flame subtends
+at the principal focus of the lens</i>, the maximum of which, produced
+at the vertex of <span class="smcap">Fresnel’s</span> great lens by the lamp of four
+concentric wicks, is about 5° 9′.<a id="FNanchor60" href="#Footnote60" class="fnanchor">[60]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote60" href="#FNanchor60" class="label">[60]</a> This will be easily seen by examining the annexed
+<a href="#Fig64">figure (64)</a>, in which Q&#160;<i>q</i> represents
+the lens. A its centre, F the principal focus, <i>b</i>&#160;F and <i>b′</i>&#160;F the radius of the flame; then is the
+angle <i>b</i>&#160;A&#160;<i>b′</i> equal to the maximum divergence of the lens. Sin&#160;<i>b</i>&#160;AF =
+<span class="divide"><span class="num"><i>b</i>&#160;F</span><span class="denom">AF</span></span> = sin&#160;<i>b′</i>&#160;AF =
+<span class="divide"><span class="num">Rad. of flame</span><span class="denom">Focal distance</span></span>;
+and twice <i>b</i>&#160;AF = the whole divergence at A. Then for the divergence at
+the margin of the lens, or at any other point, we have, FQ = √<span class="bt">AQ² + AF²</span> and Q&#160;<i>x</i>
+= √<span class="bt">QF² + F&#160;<i>x</i>²</span>; and for any angle at Q, we have sin&#160;FQ&#160;<i>x</i> =
+<span class="divide"><span class="num">F&#160;<i>x</i></span><span class="denom">FQ</span></span>.</p>
+
+<div class="container w40emmax" id="Fig64">
+
+<p class="caption">Fig. 64.</p>
+
+<img src="images/illo258.jpg" alt="Refraction of Fresnel lens">
+
+</div><!--container-->
+
+</div><!--footnote-->
+
+<p><span class="sidenote">Illuminating
+Power of Lenses.</span>
+On the subject of the illuminating power of the lenses, it seems
+enough to say, that the same general principle regulates the estimate
+as in reflectors. Owing to the square form of the lens, however,
+there is a greater difficulty in finding a <i>mean focal distance</i> whereby
+to correct our estimate of the angle subtended by the light, so as
+to equate the varying distance of the several parts of the surface;
+but, practically, we shall not greatly err if we consider the <i>quotient
+of the surface of the lens divided by the surface of the flame</i> as the
+increased power of illumination by the use of the lens. The illuminating
+effect of the great lens, as measured at moderate distances,<span class="pagenum" id="Page258">[258]</span>
+has generally been taken at 3000 Argand flames, the value of the
+great flame in its focus being about 16, thus giving its increasing
+power as nearly equal to 180. The more perfect lenses have produced
+a considerably greater effect.</p>
+
+<p>The application of lenses to Lighthouses is so obvious as
+scarcely to admit of farther explanation than simply to state, <span class="sidenote">Arrangement of
+the Lenses
+in a Lighthouse.</span> that
+those instruments are arranged round a lamp placed in their centre,
+and on the level of the focal plane in the manner shewn in <a href="#Plate13">Plates
+XIII.</a> and <a href="#Plate14">XIV.</a>,<a id="FNanchor61" href="#Footnote61" class="fnanchor">[61]</a>
+so as to form by their union a right octagonal
+hollow prism, circulating round the flame which is fixed in the
+centre, and shewing to a distant observer successive flashes or
+blazes of light, whenever they cross a line joining his eye and the<span class="pagenum" id="Page259">[259]</span>
+lamp, in a manner similar to that already noticed in describing the
+action of the mirrors. The chief difference in the effect consists in
+the greater intensity and shorter duration of the blaze produced
+by the lens; which latter quantity is, of course, proportional to the
+divergence of the resultant beam. Each lens subtends a central
+horizontal pyramid of light of about 46° of inclination, beyond
+which limits the lenticular action could not be advantageously
+pushed, owing to the extreme obliquity of the incidence of light;
+but <span class="smcap">Fresnel</span> at once conceived the idea of pressing into the service
+of the mariner, by means of two very simple expedients, the
+light which would otherwise have uselessly escaped above and below
+the lenses.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote61" href="#FNanchor61" class="label">[61]</a> The Plates shew the nature of the mechanical power which gives movement to the
+lenses. It consists of a clockwork movement driven by a weight which sets in motion a
+plate bearing brackets that carry the lenses. All this, however, can be seen from the
+Plates; and I am unwilling to expend time in a detailed explanation of what is obvious by
+inspection.</p>
+
+</div><!--footnote-->
+
+<p>For intercepting the upper portion of the light, <span class="smcap">Fresnel</span> employed
+eight smaller lenses of 500 mm. focal distance (19·68 inches)
+inclined inwards towards the lamp, which is also their common
+focus and thus forming, by their union, <span class="sidenote">Pyramidal Lenses
+and Mirrors.</span>
+a frustum of a hollow
+octagonal pyramid of 50° of inclination. The light falling on those
+lenses is formed into eight beams parallel to the axis of the smaller
+lenses, and rising upwards at an angle of 50° inclination. Above
+them are ranged eight plane mirrors, so inclined (see <a href="#Plate13">Plates XIII.</a>
+and <a href="#Plate14">XIV.</a>) as to project the beams transmitted by the small lenses
+in the horizontal direction, so as finally to increase the effect of the
+light. In placing those upper lenses, it is generally thought advisable
+to give their axis an horizontal deviation of 7° or 8° from
+that of the great lenses and in the direction contrary to that of the
+revolution of the frame which carries the lenticular apparatus. By
+this arrangement, the flashes of the smaller lenses precede that of
+the large ones, and thus tend to correct the chief practical defect
+of revolving lenticular lights by prolonging the bright periods.
+The elements of the subsidiary lenses depend upon the very same
+principles, and are calculated by the same formulæ as those given
+for the great lenses. In fixing the focal distance and inclination
+of those subsidiary lenses, <span class="smcap">Fresnel</span> was guided by a consideration<span class="pagenum" id="Page260">[260]</span>
+of the necessity for keeping them sufficiently high to prevent interference
+with the free access to the lamp. He also restricted their
+dimensions within very moderate limits, so as to avoid too great
+weight. The focal distance is the same as that for lenses of the
+third order of lights.</p>
+
+<div class="container w20emmax" id="Fig65">
+
+<p class="caption">Fig. 65.</p>
+
+<img src="images/illo260.jpg" alt="Curved mirror">
+
+</div><!--container-->
+
+<p>Owing to the necessary arrangements of a lantern, only a
+very small portion of those rays, which escape from below the
+lenses, can be rendered available for the purposes of a Lighthouse;
+and any attempt to subject it to lenticular action, so as
+to add it to the periodic flashes, would have led to a most inconvenient
+complication of the apparatus. <span class="smcap">Fresnel</span> adopted the more
+natural and simple course of transmitting it to the horizon in the
+form of flat rings of light, or rather of divergent pencils, directed
+to various points of the horizon. <span class="sidenote">Curved Mirrors.</span>
+This he effected by means of
+small curved mirrors, disposed in tiers, one above another, like the
+leaves of a Venetian blind—an arrangement which he also adopted
+(shewn in <a href="#Plate15">Plates XV.</a> and <a href="#Plate16">XVI.</a>) for intercepting the light which
+escapes above as well as below the dioptric
+belt in fixed lights. Those curved
+mirrors are, strictly speaking, generated
+(see <a href="#Fig65">fig. 65</a>) by portions, such as a&#160;b, of
+parabolas, having their foci coincident
+with F, the common flame of the system.
+In practice, however, they are formed as
+portions of a curved surface, ground by
+the radius of the circle, which osculates
+the given parabolic segment.<a id="FNanchor62" href="#Footnote62" class="fnanchor">[62]</a> The
+mirrors are plates of glass, silvered on the back and set in flat
+cases of sheet-brass. They are suspended on a circular frame by<span class="pagenum" id="Page261">[261]</span>
+screws, which are attached to the backs of the brass cases, and
+which afford the means of adjusting them to their true inclination,
+so that they may reflect objects on the horizon of the Lighthouse<span class="pagenum" id="Page262">[262]</span>
+to an observer’s eye, placed in the common focus of the
+system.<a id="FNanchor63" href="#Footnote63" class="fnanchor">[63]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote62" href="#FNanchor62" class="label">[62]</a> To find the radius and centre of a circle, which shall osculate a given parabola, whose
+focus is in F, draw the normals to the curve from <i>p</i> and P, meeting in O, and draw N&#160;<i>e</i>
+parallel to a tangent of the curve, or to <i>p</i>&#160;P, then P&#160;O
+or <i>p</i>&#160;O is the radius required. Now, we have similar triangles
+P&#160;<i>p</i>&#160;<i>d</i> and N&#160;<i>e</i>&#160;<i>n</i>, and P&#160;H and <i>p</i>&#160;<i>h</i> are (proximate)
+ordinates; hence we have the following <span class="nowrap">analogies:—</span></p>
+
+<div class="formula">
+
+<p>P&#160;<i>d</i>&#160;∶ P&#160;<i>p</i>&#160;∷ PH&#160;∶ PN</p>
+
+<p>N&#160;<i>e</i>&#160;∶ N&#160;<i>n</i>&#160;∷ PH&#160;∶ PN</p>
+
+</div><!--formula-->
+
+<div class="container w20emmax" id="Fig66">
+
+<p class="caption">Fig. 66.</p>
+
+<img src="images/illo261.jpg" alt="Finding radius and centre of circle">
+
+</div><!--container-->
+
+<p class="noindent">Hence compounding those
+ratios (in which P&#160;<i>d</i> = N&#160;<i>n</i>
+nearly)</p>
+
+<table class="formulas">
+
+<tr>
+<td class="leftpart">N&#160;<i>e</i>&#160;∶ P&#160;<i>p</i></td>
+<td class="midpart">∷</td>
+<td class="rightpart">PH²&#160;∶ PN²</td>
+</tr>
+
+<tr>
+<td class="leftpart">also N&#160;<i>e</i>&#160;∶ P&#160;<i>p</i></td>
+<td class="midpart">∷</td>
+<td class="rightpart">NO&#160;∶ PO,</td>
+</tr>
+
+</table>
+
+<p class="noindent">(for O&#160;P&#160;<i>p</i> and N&#160;<i>o</i>&#160;<i>e</i> are similar
+triangles)</p>
+
+<table class="formulas">
+
+<tr>
+<td rowspan="3">&#160;</td>
+<td class="rightpart">PH²&#160;∶ PN²&#160;∷ NO&#160;∶ OP,</td>
+</tr>
+
+<tr>
+<td class="rightpart">then PN²- PH² = HN²</td>
+</tr>
+
+<tr>
+<td class="rightpart">and PO - NO = NP,</td>
+</tr>
+
+<tr>
+<td class="leftpart">therefore</td>
+<td class="rightpart">HN²&#160;∶ PN²&#160;∷ NP&#160;∶ PO,</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="rightpart">and finally, PO = <span class="divide"><span class="num">PN³</span>
+<span class="denom">HN²</span></span>.</td>
+</tr>
+
+</table>
+
+<table class="formulas">
+
+<tr>
+<td class="leftpart">Then put FP = HC = FN = ρ; HN</td>
+<td class="midpart">=</td>
+<td class="rightpart">ρ - <i>z</i>; then as FP² - FH² = PH² = ρ² - <i>z</i>²</td>
+</tr>
+
+<tr>
+<td class="leftpart">PN² = PH² + HN²</td>
+<td class="midpart">=</td>
+<td class="rightpart">(ρ² - <i>z</i>²) + (ρ² - 2&#160;ρ&#160;<i>z</i> + <i>z</i>²)</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="midpart">=</td>
+<td class="rightpart">2ρ² - 2&#160;ρ&#160;<i>z</i></td>
+</tr>
+
+<tr>
+<td class="leftpart">PN</td>
+<td class="midpart">=</td>
+<td class="rightpart">√<span class="bt">2&#160;ρ&#160;(ρ - <i>z</i>)</span></td>
+</tr>
+
+<tr>
+<td class="leftpart">Therefore PO</td>
+<td class="midpart">=</td>
+<td class="rightpart"><span class="divide"><span class="num">√<span class="bt">{2&#160;ρ&#160;(ρ - <i>z</i>)}³</span></span>
+<span class="denom">(ρ - <i>z</i>)²</span></span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="midpart">=</td>
+<td class="rightpart"><span class="fsize200 downpoint2">√</span><span class="divide"><span class="num bt">{2&#160;ρ&#160;(ρ - <i>z</i>)}³</span>
+<span class="denom">(ρ - <i>z</i>)⁴</span></span></td>
+</tr>
+
+<tr>
+<td class="leftpart">and finally, PO</td>
+<td class="midpart">=</td>
+<td class="rightpart">2√<span class="bt">2</span> <span class="fsize200 downpoint2">√</span><span class="divide"><span class="num bt">ρ³</span>
+<span class="denom">ρ - <i>z</i></span></span></td>
+</tr>
+
+</table>
+
+<div class="container w15emmax" id="Fig67">
+
+<p class="caption">Fig. 67.</p>
+
+<img src="images/illo262a.jpg" alt="Finding versed sine of curvature">
+
+</div><!--container-->
+
+<p>To find the versed sine of the curvature (which may be useful
+in the examination of the mirrors by a mould) we may proceed
+(see <a href="#Fig67">fig. 67</a>) to</p>
+
+<div class="centerblock">
+
+<p class="frml">put AG = <i>f</i>; BE = C; AC = R<br>
+
+then BG² = AG . GD<br>
+
+4 BG² = BE² = 4 AG . GD<br>
+
+C² = 4&#160;<i>f</i> . (2&#160;R - <i>f</i>)<br>
+
+C² = 8&#160;<i>f</i>&#160;R - 4&#160;<i>f</i>²</p>
+
+</div><!--centerblock-->
+
+<p>From which equation,</p>
+
+<div class="centerblock">
+
+<p class="frml">2&#160;<i>f</i> - 2&#160;R = ± √<span class="bt">4&#160;R² - C²</span> = -2&#160;R +
+<span class="divide"><span class="num">C²</span><span class="denom">4&#160;R</span></span> -
+<span class="divide"><span class="num">C⁴</span><span class="denom">64&#160;R³</span></span> &amp;c.<br>
+
+2&#160;<i>f</i> = <span class="divide"><span class="num">C²</span><span class="denom">4&#160;R</span></span> -
+<span class="divide"><span class="num">C⁴</span><span class="denom">64&#160;R³</span></span><br>
+
+<i>f</i> = <span class="divide"><span class="num">C²</span><span class="denom">8&#160;R</span></span> -
+<span class="divide"><span class="num">C⁴</span><span class="denom">128&#160;R³</span></span>.</p>
+
+</div><!--centerblock-->
+
+<div class="container w30emmax" id="Fig68">
+
+<p class="caption">Fig. 68.</p>
+
+<img src="images/illo262b.jpg" alt="Mirror workmanship test installation">
+
+</div><!--container-->
+
+<p>In order to test the accuracy of the workmanship of the mirrors, recourse must again
+be had, as in the case of the lenses and parabolic mirrors, to the formula of conjugate foci, in
+which we shall call R = the radius of curvature of the mirror M&#160;<i>m</i> (<a href="#Fig68">fig. 68</a>); <i>a</i> = the distance
+of a light, <i>f</i>, which is arbitrarily placed in front of the mirror; and <i>b</i> = the distance of a moveable
+screen S, on which the rays reflected from the mirror may converge in a focus. We must find
+the distance <i>b</i>, at which, with any given distance <i>a</i>, such convergence should take place.</p>
+
+<p class="noindent"><i>f</i>&#160;M′ = <i>a</i></p>
+
+<p class="noindent">SM′ = <i>b</i></p>
+
+<p class="noindent">OM′ = R</p>
+
+<p class="noindent">Then (because <i>f</i>&#160;MS is bisected by
+OM, and for points near the vertex
+of the mirror at M′)</p>
+
+<table class="formulas">
+
+<tr>
+<td>&#160;</td>
+<td class="rightpart">SM′&#160;∶ <i>f</i>&#160;M′&#160;∷ SO&#160;∶ O&#160;<i>f</i></td>
+</tr>
+
+<tr>
+<td class="leftpart">or</td>
+<td class="rightpart"><i>b</i>&#160;∶ <i>a</i>&#160;∷ R - <i>b</i>&#160;∶ <i>a</i> - R</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="rightpart"><i>a</i>&#160;<i>b</i> - R&#160;<i>a</i> = R&#160;<i>b</i> - <i>a</i>&#160;<i>b</i>.</td>
+</tr>
+
+</table>
+
+<p>From which <i>b</i> = <span class="divide"><span class="num">R&#160;<i>a</i></span>
+<span class="denom">2&#160;<i>a</i> - R</span></span>, the distance required, in which an error of ¹⁄₃₀ (of its whole
+length) may be safely admitted.</p>
+
+<p><a id="Footnote63" href="#FNanchor63" class="label">[63]</a> At such times when the horizon cannot be
+seen, the mirror may be placed, by means of a
+<i>clinometer</i>, with a spirit-level, set to the proper
+angle, which may be easily mechanically determined
+as follows: Draw a line from the focus F
+through the point O, where the centre of the mirror
+is to be, producing it beyond that point to a convenient
+distance at I; through O draw HOH, parallel
+to the horizon FH; bisect IOH by MOM,
+which coincides with a tangent to the mirror at
+its centre O; and MOH is the angle required to
+be laid off, or its complement.</p>
+
+<div class="container w15emmax" id="Fig69">
+
+<p class="caption">Fig. 69.</p>
+
+<img src="images/illo263.jpg" alt="Determination of angle">
+
+</div><!--container-->
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page263">[263]</span></p>
+
+<p><span class="sidenote">Cylindric Refractors
+for Fixed
+Lights.</span>
+Having once contemplated the possibility of illuminating Lighthouses
+by dioptric means, <span class="smcap">Fresnel</span> quickly perceived the advantage
+of employing for fixed lights a lamp placed in the centre of a
+polygonal hoop, consisting of a series of refractors, <i>infinitely small</i>
+in their length and having their axes in planes parallel to the
+horizon. Such a continuation of vertical sections, by refracting
+the rays proceeding from the focus, only in the vertical direction,
+must distribute a zone of light <i>equally brilliant</i> in every point of
+the horizon. This effect will be easily understood, by considering
+the middle vertical section of one of the great annular lenses,
+already described, abstractly from its relation to the rest of the
+instrument. It will readily be perceived that this section possesses
+the property of simply refracting the rays <i>in one plane coincident
+with the line of the section</i> and in a direction parallel to
+the horizon, and cannot collect the rays from either side of the
+vertical line; and if this section, by its revolution about a vertical
+axis, becomes the generating line of the enveloping hoop, above
+noticed, such a hoop will of course possess the property of refracting
+an equally diffused zone of light round the horizon. The difficulty,
+however, of forming this apparatus appeared so great, that
+<span class="smcap">Fresnel</span> determined to substitute for it a vertical polygon, composed<span class="pagenum" id="Page264">[264]</span>
+of what have been improperly called <i>cylindric lenses</i>, but
+which in reality are mixtilinear and horizontal prisms, distributing
+the light which they receive from the focus nearly equally over the
+horizontal sector which they subtend. This polygon has a sufficient
+number of sides to enable it to give, at the angle formed by
+the junction of two of them, a light not very much inferior to
+what is produced by one of the sides; and the upper and lower
+courses of curved mirrors are always so placed as partly to make
+up for the deficiency of the light at the angles. The effect sought
+for in a fixed light is thus obtained in a much more perfect manner,
+than by any combination of the parabolic mirrors used in the
+British Lighthouses.</p>
+
+<p><span class="sidenote">Application of
+crossed prisms to
+cause occasional
+flashes.</span>An ingenious modification of the fixed apparatus is also due to
+the inventive mind of <span class="smcap">Fresnel</span>, who conceived the idea of placing
+one apparatus of this kind in front of another, with the axis of the
+cylindric pieces crossing each other at right angles. As those cylindric
+pieces have the property of refracting all the rays which they
+receive from the focus, in a direction perpendicular to the mixtilinear
+section which generates them, it is obvious that if two refracting
+media of this sort be arranged as above described, their
+joint action will unite the rays which come from their common
+focus into a beam, whose sectional area is equal to the overlapped
+surface of the two instruments, and that they will thus produce,
+although in a disadvantageous manner, the effect of an annular lens.
+It was by availing himself of this property of crossed prisms, that
+<span class="smcap">Fresnel</span> invented the distinction for lights, which he calls <i>a fixed
+light varied by flashes</i>; in which the flashes are caused by the revolution
+of cylindric refractors with vertical axes, ranged round the
+outside of the fixed light apparatus already described.</p>
+
+<p>Having been directed by the Commissioners of the Northern
+Lighthouses to convert the fixed catoptric light of the Isle of May,
+into a dioptric light of the first order, I proposed, that an attempt
+should be made <span class="sidenote">True Cylindric
+form given to the
+Refractors and
+other improvements
+in their
+Construction.</span>
+to form a true cylindric, instead of a polygonal belt
+for the refracting part of the apparatus; and this task was successfully<span class="pagenum" id="Page265">[265]</span>
+completed by Messrs <span class="smcap">Cookson</span> of Newcastle in the year 1836.
+The disadvantage of the polygon lies in the excess of the radius of
+the circumscribing circle over that of the inscribed circle, which
+occasions an unequal distribution of light between its angles and the
+centre of each of its sides; and this fault can only be fully remedied
+by constructing a cylindric belt, whose generating line is the middle
+mixtilinear section of an <i>annular</i> lens, revolving about a vertical
+axis passing through its principal focus. This is, in fact, the only
+form which can possibly produce an equal diffusion of the incident
+light over every part of the horizon.</p>
+
+<p>I at first imagined that the whole hoop of refractors might be built
+between two metallic rings, connecting them to each other solely by
+the means employed in cementing the pieces of the annular lenses;
+but a little consideration convinced me that this construction would
+make it necessary to build the zone at the lighthouse itself, and
+would thus greatly increase the risk of fracture. I was therefore
+reluctantly induced to divide the whole cylinder into ten arcs,
+each of which being set in a metallic frame, might be capable of
+being moved separately. The chance of any error in the figure
+of the instrument has thus a probability of being confined within
+narrower limits; whilst the rectification of any defective part becomes
+at the same time more easy. One other variation from the
+mode of construction at first contemplated for the Isle of May refractors,
+was forced upon me by the repeated failures which occurred
+in attempting to form the middle zone in one piece; and it
+was at length found necessary to divide this belt by a line passing
+through the horizontal plane of the focus. Such a division of the
+central zone, however, was not attended with any appreciable loss
+of light, as the entire coincidence of the junction of the two pieces
+with the horizontal plane of the focus, confines the interception of
+the light to the fine joint at which they are cemented. With the
+exception of those trifling changes, the idea at first entertained of
+the construction of the instrument was fully realised at the manufactory
+of Messrs <span class="smcap">Cookson</span>. I also, at a subsequent period, greatly<span class="pagenum" id="Page266">[266]</span>
+improved the arrangement of this apparatus, by giving to the metallic
+frames which contain the prisms, a rhomboidal,<a id="FNanchor64" href="#Footnote64" class="fnanchor">[64]</a> instead of a
+rectangular form. The junction of the frames being thus inclined
+from the perpendicular, do not in any azimuth intercept the light
+throughout the whole height of the refracting belt, but the interception
+is confined to a small rhomboidal space, whose area is inversely
+proportional to the sine of the angle of inclination; and if
+the helical joints be formed between the opposite angles of the old
+rectangular frames, the amount of intercepted light becomes absolutely
+equal in every azimuth.<a id="FNanchor65" href="#Footnote65" class="fnanchor">[65]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote64" href="#FNanchor64" class="label">[64]</a> The form would not
+be exactly rhomboidal, but would be a portion of a flat helix intercepted
+between two planes, cutting the enveloped cylinder at right angles to its axis.</p>
+
+<p><a id="Footnote65" href="#FNanchor65" class="label">[65]</a> See my Report on the Refractors of the Isle of May Light, 8th October 1836.</p>
+
+</div><!--footnote-->
+
+<div class="container w35emmax" id="Fig70">
+
+<p class="caption">Fig. 70.</p>
+
+<img src="images/illo266.jpg" alt="Compound Fresnel belt">
+
+</div><!--container-->
+
+<p>Such an apparatus is shewn in <a href="#Plate17">Plate XVII.</a>; and the accompanying
+diagram (<a href="#Fig70">fig. 70</a>) shews an elevation ABCD, a section
+BD, and a plan ABD, of a single pannel of this improved compound
+belt. AC and BD are the diagonal joints above described.
+Time and perseverance, and the patience and skill of Monsieur<span class="pagenum" id="Page267">[267]</span>
+<span class="smcap">François Soleil</span>, whom I urged to undertake the task, were at
+length crowned with success; and I had the satisfaction at last of
+seeing a fixed light apparatus, having its form truly cylindric, and
+its central belt in one piece, while the joints were inclined to the
+horizon at such an angle as to render the light perfectly equal in
+every azimuth.</p>
+
+<p>The loss of light by reflection at the surface of the most perfect
+mirrors, and the perishable nature of the material composing their
+polish, induced me, so far back as 1835, in a Report on the Light
+of Inchkeith, which had just been altered to the dioptric system,
+to propose the substitution of <i>totally reflecting</i> prisms, even in lights
+of the first order or largest dimensions. In this attempt I was
+much encouraged by the singular liberality of Mr <span class="smcap">Leonor Fresnel</span>,
+to whose friendship (as I have often, with much pleasure, acknowledged)
+I owe all that I know of dioptric Lighthouses. He
+not only freely communicated to me the method pursued by his
+distinguished brother <span class="smcap">Augustin Fresnel</span>, in determining the
+forms of the zones of the small apparatus, introduced by him into
+the Harbour Lights of France, and his own mode of rigorously
+solving some of the preliminary questions involved in the computations;
+but put me in possession of various important suggestions,
+which substantially embrace the whole subject. Another
+friend also helped me, by pointing out certain less direct methods
+of determining some of the elements, which greatly abridged the
+labours of computation. Mr <span class="smcap">Fresnel</span> agreed with me in anticipating
+a considerable increase of the light derived from the accessory
+part of the apparatus; but he expressed his opinion, that in
+order to prevent great absorption, the rings should not greatly
+exceed those of the small apparatus in their sectional area. This
+would have required about <i>forty</i> rings to intercept the same quantity
+of light acted upon by the curved mirrors; and, although the
+difficulties of grinding were somewhat similar to those which had
+already been encountered in forming the cylindric belt for the Isle
+of May apparatus, there were also some special difficulties attending<span class="pagenum" id="Page268">[268]</span>
+the formation of the <span class="sidenote">Catadioptric
+Zones.</span>
+catadioptric zones, which appeared so
+formidable as to deter me by the expense of grinding so many
+zones, and led me to think of adopting flint glass. Considerable
+masses, of a very pure and homogeneous appearance, had been
+shewn to me by the late Dr <span class="smcap">Ritchie</span> of the London University,
+who calculated upon the uniform and permanent success of his
+process; but, whatever foundation there might have been for this
+hope, it was removed by his death, which occurred soon afterwards,
+and I was forced to return to the idea of using crown glass. In order,
+therefore, to enable me to estimate more correctly the advantage
+of the zones, I procured from Messrs <span class="smcap">Cookson</span> of Newcastle, an
+average specimen of crown glass, of the thickness of 40 mm. (about
+1¹⁄₂ inch), which is the distance traversed by the ray between its immergence
+into and its emergence out of the zones of the small apparatus;
+and having had it carefully polished, with both faces parallel,
+I found, as the result of numerous trials, conducted with
+every precaution I could think of, that the loss of light due to the
+transmission through it, was somewhat less than ²⁄₇ths of the incident
+light. According to the experiments of <span class="smcap">Bougeur</span>, the loss
+by the two refractions may be assumed at ¹⁄₂₀th; so that we could not
+sensibly err in concluding that the whole loss due to the transmission
+of the light through the zones would not much exceed ²⁄₇ths of
+the incident light. In the lights of the first order, the loss by reflection
+from the surface of the mirrors, and by the escape of light
+through the interstices which separate them, is not less than ²⁄₃ds of
+the light incident on that part of the apparatus. On the most
+moderate expectation, therefore, which this proportion seemed
+to warrant, it appeared that, without any allowance for imperfections
+in the figure of the zones, at least <i>twice</i> as much light
+would be transmitted through the zones as can be reflected by
+the mirrors. The prospect even of a part of this increase being
+obtained without the expenditure of more oil, seemed too important
+to be readily renounced, more especially when it was
+considered that the fixed lights, to which it chiefly applies, are<span class="pagenum" id="Page269">[269]</span>
+necessarily much feebler than the revolving lights, as well as more
+numerous and more expensive. So many motives pressed me to
+the work, that I commenced my labours (during my leisure hours
+while engaged at the Skerryvore), and computed Tables of the
+Elements of 45 zones, whose lesser sides were 40 millimètres in
+length, which were printed in 1840. In 1841, in consequence of
+having seen at Paris specimens of purer crown glass, I printed other
+Tables from computations of larger zones, which I had made in
+1838, but had discarded as unsuited to the inferior quality of English
+glass, whose absorption rendered the use of smaller dimensions of the
+zone imperative. In the first Table, I had adopted the form of isosceles
+triangles, to avoid the difficulty of grinding <i>annular</i> surfaces
+with radii of great length (which I found required to be nearly 30
+feet), but in the second Table, I adopted a suggestion, conveyed to
+me in a letter from M. <span class="smcap">Leonor Fresnel</span>, by giving each zone the form
+of an oblique triangle whose base is the chord of the circle which
+osculates the surface of the reflecting side of the zone. Some attempts
+were made by Messrs <span class="smcap">Cookson</span> at Newcastle to execute the
+largest of the zones; but the forms differed so widely from the
+dimensions assigned in the Table, that I had begun to despair of
+success. About this time, I received a communication from M.
+<span class="smcap">Fresnel</span>, pointing out several inaccuracies in my Tables, and more
+especially directing my attention to the disadvantage of choosing,
+for the focus of the upper series of zones, a high part of the flame,
+as I had done with the view of throwing <i>all</i> the light <i>below</i> the horizon,
+so that none might be lost. He, at the same time, informed
+me of the success of M. <span class="smcap">François Soleil</span>, in executing zones for
+the smaller apparatus, known by the name of the Third Order;
+and put me in possession of the results of his computations of large
+zones of the First Order, suited to the greatly improved quality of
+the crown glass of St Gobain, with an invitation, before I should
+adopt his dimensions, to verify his calculations. This I willingly
+undertook, and computed the elements of the zones in M. <span class="smcap">Fresnel’s</span>
+Table afresh, with results differing from his only in one or<span class="pagenum" id="Page270">[270]</span>
+two instances, to an amount whose angular value does not exceed
+more than 2″. The Table in the <a href="#App4">Appendix</a> contains the result of
+my calculations, which are verifications of those of M. <span class="smcap">Fresnel</span>.
+The subject of the zones has thus been very fully weighed; and
+it is most satisfactory to think that complete success has attended
+the perseverance and ardour of M. <span class="smcap">François Soleil</span>, who at once
+boldly undertook to furnish for the Skerryvore Lighthouse the first
+catadioptric apparatus ever constructed on so magnificent a scale.
+On the 23d December 1843, M. <span class="smcap">Fresnel</span> announced, in a letter to
+me, the complete success which had attended a trial of the apparatus
+at the Royal Observatory at Paris, whereby it appeared that
+the illuminating effect of the cupola of zones, was to that of the
+seven upper tiers of mirrors of the first order, as 140 to 87. Nothing
+can be more beautiful than an entire apparatus for a fixed light of
+the first order, such as that shewn in <a href="#Plate17">Plates XVII.</a> and <a href="#Plate18">XVIII.</a>
+It consists of a central belt of refractors, forming a hollow cylinder
+6 feet in diameter, and 30 inches high; below it are six triangular
+rings of glass, ranged in a cylindrical form, and above a crown
+of thirteen rings of glass, forming by their union a hollow cage,
+composed of polished glass, 10 feet high and 6 feet in diameter!
+I know no work of art more beautiful or creditable to the boldness,
+ardour, intelligence, and zeal of the artist.</p>
+
+<p>I must now endeavour to trace the various steps by which the
+elements of the zones given in the appended <a href="#App4">Table</a> have been determined;
+and this, I fear, I cannot do without considerable prolixity
+of detail. Referring to <a href="#Plate15">Plates XV.</a>,
+<a href="#Plate16">XVI.</a>, <a href="#Plate17">XVII.</a>, and <a href="#Plate18">XVIII.</a>,
+in which F shews the flame, RR, the refractors, and MRM and
+MRM, the spaces through which the light would escape uselessly
+<i>above</i> and <i>below</i> the lens, but for the corrective action of the mirrors
+MM, which project the rays falling on them to the horizon, I
+have to observe that a similar effect is obtained, but in a more perfect
+manner, by means of the zones ABC and A₂B₂C₂ (<a href="#Fig71">fig. 71</a>, on page
+271), whose action on the divergent rays of the lamp causes the
+rays FC, FB and FC₂, FB₂ to emerge horizontally, by refracting<span class="pagenum" id="Page271">[271]</span>
+them at the inner surfaces BC, B₂C₂, reflecting them at AB, A₂B₂,
+and a second time refracting them at AC, A₂C₂.</p>
+
+<div class="container w30emmax" id="Fig71">
+
+<p class="caption">Fig. 71.</p>
+
+<img src="images/illo271.jpg" alt="Details behind the tabulated data">
+
+</div><!--container-->
+
+<p>The problem proposed is, therefore, the determination of the
+elements and position of a triangle ABC, which, by its revolution
+about a vertical axis, passing through the focus of a system of annular
+lenses or refractors in F, would generate a ring or zone capable
+of transmitting in an horizontal direction by means of <i>total reflection</i>,
+the light incident upon its inner side BC from a lamp placed in
+the point F. The conditions of the question are based upon the
+well-known laws of <i>total reflection</i>, and require that all the rays
+coming from the focus F shall be so refracted at entering the surface
+BC, as to meet the side BA at such an angle, that instead of passing
+out they shall be <i>totally reflected</i> from it, and passing onwards to
+the side CA shall, after a second refraction at that surface, finally
+emerge from the zone in an horizontal direction. For the solution
+of this problem, we have given the positions of F the focus, of the
+apex C of the generating triangle of the zone, the length of the side
+BC or CA, and the refractive index of the glass. The form of the
+zone must then be such as to fulfil the following <span class="nowrap">conditions:—</span></p>
+
+<p>1. The extreme ray FB must suffer refraction and reflection at
+B, and pass to C, where being a second time refracted, it must follow
+the horizontal direction CH.</p>
+
+<p><span class="pagenum" id="Page272">[272]</span></p>
+
+<p>2. The other extreme ray FC must be refracted in C and passing
+to A, must at the point be reflected, and a second time reflected, so
+as to follow the horizontal course AG (see <a href="#Fig72">fig. 72</a>, on opposite page).</p>
+
+<p>These two propositions involve other two in the form of corollaries.</p>
+
+<p>1. That every intermediate ray proceeding from F, and falling
+upon BC in any point E, between B and C, must, after refraction
+at the surface BC in E into the direction EW, be so reflected at W
+from AB into the direction WI, that being parallel to BC, it shall,
+after a second refraction in I, at the surface AC, emerge horizontally
+in the line IK.</p>
+
+<p>And, 2. That the paths of the two extreme rays must therefore
+trace the position of the generating triangle of the zone.</p>
+
+<p>To these considerations it may be added, that as the angles
+BCH and FCA are each of them solely due to the refraction at C,
+as their common cause, they must be equal to each other, and BCA
+being common to both, the remaining angle ACH = the remaining
+angle BCF.</p>
+
+<p>We naturally begin by the consideration of the lowest ray FC,
+whose path being traced gives the direction of the two refracting
+sides BC and AC, leaving only the direction of the reflecting side
+BA to be determined. I shall not now explain the reason for neglecting
+entirely the consideration of the reflecting side at present,
+as I could not do so without anticipating what must be more fully
+discussed in the sequel; but I may content myself with stating,
+that as the positions of BC and AC depend upon the direction of the
+incident ray FC, and on the refractive index of the glass, this part
+of the investigation may be carried on apart from any interference
+with the reflecting side.</p>
+
+<p>As we know the relation existing between the angles of incidence
+and refraction, we might determine the relative positions of
+the sides AC and BC, by means of successive corrections obtained
+by protraction, tracing the paths of the rays from the horizontal<span class="pagenum" id="Page273">[273]</span>
+directions backwards through the zones to the focus. This method,
+however, depends entirely upon accurate protraction, and is therefore
+unsatisfactory as a final determination, or if employed for any
+other purpose than that of affording a rough approximation to the
+value of the angle, a knowledge of which may occasionally save
+trouble in the employment of more exact means of determination.
+I have not, however, on any occasion employed this process, as I
+found that a little practice enabled me to make my first estimation
+very near the truth. I shall therefore at once proceed to give a
+view of the reasoning employed in the investigation.</p>
+
+<div class="container w30emmax" id="Fig72">
+
+<p class="caption">Fig. 72.</p>
+
+<img src="images/illo273.jpg" alt="Details behind the tabulated data">
+
+</div><!--container-->
+
+<p>Referring to <a href="#Fig72">fig. 72</a>, which shews the <i>first</i> and <i>second</i> zone of
+the upper series, we have</p>
+
+<div class="formula">
+
+<p>Tan LCF = <span class="divide"><span class="num">FL</span><span class="denom">CL</span></span>;</p>
+
+</div><!--formula-->
+
+<p class="noindent">and if we make</p>
+
+<table class="formulas">
+
+<tr>
+<td class="leftpart">the known angle,</td>
+<td class="rightpart">SCF = α</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="rightpart">OCF = ξ = the complement of BCF = the angle of incidence for FC.</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="rightpart">DCΟ = γ = angle of refraction.</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="rightpart">LCF = θ = (HCF - 90°) = (2&#160;α - 90°)</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="rightpart">SCD = (α + γ - ξ)</td>
+</tr>
+
+<tr>
+<td class="leftpart">And</td>
+<td class="rightpart"><i>m</i> = the index of refraction for crown glass,</td>
+</tr>
+
+</table>
+
+<p class="noindent">we obtain the means of determining the angles γ and ξ in two equations,
+which are based upon the relation between the angles of incidence<span class="pagenum" id="Page274">[274]</span>
+and refraction, and on the interdependence of the various
+angles about C. These primary equations are:</p>
+
+<div class="centerblock fsize90">
+
+<p class="frml">sin&#160;ξ = <i>m</i> . sin&#160;γ<br>
+<span class="padl5">and</span><br>
+<a id="FNanchor66" href="#Footnote66" class="fnanchor"><span class="fsize110">[66]</span></a>γ = 2&#160;ξ - θ (making 2&#160;α - 90° = θ)</p>
+
+</div><!--centerblock-->
+
+<div class="footnote">
+
+<p><a id="Footnote66" href="#FNanchor66" class="label">[66]</a> The truth of the first
+of these equations (sin&#160;ξ = <i>m</i> . sin&#160;γ) which merely expresses the
+ratio of the sines of the angles of incidence and refraction is obvious; but owing to the great
+number of small angles about C, a little consideration may be required to enable one to perceive
+the truth of the second. I therefore subjoin the steps by which I reached it. It is obvious
+(see <a href="#Fig72">fig. 72</a>), that as ACH and BCF are equal, the line SC bisecting HCF must bisect
+ACB. But the production of AC clearly gives SCD opposite and equal to ACW and SCD is
+by construction = (α - ξ + γ) = (α + γ - ξ), and, therefore, ACB, which is twice ACW or
+SCD = (2&#160;α + 2&#160;γ - 2&#160;ξ). Now, by construction OC is a normal to the refracting surface CB
+and its production C&#160;<i>g</i> gives AC&#160;<i>g</i> = γ. But γ =
+ACB - <i>g</i>&#160;CB = (2&#160;α + 2&#160;γ - 2&#160;ξ) - <i>g</i>&#160;CB
+= (2&#160;α + 2&#160;γ - 2&#160;ξ) - 90°, hence</p>
+
+<table class="formulas">
+
+<tr>
+<td class="leftpart">γ</td>
+<td class="midpart">=</td>
+<td class="rightpart">{2&#160;α + 2&#160;γ - 2&#160;ξ} - 90°,</td>
+</tr>
+
+<tr>
+<td class="leftpart">and γ - 2&#160;γ</td>
+<td class="midpart">=</td>
+<td class="rightpart">-γ = -2&#160;ξ + (2&#160;α - 90°) by transposition, and finally changing signs, we have as above:</td>
+</tr>
+
+<tr>
+<td class="leftpart">γ</td>
+<td class="midpart">=</td>
+<td class="rightpart">2&#160;ξ - (2&#160;α - 90°)</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="midpart">=</td>
+<td class="rightpart">2&#160;ξ - θ.</td>
+</tr>
+
+</table>
+
+</div><!--footnote-->
+
+<p>Eliminating γ between these two equations we obtain:</p>
+
+<div class="formula">
+
+<p>sin&#160;ξ = <i>m</i> . sin&#160;(2&#160;ξ - θ)</p>
+
+</div><!--formula-->
+
+<p class="noindent">an expression, which, after various transformations of circular
+functions, assumes the form</p>
+
+<div class="formula">
+
+<p>sin⁴ ξ - <span class="divide"><span class="num">1</span><span class="denom"><i>m</i></span></span> sin&#160;θ .
+sin³&#160;ξ + <span class="fsize200 downpoint2">(</span><span class="divide"><span class="num">1</span>
+<span class="denom">4&#160;<i>m</i>²</span></span> - 1<span class="fsize200 downpoint2">)</span> .
+sin²&#160;ξ + <span class="divide"><span class="num">1</span><span class="denom">2&#160;<i>m</i></span></span>
+sin&#160;θ . sin&#160;ξ + ¹⁄₄&#160;sin²&#160;θ = 0<a id="FNanchor67" href="#Footnote67" class="fnanchor">[67]</a></p>
+
+</div><!--formula-->
+
+<div class="footnote">
+
+<p><a id="Footnote67" href="#FNanchor67" class="label">[67]</a> This expression is equivalent to that of M. Fresnel, but owing to a simplification in the
+fractional coefficients, it is not <i>literally</i> the same. I was led to it by the following steps,
+starting from the original equation sin&#160;ξ = <i>m</i>&#160;sin&#160;(2&#160;ξ - θ)</p>
+
+<table class="formulas">
+
+<tr>
+<td class="leftpart">sin&#160;ξ</td>
+<td class="midpart">=</td>
+<td class="rightpart"><i>m</i>&#160;sin&#160;(2&#160;ξ - θ)</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="midpart">=</td>
+<td class="rightpart"><i>m</i>{sin&#160;2&#160;ξ . cos&#160;θ - cos&#160;2&#160;ξ&#160;sin θ}</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="midpart">=</td>
+<td class="rightpart"><i>m</i>&#160;cos&#160;θ . sin&#160;2&#160;ξ - <i>m</i>&#160;sin&#160;θ . cos&#160;2&#160;ξ</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="midpart">=</td>
+<td class="rightpart"><i>m</i>&#160;cos&#160;θ . 2&#160;sin&#160;ξ . cos&#160;ξ - <i>m</i>&#160;sin&#160;θ . {1 - 2&#160;sin²&#160;ξ}</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="midpart">=</td>
+<td class="rightpart">2&#160;<i>m</i>&#160;cos&#160;θ . sin&#160;ξ . cos&#160;ξ -
+<i>m</i>&#160;sin&#160;θ + 2&#160;<i>m</i>&#160;sin&#160;θ . sin²&#160;ξ.</td>
+</tr>
+
+</table>
+
+<p class="noindent">Therefore, <i>m</i>&#160;sin&#160;θ + sin&#160;ξ - 2&#160;<i>m</i>&#160;sin&#160;θ&#160;sin²&#160;ξ =
+2&#160;<i>m</i>&#160;cos&#160;θ . sin&#160;ξ . cos&#160;ξ.</p>
+
+<p>Then:</p>
+
+<p class="noindent"><i>m</i>²&#160;sin²&#160;θ + 2&#160;<i>m</i>&#160;sin&#160;θ . sin&#160;ξ - 4&#160;<i>m</i>²&#160;sin²&#160;θ&#160;sin²&#160;ξ
++ sin²&#160;ξ - 4&#160;<i>m</i>&#160;sin&#160;θ . sin³&#160;ξ + 4&#160;<i>m</i>²&#160;sin²&#160;θ . sin⁴&#160;ξ
+= 4&#160;<i>m</i>²&#160;cos²&#160;θ&#160;sin²&#160;ξ&#160;(1 - sin²&#160;ξ) = 4&#160;<i>m</i>² . cos²&#160;θ . sin²&#160;ξ -
+4&#160;<i>m</i>²&#160;cos²&#160;θ&#160;sin⁴&#160;ξ.</p>
+
+<p>Hence we have:</p>
+
+<p class="noindent"><i>m</i>²&#160;sin²&#160;θ + 2&#160;<i>m</i>&#160;sin&#160;θ . sin&#160;ξ + 
+(1 - 4&#160;<i>m</i>²) . sin²&#160;ξ - 4&#160;<i>m</i>&#160;sin&#160;θ .
+sin³&#160;ξ + 4&#160;<i>m</i>²&#160;sin⁴&#160;ξ = 0</p>
+
+<p>Then dividing by 4&#160;<i>m</i>² and arranging according to powers of ξ, we have as above:</p>
+
+<p class="noindent">sin⁴&#160;ξ - <span class="divide"><span class="num">1</span>
+<span class="denom"><i>m</i></span></span>&#160;sin&#160;θ . sin³&#160;ξ +
+<span class="fsize200 downpoint2">(</span><span class="divide"><span class="num">1</span>
+<span class="denom">4&#160;<i>m</i>²</span></span> - 1<span class="fsize200 downpoint2">)</span> .
+sin²&#160;ξ + <span class="divide"><span class="num">1</span><span class="denom">2&#160;<i>m</i></span></span> .
+sin&#160;θ . sin&#160;ξ + ¹⁄₄&#160;sin²&#160;θ = 0</p>
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page275">[275]</span></p>
+
+<p class="noindent">The solution of this equation, which is of the fourth degree, is
+somewhat tedious; but as the root, which will satisfy the optical
+conditions of the question, must be the sine of an angle, and necessarily
+lies between <i>zero</i> and <i>unity</i>; and as the protraction, if conducted
+with due care in the manner already described, affords the
+means of at once assuming a probable value of ξ not very distant
+from the truth, the labour of the calculation, in this particular
+case, is not quite so great as might be expected. But notwithstanding
+all the abridgments of which the particular case admits, a
+considerable amount of labour is required, and a corresponding risk
+of error incurred, in merely introducing the numerical values into
+the equation preparatory to its solution; and any other method
+requiring less arithmetical operation, is, of course, greatly to be
+preferred. I therefore willingly adopted the suggestion of a friend,
+the benefit of whose advice I have on many occasions experienced,
+and made use of the following ordinary method of approximating
+to the root of the equation.</p>
+
+<p>If the equation <span class="formula">sin&#160;ξ - <i>m</i>&#160;sin&#160;(2&#160; - θ) = 0</span>
+(see <a href="#Page274">page 274</a>) be regarded
+as an expression for the error, when the true value of ξ which
+would satisfy the equation has been introduced into its first member,
+we may consider any error in the value of ξ as expressed by
+the equation:</p>
+
+<div class="formula">
+
+<p>sin&#160;ξ - <i>m</i> . sin&#160;(2 ξ - θ) = ε</p>
+
+</div><!--formula-->
+
+<p class="noindent">and differentiating this expression we have:</p>
+
+<table class="formulas">
+
+<tr>
+<td class="leftpart"><i>d</i>&#160;ε</td>
+<td class="midpart">=</td>
+<td class="rightpart">cos&#160;ξ . <i>d</i>&#160;ξ - 2&#160;<i>m</i>&#160;cos&#160;(2&#160;ξ - θ) . <i>d</i>&#160;ξ</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="midpart">=</td>
+<td class="rightpart">{cos&#160;ξ - 2&#160;<i>m</i>&#160;cos&#160;(2&#160;ξ - θ)} . <i>d</i>&#160;ξ</td>
+</tr>
+
+</table>
+
+<p><span class="pagenum" id="Page276">[276]</span></p>
+
+<p class="noindent">Then dividing by the differential coefficient we obtain</p>
+
+<div class="formula">
+
+<p><i>d</i>&#160;ξ = <span class="divide"><span class="num"><i>d</i>&#160;ε</span>
+<span class="denom">cos&#160;ξ - 2&#160;<i>m</i>&#160;cos&#160;(2&#160;ξ - θ)</span></span></p>
+
+<p>But when ξ becomes ξ + <i>d</i>&#160;ξ, ε will also become ε + <i>d</i>&#160;ε; but</p>
+
+<p>ε + <i>d</i>&#160;ε = 0</p>
+
+<p>therefore <i>d</i>&#160;ε = -ε</p>
+
+<p>hence by substitution we have</p>
+
+<p><i>d</i>&#160;ξ = <span class="divide"><span class="num">-ε</span>
+<span class="denom">cos&#160;ξ - 2&#160;<i>m</i>&#160;cos&#160;(2&#160;ξ - θ)</span></span></p>
+
+<p><span class="dontshow"><i>d</i>&#160;ξ</span> = <span class="divide"><span class="num">-{sin&#160;ξ - <i>m</i>&#160;sin&#160;(2&#160;ξ - θ)}</span>
+<span class="denom">cos&#160;ξ - 2&#160;<i>m</i>&#160;cos&#160;(2&#160;ξ - θ)</span></span></p>
+
+<p><i>d</i>&#160;ξ = <span class="divide"><span class="num">-sin&#160;ξ + <i>m</i>&#160;sin&#160;(2&#160;ξ - θ)</span>
+<span class="denom">cos&#160;ξ - 2&#160;<i>m</i>&#160;cos&#160;(2ξ&#160; - θ)</span></span></p>
+
+</div><!--formula-->
+
+<p class="noindent">By substituting, therefore, in this last equation the known values
+of <i>m</i> and θ, and the assumed value of ξ, a correction is obtained,
+which being applied to ξ and the same process repeated, new corrections
+may be found until the value of <i>d</i>&#160;ξ falls within the limits
+of error, which may be considered safe in the particular case. I
+need hardly say, that where so great a body of flame is employed
+as in the lights of the first order, these limits are soon passed, more
+especially as one soon acquires by a little experience the means
+of guessing a value of ξ not very far from the truth. It is this
+method I have employed in calculating the appended <a href="#App4">tables</a> of the
+zones, in which I have on all occasions, though, perhaps, with
+needless exactness, pushed my angular determinations to <i>seconds</i>.</p>
+
+<p>Having in this manner determined the angles of BCF, the obtuse
+angle BCA of the generating triangle of the zone is easily and
+directly deduced by the following expression, which results from
+the obvious relations existing among the known angles about C;
+and we have (see <a href="#Fig73">fig. 73</a>),</p>
+
+<div class="formula">
+
+<p>BCA = 90° + γ = 90° + 2&#160;ξ - θ.</p>
+
+</div><!--formula-->
+
+<p class="noindent">We next proceed to consider the form of BA, the reflecting side
+of the zone, which is a point of the greatest consequence, as an
+error in the inclination of any part of its surface is doubled in the<span class="pagenum" id="Page277">[277]</span>
+resulting direction of the reflected rays. The conditions of the
+question require, that every ray EW, after reflection at the surface
+AB, shall, like WI, be parallel to the first ray, which is reflected
+in the direction BC, and after a second refraction at C, emerges
+horizontally in CH. But, let us trace backwards the rays as they
+emerge in their horizontal directions IK, and it is obvious that if
+BA be made a straight line, then will every ray EW meet the first
+refracting side BC at the same angle, and there suffering the same
+refraction, they will go on parallel to each other, and never meet
+in the focus F. This convergence to F, which is a necessary condition
+of the problem, may, however, be produced by a curvature
+of AB, such that all the rays shall have a degree of convergence before
+falling on BC, sufficient to cause them to be finally refracted,
+so as to meet in F. On this account, they will occupy <i>less</i> space
+in passing through BC, than they did in passing through AC; and
+thus BC will be <i>shorter</i> than AC by some quantity which shall give
+to that part of AB which is at B the amount of <i>downward</i> inclination
+required for causing the ray BF finally to converge to F; and
+the line joining B and A must be a curve, every point of which has
+its tangent inclined so as to serve the same purpose.</p>
+
+<div class="container w30emmax" id="Fig73">
+
+<p class="caption">Fig. 73.</p>
+
+<img src="images/illo277.jpg" alt="Schematic reflecting side of lens">
+
+</div><!--container-->
+
+<p>To trace tangents to this curve, is therefore the next step in the
+process. The direction of the
+first tangent AZ depends upon
+very simple considerations;
+and all that is necessary to be
+done is to draw a line AU (<a href="#Fig73">fig.
+73</a>), parallel to BC (which is
+the parallel to the direction of
+the reflected rays), and forming
+an angle CAU, which is,
+of course, equal to the inclination
+of the extreme rays refracted
+by CB at C, with rays<span class="pagenum" id="Page278">[278]</span>
+reflected from the arc which we have yet to trace. The line AX
+bisecting this angle, must therefore be a normal to the reflecting
+surface at A, and AB drawn perpendicular to AX, is consequently
+a tangent to the reflecting arc.</p>
+
+<p>We must next find the direction of the second tangent Z&#160;<i>b</i>,
+which must be so inclined that the ray F&#160;<i>b</i> will, after refraction
+at <i>b</i>, be reflected into the direction, <i>b</i>&#160;C; but as the rigorous determination
+of this is difficult, I shall describe two approximations suggested
+to me by M. <span class="smcap">Leonor Fresnel</span>. The first method is based
+upon assuming the inclination of the ray refracted at <i>b</i> to the ray
+refracted at C as equal to:</p>
+
+<div class="formula">
+
+<p><span class="divide"><span class="num"><i>b</i>&#160;FC</span><span class="denom"><i>m</i></span></span></p>
+
+</div><!--formula-->
+
+<p class="noindent">(in which expression, <i>m</i> is the refractive index of the glass); a supposition
+which obviously differs very little from the truth, as small
+arcs may be assumed as nearly equal to their sines. Now, it will
+be recollected, that the rays refracted at C and <i>b</i>, must be reflected
+at A and <i>b</i>, in a direction parallel to C&#160;<i>b</i>, and therefore the inclination
+of the reflecting surfaces, or that which should be formed by
+the tangents ZA and Z&#160;<i>b</i>, being half that of the incident rays, is,
+according to the assumption, equal to
+<span class="divide"><span class="num"><i>b</i>&#160;FC</span><span class="denom">2&#160;<i>m</i></span></span>, which may be expressed
+by ¹⁄₃&#160;<i>b</i>&#160;FC, <i>m</i> being equal to 1·51. But as the inclination of the
+two radii AX and BX is equal to the inclination of the tangents of
+the reflecting surfaces to which they are normals, we obtain for
+the excess B&#160;β of the secant of the reflecting arc over its radius the
+following expression:</p>
+
+<div class="formula">
+
+<p>Bβ = ¹⁄₂&#160;AB . tan&#160;¹⁄₃&#160;BFC.<a id="FNanchor68" href="#Footnote68" class="fnanchor">[68]</a></p>
+
+</div><!--formula-->
+
+<p class="noindent">The value of B&#160;<i>b</i> gives, of course, the direction of the second
+tangent Z&#160;<i>b</i> (which must be equal in length to AZ), whence we
+easily deduce the chord of the reflecting side A&#160;<i>b</i>.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote68" href="#FNanchor68" class="label">[68]</a> The following steps will shew the mode of
+obtaining this expression: Suppose (<a href="#Fig74">fig. 74</a>,
+on opposite page) F&#160;<i>n</i> to be a ray incident on the surface BC very near <i>b</i> or B (which, although
+exaggerated in the figure for more easy reference, are close together), and let this ray F&#160;<i>n</i> be refracted
+in the direction <i>n</i>&#160;O, and draw <i>n</i>&#160;<i>n′</i> parallel to CA, the ray which is refracted at C, then
+will <i>n′</i>&#160;<i>n</i>&#160;O = <i>m</i> . <i>b</i>&#160;FC = ²⁄₃&#160;<i>b</i>&#160;FC.
+But the tangent AZ should make with the tangent <i>b</i>&#160;Z an angle
+equal ¹⁄₃&#160;<i>b</i>&#160;FC, or <i>one-half</i> the inclination of the rays refracted at <i>b</i> and C, which are afterwards
+by the agency of those tangents, to be reflected in the directions parallel to <i>b</i>&#160;C and to
+each other. Hence we have AX&#160;<i>b</i> (which is the inclination of the normals to those tangents),</p>
+
+<div class="formula">
+
+<p>or AX&#160;<i>b</i> = BZ&#160;<i>b</i> = <span class="divide"><span class="num"><i>b</i>&#160;FC</span>
+<span class="denom">2&#160;<i>m</i></span></span> = <span class="divide"><span class="num"><i>b</i>&#160;FC</span>
+<span class="denom">3</span></span> nearly.</p>
+
+</div><!--formula-->
+
+<div class="container w25emmax" id="Fig74">
+
+<p class="caption">Fig. 74.</p>
+
+<img src="images/illo279.jpg" alt="Explanation of formula">
+
+</div><!--container-->
+
+<p class="noindent">But putting AXB (<a href="#Fig7">fig. 73</a>, p. 277) for AX&#160;<i>b</i>, and BFC for <i>b</i>&#160;FC, a supposition which may
+be safely made when the differences are so small, and founding upon the analogy</p>
+
+<p>AX&#160;∶ AB&#160;∷ R&#160;∶ tan&#160;AXB, we have BA = AX . tan&#160;AXB = AX . tan&#160;¹⁄₃&#160;BFC. Then</p>
+
+<table class="formulas">
+
+<tr>
+<td class="leftpart">AB²</td>
+<td class="midpart">=</td>
+<td class="rightpart">B&#160;β&#160;(B&#160;β + 2&#160;AX)</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="midpart">=</td>
+<td class="rightpart">B&#160;β² + 2&#160;B&#160;β . AX</td>
+</tr>
+
+</table>
+
+<p class="noindent">and neglecting B&#160;β², which is very small, we
+have:</p>
+
+<div class="formula">
+
+<p>BA² = B&#160;β . 2&#160;AX nearly,</p>
+
+<p>hence B&#160;β = <span class="divide"><span class="num">BA²</span><span class="denom">2&#160;AX</span></span></p>
+
+<p>But as above AX = <span class="divide"><span class="num">BA</span><span class="denom">tan&#160;¹⁄₃&#160;BFC</span></span></p>
+
+</div><!--formula-->
+
+<p class="noindent">and substituting this value of AX we obtain:</p>
+
+<div class="formula">
+
+<p><span class="tripleline1">B&#160;β =</span> <span class="divide"><span class="num">BA²</span>
+<span class="denom">2&#160;<span class="divide"><span class="num">BA</span><span class="denom">tan&#160;¹⁄₃&#160;BFC</span></span></span></span></p>
+
+</div><!--formula-->
+
+<p class="center">hence we have, as in the text,</p>
+
+<div class="formula">
+
+<p>B&#160;β = ¹⁄₂&#160;BA . tan&#160;¹⁄₃&#160;BFC</p>
+
+</div><!--formula-->
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page279">[279]</span></p>
+
+<p>The second mode proposed by M. <span class="smcap">Fresnel</span>, and that which I
+found most convenient in practice, consists in forming successive
+hypotheses as to the length of the side BC, and tracing the path
+of the incident ray FB, which being refracted at B, so as to make
+with the normal BK an angle = BKY = <i>y′</i>, and finally reflected in
+the direction BC, must make the angle YBZ = MBC. I shall describe<span class="pagenum" id="Page280">[280]</span>
+it as follows: In the annexed
+figure (<a href="#Fig75">fig. 75</a>) MBZ is
+a tangent to the reflecting surface
+at B, and KBF is the
+angle of incidence of the ray
+BF before its refraction at B.
+If KBF = <i>x´</i>, and the angle of
+incidence of FC = ECF = <i>x</i>, we
+have BFC (which is the inclination
+of those rays to each
+other, and must be equal to
+the difference of their angles of
+incidence to the same surface) = <i>x</i> - <i>x´</i>, whence knowing <i>x</i>, we
+easily find a value of <i>x´</i> corresponding to the length of BC. Then
+for finding the angle of refraction KBY = <i>y´</i> we have:</p>
+
+<div class="formula">
+
+<p>sin&#160;<i>y´</i> = <span class="divide"><span class="num">sin&#160;<i>x´</i></span><span class="denom"><i>m</i></span></span></p>
+
+</div><!--formula-->
+
+<div class="container w30emmax" id="Fig75">
+
+<p class="caption">Fig. 75.</p>
+
+<img src="images/illo280.jpg" alt="Refraction in lens">
+
+</div><!--container-->
+
+<p>Now, if FB be refracted, so as to make with the reflecting side an
+angle equal to ZBY, it must (if the position of B be rightly chosen),
+be reflected so as to follow BC, thus making MBC = YBZ, and
+calling each of these angles = μ, we have the right angle NBZ made
+up of μ + <i>y´</i> + NBK. But NBK clearly equals μ, because it is the inclination
+of the normals to BC and BZ, and hence <i>y´</i> + 2&#160;μ = 90°.
+This, therefore, forms a crucial test for the length of BC. I may
+only remark, that we already know the numerical value of <i>y</i>; and
+that of μ is easily found, for μ = CBA + ABM = CBA + BAM = CBA +
+(MAC - BAC) = CBA + ¹⁄₂&#160;(180° - υ) - BAC. Thus knowing μ and <i>y´</i>,
+we have only to see whether</p>
+
+<div class="formula">
+
+<p>(<i>y´</i> - 2&#160;μ) - 90° = 0</p>
+
+</div><!--formula-->
+
+<p>We have now only to find the length of the radius AX or <i>b</i>&#160;X
+(see <a href="#Fig73">fig. 73</a>, p. 277), which will describe the reflecting surface or
+arc AZ&#160;<i>b</i>, and to determine the position of its centre X. We
+already know the values of <i>y′</i> and <i>y</i>, the angles of refraction of C<span class="pagenum" id="Page281">[281]</span>
+and <i>b</i>, and their difference <i>y</i> - <i>y′</i> gives us the inclination of the
+rays which are to be reflected (into directions parallel to C&#160;<i>b</i>) at <i>b</i>
+and at A. This quantity is, of course, double the inclination of
+tangents to the reflecting surface AZ and <i>b</i>&#160;Z, and of their normals
+AX and <i>b</i>&#160;X. Again, we have the chord line</p>
+
+<div class="formula">
+
+<p>A&#160;<i>b</i> = AC . <span class="divide"><span class="num">sin&#160;AC&#160;<i>b</i></span>
+<span class="denom">sin&#160;(<i>b</i>&#160;CA);</span></span></p>
+
+</div><!--formula-->
+
+<p class="noindent">and, as above,</p>
+
+<div class="formula">
+
+<p>AX&#160;<i>b</i> = ¹⁄₂&#160;<i>y</i> - <i>y′</i> = φ</p>
+
+<p>And AX = <i>b</i>&#160;X = ρ = <span class="divide"><span class="num">A&#160;<i>b</i> . sin&#160;¹⁄₂&#160;(180° - φ)</span>
+<span class="denom">sin&#160;φ</span></span> = ¹⁄₂&#160;A&#160;<i>b</i> . cosec&#160;¹⁄₂&#160;φ.</p>
+
+</div><!--formula-->
+
+<p>And, lastly, for the co-ordinates to X, the centre of curvature
+for the reflecting arc, we have</p>
+
+<table class="formulas">
+
+<tr>
+<td class="leftpart">OX</td>
+<td class="midpart">=</td>
+<td class="rightpart">ρ . sin&#160;OAX</td>
+</tr>
+
+<tr>
+<td class="leftpart">and OA</td>
+<td class="midpart">=</td>
+<td class="rightpart">ρ . cos&#160;OAX.<a id="FNanchor69" href="#Footnote69" class="fnanchor">[69]</a></td>
+</tr>
+
+</table>
+
+<div class="footnote">
+
+<p><a id="Footnote69" href="#FNanchor69" class="label">[69]</a> The angle OAX is easily found,
+as will be seen by referring to <a href="#Fig73">fig. 73</a>, p. 277;
+for, AH being horizontal by construction and AO vertical, HAO = 90°; and HAC and
+CAU being both known, we have</p>
+
+<div class="formula">
+
+<p>OAX = 90° - (HAU + UAX) = 90° - (HAU + ¹⁄₂&#160;CAU).</p>
+
+</div><!--formula-->
+
+</div><!--footnote-->
+
+<div class="container w30emmax" id="Fig76">
+
+<p class="caption">Fig. 76.</p>
+
+<img src="images/illo281.jpg" alt="Finding the position of two of three apices">
+
+</div><!--container-->
+
+<p>The positions of the apices A and B of the angles of the zones
+are also easily found in reference to the focus, and are given in the
+<a href="#App4">Table</a> in the Appendix. In <a href="#Fig76">fig. 76</a> we may, in reference to the
+known position of C, find that of A
+or B, by simply adding the quantities
+AH, HC, and BK, to C&#160;<i>y</i> or C&#160;<i>x</i>,
+and by deducting CK from C&#160;<i>y</i>; while
+it is obvious that those quantities
+are respectively proportional to the
+length of the known sides AC and
+BC, modified by the inclination of
+those sides with the horizon. Hence
+we have AH = AC . sin&#160;ACH; HC =
+AC . cos&#160;ACH; BK = BC . sin&#160;BCK;
+and CK = BC . cos&#160;BCK.</p>
+
+<p>In the process of grinding the zones, it is found convenient for<span class="pagenum" id="Page282">[282]</span>
+the workman to give a curved form to the refracting sides BC and
+AC, the one being made convex and the other concave, so that both
+being ground to the same radius, the convergence of the rays produced
+by the first shall be neutralized by the divergence caused by
+the second. By this arrangement we have three points given in space
+from which, with given radii, to describe a curvilinear triangle whose
+revolution round the vertical axis of the system generates the zone
+required. Co-ordinates to those two centres of curvature for the
+surfaces AC and BC were determined in reference to arris A of
+each zone, and will be found in the <a href="#App4">Appendix</a>. The mode of finding
+those co-ordinates is, of course, similar to that already given;
+and, the radii being assumed at 4000 millimètres, the co-ordinates
+are respectively proportional to the sine and cosine of the inclination
+of the radius at A to the vertical line, which inclination depends
+upon the relations of known angles around A and C.</p>
+
+<p>The section ABC (<a href="#Fig71">fig. 71</a>, p. 271) of the first zone being thus
+determined, we proceed by fixing the point C₂ of the second zone,
+which is at the intersection of the horizon GAG₂ with the ray
+FBC₂ passing through B. This arrangement prevents any loss of
+light between the adjacent zones. The calculation of the elements
+of the second and of every following zone, is precisely similar to
+that of the first.</p>
+
+<p>The mode of grinding the zones I shall not notice here; but
+shall refer the more curious reader to the <a href="#App3">Appendix</a>, in which I
+have given the details of the process followed by M. <span class="smcap">Theodore
+Letourneau</span>, who now manufactures the apparatus for the Northern
+Lights Board, in the room of M. <span class="smcap">François Soleil</span>, who is engaged
+at St Petersburg in the same work. I accordingly proceed
+to consider what mode should be followed in <span class="sidenote">Testing of Zones.</span>
+testing the accuracy
+of the zones. For this purpose, various expedients suggested themselves,
+such as the application of gauges in the form of a radius,
+having at one end a plate with a triangular space cut through it,
+equal and similar to the cross section of the zone. The horizontal
+motion of this arm would, of course, detect the inaccuracies of the<span class="pagenum" id="Page283">[283]</span>
+successive sections of the inclosed zone. The application of such a
+gauge, however, seemed difficult, and in order to test the <i>form</i> of the
+zones, I satisfied myself with using callipers (similar to the sliding
+rules used by shoemakers) for measuring the <i>length</i> of the sides of the
+zone, and a goniometer for the angles, which is represented in the
+figure (<a href="#Fig77">fig. 77</a>), in which ABC represents
+the prism, with one angle
+inclosed between the arms AC and
+AB, moveable round a centre O,
+and RR the graduated limb. This
+instrument is inconvenient and defective,
+as the convexity of the sides
+AB and BC of the zone requires
+some skill in getting the arms to
+be tangents to them.</p>
+
+<div class="container w35emmax" id="Fig77">
+
+<p class="caption">Fig. 77.</p>
+
+<img src="images/illo283.jpg" alt="Goniometer">
+
+</div><!--container-->
+
+<div class="container w40emmax" id="Fig78">
+
+<p class="caption">Fig. 78.</p>
+
+<img src="images/illo284.jpg" alt="Spirit level and cross-hair telescope">
+
+</div><!--container-->
+
+<p>A practical test, however, yet remained to be made of the
+zones when fixed in the brass frames (shewn at <a href="#Plate18">Plate XVIII.</a>),
+and assembled around the common focus of the system, by measuring
+the final inaccuracy in the path of the rays emergent from
+them. I have successfully used the following mode. Having
+mounted the frames containing the zones on a carriage revolving
+round a small flame placed truly in the common focus, I carefully
+marked with a piece of soap the centre of the emergent <i>surface</i> of
+each zone; and having attached to a vertical rod of metal a telescope,
+provided with a spirit-level and cross-hairs (for cutting the
+centre of the image of the flame reflected through the zone) in such
+a manner as to be capable of sliding on the rod, I observed the cutting
+of the centre of the flame by the cross-hairs. In the case of
+any aberration from a normal emergence of the central ray, I had
+thus the means of at once determining its amount and direction.
+The telescope was moved up or down, and its vertical inclination
+was varied until the axis of the instrument coincided with the direction
+of the ray emergent from the centre of each zone, which was
+made to circulate round the flame, the observer noting any change
+in the position of the reflected image of the flame, and causing an<span class="pagenum" id="Page284">[284]</span>
+attendant to mark the zones in which the change occurred, that
+they might again be subjected to separate examination of the same
+kind, by adjusting the telescope to the error of each. The vertical
+inclination of the telescope and the consequent aberration of
+the ray, was then measured by a graduated arc, with an adjusting
+spirit-level, moved by a rack and pinion. The accompanying figure
+(<a href="#Fig78">fig. 78</a>) shews the arrangement just described. E is the small
+flame in the focus; ABC is the zone; TT is the telescope; and R
+a graduated limb, on which is read the angular deviation θ of the
+axis of the telescope from the horizon. In the figure, the ray
+emergent from the centre of AC is shewn dipping below the <i>true
+level</i>, to which the line TC is supposed to be parallel. I have succeeded
+by this method in detecting the inaccurate position of some
+of the zones in the frame; and the error has been reduced by carefully
+resetting them, so as to diminish considerably the error of a
+great proportion of the emergent rays. Another mode, and that
+which, owing to its convenience, was chiefly employed in preference
+to that just described, was to measure the vertical inclination
+(given in the <a href="#App4">Table</a> in the Appendix), of each surface of the zone,<span class="pagenum" id="Page285">[285]</span>
+and more especially the reflecting surface, by means of the instrument,
+shewn in <a href="#Fig79">figures 79</a> and
+<a href="#Fig80">80</a>, after the zones were fixed
+in their place. The figure (<a href="#Fig79">No.
+79</a>) shews the mode of gauging
+the reflecting side AB of a zone
+of the upper series; and the second
+(<a href="#Fig80">No. 80</a>) shews the position
+of the instrument in gauging the
+reflecting side AB of a zone of
+the under series. In those
+figures, L is a spirit-level; R, a
+graduated limb for reading the
+angular deviation from the true
+inclination of the tangents to
+each surface; and SS are studs
+which rest on the convex surfaces
+AB and BC of the zones, so as to make the ruler parallel to the
+tangents of those sides. I have only to add, that I have restricted
+the error, in the position of the reflecting side of the zones, to 50′
+as an extreme limit; and I have invariably endeavoured, in altering
+the position of the zone in the frame, to throw any error on the
+side of safety, by causing the rays to <i>dip</i> below the horizon, rather
+than to rise above it.<a id="FNanchor70" href="#Footnote70" class="fnanchor">[70]</a></p>
+
+<div class="container w35emmax" id="Fig79">
+
+<p class="caption">Fig. 79.</p>
+
+<img src="images/illo285a.jpg" alt="Lens gauge">
+
+</div><!--container-->
+
+<div class="container w35emmax" id="Fig80">
+
+<p class="caption">Fig. 80.</p>
+
+<img src="images/illo285b.jpg" alt="Lens gauge">
+
+</div><!--container-->
+
+<div class="footnote">
+
+<p><a id="Footnote70" href="#FNanchor70" class="label">[70]</a> In connection with the use of the clinometer,
+I determined the inclinations of the tangents
+or chords of the three curve surfaces AB, BC,
+and AC of each zone with NP, the axis of the
+system, by means of the obvious relations of the
+known angles about C, A, and B. Those inclinations
+(<a href="#Fig81">fig. 81</a>) are shewn by the angles BNO,
+BON, and CPF; and are given in the <a href="#App4">Table of
+the Zones</a> in the Appendix.</p>
+
+<div class="container w30emmax" id="Fig81">
+
+<p class="caption">Fig. 81.</p>
+
+<img src="images/illo285c.jpg" alt="Schematic of cords of curved surfaces">
+
+</div><!--container-->
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page286">[286]</span></p>
+
+<p><span class="sidenote">Framing of
+Zones.</span>
+The mode of framing the greater zones is shewn in <a href="#Plate18">Plate XVIII.</a>
+and is nearly the same as that used for the Small Harbour Light
+apparatus of the fourth order (<a href="#Plate19">Plate XIX.</a>). The chief difference
+consists in the diagonal framing, which I adopted for supporting
+the cupola of 13 zones, which, from its great weight, could not
+be safely made to rest on the dioptric belt below. That frame is
+seen in <a href="#Plate17">Plates XVII.</a> and <a href="#Plate18">XVIII.</a> and is in accordance with the
+mode of jointing the refractors already described. This system
+has now been rendered still more complete by the adoption of
+lanterns composed of diagonal framework, afterwards described
+and shewn at <a href="#Plate26">Plate XXVI.</a></p>
+
+<p><span class="sidenote">Mechanical Lamp.</span>
+We have next to consider the great Lamp, to the proper distribution
+of whose light, the whole of the apparatus, above described,
+is applied. <span class="smcap">Fresnel</span> immediately perceived the necessity of combining
+with the dioptric instruments which he had invented, a burner
+capable of producing a large volume of flame; and the rapidity
+with which he matured his notions on this subject and at once
+produced an instrument admirably adapted for the end he had in
+view, affords one of the many proofs of that happy union of practical
+with theoretical talent, for which he was so distinguished.
+<span class="smcap">Fresnel</span> himself has modestly attributed much of the merit of the
+invention of this Lamp to M. <span class="smcap">Arago</span>; but that gentleman, with
+great candour, gives the whole credit to his deceased friend, in a
+notice regarding lighthouses, which appeared in the <i>Annuaire du
+Bureau des Longitudes</i> of 1831. The lamp has four concentric
+burners, which are defended from the action of the excessive heat,
+produced by their united flames, by means of a superabundant supply
+of oil, which is thrown up from a cistern below by a clockwork
+movement and constantly overflows the wicks, as in the
+mechanical lamp of Carcel. A very tall chimney is found to be
+necessary, in order to supply fresh currents of air to each wick
+with sufficient rapidity to support the combustion. The carbonisation
+of the wicks, however, is by no means so rapid as might
+be expected, and it is even found that after they have suffered a
+good deal, the flame is not sensibly diminished, as the great heat<span class="pagenum" id="Page287">[287]</span>
+evolved from the mass of flame, promotes the rising of the oil in
+the cotton. I have seen the large lamp at the Tour de Corduan
+burn for seven hours without being snuffed or even having the
+wicks raised; and, in the Scotch Lighthouses, it has often, with
+Colza oil, maintained, untouched, a full flame for no less a period
+than seventeen hours.</p>
+
+<div class="split5050">
+
+<div class="left5050">
+
+<div class="container w25emmax" id="Fig82">
+
+<p class="caption">Fig. 82.</p>
+
+<img src="images/illo287a.jpg" alt="Plan of burner">
+
+</div><!--container-->
+
+</div><!--left5050-->
+
+<div class="right5050">
+
+<div class="container w25emmax" id="Fig83">
+
+<p class="caption">Fig. 83.</p>
+
+<img src="images/illo287b.jpg" alt="Section of burner">
+
+</div><!--container-->
+
+</div><!--right5050-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split0550-->
+
+<div class="container left w10emmax" id="Fig84">
+
+<p class="caption">Fig. 84.</p>
+
+<img src="images/illo287c.jpg" alt="Burner with chimney and damper">
+
+</div><!--container-->
+
+<p>The annexed diagrams will give a perfect idea of the nature of
+the concentric burner. The first (<a href="#Fig82">fig. 82</a>) shews a plan of a burner
+of four concentric wicks. The intervals which separate the wicks
+from each other and allow the currents of air to pass, diminish a
+little in width as they recede from the centre. The next (<a href="#Fig83">fig. 83</a>)
+shews a section of this burner. C, C′, C″, C‴ are the
+rack-handles for raising or depressing each wick; AB
+is the horizontal duct which leads the oil to the four
+wicks; L, L, L, are small plates of tin by which the
+burners are soldered to each other, and which are so
+placed as not to hinder the free passage of the air; P is
+a clamping screw, which keeps at its proper level the
+gallery R, R, which carries the chimney. The last
+figure (<a href="#Fig84">No. 84</a>) shews the burner with its glass chimney
+and damper. E is the glass chimney; F is a sheet-iron
+cylinder, which serves to give it a greater length,
+and has a small damper D, capable of being turned by
+a handle, for regulating the currents of air; and B<span class="pagenum" id="Page288">[288]</span>
+is the pipe which supplies the oil to the wicks. The only risk in
+using this lamp arises from the liability to occasional derangement
+of its leathern valves that force the oil by means of clockwork;
+and several of the lights on the French coast, and more especially
+the Corduan, have been extinguished by the failure of the lamp for a
+few minutes, an accident which has never happened, and scarcely
+can occur with the fountain lamps which illuminate the reflectors.
+To prevent the occurrence of such accidents, and to render their
+consequences less serious, various precautions have been resorted
+to. Amongst others, an alarum is attached to the lamp, consisting
+of a small cup pierced in the bottom, which receives part of the
+overflowing oil from the wicks, and is capable, when full, of balancing
+a weight placed at the opposite end of a lever. The moment
+the machinery stops, the cup ceases to receive the supply of
+oil, and, the remainder running out at the bottom, the equilibrium
+of the lever is destroyed, so that it falls and disengages a spring
+which rings a bell sufficiently loud to waken the keeper should he
+chance to be asleep. It may justly be questioned whether this
+alarum would not prove a temptation to the keepers to relax in
+their watchfulness and fall asleep; and I have, in all the lamps of
+the dioptric lights on the Scotch coast, adopted the converse mode
+of causing the bell to cease when the clockwork stops. There is
+another precaution of more importance, which consists of having
+always at hand in the light-room a spare lamp, trimmed and adjusted
+to the height for the focus, which may be substituted for
+the other in case of accident. It ought to be noticed, however,
+that it takes about twenty minutes from the time of applying the
+light to the wicks to bring the flame to its full strength, which, in
+order to produce its best effect, should stand at the height of nearly
+four inches (10<sup>cm.</sup>). The inconveniences attending this lamp have led
+to several attempts to improve it; and, amongst others, M. <span class="smcap">Delaveleye</span>
+has proposed to substitute a pump having a metallic piston,
+in place of the leathern valves, which require constant care, and
+must be frequently renewed. A lamp was constructed in this<span class="pagenum" id="Page289">[289]</span>
+manner by M. <span class="smcap">Lepaute</span>, and tried at Corduan; but was afterwards
+discontinued until some further improvements could be made upon
+it. It has lately been much improved by M. <span class="smcap">Wagner</span>, an ingenious
+artist whom M. <span class="smcap">Fresnel</span> employed to carry some of his improvements
+into effect. In the dioptric lights on the Scotch
+coast, a common lamp, with a large wick, is kept constantly ready
+for lighting; and, in the event of the sudden extinction of the
+mechanical lamp by the failure of the valves, it is only necessary
+to unscrew and remove its burner, and put the reserve-lamp in its
+place. The height of this lamp is so arranged, that its flame is
+in the focus of the lenses, when the lamp is placed on the ring
+which supports the burner of the mechanical lamp; and as its
+flame, though not very brilliant, has a considerable volume, it
+will answer the purpose of maintaining the light in a tolerably
+efficient state for a short time, until the light-keepers have time to
+repair the valves of the mechanical lamp. Only three occasions
+for the use of this reserve-lamp have yet occurred.</p>
+
+<p><span class="sidenote">Height of the
+flame of the Mechanical
+Lamp.</span>The most advantageous heights for the flames in dioptric lights
+are as <span class="nowrap">follows:—</span></p>
+
+<table class="standard">
+
+<tr>
+<th colspan="4">&#160;</th>
+<th>Inches.</th>
+</tr>
+
+<tr>
+<td class="text"><span class="padr4">1st Order,</span></td>
+<td class="text">10 to 11</td>
+<td class="text">centimètres</td>
+<td class="cntr">=</td>
+<td class="cntr">3·94 to 4·33</td>
+</tr>
+
+<tr>
+<td class="text"><span class="padr4">2d Order,</span></td>
+<td class="text">&#8199;8 to &#8199;9</td>
+<td class="cntr">......</td>
+<td class="cntr">=</td>
+<td class="cntr">3·15 to 3·54</td>
+</tr>
+
+<tr>
+<td class="text"><span class="padr4">3d Order,</span></td>
+<td class="text">&#8199;7 to &#8199;8</td>
+<td class="cntr">......</td>
+<td class="cntr">=</td>
+<td class="cntr">2·76 to 3·15</td>
+</tr>
+
+</table>
+
+<p>Those heights of flame can be obtained only by a careful adjustment
+of the heights of the wicks and the relative levels of the
+<i>shoulder</i> of the glass-chimney and the burner, together with a due
+proportion for the area of the opening of the iron-damper which
+surmounts it. The wicks must be gradually raised during the first
+hours of burning to the level of 7 millimètres (0·27 inch) above
+the burner, a height which they may only very rarely and but
+slightly exceed. By raising the shoulder of the glass-chimney the
+volume of the flame is increased; but, after a certain height is
+exceeded, the flame, on the other hand, becomes reddish, and its<span class="pagenum" id="Page290">[290]</span>
+brilliancy is diminished. The height of the flame is decreased, and it
+becomes whiter by lowering the chimney. The chimney is lowered
+or raised by simply turning to the right or to the left the cylindric
+<i>glass-holder</i> in which it rests (see <a href="#Plate25">Plate XXV.</a>). In regulating the
+flame, however, recourse is most frequently had to the use of the
+damper, by enlarging the opening of which the flame falls and becomes
+whiter and purer; while by diminishing its aperture, the contrary
+effect is produced. The area of the opening depends on the
+inclination of a circular disc capable of turning, vertically through a
+quadrant, on a slender axle of wire, which is commanded by the
+light-keeper by means of a fine cord which hangs from it to the
+table below. When the disc (see <a href="#Fig84">fig. 84</a>, p. 287) is in a horizontal
+plane the chimney is shut, when in a vertical plane it is open;
+and each intermediate inclination increases or decreases the aperture.</p>
+
+<p>I need scarcely add, that in order to produce the proper effect
+of a system of lenses or refractors, the vertical axis of the flame
+should <span class="sidenote">Position of flame
+in reference to
+focus of apparatus.</span>
+coincide with their common axis; and it is further necessary,
+in order to bring the best portion of the flame into a suitable
+position with reference to the apparatus, that the top of the burner
+should be quite level, and should stand <i>below</i> the plane of the focus
+in the following proportions, <span class="nowrap">viz.:—</span></p>
+
+<table class="standard">
+
+<tr>
+<td class="text">For</td>
+<td class="text">1st order,</td>
+<td class="cntr">28</td>
+<td class="text">millimètres</td>
+<td class="cntr">=</td>
+<td class="cntr">1·10</td>
+<td class="text">inches.</td>
+</tr>
+
+<tr>
+<td class="cntr">...</td>
+<td class="text">2d order,</td>
+<td class="cntr">26</td>
+<td class="cntr">...</td>
+<td class="cntr">=</td>
+<td class="cntr">1·02</td>
+<td class="cntr">...</td>
+</tr>
+
+<tr>
+<td class="cntr">...</td>
+<td class="text">3d order,</td>
+<td class="cntr">24</td>
+<td class="cntr">...</td>
+<td class="cntr">=</td>
+<td class="cntr">0·95</td>
+<td class="cntr">...</td>
+</tr>
+
+</table>
+
+<div class="container left w15emmax" id="Fig85">
+
+<p class="caption">Fig. 85.</p>
+
+<img src="images/illo291.jpg" alt="Spherical segment spirit level">
+
+</div><!--container-->
+
+<p>For the purpose of placing the lamp in the centre of the apparatus,
+a plumbet with a sharp point suspended in the axis of the
+apparatus, is used to indicate, by its apex, the place for the centre
+of the burner. The lamp is then raised or lowered as required by
+means of four adjusting screws Q at the bottom of its pedestal
+(<a href="#Plate20">Plate XX.</a>); and the top of the burner is made horizontal by a
+spirit-level, the most convenient form of which is that of the spherical
+segment, which acts in every azimuth. Its application to<span class="pagenum" id="Page291">[291]</span>
+this purpose is due, I believe, to M. <span class="smcap">Letourneau</span>, the successor
+of M. <span class="smcap">François</span> in the construction of dioptric apparatus at Paris.
+This level is shewn in the annexed figure (<a href="#Fig85">fig. 85</a>), in which <i>a</i>&#160;<i>b</i> is
+the brass frame containing the level, and O the air-bubble;
+and <i>e</i> shews circles of equal altitudes engraved
+on the glass. After the first application of
+this level, the adjustment of the burner as to its
+central position is carefully repeated by means of
+a centre gauge (shewn at <a href="#Fig90">fig. 90</a>, p. 295), with reference
+to the vertex of each lens, or to many points on the internal
+surface of the refractors; and being found correct, the level is
+again applied to the top of the burner, to detect any deviation
+from horizontality that may have occurred during the process of
+adjusting it to the axis.</p>
+
+<p>The lamp is subject to derangement, chiefly from the stiffness of
+the clack-valves for want of regular cleaning, bursting of the
+leathern valves of the oil-box, stiffness of the regulator, and the
+wearing of the bevelled gearing which gives motion to the connecting-rod
+that works the valves of the oil-pumps.</p>
+
+<p><span class="sidenote">Working of the
+Pumps of the
+Lamp.</span>
+The pumps of the lamp should raise, in a given time, <i>four</i> times
+the quantity of oil actually consumed by burning during that time.
+Their hourly produce should be,</p>
+
+<table class="standard">
+
+<tr>
+<th colspan="2">&#160;</th>
+<th>lb.<br>avoirdupois.</th>
+</tr>
+
+<tr>
+<td class="text">For the lamp with</td>
+<td class="text"><span class="padr4">four wicks,</span></td>
+<td class="cntr">6·615</td>
+</tr>
+
+<tr>
+<td class="cntr">......</td>
+<td class="text"><span class="padr4">three wicks,</span></td>
+<td class="cntr">4·410</td>
+</tr>
+
+<tr>
+<td class="cntr">......</td>
+<td class="text"><span class="padr4">two wicks,</span></td>
+<td class="cntr">1·675</td>
+</tr>
+
+</table>
+
+<p>This surplus of <i>three</i> times what is burned is necessary to prevent
+the wick from being carbonised too quickly; and it has been
+found quite sufficient for that purpose. The discharge from the
+pumps is, of course, regulated by changes in the angle of the fans
+of the regulator, or in the amount of the moving weight.</p>
+
+<p>Care must be taken, in preparing the leathern valves of the
+pump-box or chamber, shewn in <a href="#Plate22">Plate XXII.</a>, that they be neither
+too flaccid from largeness nor too tense from smallness; and also
+that, after being fitted, they draw no air. To remove the old valves<span class="pagenum" id="Page292">[292]</span>
+and replace them by fresh ones, is a very simple process, more especially
+when a proper die or mould is used, which at once cuts the
+kid-leather, of which the valves are formed, to the required size and
+squeezes them into the proper shape. In <a href="#Plate20">Plates XX.</a>, <a href="#Plate21">XXI.</a>, <a href="#Plate22">XXII.</a>,
+<a href="#Plate23">XXIII.</a>, <a href="#Plate24">XXIV.</a>, and <a href="#Plate25">XXV.</a>, the most minute details are given
+as to the clockwork, pumps, burners, and flame of the great lamp.<a id="FNanchor71" href="#Footnote71" class="fnanchor">[71]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote71" href="#FNanchor71" class="label">[71]</a> See also M.
+<span class="smcap">Leonor Fresnel’s</span> <i>Instructions sur l’organisation et la surveillance du
+service des Phares et Fanaux de France</i>. Paris, 1842, pp. 12, 13, 14, and 15.</p>
+
+</div><!--footnote-->
+
+<p>The focal point for the lenses and refractors is in the centre of the
+flame and on the level of its brightest film, as shewn in <a href="#Plate25">Plate XXV.</a>
+<span class="sidenote">Choice of Focal
+Point for various
+parts of the apparatus.</span>
+The choice of a focus for the zones naturally formed a most important
+practical consideration in their arrangement; and the judicious
+remarks of M. <span class="smcap">Leonor Fresnel</span> on that subject, already noticed,
+would alone have induced me to discard my former calculations in
+favour of his. For the upper zones, M. <span class="smcap">Fresnel</span> had adopted a
+point in the centre of the flame 10 millimètres above the focus of
+the lenses, so that all the light <i>below</i>
+that point necessarily falls between
+the horizon and the Lighthouse;
+but for the lower zones, it
+was necessary, owing to their arrangement
+for convenience in a
+cylindric form, to adopt a separate
+focus for each zone in the direction
+of the centre of gravity of that
+part of the flame which would light
+each zone. In this manner (<a href="#Fig86">fig. 86</a>)
+the foci of the zones recede upwards
+from <i>a</i> to <i>f</i> in proportion
+to the depression of the zones
+<i>a</i>, <i>b</i>, <i>c</i>, <i>d</i>, <i>e</i>, <i>f</i>, so that the line joining each zone and its focus, must
+revolve as a <i>radius vector</i> round some point O between them. The
+details of this arrangement are shewn in <a href="#Plate28">Plate XVIII.</a>; and are
+also given in the <a href="#App4">Table</a> of the Catadioptric Zones in the Appendix.</p>
+
+<div class="container w20emmax" id="Fig86">
+
+<p class="caption">Fig. 86.</p>
+
+<img src="images/illo292.jpg" alt="Foci of individual lenses">
+
+</div><!--container-->
+
+<p><span class="pagenum" id="Page293">[293]</span></p>
+
+<div class="container w35emmax" id="Fig87">
+
+<p class="caption">Fig. 87.</p>
+
+<img src="images/illo293.jpg" alt="Spherical mirror in dioptric light">
+
+</div><!--container-->
+
+<p>In the arc next the land, in fixed lights, a great loss of light
+ensues from the escape of the rays uselessly in that direction. So
+far back as 1834, I suggested the <span class="sidenote">Application of
+Spherical Mirrors
+to fixed Dioptric
+Lights.</span>
+placing a segment of a spherical
+mirror, with its centre of curvature coincident with F the focus of
+the system, so that the luminous pyramid MFM, of which the mirror
+MM forms the base,
+might be thrown back
+through the focal
+point and finally refracted
+into such a
+direction as to contribute
+to the effect of
+the lens QA<i>q</i> in seaward
+and opposite arc. In the diagram (<a href="#Fig87">fig. 87</a>), <i>r</i>&#160;<i>r</i> indicate rays
+proceeding directly from F; <i>r′</i>&#160;<i>r′</i>  rays reflected from MM through
+F, and finally refracted at QA&#160;<i>q</i>; and <i>r″</i>&#160;<i>r″</i> is the beam compounded
+of both. In the best glass-silvered mirrors, this accession of light
+would amount to nearly half of the light incident on them. In
+such an arrangement, a considerable radius is desirable to decrease
+the amount of aberration produced by a large flame. In the case
+of revolving lights of the first order, the radius would, of course,
+be limited to somewhat less than three feet, which is the focal distance
+of the lenses, between which and the focus, the reflecting segment
+must be placed; but in fixed lights, the lantern is the limit of
+radius, so that a focal length of five feet ten inches may be obtained.
+M. <span class="smcap">François</span> ground some beautiful mirrors of three feet radius,
+which were afterwards <i>tinned</i> by his successor, M. <span class="smcap">Letourneau</span>,
+by a new process discovered by himself;<a id="FNanchor72" href="#Footnote72" class="fnanchor">[72]</a> and that gentleman is at
+present engaged in the construction of reflecting spherical segments
+1200<sup>mm.</sup> square (about 16 superficial feet), to a radius of 1770<sup>mm.</sup>
+(5 feet 10 inches), which subtend a vertical arc of about 40°.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote72" href="#FNanchor72" class="label">[72]</a> See notice of a similar process practised
+about the year 1750 by Mr <span class="smcap">Rogers</span> of London,
+<i>ante</i>, <a href="#Page240">p. 240</a>.</p>
+
+</div><!--footnote-->
+
+<p><span class="sidenote">Arrangement of
+Dioptric Apparatus.</span>
+The arrangements of the dioptric apparatus in the lightroom
+will be more fully understood by referring to the Plates.</p>
+
+<p><a href="#Plate13">Plate XIII.</a> shews an elevation of a revolving dioptric apparatus
+of the first order; F is the focal point, in which the flame is placed;<span class="pagenum" id="Page294">[294]</span>
+L, L great annular lenses, forming by their union an octagonal
+prism, with the lamp in its axis, and projecting, in horizontal beams,
+the light which they receive from the focus; L′L′, the upper lenses,
+forming by their union a frustum of an octagonal pyramid of 50° of
+inclination, and having their foci coinciding in the point F. They
+parallelise the rays of light which pass over the lenses. M, M are
+plane mirrors, placed above the pyramidal lenses L′L′, and so inclined
+as to project the beams reflected from them in planes parallel
+to the horizon; Z, Z are the lower zones, first used at Skerryvore,
+in the room of the curved mirrors which were used at Corduan. The
+lower part of <a href="#Plate13">Plate XIII.</a> shews the moveable framework which
+carries the lenses and mirrors, and the rollers on which it circulates,
+with the clockwork which gives motion to the whole. <a href="#Plate14">Plate
+XIV.</a> is the plan of the apparatus shewn in <a href="#Plate13">Plate XIII.</a></p>
+
+<p><a href="#Plate15">Plate XV.</a> shews a section of a fixed dioptric light of the first
+order. F is the focal point in which the flame is placed; R, R
+cylindric refractors, forming by their union a prism of thirty-two
+sides, or a true cylinder, with the lamp in its axis, and producing
+a zone of light of equal intensity in every point of the horizon;
+M, M, curved mirrors, ranged in tiers above and below the cylindric
+refractors, and having their foci coinciding in the point F; the
+effect of the mirrors increases the power of the light, by collecting
+and transmitting the rays which would otherwise pass above and
+below them, without increasing the effect of the light. <a href="#Plate16">Plate XVI.</a>
+gives the elements of the curved mirrors MM of <a href="#Plate15">Plate XV.</a></p>
+
+<p>After the details given of the nature of the catadioptric zones,
+all that is needful is briefly to refer to <a href="#Plate17">Plate XVII.</a>, in which ABC
+and A′B′C′ shew the upper and lower zones which supply the
+place of the mirrors shewn at M, M, in <a href="#Plate15">Plate XV.</a>; while DEF
+shews the cylindric belt as lately improved, with the diagonal
+joints M, N, C; and X, X, represent the diagonal supports for the
+cupola ABC. This plate, in connection with the enlarged view
+of the same apparatus at <a href="#Plate18">Plate XVIII.</a>, affords a complete explanation
+of the arrangement of all the parts.</p>
+
+<p><span class="sidenote">Arrangement of
+the Dioptric Apparatus
+in the Lightroom.</span>
+For the purpose of arranging the various parts of the dioptric
+apparatus in their proper positions, <i>three</i> gauges are employed.<span class="pagenum" id="Page295">[295]</span>
+The first (<a href="#Fig88">fig. 88</a>) is for ascertaining that the lenses <i>l</i>, <i>l</i>, meet at the
+proper horizontal angle,
+so that their axes shall
+meet with the proper inclination
+in F the focus.
+This is done by means of
+two arms, whose projecting
+points <i>r</i>, <i>r</i>, <i>r</i>, <i>r</i> touch
+the backs of the lenses,
+while the graduated arc
+<i>c</i> indicates the inclination
+of <i>l</i>, <i>l</i>, to <i>l</i>, <i>l</i>, or the complement
+of that inclination
+at F.</p>
+
+<div class="container w35emmax" id="Fig88">
+
+<p class="caption">Fig. 88.</p>
+
+<img src="images/illo295a.jpg" alt="Gauge">
+
+</div><!--container-->
+
+<div class="container w30emmax" id="Fig89">
+
+<p class="caption">Fig. 89.</p>
+
+<img src="images/illo295b.jpg" alt="Clinometer">
+
+</div><!--container-->
+
+<p>Again, for ascertaining the verticality
+of the main lenses, or for setting
+the subsidiary lenses or mirrors shewn
+in <a href="#Plate13">Plates XIII.</a> and <a href="#Plate14">XIV.</a>, at the required
+angle of inclination, recourse
+is had to a clinometer (<a href="#Fig89">fig. 89</a>) touching
+the back of the lens LL by means
+of studs at A, A, while the spirit-level
+S indicates, on the graduated limb, the amount of deviation
+from the vertical position of the instrument, whether accidental or
+intentional.</p>
+
+<div class="container w35emmax" id="Fig90">
+
+<p class="caption">Fig. 90.</p>
+
+<img src="images/illo295c.jpg" alt="Gauge">
+
+</div><!--container-->
+
+<p>Lastly, to test the true
+position of the lamp itself,
+with reference to the
+lenses thus properly arranged,
+we apply a radius
+or trainer (<a href="#Fig90">fig. 90</a>) which
+fits into the centre burner
+at F, while its point A
+touches the centre of the<span class="pagenum" id="Page296">[296]</span>
+lens <i>l</i>, <i>l</i>; at B is a graduated slide, which admits of the trainer being
+lengthened or shortened to suit various focal distances; and
+the spirit-level at <i>c</i> at once corrects any error in the length of the
+trainer arising from depression or elevation, and also serves to indicate
+the proper level for the burner which is noticed at <a href="#Page290">page 290</a>,
+in speaking of the lamp. The dotted line F&#160;<i>c′</i>&#160;B′A′ shews the
+position of the trainer in reference to an adjacent lens.</p>
+
+<p>The elegant apparatus invented by <span class="smcap">Augustin Fresnel</span> for Harbour
+Lights, on the same principle as that just described for Sea
+Lights, is shewn beneath (<a href="#Fig91">fig. 91</a>). It consists of thirteen rings of
+glass of various diameters arranged one above another, in an oval
+form. The five middle rings have an interior diameter of 11·81
+inches (30<sup>cm.</sup>), and like those of the larger apparatus, refract equally
+over the horizontal plane of the focus the light which they receive
+from it. The other rings or prisms, five of which are upper and
+three lower, are ground and set in such a manner, that they project
+all the light derived from the focus in a direction parallel to
+the other rays by <i>total reflection</i>.</p>
+
+<div class="container w30emmax" id="Fig91">
+
+<p class="caption">Fig. 91.</p>
+
+<img src="images/illo296.jpg" alt="Fresnel's harbour light apparatus">
+
+</div><!--container-->
+
+<p>The arrangements of this apparatus, which is distinguished by
+the addition of external refractors arranged vertically, will be more
+fully understood by a reference to <a href="#Fig91">fig. 91</a>, which shews its section
+and plan. F is the focal point in
+which the flame is placed; <i>r</i>, <i>r</i> cylindric
+refractors, forming by their union a cylinder
+with a lamp in its axis, and producing
+a zone of light of equal intensity
+all round the horizon; <i>x</i>, <i>x</i> are catadioptric
+prismatic rings acting by <i>total reflection</i>,
+and giving out zones of light of
+equal intensity at every point of the horizon.
+The dotted lines shew the course
+traversed by the rays of light which proceed
+from the lamp, and are acted upon
+by the rings of glass. The letters <i>r′</i>&#160;<i>r′</i> shew the external prisms,<span class="pagenum" id="Page297">[297]</span>
+having their axes at right angles to those of the principal bent prisms,
+composing the refractors at <i>r</i>, <i>r</i>, and revolving around them. This
+ingenious application of the property of crossed prism is already described
+at <a href="#Page264">page 264</a>.</p>
+
+<p>When this apparatus is employed to light only a part of the
+horizon, the rings are discontinued on the side next the land, and
+room is thus obtained for using a common fountain lamp; but when
+the whole horizon is illuminated, the apparatus must inclose the
+flame on every side; and it has in that case been found most convenient
+to employ the hydrostatic lamp of <span class="smcap">Thilorier</span>, which has
+a balance of <i>sulphate of zinc in solution</i>.</p>
+
+<p>An instrument differing from this small apparatus only in size,
+has lately been introduced into the Lighthouses in France, and has
+also been adopted in Scotland for lights in narrow seas. It has
+the same number of rings of glass as the small apparatus, and of
+the same <i>proportional</i> dimensions. Its internal diameter, however,
+is 500 millimètres (about 19¹⁄₂ inches). Drawings of the smaller
+apparatus are given at <a href="#Plate19">Plate XIX.</a>, which also contains the radii
+and the centre of curvature for the rings of the central dioptric
+belt; while the following Table gives the elements of the eight
+prismatic zones (above and below the belt), with the co-ordinates
+to their centres of curvature, measured from the arris A of the
+outer or emergent surfaces, in whatever position the zone may lie
+on the lathe. The dimensions are in millimètres; but may be
+easily converted into imperial inches, in the manner described in
+the <a href="#App4">Table</a> of the Great Zones, which will be found in the <span class="nowrap">Appendix:—</span></p>
+
+<p><span class="pagenum" id="Page298">[298]</span></p>
+
+<table class="standard">
+
+<tr class="bt2 bb">
+<th class="bl2 br">Number<br>of<br>Zone.</th>
+<th class="br">Radii<br>of<br>curvature.</th>
+<th class="br">Horizontal<br>distance<br>from the<br>axis of<br>the system.</th>
+<th class="brd">Vertical<br>distance<br>from the<br>outer<br>arris.</th>
+<th class="br">Number<br>of<br>Zone.</th>
+<th class="br">Radii<br>of<br>curvature.</th>
+<th class="br">Horizontal<br>distance<br>from the<br>axis of<br>the system.</th>
+<th class="br2">Vertical<br>distance<br>from the<br>outer<br>arris.</th>
+</tr>
+
+<tr class="bt">
+<th colspan="8" class="highline075 bl2 br2"><span class="smcap">Reflecting Surfaces</span> (<span class="smcap">Convex</span>).</th>
+</tr>
+
+<tr>
+<td class="right bl2 br">I.</td>
+<td class="cntr br">1094·5</td>
+<td class="cntr br">&#8199;723·5&#8199;</td>
+<td class="cntr brd">&#8199;833·78</td>
+<td class="right br">V.</td>
+<td class="cntr br">1222·9&#8199;</td>
+<td class="cntr br">&#8199;523·6&#8199;</td>
+<td class="cntr br2">1169·1&#8199;</td>
+</tr>
+
+<tr>
+<td class="right bl2 br">II.</td>
+<td class="cntr br">1045·7</td>
+<td class="cntr br">&#8199;652·8&#8199;</td>
+<td class="cntr brd">&#8199;891·01</td>
+<td class="right br">VI.</td>
+<td class="cntr br">1249·4&#8199;</td>
+<td class="cntr br">&#8199;544·0&#8199;</td>
+<td class="cntr br2">1192·1&#8199;</td>
+</tr>
+
+<tr>
+<td class="right bl2 br">III.</td>
+<td class="cntr br">1044·5</td>
+<td class="cntr br">&#8199;598·4&#8199;</td>
+<td class="cntr brd">&#8199;933·67</td>
+<td class="right br">VII.</td>
+<td class="cntr br">1150·4&#8199;</td>
+<td class="cntr br">&#8199;593·5&#8199;</td>
+<td class="cntr br2">1062·9&#8199;</td>
+</tr>
+
+<tr>
+<td class="right bl2 br">IV.</td>
+<td class="cntr br">1087·3</td>
+<td class="cntr br">&#8199;551·9&#8199;</td>
+<td class="cntr brd">1010·20</td>
+<td class="right br">VIII.</td>
+<td class="cntr br">1113·6&#8199;</td>
+<td class="cntr br">&#8199;650·5&#8199;</td>
+<td class="cntr br2">&#8199;985·9&#8199;</td>
+</tr>
+
+<tr class="bt">
+<th colspan="8" class="highline075 bl2 br2"><span class="smcap">Outer Refracting Surfaces</span> (<span class="smcap">Concave</span>).</th>
+</tr>
+
+<tr>
+<td class="right bl2 br">I.</td>
+<td class="cntr br">1250·0</td>
+<td class="cntr br">1290·7&#8199;</td>
+<td class="cntr brd">&#8199;303·19</td>
+<td class="right br">V.</td>
+<td class="cntr br">1250·00</td>
+<td class="cntr br">1100·22</td>
+<td class="cntr br2">&#8199;829·52</td>
+</tr>
+
+<tr>
+<td class="right bl2 br">II.</td>
+<td class="cntr br">1250·0</td>
+<td class="cntr br">1274·2&#8199;</td>
+<td class="cntr brd">&#8199;445·89</td>
+<td class="right br">VI.</td>
+<td class="cntr br">1250·00</td>
+<td class="cntr br">1112·74</td>
+<td class="cntr br2">&#8199;821·16</td>
+</tr>
+
+<tr>
+<td class="right bl2 br">III.</td>
+<td class="cntr br">1250·0</td>
+<td class="cntr br">1234·0&#8199;</td>
+<td class="cntr brd">&#8199;587·05</td>
+<td class="right br">VII.</td>
+<td class="cntr br">1250·00</td>
+<td class="cntr br">1190·50</td>
+<td class="cntr br2">&#8199;698·00</td>
+</tr>
+
+<tr>
+<td class="right bl2 br">IV.</td>
+<td class="cntr br">1250·0</td>
+<td class="cntr br">1173·0&#8199;</td>
+<td class="cntr brd">&#8199;717·71</td>
+<td class="right br">VIII.</td>
+<td class="cntr br">1250·00</td>
+<td class="cntr br">1251·90</td>
+<td class="cntr br2">&#8199;557·22</td>
+</tr>
+
+<tr class="bt">
+<th colspan="8" class="highline075 bl2 br2"><span class="smcap">Inner Refracting Surfaces</span> (<span class="smcap">Convex</span>).</th>
+</tr>
+
+<tr>
+<td class="right bl2 br">I.</td>
+<td class="cntr br">1250·0</td>
+<td class="cntr br">&#8199;150·67</td>
+<td class="cntr brd">1211·90</td>
+<td class="right br">V.</td>
+<td class="cntr br">1250·00</td>
+<td class="cntr br">&#8199;452·23</td>
+<td class="cntr br2">1184·20</td>
+</tr>
+
+<tr>
+<td class="right bl2 br">II.</td>
+<td class="cntr br">1250·0</td>
+<td class="cntr br">&#8199;228·19</td>
+<td class="cntr brd">1208·80</td>
+<td class="right br">VI.</td>
+<td class="cntr br">1250·00</td>
+<td class="cntr br">&#8199;453·07</td>
+<td class="cntr br2">1185·20</td>
+</tr>
+
+<tr>
+<td class="right bl2 br">III.</td>
+<td class="cntr br">1250·0</td>
+<td class="cntr br">&#8199;305·10</td>
+<td class="cntr brd">1203·35</td>
+<td class="right br">VII.</td>
+<td class="cntr br">1250·00</td>
+<td class="cntr br">&#8199;374·60</td>
+<td class="cntr br2">1196·00</td>
+</tr>
+
+<tr class="bb2">
+<td class="right bl2 br">IV.</td>
+<td class="cntr br">1250·0</td>
+<td class="cntr br">&#8199;381·00</td>
+<td class="cntr brd">1195·30</td>
+<td class="right br">VIII.</td>
+<td class="cntr br">1250·00</td>
+<td class="cntr br">&#8199;294·35</td>
+<td class="cntr br2">1203·80</td>
+</tr>
+
+</table>
+
+<p><span class="sidenote">Power of Dioptric
+Instruments.</span>
+The effect of an annular lens, in combination with the great
+lamp, may be estimated at moderate distances to be nearly equal
+to that of 3000 Argand flames of about an inch diameter; that of a
+cylindric refractor at about 250; and that of a curved mirror may
+perhaps on an average be assumed at about 10 Argand flames.</p>
+
+<p><span class="sidenote">Orders of the
+French Lights.</span>
+The dioptric lights used in France are divided into four orders,
+in relation to their power and range; but in regard to their characteristic
+appearances, this division does not apply, as, in each of<span class="pagenum" id="Page299">[299]</span>
+the orders, lights of identically the same character may be found,
+differing only in the distance at which they can be seen, and in the
+expense of their maintenance. The four orders may be briefly described
+as <span class="nowrap">follows:—</span></p>
+
+<p>1<i>st</i>, Lights of the first order having an interior radius or focal
+distance of 36·22 inches (92<sup>cm.</sup>), and lighted by a lamp of four concentric
+wicks, consuming 570 gallons of oil per annum.</p>
+
+<p>2<i>d</i>, Lights of the second order having an interior radius of
+27·55 inches (70<sup>cm.</sup>), lighted by a lamp of three concentric wicks,
+consuming 384 gallons of oil per annum.</p>
+
+<p>3<i>d</i>, Lights of the third order, lighted by a lamp of two concentric
+wicks, consuming 183 gallons of oil per annum. The instruments
+used in those lights are of two kinds, one having a focal
+distance of 19·68 inches (50<sup>cm.</sup>), and the other of 9·84 inches
+(25<sup>cm.</sup>).</p>
+
+<p>4<i>th</i>, Lights of the fourth order, or harbour-lights, having an
+internal radius of 5·9 inches (15<sup>cm.</sup>), and lighted by a lamp of one
+wick, or Argand burner, consuming 48 gallons of oil per annum.
+This apparatus is, as already noticed, now more generally used of a
+larger scale, having a focal distance of 9·84 inches (25<sup>cm.</sup>), and a
+lamp of two concentric wicks, consuming about 130 gallons of oil
+per annum.<a id="FNanchor73" href="#Footnote73" class="fnanchor">[73]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote73" href="#FNanchor73" class="label">[73]</a> An apparatus of
+0<sup>m.</sup>·185<sup>cm.</sup> was recently added to the list of French lights under
+the name of the <i>Fifth</i> order; while that of 25<sup>cm.</sup> radius has been called the <i>Fourth</i>, and
+that of 15<sup>cm.</sup> radius is styled the <i>Sixth</i> order. Those minute subdivisions I consider to be
+unnecessary.</p>
+
+</div><!--footnote-->
+
+<p><span class="sidenote">Distinctions of the
+Dioptric Lights.</span>
+Those four orders are not intended as distinctions; but are
+characteristic of the power and range of lights, which render them
+suitable for different localities on the coast, according to the distance
+at which they can be seen. This division, therefore, is analogous
+to that which separates our lights into <i>sea-lights</i>, <i>secondary
+lights</i>, and <i>harbour-lights</i>, terms which are used to designate the
+power and position, and not the appearance of the lights to which
+they are applied.</p>
+
+<p><span class="pagenum" id="Page300">[300]</span></p>
+
+<p>Each of the above orders is susceptible of certain combinations,
+which produce various appearances, and constitute the distinctions
+used for dioptric lights; but the following are those which have
+been actually employed as the most useful in <span class="nowrap">practice:—</span></p>
+
+<p>The first order contains, 1<i>st</i>, Lights producing, once in every
+minute, a great flash, preceded by a smaller one, by the revolution
+of eight great lenses and eight smaller ones combined with eight
+mirrors; 2<i>d</i>, Lights flashing once in every half minute, and composed
+of sixteen half lenses. Those lights may have the subsidiary
+parts simply catoptric, or diacatoptric; and, 3<i>d</i>, Fixed lights, composed
+of a combination of cylindric pieces, with curved mirrors or
+catadioptric zones ranged in tiers above and below them.</p>
+
+<p>The second order comprises revolving lights with sixteen or
+twelve lenses, which make flashes every half minute; and fixed
+lights varied by flashes once in every four minutes, an effect which,
+as already noticed, is produced by the revolution of exterior cylindrical
+pieces.</p>
+
+<p>The third order (larger diameter) contains common fixed lights,
+and fixed lights varied by flashes once in every four minutes.</p>
+
+<p>The third order (smaller diameter) contains fixed lights, varied
+by flashes once in three minutes.</p>
+
+<p>The fourth order has fixed lights varied by flashes once in
+every three minutes, and fixed lights of the common kind. It has
+been thought necessary to change the term “fixed lights varied by
+flashes,” for “fixed light with short eclipses,” because it has been
+found that, at certain distances, a momentary eclipse precedes the
+flash.</p>
+
+<p>These distinctions depend upon the periods of revolution, rather
+than upon the <i>characteristic appearance</i> of the light; and therefore
+seems less calculated to strike the eye of a seaman, than those employed
+on the coasts of Great Britain and Ireland. In conformity
+with this system, and in consideration of the great loss of light
+which results from the application of coloured media, all distinctions
+based upon colour have been discarded in the French lights.</p>
+
+<p><span class="pagenum" id="Page301">[301]</span></p>
+
+<p>The distinctions are, in fact, only <i>four</i> in number, viz.: Fixed;
+Fixed, varied by flashes;<a id="FNanchor74" href="#Footnote74" class="fnanchor">[74]</a> Revolving, with flashes once a minute;
+and Revolving, with flashes every half minute. To those might
+be added, Revolving, with bright periods once in two minutes, and
+perhaps <i>Flashing</i> once in <i>five seconds</i> (as introduced by me at the
+Little Ross, but I cannot say with such complete success as would
+induce me to recommend its general adoption). My own experience
+would also lead me to reject the distinction called “Fixed,
+varied by flashes,” which I do not consider as possessing a marked
+or efficient character.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote74" href="#FNanchor74" class="label">[74]</a> The “Feu fixe, varié par des éclats,” or “Feu fixe, à courtes éclipses,” of Fresnel.</p>
+
+</div><!--footnote-->
+
+<p><span class="sidenote">Comparison of
+Dioptric and Catoptric
+Apparatus
+for Revolving
+Lights.</span>
+Having thus fully described the nature of the catoptric and
+dioptric modes of illuminating lighthouses, I shall next compare
+the merits of both systems, with a view to determine their eligibility
+in revolving or in fixed lights.</p>
+
+<p>Repeated experiments were made at Gullan-hill, which is distant
+from Edinburgh about fifteen miles, during the winters of 1832
+and 1833, under the inspection of the Commissioners of Northern
+Lights, the result of which was, that the light of one of the great
+annular lenses used in the revolving lights of the first order, was
+equal to the united effect of about eight of the large reflectors employed
+in the revolving lights on the Scotch coast. It may be
+said, however, that the dia-catoptric<a id="FNanchor75" href="#Footnote75" class="fnanchor">[75]</a> combination of pyramidal
+lenses and plane mirrors of Corduan, adds the power of more than
+two reflectors to the effect of the great lens; but it ought to be remembered
+that in the French lights, this additional power is used
+only to compensate for one of the defects of the system by lengthening
+the duration of the flash, and therefore contributes, if at all,
+only in a very indirect manner, to render the light visible to the
+mariner at a greater distance. M. <span class="smcap">Fresnel</span> found, from the smaller
+divergence of the lens, that the eclipses were too long and the bright
+periods of the revolution too short; and he therefore determined to<span class="pagenum" id="Page302">[302]</span>
+adopt the horizontal deviation of 7° for the upper lenses, with a
+view to remedy this defect. Assuming, therefore, that it were required
+to increase the number of reflectors in a revolving light of
+three sides, so as to render it equal in power to a dioptric revolving
+light of the first order, it would be necessary to place eight reflectors
+on each face, so that the greatest number of reflectors required
+for this purpose may be taken at <i>twenty-four</i>. M. <span class="smcap">Fresnel</span> has
+stated the expenditure of oil in the lamp of four concentric wicks
+at 750 grammes of colza oil per hour; and it is found by experience
+at the Isle of May and Inchkeith, that the quantity of spermaceti
+oil consumed by the great lamp, is equal to that burned by
+from fourteen to sixteen of the Argand lamps used in the Scotch
+lights. It therefore follows that, by dioptric means, the consumption
+of oil necessary for between fourteen and sixteen reflectors,
+will produce a light as powerful as that which would require the
+oil of twenty-four reflectors in the catoptric system of Scotland;
+and, consequently, that there is an excess of oil equal to that consumed
+by ten reflectors, or 400 gallons in the year, against the
+Scotch system. But in order fully to compare the economy of producing
+two revolving lights of equal power by those two methods,
+it will be necessary to take into the calculation the interest of the
+first outlay in establishing them.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote75" href="#FNanchor75" class="label">[75]</a> I use this word to designate the arrangement of pyramidal lenses and plane mirrors,
+by which the light is first <i>refracted</i>, and then <i>reflected</i>.</p>
+
+</div><!--footnote-->
+
+<p>The expense of fitting up a revolving light with twenty-four
+reflectors, ranged on three faces, may be estimated at L.1298, and
+the annual maintenance, including the interest of the first cost of
+the apparatus, may be calculated at L.418, 8s. 4d. The fitting up a
+revolving light with eight lenses and the dia-catoptric accessory apparatus,
+may be estimated at L.1459, and the annual maintenance
+at L.354, 10s. 4d. It therefore follows, that to establish and afterwards
+maintain a catoptric light of the kind called <i>revolving white</i>,
+with a frame of three faces, each equal in power to a face of the
+dioptric light of Corduan, an annual outlay of L.63, 18s. more
+would be required for the reflecting light than for the lens light;
+while for a light of the kind called <i>revolving red and white</i>, whose<span class="pagenum" id="Page303">[303]</span>
+frame has four faces, at least thirty-six reflectors would be required
+in order to make the light even approach an equality to that of
+Corduan; and the catoptric light would in that case cost L.225
+more than the dioptric light.</p>
+
+<p>The effect produced by burning an equal quantity of oil, in revolving
+lights on either system, may be estimated as follows:—In
+a revolving light, like that of Skerryvore, having eight sides, each
+lighting with its greatest power a horizontal sector of 4°, we have
+32° (or <i>units</i>) of the horizon illuminated with the full power of 3200
+Argand flames, and consequently an aggregate effect of 102,400
+flames, produced by burning the oil required for <i>sixteen</i> reflectors;
+while in a catoptric apparatus, like that of the old light at Inchkeith,
+having seven sides of one reflector, each lighting with its
+greatest power a sector of 4°·25′, we have nearly 31° (or <i>units</i>) of
+the horizon illuminated with the full power of 400 Argand flames,
+and consequently an aggregate effect of 12,400 flames as the result
+of burning the oil required for <i>seven</i> reflectors. Hence, the <i>effect</i>
+of burning the same quantity of oil in revolving lights on either
+system, will be represented respectively by <span class="divide fsize80"><span class="num">16</span>
+<span class="denom">7</span></span>&#160;12,400 = 28,343 for
+the catoptric, contrasted with 102,400 for the dioptric light; or, in
+other words, revolving lights on the dioptric principle use the oil
+more <i>economically</i> than those on the catoptric plan, nearly in the
+ratio of 3·6 to 1.</p>
+
+<p><span class="sidenote">Comparison of
+Catoptric and Dioptric
+Apparatus
+for Fixed Lights.</span>
+I shall now speak of fixed lights, to which the dioptric method
+is peculiarly well adapted. The effect produced by the consumption
+of a gallon of oil in a fixed light, with twenty-six reflectors,
+which is the smallest number that can be properly employed, may
+be estimated as follows:—The <i>mean</i> effect of the light spread
+over the horizontal sector, subtended by one reflector, as deduced
+from measurements made at each horizontal degree, by the method
+of shadows, is equal to 174 unassisted Argand burners. If, then,
+this quantity be multiplied by 360 degrees, we shall obtain an aggregate
+effect of 62,640, which, divided by 1040 (the number of<span class="pagenum" id="Page304">[304]</span>
+gallons burned during a year in <i>twenty-six</i> reflectors), would give
+60 Argand flames for the effect of the light maintained throughout
+the year by the combustion of a gallon of oil. On the other hand,
+the power of a catadioptric light of the first order, like that lately
+established at Girdleness, may be estimated thus:—The <i>mean</i> effect
+of the light produced by the joint effect of both the dioptric and
+catadioptric parts of a fixed light apparatus, may be valued at 450
+Argand flames, which, multiplied by 360 degrees, gives an aggregate
+of 162,000; and if this quantity be divided by 570 (the number
+of gallons burned by the great lamp in a year), we shall have about
+284 Argand flames for the effect of the light produced by the combustion
+of a gallon of oil. It would thus appear that in fixed lights,
+the French apparatus, as lately improved, produces, as the <i>average</i>
+effect of the combustion of the same quantity of oil over the whole
+horizon, upwards of <i>four times</i> the amount of light that is obtained
+by the catoptric mode; although, in certain directions, opposite the
+axis of each reflector, the catoptric light be fully 50 <i>per centum</i>
+more powerful than the dioptric light.</p>
+
+<p>But the great superiority of the dioptric method chiefly rests
+upon its <i>perfect</i> fulfilment of an important condition required in a
+fixed light, by distributing the rays <i>equally</i> in every point of the
+horizon. In the event of the whole horizon not requiring to be
+illuminated, the dioptric light would lose a part of its superiority
+in economy, and when half the horizon only is lighted, it would
+be more expensive than the reflected light; but the greater power
+and more equal distribution of the light, may be considered of so
+great importance, as far to outweigh the difference of expense. In
+the latter case, too, an additional power (as noticed <a href="#Page293">p. 293</a>) can be
+given to the dioptric light, by placing at the landward side of the
+lightroom, spherical mirrors with their centres in the focus of the
+refracting apparatus.<a id="FNanchor76" href="#Footnote76" class="fnanchor">[76]</a>
+The luminous cones, or pyramids of which<span class="pagenum" id="Page305">[305]</span>
+such reflectors would form the bases, instead of passing off uselessly
+to the land, would thus be thrown back through the focal point,
+and finally refracted, so as to increase the effect of the light seaward,
+by nearly <i>one-third</i> of the light which would otherwise be
+lost.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote76" href="#FNanchor76" class="label">[76]</a> A similar arrangement can also be made in revolving lights by making the radius
+of the mirrors somewhat less than that of the inscribed circle of the octagon bounded by the
+lenses, so that they may circulate freely round the backs of the mirrors. The shortness of
+the radius of the reflecting surface would, of course, increase the divergence of the beam of
+light refracted through the lenses, as the flame would, in this case, subtend a greater angle
+at the face of the mirrors.</p>
+
+</div><!--footnote-->
+
+<p>The expense of establishing a fixed light composed of twenty-six
+reflectors, may be estimated at L.950, and its annual maintenance,
+including interest on the first cost of the apparatus, may be
+reckoned at L.425, 10s.: and the expense of fitting up a fixed light
+on the dioptric principle with catadioptric zones is L.1511, while
+its annual maintenance may be taken at L.285, 6s. 4d. It thus
+appears that the annual expenditure of the dioptric fixed light is
+L.140, 3s. 8d. less than that of a fixed light composed of twenty-six
+reflectors; while the <i>average</i> effect, equally diffused over the horizon,
+is <i>four times</i> greater.</p>
+
+<p>The comparative views already given of the catoptric and dioptric
+modes of illuminating lighthouses, demonstrate that the latter
+produces more powerful lights by the combustion of the same
+quantity of oil; while it is obvious that the catoptric system insures
+a more certain exhibition of the light, from the fountain-lamps
+being less liable to derangement than the mechanical lamps used
+in dioptric lights. The balance, therefore, of real advantages or
+disadvantages, and, consequently, the propriety of adopting the one
+or the other system, involves a mixed question, not susceptible of
+a very precise solution, and leaving room for different decisions,
+according to the value which may be set upon obtaining a cheaper
+and better light, on the one hand, as contrasted, on the other, with
+less certainty in its exhibition.</p>
+
+<p><span class="sidenote">Summary of considerations
+as to
+the fitness of the
+two systems for
+Revolving Lights.</span>
+A few general considerations, serving briefly to recapitulate the
+arguments for and against the two systems, may not be out of<span class="pagenum" id="Page306">[306]</span>
+place. And, first, regarding the fitness of dioptric instruments for
+revolving lights, it appears from the details above <span class="nowrap">given,—</span></p>
+
+<p>1<i>st</i>, That by placing eight reflectors on each face of a revolving
+frame, a light may be obtained as brilliant as that derived from the
+great annular lens; and that, in the case of a frame of three sides,
+the excess of expense by the reflecting mode, would be L.63, 18s.;
+and in the case of a frame of four sides, the excess would amount
+to L.225.</p>
+
+<p>2<i>d</i>, That for burning oil economically in revolving lighthouses,
+which illuminate every point of the horizon successively, the lens
+is more advantageous than the reflector in the ratio of 3·6 to 1.</p>
+
+<p>3<i>d</i>, That the divergence of the rays from the lens being less than
+from the reflector, it becomes difficult to produce, by lenses, the
+appearance which characterises the catoptric revolving lights, already
+so well known to British mariners; and any change of existing
+lights which would, of course, affect their appearance, must,
+therefore, involve many grave practical objections which would
+not at all apply to the case of new lights.</p>
+
+<p>4<i>th</i>, That the uncertainty in the management of the lamp renders
+it more difficult to maintain the revolving dioptric lights without
+risk of extinction, an accident which has several times occurred
+at Corduan and other lighthouses both in France and elsewhere.</p>
+
+<p>5<i>th</i>, That the extinction of one lamp in a revolving catoptric light
+is not only less probable, but leads to much less serious consequences
+than the extinction of the single lamp in a dioptric light; because,
+in the first case, the evil is limited to diminishing the power of <i>one
+face</i> by an <i>eighth part</i>; whilst, in the second, <i>the whole horizon is totally
+deprived of light</i>. The extinction of a lamp, therefore, in a
+dioptric light, leads to evils which may be considered <i>infinitely
+great</i> in comparison with the consequences which attend the same
+accident in a catoptric light.</p>
+
+<p><span class="sidenote">Summary of considerations
+as to
+the fitness of the
+two systems for
+Fixed Lights.</span>
+In comparing the fixed dioptric, and the fixed catoptric apparatus,
+the results may be summed up under the following <span class="nowrap">heads:—</span></p>
+
+<p><span class="pagenum" id="Page307">[307]</span></p>
+
+<p>1<i>st</i>, It is impossible, by means of any practicable combination of
+paraboloïdal reflectors, to distribute round the horizon a zone of
+light of exactly <i>equal intensity</i>; while this may be easily effected, by
+dioptric means, in the manner already described. In other words,
+the qualities required in fixed lights cannot be so fully obtained by
+reflectors as by refractors.</p>
+
+<p>2<i>d</i>, The <i>average</i> light produced in every azimuth by burning
+one gallon of oil in Argand lamps, with reflectors, is only about
+<i>one-fourth</i> of that produced by burning the same quantity in the
+dioptric apparatus; and the annual expenditure is L.140, 3s. 8d.
+less for the entire dioptric light than for the catoptric light.</p>
+
+<p>3<i>d</i>, The <i>characteristic</i> appearance of the fixed reflecting light
+in any one azimuth would not be changed by the adoption of the
+dioptric method, although its increased <i>mean</i> power would render
+it visible at a greater distance in almost every direction; the only
+exception being in the azimuths opposite the axis of each reflector,
+where the catoptric light has an <i>excess</i> of power equal to about
+50 <i>per centum</i>.</p>
+
+<p>4<i>th</i>, From the equal distribution of the rays, the dioptric light
+would be observed at equal distances in every point of the horizon;
+an effect which cannot be fully attained by any practicable combination
+of paraboloïdal reflectors.</p>
+
+<p>5<i>th</i>, The inconveniences arising from the uncertainty which attends
+the use of the mechanical lamp, are not perhaps so much
+felt in a fixed as in a revolving light, because the greater simplicity
+of the apparatus admits of easier access to it, in case of accident.</p>
+
+<p>6<i>th</i>, But the extinction of a lamp in a catoptric light, leaves
+only one <i>twenty-sixth part</i> of the horizon without the benefit of
+the light, and the chance of accident arising to vessels from it, may,
+therefore, be considered as incalculably less than the danger resulting
+from the extinction of the single lamp of the dioptric light,
+which deprives the whole horizon of light.</p>
+
+<p>7<i>th</i>, There may also, in certain situations, be some risk arising
+from irregularity in the distances at which the same fixed catoptric<span class="pagenum" id="Page308">[308]</span>
+light can be seen in the different azimuths. This defect, of course,
+does not exist in the dioptric light.</p>
+
+<p><span class="sidenote">Advantages and
+disadvantages of
+both systems under
+certain circumstances.</span>
+There can be little doubt, that the more fully the system of
+<span class="smcap">Fresnel</span> is understood, the more certainly will it be preferred to
+the catoptric system of illuminating lighthouses, at least in those
+countries where this important branch of administration is conducted
+with the care and solicitude which it deserves. It must not,
+however, be imagined, that there are no circumstances in which the
+catoptric system is not absolutely preferable to illumination by
+means of lenses. We have hitherto attended only to horizontal
+divergence and its effects, and this is unquestionably the more important
+view; but the consideration of vertical divergence must
+not be altogether overlooked. Now, while it is obvious that vertical
+divergence, at least above the horizon, involves a total loss of
+the light which escapes uselessly upwards into space, it is no
+less true, that if the sheet of light which reaches the most distant
+horizon of the lighthouse, however brilliant, were as thin as the
+absence of all vertical divergence would imply, it would be practically
+useless; and some measure of dispersion in the arc <i>below</i>
+the horizon is therefore absolutely indispensable to constitute a
+really useful light. In the reflector, the greatest vertical divergence
+below the horizontal plane of the focus is 16° 8′, and that of the lens
+is about 4° 30′.</p>
+
+<p>Let us consider for a moment the bearing of those facts upon
+the application of the two modes of illumination to special circumstances.
+The powerful beam of light transmitted by the lens, peculiarly
+fits that instrument for the great sea-lights which are intended
+to warn the mariner of his approach to a distant coast which he first
+makes on an <i>over-sea</i> voyage; and the deficiency of its divergence,
+whether horizontal or vertical, is not practically felt as an inconvenience
+in lights of that character, which seldom require to serve
+the double purpose of being visible at a great distance, and at the
+same time of acting as guides for dangers near the shore. For
+such purposes, the lens applies the light much more economically<span class="pagenum" id="Page309">[309]</span>
+than the reflector, because, while the duration of its <i>least</i> divergent
+beam is nearly equal to that of the reflector, it is <i>eight</i> times
+more powerful. A revolving system of eight lenses illuminates
+an horizontal arc of 32° with this bright beam. The reflector,
+on the other hand, spreads the light over a larger arc of the horizon;
+and, while its <i>least</i> divergent beam is much less powerful
+than that of the lens, the light which is shed over its <i>extreme</i>
+arc is so feeble as to be practically of little use in lights of extensive
+range, even during clear weather. When a lighthouse is placed
+on a very high headland, however, the deficiency of divergence in
+the vertical direction is often found to be productive of some practical
+inconvenience; but this defect may be partially remedied by giving
+to the lenses a slight inclination outwards from the vertical
+plane of the focus, so as to cause the most brilliant portion of the
+emergent beam to reach the <i>visible horizon</i> which is due to the
+height of the lantern. It may be observed, also, that a lantern at
+the height of 150 feet, which, taking into account the common
+height of the observer’s eye at sea, commands a range of upwards
+of 20 English miles, is sufficient for all the ordinary purposes of
+the navigator, and that the intermediate space is practically easily
+illuminated, even to within a mile of the lighthouse, by means
+of a slight inclination of the subsidiary mirrors, even where the
+light from the principal part of the apparatus passes over the seaman’s
+head. For the purpose of leading lights, in narrow channels,
+on the other hand, and for the illumination of certain narrow
+seas, there can be no doubt that reflectors are much more suitable
+and convenient. In such cases, the amount of vertical divergence
+below the horizon, forms an important element in the question,
+because it is absolutely necessary that the mariner should
+keep sight of the lights even when he is very near them; while
+there is not the same call for a very powerful beam which exists
+in the case of sea-lights. Yet even in narrow seas, where low
+towers, corresponding to the extent of the <i>range</i> of the light, are
+used, but where it is, at the same time, needful to illuminate the<span class="pagenum" id="Page310">[310]</span>
+whole or the greater part of the horizon, the use of dioptric instruments
+will be found almost unavoidable, especially in fixed lights,
+as well from their equalizing the distribution of the light in every
+azimuth, as from their much greater economy in situations where a
+large annual expenditure would often be disproportionate to the revenue
+at disposal. In such places, where certain peculiarities of the
+situation require the combination of a light equally diffused over the
+greater portion of the horizon, along with a greater vertical divergence
+in certain azimuths, than dioptric instruments afford, I have
+found it convenient and economical to add to the fixed refracting
+apparatus a single paraboloïdal reflector, in order to produce the
+desired effect, instead of adapting the whole light to the more expensive
+plan for the sake of meeting the wants of a single narrow
+sector of its range. In other cases, where the whole horizon is to
+be illuminated, and great vertical divergence is at the same time
+desirable, a slight elevation of the burner, at the expense, no doubt,
+of a small loss of light, is sometimes resorted to, and is found to
+produce, with good effect, the requisite depression of the emergent
+rays.</p>
+
+<p>In certain situations, where a great range and, consequently,
+a powerful light must be combined with tolerably powerful illumination
+in the immediate vicinity of the lighthouse, we might,
+perhaps, advantageously adopt a variation of the form and dimensions
+of the mirrors employed, so as to resemble those formerly
+employed at the Tour de Corduan, which were of considerably
+larger surface and longer focal distance than those which are used
+in Britain. If such a form were adopted, the power of the light for
+the purpose of the distant range would be increased; and I would
+propose to compensate for the deficiency of divergence consequent
+on a long focal distance, by placing a second burner in some position
+between the parameter and the vertex, and slightly elevated
+above the axis of the instrument, so as to throw the greater portion
+of the beam resulting from this second burner below the horizontal
+plane of the focus. Such an expedient is no doubt somewhat<span class="pagenum" id="Page311">[311]</span>
+clumsy and would at the same time involve the consumption
+of twice the quantity of oil used in an ordinary catoptric light;
+but I can still conceive it to be preferable, in certain situations, to
+the use of lenses alone.</p>
+
+<p>Thus it appears that we must not too absolutely conclude
+against one, or in favour of the other mode of illumination for lighthouses;
+but, as in every other department of the arts, we shall find
+the necessity of patiently weighing all the circumstances of each
+particular case that comes before us, before selecting that instrument,
+or combination of instruments, which appears most suitable.</p>
+
+<p><span class="sidenote">Distinctions of the
+Dioptric Lights,
+and the application
+of coloured
+media.</span>
+The mode of distinguishing lights in the system of <span class="smcap">Fresnel</span>,
+depends more upon their <i>magnitude</i> and the <i>measured interval</i> of the
+time of their revolution, than upon their <i>appearance</i>; and no other
+very marked distinctions, except Fixed and Revolving, have been
+successfully attempted in France. As above stated, I consider the
+distinction of the <i>fixed light varied by flashes</i>, to possess an appearance
+too slightly differing from that of a revolving light, to admit
+of its being safely adopted in situations where revolving lights are
+near. The trial which I made at the Little Ross, in the Solway
+Frith, of producing, by means of lenses, a light flashing once in five
+seconds of time, although successful so far as mere distinction is concerned,
+has several practical defects, arising from the shortness of
+the duration of the flashes, compared with the powerful effect of the
+fixed part of the apparatus, which I consider sufficient to prevent its
+adoption in future, especially considering that a much more marked
+appearance can be produced, by means of reflectors, as has been
+done at the Buchanness in Aberdeenshire, and the Rhinns of Islay
+in Argyllshire. Coloured media have never, so far as I know,
+been applied to Dioptric apparatus, except in the case of the Maplin
+Light at the mouth of the Thames, and Cromarty Point Light
+at the entrance to the Cromarty Frith, and in both instances successfully.
+The enormous loss of light, however, amounting to no
+less than 0·80 of the whole incident rays, forms a great bar to the
+adoption of colour as a distinction; and any means which could<span class="pagenum" id="Page312">[312]</span>
+tend to lessen that absorption, and at the same time produce the
+characteristic appearance, would be most valuable. I have tried
+some glasses of a pink tinge, prepared by M. <span class="smcap">Letourneau</span> of Paris,
+whose absorption does not exceed 0·57 of the incident rays; but the
+appearance of the light, at a distance, is much less marked than that
+produced by the glasses used in Britain.<a id="FNanchor77" href="#Footnote77" class="fnanchor">[77]</a> Such deficiency of characteristic
+colour might lead to serious consequences, as the transmission
+of white rays, through a hazy atmosphere, too often produces,
+by absorption, a reddish tinge of the light, for which the less
+marked appearance given by the paler media might be easily mistaken.
+This colouring power of absorption is so well known, that
+red lights are seldom used except in direct contrast with white
+ones; but, on a coast so thickly studded with Lighthouses as that
+of Britain, the number of distinctions is insufficient to supply all our
+wants, so that we are sometimes reluctantly compelled to adopt a
+<i>single red light</i> in some situation of lesser importance, or which, from
+some local circumstances and the appearance of the lights which
+must be seen by the mariner before passing it, is not likely to be
+mistaken. The great loss of light by coloured media causes the red
+beam, in a revolving light, to be seen at a shorter distance than the
+white; and it is conceivable that, in certain circumstances, this
+might lead the mariner to mistake a <i>red and white light</i> for a <i>white</i>
+light revolving at half the velocity. Such a mistake might perhaps
+prove dangerous; but the lights are generally so situated that
+there is ample time for the mariner, after first discovering the red
+light, and thus correcting any mistake, to shape his course accordingly.
+All other coloured media except <i>red</i> have been found useless
+as distinctions for any lights of extensive range, and fail to be
+efficient, owing to the necessity of absorbing almost all the light
+before a marked appearance can be obtained. In a few pier or
+ferry lights, green and blue media have been tried, and found available
+at the distance of a few cables’ lengths.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote77" href="#FNanchor77" class="label">[77]</a> See <a href="#Page229">page 229</a>, <i>ante</i>.</p>
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page313">[313]</span></p>
+
+<p>It seems to be a natural consequence of the physical distribution
+of light, that fixed lights, which illuminate the whole horizon,
+should be less powerful than revolving lights which have their effect
+concentrated within narrow sectors of the horizon. Any attempt
+to increase the power of fixed lights is, therefore, worthy of
+attention; <span class="sidenote">Captain <span class="smcap">Basil
+Hall</span>’s proposal
+for producing the
+appearance of
+Fixed Lights by
+rapid movement.</span>
+and when the late Captain <span class="smcap">Basil Hall</span> proposed a plan
+for effecting this object, it received, as it deserved, the full consideration
+of the Lighthouse Board, who authorised me to repeat
+Captain <span class="smcap">Hall’s</span> experiments, and verify his results by observations
+made at a considerable distance. As some interesting phenomena
+of irradiation were evolved in the course of those trials, I think it
+right to give some account of the results which were obtained,
+as they bear upon various questions connected with the practical
+arrangements of Lighthouses, under certain circumstances.</p>
+
+<p>In revolving lights on the dioptric principle, the annular lens
+of Fresnel, as formerly stated, is employed. This instrument, as
+the reader already knows, possesses the property of projecting to
+the horizon, in the form of <i>one</i> pencil or beam, all the light which
+falls on its inner surface from a lamp placed in its principal focus.
+The consequence of this action is, that when several lenses are so
+arranged as to form a right prism which circulates round a lamp
+placed in the common focus, a distant observer receives from each
+lens, as its axis crosses his line of vision, a bright flash, which is
+succeeded by total darkness, when one of the dark spaces intermediate
+between the lenses passes over his eye; and this succession
+of bright flashes alternating with dark intervals, produces the characteristic
+appearance of a revolving light.</p>
+
+<p>The fixed light, on the other hand, presents to the eye a steady
+and unchanging appearance; and the chief object to be obtained
+in its construction, is to unite the greatest brilliancy with an equal
+distribution of the light in every direction. The condition of perfect
+distribution, as already said, is most rigorously fulfilled by the
+use of refracting zones or belts, which form, by their union, a
+cylinder enveloping the flame placed in its centre, and possess the
+property of refracting the light in the vertical direction only, without<span class="pagenum" id="Page314">[314]</span>
+affecting its natural divergence horizontally. The light from
+the focus which is incident on the inner surface of the belt is
+therefore projected forwards in the shape of a flat ring of equal
+brilliancy all round the horizon.</p>
+
+<p>This repetition may seem needless, but it is hoped it will be
+found useful in rendering intelligible the following outline of the
+plan proposed by Captain <span class="smcap">Hall</span> for the improvement of fixed lights,
+and the account of the trials that were made with that object in
+view.</p>
+
+<p>The familiar experiment of whirling a burning stick quickly
+round the head, so as to produce a ribbon of light, proves the possibility
+of causing a continuous impression on the retina by intermittent
+images succeeding each other with a certain rapidity.
+From the moderate velocity at which this continuity of impression
+is obtained, we should be warranted in concluding, <i>a priori</i>, that
+the time required to make an impression on the retina is considerably
+less than the duration of the impression itself; for the continuity
+of effect must, of course, be caused by fresh impulses succeeding
+each other before the preceding ones have entirely faded.
+If it were otherwise, and the time required to make the impression
+were equal to the duration of the sensation, it would obviously
+be impossible to obtain a series of impulses so close or continuous
+in their effects as to run into and overlap each other, and thus throw
+out the intervals of darkness; because the same velocity which
+would tend to shorten the dark intervals, would also curtail the
+bright flashes, and thus prevent their acting on the eye long enough
+to cause an impression. Accordingly, we find that the duration of
+an impression is in reality much greater than the time required for
+producing the effect on the retina. It is stated by Professor
+<span class="smcap">Wheatstone</span>, in the London Transactions for 1834, that only
+about <i>one millionth part</i> of a second is required for making a distinct
+impression on the eye; and it appears, from a statement made by
+Lamé, at p. 425 of his Cours de Physique, that M. <span class="smcap">Plateau</span> found
+that an impression on the retina preserved its intensity unabated
+during <i>one hundredth</i> of a second, so that, however small those<span class="pagenum" id="Page315">[315]</span>
+times may be in themselves, the one is yet 10,000 greater than the
+other.</p>
+
+<p>It has been ascertained by direct experiment,<a id="FNanchor78" href="#Footnote78" class="fnanchor">[78]</a> that the eye can
+receive a fresh impression before the preceding one has faded; and,
+indeed, if this were impossible, absolute continuity of impression
+from any succession of impulses, however rapid, would seem to be
+unattainable; and the approach to perfect continuity would be inversely
+as the time required to make an impression.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote78" href="#FNanchor78" class="label">[78]</a> Lamé, Cours de Physique, p. 424. “L’impression peut subsister encore lorsque la
+suivante a lieu.”</p>
+
+</div><!--footnote-->
+
+<p><span class="sidenote">Effects of rapid
+motion on the
+power of Lights.</span>
+From this property which bright bodies passing rapidly before
+the eye possess of communicating a continuous impression to the
+sense of sight, Captain <span class="smcap">Hall</span> conceived the idea, not merely of obtaining
+all the effects of a fixed light, by causing a system of lenses
+to revolve with such a velocity as to produce a continuous impression,
+but, at the same time, of obtaining a much more brilliant appearance,
+by the compensating influence of the bright flashes, which
+he expected would produce impulses sufficiently powerful and
+durable to make the deficiency of light in the dark spaces almost
+imperceptible. The mean effect of the whole series of changes
+would, he imagined, be thus greatly superior to that which can be
+obtained from the same quantity of light equally distributed, as in
+fixed lights, over the whole horizon. Now this expectation, if it
+be considered solely in reference to the physical distribution of the
+light, involves various difficulties. The quantity of light subjected
+to instrumental action is the same whether we employ the refracting
+zones at present used in fixed dioptric lights, or attempt to obtain
+continuity of effect by the rapid revolution of lenses; and the
+only difference in the action of those two arrangements is this, that
+while the zones distribute the light equally over the whole horizon,
+or rather do not interfere with its natural horizontal distribution,
+the effect of the proposed method is to collect the light into pencils,
+which are made to revolve with such rapidity, that the impression
+from each pencil succeeds the preceding one in time to prevent a
+sensible occurrence of darkness. To expect that the mean effect of<span class="pagenum" id="Page316">[316]</span>
+the light, so applied, should be greater than when it is left to its
+natural horizontal divergence, certainly appears at first to involve
+something approaching to a contradiction of physical laws. In both
+cases, the same quantity of light is acted upon by the instrument;
+and in either case, any one observer will receive an impression similar
+and equal to that received by any other stationed at a different
+part of the horizon; so that, unless we imagine that there is
+some loss of light peculiar to one of the methods, we are, in the
+physical view of the question, shut up to the conclusion, that the
+impressions received by each class of observers must be of equal
+intensity. In other words, the same quantity of light is by both
+methods employed to convey a continuous impression to the senses
+of spectators in every direction, and in both methods equality of
+distribution is effected, since it does not at all consist with our hypothesis,
+that any one observer in the same class should receive
+more or less than his equal share of the light. Then, as to the
+probability of the loss of light, it seems natural to expect that this
+should occur in connection with the revolving system, because the
+velocity is an extraneous circumstance, by no means necessary to
+an equal distribution of the light, which can, as we already know,
+be more naturally and at the same time perfectly, attained by the
+use of the zones.</p>
+
+<p>On the other hand, it must not be forgotten, that although the
+effect of both methods is to give each part of the horizon an equal
+share of light, there is yet this difference between them, that while
+the light from the zones is equally intense at every instant of time,
+that evolved by the rapidly circulating lenses is constantly passing
+through every phase between total darkness and the brightest flash
+of the lens; and this difference, taken in connection with some curious
+physiological observations regarding the sensibility of the retina,
+gives considerable countenance to the expectation on which
+Captain <span class="smcap">Hall’s</span> ingenious expedient is based. The fact which has
+already been noticed, and which the beautiful experiments of M.
+<span class="smcap">Plateau</span> and Professor <span class="smcap">Wheatstone</span> have of late rendered more
+precise, that the duration of an impression on the retina is not only<span class="pagenum" id="Page317">[317]</span>
+appreciable, but is much greater than the time required to cause it,
+seems to encourage us in expecting, that while the velocity required
+to produce continuity of effect would not be found so great as to
+interfere with the formation of a full impression, the duration of
+the impulse from each flash would remain unaltered, and the dark
+intervals which do not excite the retina would, at the same time,
+be shortened, and that, therefore, we might in this manner obtain
+an effect on the senses exceeding the brilliancy of a steady light
+distributed equally in every direction by the ordinary method.
+Some persons, indeed, who have speculated on this subject, seem
+even to be of opinion, that, so far from the whole effect of the series
+of continuous impressions being weakened by a blending of
+the dark with the bright intervals, the eye would in reality be stimulated
+by the contrast of light and darkness, so as thereby to receive
+a more complete and durable impulse from the light. It is
+obvious, however, that this question regarding the probable effect
+to be anticipated from a revolution so rapid as to cause a continuous
+impression, could only have been satisfactorily answered by an appeal
+to experiment.</p>
+
+<p>In experimenting on this subject, I used the apparatus formerly
+employed by Captain <span class="smcap">Hall</span>. It consisted of an octagonal frame,
+which carried eight of the discs that compose the central part of
+Fresnel’s compound lens, and was susceptible of being revolved
+slowly or quickly at pleasure, by means of a crank-handle and
+some intermediate gearing. The experiments were nearly identical
+with those made by Captain <span class="smcap">Hall</span>, who contrasted the effect of
+a single lens at rest, or moving very slowly, with that produced by
+the eight lenses, revolving with such velocity as to cause an apparently
+continuous impression on the eye. To this experiment I
+added that of comparing the beam thrown out by the central portion
+of a cylindric refractor, such as is used at the fixed light of
+the Isle of May, with the continuous impression obtained by the
+rapid revolution of the lenses. Captain <span class="smcap">Hall</span> made all his comparisons
+at the short distance of 100 yards; and in order to obtain<span class="pagenum" id="Page318">[318]</span>
+some measure of the intensity, he viewed the lights through plates
+of coloured glass until the luminous discs became invisible to the
+eye. I repeated those experiments at Gullan, under similar circumstances,
+but with very different results. I shall not, however,
+enter upon the discussion of those differences here, although
+they are susceptible of explanation, and are corroborative of the
+conclusions at which I arrived, by comparing the lights from a distance
+of 14 miles; but shall briefly notice the more important results
+which were obtained by the distant view. They are as <span class="nowrap">follows:—</span></p>
+
+<p>1. The flash of the lens revolving slowly was very much larger
+than that of the rapidly revolving series; and this decrease of size
+in the luminous object presented to the eye, became more marked
+as the rate of revolution was accelerated, so that, at the velocity of
+eight or ten flashes in a second, the naked eye could hardly detect
+it, and only a few of the observers saw it; while the steady light
+from the fixed refractor was distinctly visible.</p>
+
+<p>2. There was also a marked falling off in the brilliancy of the
+rapid flashes as compared with that of the slow ones; but this effect
+was by no means so striking as the decrease of volume.</p>
+
+<p>3. Continuity of impression was not attained at the rate of five
+flashes in a second, but each flash appeared to be distinctly separated
+by an interval of darkness; and even when the nearest approach
+to continuity was made, by the recurrence of eight or ten
+flashes in a second, the light still presented a twinkling appearance,
+which was well contrasted with the steady and unchanging effect
+of the cylindric refractor.</p>
+
+<p>4. The light of the cylindric refractor was, as already stated,
+steady and unchanging, and of much larger volume than the rapidly
+revolving flashes. It did not, however, appear so brilliant as the
+flashes of the quickly revolving lenses, more especially at the lower
+rate of five flashes in a second.</p>
+
+<p>5. When viewed through a telescope, the difference of volume
+between the light of the cylindric refractor and that produced by<span class="pagenum" id="Page319">[319]</span>
+the lenses at their greatest velocity was very striking. The former
+presented a large diffuse object of inferior brilliancy, while the
+latter exhibited a sharp pin-point of brilliant light.</p>
+
+<p>Upon a careful consideration of these facts it appears warrantable
+to draw the following general <span class="nowrap">conclusions:—</span></p>
+
+<p>1. That our expectations as to the effects of light, when distributed
+according to the law of its natural horizontal divergence, are
+supported by observed facts as to the visibility of such lights, contrasted
+with those whose continuity of effect is produced by collecting
+the whole light into bright pencils, and causing them to revolve
+with great velocity.</p>
+
+<p>2. It appears that this deficiency of visibility seems to be chiefly
+due to a want of volume in the luminous object, and also, although
+in a less degree, to a loss of intensity, both of which defects appear
+to increase in proportion as the motion of the luminous object is
+accelerated.</p>
+
+<p>3. That this deficiency of volume is the most remarkable optical
+phenomenon connected with the rapid motion of luminous bodies,
+and that it appears to be directly proportional to the velocity of
+their passage over the eye.</p>
+
+<p>4. That there is reason to suspect that the visibility of distant
+lights depends on the volume of the impression in a greater degree
+than has perhaps been generally imagined.</p>
+
+<p>5. That, as the size and intensity of the radiants causing these
+various impressions to a distant observer were the same, the volume
+of the light and, consequently, <i>cæteris paribus</i>, its visibility,
+are, within certain limits, proportionate to the time during which
+the object is present to the eye.</p>
+
+<p>Such appear to be the general conclusions which those experiments
+warrant us in drawing; and the practical result, in so far as
+lighthouses are concerned, is sufficient to discourage us from attempting
+to improve the visibility of fixed lights in the manner
+proposed by Captain <span class="smcap">Hall</span>, even supposing the practical difficulties
+connected with the great centrifugal force generated by the rapid
+revolution of the lenses to be less than they really are.</p>
+
+<p><span class="pagenum" id="Page320">[320]</span></p>
+
+<p><span class="sidenote">Connection of the
+experiments with
+Irradiation.</span>
+This decrease in the volume of the luminous object caused by
+the rapid motion of the lights is interesting, from its apparent
+connection with the curious phenomenon of irradiation. When
+luminous bodies, such as the lights of distant lamps, are seen
+by night, they appear much larger than they would do by day;
+and this effect is said to be produced by irradiation. M. <span class="smcap">Plateau</span>,
+in his elaborate essay on this subject, after a careful examination
+of all the theories of irradiation, states it to be his opinion,
+that the most probable mode of accounting for the various observed
+phenomena of irradiation is to suppose, that, in the case of
+a night-view, the excitement caused by light is propagated over
+the retina beyond the limits of the day-image of the object, owing
+to the increased stimulus produced by the contrast of light and
+darkness; and he also lays it down as a law confirmed by numerous
+experiments, that irradiation increases with the duration of the
+observation. It appears, therefore, not unreasonable to conjecture,
+that the deficiency of volume observed during the rapid revolution
+of the lenses may have been caused by the light being present to
+the eye so short a time, that the retina was not stimulated in a degree
+sufficient to produce the amount of irradiation required for
+causing a large visual object. When, indeed, the statement of
+M. <span class="smcap">Plateau</span>, that irradiation is proportional to the duration of the
+observation, is taken in connection with the observed fact, that the
+volume of the light decreased as the motion of the lenses was accelerated,
+it seems almost impossible to avoid connecting together
+the two phenomena as cause and effect.</p>
+
+<div class="chapter">
+
+<h3 class="nobreak"><span class="chapname">VARIOUS GENERAL CONSIDERATIONS CONNECTED WITH
+LIGHTHOUSES.</span></h3>
+
+</div><!--chapter-->
+
+<p>In the course of supplying the numerous wants of navigation, it
+will often be found necessary to <i>cut off</i>, on a given bearing, the beam
+proceeding from a Lighthouse, as a guide to the seaman to avoid
+some shoal, or as a hint to put about and seek the opposite side of
+a channel. This is attended with some little practical difficulty,<span class="pagenum" id="Page321">[321]</span>
+especially in lights from reflectors arranged externally on a circle,
+because a certain portion of light, chiefly due to the divergence
+caused by the size of the flames, and partly from the effects of the
+diffraction or inflexion of the light, spreads faintly over a narrow
+sector between the light arc and the dark one. <span class="sidenote">Masking Lights.</span>
+It becomes necessary,
+of course, to make allowance for this penumbral arc by increasing
+the masked portion of the lantern; and, where a very
+sharp line of demarcation is required, a board is sometimes placed
+on the outside of the Lightroom, in such a position, and of such
+length, that while it does not enter the boundaries of the luminous
+sector, it prevents the more powerful part of the penumbral beam
+from reaching the observer’s eye. This effect is, of course, more
+conveniently produced, where the circumstances admit of its adoption,
+by distributing the reflectors round the concave side of the
+lantern, towards the land; but such an arrangement is inapplicable
+when the illuminated sector exceeds the dark one. I have found,
+by observation, that the sector intercepted between the azimuth
+on which the lantern is masked and that on which total darkness
+is produced to an observer, at moderate distances, may be estimated
+at not less than 3° for dioptric, and 7° for catoptric lights of the
+highest class.<a id="FNanchor79" href="#Footnote79" class="fnanchor">[79]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote79" href="#FNanchor79" class="label">[79]</a> The method which I adopted for determining those quantities, was to mask a certain
+portion of the lantern of a lighthouse subtending an horizontal sector of about 30° or 40°,
+and at night to fix, by actual observation, at the distance of 5 or 6 miles, two points on
+the coast between which the light so masked was obscured. The angle included between
+the lines joining those points and the centre of the lantern was then determined by triangulation
+next day, and <i>half the difference</i> between the observed angle (which is always the
+<i>lesser</i> of the two) and the computed subtense of the masked sector of the lantern, is, in
+each case, the amount of the allowance stated in the text.</p>
+
+</div><!--footnote-->
+
+<p>Those quantities may therefore serve to guide the Lighthouse
+engineer to approximate more rapidly to his object, as he will generally
+be safe in increasing the dark sector, by one or other of the
+above constants, according to the kind of apparatus employed. I
+need not add, that in a matter of this kind, a final appeal to actual
+observation is, in all cases, indispensable.</p>
+
+<p><span class="pagenum" id="Page322">[322]</span></p>
+
+<p>A few words on the subject of double lights, naturally spring out
+of what has been said about the masking of lights. <span class="sidenote">Double Lights.</span>
+The term <i>double
+lights</i> is properly and distinctly confined to lights on different levels,
+but not <i>necessarily</i> (as <i>leading-lights</i> are) in separate towers. The
+sole object of using double lights is for <i>distinction</i> from neighbouring
+lights; and they are unquestionably most effective in this respect,
+when they are placed in the same tower. In this point of view, therefore,
+I shall speak of them; and it is obvious that all that peculiarly
+belongs to them is, that the difference of level between them shall
+be sufficiently great to present the lights as separate objects to the
+eye of the seaman, when placed at the greatest distance at which
+it may be desirable that he should be able to recognise their characteristic
+appearance. In many cases it is not necessary (but it is
+certainly always desirable) that the lights should, from the first moment
+of their being seen, be known as <i>double lights</i>; but in others,
+it may well consist with safety, that two lights, which appear as a
+single light when first seen at the distance of 20 miles, shall at 15
+or 10 miles distance be discovered to be <i>double</i>. Now we should
+at first be apt hastily to imagine, that all that is required to produce
+that effect, is to raise the one light above the other to such an extent,
+that the distance between them shall be somewhat more than
+a <i>minimum visibile</i> at the most distant point of observation, or, in
+other words, that the difference of the height of the lights should be
+such as to subtend to the eye at the point of observation, an angle
+greater than 13″·02, which is the subtense of a <i>minimum visibile</i>
+during the day.<a id="FNanchor80" href="#Footnote80" class="fnanchor">[80]</a> But the effect of irradiation, to which I have already
+alluded, tends to blend together the images of the lights long
+before their distance apart has become so low a fraction of the observer’s<span class="pagenum" id="Page323">[323]</span>
+distance from the Lighthouse, as to subtend so small an
+angle; and I have accordingly found by experiments, conducted
+under various circumstances, and at various distances, that repeated
+observations gave me 3′ 18″ as the mean of the subtenses calculated
+in reference to the distances at which the lights began to be blended
+into <i>one</i>.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote80" href="#FNanchor80" class="label">[80]</a> This quantity is deduced
+from observations made by my friend Mr <span class="smcap">James Gardner</span>,
+while engaged on the Ordnance Survey, and may be regarded as the <i>extreme</i> limit of visibility,
+under the most favourable circumstances as to the state of the atmosphere and also the
+contrast of colours. The observed object, also, was a pole, not a <i>round</i> disc; and it is familiar
+to every one accustomed to view distant objects, that <i>vertical length</i> is an important
+constituent in their visibility.</p>
+
+</div><!--footnote-->
+
+<p>Adopting this as the smallest angle which the two lights should
+subtend at the observer’s eye, we may find the least vertical distance
+between them which will cause them to appear as separate
+objects by the following formula:</p>
+
+<div class="formula">
+
+<p>H = 2&#160;Δ . tan&#160;θ</p>
+
+</div><!--formula-->
+
+<p class="noindent">in which Δ is the observer’s distance in feet; θ, half the subtense,
+= 1′ 39″; and H the required height of the tower between
+the two lights in feet. The following Table gives the height in
+feet corresponding to the distance in nautic miles, from 1 to 20
+inclusive: the heights, which are the bases of <i>similar</i> isosceles triangles,
+increase, of course, in an arithmetical series:</p>
+
+<table class="standard">
+
+<tr class="bt2 bb">
+<th class="bl2 br">Distance<br>of the<br>observer<br>in<br>Nautic<br>Miles.</th>
+<th class="brd">Vertical<br>distance<br>in feet<br>between<br>the Lights.</th>
+<th class="br">Distance<br>of the<br>observer<br>in<br>Nautic<br>Miles.</th>
+<th class="br2">Vertical<br>distance<br>in feet<br>between<br>the Lights.</th>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;1</td>
+<td class="cntr brd">&#8199;6·02</td>
+<td class="cntr br">11</td>
+<td class="cntr br2">&#8199;66·22</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;2</td>
+<td class="cntr brd">12·04</td>
+<td class="cntr br">12</td>
+<td class="cntr br2">&#8199;72·24</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;3</td>
+<td class="cntr brd">18·06</td>
+<td class="cntr br">13</td>
+<td class="cntr br2">&#8199;78·26</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;4</td>
+<td class="cntr brd">24·08</td>
+<td class="cntr br">14</td>
+<td class="cntr br2">&#8199;84·28</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;5</td>
+<td class="cntr brd">30·10</td>
+<td class="cntr br">15</td>
+<td class="cntr br2">&#8199;90·30</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;6</td>
+<td class="cntr brd">36·12</td>
+<td class="cntr br">16</td>
+<td class="cntr br2">&#8199;96·32</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;7</td>
+<td class="cntr brd">42·14</td>
+<td class="cntr br">17</td>
+<td class="cntr br2">102·34</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;8</td>
+<td class="cntr brd">48·16</td>
+<td class="cntr br">18</td>
+<td class="cntr br2">108·36</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;9</td>
+<td class="cntr brd">54·18</td>
+<td class="cntr br">19</td>
+<td class="cntr br2">114·38</td>
+</tr>
+
+<tr class="bb2">
+<td class="cntr bl2 br">10</td>
+<td class="cntr brd">60·20</td>
+<td class="cntr br">20</td>
+<td class="cntr br2">120·40</td>
+</tr>
+
+</table>
+
+<p>Akin to the subject of <i>Double Lights</i>, is that of <span class="sidenote">Leading Lights.</span>
+<i>Leading Lights</i>,<span class="pagenum" id="Page324">[324]</span>
+the object of which is to indicate to the mariner a given line of
+direction by their being seen <i>in one line</i>. In most instances, this
+line of direction is used to point out the central part of a narrow
+channel; and the alternate <i>opening</i> of the lights, on either side of
+their <i>conjunction</i>, serves to indicate to the mariner (who ought to
+conjoin with his watching of the lights the observation of the
+elapsed time and also frequent soundings) the proper moment for
+changing his tack. In some places, the line of conjunction of the
+lights is placed nearer to one side of a channel than the other, according
+as the set of the tides, or the position of shoals, may seem
+to require. In other situations, this line only serves as a <i>cross-bearing</i>
+to shew the mariner his approach to some danger, or to indicate
+his having passed it, and thus to assure him of his entry on
+wider <i>sea-room</i>. Similar considerations to those which determine
+the difference of elevation for <i>double lights</i> regulate the choice of
+the distance between two leading lights; but the question is less
+narrow, and may be generally solved graphically by simply drawing
+the lines on an accurate chart of the locality. In some few
+situations, the configuration of the coast does not admit of a separation
+between the lights, sufficient to cause what is called a <i>sharp
+intersection</i>; but, in most cases, there is room enough to place
+them so far apart, that but a few yards of deviation in the vessel’s
+course, from the exact line of the conjunction of the lights <i>in one</i>,
+produces a distinct opening between them on the opposite side of
+that line. In order to insure the requisite sharpness of intersection,
+the distance between the lights, wherever attainable, should
+be not less than <i>one-sixth</i> of the distance between the more seaward
+of the two Towers and that point at which the seaman begins
+to use the line of conjunction as his guide. I have only
+to add, that in situations where the land prevents a considerable
+separation between leading lights, they should be placed as nearly
+on <i>one level</i> as is consistent with their being seen as <i>vertically</i> separated,
+so as in some measure to compensate for their horizontal
+nearness, by rendering their intersection more sharp and striking<span class="pagenum" id="Page325">[325]</span>
+than it can be where the observer must draw from the upper light
+an imaginary perpendicular in his mind, and then estimate the separation
+of the lights by the sine of an angle, which decreases as
+the difference of their apparent elevations increases.</p>
+
+<p><span class="sidenote">Distribution of
+Lights on a Coast.</span>
+The considerations which enter into the choice of the position
+and character of the Lights on a line of coast, are either, on the
+one hand, so simple and self-evident as scarcely to admit of being
+stated in a general form, without becoming mere truisms; or are,
+on the other hand, so very numerous and often so complicated as
+scarcely to be susceptible of compression into any general laws.
+I shall not, therefore, do more than very briefly allude to a few of
+the chief considerations which should guide us in the selection of
+the sites and characteristic appearance of the Lighthouses to be
+placed on a line of coast. Perhaps those views may be most conveniently
+stated in the form of distinct <span class="nowrap">propositions:—</span></p>
+
+<p>1. The most prominent points of a line of coast, or those first
+made on <i>over-sea</i> voyages, should be first lighted; and the most
+powerful lights should be adapted to them, so that they may be discovered
+by the mariner as long as possible before his reaching land.</p>
+
+<p>2. So far as is consistent with a due attention to distinction,
+revolving lights of some description, which are necessarily more
+powerful than fixed lights, should be employed at the outposts on
+a line of coast.</p>
+
+<p>3. Lights of precisely identical character and appearance should
+not, if possible, occur within a less distance than 100 miles of each
+other on the same line of coast, which is made by over-sea vessels.</p>
+
+<p>4. In all cases, the distinction of colour should never be adopted
+except from absolute necessity.</p>
+
+<p>5. Fixed lights and others of less power, may be more readily
+adopted in narrow seas, because the <i>range</i> of the lights in such
+situations is generally less than that of open sea-lights.</p>
+
+<p>6. In narrow seas also, the distance between lights of the same
+appearance may often be safely reduced within much lower limits
+than is desirable for the greater sea-lights; and there are many instances
+in which the distance separating lights of the same character<span class="pagenum" id="Page326">[326]</span>
+need not exceed 50 miles, and there are peculiar cases in which
+even a much less separation between similar lights may be sufficient.</p>
+
+<p>7. Lights intended to guard vessels from reefs, shoals, or other
+dangers, should in every case be placed, where practicable, to the
+seaward of the danger itself, as it is desirable that seamen be
+enabled to make the lights with confidence.</p>
+
+<p>8. Views of economy in the first cost of a Lighthouse should
+never be permitted to interfere with placing it in the best possible
+position; and, when funds are deficient, it will generally be found
+that the wisest course is to delay the work until a sum shall have
+been obtained sufficient for the erection of the lighthouse on the
+best site.</p>
+
+<p>9. The elevation of the lantern above the sea should not, if possible,
+for sea-lights, exceed 200 feet; and about 150 feet is sufficient,
+under almost any circumstances, to give the range which is
+required. Lights placed on high headlands are subject to be frequently
+wrapped in fog, and are often thereby rendered useless, at
+times when lights on a lower level might be perfectly efficient.
+But this rule must not, and indeed cannot, be strictly followed,
+especially on the British coast, where there are so many projecting
+cliffs, which, while they subject the lights placed on them to
+occasional obscuration by fog, would also entirely and permanently
+hide from view lights placed on the lower land adjoining
+them. In such cases, all that can be done is carefully to weigh
+all the circumstances of the locality, and choose that site for the
+lighthouse which seems to afford the greatest balance of advantage
+to navigation. As might be expected, in questions of this kind,
+the opinions of the most experienced persons are often very conflicting,
+according to the value which is set on the various elements
+which enter into the inquiry.</p>
+
+<p>10. The best position for a sea-light ought rarely to be neglected
+for the sake of some neighbouring port, however important
+or influential; and the interests of navigation, as well as the true
+welfare of the port itself, will generally be much better served by
+placing the sea-light <i>where it ought to be</i>, and adding, on a smaller<span class="pagenum" id="Page327">[327]</span>
+scale, such subsidiary lights as the channel leading to the entrance
+of the port may require.</p>
+
+<p>11. It may be held as a general maxim, that the fewer lights
+that can be employed in the illumination of a coast the better, not
+only on the score of economy, but also of real efficiency. Every
+light needlessly erected may, in certain circumstances, become a
+source of confusion to the mariner, and, in the event of another
+light being required in the neighbourhood, it becomes a <i>deduction</i>
+from the means of distinguishing it from the lights which existed
+previous to its establishment. By the needless erection of a new
+Lighthouse, therefore, we not only expend public treasure, but
+waste the means of distinction among the neighbouring lights.</p>
+
+<p>12. Distinctions of lights, founded upon the minute estimation
+of intervals of time between flashes, and especially on the measurement
+of the duration of light and dark periods, are less satisfactory
+to the great majority of coasting seamen, and are more liable to
+derangement by atmospheric changes, than those distinctions which
+are founded on what may more properly be called the <i>characteristic
+appearance</i> of the lights, in which the times for the recurrence of
+certain appearances differ so widely from each other as not to require
+for their detection any very minute observation in a stormy
+night. Thus, for example, flashing lights of five seconds interval,
+and revolving lights of half a minute, one minute, and two minutes,
+are much more characteristic than those which are distinguished
+from each other by intervals varying according to a slower series
+of 5″, 10″, 20″, 40″, &amp;c.</p>
+
+<p>13. Harbour and local lights, which have a circumscribed
+range, should generally be fixed instead of revolving; and may
+often, for the same reason, be safely distinguished by coloured
+media. In many cases also, where the purpose of guiding into a
+narrow channel is to be gained, the leading lights which are used,
+should, at the same time, be so arranged as to serve for a distinction
+from any neighbouring lights.</p>
+
+<p>14. Floating lights, which are very expensive and more or less
+uncertain from their liability to drift from their moorings, as well<span class="pagenum" id="Page328">[328]</span>
+as defective in power, should never be employed to indicate a
+turning point in a navigation in any situation where the conjunction
+of lights on the shore can be applied at any reasonable expense.</p>
+
+<p><span class="sidenote">Height of Lighthouse
+Tower,
+and its relation to
+range of Light.</span>
+The spheroïdal form of the Earth requires that the height of a
+Lighthouse Tower should increase proportionally to the difference
+between the Earth’s radius and the secant of the angle intercepted
+between the normal to the spheroïd at the Lighthouse and the
+normal at the point of the light’s occultation from the view of a
+distant observer. The effect of atmospheric refraction, however,
+is too considerable to be neglected in estimating the <i>range</i> of a
+light, or in computing the height of a Tower which is required to
+give to any light a given range; and we must, therefore, in accordance
+with the influence of this element, on the one hand <i>increase</i> the
+range due to any given height, and
+<i>vice versa reduce</i> the height required
+for any given range, which a simple
+consideration of the form of the globe
+would assign. In considering this
+height, we may proceed as <span class="nowrap">follows:—</span></p>
+
+<div class="container w30emmax" id="Fig92">
+
+<p class="caption">Fig. 92.</p>
+
+<img src="images/illo328.jpg" alt="Earth curvature illustrated">
+
+</div><!--container-->
+
+<p>Referring to the accompanying
+figure (<a href="#Fig92">No. 92</a>), in which S′&#160;<i>d</i>&#160;L′ is a
+segment of the ocean’s surface, O the
+centre of the earth, L′L a Lighthouse,
+and S the position of the mariner’s
+eye, we obtain the value of LL′ = H′,
+the height of the tower in feet by the formula,</p>
+
+<div class="formula">
+
+<p>H′ = <span class="divide"><span class="num">2&#160;<i>l</i>²</span>
+<span class="denom">3</span></span>
+<span class="formnr">(1.)</span></p>
+
+</div><!--formula-->
+
+<p class="noindent">in which <i>l</i> = the distance in English miles L′<i>d</i> at which the light
+would strike the ocean’s surface. We then reduce this value of H′
+by the correction for mean refraction, which permits the light to be
+seen at a greater distance, and which =</p>
+
+<div class="formula">
+
+<p><span class="divide"><span class="num">2&#160;<i>l</i>²</span>
+<span class="denom">21</span></span>,
+<span class="formnr">(2.)</span></p>
+
+<p>So as to get, H = <span class="divide"><span class="num">2&#160;<i>l</i>²</span><span class="denom">3</span></span> -
+<span class="divide"><span class="num">2&#160;<i>l</i>²</span><span class="denom">21</span></span> =
+<span class="divide"><span class="num">4&#160;<i>l</i>²</span><span class="denom">7</span></span>
+<span class="formnr">(3.)</span></p>
+
+</div><!--formula-->
+
+<p class="noindent">an expression which at once gives the height of the tower required,<span class="pagenum" id="Page329">[329]</span>
+if the eye of the mariner were just on the surface of the water at
+<i>d</i>, where the tangent between his eye at S and the light at L
+would touch the sea. We must, therefore, in the first instance,
+find the distance <i>d</i>&#160;S = <i>l′</i>, which is the radius of the visible horizon
+due to the height SS′ = <i>h</i> of his eye above the water, and is, of
+course, at once obtained conversely by the <span class="nowrap">expression:—</span></p>
+
+<div class="formula">
+
+<p><i>l′</i> = <span class="divide"><span class="num">√<span class="bt">7&#160;<i>h</i></span></span>
+<span class="denom">2</span></span>
+<span class="formnr">(4.)</span></p>
+
+</div><!--formula-->
+
+<p class="noindent">Deducting this distance from SL, the whole effective range of the
+light, we have L&#160;<i>d</i> = <i>l</i>, and operating with this value in the former
+equation,</p>
+
+<div class="formula">
+
+<p>H = <span class="divide"><span class="num">4&#160;<i>l</i>²</span><span class="denom">7</span></span></p>
+
+</div><!--formula-->
+
+<p class="noindent">we find the height of the tower which answers the conditions of
+the case.<a id="FNanchor81" href="#Footnote81" class="fnanchor">[81]</a> From the above data the following Table has been
+computed.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote81" href="#FNanchor81" class="label">[81]</a> In the above expressions <i>l</i> and <i>l′</i> are given in English miles, which in Scotland may be
+considered as bearing to nautical miles the ratio of 5280 to 6088. In order to convert a
+distance given in nautical miles to English miles, all that is needful is to add the log of the
+number of nautical miles to log 5280, and subtract log 6088.</p>
+
+</div><!--footnote-->
+
+<table class="standard">
+
+<tr class="bt2">
+<th class="bl2 br">H</th>
+<th class="br">λ</th>
+<th class="brd">λ′</th>
+<th class="br">H</th>
+<th class="br">λ</th>
+<th class="brd">λ′</th>
+<th class="br">H</th>
+<th class="br">λ</th>
+<th class="br2">λ′</th>
+</tr>
+
+<tr class="bb">
+<th class="bl2 br">Heights<br>in Feet.</th>
+<th class="br">Lengths<br>in<br>English<br>Miles.</th>
+<th class="brd">Lengths<br>in<br>Nautical<br>Miles.</th>
+<th class="br">Heights<br>in<br>Feet.</th>
+<th class="br">Lengths<br>in<br>English<br>Miles.</th>
+<th class="brd">Lengths<br>in<br>Nautical<br>Miles.</th>
+<th class="br">Heights<br>in<br>Feet.</th>
+<th class="br">Lengths<br>in<br>English<br>Miles.</th>
+<th class="br2">Lengths<br>in<br>Nautical<br>Miles.</th>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;5</td>
+<td class="cntr br">&#8199;2·958</td>
+<td class="cntr brd">2·565</td>
+<td class="cntr br">&#8199;70</td>
+<td class="cntr br">11·067</td>
+<td class="cntr brd">&#8199;9·598</td>
+<td class="cntr br">&#8199;250</td>
+<td class="cntr br">20·916</td>
+<td class="cntr br2">18·14&#8199;</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">10</td>
+<td class="cntr br">&#8199;4·184</td>
+<td class="cntr brd">3·628</td>
+<td class="cntr br">&#8199;75</td>
+<td class="cntr br">11·456</td>
+<td class="cntr brd">&#8199;9·935</td>
+<td class="cntr br">&#8199;300</td>
+<td class="cntr br">22·912</td>
+<td class="cntr br2">19·87&#8199;</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">15</td>
+<td class="cntr br">&#8199;5·123</td>
+<td class="cntr brd">4·443</td>
+<td class="cntr br">&#8199;80</td>
+<td class="cntr br">11·832</td>
+<td class="cntr brd">10·26&#8199;</td>
+<td class="cntr br">&#8199;350</td>
+<td class="cntr br">24·748</td>
+<td class="cntr br2">21·46&#8199;</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">20</td>
+<td class="cntr br">&#8199;5·916</td>
+<td class="cntr brd">5·130</td>
+<td class="cntr br">&#8199;85</td>
+<td class="cntr br">12·196</td>
+<td class="cntr brd">10·57&#8199;</td>
+<td class="cntr br">&#8199;400</td>
+<td class="cntr br">26·457</td>
+<td class="cntr br2">22·94&#8199;</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">25</td>
+<td class="cntr br">&#8199;6·614</td>
+<td class="cntr brd">5·736</td>
+<td class="cntr br">&#8199;90</td>
+<td class="cntr br">12·549</td>
+<td class="cntr brd">10·88&#8199;</td>
+<td class="cntr br">&#8199;450</td>
+<td class="cntr br">28·062</td>
+<td class="cntr br2">24·33&#8199;</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">30</td>
+<td class="cntr br">&#8199;7·245</td>
+<td class="cntr brd">6·283</td>
+<td class="cntr br">&#8199;95</td>
+<td class="cntr br">12·893</td>
+<td class="cntr brd">11·18&#8199;</td>
+<td class="cntr br">&#8199;500</td>
+<td class="cntr br">29·580</td>
+<td class="cntr br2">25·65&#8199;</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">35</td>
+<td class="cntr br">&#8199;7·826</td>
+<td class="cntr brd">6·787</td>
+<td class="cntr br">100</td>
+<td class="cntr br">13·228</td>
+<td class="cntr brd">11·47&#8199;</td>
+<td class="cntr br">&#8199;550</td>
+<td class="cntr br">31·024</td>
+<td class="cntr br2">26·90&#8199;</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">40</td>
+<td class="cntr br">&#8199;8·366</td>
+<td class="cntr brd">7·255</td>
+<td class="cntr br">110</td>
+<td class="cntr br">13·874</td>
+<td class="cntr brd">12·03&#8199;</td>
+<td class="cntr br">&#8199;600</td>
+<td class="cntr br">32·403</td>
+<td class="cntr br2">28·10&#8199;</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">45</td>
+<td class="cntr br">&#8199;8·874</td>
+<td class="cntr brd">7·696</td>
+<td class="cntr br">120</td>
+<td class="cntr br">14·490</td>
+<td class="cntr brd">12·56&#8199;</td>
+<td class="cntr br">&#8199;650</td>
+<td class="cntr br">33·726</td>
+<td class="cntr br2">29·25&#8199;</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">50</td>
+<td class="cntr br">&#8199;9·354</td>
+<td class="cntr brd">8·112</td>
+<td class="cntr br">130</td>
+<td class="cntr br">15·083</td>
+<td class="cntr brd">13·08&#8199;</td>
+<td class="cntr br">&#8199;700</td>
+<td class="cntr br">35·000</td>
+<td class="cntr br2">30·28&#8199;</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">55</td>
+<td class="cntr br">&#8199;9·811</td>
+<td class="cntr brd">8·509</td>
+<td class="cntr br">140</td>
+<td class="cntr br">15·652</td>
+<td class="cntr brd">13·57&#8199;</td>
+<td class="cntr br">&#8199;800</td>
+<td class="cntr br">37·416</td>
+<td class="cntr br2">32·45&#8199;</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">60</td>
+<td class="cntr br">10·246</td>
+<td class="cntr brd">8·886</td>
+<td class="cntr br">150</td>
+<td class="cntr br">17·201</td>
+<td class="cntr brd">14·91&#8199;</td>
+<td class="cntr br">&#8199;900</td>
+<td class="cntr br">39·836</td>
+<td class="cntr br2">34·54&#8199;</td>
+</tr>
+
+<tr class="bb2">
+<td class="cntr bl2 br">65</td>
+<td class="cntr br">10·665</td>
+<td class="cntr brd">9·249</td>
+<td class="cntr br">200</td>
+<td class="cntr br">18·708</td>
+<td class="cntr brd">16·22&#8199;</td>
+<td class="cntr br">1000</td>
+<td class="cntr br">41·833</td>
+<td class="cntr br2">36·28&#8199;</td>
+</tr>
+
+</table>
+
+<p><span class="pagenum" id="Page330">[330]</span></p>
+
+<p>If the distance at which a light of given height can be seen by
+a person on a given level be required, it is only needful to add together
+the two numbers in the column of lengths λ or λ′ (according
+as Nautical or English miles may be sought) corresponding to those
+in the column of heights H, which represent respectively the height
+of the observer’s eye and the height of the lantern above the sea.
+When the height required to render a light visible at a given distance
+is required, we must seek first for the number in λ or λ′ corresponding
+to the height of the observer’s eye, and deduct this
+from the whole proposed range of the light, and opposite the remainder
+in λ or λ′ seek for the corresponding number in H.</p>
+
+<p>A considerable practical defect in all the lighthouse lanterns
+which I have ever seen, with the exception of those recently constructed
+for the Scotch Lighthouses, consists in the vertical direction
+of the astragals, which, of course, tend to intercept the whole
+or a great part of the light in the azimuth which they subtend.<a id="FNanchor82" href="#Footnote82" class="fnanchor">[82]</a>
+The consideration of the improvement which I had effected in
+giving a <span class="sidenote">Diagonal Lantern.</span>
+diagonal direction to the joints of the fixed refractors, first
+led me (as stated at <a href="#Page266">p. 266</a>, <i>ante</i>), to adopt a diagonal arrangement
+of the framework which carries the cupola of zones and afterwards
+for the astragals of the lantern. Not only is this <i>direction</i> of the
+astragals more advantageous for equalising the effect of the light;
+but the greater stiffness and strength which this arrangement gives
+to the frame-work of the lantern make it safe to use more slender
+bars and thus also absolutely <i>less</i> light is intercepted. The panes
+of glass at the same time become triangular, and are necessarily
+stronger than rectangular panes of equal surface. This form of
+lantern is extremely light and elegant, and is shewn, with detailed
+drawings of some of its principal parts, in <a href="#Plate26">Plate XXVI.</a> To
+avoid the necessity of painting, which, in situations so exposed
+as those which lighthouses generally occupy, is attended with many
+inconveniences and no small risk, the framework of the lantern is
+now formed of gun-metal and the dome is of copper; so that a first<span class="pagenum" id="Page331">[331]</span>
+order lantern of 12 feet diameter and 10 feet height of glass costs,
+when glazed, about L.1260. In order to give the lightkeepers
+free access to cleanse and wash the upper panes of the lantern (an
+operation which in snowy weather must sometimes be frequently
+repeated during the night), a narrow gangway, on which they may
+safely stand, is placed on the level of the top of the lower panes,
+and at the top of the second panes, rings are provided of which the
+lightkeepers may lay hold for security in stormy weather. A light
+trap-ladder is also attached to the outside of the lantern by means
+of which there is an easy access to the ventilator on the dome.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote82" href="#FNanchor82" class="label">[82]</a> I must also except the small pier light at Kirkcaldy, erected (I believe in 1836)
+by my friend Mr <span class="smcap">Edward Sang</span>.</p>
+
+</div><!--footnote-->
+
+<p><span class="sidenote">Glazing of the
+Lantern.</span>
+Great care is bestowed on the glazing of the lantern, in order
+that it may be quite impervious to water, even during the heaviest
+gales. When iron is used for the frames, they are carefully and
+frequently painted; but gun-metal, as just noticed, is now generally
+used in the Scotch Lighthouses. There is great risk of the
+glass plates being broken by the shaking of the lantern during high
+winds; and as much as possible to prevent this, various precautions
+are adopted. The arris of each plate is always carefully rounded
+by grinding; and grooves about ¹⁄₂ inch wide, capable of holding a
+good thickness of putty, are provided in the astragals for receiving
+the glass, which is ¹⁄₄ inch thick. Small pieces of lead or wood are
+inserted between the frames and the plates of glass against which
+they may press, and by which they are completely separated from
+the more unyielding material of which the lantern-frames are composed.
+Panes glazed in frames padded with cushions, and capable
+of being temporarily fixed in a few minutes, in the room of a
+broken plate, are kept ready for use in the Store-room. Those
+framed plates are called <i>storm-panes</i>, and have been found very useful
+on several occasions, when the glass has been shattered by large
+sea-birds coming against it in a stormy night, or by small stones
+violently driven against the lantern by the force of the wind.</p>
+
+<p><span class="sidenote">Ventilation of the
+Lanterns.</span>
+The ventilation of the lanterns forms a most important element
+in the preservation of a good and efficient light. An ill-ventilated
+lantern has its sides continually covered with the water of condensation,
+which is produced by the contact of the ascending current<span class="pagenum" id="Page332">[332]</span>
+of heated air; and the glass thus obscured obstructs the passage of
+the rays, and diminishes the power of the light. In the Northern
+Lighthouses, ventilators, capable of being opened and shut at pleasure,
+so as to admit from without a supply of air when required, are
+provided in the parapet-wall on which the lantern stands; the lantern
+roof also is surmounted by a cover which, while it closes the
+top of an open cylindric tube against the entrance of rain, and descends
+over it only so far as is needful for that purpose, still leaves
+an open air-space between it and the dome. This arrangement permits
+the current of heated air, which is continually flowing from the
+lantern through the cylindric tube, to pass between it and the outer
+cover, from which it finally escapes to the open air through the space
+between the cover and the dome. The door which communicates
+from the lightroom through the parapet to the balcony outside,
+is also made the means of ventilating the lightroom; and, for that
+purpose, it is provided with a sliding bolt at the bottom, which,
+being dropped into one or other of the holes cut in the balcony for
+its reception, serves to keep the door open at any angle that may
+be found necessary. A useful precaution was introduced by my
+predecessor, as Engineer to the Northern Lights Board, in order
+to prevent the too rapid condensation of heated air on the large internal
+surface of the lantern roof, which consists in having two
+domes with an air-space between them, as shewn in the enlarged
+diagrams in <a href="#Plate26">Plate XXVI.</a></p>
+
+<p>An important improvement in the ventilation of Lighthouses
+was some years ago introduced by Dr <span class="smcap">Faraday</span> into several of the
+Lighthouses belonging to the Trinity House, and has since been
+adopted in all the dioptric lights belonging to the Commissioners
+of Northern Lighthouses. After mentioning several proofs of extremely
+bad ventilation in Lighthouses, Dr <span class="smcap">Faraday</span> thus describes
+his apparatus:<a id="FNanchor83" href="#Footnote83" class="fnanchor">[83]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote83" href="#FNanchor83" class="label">[83]</a> Minutes of Institution of Civil Engineers, vol. i., p. 207.</p>
+
+</div><!--footnote-->
+
+<p>“The ventilating pipe or chimney is a copper tube, 4 inches
+in diameter, not, however, in one length, but divided into three or
+four pieces; the lower end of each of these pieces for about 1¹⁄₂ inch<span class="pagenum" id="Page333">[333]</span>
+is opened out into a conical form, about 5¹⁄₂ inches in diameter at
+the lowest part. When the chimney is put together, the upper
+end of the bottom piece is inserted about ¹⁄₂ inch into the cone of
+the next piece above, and fixed there by three ties or pins, so that
+the two pieces are firmly held together; but there is still plenty
+of air-way or entrance into the chimney between them. The same
+arrangement holds good with each succeeding piece. When the
+ventilating chimney is fixed in its place, it is adjusted so that the
+lamp-chimney enters about ¹⁄₂ inch into the lower cone, and the top
+of the ventilating chimney enters into the cowl or head of the
+lantern.</p>
+
+<p>“With this arrangement, it is found that the action of the ventilating
+flue is to carry up every portion of the products of combustion
+into the cowl; none passes by the cone apertures out of
+the flue into the air of the lantern, but a portion of the air passes
+from the lantern by these apertures into the flue, and so the lantern
+itself is in some degree ventilated.</p>
+
+<p>“The important use of these cone apertures is that when a
+sudden gust or eddy of wind strikes into the cowl of the lantern,
+it should not have any effect in disturbing or altering the flame.
+It is found that the wind may blow suddenly in at the cowl, and
+the effect never reaches the lamp. The upper, or the second, or
+the third, or even the fourth portion of the ventilating flue might
+be entirely closed, yet without altering the flame. The cone junctions
+in no way interfere with the tube in carrying up all the products
+of combustion; but if any downward current occurs, they
+dispose of the whole of it into the room without ever affecting the
+lamp. The ventilating flue is in fact a tube, which, as regards the
+lamp, can carry everything <i>up</i> but conveys nothing <i>down</i>.”</p>
+
+<p>The advantages of this arrangement, as applied to the Northern
+Lighthouses, were much less palpable than those which are described
+in the beginning of Dr <span class="smcap">Faraday’s</span> paper, because their
+ventilation was very good before its introduction; and the flame
+in particular was perfectly steady, being by no means subject to<span class="pagenum" id="Page334">[334]</span>
+derangement from sudden gusts of wind from the roof in the manner
+noticed above.</p>
+
+<p><span class="sidenote">Arrangements and
+internal management
+of a Lighthouse.</span>
+All the Lighthouses in the district of the Commissioners are
+under the charge of at least two Lightkeepers, whose duties are to
+cleanse and prepare the apparatus for the night illumination, to
+mount guard singly after the light is exhibited, and to relieve each
+other at stated hours, fixed by the printed regulations and instructions,
+under which they act. The rule is, that no keeper on watch
+shall, under any circumstances, leave the Lightroom until relieved
+by his comrade; and, for the purpose of cutting off all pretext for the
+neglect of this universal law, the dwelling-houses are built close to
+the Light Tower, and means are provided for making signals directly
+from the Lightroom to the sleeping apartments below. These
+signals are communicated by air-tubes, through which, by means
+of a small piston, or a puff of wind from the mouth, calls can be
+exchanged between the keepers, enabling the man on guard in the
+Lightroom, at the end of the watch, or on any sudden emergence,
+to summon his comrade from below, who, on being thus called, answers
+by a counter-blast, to shew that the summons has been heard
+and will be obeyed. For the purpose of greater security, in such
+situations as the Bell Rock and the Skerryvore, four keepers are
+provided for one lightroom; one being always ashore on leave with
+his family, and the other three being at the Lighthouse, so that, in
+case of the illness of one lightkeeper, an efficient establishment of
+two keepers for watching the light may remain. At all the land-lighthouses
+also, an agreement is made with some steady person
+residing in the neighbourhood, who is instructed in the management
+of the light and cleansing of the apparatus, and comes under
+an obligation to be ready to do duty in the light-room when called
+upon, in the event of the sickness or absence of one of the lightkeepers.
+This person is called the <i>occasional keeper</i>, and receives
+pay only while actually employed at the Lighthouse; but in order
+to keep him in the practice of the duty, he is required to serve in
+the lightroom for a fortnight annually in the month of January.
+The details of the lightkeeper’s duty may be seen by referring to<span class="pagenum" id="Page335">[335]</span>
+the <a href="#App10">instructions</a> already alluded to, which will be found in the Appendix.</p>
+
+<p>Each of the two lightkeepers has a house for himself and family,
+both being under a common roof, but entering by separate doors,
+as shewn in <a href="#Plate27">Plates XXVII.</a> and <a href="#Plate28">XXVIII.</a>, which exhibit the buildings
+for the new Lighthouse at Ardnamurchan Point, on the coast
+of Argyllshire. The principal keeper’s house consists of six rooms,
+two of which are at the disposal of the visiting officers of the Board,
+whose duty in inspecting the Lighthouse, or superintending repairs,
+may call them to the station; and the assistant has four rooms, one
+of which is used as a barrack-room for the workmen, who, under
+the direction of the Foreman of the lightroom works, execute the
+annual repairs of the apparatus.</p>
+
+<p>The early Lighthouses contained accommodation for the lightkeepers
+in the Tower itself; but the dust caused by the cleaning
+of those rooms in the Tower was found to be very injurious to the
+delicate apparatus and machinery in the lightroom. Unless, therefore,
+in situations such as Skerryvore, where it is unavoidable, the
+dwellings of the lightkeepers ought not to be placed in the Light
+Tower, but in an adjoining building.</p>
+
+<p>Great care should be bestowed to produce the utmost cleanliness
+in everything connected with a Lighthouse, the optical apparatus
+of which is of such a nature as to suffer materially from the effect
+of dust in injuring its polish. For this purpose covered ash-pits are
+provided at all the dwelling-houses, in order that the dust of the
+fire-places may not be carried by the wind to the lightroom; and
+for similar reasons, iron floors are used for the lightrooms instead
+of stone, which is often liable to abrasion, and all the stonework
+near the lantern is regularly painted in oil.</p>
+
+<p>If, in all that belongs to a lighthouse, the greatest cleanliness
+be desirable, it is in a still higher degree necessary in every part of
+the lightroom apparatus, without which the optical instruments and
+the machinery will neither last long nor work well. <span class="sidenote">Cleansing of Apparatus.</span>
+Every part
+of the apparatus, whether lenses or reflectors, should be carefully<span class="pagenum" id="Page336">[336]</span>
+freed from dust before being either washed or burnished; and without
+such a precaution, the cleansing process would only serve
+to scratch them. For burnishing the reflectors, prepared <i>rouge</i>
+(tritoxide of iron) of the finest description, which should be in the
+state of an impalpable powder of a deep orange-red colour, is applied,
+by means of soft chamois skins, as occasion may require;
+but the great art of keeping reflectors clean consists in the daily,
+patient, and skilful application of manual labour in rubbing the
+surface of the instrument with a perfectly dry, soft, and clean skin,
+without rouge. The form of the hollow paraboloid is such, that
+some practice is necessary in order to acquire a free movement of
+the hand in rubbing reflectors; and its attainment forms one of the
+principal lessons in the course of the preliminary instruction, to
+which candidates for the situation of a light-keeper are subjected
+at the Bell Rock Lighthouse. For cleansing the lenses and glass
+mirrors, spirit of wine is used. Having washed the surface of the
+instrument with a linen cloth steeped in spirit of wine, it is carefully
+dried with a soft and dry linen rubber, and finally rubbed with
+a fine chamois skin, free from any dust which would injure the
+polish of the glass, as well as from grease. It is sometimes necessary
+to use a little fine rouge with a chamois skin, for restoring
+any deficiency of polish which may occur from time to time; but
+in a well-managed lighthouse this application will seldom, if ever,
+be required.</p>
+
+<p>The machinery of all kinds, whether that of the mechanical
+lamp or the revolving apparatus, should also be kept scrupulously
+clean, and all the journals should be carefully oiled.</p>
+
+<p><span class="sidenote">Mode of measuring
+the relative
+intensity and
+power of Lights.</span>
+As I have had frequent occasion to speak of the comparative
+power of lights, it will not be out of place to present the reader
+with a few practical observations, chiefly drawn from the excellent
+work of M. <span class="smcap">Peclet</span> to which I have so often referred, on the measurement
+of the intensity of lights by the method of shadows.</p>
+
+<div class="container w30emmax" id="Fig93">
+
+<p class="caption">Fig. 93.</p>
+
+<img src="images/illo337a.jpg" alt="Light beam">
+
+</div><!--container-->
+
+<p>The intensity of light decreases as the observer recedes from
+the luminous body, in proportion to the square of his distance.<span class="pagenum" id="Page337">[337]</span>
+Suppose a <a href="#Fig93">beam of light</a> to proceed from a
+radiant at F, and we shall have the rays
+which, of course, move in straight lines,
+gradually receding from each other, as
+<i>b</i>, <i>b′</i>, <i>b″</i>, <i>b‴</i>, and <i>c</i>, <i>c′</i>, <i>c″</i>, <i>c‴</i>, so that the section
+of the beam will increase with the
+distances F&#160;<i>b</i>, and F&#160;<i>c</i>; and the same number
+of rays, being thus spread over spaces continually increasing,
+will illuminate the surfaces with a less intensity. This decrease of
+intensity will, therefore, be in the inverse ratio of the extent of
+the transverse parallel sections of the luminous cones at <i>b</i> and <i>c</i>,
+which, we know, increase as the square of their distances from the
+apex of the cone at F. Hence we conclude, that the <i>intensity of
+any section of a divergent beam of light decreases as the square of its
+distance from the radiant</i>. This law furnishes us with a simple
+measure of the comparative intensity of lights. If we suppose two
+lights so placed that they may separately illuminate adjacent portions
+of a vertical screen of paper, we may, by repeatedly comparing
+the luminousness of those surfaces, and moving one of the
+lights farther from, or nearer to the screen, at length cause the separate
+portions of the paper to become equally luminous. This arrangement,
+however, has many practical difficulties, which I shall
+not wait to specify; but shall at once indicate a more simple and
+equally correct mode of obtaining the same result, by means of the
+shadows cast by the lights from an opaque rod, in a vertical position
+at O (<a href="#Fig94">fig. 94</a>), placed between them, and a screen covered with
+white paper on which the shadows fall. It is obvious that the light
+at F would cause the object O to cast a shadow
+at SS, while the light at F′ would cast a
+shadow at S′S′. But while the shadow at S
+would still receive light from F′, S′ would
+receive light from F, so that those two
+shadows are, in fact, the only portions of
+the screen which are each illuminated only
+by one of the lights, while every other portion<span class="pagenum" id="Page338">[338]</span>
+of its surface receives light from both the radiants at F and
+F′. If we suppose F to be the weaker light, we can bring it
+nearer the screen, until the shadow S′S′, shall become similar in
+appearance to the shadow SS; and we shall have the ratio of the
+intensity of the light at F to that of the light at F′, as (FS′)² is
+to (F′S)², which distances must be measured with the greatest
+exactness. Such is the mode commonly used in estimating the
+comparative intensities of two lights; but there are various precautions
+which are needful in order to prevent errors in comparing
+the deepness of the shadows, and to insure the greatest attainable
+accuracy in the estimate of the power of the lights, which I shall
+endeavour briefly to describe.</p>
+
+<div class="container w30emmax" id="Fig94">
+
+<p class="caption">Fig. 94.</p>
+
+<img src="images/illo337b.jpg" alt="Measuring light intensity">
+
+</div><!--container-->
+
+<p><span class="sidenote">More accurate comparison
+of the intensity
+of Lights.</span>
+The difficulties of estimating the deepness or sharpness of the
+shadow is very great, and many persons seem quite incapable of
+arriving at any right judgment in this matter. The same person
+also will discover such unaccountable variations in his decision after
+observations made at short intervals of time, as, one would think,
+can only arise from a sudden change of the intensity of one or
+both lights. M. Peclet, in his <i>Traité de l’éclairage</i>, gives, as the
+result of his experience (and I can fully confirm his result by my
+own), that those differences depend less frequently on any real
+difficulty of estimating the deepness of the shadows, than on variations
+in the position of the observer, or rather in the angle at which
+he views the shadows, and that, consequently, in proportion to the
+distance between the two shadows, this source of error is increased.
+Any thing like a glossy texture of the surface of the
+screen, which then, of course, becomes a reflector, also tends to
+aggravate this evil. Thus, if the two lights which are to be compared
+be placed on a table, in such situations as to spread pretty
+far apart on the screen the shadows of a vertical rod placed between
+them; and if the shadow nearer to the observer seem to be
+a little deeper or sharper than the other, let the observer look at
+them from the other side of the table, and their difference will be
+reversed, and that which seemed the paler, will become the deeper.
+Again, if the difference between the two shadows be very great<span class="pagenum" id="Page339">[339]</span>
+when seen from the right side of the screen, it may happen that,
+on viewing them from the left hand, the difference may still be in
+favour of the same shadow, but in a much less degree.</p>
+
+<p>“When I observed this effect,” says M. Peclet,<a id="FNanchor84" href="#Footnote84" class="fnanchor">[84]</a> “I tried to
+view the shadows through a transparent screen, but I remarked
+the same variations. They were indeed even more sensible; for a
+variation in the distance of the eye of a few centimètres, made a
+prodigious change in the deepness of the shadows. I observed also
+that the shadow was much deeper when seen in the line of the light,
+and that in every other direction, it became paler in proportion as
+the eye receded from that direction.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote84" href="#FNanchor84" class="label">[84]</a> Traité de l’éclairage, p. 214.</p>
+
+</div><!--footnote-->
+
+<p>“In all the cases which I have just described, the differences
+of the tints when the position is changed, increase in proportion as
+the shadows are farther separate; and they grow very minute
+when the shadows are almost touching each other.</p>
+
+<div class="container w25emmax" id="Fig95">
+
+<p class="caption">Fig. 95.</p>
+
+<img src="images/illo339a.jpg" alt="Studying shadows">
+
+</div><!--container-->
+
+<p>“Let AB (<a href="#Fig95">fig. 95</a>) be a white opaque surface, <i>a</i>, a luminous
+body, and <i>m</i>, a black opaque body, then the
+shadow <i>b′</i> cast on AB, will appear deeper
+when observed from P, than as seen from
+Q. This is a fact which may be easily verified,
+and the cause of which is easily conceived.
+In fact, the surface AB, although
+it disperses the light, must still reflect more
+of it, in the directions in which the regular reflection takes place;
+and hence the rays which are reflected round about the shadow,
+must have a greater intensity in the direction of P than in that
+of Q, and, consequently, the shadow <i>b′</i> must appear deeper from the
+point P than from Q.</p>
+
+<div class="container w25emmax" id="Fig96">
+
+<p class="caption">Fig. 96.</p>
+
+<img src="images/illo339b.jpg" alt="Studying shadows">
+
+</div><!--container-->
+
+<p>“If we now place (<a href="#Fig96">fig. 96</a>) two lights
+in front of the screen AB, at such distances
+that the two shadows <i>a′</i> and <i>b′</i> should have
+equal intensities, it is evident that if the
+eye be placed at P, the shadow <i>b′</i> must appear<span class="pagenum" id="Page340">[340]</span>
+more intense than the shadow <i>a′</i>, and that the reverse will
+take place if the eye be at Q. But the difference which is then observed,
+arises not only from the difference in the brightness of the
+parts surrounding the shadows, but also from a difference in the
+intensity of the shadows themselves; for the shadow <i>b′</i> is illuminated
+by <i>b</i>, and radiates much more towards Q than towards P;
+and, on the contrary, the shadow <i>a′</i>, which is illuminated by <i>a</i>,
+radiates much more towards P than towards Q. We perceive also
+why the <i>differences</i> of the tints increase with the separation of the
+two shadows, and why they become very small when the shadows
+touch each other; it is because, in proportion as the shadows are
+farther apart, each of them is illuminated more obliquely, and a
+greater quantity of light is radiated (by reflection) in the regular
+direction. When they touch each other, on the contrary, they
+are illuminated almost perpendicularly, and consequently the shadows
+radiate light almost equally on either side.</p>
+
+<p>“Those anomalies of a like kind which are observed when the
+shadows are viewed through a translucent body, such as paper
+or linen, may be referred to a similar cause. We know, in fact,
+that, in looking through a translucent medium, we always, more
+or less, distinctly perceive the luminous body behind it, and, also,
+that there is a very large proportion of the rays which traverse the
+body, which stray but a little from the direction which they would
+follow if the substance were absolutely transparent. Consequently,
+the space which surrounds the shadow is more luminous in proportion
+as we come nearer to the direction of the shadow; and as
+the absolute intensity of the shadows diminishes as we come nearer
+to the direction of the rays which light them, those two effects
+concur to increase the intensity of that shadow to which the eye
+is nearer.</p>
+
+<p>“As the dispersion by reflection is much more complete than
+by refraction, the variations of which we have just spoken are much
+greater with a transparent screen, through which the shadows
+are viewed, than with an opaque screen (from which they are
+reflected).</p>
+
+<p><span class="pagenum" id="Page341">[341]</span></p>
+
+<p>“This, then, is the mode of observing which has appeared to
+me the best, and by means of which we may obtain very great
+precision in measuring the intensity of two lights. I view, first,
+the two shadows in such a manner that both of them may be seen
+in succession from either side of the body which produces them,
+and at equal distances. For this purpose I use a good opera-glass.
+I alter the distance of the flames until in those two positions I perceive
+the differences (of the intensity in the shadows) to be in opposite
+directions. The distances of the lamps may then be considered
+as very nearly in the proper proportion for producing equal
+shadows, and to make them exactly so, the differences, which are
+observed on either side (of the centre line between them), should
+be equal; and, of course, the two shadows themselves, seen at
+one moment from either side of the opaque body, should be perfectly
+equal also.<a id="FNanchor85" href="#Footnote85" class="fnanchor">[85]</a> These three observations, which mutually serve
+to verify or correct each other, will lead, with a little practice,
+to very great precision in the result. We may, also, by using a
+narrow screen, bring the shadows sufficiently near to touch each
+other; the variations of the tints then become very small by any
+change of our position, and we may, in this case, rest content
+with observing them from one point. To get rid of large penumbrae
+which are always an obstacle in forming a right estimate of
+the tints of the shadows, I place the opaque body very near the
+screen.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote85" href="#FNanchor85" class="label">[85]</a> I prefer to view the exterior portions of both shadows from the central line itself,
+in which case the opaque rod stands between them, because, in this manner, I obtain a more
+correct comparison by the direct contrast of the surfaces than by successive views of them,
+however quickly taken.</p>
+
+</div><!--footnote-->
+
+<div class="container w45emmax" id="Fig97">
+
+<p class="caption">Fig. 97.</p>
+
+<img src="images/illo342.jpg" alt="Observation table">
+
+</div><!--container-->
+
+<p>“When we wish to make a great many observations, it is very
+convenient to mark divisions on the table (which carries the
+lights), in order to read off, by means of them, the distance of the
+lamps from the shadows which they illuminate. By this means,
+each observation need not occupy more than two minutes. I<span class="pagenum" id="Page342">[342]</span>
+generally use a table CC&#160;DD (<a href="#Fig97">fig. 97</a>), about two mètres long
+(6 feet 6 inches), by 80 centimètres wide (2 feet 8 inches). At one
+end I place the screen AB, covered with white paper, dull (or not
+glazed), and kept in a vertical plane by two small pieces P and Q.
+Through the point M, the centre of the opaque body, I draw two
+lines M<i>f</i> and M<i>g</i>, equally inclined to the central line <i>x</i>&#160;<i>y</i>, whose
+extremities <i>b′</i>, <i>a′</i> are the axes of the two shadows. These lines must
+be inclined in such a manner that the distance of the shadows may
+be a little less than the diameter of the opaque body, or so that
+they may actually touch each other, according to the mode of observing
+which you wish to follow. These lines M&#160;<i>f</i>, M&#160;<i>g</i> I divide
+into decimètres and centimètres, starting from the points <i>a′</i>, <i>b′</i> and
+over these lines I place the centres of the flames; the distance between
+the shadows remains always the same, whatever may be the
+distance of the lamps: to determine the distance of each lamp from
+the shadow which it illuminates, we ought, strictly speaking, to
+take the distance of the centre of the flame <i>b</i> from the point <i>a′</i>;
+but as the distance from the point <i>b</i> to the point <i>a′</i> differs little
+from the distance between the points <i>b</i> and <i>b′</i>, we assume the latter
+for the former, without causing any sensible error. That distance
+may be obtained very conveniently by taking the half of the
+sum of the distances of the two extremities <i>z</i> and <i>z′</i> of the diameter
+of the pedestal of the lamp. When the burner is not placed over
+the centre of the pedestal, we may suspend from it a small plummet,<span class="pagenum" id="Page343">[343]</span>
+whose point will touch some division and indicate the distance
+between the centre of the burner and the shadow.</p>
+
+<p>“When the lights are coloured, the shadows are coloured also,
+and it is then far more difficult to judge accurately of their intensity.
+They may in that case be much better seen from the
+point <i>x</i>, as the black opaque body which is interposed between them
+renders the difference of colour less sensible to the eye.</p>
+
+<p>“The opaque body M is a cylindric rod of iron, whose upper
+part is blackened in the flame of a lamp, in order to prevent the
+reflection which might interfere with the <i>sharpness</i> (<i>netteté</i>) of the
+shadows, and to make them more distinct when they are viewed
+from the point x.”<a id="FNanchor86" href="#Footnote86" class="fnanchor">[86]</a></p>
+
+<div class="footnote">
+
+<p><a id="Footnote86" href="#FNanchor86" class="label">[86]</a> Those who feel a curiosity to look farther into this subject may consult Count Rumford’s
+elaborate paper in the Phil. Trans. for 1794, p. 67.</p>
+
+</div><!--footnote-->
+
+<p>I shall make a few trifling additions to M. Peclet’s clear
+description of his excellent mode of measuring the intensity of
+lights. It is, of course, presumed throughout, that the centres of
+the flames should be on one level; and I have found it most convenient
+to place the lamps on small carriages with rollers, which
+are guided by means of fine strips of wood nailed along the table
+in the directions <i>g</i>M and <i>f</i>M, and carrying the divided scales of
+centimètres. This affords the means of making any slight change
+in the position of the lamps so easily, as entirely to avoid the disturbance
+of the flame which ensues from lifting the lamp and readjusting
+it in another position; and will, in practice, be found
+very convenient when many observations are to be made. I have
+already said that my own experience has satisfied me that, with
+the aid of a good opera-glass, the central observation of the two
+shadows, with the opaque rod between them, is by far the best, and
+conducts, at once, to a result which is confirmed by the observations
+of two assistants who watch the shadows at the same time
+on opposite sides of the table, and at equal distances from them. I
+have found it convenient in comparing lights, to cover the table
+with dull black linen cloth, and to surround it with curtains of the
+same material, hung from slender brackets, in such a manner<span class="pagenum" id="Page344">[344]</span>
+as to leave space for the observer to move freely round the table
+within them. The curtains prevent reflection from the walls of
+the chamber in which the experiments may be conducted, and
+also lessen the disturbing effects of currents of air. When a comparison
+of the <i>intensity</i>, and not of the <i>aggregate power</i> of two
+flames, is to be made, it is necessary to adopt the precaution of inclosing
+the lights in opaque boxes, with slits of equal area in each,
+placed on the same level, and so arranged, in reference to the flames,
+as to be directly opposite the brightest portion of each. After
+what has been said, it will be almost needless to add that the <i>quotient
+of the square of the greater observed distance divided by the
+lesser, is the ratio of the illuminating power of the two flames</i>. The
+most convenient mode of registering observations, and that which
+is generally practised, is in the form of a Table like the <span class="nowrap">following:—</span></p>
+
+<table class="standard">
+
+<tr class="bt2 bb">
+<th rowspan="2" class="bl2 brd">Trials.</th>
+<th colspan="2" class="brd">Distance.</th>
+<th colspan="2" class="brd">Squares of<br>Distances.</th>
+<th colspan="2" class="br2">Illuminating Power,<br>or<br>Quotient of Squares.</th>
+</tr>
+
+<tr class="bb">
+<th class="br">Lamp A.</th>
+<th class="brd">Lamp B.</th>
+<th class="br">Lamp A.</th>
+<th class="brd">Lamp B.</th>
+<th class="br">Lamp A.</th>
+<th class="br2">Lamp B.</th>
+</tr>
+
+<tr>
+<td class="bl2 brd">1</td>
+<td class="cntr br">143</td>
+<td class="cntr brd">140</td>
+<td class="cntr br">20,449</td>
+<td class="cntr brd">19,700</td>
+<td class="cntr br">1·00</td>
+<td class="cntr br2">0·958</td>
+</tr>
+
+<tr class="bb2">
+<td class="bl2 brd">2</td>
+<td class="cntr br">117</td>
+<td class="cntr brd">114</td>
+<td class="cntr br">13,689</td>
+<td class="cntr brd">12,996</td>
+<td class="cntr br">1·00</td>
+<td class="cntr br2">0·949</td>
+</tr>
+
+</table>
+
+<p>As a standard lamp by which to test others, I believe few will
+be found superior to the best Carcel lamp, which has a clockwork
+movement, and whose flame continues to increase in power for
+about four hours after it is lighted; after which it maintains its
+state permanently, until the supply of oil fails. This fact was verified
+by M. Peclet with the greatest care. “I took,” says he,
+“two similar lamps. They were lighted at the same time, and
+their relative intensities were measured. One was then extinguished,
+without touching the wick, and its clockwork movement
+was stopped. One hour afterwards, I set the clockwork in motion
+and relighted the lamp, but without touching the wick. It
+was found in the same state as at the first comparison, and I measured
+its intensity in reference to the first. Those experiments<span class="pagenum" id="Page345">[345]</span>
+I repeated every hour, and these are the results which I obtained.
+The lamp which I call No. 1, is that which remained continually
+burning; No. 2, is that which was only lighted during the continuance
+of the (successive) observations.”</p>
+
+<table class="standard">
+
+<tr class="bt2 bb">
+<th rowspan="2" colspan="2" class="bl2 brd">Times of<br>Observation.</th>
+<th colspan="2" class="br2">Intensities.</th>
+</tr>
+
+<tr class="bb">
+<th class="br">Lamp,<br>No. 1.</th>
+<th class="br2">Lamp,<br>No. 2.</th>
+</tr>
+
+<tr>
+<th class="bl2">H.</th>
+<th class="brd">M.</th>
+<th class="br">&#160;</th>
+<th class="br2">&#160;</th>
+</tr>
+
+<tr>
+<td class="bl2 br">&#8199;5</td>
+<td class="cntr brd">30</td>
+<td class="cntr br">100</td>
+<td class="cntr br2">100</td>
+</tr>
+
+<tr>
+<td class="bl2 br">&#8199;6</td>
+<td class="cntr brd">30</td>
+<td class="cntr br">103</td>
+<td class="cntr br2">100</td>
+</tr>
+
+<tr>
+<td class="bl2 br">&#8199;7</td>
+<td class="cntr brd">30</td>
+<td class="cntr br">106</td>
+<td class="cntr br2">100</td>
+</tr>
+
+<tr>
+<td class="bl2 br">&#8199;8</td>
+<td class="cntr brd">30</td>
+<td class="cntr br">110</td>
+<td class="cntr br2">100</td>
+</tr>
+
+<tr>
+<td class="bl2 br">&#8199;9</td>
+<td class="cntr brd">30</td>
+<td class="cntr br">117</td>
+<td class="cntr br2">100</td>
+</tr>
+
+<tr>
+<td class="bl2 br">10</td>
+<td class="cntr brd">30</td>
+<td class="cntr br">117</td>
+<td class="cntr br2">100</td>
+</tr>
+
+<tr>
+<td class="bl2 br">11</td>
+<td class="cntr brd">30</td>
+<td class="cntr br">117</td>
+<td class="cntr br2">100</td>
+</tr>
+
+<tr class="bb2">
+<td class="bl2 br">12</td>
+<td class="cntr brd">30</td>
+<td class="cntr br">117</td>
+<td class="cntr br2">100</td>
+</tr>
+
+</table>
+
+<p>This curious scale of increase in power, seems to be solely due
+to a peculiarity of the manner in which the lamp, that derives its
+supply of oil by clockwork, becomes heated; and the effect may be
+described as follows: The heating of the wicks, the chimney, and
+the oil in this burner, as in that of all other lamps, tends to increase
+the light; but, in an ordinary lamp, acting by a constant pressure,
+this <i>maximum</i> of heat is soon attained; whereas in the clockwork-lamp,
+into the burner of which the oil is thrown up by a pump,
+the whole of the oil in the cistern must reach its maximum temperature
+before the <i>best</i> effect of that lamp is produced. After this
+state has been reached, there is no disturbing influence at work,
+and the lamp burns steadily as long as the oil lasts.</p>
+
+<p>I have myself tried what may naturally appear to be the most
+simple mode of obtaining an unvarying standard-light, by employing
+a gas-burner, supplied from a gasometer under a constant pressure;
+but I found it very difficult to obtain satisfactory proof of the
+constancy of the pressure; and in a large town, where there are
+many burners around one, their lighting or extinction is found to<span class="pagenum" id="Page346">[346]</span>
+exercise a material influence in changing the condition of the flame.
+I must confess that I have always been disappointed in attempting
+to use a gas-flame as a standard of comparison.</p>
+
+<p>There are various dangers on the shores of Britain, more especially
+at the entrance of the great estuaries of England and also in
+Ireland, whose position is such as to put them beyond the reach of
+regular lighthouses. Sand-banks which are too soft to sustain a
+solid structure, and have too deep water on them to admit of the
+erection of screw-pile lighthouses, are often the sites for <span class="sidenote">Floating Lights.</span>
+mooring
+light-vessels, to guide the mariner into the entrance of some estuary,
+or enable him to thread his way through the mazes of <i>gats</i> and
+channels, which, even during the daytime, baffle the mariner, who
+sees no natural object on the low sandy shores of the neighbouring
+coast to help him to guess at his true position. The first Light-vessel
+moored on the coast of Great Britain, was that at the Nore
+in 1734. There are now no fewer than 26 floating lights on the
+coast of England.</p>
+
+<p>By the kindness of the Elder Brethren of the Corporation of
+Trinity House of Deptford Strond, I am enabled to give the following
+brief sketch of the nature and peculiarities of Floating
+Lights which was communicated to me by Mr Herbert, the secretary
+of the <span class="nowrap">Corporation:—</span></p>
+
+<p>“The annual expense of maintaining a Floating Light, including
+the wages and victualling of the crew, who are eleven in number,
+is, on an average, L.1000; and the first cost of such a vessel,
+fitted complete with lantern and lighting apparatus, anchors, cables,
+&amp;c., is nearly L.5000. The lanterns are octagonal in form, 5 feet
+6 inches in diameter; and, where fixed lights are exhibited, they
+are fitted with eight Argand lamps, each in the focus of a parabolic
+reflector of twelve inches diameter; but, in the revolving
+lights, four lamps and reflectors only are fitted. The greatest depth
+of water in which any light-vessel belonging to the Corporation of
+Trinity House of Deptford Strond at present rides, is about 40
+fathoms (which is at the station of the <i>Seven Stones</i> between the
+Scilly Islands and the coast of Cornwall).</p>
+
+<p><span class="pagenum" id="Page347">[347]</span></p>
+
+<p>“The Corporation’s light-vessels are moored with chain-cables
+of 1¹⁄₂ inch diameter, and a single mushroom anchor of
+32 cwt., in which cases the chain-cables are 200 fathoms in length;
+some of the said vessels are moored to <i>span-ground</i> moorings, consisting
+of 100 fathoms of chain to each arm, and a mushroom anchor
+of similar weight at the end of each; a riding cable of 150
+fathoms being in such cases attached to the centre ring of the
+ground chain. The tonnage and general dimensions of the light-vessel
+are given on the drawing of the lines.” (See <a href="#Plate29">Plate XXIX.</a>)</p>
+
+<p>Still lower in the scale of “signs and marks of the sea,” are
+<span class="sidenote">Beacons and
+Buoys.</span>
+Beacons and Buoys, which are used to point out those dangers
+which, either owing to the difficulty and expense that would attend
+the placing of more efficient marks to serve by night as well
+as by day, are necessarily left without lights, or which, from the
+peculiarity of their position, in passages too intricate for navigation
+by night, are, in practice, considered to be sufficiently indicated by
+day-marks alone. Beacons, as being more permanent, are preferred
+to Buoys; but they are generally placed only on rocks or banks
+which are dry at some period of the tide. On rocks, in exposed
+situations, the kind of Beacon used is generally that of squared
+masonry, secured by numerous joggles (as shewn at <a href="#Plate32">Plate XXXII.</a>);
+and in situations difficult of access, and in which works of uncompleted
+masonry could not be safely left during the winter season,
+an open framework of cast-iron pipes, firmly trussed and braced,
+and secured to the rock with strong <i>louis-bats</i>, is preferred. The
+details of this framework are shewn at <a href="#Plate30">Plates XXX.</a> and <a href="#Plate31">XXXI.</a>
+A stone Beacon of the form and dimensions shewn in <a href="#Plate32">Plate XXXII.</a>,
+may be erected for about L.700, and the iron Beacon shewn at
+<a href="#Plate30">Plate XXX.</a>, for about L.640. In less exposed places, where
+the bottom is gravel or hard sand, a conical form of Beacon, composed
+of cast-iron plates, united with flanges and screws, with rust-joints
+between them, is sometimes used. A Beacon of this kind is
+shewn at <a href="#Plate32">Plate XXXII.</a>, which can be erected for about L.400.</p>
+
+<p>Lastly, Buoys, which may be regarded as the least efficient<span class="pagenum" id="Page348">[348]</span>
+kind of mark, and as bearing the same relation to a Beacon that a
+Floating-light does to a Lighthouse, are used to mark by day <i>dangers</i>
+which are always covered even at low water, and also to line out
+the fair-ways of channels. They are, for the most part, of one of
+the three forms shewn in <a href="#Plate33">Plate XXXIII.</a>, viz., the <i>Nun-buoy</i>, in
+the form of a parabolic spindle, generally truncated at one end, so
+as to carry a mast or frame of cage-work, and loaded at the other
+end, so as to float in a vertical position; the <i>Can-buoy</i>, which is a
+conoid floating on its side; and, lastly, the <i>Cask-buoy</i>, which is a
+short frustum of a spindle truncated at both ends, but almost exclusively
+used for carrying the warps of vessels riding at moorings.
+Those buoys are of various sizes and differ in cost. Mast-buoys,
+from 10 to 15 feet in length, cost from L.23, 15s. to L.48; and
+those of the Ribble and the Tay, which are 21 and 24 feet long, cost
+respectively L.105 and L.79; the <i>Can-buoys</i> are from 5 to 8 feet
+long, and cost from L.13, 13s. to L.20, 5s. Large buoys are often
+built on <i>kneed</i> frames resembling the timbers of vessels. The Cask-buoy
+is generally 6 feet long, and costs L.22, 15s. All these buoys
+are formed of strong oaken barrel-staves, well hooped with iron
+rings, and shielded with soft timber; and the nozzle-pieces at the
+small end of the <i>Nun</i> and <i>Can</i> buoys are generally solid quoins
+of oak, formed with a <i>raglet</i> or groove to receive the ends of the
+staves. Much skill, on the part of the cooper, is required in heating
+and moulding the staves to the required form; and great care
+must be taken that they be of well-seasoned timber. Buoys are
+not caulked with oakum, but with dry flags closely compressed
+between the edges of the staves, which swell on being wet; and
+they are carefully proved by <i>steaming</i> them like barrels, to see if
+they be quite tight. Buoys are also formed of sheet-iron, in which
+case they are sometimes protected with fenders of timber; but they
+have been found more troublesome for transport, and, for most
+situations, are considered less convenient than those of timber.</p>
+
+<p>In the beginning of 1845, I suggested the idea of rendering
+Beacons and Buoys useful during night, by coating them with some<span class="pagenum" id="Page349">[349]</span>
+phosphorescent substance, or surmounting them with a globe of
+strong glass filled with such a preparation, whose combustion is
+very slow, and emits a dull whitish light and little heat. Some
+experiments were accordingly made by my suggestion; but I cannot
+add that any practically useful result has been obtained.</p>
+
+<p>In laying down Beacons or Buoys, their position is fixed, as
+may be seen in the <a href="#App8">Table</a> in the Appendix, either by the intersection
+of two lines drawn through two leading objects on the shore
+(the magnetic bearings of which are given for the sake of easy reference
+on the spot, in finding out the marks), or by means of the
+angles contained between lines drawn to various objects on the
+shore, which meet at the Beacon or Buoy from which they are
+measured by means of a sextant. In the latter case, the angles are
+always measured around the whole horizon, thus affording a check
+by the difference of their sum from 360°. The magnetic bearing
+of one of those lines is afterwards carefully ascertained, by means
+of the prismatic compass (if possible from one of the objects on
+shore, and if not, conversely from the Beacon or Buoy), so as to
+afford the means of translating the whole into magnetic bearings
+for the use of seamen. The buoys are moored, as shewn in <a href="#Plate33">Plate
+XXXIII.</a>, by means of chains and iron sinkers, with a sufficient
+allowance in the length of the chain to permit them to <i>ride</i> easily.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page350">[350-<br>351]<a id="Page351"></a></span></p>
+
+<h2 class="nobreak"><span class="partname app"><span class="gesp2">APPENDIX</span>.</span></h2>
+
+</div><!--chapter-->
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter" id="App1">
+
+<p><span class="pagenum" id="Page352">[352-<br>353]<a id="Page353"></a></span></p>
+
+<h3 class="nobreak"><span class="chapno">APPENDIX, No. I.</span><br>
+<span class="chapname">TABLE OF CO-ORDINATES OF AN HYPERBOLIC COLUMN WHOSE
+DIAMETER AT THE TOP = 16 FEET, AT THE BASE = 42 FEET,
+AND HEIGHT = 120·25 FEET.</span></h3>
+
+</div><!--chapter-->
+
+<p>The column is generated by the revolution of a rectangular hyperbola about
+one of its asymptotes. In the annexed figure (<a href="#Fig98">No. 98</a>), <i>a</i>&#160;<i>f</i> is the height of the column,
+<i>a</i>&#160;<i>c</i> and <i>f</i>&#160;<i>h</i> the radii of its base and top; and we have to determine the particular
+hyperbola which will pass through the points <i>c</i>, <i>h</i>.</p>
+
+<p>Putting <i>b</i>&#160;<i>e</i> = <i>x</i>; <i>e</i>&#160;<i>g</i> = <i>y</i>, the equation to the curve, referred to its asymptotes, is</p>
+
+<div class="formula">
+
+<p><i>x</i>&#160;<i>y</i> = <span class="divide"><span class="num"><i>a</i>²</span><span class="denom">2</span></span>,</p>
+
+</div><!--formula-->
+
+<p class="noindent">in which the value of the constant <span class="formula"><span class="divide"><span class="num"><i>a</i>²</span>
+<span class="denom">2</span></span></span> is to be found. For this purpose we have the
+conditions <i>a</i>&#160;<i>c</i> = 21; <i>f</i>&#160;<i>h</i> = 8; and <i>a</i>&#160;<i>f</i> = 120·25. Let the co-ordinates
+of the point <i>c</i> be <i>x′</i>, <i>y′</i>, and of <i>h</i>, <i>x″</i>, <i>y″</i>, then
+<i>y′</i> = 21; <i>y″</i> = 8; <i>x″</i> = <i>x′</i> + 120·25.</p>
+
+<div class="container w15emmax" id="Fig98">
+
+<p class="caption">Fig. 98.</p>
+
+<img src="images/illo353.jpg" alt="Hyperbola">
+
+</div><!--container-->
+
+<table class="formulas">
+
+<tr>
+<td class="rightpart"><span class="padr4">And since</span></td>
+<td class="midpart"><i>x′</i>&#160;<i>y′</i> =
+<span class="divide"><span class="num"><i>a</i>²</span><span class="denom">2</span></span> = <i>x″</i>&#160;<i>y″</i></td>
+</tr>
+
+<tr>
+<td class="rightpart"><span class="padr4">we have</span></td>
+<td class="midpart">21&#160;<i>x′</i> = 8&#160;(<i>x′</i> + 120·25)</td>
+</tr>
+
+<tr>
+<td class="rightpart"><span class="padr4">from which</span></td>
+<td class="midpart"><i>x′</i> = 74</td>
+</tr>
+
+<tr>
+<td class="rightpart"><span class="padr4">and</span></td>
+<td class="midpart"><span class="divide"><span class="num"><i>a</i>²</span><span class="denom">2</span></span>
+= <i>x′</i>&#160;<i>y′</i> = 74 × 21 = 1554.</td>
+</tr>
+
+<tr>
+<td class="rightpart"><span class="padr4">Therefore</span></td>
+<td class="midpart"><i>x</i>&#160;<i>y</i> = 1554.</td>
+</tr>
+
+</table>
+
+<p>Transferring the origin to <i>a</i>, <i>x</i> becomes <i>x</i> - <i>x′</i> = <i>x</i> - 74,
+and <i>y</i>&#160;(<i>x</i> - 74) = 1554, and the required equation by which
+the following Table was computed is, <i>y</i> = <span class="formula"><span class="divide"><span class="num">1554</span>
+<span class="denom"><i>x</i> - 74</span></span></span>.</p>
+
+<p><span class="pagenum" id="Page354">[354]</span></p>
+
+<p class="tabhead"><span class="smcap">Table</span> <i>of the Radii of the Hyperbolic Column at each foot of its
+Height</i>.</p>
+
+<table class="standard">
+
+<tr class="bt2 bb">
+<th class="bl2 br">Height.</th>
+<th class="brd">Radius.</th>
+<th class="br">Height.</th>
+<th class="brd">Radius.</th>
+<th class="br">Height.</th>
+<th class="brd">Radius.</th>
+<th class="br">Height.</th>
+<th class="br2">Radius.</th>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;0</td>
+<td class="cntr brd">21·000</td>
+<td class="cntr br">31</td>
+<td class="cntr brd">14·800</td>
+<td class="cntr br">62</td>
+<td class="cntr brd">11·426</td>
+<td class="cntr br">&#8199;93&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">9·305</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;1</td>
+<td class="cntr brd">20·720</td>
+<td class="cntr br">32</td>
+<td class="cntr brd">14·660</td>
+<td class="cntr br">63</td>
+<td class="cntr brd">11·343</td>
+<td class="cntr br">&#8199;94&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">9·250</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;2</td>
+<td class="cntr brd">20·447</td>
+<td class="cntr br">33</td>
+<td class="cntr brd">14·523</td>
+<td class="cntr br">64</td>
+<td class="cntr brd">11·261</td>
+<td class="cntr br">&#8199;95&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">9·195</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;3</td>
+<td class="cntr brd">20·182</td>
+<td class="cntr br">34</td>
+<td class="cntr brd">14·389</td>
+<td class="cntr br">65</td>
+<td class="cntr brd">11·180</td>
+<td class="cntr br">&#8199;96&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">9·141</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;4</td>
+<td class="cntr brd">19·923</td>
+<td class="cntr br">35</td>
+<td class="cntr brd">14·257</td>
+<td class="cntr br">66</td>
+<td class="cntr brd">11·100</td>
+<td class="cntr br">&#8199;97&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">9·088</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;5</td>
+<td class="cntr brd">19·671</td>
+<td class="cntr br">36</td>
+<td class="cntr brd">14·127</td>
+<td class="cntr br">67</td>
+<td class="cntr brd">11·021</td>
+<td class="cntr br">&#8199;98&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">9·035</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;6</td>
+<td class="cntr brd">19·425</td>
+<td class="cntr br">37</td>
+<td class="cntr brd">14·000</td>
+<td class="cntr br">68</td>
+<td class="cntr brd">10·944</td>
+<td class="cntr br">&#8199;99&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·983</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;7</td>
+<td class="cntr brd">19·185</td>
+<td class="cntr br">38</td>
+<td class="cntr brd">13·875</td>
+<td class="cntr br">69</td>
+<td class="cntr brd">10·867</td>
+<td class="cntr br">100&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·931</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;8</td>
+<td class="cntr brd">18·951</td>
+<td class="cntr br">39</td>
+<td class="cntr brd">13·752</td>
+<td class="cntr br">70</td>
+<td class="cntr brd">10·792</td>
+<td class="cntr br">101&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·880</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">&#8199;9</td>
+<td class="cntr brd">18·723</td>
+<td class="cntr br">40</td>
+<td class="cntr brd">13·632</td>
+<td class="cntr br">71</td>
+<td class="cntr brd">10·717</td>
+<td class="cntr br">102&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·830</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">10</td>
+<td class="cntr brd">18·500</td>
+<td class="cntr br">41</td>
+<td class="cntr brd">13·513</td>
+<td class="cntr br">72</td>
+<td class="cntr brd">10·644</td>
+<td class="cntr br">103&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·780</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">11</td>
+<td class="cntr brd">18·282</td>
+<td class="cntr br">42</td>
+<td class="cntr brd">13·397</td>
+<td class="cntr br">73</td>
+<td class="cntr brd">10·571</td>
+<td class="cntr br">104&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·730</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">12</td>
+<td class="cntr brd">18·070</td>
+<td class="cntr br">43</td>
+<td class="cntr brd">13·282</td>
+<td class="cntr br">74</td>
+<td class="cntr brd">10·500</td>
+<td class="cntr br">105&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·681</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">13</td>
+<td class="cntr brd">17·862</td>
+<td class="cntr br">44</td>
+<td class="cntr brd">13·170</td>
+<td class="cntr br">75</td>
+<td class="cntr brd">10·430</td>
+<td class="cntr br">106&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·633</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">14</td>
+<td class="cntr brd">17·659</td>
+<td class="cntr br">45</td>
+<td class="cntr brd">13·059</td>
+<td class="cntr br">76</td>
+<td class="cntr brd">10·360</td>
+<td class="cntr br">107&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·586</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">15</td>
+<td class="cntr brd">17·461</td>
+<td class="cntr br">46</td>
+<td class="cntr brd">12·950</td>
+<td class="cntr br">77</td>
+<td class="cntr brd">10·291</td>
+<td class="cntr br">108&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·539</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">16</td>
+<td class="cntr brd">17·267</td>
+<td class="cntr br">47</td>
+<td class="cntr brd">12·843</td>
+<td class="cntr br">78</td>
+<td class="cntr brd">10·224</td>
+<td class="cntr br">109&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·492</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">17</td>
+<td class="cntr brd">17·077</td>
+<td class="cntr br">48</td>
+<td class="cntr brd">12·738</td>
+<td class="cntr br">79</td>
+<td class="cntr brd">10·157</td>
+<td class="cntr br">110&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·446</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">18</td>
+<td class="cntr brd">16·891</td>
+<td class="cntr br">49</td>
+<td class="cntr brd">12·634</td>
+<td class="cntr br">80</td>
+<td class="cntr brd">10·091</td>
+<td class="cntr br">111&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·400</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">19</td>
+<td class="cntr brd">16·710</td>
+<td class="cntr br">50</td>
+<td class="cntr brd">12·532</td>
+<td class="cntr br">81</td>
+<td class="cntr brd">10·026</td>
+<td class="cntr br">112&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·355</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">20</td>
+<td class="cntr brd">16·532</td>
+<td class="cntr br">51</td>
+<td class="cntr brd">12·432</td>
+<td class="cntr br">82</td>
+<td class="cntr brd">&#8199;9·962</td>
+<td class="cntr br">113&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·310</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">21</td>
+<td class="cntr brd">16·358</td>
+<td class="cntr br">52</td>
+<td class="cntr brd">12·333</td>
+<td class="cntr br">83</td>
+<td class="cntr brd">&#8199;9·898</td>
+<td class="cntr br">114&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·266</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">22</td>
+<td class="cntr brd">16·188</td>
+<td class="cntr br">53</td>
+<td class="cntr brd">12·236</td>
+<td class="cntr br">84</td>
+<td class="cntr brd">&#8199;9·835</td>
+<td class="cntr br">115&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·222</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">23</td>
+<td class="cntr brd">16·021</td>
+<td class="cntr br">54</td>
+<td class="cntr brd">12·141</td>
+<td class="cntr br">85</td>
+<td class="cntr brd">&#8199;9·774</td>
+<td class="cntr br">116&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·179</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">24</td>
+<td class="cntr brd">15·857</td>
+<td class="cntr br">55</td>
+<td class="cntr brd">12·046</td>
+<td class="cntr br">86</td>
+<td class="cntr brd">&#8199;9·712</td>
+<td class="cntr br">117&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·136</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">25</td>
+<td class="cntr brd">15·697</td>
+<td class="cntr br">56</td>
+<td class="cntr brd">11·954</td>
+<td class="cntr br">87</td>
+<td class="cntr brd">&#8199;9·652</td>
+<td class="cntr br">118&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·094</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">26</td>
+<td class="cntr brd">15·540</td>
+<td class="cntr br">57</td>
+<td class="cntr brd">11·862</td>
+<td class="cntr br">88</td>
+<td class="cntr brd">&#8199;9·593</td>
+<td class="cntr br">119&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·052</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">27</td>
+<td class="cntr brd">15·386</td>
+<td class="cntr br">58</td>
+<td class="cntr brd">11·773</td>
+<td class="cntr br">89</td>
+<td class="cntr brd">&#8199;9·534</td>
+<td class="cntr br">120&#8200;&#8199;&#8199;</td>
+<td class="cntr br2">8·010</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">28</td>
+<td class="cntr brd">15·235</td>
+<td class="cntr br">59</td>
+<td class="cntr brd">11·684</td>
+<td class="cntr br">90</td>
+<td class="cntr brd">&#8199;9·476</td>
+<td class="cntr br">120·25</td>
+<td class="cntr br2">8·000</td>
+</tr>
+
+<tr>
+<td class="cntr bl2 br">29</td>
+<td class="cntr brd">15·087</td>
+<td class="cntr br">60</td>
+<td class="cntr brd">11·597</td>
+<td class="cntr br">91</td>
+<td class="cntr brd">&#8199;9·418</td>
+<td class="cntr br">...</td>
+<td class="cntr br2">...</td>
+</tr>
+
+<tr class="bb2">
+<td class="cntr bl2 br">30</td>
+<td class="cntr brd">14·942</td>
+<td class="cntr br">61</td>
+<td class="cntr brd">11·511</td>
+<td class="cntr br">92</td>
+<td class="cntr brd">&#8199;9·361</td>
+<td class="cntr br">...</td>
+<td class="cntr br2">...</td>
+</tr>
+
+</table>
+
+<p><span class="pagenum" id="Page355">[355]</span></p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter" id="App2">
+
+<h3 class="nobreak"><span class="chapno">APPENDIX, No. II.</span><br>
+<span class="chapname">NOTES ON THE MANUFACTURE OF PARABOLOÏDAL REFLECTORS,<br>
+<span class="fsize90">from Information furnished by Mr <span class="smcap">James Murdoch, of the Northern Lights
+Service</span>.</span></span></h3>
+
+</div><!--chapter-->
+
+<div class="container right w08emmax" id="Fig99">
+
+<p class="caption">Fig. 99.</p>
+
+<img src="images/illo355.jpg" alt="Mallet">
+
+</div><!--container-->
+
+<p>The reflector-plate consists of virgin-silver and the purest copper (from
+the ingot), in the proportion of 6 oz. of silver to 16 oz. of copper. The two
+metals are in pieces, forming a flat parallelopepid of about nine inches of
+surface. Being first thoroughly scraped and cleared from rust with a file,
+they are tied together with wire and placed in the furnace, where they are
+united by means of a flux composed of burnt borax and nitre, mixed to the
+consistence of cream. Their thickness is sufficient to admit of their being
+repeatedly passed through the rolling-mill, so as at last to come out a plate
+twenty-eight inches square. Every time it is passed through the rollers,
+the plate is annealed in the furnace before being again pressed. It is then
+cut into a circular disc ready for working; and great care should be taken
+to keep the metal perfectly clean during the whole of the hammering and
+polishing processes. The first step towards forming the plate to the curve,
+is to raise the back or copper side to a slight convexity by beating, with the
+boxwood mallet (<a href="#Fig99">fig. 99</a>), rounded at each end, <i>c</i> and <i>d</i>, its inner or silver
+side upon a large block of beechwood, of a form slightly concave. This
+beating is begun at the edge of the plate, and gradually reaches the centre.
+After the disc has been raised to the proper height on the wooden block,<span class="pagenum" id="Page356">[356]</span>
+the next step is to take it to the <i>horse</i> (<a href="#Fig103">fig. 103</a>, opposite page), where it is
+beaten with the wooden mallet (<a href="#Fig100">fig. 100</a>), its concave face being in contact
+with the bright steel-head <i>a</i> (<a href="#Fig103">fig. 103</a>), until it has nearly reached the proper
+height for the reflector, for which the workman has a gauge or mould to guide
+him; in this course of <i>raising</i>, as it is called, the <i>peened</i> face
+<i>b</i>&#160;<i>a</i>&#160;<i>b</i> (<a href="#Fig100">fig. 100</a>) is
+first used, and then recourse is had to the opposite or flat face for smoothing
+it after being raised. In this last course of raising, as well as in the process
+of smoothing the reflector all over, the workman bestrides the <i>horse</i>.</p>
+
+<div class="container w45emmax">
+
+<div class="split2575">
+
+<div class="left2575">
+
+<div class="container" id="Fig100">
+
+<p class="caption">Fig. 100.</p>
+
+<img src="images/illo356a.jpg" alt="Mallet">
+
+</div><!--container-->
+
+</div><!--left-->
+
+<div class="right2575">
+
+<div class="container" id="Fig101">
+
+<p class="caption">Fig. 101.</p>
+
+<img src="images/illo356b.jpg" alt="Mould">
+
+</div><!--container-->
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+</div><!--container-->
+
+<p>During the process of raising with the peened side of the mallet, an external
+mould FGHF (<a href="#Fig101">fig. 101</a>), with a needle-point P, at its vertex, is applied,
+to indicate its proper position with reference to the mould; and allowance
+is made on the height and diameter of the reflector to meet the expansion
+of the metal during the <i>hard-hammering</i> which is to follow. After
+each course of the raising with the wooden mallets, the reflector must be
+annealed in the following manner:—The reflector is first damped with
+clean water, and its surface dusted over with a powder, composed of one
+pint of powdered charcoal to one ounce of saltpetre, which is applied by
+means of a thin flannel bag. The reflector is then put on a clear charcoal
+fire, where it is turned round as the powder flies off, which is an indication
+that the metal is duly heated. Over-heating is very injurious. When removed
+from the fire, the reflector is plunged into a large tub, containing
+what is called the <i>pickle</i>, which is a solution of one quart of vitriol in five
+or six gallons of water. After this it is washed with clean water, and
+scoured with Calais sand.</p>
+
+<p>The next step is to put the reflector, thus raised <i>nearly</i> to its true form,
+into an iron stool, where a small hole being drilled in its vertex, a circle
+is described from this point with a beam-compass, so as to cut the paraboloïd
+to the proposed size.</p>
+
+<p><span class="pagenum" id="Page357">[357]</span></p>
+
+<div class="container">
+
+<div class="split1585">
+
+<div class="left1585">
+
+<div class="container notopbot w05emmax" id="Fig102">
+
+<p class="caption">Fig. 102.</p>
+
+<img src="images/illo357a.jpg" alt="Planishing hammer">
+
+</div><!--container-->
+
+</div><!--left1585-->
+
+<div class="right1585">
+
+<div class="split8515">
+
+<div class="left8515">
+
+<div class="container notopbot w40emmax" id="Fig103">
+
+<p class="caption">Fig. 103.</p>
+
+<img src="images/illo357b.jpg" alt="Planishing a mirror">
+
+</div><!--container-->
+
+</div><!--left8515-->
+
+<div class="right8515">
+
+<div class="container notopbot w05emmax" id="Fig104">
+
+<p class="caption">Fig. 104.</p>
+
+<img src="images/illo357c.jpg" alt="Lighter hammer">
+
+</div><!--container-->
+
+</div><!--right8515-->
+
+</div><!--split8515-->
+
+</div><!--right1585-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split1585-->
+
+</div><!--container-->
+
+<div class="container w30emmax" id="Fig105">
+
+<p class="caption">Fig. 105.</p>
+
+<img src="images/illo357d.jpg" alt="Checking shape of lens">
+
+</div><!--container-->
+
+<p>The reflector is next <i>hard-hammered</i> all over (or <i>planished</i>, as it is technically
+termed) on the bright steel-head <i>a</i> (<a href="#Fig103">fig. 103</a>), with the planishing
+hammer (<a href="#Fig102">fig. 102</a>); and to facilitate working, the reflector is slung in a
+flexible frame SS, and counterbalanced by a weight <i>w</i>, hanging by a cord
+over the pulleys <i>p</i>&#160;<i>p</i>. When the reflector is all <i>planished</i> over, the next
+process is the <i>smoothing</i>, which is done on the steel-head <i>a</i>, with a lighter
+hammer (<a href="#Fig104">fig. 104</a> ), muffled with fine parchment at each end. After it is
+smoothed comes the <i>finishing</i>, or what is called the <i>filling up to the mould</i>.
+This is a tedious process, and the workman requires continually to have recourse
+to the marble table at M, on which he lays the reflector, as shewn
+in <a href="#Fig105">fig. 105</a>, and applies to successive portions of its surface the mould <i>g</i>&#160;<i>n</i>,
+which has a needle-point centred at <i>n</i>,
+in the small hole drilled in the vertex.
+During this examination, he marks
+with a fine slate-pencil those portions
+of the reflector which do not meet the
+mould <i>g</i>&#160;<i>n</i>. The parts, so marked, are
+gently gone over with the muffled
+hammer, until every point touches the
+mould. This last process requires
+great caution; for, if any part of the
+surface be raised above the gauge, it
+is hardly possible to remedy it. Such
+a mistake, indeed, can only be corrected by annealing the reflector afresh,<span class="pagenum" id="Page358">[358]</span>
+and bringing it back to the true form with the mallet; but reflectors so
+<i>cobbled</i> are never good. The table M (<a href="#Fig105">fig. 105</a>) rests on a square box C,
+in which the tools and moulds are kept.</p>
+
+<div class="container w35emmax" id="Fig106">
+
+<p class="caption">Fig. 106.</p>
+
+<img src="images/illo358.jpg" alt="Apparatus to adjust burner">
+
+</div><!--container-->
+
+<p>When thus finished from the hammer, the reflector is put into the apparatus
+shewn in <a href="#Fig106">fig. 106</a>, which is placed at the end of a long dark corridor.
+RR is a wooden frame fixed to the wall with projecting brackets at
+K, which carry the reflector, fixed at E, E, by means of screws, so as always
+to have a definite position with reference to the bracket B, which
+carries the lamp and its fountain <i>f</i>, so arranged that its flame may admit
+of perfect adjustment to the point which <i>ought</i> to be the focus of the reflector.
+For the purpose of this
+adjustment, S shews screws for
+raising and depressing the level
+of the burner; and the lines
+or marks M, M′ shewn at the
+sockets J being brought <i>into
+line</i>, regulate the <i>position</i> of
+the burner in <i>the plane of the
+focus</i>, after it has been raised
+to the level of that plane by
+means of the screws at S. The
+lamp being lighted and thus
+properly placed, its effect on the
+reflector’s surface is observed by
+some one stationed at a convenient distance; and if the whole surface appear
+luminous, the instrument is considered fit for polishing; but if any
+dark spaces be found in it, the whole reflector must be again carefully tested
+by means of the mould, and the defective parts remedied in the manner
+above described.</p>
+
+<p>The next step is to turn over the edge of the reflector, so as to stiffen it.
+For this purpose it is placed in the matrix P′P′ (<a href="#Fig107">fig. 107</a>), and the needle-point
+at V is adjusted by the screw at D, so as just to enter the small hole
+formerly drilled in the vertex of the reflector. The die-plate PP (which is
+worked by means of the arms AA, which turn the screw S) then descends
+and presses the edge <i>over</i>, which is finished with a finely polished tool C,
+revolving round the axis of the instrument, which coincides with the centre
+of the matrix and die. In order to ensure a steady vertical movement of
+the die-plate PP, cross-arms FF, which are provided with sockets HH,<span class="pagenum" id="Page359">[359]</span>
+which slide over the rods GG, GG, are added to prevent any lateral shake
+or derangement. The whole frame is stiffened by the cross-head in which
+the screw S works.</p>
+
+<div class="container">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<div class="container w20emmax" id="Fig107">
+
+<p class="caption">Fig. 107.</p>
+
+<img src="images/illo359a.jpg" alt="Matrix for edge stiffening">
+
+</div><!--container-->
+
+</div><!--left-->
+
+<div class="right5050">
+
+<div class="container w20emmax" id="Fig108">
+
+<p class="caption">Fig. 108.</p>
+
+<img src="images/illo359b.jpg" alt="Cast-iron polishing table">
+
+<p class="caption" id="Fig109">Fig. 109.</p>
+
+<img src="images/illo359c.jpg" alt="Cast-iron polishing table">
+
+</div><!--container-->
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+</div><!--container-->
+
+<p>The reflector is then placed on the circular cast-iron table (<a href="#Fig108">figs. 108</a>,
+<a href="#Fig109">109</a>), to which it is attached by the clamp-screws S, S. In this position,
+the bizzle W (<a href="#Fig108">fig. 108</a>) and back-belt NAN (<a href="#Fig109">fig. 109</a>), are soldered on. After
+this the reflector is ready for being finally polished; for which purpose,
+it is placed in a <i>chaise percée</i>, padded round the edges, and is first scoured
+all over with a piece of pure charcoal of hard wood, and next with a mixture
+of Florence oil and finely washed rottenstone, applied by means of a
+large ball of superfine cloth. It is then carefully cleansed with a piece of
+fine flannel dipped in Florence oil, and afterwards dusted over with the<span class="pagenum" id="Page360">[360]</span>
+powder of well washed whiting, and wiped out with a soft cotton cloth.
+Lastly, it is carefully rubbed by the naked hand, with finely washed
+rouge and clean water, and wiped with a smooth chamois skin. In all the
+polishing and cleansing processes, some skill in manipulation is required,
+as the hand is generally moved in such a manner as to describe successive
+circles with their planes parallel to the lips of the reflector, and their
+centres in the axis of the generating curve.</p>
+
+<p>The prices paid to the workmen for the various departments of the reflector-making
+are generally as <span class="nowrap">follows:—</span></p>
+
+<table class="standard">
+
+<tr>
+<td class="text"><span class="padr4">Raising the plate to the curve, with the wooden mallet,</span></td>
+<td class="numbers">L.0</td>
+<td class="numbers">10</td>
+<td class="numbers">0</td>
+</tr>
+
+<tr>
+<td class="text"><span class="padr4">Hammering and smoothing to the mould,</span></td>
+<td class="numbers">1</td>
+<td class="numbers">5</td>
+<td class="numbers">0</td>
+</tr>
+
+<tr>
+<td class="text"><span class="padr4">Finishing in the die, and putting on bizzle and back-belt,</span></td>
+<td class="numbers">0</td>
+<td class="numbers">6</td>
+<td class="numbers">0</td>
+</tr>
+
+<tr>
+<td class="text"><span class="padr4">Polishing,</span></td>
+<td class="numbers bb">0</td>
+<td class="numbers bb">12</td>
+<td class="numbers bb">0</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="numbers">L.2</td>
+<td class="numbers">13</td>
+<td class="numbers">0</td>
+</tr>
+
+</table>
+
+<p>The prices paid to the manufacturer were for the large reflectors of 24
+inches aperture, L.43; for the small ones of 21 inches, L.31, 12s. The lamp
+with the sliding-carriage, required for each, costs L.6.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter" id="App3">
+
+<p><span class="pagenum" id="Page361">[361]</span></p>
+
+<h3 class="nobreak"><span class="chapno">APPENDIX, No. III.</span><br>
+<span class="chapname">NOTES ON THE GRINDING OF THE VARIOUS PIECES COMPOSING
+THE INSTRUMENTS USED IN DIOPTRIC LIGHTHOUSES, CHIEFLY
+FROM NOTES FURNISHED BY M. THEODORE LETOURNEAU OF
+PARIS.</span></h3>
+
+</div><!--chapter-->
+
+<p>The glass used in all the parts of the optical apparatus of the dioptric
+Lighthouses is that of St Gobain, whose index of refraction is 1·51.</p>
+
+<p>As well on account of the difficulty experienced in producing at all
+times regular castings of glass from the moulds, as in order to compensate
+for the frequent accidents, which occur in the first application of the rubbers
+to the inequalities of the surface of the glass, the castings, whether for
+rings of lenses or prisms, are made from moulds, exceeding the intended size
+of the finished pieces by <i>one-eighth part</i>.</p>
+
+<p>We shall take as an example, which is well calculated to illustrate the
+difficulties of the grinding process, one of the prismatic rings of a Catadioptric
+Light of the first order. The first operation will be to take off the rough
+arris at the angles of the pieces as they come from the moulds, and to reduce
+to equality the length of each of the four quadrantal prisms or segments by
+removing from each the quantity that may be necessary to make those
+four pieces, when placed on a circle, exactly equal to that of the finished
+zones. Each of them must have an excess of material at the various surfaces
+just sufficient to insure
+the rubber having scope
+enough to remove all the
+flaws or defects of the two
+surfaces to be first ground,
+which are the (concave and
+convex) refracting faces of
+the zone (the sides AC and
+BC in the <a href="#App4">Table</a> in the Appendix,
+No. IV.)</p>
+
+<div class="container w35emmax" id="Fig110">
+
+<p class="caption">Fig. 110.</p>
+
+<img src="images/illo361.jpg" alt="Lens pieces on lathe table">
+
+</div><!--container-->
+
+<p>The pieces must be
+placed end to end on the
+horizontal plane or table of
+the lathe at AA (<a href="#Fig110">fig. 110</a>),
+and must rest on the exterior arris A of the reflecting side, on which arris<span class="pagenum" id="Page362">[362]</span>
+there is ground a narrow plane whose width is proportionate to the projection
+of the outer edge beyond the inner edge of the zone, <i>foreshortened</i> by the
+<i>bevel</i> or inclination of the reflecting side, when resting (as in <a href="#Fig110">fig. 110</a>) on
+the circular iron belt, which is screwed to the table of the lathe provided for
+its reception. This narrow plane at the arris A should be sufficient to give
+the prism a solid and regular bearing on the circular iron belt. In this figure
+(<a href="#Fig110">fig. 110</a>) <i>a</i>&#160;<i>b</i> is the vertical axis of the lathe, <i>n</i> the point from which the co-ordinates
+for O, the grinding centre for the exterior <i>concave</i> refracting surface
+AC, are measured, and <i>e</i>&#160;AC the arc swept by the grinding surface. Conversely,
+<i>n′</i> is the origin of the co-ordinates for the grinding centre O of the
+interior <i>convex</i> refracting surface BC, and <i>e</i>&#160;CB the arc swept by its grinding
+surface. Some skill is required in fixing the prism on the belt, for, on the
+one hand, there is an obstacle to correct workmanship from the dragging motion
+of the platform, and, on the other, by the unequal subdivision of the
+weight of the glass, which should be nearly balanced. This narrow plane
+being perfectly adjusted for all the segments so as to bed them quite level,
+the circular iron belt on which the ring should be ground, is placed on its
+platform, in the manner represented in the <a href="#Fig110">figure</a>. It should be as truly
+levelled as possible, otherwise all the subsequent operations will be deranged
+by it. This iron belt is heated by means of heating <i>pans</i>; and the
+degree of heat may be practically judged of by the ebullition of drops of
+water let fall on it. The segments of glass are also at the same time placed
+in a stove heated with steam, and are generally raised to about 120° centigrade.
+The difference between the time required for the two operations of
+heating the iron belt and the glass segments is employed in laying or bedding
+a quantity of cement on the reflecting side of the segment, so as to fill up the
+angular space between the glass and the iron belt, and also to serve as a seat
+for the segment in the manner shewn in <a href="#Fig110">fig. 110</a>. This operation is performed
+on a plane surface, in order that the lower part of the mastic may be precisely
+on a level with the narrow plane already ground on the outer arris of
+the reflecting side. After being sure that the heat is equally spread over
+every part of the circular iron belt, the segment is arranged on it; and the
+workman must, at this juncture, exert all his skill in placing the parts of
+the segment in a position nearly concentric with the belt, or in a truly circular
+form, making due allowance, however, for the inequalities existing at
+various parts of the rough material, and at the same time taking care that
+there should be an interval of at least two millimètres (or about ¹⁄₁₂th inch)
+between the ends of each of the two adjacent segments. Without this interval
+the heat evolved during the polishing would either dilate the glass so<span class="pagenum" id="Page363">[363]</span>
+much as to cause the ends of the segments to fly into splinters, or make it
+needful to remove the zone before this should take place, the inevitable consequence
+of which would be the fracture of the pieces. Those intervals between
+the segments are filled with statuary’s plaster, which must be carefully
+washed and brushed at each change of the emery employed in grinding.</p>
+
+<p>The exterior diameter of the circular iron belt must be precisely equal
+to that of the ring, because, if larger, the free movement of the rubbers to
+and fro on the concave refracting surface AC (<a href="#Fig110">fig. 110</a>) could not take place.</p>
+
+<p>By what is already said, it will be obvious that the grinding process is
+begun at the refracting sides AC and BC, and a few words will shew that this
+could hardly be otherwise. If a commencement be made on the reflecting
+side, which appears at first sight more natural, the consequence is obvious.
+Having provided for an excess of material in every direction, the segment must
+consequently be larger than it will be when finished; and the surfaces therefore
+cannot be true and perfect, except they be ground throughout their entire
+segmental section, from their centres of curvature, in reference to some given
+apex of the generating triangle. Now, if the reflecting side were finished
+first, it might continue to possess this excess of size after being finished, and
+would, therefore, afford no accurate starting point for the grinding of the
+other surfaces; it would also present no <i>surface</i> or narrow plane for resting
+firmly on the iron belt, but would then depend merely on its own finished
+plane, which, being curved and considerably
+inclined, would not give a solid
+bearing for the glass. The other mode
+of commencing with the two refracting
+sides, on the contrary, gives a solid
+bearing on the narrow plane already
+ground on the reflecting side at A; and
+after these surfaces have been ground,
+and the segments inverted (as shewn
+in <a href="#Fig111">fig. 111</a>), the outer edge of this narrow
+plane at the arris A, which has
+been fully defined by the intersection
+of the finished surface AC just ground,
+and also the apex at C, which has
+been determined by the intersection of
+AC and BC, combine to fix an accurate starting point for the rubber, in
+grinding the reflecting surface AB.</p>
+
+<div class="container w30emmax" id="Fig111">
+
+<p class="caption">Fig. 111.</p>
+
+<img src="images/illo363.jpg" alt="Inverted ring segment">
+
+</div><!--container-->
+
+<p><span class="pagenum" id="Page364">[364]</span></p>
+
+<h4><i>Dressing off the rough part of the Ring.</i></h4>
+
+<p>The ring is generally reduced from the rough state by means of fixed rubbers,
+the adjustment of which is more easily regulated than that of the moveable
+beam or radius of the arc, which is used to give the exact curvature of
+the surface. Those fixed rubbers are 150 millimètres (nearly 6 inches) wide,
+by 200 millimètres (nearly 8 inches) long, and are of cast-iron. Three such
+rubbers are placed at equidistant points of the circle. Two cutters of sheet-iron
+attached to arms placed vertically (as are also those which carry the
+rubbers), and moving in grooves radiating towards the centre of the lathe,
+so as to admit of adjustment to suit the varying radii of the zones, serve
+gradually to abrade the outer and inner arrises of the segments, so as to prevent
+the splintering to which, from becoming too sharp, those arrises, without
+this precaution, would be liable. Those rubbers are, besides, fixed by stems
+to frames, in the form of quadrants of the circle, which allow of a change
+in the direction of the planes, as occasion may require.</p>
+
+<p>Instead of the siliceous sand formerly used, the powder of pounded freestone
+is employed, as it is found to wear the tools less, and to form a better
+preparation for the subsequent grinding operations. It is easy to conceive
+that the action of the fixed rubbers necessarily produces ruts or inequalities
+in the circular direction. The operation of rough dressing, therefore, is
+not finished until, when those first rubbers are removed, the surfaces of the
+segments have been subject, for the required time, to the action of moveable
+rubbers, attached to arms working as radii of curvature, in a plane at right
+angles to the horizontal movement of the lathe, which carries the zones.</p>
+
+<h4><i>The Emery Grinding.</i></h4>
+
+<p>The form of the segment should be nearly perfect, after the rough grinding
+is finished. The lathe and the zone are then subjected to an extremely
+careful washing. Every place where the stone-powder might adhere is
+dusted. The radius of curvature is verified afresh, agreeably to the co-ordinates
+(<a href="#App4">Appendix, No. IV.</a>); and emery is used instead of powdered stone;
+beginning with that called No. 1, which is drawn after suspension in water
+for one minute. Brushes are used for spreading the emery on the surface
+of the glass. The quantity ought always to be sufficient to prevent the direct
+contact of the cast-iron rubber with the glass. Splintering or scratching,<span class="pagenum" id="Page365">[365]</span>
+which cannot be easily effaced, may result from the neglect of this precaution.</p>
+
+<p>Practice alone, and an eye duly trained by continual experience, can determine
+the point of time at which each kind of emery must be discontinued.
+The celerity of the work depends on circumstances very difficult to appreciate,
+such as the amount of the pressure of the rubbers, or the degree of
+accuracy with which the radius of curvature has been adjusted, during the
+rough grinding. Each kind of emery in succession thus corrects the form
+of the zone and refines the grain of the surface of the glass; and each change
+to a fresh material requires the same attention to cleanliness, so as to remove
+every trace of the substance last used in grinding, and thus to give each
+successive process its full and legitimate effect. The <i>douci</i> is the <i>fifth</i> and
+<i>last</i> kind of emery which precedes the <i>polish</i>. It is drawn off after ten
+minutes’ suspension in water, and is extremely fine. Before applying it, the
+greatest care is necessary to insure cleanliness, as a single grain of any of
+the preceding kinds of emery might cause scratches, which the polish cannot
+remove.</p>
+
+<h4><i>The Polish.</i></h4>
+
+<p>The same considerations which induce the workman most carefully to
+cleanse the lathe and everything connected with it, before employing the last
+emery called the <i>douci</i>, are still more urgent in the case of the final <i>polish</i>.
+The only change which is made at this last stage of the work is to replace
+the first rubber by a new one, both longer and wider by about 50 millimètres
+(nearly 2 inches). On its lower face is attached with cement a piece of
+soft carpet, whose edges are fixed to the rubber by means of flat bands of iron,
+attached with screws. This security, added to that given by the cement, is
+necessary to fit it to resist the great pressure it must sustain. A practical
+question, which experience alone can resolve, occurs at this stage, as the
+operation of polishing may, in the hands of unskilful persons, be so inopportunely
+commenced, as to make that work almost endless. Thus, the mere
+circumstance of spreading at the beginning too thick layers of rouge, or
+using unsuitable kinds of carpet, would cut scratches in the glass, and thus
+perhaps make it necessary to return to the use of the emery called <i>douci</i>.
+Sometimes, also, if the carpets be not washed at the very time of using them,
+scratches are formed by the dust which they may contain. This shews, that
+the use of rouge should be rather sparing than otherwise, at the commencement
+of the polish; and that the carpet-cloths should be brushed and washed<span class="pagenum" id="Page366">[366]</span>
+<i>twice</i> rather than <i>once</i>. In all cases, the quality of the carpet forms an important
+element in the success of the working.</p>
+
+<p>When the <i>polish</i> is finished, the ring is detached from the circular belt,
+simply by the tap of a hammer, on the inner edge of the circle. The division
+of the zones (which are quarters of the circle) into <i>eighths</i>, is done by means
+of a sawing machine consisting of a flat copper-wheel, one-half millimètre
+(¹⁄₅₀th inch) in thickness, attached to an arm with a counterpoise. This
+wheel descends and cuts the zone by means of emery, which is continually
+applied to it; the direction of the cut is radial. The two halves of the zone
+are detached from each other, as soon as their weight exceeds the resistance
+of the part which remains to be sawn.</p>
+
+<h4><i>Adjustment of the Prisms.</i></h4>
+
+<p>The adjustment of the prisms in the frames, involves an operation which
+is not without risk. Much care is required in handling the sharp arrises
+of the glass, which are very acute and delicate and at the same time lie in
+a curved direction, which makes them liable to be splintered in the hands
+of unskilful persons.</p>
+
+<p>With the exception of the plane vertical surfaces of the annular lenses,
+and the central band and rings of the dioptric belts of fixed lights, which are
+ground by means of vertical rubbers with a reciprocating movement, every
+other plane surface is executed by hand on a flat table.</p>
+
+<h4><i>Composition of the Cement for fixing the glass on the lathe.</i></h4>
+
+<table class="standard fsize90">
+
+<tr>
+<td class="numbers">8</td>
+<td class="text">parts Swedish pitch.</td>
+</tr>
+
+<tr>
+<td class="numbers">1</td>
+<td class="text">do. of wood ashes.</td>
+</tr>
+
+</table>
+
+<p>The whole is heated in an iron pot until fully liquified and thoroughly
+mixed. This cement is used almost in a state of ebullition, so that it
+cannot be handled without the precaution of continually dipping the hands
+in cold water.</p>
+
+<h4><i>Composition of cement used for the adjustment of the pieces of glass which
+touch each other.</i></h4>
+
+<table class="standard fsize90">
+
+<tr>
+<td class="numbers">12</td>
+<td class="text">parts</td>
+<td class="text">white lead.</td>
+</tr>
+
+<tr>
+<td class="numbers">1</td>
+<td class="cntr">do.</td>
+<td class="text">minium or red lead.</td>
+</tr>
+
+<tr>
+<td class="numbers">5</td>
+<td class="cntr">do.</td>
+<td class="text">boiled lintseed oil.</td>
+</tr>
+
+</table>
+
+<p><span class="pagenum" id="Page367">[367]</span></p>
+
+<p>The whole is pounded on an iron table by means of a
+flat mullet, like that used by painters (<a href="#Fig112">fig. 112</a>), whose
+grinding surface is <i>a</i>&#160;<i>b</i>, and <i>c</i> the knob for the hand. This
+cement is applied liquid so as to offer no resistance to
+the close union of the pieces, which it is intended to unite.</p>
+
+<div class="container w10emmax" id="Fig112">
+
+<p class="caption">Fig. 112.</p>
+
+<img src="images/illo367a.jpg" alt="Painter's mullet">
+
+</div><!--container-->
+
+<h4><i>Cement for filling up voids, and fixing the rings in the frames.</i></h4>
+
+<table class="standard fsize90">
+
+<tr>
+<td class="numbers">12</td>
+<td class="text">parts</td>
+<td class="text">white lead.</td>
+</tr>
+
+<tr>
+<td class="numbers">3</td>
+<td class="cntr">do.</td>
+<td class="text">whiting.</td>
+</tr>
+
+<tr>
+<td class="numbers">1</td>
+<td class="cntr">do.</td>
+<td class="text">minium.</td>
+</tr>
+
+<tr>
+<td class="numbers">4</td>
+<td class="cntr">do.</td>
+<td class="text">boiled lintseed oil.</td>
+</tr>
+
+</table>
+
+<p>This last composition differs from the former only in the introduction of
+whiting, which, while like minium it has a desiccative property, gives more
+body to the cement and prevents
+the formation of cracks.
+The oil is also decreased in
+quantity, as the cement must
+be used in a more compact
+state. The trituration of this
+cement is performed by means
+of a cylindric iron roller <i>a</i>&#160;<i>b</i>, with a centre-spoke <i>c</i>&#160;<i>d</i> for the hand (<a href="#Fig113">fig. 113</a>).</p>
+
+<div class="container w35emmax" id="Fig113">
+
+<p class="caption">Fig. 113.</p>
+
+<img src="images/illo367b.jpg" alt="Roller">
+
+</div><!--container-->
+
+<p>It is essential for the production of good cement, that the mixture of
+the ingredients be complete.</p>
+
+<h4><i>Prices of the various parts of the Dioptric Apparatus.</i></h4>
+
+<p>The expense of the various parts of the Dioptric apparatus is as follows:
+Great lens of first order, L.58 (8 of which are required); pyramidal
+lens and mirror, L.14, 12s. (8 of which are required); catadioptric cupola,
+L.480; catadioptric rings below lenses, L.360; pannel of dioptric belt for
+fixed light of first order, L.56 (of which 8 are required for the whole circle);
+apparatus of fourth order, for a fixed light, for whole horizon, L.128; apparatus
+of sixth order, for whole horizon, L.44. The expense of the mechanical
+lamp of the first order with four wicks, as made for the Scotch
+Lighthouses by Mr <span class="smcap">John Milne</span> of Edinburgh, is L.30.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter" id="App4">
+
+<p><span class="pagenum" id="Page368">[368]</span></p>
+
+<h3><i>Diagrams illustrative of the <a href="#Ref2">Table</a>, Appendix, No. IV.</i></h3>
+
+</div><!--chapter-->
+
+<div class="container w30emmax" id="Fig114">
+
+<p class="caption">Fig. 114.</p>
+
+<img src="images/illo368a.jpg" alt="References to table">
+
+</div><!--container-->
+
+<div class="container w30emmax" id="Fig115">
+
+<p class="caption">Fig. 115.</p>
+
+<img src="images/illo368b.jpg" alt="References to table">
+
+</div><!--container-->
+
+<div class="split5050">
+
+<div class="left5050">
+
+<div class="container w20emmax" id="Fig116">
+
+<p class="caption">Fig. 116.</p>
+
+<img src="images/illo368c.jpg" alt="References to table">
+
+</div><!--container-->
+
+</div><!--left-->
+
+<div class="right5050">
+
+<div class="container w20emmax" id="Fig117">
+
+<p class="caption">Fig. 117.</p>
+
+<img src="images/illo368d.jpg" alt="References to table">
+
+</div><!--container-->
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<h3><span class="chapno">APPENDIX, No. IV.</span><br>
+<span class="chapname">TABLE OF THE ELEMENTS OF CATADIOPTRIC ZONES SUITED FOR LIGHTS OF
+THE FIRST ORDER IN THE SYSTEM OF AUGUSTIN FRESNEL.</span></h3>
+
+<table class="app4table" id="Ref2">
+
+<tr>
+<td colspan="66" class="note"><span class="smcap">Note.</span>—The
+Six co-ordinates of the Generating Triangle of each Zone in these Tables have the Focus of the Principal Lenses of the System
+for their origin; it being considered more convenient, in executing the necessary protractions, preparatory to the
+construction of the grinding apparatus, at once to refer the whole of the grinding machinery to the axis of the
+apparatus. To prevent the appearance of any inconsistency, however, it is proper to mention, that the radiant points
+of the series of Zones, do not exactly coincide with the Focus of the Lenses nor with each other; and that to avoid
+the parallax which the distance of the radiant points from the origin of the co-ordinates would occasion, it is necessary to
+make some corrections upon the linear dimensions, so as to find the line corresponding to the angles θ, ξ, and the
+distance Δ. In the Hyperpyral series, which stands <i>above</i>
+the flame, the Zones have the radiant point 10 millimetres above the Focus of the Lenses, and each <i>y</i> of this
+series, therefore, requires a reduction of that quantity; while the <i>x</i>
+remains unchanged. In the Hypopyral series, which stands <i>below</i>
+the flame, the Focus or radiant points of each Zone, varies its place in the flame, moving upwards as the Zone is
+lower, so that the line joining the Zones and the Foci, revolves as a radius vector round a point between them. In
+this way, the <i>x</i>’s remain unaltered; but the <i>y</i>’s will be lengthened successively
+by the addition of 10, 14, 19, 25, 32, and 40 millimetres. As these Tables contain the dimensions of Zones which
+are intended as an addition to the apparatus of <span class="smcap">Fresnel</span>,
+I have adopted the metric scale, so as to render them at once applicable to the existing protractions of that system.
+It is only necessary to add, that the conversion of millimetres
+into imperial inches, is easily effected by adding the log. millimetres to the log. ̅2·59516, the sum being the log. of
+the equivalent of the first term in imperial inches.</td>
+</tr>
+
+<tr class="bt">
+<th rowspan="3" colspan="3" class="br">&#160;</th>
+<th class="brd">&#160;</th>
+<th colspan="3" class="br">θ</th>
+<th colspan="3" class="brd">ξ</th>
+<th colspan="3" class="br">BCA,</th>
+<th colspan="3" class="br">ABC,</th>
+<th colspan="3" class="brd">BAC,</th>
+<th class="br">BA,</th>
+<th class="br">BC,</th>
+<th class="brd">AC,</th>
+<th colspan="6" class="txt wrappable brd bb">Co-ordinates of the Apices of the Generating Triangle, in Millimetres,
+having the Axis of the System cut by the horizontal plane of the focus of the Annular Lenses, for its origin. (<a href="#Fig116">Fig. 116</a>.)</th>
+<th colspan="9" class="txt wrappable brd bb">Inclination of the Sides of the Generating Triangle to the Vertical
+Axis of the System. (<a href="#Fig117">Fig. 117</a>.)</th>
+<th colspan="9" class="brd bb">AB, Reflecting Surfaces (convex). (<a href="#Fig115">Fig. 115</a>.)</th>
+<th colspan="9" class="brd bb">AC, Outer Refracting Surfaces (concave).</th>
+<th colspan="9" class="brd bb">BC, Inner Refracting Surfaces (convex).</th>
+<th class="brd">Δ,</th>
+<th>&#160;</th>
+</tr>
+
+<tr>
+<th class="brd">No.<br>of<br><span class="smcap">Zone</span>.</th>
+<th colspan="3" class="br">Inclination<br>of Ray FC<br>to the<br>Vertical<br>Axis<br>of the<br>System.</th>
+<th colspan="3" class="brd">Incidence<br>of<br>Ray FC<br>on Side<br>BC of<br>Zone.</th>
+<th colspan="3" class="br">Obtuse<br>Angle<br>of the<br>Generating<br>Triangle<br>of the<br>Zone.</th>
+<th colspan="3" class="br">Angle of<br>Generating<br>Triangle<br>of Zone.</th>
+<th colspan="3" class="brd">Angle of<br>Generating<br>Triangle<br>of Zone.</th>
+<th class="br">Reflecting<br>Side of<br>Zone in<br>Millimetres<br>being<br>Chord<br>of the<br>Arc <i>b</i>&#160;A.</th>
+<th class="br">Inner<br>Refracting<br>Side of<br>Zone in<br>Millimetres.</th>
+<th class="brd">Outer<br>Refracting<br>Side of<br>Zone in<br>Millimetres.</th>
+<th class="br">A<sub><i>y</i></sub></th>
+<th class="br">A<sub><i>x</i></sub></th>
+<th class="br">B<sub><i>y</i></sub></th>
+<th class="br">B<sub><i>x</i></sub></th>
+<th class="br">C<sub><i>y</i></sub></th>
+<th class="brd">C<sub><i>x</i></sub></th>
+<th colspan="3" class="br">Inclination<br>of AB.</th>
+<th colspan="3" class="br">Inclination<br>of BC.</th>
+<th colspan="3" class="brd">Inclination<br>of AC.</th>
+<th class="br">Radius of<br>Curvature<br>in<br>Millimetres,<br>XA or X&#160;<i>b</i>.</th>
+<th class="br">Horizontal<br>distance<br>of centre<br>of<br>curvature<br>X from<br>the axis<br>of the<br>System in<br>Millimetres<br>= OX.</th>
+<th class="wrappable br">Vertical<br>distance<br>of centre<br>of<br>curvature<br>X <i>below</i><br>the <i>outer</i>
+arris of the<br><i>Zone</i> at A in<br>Millimetres<br>= OA.</th>
+<th colspan="3" class="br">Inclination<br>of the<br>Two Radii<br>in<br>A and B.</th>
+<th colspan="3" class="brd">Inclination<br>of the<br>Outer<br>Radius<br>in A<br>to the<br>Vertex.</th>
+<th class="br">Radius of<br>Curvature<br>in<br>Millimetres.</th>
+<th class="br">Horizontal<br>distance<br>of centre<br>of<br>curvature<br>from the<br>axis<br>of the<br>System in<br>Millimetres.</th>
+<th class="wrappable br">Vertical<br>distance<br>of centre<br>of<br>curvature<br><i>above</i><br>the outer<br>arris
+of the<br><i>Zone</i> at A<br>in<br>Millimetres.</th>
+<th colspan="3" class="br">Inclination<br>of the<br>Radii<br>in A<br>and C.</th>
+<th colspan="3" class="brd">Inclination<br>of the<br>Outer<br>Radius<br>at A to the<br>Vertex.</th>
+<th class="br">Radius<br>of<br>Curvature<br>in<br>Millimetres.</th>
+<th class="br">Horizontal<br>distance<br>of centre<br>of<br>curvature<br>from the<br>axis of<br>the System<br>in<br>Millimetres.</th>
+<th class="wrappable br">Vertical<br>distance<br>of centre<br>of<br>curvature<br><i>below</i> the<br>outer arris
+of the<br><i>Zone</i> at A<br>in<br>Millimetres.</th>
+<th colspan="3" class="br">Inclination<br>of the<br>Radii in<br>C and B.</th>
+<th colspan="3" class="brd">Inclination<br>of the<br>Outer<br>Radius<br>in C to<br>the Vertex.</th>
+<th class="brd">Distance<br>of C<br>from the<br>Focus for<br>the Zones,<br>in<br>Millimetres<br>= FC.</th>
+<th>No.<br>of<br><span class="smcap">Zone</span>.</th>
+</tr>
+
+<tr class="bb">
+<th class="brd">&#160;</th>
+<th colspan="3" class="br">(<a href="#Fig114">Fig. 114</a>.)</th>
+<th colspan="3" class="brd">(<a href="#Fig114">Fig. 114</a>.)</th>
+<th colspan="3" class="br">(<a href="#Fig114">Fig. 114</a>.)</th>
+<th colspan="3" class="br">(<a href="#Fig114">Fig. 114</a>.)</th>
+<th colspan="3" class="brd">(<a href="#Fig114">Fig. 114</a>.)</th>
+<th class="br">(<a href="#Fig115">Fig. 115</a>.)</th>
+<th class="br">(<a href="#Fig115">Fig. 115</a>.)</th>
+<th class="brd">(<a href="#Fig115">Fig. 115</a>.)</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="brd">&#160;</th>
+<th colspan="3" class="br">&#160;</th>
+<th colspan="3" class="br">&#160;</th>
+<th colspan="3" class="brd">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th colspan="3" class="br">&#160;</th>
+<th colspan="3" class="brd">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th colspan="3" class="br">&#160;</th>
+<th colspan="3" class="brd">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th colspan="3" class="br">&#160;</th>
+<th colspan="3" class="brd">&#160;</th>
+<th class="brd">(<a href="#Fig114">Fig. 114</a>.)</th>
+<th>&#160;</th>
+</tr>
+
+<tr>
+<th colspan="3" class="br">&#160;</th>
+<th class="brd">&#160;</th>
+<th>°</th>
+<th>′</th>
+<th class="br">″</th>
+<th>°</th>
+<th>′</th>
+<th class="brd">″</th>
+<th>°</th>
+<th>′</th>
+<th class="br">″</th>
+<th>°</th>
+<th>′</th>
+<th class="br">″</th>
+<th>°</th>
+<th>′</th>
+<th class="brd">″</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="brd">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="brd">&#160;</th>
+<th>°</th>
+<th>′</th>
+<th class="br">″</th>
+<th>°</th>
+<th>′</th>
+<th class="br">″</th>
+<th>°</th>
+<th>′</th>
+<th class="brd">″</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th>°</th>
+<th>′</th>
+<th class="br">″</th>
+<th>°</th>
+<th>′</th>
+<th class="brd">″</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th>°</th>
+<th>′</th>
+<th class="br">″</th>
+<th>°</th>
+<th>′</th>
+<th class="brd">″</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th class="br">&#160;</th>
+<th>°</th>
+<th>′</th>
+<th class="br">″</th>
+<th>°</th>
+<th>′</th>
+<th class="brd">″</th>
+<th class="brd">&#160;</th>
+<th>&#160;</th>
+</tr>
+
+<tr>
+<td rowspan="13">HYPER-<br>PYRAL<br>SERIES<br>OF<br>ZONES.</td>
+<td rowspan="13" class="brace bt br bb">&#160;</td>
+<td rowspan="13" class="brace br"><span class="padr1">-</span></td>
+<td class="brd">&#8199;1</td>
+<td>60</td>
+<td>45</td>
+<td class="br">38</td>
+<td>44</td>
+<td>06</td>
+<td class="brd">09</td>
+<td>117</td>
+<td>26</td>
+<td class="br">40</td>
+<td>31</td>
+<td>48</td>
+<td class="br">10</td>
+<td>30</td>
+<td>45</td>
+<td class="brd">10</td>
+<td class="br">160·331</td>
+<td class="br">92·379</td>
+<td class="brd">95·209</td>
+<td class="br">&#8199;593·369</td>
+<td class="br">986·260</td>
+<td class="br">&#8199;551·481</td>
+<td class="br">831·497</td>
+<td class="br">&#8199;525·000</td>
+<td class="brd">920·000</td>
+<td>74</td>
+<td>51</td>
+<td class="br">19</td>
+<td>73</td>
+<td>20</td>
+<td class="br">31</td>
+<td>44</td>
+<td>06</td>
+<td class="brd">09</td>
+<td class="br">8750·19</td>
+<td class="br">3194·76</td>
+<td class="br">8466·88</td>
+<td>1</td>
+<td>02</td>
+<td class="brd">59</td>
+<td>14</td>
+<td>38</td>
+<td class="brd">11</td>
+<td class="br">4000·00</td>
+<td class="br">3825·31</td>
+<td class="br">2817·77</td>
+<td>1</td>
+<td>21</td>
+<td class="br">50</td>
+<td>45</td>
+<td>12</td>
+<td class="brd">56</td>
+<td class="br">4000·00</td>
+<td class="br">2021·19</td>
+<td class="br">3777·07</td>
+<td>1</td>
+<td>19</td>
+<td class="br">24</td>
+<td>15</td>
+<td>58</td>
+<td class="brd">47</td>
+<td class="brd">1054·34</td>
+<td>&#8199;1</td>
+</tr>
+
+<tr>
+<td class="brd">&#8199;2</td>
+<td>56</td>
+<td>55</td>
+<td class="br">38</td>
+<td>41</td>
+<td>28</td>
+<td class="brd">10</td>
+<td>116</td>
+<td>00</td>
+<td class="br">42</td>
+<td>32</td>
+<td>32</td>
+<td class="br">01</td>
+<td>31</td>
+<td>27</td>
+<td class="brd">17</td>
+<td class="br">155·430</td>
+<td class="br">90·249</td>
+<td class="brd">93·011</td>
+<td class="br">&#8199;663·063</td>
+<td class="br">957·410</td>
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+<td class="thinline brd">&#160;</td>
+<td colspan="3" class="thinline br">&#160;</td>
+<td colspan="3" class="thinline br">&#160;</td>
+<td colspan="3" class="thinline brd">&#160;</td>
+<td class="thinline br">&#160;</td>
+<td class="thinline br">&#160;</td>
+<td class="thinline br">&#160;</td>
+<td colspan="3" class="thinline br">&#160;</td>
+<td colspan="3" class="thinline brd">&#160;</td>
+<td class="thinline br">&#160;</td>
+<td class="thinline br">&#160;</td>
+<td class="thinline br">&#160;</td>
+<td colspan="3" class="thinline br">&#160;</td>
+<td colspan="3" class="thinline brd">&#160;</td>
+<td class="thinline br">&#160;</td>
+<td class="thinline br">&#160;</td>
+<td class="thinline br">&#160;</td>
+<td colspan="3" class="thinline br">&#160;</td>
+<td colspan="3" class="thinline brd">&#160;</td>
+<td class="thinline brd">&#160;</td>
+<td class="thinline">&#160;</td>
+</tr>
+
+</table>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter" id="App5">
+
+<p><span class="pagenum" id="Page369">[369]</span></p>
+
+<h3 class="nobreak"><span class="chapno">APPENDIX, No. V.</span><br>
+<span class="chapname">NOTICE TO MARINERS.—SKERRYVORE LIGHTHOUSE.</span></h3>
+
+</div><!--chapter-->
+
+<p>The Commissioners of the Northern Lighthouses hereby give notice,
+that a Lighthouse has been erected upon the Skerryvore Rock, which lies
+off the Island of Tyree, in the county of Argyll, the Light of which will be
+exhibited on the Night of the 1st February 1844, and every Night thereafter,
+from sunset to sunrise.</p>
+
+<p>A <a href="#Ref3">specification</a> of the bearings of the Lighthouse and character of the
+Light will be found on the next page.</p>
+
+<p>And the Commissioners hereby further give notice, that by virtue of a
+Warrant from the Queen in Council, of date the 13th December 1843,
+the following Tolls will be levied for voyages in respect of which benefit
+will be derived from this Light, viz., from every British Vessel (the same
+not belonging to Her Majesty, or being navigated wholly in ballast), and
+for every Foreign Vessel which, by any Act of Parliament, Order in Council,
+Convention, or Treaty, shall be privileged to enter the Ports of the
+United Kingdom of Great Britain and Ireland, upon paying the same
+duties of tonnage as are paid by British Vessels (the same not being navigated
+wholly in ballast), the Toll of One Penny per Ton of the Burden of
+every such Vessel; and for every Foreign Vessel not so privileged, the
+Toll of Two Pence per Ton.</p>
+
+<p class="center highline2"><i>By Order of the Commissioners</i>,</p>
+
+<div class="cunsign">
+
+<div class="split7525">
+
+<div class="left7525">
+
+<p class="noindent"><span class="padr4">(Signed)</span><span class="smcap">C. Cuningham</span>,<br>
+<span class="dontshow padr4">(Signed)</span><span class="smcap">Alex. Cuningham</span>,</p>
+
+</div><!--left-->
+
+<div class="right7525">
+
+<p class="noindent"><span class="fsize175">}</span><i>Joint Secs.</i></p>
+
+</div><!--right-->
+
+</div><!--split-->
+
+</div><!--cunsign-->
+
+<p class="allclear highline4 padl6 fsize80"><span class="smcap">Edinburgh</span>, <i>23d December 1843</i>.</p>
+
+<p><span class="pagenum" id="Page370">[370]</span></p>
+
+<p id="Ref3">The following is a Specification of the Position of the Lighthouse, and
+the Appearance of the Light, by Mr <span class="smcap">Alan Stevenson</span>, Engineer to
+the Commissioners.</p>
+
+<p>The Skerryvore Rock lies off the Island of Tyree, in Lat. 56° 19′ 22″
+N.; Long. 7° 6′ 32″ W.</p>
+
+<p>By Compass, the Lighthouse bears from Barrahead Lighthouse S. ¹⁄₄ E.,
+distant 33 nautic miles; from Hynish Point, in Tyree, WSW. ¹⁄₂ W.,
+distant 10¹⁄₃ miles; from Iona Island, WNW. ³⁄₄ N., distant 20 miles;
+from Rhinns of Islay Lighthouse, N. ¹⁄₄ E., distant 44 miles; and from
+Innistrahull Lighthouse in Ireland, NE. by N., distant 53¹⁄₂ miles.</p>
+
+<p>Owing to the distance to which the foul ground extends on every side
+of the rock on which the Lighthouse is placed, and the weight of sea which
+breaks on the shallow ground all round it, it is necessary to give the Light
+a wide berth. The better to enable seamen to judge of this, their attention
+is called to the prefixed <a href="#Plate2">Chart</a>,<a id="FNanchor87" href="#Footnote87" class="fnanchor">[87]</a>
+which exhibits the relative position
+of the Skerryvore Rock, and the various dangers around it. In particular,
+it is necessary to notice the position of those rocks which lie seaward of
+the Lighthouse, viz. Mackenzie’s Rock, about 3 miles W. by S. ¹⁄₄ S. from
+the Lighthouse; Stevenson’s, 2¹⁄₄ miles W. ¹⁄₂ N.; and Fresnel’s, which lies
+between these two Rocks. To the left of the prefixed <a href="#Plate2">Chart</a> is a small
+diagram, which exhibits the position of the Skerryvore Rock in reference
+to the principal landmarks above noticed.</p>
+
+<div class="footnote">
+
+<p><a id="Footnote87" href="#FNanchor87" class="label">[87]</a> A copy of the Chart referred to will
+be found at <a href="#Plate2">Plate II.</a> at the end of this volume.</p>
+
+</div><!--footnote-->
+
+<p>The Skerryvore Light will be known to mariners as a Revolving Light,
+producing a Bright Flash once every minute. The Lantern, which is open
+all round, is elevated 150 feet above the level of the sea. In clear weather
+the flashes of the Light will be seen at the distance of six leagues, and at
+lesser distances according to the state of the atmosphere; and to a near observer,
+in favourable circumstances, the Light will not wholly disappear
+between the flashes.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter" id="App6">
+
+<p><span class="pagenum" id="Page371">[371]</span></p>
+
+<h3><span class="chapno">APPENDIX, No. VI.</span><br>
+<span class="chapname">ACCOUNT OF THE EXPENSE OF ERECTING THE SKERRYVORE
+LIGHTHOUSE AND OF THE SUBSIDIARY WORKS.</span></h3>
+
+</div><!--chapter-->
+
+<table class="costs">
+
+<colgroup>
+<col class="w01em">
+<col class="wauto">
+<col span="3" class="w015em">
+<col span="9" class="wauto">
+</colgroup>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Establishment at Hynish.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of the different workmen quarrying and dressing the stones, and building the dwelling-houses,
+barracks, storehouses, inclosure and subdivision dykes, draining and trenching the ground, &amp;c., at Hynish, and the wages of joiners
+preparing and fitting up the joiner work,</td>
+<td class="amount">£2996</td>
+<td class="amount">7</td>
+<td class="intpart">7</td>
+<td>&#160;</td>
+<td rowspan="4" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Timber, pavement, bricks, ironmongery, glass, &amp;c., &amp;c., used in the erections,</td>
+<td class="amount">1376</td>
+<td class="amount">16</td>
+<td class="intpart">9</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Slater, plaster, and plumber work of the houses,</td>
+<td class="amount">436</td>
+<td class="amount">1</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Paid the tenant of Hynish for a barn which was used as a barrack to accommodate the workmen when
+they first landed at Tyree,</td>
+<td class="amount bb">13</td>
+<td class="amount bb">0</td>
+<td class="intpart bb">0</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">£4822</td>
+<td class="amount">5</td>
+<td class="intpart">4</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="note"><span class="smcap">Note.</span>—Although these buildings had been erected for the purposes of the
+works, yet the greater part of them were designed to serve as part of the permanent accommodation required at Tyree in connection
+with the Lighthouse Establishment, and have accordingly been so applied.</td>
+<td colspan="8">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap"><span class="pagenum" id="Page372">[372]</span>Rock Barrack</span>, No. 1.</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the barrack on the Rock, which was destroyed, including the contractor’s account for extra
+work, &amp;c.,</td>
+<td class="amount">£742</td>
+<td class="amount">17</td>
+<td class="intpart">7</td>
+<td>&#160;</td>
+<td rowspan="3" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Lead for running up the bats and for other purposes about the barrack,</td>
+<td class="amount">14</td>
+<td class="amount">11</td>
+<td class="intpart">6</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">A smith’s forge, bellows, anvil, and smith’s tools used at Rock in erecting the barrack,</td>
+<td class="amount bb">32</td>
+<td class="amount bb">19</td>
+<td class="intpart bb">1</td>
+<td class="fracpart bb">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">790</td>
+<td class="amount">8</td>
+<td class="intpart">2</td>
+<td class="fracpart">³⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Rock Barrack</span>, No. 2.</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the carpenter and joiner work on the second barrack, the expense of fitting and erecting it
+at Greenock, the wages of four joiners and a smith, furnished by the contractor to assist in its erection at Skerryvore, including
+sundry other minor charges,</td>
+<td class="amount">£911</td>
+<td class="amount">14</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+<td rowspan="6" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the iron-work of the barrack,</td>
+<td class="amount">369</td>
+<td class="amount">11</td>
+<td class="intpart">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Lead for running up the bats and protecting the timber of cooking apartment, &amp;c.,</td>
+<td class="amount">29</td>
+<td class="amount">11</td>
+<td class="intpart">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cooking apparatus for the cook-room of barrack, sheet-iron smoke tube, cooking utensils, &amp;c.,</td>
+<td class="amount">54</td>
+<td class="amount">16</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Bedding for beds of barrack,</td>
+<td class="amount">90</td>
+<td class="amount">9</td>
+<td class="intpart">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Expense of upholding and making sundry small repairs on the barrack since its erection,</td>
+<td class="amount bb">22</td>
+<td class="amount bb">18</td>
+<td class="intpart bb">6</td>
+<td class="fracpart bb">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">1479</td>
+<td class="amount">1</td>
+<td class="intpart">11</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the furniture, bedding, and other utensils required for the dwelling-houses, barracks, &amp;c.,
+connected with the different establishments of the works,</td>
+<td colspan="4">&#160;</td>
+<td class="amount">830</td>
+<td class="amount">19</td>
+<td class="intpart">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Establishment at North Bay.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of the quarriers, masons, joiners, &amp;c., quarrying stones, building the barracks, storehouses,
+&amp;c., &amp;c., and fitting up the joiner work,</td>
+<td class="amount">£378</td>
+<td class="amount">11</td>
+<td class="intpart">9</td>
+<td>&#160;</td>
+<td rowspan="3" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Timber and other furnishings for the erections, the expense of making the doors and
+windows,<span class="pagenum" id="Page373">[373]</span> including furnishings required for erecting the habitable part of Skerryvore
+Barrack at North Bay as a temporary accommodation for the workmen, and sundry other charges,</td>
+<td class="amount">361</td>
+<td class="amount">4</td>
+<td class="intpart">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Sundry furnishings—such as utensils for provision store, smithy, &amp;c.,</td>
+<td class="amount bb">13</td>
+<td class="amount bb">2</td>
+<td class="intpart bb">5</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">752</td>
+<td class="amount">18</td>
+<td class="intpart">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Quarries at North Bay.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of rails and timber for railway and timber, &amp;c., for shipping-pier at North Bay,</td>
+<td class="amount">£131</td>
+<td class="amount">5</td>
+<td class="intpart">1</td>
+<td>&#160;</td>
+<td rowspan="2" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of workmen who were employed at quarries in North Bay, quarrying the lighthouse blocks,
+constructing the pier, railway, &amp;c.,</td>
+<td class="amount bb">1752</td>
+<td class="amount bb">5</td>
+<td class="intpart bb">3</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">1883</td>
+<td class="amount">10</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Temporary Wharf and Railway at the Skerryvore Rock.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of timber used in the wharf and railway at the Skerryvore Rock,</td>
+<td class="amount">£103</td>
+<td class="amount">18</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+<td rowspan="3" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Iron bats, bolts, &amp;c., for fastening the timber, rails for railway, and sundry furnishings connected
+with an apparatus for blasting under water,</td>
+<td class="amount">119</td>
+<td class="amount">7</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of the workmen constructing the railway, fastening the timber of wharf, &amp;c.,</td>
+<td class="amount bb">34</td>
+<td class="amount bb">10</td>
+<td class="intpart bb">5</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">257</td>
+<td class="amount">16</td>
+<td class="intpart">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Excavation at Rock and Platform</span>, &amp;c.</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of the workmen excavating the foundation for the Lighthouse Tower, on the Skerryvore Rock,</td>
+<td class="amount">£609</td>
+<td class="amount">2</td>
+<td class="intpart">3</td>
+<td class="fracpart">¹⁄₂</td>
+<td rowspan="4" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">A portable forge, and other smith’s tools, used at the rock for this work,</td>
+<td class="amount">21</td>
+<td class="amount">15</td>
+<td class="intpart">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr"><span class="pagenum" id="Page374">[374]</span>Wages of the workmen excavating the site of a platform
+at the workyard in Hynish, and quarrying and dressing stones for sill of platform,</td>
+<td class="amount">£107</td>
+<td class="amount">16</td>
+<td class="intpart">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of freestone from Garscube Quarry, Glasgow, for part of the sill of platform,</td>
+<td class="amount bb">24</td>
+<td class="amount bb">14</td>
+<td class="intpart bb">0</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">763</td>
+<td class="amount">8</td>
+<td class="intpart">6</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Dressing Lighthouse Blocks.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of masons, including the assistance of labourers, carters, &amp;c., in dressing the blocks
+for the Lighthouse Tower at Hynish,</td>
+<td class="amount">£8589</td>
+<td class="amount">8</td>
+<td class="intpart">7</td>
+<td class="fracpart">¹⁄₂</td>
+<td rowspan="3" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Timber for moulds of the various blocks, and the joiners’ wages making the moulds,</td>
+<td class="amount">384</td>
+<td class="amount">18</td>
+<td class="intpart">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Timber, &amp;c., and wages of joiners in erecting sheds for the masons,</td>
+<td class="amount bb">955</td>
+<td class="amount bb">4</td>
+<td class="intpart bb">5</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">9929</td>
+<td class="amount">11</td>
+<td class="intpart">10</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Expense of victualling the workmen and others who were employed at the rock during the operation of the whole works,</td>
+<td colspan="4">&#160;</td>
+<td class="amount">1503</td>
+<td class="amount">18</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Implements and Tools for Masons, Smiths</span>, &amp;c.</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Amount paid to sundry persons for the implements and tools used by the workmen in all the departments of the works,</td>
+<td class="amount">£1176</td>
+<td class="amount">9</td>
+<td class="intpart">6</td>
+<td class="fracpart">¹⁄₂</td>
+<td rowspan="2" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of the smiths and their hammermen keeping these tools in repair and making others,</td>
+<td class="amount bb">908</td>
+<td class="amount bb">16</td>
+<td class="intpart bb">5</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">2085</td>
+<td class="amount">5</td>
+<td class="intpart">11</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Machinery for the Works at the Rock, Hynish, and North Bay.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of cranes, crabs, winches, trucks, iron blocks, chains, rope-guys, &amp;c., with sundry other
+furnishings connected with these articles,</td>
+<td class="amount">£1516</td>
+<td class="amount">9</td>
+<td class="intpart">5</td>
+<td>&#160;</td>
+<td rowspan="4" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">1 Woolwich or sling-cart, a janker for wood, and four jack-screws,</td>
+<td class="amount">89</td>
+<td class="amount">6</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr"><span class="pagenum" id="Page375">[375]</span>Large balance crane used in building the Lighthouse Tower,</td>
+<td class="amount">533</td>
+<td class="amount">10</td>
+<td class="intpart">0</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Hoisting beams or needles, and a pair of strong sheer-poles, used in building the Lighthouse Tower,</td>
+<td class="amount bb">42</td>
+<td class="amount bb">11</td>
+<td class="intpart bb">2</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">2181</td>
+<td class="amount">16</td>
+<td class="intpart">11</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Cartage Account.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of 3 large draught horses and a pony, for the use of the works,</td>
+<td class="amount">£127</td>
+<td class="amount">9</td>
+<td class="intpart">10</td>
+<td class="fracpart">¹⁄₂</td>
+<td rowspan="4" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Carts and stable utensils,</td>
+<td class="amount">65</td>
+<td class="amount">14</td>
+<td class="intpart">2</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Harness and other furniture, and keeping them in repair,</td>
+<td class="amount">52</td>
+<td class="amount">2</td>
+<td class="intpart">3</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Provender for the horses for seven years,</td>
+<td class="amount bb">858</td>
+<td class="amount bb">14</td>
+<td class="intpart bb">8</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">1104</td>
+<td class="amount">1</td>
+<td class="intpart">0</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Mortar Account.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the lime which was used for all the departments of the works,</td>
+<td class="amount">£331</td>
+<td class="amount">9</td>
+<td class="intpart">8</td>
+<td>&#160;</td>
+<td rowspan="5" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Pozzolano which was used for the building of the Lighthouse Tower, excepting a small portion for
+the works of the harbour or dock,</td>
+<td class="amount">376</td>
+<td class="amount">16</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Mastic, cements, and stucco,</td>
+<td class="amount">39</td>
+<td class="amount">6</td>
+<td class="intpart">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of labourers grinding and sifting Pozzolano at Hynish, and burning and sifting a portion of the lime,</td>
+<td class="amount">121</td>
+<td class="amount">18</td>
+<td class="intpart">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Packages to contain Pozzolano, to prevent its admixture with other cargo when on board ship,</td>
+<td class="amount bb">20</td>
+<td class="amount bb">0</td>
+<td class="intpart bb">1</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">889</td>
+<td class="amount">11</td>
+<td class="intpart">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Signal Tower at Hynish.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Expense of quarrying, dressing, and building the stones, and executing the joiner work of the
+Signal Tower at Hynish,</td>
+<td class="amount">£370</td>
+<td class="amount">13</td>
+<td class="intpart">2</td>
+<td>&#160;</td>
+<td rowspan="7" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Pavement and bricks for the interior,</td>
+<td class="amount">32</td>
+<td class="amount">13</td>
+<td class="intpart">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cast-iron floor, with lintels and sole plates for windows, and cast-iron supports for do.,</td>
+<td class="amount">110</td>
+<td class="amount">13</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr"><span class="pagenum" id="Page376">[376]</span>Timber for joisting of floors, lining of walls and
+windows, including the glazing of them, a wooden trap, flag-pole, and other furnishings for interior,</td>
+<td class="amount">284</td>
+<td class="amount">9</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Plumber work of roof,</td>
+<td class="amount">35</td>
+<td class="amount">9</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">A 5 feet achromatic telescope, with stand, &amp;c., for Signal Tower,</td>
+<td class="amount">35</td>
+<td class="amount">10</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of a code of signals, flags, return books, and other furnishings,</td>
+<td class="amount bb">11</td>
+<td class="amount bb">10</td>
+<td class="intpart bb">6</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">880</td>
+<td class="amount">18</td>
+<td class="intpart">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Lights Account.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Expense of the apparatus required for the lights at the Pier and Signal Tower at Hynish,
+including fitting up, &amp;c.,</td>
+<td class="amount">£66</td>
+<td class="amount">7</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+<td rowspan="3" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of oil and other requisites for upholding these lights,</td>
+<td class="amount">136</td>
+<td class="amount">5</td>
+<td class="intpart">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Salary of the Lightkeepers, &amp;c.,</td>
+<td class="amount bb">131</td>
+<td class="amount bb">11</td>
+<td class="intpart bb">7</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">334</td>
+<td class="amount">4</td>
+<td class="intpart">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">“Skerryvore” Steamer.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">First cost and complete outfit of the steamer Skerryvore,</td>
+<td class="amount">£5930</td>
+<td class="amount">0</td>
+<td class="intpart">11</td>
+<td>&#160;</td>
+<td rowspan="4" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Alteration on the engines, by raising the shafts, &amp;c.,</td>
+<td class="amount">423</td>
+<td class="amount">5</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Repairs on the hull and engines, on various occasions, during the progress of the works,</td>
+<td class="amount">1057</td>
+<td class="amount">4</td>
+<td class="intpart">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Sailing expenses (exclusive of the cost of coals supplied when the steamer was at Hynish),
+and sundry other minor charges,</td>
+<td class="amount bb">5538</td>
+<td class="amount bb">10</td>
+<td class="intpart bb">11</td>
+<td class="fracpart bb">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">12,949</td>
+<td class="amount">1</td>
+<td class="intpart">0</td>
+<td class="fracpart">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">“Queen” Tender.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">First cost and complete outfit of the “Queen” Tender,</td>
+<td class="amount">£935</td>
+<td class="amount">13</td>
+<td class="intpart">3</td>
+<td>&#160;</td>
+<td rowspan="3" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Sailing expenses and other charges,</td>
+<td class="amount">1010</td>
+<td class="amount">7</td>
+<td class="intpart">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Repairs on the hull, rigging, sails, &amp;c.,</td>
+<td class="amount bb">77</td>
+<td class="amount bb">12</td>
+<td class="intpart bb">8</td>
+<td class="fracpart bb">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">2023</td>
+<td class="amount">13</td>
+<td class="intpart">8</td>
+<td class="fracpart">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="pagenum"><a id="Page377"></a>[377]</span><span class="smcap">Stone
+Lighters.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">First cost and outfit of four lighters for transporting the Lighthouse blocks, &amp;c.,
+from Hynish to the Skerryvore Rock,</td>
+<td class="amount">£1666</td>
+<td class="amount">15</td>
+<td class="intpart">6</td>
+<td class="fracpart">¹⁄₂</td>
+<td rowspan="5" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Hawsers for towing, mooring-ropes, heaving-lines, &amp;c., used in the course of transporting
+the stones to the Rock,</td>
+<td class="amount">249</td>
+<td class="amount">1</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Upholding the lighters in repair, and sundry other charges,</td>
+<td class="amount">178</td>
+<td class="amount">9</td>
+<td class="intpart">9</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Expense transporting the lighters on various occasions to different places,</td>
+<td class="amount">58</td>
+<td class="amount">15</td>
+<td class="intpart">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Expense shifting and attending upon the lighters when lying at Leith, and advertising them for sale,</td>
+<td class="amount bb">19</td>
+<td class="amount bb">9</td>
+<td class="intpart bb">10</td>
+<td class="fracpart bb">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">2172</td>
+<td class="amount">12</td>
+<td class="intpart">6</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Moorings.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the buoys for mooring the vessels belonging to the works in Hynish Bay, and at the
+Rock, when lying there,</td>
+<td class="amount">£240</td>
+<td class="amount">1</td>
+<td class="intpart">3</td>
+<td>&#160;</td>
+<td rowspan="5" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cast-iron mushroom anchors for mooring the buoys,</td>
+<td class="amount">118</td>
+<td class="amount">7</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wrought-iron common anchors, grapnels, &amp;c., for mooring the vessels, warping, kedging, &amp;c.,</td>
+<td class="amount">48</td>
+<td class="amount">16</td>
+<td class="intpart">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Chains and shackles for do., &amp;c.,</td>
+<td class="amount">354</td>
+<td class="amount">2</td>
+<td class="intpart">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Upholding and keeping in repair the buoys,</td>
+<td class="amount bb">4</td>
+<td class="amount bb">17</td>
+<td class="intpart bb">1</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">766</td>
+<td class="amount">4</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Boats and Attendance.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of 8 boats, with oars, sails, tackling, &amp;c.,</td>
+<td class="amount">£207</td>
+<td class="amount">19</td>
+<td class="intpart">11</td>
+<td class="fracpart">¹⁄₂</td>
+<td rowspan="3" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Upholding these boats in repair,</td>
+<td class="amount">28</td>
+<td class="amount">13</td>
+<td class="intpart">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Amount paid for the use of boats and their crews assisting to discharge cargoes from vessels
+previous to the pier being built,</td>
+<td class="amount bb">119</td>
+<td class="amount bb">6</td>
+<td class="intpart bb">0</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">355</td>
+<td class="amount">19</td>
+<td class="intpart">8</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Amount paid the owners of hired vessels, as freights of the Lighthouse blocks from the quarries
+at North Bay, in Mull, to the workyard at Hynish,</td>
+<td colspan="4">&#160;</td>
+<td class="amount">1300</td>
+<td class="amount">14</td>
+<td class="intpart">8</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="pagenum"><a id="Page378"></a>[378]</span><span class="smcap">Freight and
+Sailing Expenses.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Freights and other charges paid the owners of hired vessels, vessels, for the materials
+which were imported for the use of various departments of the works, exclusive of the Lighthouse blocks from North Bay,</td>
+<td rowspan="5" colspan="4">&#160;</td>
+<td class="amount">4045</td>
+<td class="amount">9</td>
+<td class="intpart">7</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of labourers, &amp;c., discharging the cargoes from the vessels at the Pier at Hynish,
+and the wages of workmen quarrying stones for ballast, and putting it on board the vessels,</td>
+<td class="amount">933</td>
+<td class="amount">12</td>
+<td class="intpart">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Amount paid for travelling expenses, and other charges connected with the transport of the
+workmen, including the expenses of the Officers, &amp;c., travelling on the business of the works,</td>
+<td class="amount">1711</td>
+<td class="amount">11</td>
+<td class="intpart">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the coals supplied to the steamer “Skerryvore,” when plying between the Skerryvore Rock,
+Hynish, &amp;c., for the household purposes of the different departments of the works, and also for the smith’s forge,</td>
+<td class="amount">1463</td>
+<td class="amount">0</td>
+<td class="intpart">7</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the blasting powder used for the purpose of quarrying stones, excavating rocks, &amp;c.</td>
+<td class="amount">375</td>
+<td class="amount">14</td>
+<td class="intpart">2</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Lighthouse Tower.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of the workmen who were engaged at Skerryvore Rock in building the Tower, and shipping
+the materials at Hynish for Rock, including the wages of masons, &amp;c., assisting the other tradesmen in the respective
+departments of their work, after the completion of the building operations,</td>
+<td class="amount">£2381</td>
+<td class="amount">11</td>
+<td class="intpart">7</td>
+<td>&#160;</td>
+<td rowspan="24" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the wainscot and other articles for the joinery of the interior of the Lighthouse; the
+wages of the joiners preparing the wood at Hynish, and fitting it up at the Tower,</td>
+<td class="amount">1415</td>
+<td class="amount">5</td>
+<td class="intpart">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Green heart and oak for treenails, for securing the lower courses of Lighthouse Tower,</td>
+<td class="amount">40</td>
+<td class="amount">10</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr"><span class="pagenum" id="Page379">[379]</span>Plate-glass for windows and borrowed lights in
+partitions of Tower,</td>
+<td class="amount">84</td>
+<td class="amount">7</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Lewis bats, hinges, &amp;c., for entrance-door and shutters of Tower, and the locks and other
+mounting for the interior,</td>
+<td class="amount">218</td>
+<td class="amount">15</td>
+<td class="intpart">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">14 Copper oil-cisterns, a copper-pump, gauging-rods for do.,</td>
+<td class="amount">276</td>
+<td class="amount">10</td>
+<td class="intpart">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cast-iron water-tanks and coal-boxes, for interior of Tower,</td>
+<td class="amount">160</td>
+<td class="amount">13</td>
+<td class="intpart">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">A large cooking apparatus for kitchen of Tower, a stove to heat the lower apartments, and cast-iron
+smoke-tubes for both fire-places,</td>
+<td class="amount">117</td>
+<td class="amount">17</td>
+<td class="intpart">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">A bell-metal railing for balcony,</td>
+<td class="amount">341</td>
+<td class="amount">13</td>
+<td class="intpart">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">A bell-metal ladder from rock to entrance-door of Tower,</td>
+<td class="amount">194</td>
+<td class="amount">13</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">A cast-iron pillar to support floor of light-room,</td>
+<td class="amount">17</td>
+<td class="amount">8</td>
+<td class="intpart">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">A bell-metal lightning-conductor for Tower, and fixtures,</td>
+<td class="amount">65</td>
+<td class="amount">13</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cast-iron permanent railway on the Skerryvore Rock, from the landing creek to the Tower; a cast-iron
+platform near the Tower, and stairs at landing creek,</td>
+<td class="amount">493</td>
+<td class="amount">11</td>
+<td class="intpart">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">A crane erected at the landing creek, for landing materials on the rock,</td>
+<td class="amount">98</td>
+<td class="amount">13</td>
+<td class="intpart">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">A copper flagstaff and ball for the top of the Lighthouse Tower, with bell-metal base, fixtures,
+pulleys, &amp;c.,</td>
+<td class="amount">66</td>
+<td class="amount">10</td>
+<td class="intpart">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">A brass force-pump, for pumping water up from tanks to kitchen of Lighthouse,</td>
+<td class="amount">31</td>
+<td class="amount">17</td>
+<td class="intpart">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Premiums paid the seamen who were employed in the shipping department, in lieu of extra time,</td>
+<td class="amount">454</td>
+<td class="amount">2</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr"><span class="pagenum" id="Page380">[380]</span>Premiums paid 17 seamen who were employed in the
+building works at the Rock during the season of 1842, in lieu of extra time,</td>
+<td class="amount">121</td>
+<td class="amount">11</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Premiums of the landing master at Rock, foreman of masons, &amp;c.,</td>
+<td class="amount">96</td>
+<td class="amount">12</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the furniture, bedding, utensils, books, &amp;c., for the Lighthouse Tower,</td>
+<td class="amount">304</td>
+<td class="amount">6</td>
+<td class="intpart">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Sundry furnishings connected with the building of the Lighthouse Tower,—the wages of workmen quarrying
+stones at Hynish for Lighthouse Tower, previous to opening quarries at North Bay, and the wages of workmen, and furnishings for the
+general purposes of the works,</td>
+<td class="amount">1386</td>
+<td class="amount">18</td>
+<td class="intpart">5</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of three models, in stucco, of different forms of the Lighthouse,</td>
+<td class="amount">22</td>
+<td class="amount">4</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cast-iron water-tanks, which were built and secured into recesses of the rock, for the supplying
+of the rock works,—new water-casks, and their repairs, for taking off water,</td>
+<td class="amount">17</td>
+<td class="amount">5</td>
+<td class="intpart">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Feu-duty, rent of ground, assessed taxes, &amp;c., for the establishment at Hynish,</td>
+<td class="amount bb">143</td>
+<td class="amount bb">6</td>
+<td class="intpart bb">4</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">8551</td>
+<td class="amount">19</td>
+<td class="intpart">10</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the iron and steel which were used for all the departments of the works,</td>
+<td colspan="4">&#160;</td>
+<td class="amount">1299</td>
+<td class="amount">3</td>
+<td class="intpart">5</td>
+<td class="fracpart">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Lightroom and Apparatus.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of the lantern of cast-iron, with facings of bell-metal, including the cleaning and trimming
+paths, and bell-metal ladder outside of lantern, and the wages of the contractor’s workmen fitting them up at Skerryvore,</td>
+<td class="amount">£863</td>
+<td class="amount">13</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+<td rowspan="4" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Plate-glass for the lantern,</td>
+<td class="amount">268</td>
+<td class="amount">4</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Copper dome of lantern, including the internal frame of do., drip-pan, copper steps,
+<span class="pagenum" id="Page381">[381]</span>handles, air-tubes, rain-water pipes, a platform outside of dome for cleaning
+the vents, with the wages of the contractor’s workmen fitting them up at Skerryvore,</td>
+<td class="amount">348</td>
+<td class="amount">16</td>
+<td class="intpart">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Machinery of the revolving apparatus, and brass case for do. complete; three machines for pumping
+the oil for supplying the burner; the expense of the lamps, fountains, &amp;c.; and bell-metal frames for annular lenses, zones,
+pyramidal lenses, &amp;c., with the wages of the contractor’s workmen fitting up the above apparatus at Skerryvore,</td>
+<td class="amount">1244</td>
+<td class="amount">10</td>
+<td class="intpart">6</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="descr">The charge of Mr François of Paris furnishing eight annular lenses, and two spare do., with eight catadioptric
+frames of the first order for lower part, and eight pyramidal lenses, with mirrors, for upper part,</td>
+<td class="amount">£762</td>
+<td class="amount">0</td>
+<td class="intpart">0</td>
+<td colspan="9">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="descr">Expense of transporting the whole apparatus to Leith,</td>
+<td class="amount bb">79</td>
+<td class="amount bb">7</td>
+<td class="intpart bb">10</td>
+<td class="bb">&#160;</td>
+<td colspan="8">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="6">&#160;</td>
+<td class="amount">841</td>
+<td class="amount">7</td>
+<td class="intpart">10</td>
+<td colspan="5">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="descr">Cost of two bells, and one spare do., used during foggy weather,</td>
+<td class="amount">£107</td>
+<td class="amount">6</td>
+<td class="intpart">3</td>
+<td>&#160;</td>
+<td rowspan="2" colspan="8">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="descr">Shafting for do.; bevel wheels, levers, hammers, &amp;c., connecting with the machinery of apparatus,</td>
+<td class="amount bb">63</td>
+<td class="amount bb">14</td>
+<td class="intpart bb">11</td>
+<td class="fracpart bb">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="6">&#160;</td>
+<td class="amount">171</td>
+<td class="amount">1</td>
+<td class="intpart">2</td>
+<td class="fracpart">¹⁄₂</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Eighteen screens for lantern, cased with iron, and brass mounted, with rollers, &amp;c., and the
+time of workmen fitting them up at Skerryvore,</td>
+<td class="amount">48</td>
+<td class="amount">7</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+<td rowspan="4" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Air watch-bells from lightroom to bedrooms and kitchen, time of workmen fitting them up at Skerryvore,
+and furnishings for the complete working of do.,</td>
+<td class="amount">34</td>
+<td class="amount">13</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr"><span class="pagenum" id="Page382">[382]</span>Brass medallion heads and copper tubes for
+ventilation of lightroom,</td>
+<td class="amount">8</td>
+<td class="amount">9</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wood and workmanship making models of the catadioptric zones to a full size, and a brass model
+of frame for zones to a small scale,</td>
+<td class="amount bb">22</td>
+<td class="amount bb">1</td>
+<td class="intpart bb">2</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">3851</td>
+<td class="amount">5</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Salaries, Agencies, and Office Expenses.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Salaries of the Engineer, Surveyor, Clerk, and Store-keeper, including expenses of the survey
+of the rocks and adjoining Islands,</td>
+<td class="amount">£3262</td>
+<td class="amount">10</td>
+<td class="intpart">5</td>
+<td>&#160;</td>
+<td rowspan="3" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Agency of the Agent at Aberdeen, who made the monthly payments to the workmen’s relatives, and
+for some time superintending the making of tools; and the agency of the Lighthouse Agent at Greenock transacting business for the works,</td>
+<td class="amount">294</td>
+<td class="amount">13</td>
+<td class="intpart">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Iron safe, &amp;c., books, and other stationery for the various departments of the works,</td>
+<td class="amount bb">99</td>
+<td class="amount bb">10</td>
+<td class="intpart bb">10</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">3656</td>
+<td class="amount">15</td>
+<td class="intpart">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Petty disbursements and miscellaneous expenses, made on account of the general purposes of the works,</td>
+<td colspan="4">&#160;</td>
+<td class="amount">308</td>
+<td class="amount">7</td>
+<td class="intpart">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Lightkeepers’ Houses.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of workmen, quarrying, dressing, and building the stones of houses at Hynish for light-keepers,
+building the brick partitions and lining of walls, and the wages of joiners executing the joiner-work,</td>
+<td class="amount">£1893</td>
+<td class="amount">6</td>
+<td class="intpart">2</td>
+<td>&#160;</td>
+<td rowspan="10" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Timber and other articles used in the joinery of the houses,</td>
+<td class="amount">462</td>
+<td class="amount">19</td>
+<td class="intpart">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Plumber-work of roof, including the expense of bringing the water into the houses, &amp;c.,</td>
+<td class="amount">963</td>
+<td class="amount">18</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Bricks for partitions, lining of external walls, &amp;c.,</td>
+<td class="amount">73</td>
+<td class="amount">10</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Pavement for floors, water-cisterns, &amp;c.,</td>
+<td class="amount">51</td>
+<td class="amount">16</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Workmanship, executing the plaster-work (the lime being charged in a special account for this article),</td>
+<td class="amount">38</td>
+<td class="amount">12</td>
+<td class="intpart">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Glass for glazing the windows and fan-lights,</td>
+<td class="amount">20</td>
+<td class="amount">12</td>
+<td class="intpart">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr"><span class="pagenum" id="Page383">[383]</span>Locks, hinges, and other mounting for the doors and windows,</td>
+<td class="amount">101</td>
+<td class="amount">11</td>
+<td class="intpart">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cans for the chimney heads,</td>
+<td class="amount">9</td>
+<td class="amount">16</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Furniture, bedding, utensils, &amp;c., supplied for these houses,</td>
+<td class="amount bb">299</td>
+<td class="amount bb">0</td>
+<td class="intpart bb">4</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">3915</td>
+<td class="amount">4</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Pier at Hynish.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of masons, quarriers, carters, labourers, &amp;c., quarrying, dressing, and building the stones
+of a pier at Hynish for the landing and shipping of materials,</td>
+<td class="amount">£2300</td>
+<td class="amount">17</td>
+<td class="intpart">1</td>
+<td class="fracpart">¹⁄₂</td>
+<td rowspan="4" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Iron rails for the works of building the pier,</td>
+<td class="amount">53</td>
+<td class="amount">10</td>
+<td class="intpart">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Timbers for fenders of pier, and other purposes connected with the building of it,</td>
+<td class="amount">130</td>
+<td class="amount">19</td>
+<td class="intpart">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of a pont for building the pier,</td>
+<td class="amount bb">106</td>
+<td class="amount bb">8</td>
+<td class="intpart bb">11</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">2591</td>
+<td class="amount">15</td>
+<td class="intpart">5</td>
+<td class="fracpart">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Dock or Harbour for Tender.</span></td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Wages of workmen, quarrying, dressing, and building stones to form a talus wall and parapet
+along the south side and round the point of the pier at Hynish; raising the pier one course; excavating rock in the interior
+of the harbour or dock and along the point of pier; quarrying, dressing, and building the stones of boom-heads and walls of
+dock; excavating reservoir and forming embankment of do, for scouring sand, &amp;c., from the dock; forming the feeders to
+reservoir, and the tail-race from reservoir to dock, refreshments to workmen during night and tide works, &amp;c.,</td>
+<td class="amount">£6676</td>
+<td class="amount">10</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+<td rowspan="9" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Timber for double set of boom-gates of dock, copper for sheathing their ends, and mounting for booms,</td>
+<td class="amount">101</td>
+<td class="amount">2</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Timber used in constructing coffer-dams, and for the general purposes of the harbour works,</td>
+<td class="amount">135</td>
+<td class="amount">18</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of two sluices, and of the machinery, &amp;c., complete for working them,</td>
+<td class="amount">81</td>
+<td class="amount">14</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Two cast-iron ladders for sides of pier and dock,</td>
+<td class="amount">13</td>
+<td class="amount">1</td>
+<td class="intpart">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Cost of sea-boots, &amp;c., and keeping them in repair, which were used by the workmen at tide works,</td>
+<td class="amount">26</td>
+<td class="amount">12</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr"><span class="pagenum" id="Page384">[384]</span>Cost of silt-pumps, and furnishings of leather, &amp;c.,
+for making others, and keeping them in repair,</td>
+<td class="amount">9</td>
+<td class="amount">10</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Compensation paid the tenant of the farm of Hynish, for liberty to cut drains for a supply of water
+for a reservoir,</td>
+<td class="amount">5</td>
+<td class="amount">0</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Two signal lamps, two torches, turpentine, &amp;c., for signalizing when the tender enters the dock at night,</td>
+<td class="amount bb">5</td>
+<td class="amount bb">14</td>
+<td class="intpart bb">8</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount bb">7055</td>
+<td class="amount bb">3</td>
+<td class="intpart bb">5</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="6">&#160;</td>
+<td colspan="4" class="center"><span class="smcap">Total</span>,</td>
+<td class="amount">£89,817</td>
+<td class="amount">6</td>
+<td class="intpart">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="category"><span class="smcap">Deductions</span>—</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Price of steamer “Skerryvore,” sold,</td>
+<td class="amount">£1616</td>
+<td class="amount">0</td>
+<td class="intpart">6</td>
+<td>&#160;</td>
+<td rowspan="5" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Do. of sloop “Queen,” sold,</td>
+<td class="amount">200</td>
+<td class="amount">0</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Do. of 4 Stone Lighters, sold,</td>
+<td class="amount">225</td>
+<td class="amount">0</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Do. of Horses and Carts, sold,</td>
+<td class="amount">60</td>
+<td class="amount">0</td>
+<td class="intpart">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="descr">Implements sold or afterwards used at other works of the Board,</td>
+<td class="amount bb">738</td>
+<td class="amount bb">8</td>
+<td class="intpart bb">10</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount bb">2839</td>
+<td class="amount bb">9</td>
+<td class="intpart bb">4</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10">&#160;</td>
+<td class="amount">£86,977</td>
+<td class="amount">17</td>
+<td class="intpart">7</td>
+<td>&#160;</td>
+</tr>
+
+</table>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter" id="App7">
+
+<p><span class="pagenum" id="Page385">[385]</span></p>
+
+<h3 class="nobreak"><span class="chapno">APPENDIX, No. VII.</span><br>
+<span class="chapname">EXCERPTS FROM AN ACCOUNT OF EXPERIMENTS UPON THE FORCE
+OF THE WAVES OF THE ATLANTIC AND GERMAN OCEANS.<br><span class="fsize90">By<br>
+<span class="smcap">Thomas Stevenson, F.R.S.E., Civil-Engineer, Edinburgh.</span></span><br>
+<span class="fsize80">(From the Transactions of the Royal Society of Edinburgh, Vol. XVI.)</span></span></h3>
+
+</div><!--chapter-->
+
+<p>The letters (see <a href="#Plate4">Plate IV.</a>) D&#160;E&#160;F&#160;D represent a cast-iron cylinder, which
+is firmly bolted at the projecting flanges G to the rock where the experiments
+are wanted. This cylinder has a flange at D&#160;D. L&#160;L is a door,
+which is opened when the observation is to be read off. A&#160;A is of iron, and
+forms a circular plate or disc, on which the sea impinges. Fastened to the
+disc are four guide-rods B&#160;B&#160;B&#160;B. These rods pass through a circular plate
+C&#160;C (which is screwed down to the flange D&#160;D), and also through holes in the
+bottom E&#160;F. Within the cylinder there is attached to the plate C&#160;C a
+powerful steel spring, to the other or free end of which is fastened the small
+circular plate K&#160;K, which again is secured to the guide-rods B&#160;B&#160;B&#160;B. There
+are also rings of leather T&#160;T, that slide on the guide-rods, and serve as
+indices for registering how far the rods are pushed through the holes in the
+bottom; or, in other words, how much the spring has been drawn out or
+lengthened by the force of the sea acting upon the plate or disc A&#160;A. The
+object of having four leathern rings, where one might have answered the
+purpose, was merely that they might serve as a check upon each other;
+and so perfectly did they answer the purpose intended, that in every instance
+they were found equidistant from the bottom of the cylinder; proving
+thereby, that after the recoil of the spring, they had all kept their places.
+The guide-rods are graduated, so as to enable the observer to note exactly
+the quantity that the spring has yielded.</p>
+
+<p>This instrument, which may, perhaps, be not improperly termed a
+<i>Marine Dynamometer</i>, is, therefore, a self-registering apparatus which indicates
+the maximum force of the waves. In the graduation of the instrument,
+the power of the spring is ascertained by carefully loading the disc
+with weights, so that when the quantity that the spring has yielded by the
+action of the sea is known, the pressure due to the area of the disc exposed
+is known also. The discs employed were from 3 to 9 inches diameter, but<span class="pagenum" id="Page386">[386]</span>
+generally 6 inches, and the powers of the springs varied from 10 lb. to about
+50 lb. for every ¹⁄₈ inch of elongation. Their respective effects were afterwards
+reduced to a value per square foot. The instrument was generally
+placed so as to be immersed at about three-fourths tide, and in such situations
+as would afford a considerable depth of water. It is not desirable to
+have the instrument placed at a much lower level, as it has not unfrequently
+happened during a gale, that for days together no one could approach it to
+read off the result and readjust the indices to zero. It must, however, at
+the same time be remarked, that it is in most situations almost impossible
+to receive the force unimpaired, as the waves are more or less broken by
+hidden rocks or shoal ground before they reach the instrument.</p>
+
+<p>In connection with the apparatus above described, a graduated pole was
+erected on an outlying sunken rock, for the purpose of ascertaining the
+height of the waves; but the observations were not of so satisfactory a
+nature as could have been desired, and the poles soon worked loose from
+their attachments, and disappeared.</p>
+
+<p>With the instrument which has been explained, I entered upon the following
+train of <span class="nowrap">observations:—</span></p>
+
+<p>In 1842 several observations were made on the waves of the Irish Sea
+at the island of Little Ross, lying off the Bay of Kirkcudbright. Since
+April 1843 till now, continued observations have been made on the Atlantic
+at the Skerryvore and neighbouring rocks lying off the island of Tyree,
+Argyllshire; and in 1844 a series of observations was begun on the German
+Ocean at the Bell Rock. It will be seen, that in selecting these localities
+a varied exposure has been embraced, comprising the comparatively sheltered
+Irish Sea, the more exposed eastern shore of Scotland, and the wild
+Rocks of Skerryvore, which are open to the full fury of the Atlantic, the far
+distant shores of North America being the nearest land on the west.</p>
+
+<p>Referring for more full information to the <a href="#Ref4">tables</a> of experiments which
+are given at the end of this paper, it will be sufficient in this place to state
+generally the following as the results obtained.</p>
+
+<p>In the <i>Atlantic Ocean</i>, according to the observations made at the Skerryvore
+rocks, the average of results for five of the <i>summer</i> months during the
+years 1843 and 1844, is 611 lb. per square foot. The average results for six
+of the <i>winter</i> months (1843 and 1844), is 2086 lb. per square foot, or thrice
+as great as in the summer months.</p>
+
+<p>The <i>greatest result</i> yet obtained at Skerryvore was during the heavy<span class="pagenum" id="Page387">[387]</span>
+westerly gale of 29th March 1845, when a pressure of 6083 lb. per square
+foot was registered. The next highest is 5323 lb.</p>
+
+<p>In the <i>German Ocean</i>, according to the observations made at the Bell
+Rock, the greatest result yet obtained is 3013 lb. per square foot.</p>
+
+<p>It thus appears, that the greatest effect of the sea, which has been observed,
+is that of the Atlantic at Skerryvore, which is nearly equal to three
+tons per square foot.</p>
+
+<p>These experiments, amounting to 267 in number, and on the Atlantic
+alone, extending over 23 months continuously, are not intended to prove anything
+farther than the simple fact, that the sea has been known to exert a
+force equivalent to a pressure of three tons per square foot, however much
+more.</p>
+
+<p>It is proper, however, to observe, that there may be some objection to
+referring the action of the sea to a statical value. Although the instrument
+might perhaps be made capable of giving a dynamical result, it was considered
+unnecessary, in these preliminary experiments, to do anything more
+than represent the maximum pressure registered by the spring, because the
+effects of the waves may, from supposing them to have continuity of action,
+be perhaps regarded as similar to a statical pressure, rather than to the impact
+of a hard body. The near coincidence, or indeed almost perfect agreement
+of the results of the experiments made with different instruments, goes
+far to shew that the waves act in very much the same manner as a pressure,
+although both pressure and impact must obviously enter into their effect.
+In the experiments, begun February 1844, and given at the end of the
+paper, the three instruments had not only different areas of discs, but very
+different powers of springs, and yet the results were almost identical. Now,
+the same force, supposing the waves to act like the impact of a hard body,
+would, in the Marine Dynamometer, have assumed very different statical
+values, according to the spaces in which that force was expended or developed;
+so that with the same force of impact, the indication of a weak
+spring would be less than that of a stronger.</p>
+
+<p>In future experiments it may be interesting, however, to test the springs
+dynamically, by means of the impact of a heavy body dropped from a given
+height upon the plate or disc of the instrument. In some experiments lately
+made in this way, by dropping a cannon-ball upon the disc, it appeared,
+that, within the limits of the experiments, there was for each individual
+spring a ratio between the value registered by the leathern index and
+the calculated momentum of the impinging body. These ratios were, of<span class="pagenum" id="Page388">[388]</span>
+course, found to vary in springs of different power, and to be constant only
+for springs of the same power. Did the waves, therefore, act by a sudden
+finite impact, like the cannon-ball employed in this instance, we could
+scarcely have found such harmony between the results of instruments with
+different springs, as the experiments alluded to afford. At the same time,
+the result cannot, perhaps, be in strictness considered correct; but, from the
+elongation of the spring being very small, the results may be regarded as
+practically correct,—the more so when we find so remarkable a coincidence
+of results as that alluded to.</p>
+
+<p class="fsize90 blankbefore75"><span class="smcap">Experiments.</span>—With reference to the following experiments I have only
+to observe, that those which were made at Little Ross, upon the Irish Sea, cannot,
+from the unusual fineness of the weather at the time, be regarded as affording
+a true value of the effects of a hard gale in these seas. Of the others it is
+to be noticed, that where two or three instruments were for some time employed as
+a check upon each other, and only one or two readings are given, the want has
+occurred either from the instruments being under repair, or being difficult of access
+in stormy weather, or during neap tides. It often happened also, in consequence
+of the springs proving too weak, when new ones had to be made, or the area of
+the disc reduced. Registers of the state of the weather, apparent height of
+spray, &amp;c., were generally kept; but it was not considered necessary to complicate
+the Tables by inserting these, excepting in one or two instances.</p>
+
+<p><span class="pagenum" id="Page389">[389]</span></p>
+
+<table class="waveforce" id="Ref4">
+
+<colgroup>
+<col class="w05em">
+<col class="w01em">
+<col span="2" class="wauto">
+<col class="w05em">
+<col class="w08em">
+</colgroup>
+
+<tr>
+<th colspan="2" class="br">Dates.</th>
+<th colspan="4">lbs. to a Square Foot.</th>
+</tr>
+
+<tr>
+<td colspan="6" class="remarks">Observations at Little Ross.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="year">1842.</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="month">April</td>
+<td class="date">25</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;&#8199;15&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">28</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;&#8199;51&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="5" class="month">June</td>
+<td class="date">1</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;&#8199;36&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">4</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;&#8199;81·5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">20</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;&#8199;86·5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">24</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;840·0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">25</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;458·0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="month">July</td>
+<td class="date">25</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;380·0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="month">Aug.</td>
+<td class="date">2</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;570·0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">5</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;665·0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">6</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;380·0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">9</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;380·0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="6" class="remarks">The Observations at the Skerryvore Rock, and the neighbouring Island of Tyree,
+distant 13 miles from the Skerryvore, are as follows:—</td>
+</tr>
+
+<tr>
+<td colspan="2" class="year">1843.</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="month">April</td>
+<td class="date">24</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;455&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">25</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;707&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="6" class="month">May</td>
+<td class="date">7</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;243&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">11</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;182&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">12</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;243&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">16</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;364&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="date">20</td>
+<td rowspan="2" class="brace">-</td>
+<td rowspan="2" class="brace bt bb bl">&#160;</td>
+<td class="force">&#8199;495&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="force">&#8199;476&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="5" class="month">June</td>
+<td class="date">3</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;182&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">4</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;519&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">7</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;428&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">8</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;855&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">9</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;173&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="month">July</td>
+<td class="date">2</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;476&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="date">3</td>
+<td rowspan="2" class="brace">-</td>
+<td rowspan="2" class="brace bt bb bl">&#160;</td>
+<td class="force">&#8199;723&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="force">&#8199;866&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">30</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;433&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="month">Aug.</td>
+<td class="date">9</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;346&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">22</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;723&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">30</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;389&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="month">Sept.</td>
+<td class="date">5</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;866&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">21</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;952&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="month">Oct.</td>
+<td class="date">5</td>
+<td colspan="2">&#160;</td>
+<td class="force">1535&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">6</td>
+<td colspan="2">&#160;</td>
+<td class="force">1606&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="month">Nov.</td>
+<td class="date">18</td>
+<td colspan="2">&#160;</td>
+<td class="force">1711&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">19</td>
+<td colspan="2">&#160;</td>
+<td class="force">1497&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">27</td>
+<td colspan="2">&#160;</td>
+<td class="force">1497&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">29</td>
+<td colspan="2">&#160;</td>
+<td class="force">2353&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="5" class="month">Dec.</td>
+<td class="date">5</td>
+<td colspan="2">&#160;</td>
+<td class="force">2674&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="date">8</td>
+<td rowspan="2" class="brace">-</td>
+<td rowspan="2" class="brace bt bb bl">&#160;</td>
+<td class="force">3421&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="left">At least</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">14</td>
+<td colspan="2">&#160;</td>
+<td class="force">2460&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">26</td>
+<td colspan="2">&#160;</td>
+<td class="force">1947&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="6" class="remarks">In January, two instruments were placed beside each other, but not set parallel.
+These instruments had springs of different power, the one being about double that of the other, and one had a disc
+of 3 inches diameter, the other 6 inches.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="year">1844.</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="8" class="month">Jan.</td>
+<td class="date">6</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;962&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;928&#8200;&#8199;</td>
+<td>&#160;</td>
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+
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+<td class="date">7</td>
+<td colspan="2">&#160;</td>
+<td class="force">2353&#8200;&#8199;</td>
+<td>&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;357&#8200;&#8199;</td>
+<td>&#160;</td>
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+
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+<td class="date">9</td>
+<td colspan="2">&#160;</td>
+<td class="force">1925&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">1000&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">10</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;826&#8200;&#8199;</td>
+<td>&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">1000&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
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+<td colspan="6" class="remarks">Both instruments set parallel.</td>
+</tr>
+
+<tr>
+<td rowspan="2">&#160;</td>
+<td class="date">16</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;424&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;427&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="6" class="remarks">Another instrument was placed beside them, but the two marked thus* were found to
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+</tr>
+
+<tr>
+<td rowspan="3">&#160;</td>
+<td class="date">28</td>
+<td colspan="2">&#160;</td>
+<td class="force">3422&#8200;&#8199;</td>
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+
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+<td rowspan="2" class="br">&#160;</td>
+<td colspan="2" rowspan="2">&#160;</td>
+<td class="force">2285&#8200;&#8199;</td>
+<td class="left">*</td>
+</tr>
+
+<tr>
+<td class="force">3313&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="21" class="month">Feb.</td>
+<td class="date">2</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;429&#8200;&#8199;</td>
+<td>&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;457&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">3</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;429&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;457&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">13</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;214&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;228&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">15</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;321&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;280&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;321&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">16</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;428&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;402&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;343&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">24</td>
+<td colspan="2">&#160;</td>
+<td class="force">1284&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">1364&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;685&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">26</td>
+<td colspan="2">&#160;</td>
+<td class="force">2032&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">2068&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;399&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">27</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;321&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;321&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;342&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="18" class="month">March</td>
+<td class="date">4</td>
+<td colspan="2">&#160;</td>
+<td class="force">3316&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">3369&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">3427&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">7</td>
+<td colspan="2">&#160;</td>
+<td class="force">1069&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;963&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;913&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">10</td>
+<td colspan="2">&#160;</td>
+<td class="force">1925&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">1925&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">1713&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">11</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;535&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;481&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;456&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">12</td>
+<td colspan="2">&#160;</td>
+<td class="force">3316&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">4011&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">2970&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">13</td>
+<td colspan="2">&#160;</td>
+<td class="force">1142&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">1283&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">1283&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="35" class="month">April</td>
+<td class="date">10</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;457&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;428&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;481&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">11</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;800&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">12</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;343&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;321&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">14</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;571&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;535&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">16</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;571&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;642&#8200;&#8199;</td>
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+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;481&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">17</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;800&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;856&#8200;&#8199;</td>
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+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;862&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">18</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;571&#8200;&#8199;</td>
+<td>&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
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+<td class="force">&#8199;481&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">19</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;800&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
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+<td class="force">&#8199;535&#8200;&#8199;</td>
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+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;481&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">22</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;913&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;482&#8200;&#8199;</td>
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+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;962&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">24</td>
+<td colspan="2">&#160;</td>
+<td class="force">1942&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">1604&#8200;&#8199;</td>
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+<td class="br">&#160;</td>
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+<td class="force">1370&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">25</td>
+<td colspan="2">&#160;</td>
+<td class="force">1283&#8200;&#8199;</td>
+<td>&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
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+<td class="force">&#8199;343&#8200;&#8199;</td>
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+
+<tr>
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+<td class="force">&#8199;321&#8200;&#8199;</td>
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+
+<tr>
+<td class="date">27</td>
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+<td class="force">&#8199;457&#8200;&#8199;</td>
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+
+<tr>
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+<tr>
+<td rowspan="2" class="br">&#160;</td>
+<td rowspan="2" class="brace">-</td>
+<td rowspan="2" class="brace bt bb bl">&#160;</td>
+<td class="left">Night</td>
+<td rowspan="2" class="left">800</td>
+</tr>
+
+<tr>
+<td class="left">tide</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;642&#8200;&#8199;</td>
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+
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+<td class="date">30</td>
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+
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+<td class="br">&#160;</td>
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+<td class="force">&#8199;241&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="month">May</td>
+<td class="date">15</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;343&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">14</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;481&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="month">June</td>
+<td class="date">6</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;571&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">15</td>
+<td colspan="2">&#160;</td>
+<td class="force">1828&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="11" class="month">July</td>
+<td class="date">11</td>
+<td colspan="2">&#160;</td>
+<td class="force">1028&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">13</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;457&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">18</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;914&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">23</td>
+<td colspan="2">&#160;</td>
+<td class="force">1532&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">25</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;571&#8200;&#8199;</td>
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+
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+<td class="force">&#8199;971&#8200;&#8199;</td>
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+<td class="date">27</td>
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+<td class="force">&#8199;457&#8200;&#8199;</td>
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+
+<tr>
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+
+<tr>
+<td rowspan="6" class="month">Aug.</td>
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+<td class="force">&#8199;571&#8200;&#8199;</td>
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+
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+<td class="force">&#8199;914&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">21</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;800&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">30</td>
+<td colspan="2">&#160;</td>
+<td class="force">1713&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="6" class="month">Sept.</td>
+<td class="date">12</td>
+<td colspan="2">&#160;</td>
+<td class="force">1028&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">14</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;914&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">20</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;457&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">23</td>
+<td colspan="2">&#160;</td>
+<td class="force">1142&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">25</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;685&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">30</td>
+<td colspan="2">&#160;</td>
+<td class="force">1599&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="11" class="month">Oct.</td>
+<td class="date">2</td>
+<td colspan="2">&#160;</td>
+<td class="force">2399&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">3</td>
+<td colspan="2">&#160;</td>
+<td class="force">1485&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">4</td>
+<td colspan="2">&#160;</td>
+<td class="force">1828&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">11</td>
+<td colspan="2">&#160;</td>
+<td class="force">3427&#8200;&#8199;</td>
+<td class="left"><a id="FNanchor88" href="#Footnote88" class="fnanchor">[88]</a></td>
+</tr>
+
+<tr>
+<td class="date">14</td>
+<td colspan="2">&#160;</td>
+<td class="force">1599&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">19</td>
+<td colspan="2">&#160;</td>
+<td class="force">1599&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">20</td>
+<td colspan="2">&#160;</td>
+<td class="force">2513&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">22<span class="pagenum" id="Page390">[390]</span></td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;800&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">24</td>
+<td colspan="2">&#160;</td>
+<td class="force">1827&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">28</td>
+<td colspan="2">&#160;</td>
+<td class="force">1485&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">29</td>
+<td colspan="2">&#160;</td>
+<td class="force">&#8199;457&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="9" class="month">Nov.</td>
+<td class="date">2</td>
+<td colspan="2">&#160;</td>
+<td class="force">1942&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">10</td>
+<td colspan="2">&#160;</td>
+<td class="force">1028&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">14</td>
+<td colspan="2">&#160;</td>
+<td class="force">1257&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">15</td>
+<td colspan="2">&#160;</td>
+<td class="force">2056&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">16</td>
+<td colspan="2">&#160;</td>
+<td class="force">2056&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">22</td>
+<td colspan="2">&#160;</td>
+<td class="force">2627&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">23</td>
+<td colspan="2">&#160;</td>
+<td class="force">3427&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">27</td>
+<td colspan="2">&#160;</td>
+<td class="force">3199&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">28</td>
+<td colspan="2">&#160;</td>
+<td class="force">4112&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="6" class="month">Dec.</td>
+<td class="date">7</td>
+<td colspan="2">&#160;</td>
+<td class="force">1369&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">9</td>
+<td colspan="2">&#160;</td>
+<td class="force">2738&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">10</td>
+<td colspan="2">&#160;</td>
+<td class="force">1825&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">13</td>
+<td colspan="2">&#160;</td>
+<td class="force">1925&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">14</td>
+<td colspan="2">&#160;</td>
+<td class="force">1027&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="date">15</td>
+<td colspan="2">&#160;</td>
+<td class="force">1764&#8200;&#8199;</td>
+<td>&#160;</td>
+</tr>
+
+</table>
+
+<div class="footnote">
+
+<p><a id="Footnote88" href="#FNanchor88" class="label">[88]</a> On this occasion, 14 stones were slightly moved, and
+14 scattered, all of which had been built into the round-head or end
+of Hynish Pier, which was still in an unfinished state, and a Dynamometer which was attached to the Pier, registered on this
+occasion 2557 lb. These stones weighed from 1 to 1¹⁄₂ tons, and exposed, when built into the wall, about two square feet
+of surface. The stone to which the instrument was fixed was turned upside down, although it weighed about 1¹⁄₄ ton =
+2800 lb.</p>
+
+</div><!--footnote-->
+
+<p>A more exposed point of the Skerryvore Rock was at this time chosen
+for experiment; and with the view of ascertaining the effect of the waves
+at different heights upon the rock, two instruments were fixed, the one
+(No. I.) several feet lower, and about 40 feet seaward of the other (No. II.).
+It was observed, that about half-flood the force of the waves was a good
+deal expended before they reached the place where No. I. was placed, from
+there being so little water on the rocks outside; whereas when the tide
+was higher, the waves were, from the greater depth of water, not so much
+broken when they reached No. II. The results of the Marine Dynamometer
+shew generally about twice the force at No. II. as at No. I.; a result
+which shews how important it would be to ascertain the relative forces of
+the waves at different levels upon our breakwaters and other seaworks.</p>
+
+<table class="waveforce2">
+
+<tr class="bb">
+<th colspan="2" class="br">Date.</th>
+<th class="br">Remarks.</th>
+<th class="br">No. of<br>Instru-<br>ment.</th>
+<th class="br">Pressure<br>in lbs.<br>per<br>Square Foot.</th>
+</tr>
+
+<tr>
+<td colspan="2" class="year">1845.</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="10" class="month">Jan.</td>
+<td class="date">7</td>
+<td class="remarks">Heavy sea.</td>
+<td class="instr">I.</td>
+<td class="pressure">1714</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">...</td>
+<td class="instr">II.</td>
+<td class="pressure">4182</td>
+</tr>
+
+<tr>
+<td class="date">12</td>
+<td class="remarks">Very heavy swell.</td>
+<td class="instr">I.</td>
+<td class="pressure">2856</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">...</td>
+<td class="instr">II.</td>
+<td class="pressure">5032</td>
+</tr>
+
+<tr>
+<td class="date">16</td>
+<td class="remarks">Heavy ground swell.</td>
+<td class="instr">I.</td>
+<td class="pressure">2856</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">...</td>
+<td class="instr">II.</td>
+<td class="pressure">4752</td>
+</tr>
+
+<tr>
+<td class="date">22</td>
+<td class="remarks">A good deal of sea.</td>
+<td class="instr">I.</td>
+<td class="pressure">2856</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">...</td>
+<td class="instr">II.</td>
+<td class="pressure">5323</td>
+</tr>
+
+<tr>
+<td class="date">28</td>
+<td class="remarks">Heavy ground swell.</td>
+<td class="instr">I.</td>
+<td class="pressure">2627</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">...</td>
+<td class="instr">II.</td>
+<td class="pressure">4562</td>
+</tr>
+
+<tr>
+<td rowspan="6" class="month">Feb.</td>
+<td class="date">5</td>
+<td class="remarks">Fresh gales.</td>
+<td class="instr">I.</td>
+<td class="pressure">&#8199;856</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">...</td>
+<td class="instr">II.</td>
+<td class="pressure">3042</td>
+</tr>
+
+<tr>
+<td class="date">21</td>
+<td class="remarks">...</td>
+<td class="instr">I.</td>
+<td class="pressure">1827</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">...</td>
+<td class="instr">II.</td>
+<td class="pressure">3422</td>
+</tr>
+
+<tr>
+<td class="date">24</td>
+<td class="remarks">Fresh breezes.</td>
+<td class="instr">I.</td>
+<td class="pressure">1256</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">...</td>
+<td class="instr">II.</td>
+<td class="pressure">3802</td>
+</tr>
+
+<tr>
+<td rowspan="9" class="month">March</td>
+<td class="date">9</td>
+<td class="remarks">Ground swell.</td>
+<td class="instr">I.</td>
+<td class="pressure">1256</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">Waves supposed about 10 feet high.</td>
+<td class="instr">II.</td>
+<td class="pressure">3041</td>
+</tr>
+
+<tr>
+<td class="date">11</td>
+<td class="remarks">Short sea.</td>
+<td class="instr">I.</td>
+<td class="pressure">1028</td>
+</tr>
+
+<tr>
+<td class="date">24</td>
+<td class="remarks">Heavy sea.</td>
+<td class="instr">I.</td>
+<td class="pressure">2281</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">Waves supposed about 20 feet high.</td>
+<td class="instr">II.</td>
+<td class="pressure">4562</td>
+</tr>
+
+<tr>
+<td class="date">26</td>
+<td class="remarks">Swell.</td>
+<td class="instr">I.</td>
+<td class="pressure">1256</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">Waves about 6 feet high.</td>
+<td class="instr">II.</td>
+<td class="pressure">3041</td>
+</tr>
+
+<tr>
+<td class="date">29</td>
+<td class="remarks">Strong gale, with heavy sea, the highest waves supposed 20 feet high, and the spray rose about 70 feet.</td>
+<td class="instr">I.</td>
+<td class="pressure">2856</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="remarks">...</td>
+<td class="instr">II.</td>
+<td class="pressure">6083</td>
+</tr>
+
+</table>
+
+<p><span class="pagenum" id="Page391">[391]</span></p>
+
+<p class="tabhead"><i>Register of Observations on the force of the Sea, made at the Bell Rock, German
+Ocean.</i></p>
+
+<table class="waveforce2">
+
+<tr class="bb">
+<th colspan="2" class="br">Dates.</th>
+<th>lbs. to a<br>Square Foot.</th>
+</tr>
+
+<tr>
+<td colspan="2" class="year">1844.</td>
+<td class="pressure">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="month">Sept.</td>
+<td class="date">15</td>
+<td class="pressure">&#8199;853</td>
+</tr>
+
+<tr>
+<td class="date">20</td>
+<td class="pressure">2260</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="month">Oct.</td>
+<td class="date">9</td>
+<td class="pressure">3013</td>
+</tr>
+
+<tr>
+<td class="date">...</td>
+<td class="pressure">2562</td>
+</tr>
+
+<tr>
+<td class="date">26</td>
+<td class="pressure">1142</td>
+</tr>
+
+<tr>
+<td class="date">27</td>
+<td class="pressure">&#8199;958</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="month">Nov.</td>
+<td class="date">12</td>
+<td class="pressure">1680</td>
+</tr>
+
+<tr>
+<td class="date">13</td>
+<td class="pressure">1920</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="month">Dec.</td>
+<td class="date">13</td>
+<td class="pressure">1560</td>
+</tr>
+
+<tr>
+<td class="date">26</td>
+<td class="pressure">1439</td>
+</tr>
+
+<tr>
+<td colspan="2" class="year">1845.</td>
+<td class="pressure">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="9" class="month">Jan.</td>
+<td class="date">7</td>
+<td class="pressure">1559</td>
+</tr>
+
+<tr>
+<td class="date">10</td>
+<td class="pressure">1439</td>
+</tr>
+
+<tr>
+<td class="date">11</td>
+<td class="pressure">1439</td>
+</tr>
+
+<tr>
+<td class="date">15</td>
+<td class="pressure">1559</td>
+</tr>
+
+<tr>
+<td class="date">25</td>
+<td class="pressure">&#8199;959</td>
+</tr>
+
+<tr>
+<td class="date">26</td>
+<td class="pressure">&#8199;719</td>
+</tr>
+
+<tr>
+<td class="date">27</td>
+<td class="pressure">1199</td>
+</tr>
+
+<tr>
+<td class="date">30</td>
+<td class="pressure">2879</td>
+</tr>
+
+<tr>
+<td class="date">31</td>
+<td class="pressure">1559</td>
+</tr>
+
+<tr>
+<td rowspan="5" class="month">Feb.</td>
+<td class="date">6</td>
+<td class="pressure">2999</td>
+</tr>
+
+<tr>
+<td class="date">24</td>
+<td class="pressure">1199</td>
+</tr>
+
+<tr>
+<td class="date">25</td>
+<td class="pressure">&#8199;959</td>
+</tr>
+
+<tr>
+<td class="date">27</td>
+<td class="pressure">&#8199;839</td>
+</tr>
+
+<tr>
+<td class="date">28</td>
+<td class="pressure">1319</td>
+</tr>
+
+<tr>
+<td rowspan="9" class="month">March</td>
+<td class="date">4</td>
+<td class="pressure">&#8199;959</td>
+</tr>
+
+<tr>
+<td class="date">7</td>
+<td class="pressure">1079</td>
+</tr>
+
+<tr>
+<td class="date">11</td>
+<td class="pressure">1919</td>
+</tr>
+
+<tr>
+<td class="date">20</td>
+<td class="pressure">2519</td>
+</tr>
+
+<tr>
+<td class="date">21</td>
+<td class="pressure">2759</td>
+</tr>
+
+<tr>
+<td class="date">24</td>
+<td class="pressure">1319</td>
+</tr>
+
+<tr>
+<td class="date">25</td>
+<td class="pressure">&#8199;959</td>
+</tr>
+
+<tr>
+<td class="date">28</td>
+<td class="pressure">&#8199;599</td>
+</tr>
+
+<tr>
+<td class="date">30</td>
+<td class="pressure">1079</td>
+</tr>
+
+</table>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter" id="App8">
+
+<p><span class="pagenum" id="Page392">[392-<br>393]<a id="Page393"></a></span></p>
+
+<h3 class="nobreak"><span class="chapno">APPENDIX, No. VIII.</span><br>
+<span class="chapname app8">LIST OF NORTHERN LIGHTHOUSES, BEACONS
+AND BUOYS.<br>
+<span class="fsize80">FOR 1848.</span></span></h3>
+
+<hr class="chap x-ebookmaker-drop">
+
+</div><!--chapter-->
+
+<p><span class="pagenum" id="Page394">[394-<br>395]<a id="Page395"></a></span></p>
+
+<table class="lighthouses">
+
+<tr class="bb">
+<th class="br">Name of Light.</th>
+<th class="br">Situation of Light.</th>
+<th class="br">Number<br>of<br> Lights.</th>
+<th class="br">Appearance of Light.</th>
+<th class="br">Distance<br>visible<br>in<br>Nautic<br>Miles.</th>
+<th class="br">Points of Compass<br>within which<br>Light is Visible.</th>
+<th class="br">Height of<br>Lantern<br>in feet<br>above<br>High-water<br>Spring<br>Tides.</th>
+<th colspan="2" class="br">North<br>Latitude.</th>
+<th colspan="2" class="br">West<br>Longitude.</th>
+<th>Date<br>of first<br>Exhibition.</th>
+</tr>
+
+<tr class="bb">
+<td class="name">INCHKEITH</td>
+<td class="txt">Highest Land on the Island of Inchkeith, in Fifeshire</td>
+<td class="other">One</td>
+<td class="txt">Revolving, and appearing in its brightest state once every minute</td>
+<td class="other">18</td>
+<td class="txt">All round the Compass</td>
+<td class="other">220</td>
+<td class="degrees">56°</td>
+<td class="minutes">&#8199;2′</td>
+<td class="degrees">3°</td>
+<td class="minutes">&#8199;8′</td>
+<td class="year">1804</td>
+</tr>
+
+<tr class="bb">
+<td class="name">ISLE OF MAY</td>
+<td class="txt">Highest Land on Isle of May, in Fifeshire</td>
+<td class="other">One</td>
+<td class="txt">Fixed</td>
+<td class="other">21</td>
+<td class="txt">All round the Compass</td>
+<td class="other">240</td>
+<td class="degrees">56°</td>
+<td class="minutes">11′</td>
+<td class="degrees">2°</td>
+<td class="minutes">33′</td>
+<td class="year">1816</td>
+</tr>
+
+<tr class="bb">
+<td class="name">DO. LEADING LIGHT</td>
+<td class="txt">Placed about 130 feet below the High Light, and to the NE. by N. of it</td>
+<td class="other">One</td>
+<td class="txt">Fixed</td>
+<td class="other">15</td>
+<td class="txt">When <i>seen in</i> <span class="allsmcap">ONE</span> <i>line</i> with the High Light, these two Lights bear NE.
+by N. ¹⁄₄ N., and SW. by S. ¹⁄₄ S., and in this line lead about <i>half a mile</i> to the Eastward of the North Carr Rock. The Lights
+must on no account be opened to the Westward</td>
+<td class="other">110</td>
+<td colspan="2" class="other">&#160;</td>
+<td colspan="2" class="other">&#160;</td>
+<td class="year">1844</td>
+</tr>
+
+<tr class="bb">
+<td class="name">BELL ROCK</td>
+<td class="txt">Bell Rock, a sunk reef, 11³⁄₄ miles S. by E. ¹⁄₃ E. off Arbroath, in Forfarshire</td>
+<td class="other">One</td>
+<td class="txt">Revolving, and shewing alternately a red and white light every 2 minutes</td>
+<td class="other">14</td>
+<td class="txt">All round the Compass</td>
+<td class="other">90</td>
+<td class="degrees">56°</td>
+<td class="minutes">26′</td>
+<td class="degrees">2°</td>
+<td class="minutes">23′</td>
+<td class="year">1811</td>
+</tr>
+
+<tr class="bb">
+<td class="name">GIRDLENESS</td>
+<td class="txt">Girdleness, Kincardineshire</td>
+<td class="other">Two</td>
+<td class="txt">Fixed Lights, one above the other</td>
+<td class="other">19 &amp; 16</td>
+<td class="txt">From NNE. to WSW. ¹⁄₂ W. Easterly and Southerly</td>
+<td class="other">185 &amp; 115</td>
+<td class="degrees">57°</td>
+<td class="minutes">&#8199;8′</td>
+<td class="degrees">2°</td>
+<td class="minutes">&#8199;3′</td>
+<td class="year">1833</td>
+</tr>
+
+<tr class="bb">
+<td class="name">BUCHANNESS</td>
+<td class="txt">Buchanness, Aberdeenshire</td>
+<td class="other">One</td>
+<td class="txt">Flashing once every 5 seconds</td>
+<td class="other">16</td>
+<td class="txt">From N. by E. to SW. by W. Easterly</td>
+<td class="other">130</td>
+<td class="degrees">57°</td>
+<td class="minutes">28′</td>
+<td class="degrees">1°</td>
+<td class="minutes">46′</td>
+<td class="year">1827</td>
+</tr>
+
+<tr class="bb">
+<td class="name">KINNAIRDHEAD</td>
+<td class="txt">Kinnairdhead, Aberdeenshire</td>
+<td class="other">One</td>
+<td class="txt">Fixed</td>
+<td class="other">15</td>
+<td class="txt">From WNW. to SE. Northerly</td>
+<td class="other">120</td>
+<td class="degrees">57°</td>
+<td class="minutes">42′</td>
+<td class="degrees">2°</td>
+<td class="minutes">&#8199;0′</td>
+<td class="year">1787</td>
+</tr>
+
+<tr class="bb">
+<td class="name">COVESEA SKERRIES</td>
+<td class="txt">Craighead, Morayshire</td>
+<td class="other">One</td>
+<td class="txt">Revolving, and appearing in its brightest state once every minute. From W. by N. ¹⁄₄ N. to SE. by E. ¹⁄₄ E. the light
+is of the natural appearance; but from SE. by E. ¹⁄₄ E. to SE. ¹⁄₄ S. it is coloured <span class="allsmcap">RED</span></td>
+<td class="other">18</td>
+<td class="txt">From W. by N. ¹⁄₄ N. to SE. ¹⁄₄ S. Northerly</td>
+<td class="other">160</td>
+<td class="degrees">57°</td>
+<td class="minutes">43′</td>
+<td class="degrees">3°</td>
+<td class="minutes">20′</td>
+<td class="year">1846</td>
+</tr>
+
+<tr class="bb">
+<td class="name">CHANONRY POINT</td>
+<td class="txt">Chanonry Point, Ross-shire</td>
+<td class="other">One</td>
+<td class="txt">Fixed</td>
+<td class="other">11</td>
+<td class="txt">From W. ¹⁄₂ N. to N. by E. Southerly</td>
+<td class="other">40</td>
+<td class="degrees">57°</td>
+<td class="minutes">35′</td>
+<td class="degrees">4°</td>
+<td class="minutes">&#8199;5′</td>
+<td class="year">1846</td>
+</tr>
+
+<tr class="bb">
+<td class="name">CROMARTY POINT</td>
+<td class="txt">Cromartyshire</td>
+<td class="other">One</td>
+<td class="txt">Fixed and red</td>
+<td class="other">9</td>
+<td class="txt">From WNW. to SE. by E. ¹⁄₄ S. Northerly</td>
+<td class="other">50</td>
+<td class="degrees">57°</td>
+<td class="minutes">41′</td>
+<td class="degrees">4°</td>
+<td class="minutes">&#8199;2′</td>
+<td class="year">1846</td>
+</tr>
+
+<tr class="bb">
+<td class="name">TARBETNESS</td>
+<td class="txt">Tarbetness, Cromartyshire</td>
+<td class="other">One</td>
+<td class="txt">Intermittent, suddenly bursting into view, and continuing in sight 2¹⁄₂ min., then suddenly eclipsed for half a
+minute. But within the Moray Frith, in Southerly and South-westerly directions from Tarbetness, the light does not intermit,
+but is permanently visible</td>
+<td class="other">18</td>
+<td class="txt">From SW. ¹⁄₂ W. to W. ¹⁄₂ N. Easterly</td>
+<td class="other">175</td>
+<td class="degrees">57°</td>
+<td class="minutes">51′</td>
+<td class="degrees">8°</td>
+<td class="minutes">48′</td>
+<td class="year">1830</td>
+</tr>
+
+<tr class="bb">
+<td class="name">NOSSHEAD</td>
+<td class="txt">Nosshead, Caithness-shire (building)</td>
+<td class="other">&#160;</td>
+<td class="txt">&#160;</td>
+<td class="other">&#160;</td>
+<td class="txt">&#160;</td>
+<td class="other">&#160;</td>
+<td colspan="2" class="other">&#160;</td>
+<td colspan="2" class="other">&#160;</td>
+<td class="year">&#160;</td>
+</tr>
+
+<tr class="bb">
+<td class="name">DUNNETHEAD</td>
+<td class="txt">Dunnethead, most northern point of the Mainland of Scotland, Caithness-shire</td>
+<td class="other">One</td>
+<td class="txt">Fixed</td>
+<td class="other">23</td>
+<td class="txt">From SE. ¹⁄₂ E. to W. Northerly</td>
+<td class="other">346</td>
+<td class="degrees">58°</td>
+<td class="minutes">40′</td>
+<td class="degrees">3°</td>
+<td class="minutes">21′</td>
+<td class="year">1831</td>
+</tr>
+
+<tr class="bb">
+<td class="name">PENTLAND SKERRIES</td>
+<td class="txt">Pentland Skerries Island, Orkney</td>
+<td class="other">Two</td>
+<td class="txt">Fixed, and 100 feet apart</td>
+<td class="other">16 &amp; 18</td>
+<td class="txt">All round the Compass</td>
+<td class="other">140 &amp; 170</td>
+<td class="degrees">58°</td>
+<td class="minutes">41′</td>
+<td class="degrees">2°</td>
+<td class="minutes">55′</td>
+<td class="year">1794</td>
+</tr>
+
+<tr class="bb">
+<td class="name">START POINT</td>
+<td class="txt">Start Point, Sanday Island, the most eastern point of Orkney</td>
+<td class="other">One</td>
+<td class="txt">Revolving, and appearing in its brightest state once every minute</td>
+<td class="other">15</td>
+<td class="txt">All round the Compass</td>
+<td class="other">100</td>
+<td class="degrees">59°</td>
+<td class="minutes">17′</td>
+<td class="degrees">2°</td>
+<td class="minutes">23′</td>
+<td class="year">1806</td>
+</tr>
+
+<tr class="bb">
+<td class="name">SUMBURGH-HEAD<span class="pagenum" id="Page396">[396-<br>397]<a id="Page397"></a></span></td>
+<td class="txt">The most southern Headland of Zetland</td>
+<td class="other">One</td>
+<td class="txt">Fixed</td>
+<td class="other">22</td>
+<td class="txt">From NE. by E. ¹⁄₄ E. to NW. by N. ¹⁄₄ N. Southerly</td>
+<td class="other">300</td>
+<td class="degrees">59°</td>
+<td class="minutes">51′</td>
+<td class="degrees">1°</td>
+<td class="minutes">16′</td>
+<td class="year">1821</td>
+</tr>
+
+<tr class="bb">
+<td class="name">CAPE WRATH</td>
+<td class="txt">Cape Wrath, north-western Headland of Sutherlandshire</td>
+<td class="other">One</td>
+<td class="txt">Revolving, and shewing alternately a red and white light every 2 minutes</td>
+<td class="other">25</td>
+<td class="txt">From SE. ¹⁄₂ E. to SW. by W. Northerly</td>
+<td class="other">400</td>
+<td class="degrees">58°</td>
+<td class="minutes">37′</td>
+<td class="degrees">5°</td>
+<td class="minutes">&#8199;0′</td>
+<td class="year">1828</td>
+</tr>
+
+<tr class="bb">
+<td class="name">ISLAND GLASS</td>
+<td class="txt">Island Glass, one of the Harris Isles, Inverness-shire</td>
+<td class="other">One</td>
+<td class="txt">Fixed</td>
+<td class="other">16</td>
+<td class="txt">From W. by S. to ENE. ¹⁄₂ E. Southerly</td>
+<td class="other">130</td>
+<td class="degrees">57°</td>
+<td class="minutes">52′</td>
+<td class="degrees">6°</td>
+<td class="minutes">33′</td>
+<td class="year">1789</td>
+</tr>
+
+<tr class="bb">
+<td class="name">BARRAHEAD</td>
+<td class="txt">Highest land on Bernera Island, Inverness-shire</td>
+<td class="other">One</td>
+<td class="txt">Intermittent, suddenly bursting into view, and continuing in sight 2¹⁄₂ min., then suddenly eclipsed for half a minute</td>
+<td class="other">32</td>
+<td class="txt">From N. by E. to ENE. Westerly and Southerly</td>
+<td class="other">680</td>
+<td class="degrees">56°</td>
+<td class="minutes">48′</td>
+<td class="degrees">7°</td>
+<td class="minutes">38′</td>
+<td class="year">1833</td>
+</tr>
+
+<tr class="bb">
+<td class="name">ARDNAMURCHAN</td>
+<td class="txt">Ardnamurchan Point, Argyleshire (building)</td>
+<td class="other">&#160;</td>
+<td class="txt">&#160;</td>
+<td class="other">&#160;</td>
+<td class="txt">&#160;</td>
+<td class="other">&#160;</td>
+<td colspan="2" class="other">&#160;</td>
+<td colspan="2" class="other">&#160;</td>
+<td class="year">&#160;</td>
+</tr>
+
+<tr class="bb">
+<td class="name">LISMORE</td>
+<td class="txt">Mousedale, small Island off Lismore, Argyleshire</td>
+<td class="other">One</td>
+<td class="txt">Fixed</td>
+<td class="other">15</td>
+<td class="txt">From E. to NE. by E. ¹⁄₄ E. Westerly</td>
+<td class="other">103</td>
+<td class="degrees">56°</td>
+<td class="minutes">30′</td>
+<td class="degrees">5°</td>
+<td class="minutes">38′</td>
+<td class="year">1833</td>
+</tr>
+
+<tr class="bb">
+<td class="name">SKERRYVORE<a id="FNanchor89" href="#Footnote89" class="fnanchor">[89]</a></td>
+<td class="txt">Skerryvore Reef, 12 miles WSW. ¹⁄₂ W. from Tyree Island, with foul ground all round it</td>
+<td class="other">One</td>
+<td class="txt">Revolving, and appearing at its brightest once every minute</td>
+<td class="other">18</td>
+<td class="txt">All round the Compass</td>
+<td class="other">150</td>
+<td class="degrees">56°</td>
+<td class="minutes">19′</td>
+<td class="degrees">7°</td>
+<td class="minutes">&#8199;7′</td>
+<td class="year">1844</td>
+</tr>
+
+<tr class="bb">
+<td class="name">RHINS OF ISLAY</td>
+<td class="txt">Oversay, small Island off Islay, Argyleshire</td>
+<td class="other">One</td>
+<td class="txt">Flashing once every 5 seconds</td>
+<td class="other">17</td>
+<td class="txt">From NNE. to SE. Southerly</td>
+<td class="other">150</td>
+<td class="degrees">55°</td>
+<td class="minutes">41′</td>
+<td class="degrees">6°</td>
+<td class="minutes">29′</td>
+<td class="year">1825</td>
+</tr>
+
+<tr class="bb">
+<td class="name">MULL OF KINTYRE</td>
+<td class="txt">South-western Headland of Argyleshire</td>
+<td class="other">One</td>
+<td class="txt">Fixed</td>
+<td class="other">22</td>
+<td class="txt">From NNE. ¹⁄₂ E. to S. by W. ¹⁄₄ W. Southerly</td>
+<td class="other">297</td>
+<td class="degrees">55°</td>
+<td class="minutes">&#8199;1′</td>
+<td class="degrees">5°</td>
+<td class="minutes">49′</td>
+<td class="year">1787</td>
+</tr>
+
+<tr class="bb">
+<td class="name">PLADDA</td>
+<td class="txt">Pladda Isle, off south-east point of Arran, county of Bute</td>
+<td class="other">Two</td>
+<td class="txt">Fixed, the one above the other</td>
+<td class="other">13 &amp; 16</td>
+<td class="txt">From NW. by W. to NE. by E. Southerly</td>
+<td class="other">77 &amp; 130</td>
+<td class="degrees">55°</td>
+<td class="minutes">26′</td>
+<td class="degrees">5°</td>
+<td class="minutes">&#8199;7′</td>
+<td class="year">1790</td>
+</tr>
+
+<tr class="bb">
+<td class="name">CORSEWALL</td>
+<td class="txt">Western side of entrance to Loch Ryan, in Wigtonshire</td>
+<td class="other">One</td>
+<td class="txt">Revolving, and shewing alternately a red and white light every 2 minutes</td>
+<td class="other">15</td>
+<td class="txt">From NE. by E. to SW. Northerly</td>
+<td class="other">112</td>
+<td class="degrees">55°</td>
+<td class="minutes">&#8199;1′</td>
+<td class="degrees">5°</td>
+<td class="minutes">&#8199;9′</td>
+<td class="year">1817</td>
+</tr>
+
+<tr class="bb">
+<td class="name">LOCH RYAN</td>
+<td class="txt">Cairn Ryan Point, within Loch Ryan, Wigtonshire</td>
+<td class="other">One</td>
+<td class="txt">Fixed</td>
+<td class="other">10</td>
+<td class="txt">From S. by W. ¹⁄₈ W. to N. ⁷⁄₈ E. Westerly</td>
+<td class="other">30</td>
+<td class="degrees">54°</td>
+<td class="minutes">58′</td>
+<td class="degrees">5°</td>
+<td class="minutes">&#8199;2′</td>
+<td class="year">1847</td>
+</tr>
+
+<tr class="bb">
+<td class="name">MULL OF GALLOWAY</td>
+<td class="txt">Southern extremity of the Mainland of Scotland, Wigtonshire</td>
+<td class="other">One</td>
+<td class="txt">Intermittent, suddenly bursting into view, and continuing in sight 2¹⁄₂ min., then suddenly eclipsed for half a minute</td>
+<td class="other">23</td>
+<td class="txt">From NE. to NW. ¹⁄₂ W. Southerly</td>
+<td class="other">325</td>
+<td class="degrees">54°</td>
+<td class="minutes">38′</td>
+<td class="degrees">4°</td>
+<td class="minutes">51′</td>
+<td class="year">1830</td>
+</tr>
+
+<tr class="bb">
+<td class="name">LITTLE ROSS</td>
+<td class="txt">Little Ross Island, Kirkcudbrightshire</td>
+<td class="other">One</td>
+<td class="txt">Flashing once every 5 seconds</td>
+<td class="other">18</td>
+<td class="txt">From N. by E. to NW. by W. Southerly</td>
+<td class="other">175</td>
+<td class="degrees">54°</td>
+<td class="minutes">46′</td>
+<td class="degrees">4°</td>
+<td class="minutes">&#8199;5′</td>
+<td class="year">1843</td>
+</tr>
+
+<tr class="bb">
+<td class="name">POINT OF AYRE</td>
+<td class="txt">Northern extremity of Isle of Man</td>
+<td class="other">One</td>
+<td class="txt">Revolving, and shewing alternately a red and white light every 2 minutes</td>
+<td class="other">15</td>
+<td class="txt">From S. by W. to W. by N. Northerly</td>
+<td class="other">106</td>
+<td class="degrees">54°</td>
+<td class="minutes">25′</td>
+<td class="degrees">4°</td>
+<td class="minutes">22′</td>
+<td class="year">1818</td>
+</tr>
+
+<tr>
+<td class="name">CALF OF MAN</td>
+<td class="txt">West side Calf Island, at the southern extremity of Isle of Man</td>
+<td class="other">Two</td>
+<td class="txt">Revolving, and shewing white lights every 2 minutes</td>
+<td class="other">22 &amp; 24</td>
+<td class="txt">From NE. ¹⁄₃ to SW. W. Southerly</td>
+<td class="other">275 &amp; 368</td>
+<td class="degrees">54°</td>
+<td class="minutes">&#8199;3′</td>
+<td class="degrees">4°</td>
+<td class="minutes">49′</td>
+<td class="year">1818</td>
+</tr>
+
+</table>
+
+<div class="footnote">
+
+<p><a id="Footnote89" href="#FNanchor89" class="label">[89]</a> At Hynish Point in Tyree Island, two fixed Lights are shewn
+from the Pier, but <span class="allsmcap">ONLY</span>
+when the Vessel which attends the Lighthouse is
+expected to enter the Dock at Hynish. In the Trinity House Chart, Skerryvore Light is erroneously described as “Intermittent.”</p>
+
+</div><!--footnote-->
+
+<p><span class="pagenum" id="Page398">[398]</span></p>
+
+<p class="tabhead"><span class="fsize125"><span class="gesp2">BEACONS AND BUOYS</span>.</span><br>
+FRITH OF FORTH DISTRICT.</p>
+
+<table class="beacons">
+
+<colgroup>
+<col span="2" class="w15pc">
+<col class="w10pc">
+<col class="wauto">
+</colgroup>
+
+<tr class="bb">
+<th class="br">Name of<br>Station.</th>
+<th class="br">Description<br>of Mark.</th>
+<th class="br">Depth at<br>Low Water<br>of<br>Spring<br>Tides.</th>
+<th class="br">Bearings of Marks and of Lines<br>of Intersection Meeting at the Station.</th>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">MIDDLE BANK, WEST END, BUOY.</td>
+<td rowspan="3" class="data">6 Feet Buoy, Red.</td>
+<td rowspan="3" class="data">3¹⁄₂ Feet.</td>
+<td class="text"><span class="smcap">Alloa Tower</span> in line with the Centre of <span class="smcap">Clackmannan Pier</span>—Bearing
+N. by E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Clackmannan Church Spire</span> in line with <span class="smcap">High Chimney-Stack</span>
+of <span class="smcap">Park-Farm House</span>—Bearing NE. ¹⁄₂ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Middle Bank Buoy</span>, East End—Bearing SE. by S.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">MIDDLE BANK, EAST END, BUOY.</td>
+<td rowspan="3" class="data">6 Feet Buoy, Red.</td>
+<td rowspan="3" class="data">4 Feet.</td>
+<td class="text"><span class="smcap">Tullyallan House</span> in line with <span class="smcap">Tullyallan Old Church Spire</span>,
+in ruins—Bearing ESE. ¹⁄₂ S.</td>
+</tr>
+
+<tr>
+<td class="text">Remarkable <span class="smcap">Clump</span> of <span class="smcap">Trees</span> on distant high land in line
+with <span class="smcap">Airth Church Spire</span>—Bearing W. by N. ¹⁄₂ N.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Buoy</span> off <span class="smcap">Inch Brake Rock</span>—Bearing S. by E.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">INCH BRAKE BUOY.</td>
+<td rowspan="3" class="data">6 Feet Buoy, Black.</td>
+<td rowspan="3" class="data">5 Feet.</td>
+<td class="text"><span class="smcap">Flagstaff</span> on the <span class="smcap">Ferry Pier, Kincardine</span>, clear outside of
+<span class="smcap">Kincardine Stone Pier</span>—Bearing N. by E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Alloa Church Spire</span> in line with South Corner of <span class="smcap">Kennet Pans
+Distillery Garden Wall</span>—Bearing N. by W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Long Annat Buoy</span>—Bearing SSE. ¹⁄₂ E.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">LONG ANNAT</td>
+<td rowspan="3" class="data">6 Feet Buoy,</td>
+<td rowspan="3" class="data">9 Feet.</td>
+<td class="text"><span class="smcap">Sands House</span>, West Wing, in line with <span class="smcap">West Face</span> of
+<span class="smcap">Annat Quarry</span>—Bearing NNE. ¹⁄₂ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Binns Monument</span> in line with the Middle of <span class="smcap">Bo’ness Pier</span>—Bearing SE. by S.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Hen</span> and <span class="smcap">Chicken’s Buoy</span>—Bearing SE. by E. ¹⁄₄ S.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">HEN AND CHICKEN’S BUOY.</td>
+<td rowspan="3" class="data">6 Feet Buoy, Black.</td>
+<td rowspan="3" class="data">12 Feet.</td>
+<td class="text">The East Wing of <span class="smcap">Culross Abbey</span> in line with Eastmost House in <span class="smcap">Culross
+Village</span>—Bearing NNE. ¹⁄₂ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Airth Castle</span>, in line with <span class="smcap">High-Water Mark</span> on
+<span class="smcap">Long Annat Point</span>—Bearing NW. ¹⁄₄ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Buoy</span> on East End of <span class="smcap">Dods’ Bank</span>—Bearing SSE. ¹⁄₂ E.</td>
+</tr>
+
+<tr>
+<td rowspan="5" class="data">DODS’ BANK BUOY.<span class="pagenum" id="Page399">[399]</span></td>
+<td rowspan="5" class="data">7 Feet Buoy, Red.</td>
+<td rowspan="5" class="data">15 Feet.</td>
+<td class="text"><span class="smcap">Berry-Law Trees</span> in line with the <span class="smcap">Chimney-Stack</span> of
+<span class="smcap">Bunyan’s Farm</span>—Bearing E. by N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Chimney Stack</span> of the <span class="smcap">Snub Coal Pit</span> (the first Stack West of
+Kinneil New Iron Works), in line with the <span class="smcap">West Pier Wall</span> of <span class="smcap">Bo’ness</span>—Bearing WSW. ³⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Comary House</span>, East Wing, in line with the West Wing of the <span class="smcap">Factor’s
+House</span>—Bearing N. by E. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Valleyfield House</span>, a little East of the Eastern House on <span class="smcap">Preston
+Island</span>, about half-way between the house and where the Island dries at half-tide—Bearing N. by E. ¹⁄₄ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text">The Buoy of <span class="smcap">Hen</span> and <span class="smcap">Chicken’s Rock</span>—Bearing NNW. ¹⁄₂ W.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">BEAMER BEACON.</td>
+<td rowspan="4" class="data">Painted Black, with Spherical Ball at top.</td>
+<td rowspan="4" class="data">Rock Dry at Low Water.</td>
+<td class="text"><span class="smcap">Bo’ness Pier</span>—Bearing NW. by W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Charleston Pier</span>, Outer End—Bearing NW. by N.</td>
+</tr>
+
+<tr>
+<td class="text">South-West Extremity of the Point at <span class="smcap">North Queensferry</span>—Bearing ESE. ¹⁄₄ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text">The <span class="smcap">Halls</span>, or principal <span class="smcap">South Queensferry Pier</span>—Bearing SSE. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">DRUM SAND EAST BUOY.</td>
+<td rowspan="4" class="data">7 Feet Buoy, Red.</td>
+<td rowspan="4" class="data">12 Feet.</td>
+<td class="text"><span class="smcap">Newbigging House</span> in line with East Edge of <span class="smcap">Carcraig Rock</span>—Bearing
+NE. ¹⁄₂ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Oxscare Beacon</span>—Bearing E. ³⁄₄ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Inchkeith Lighthouse</span>—Bearing ESE. ¹⁄₂ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text">Highest Point of <span class="smcap">Arthur’s Seat</span> in line with <span class="smcap">Nelson’s Monument</span>—Bearing
+S. by E. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">DRUM SAND WEST BUOY.</td>
+<td rowspan="4" class="data">8 Feet Buoy, Red, with Fenders.</td>
+<td rowspan="4" class="data">3¹⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">South Point</span> of <span class="smcap">Inchkeith</span> in line with <span class="smcap">Centre</span>
+of <span class="smcap">Opening</span> of <span class="smcap">Mickery Stone</span>—Bearing ESE. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Inchkeith Lighthouse</span>—Bearing ESE. ¹⁄₂ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Fordel House</span> in line with <span class="smcap">Centre</span> of <span class="smcap">Donibristle
+House</span>—Bearing N. ¹⁄₄ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Chimney-Stack</span> of <span class="smcap">Castle Landhill Farm-House</span> in line with
+<span class="smcap">End</span> of <span class="smcap">Lazarett Pier</span>—Bearing NW. ³⁄₈ N.</td>
+</tr>
+
+<tr>
+<td rowspan="6" class="data">OXSCARE BEACON.</td>
+<td rowspan="6" class="data">Painted Red, with Flat Cone at top.</td>
+<td rowspan="6" class="data">Rock Dry at Low Water.</td>
+<td class="text">South Point of <span class="smcap">Carlin’s Nose</span>—Bearing W. ³⁄₄ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Burntisland Pier</span>—Bearing ENE.</td>
+</tr>
+
+<tr>
+<td class="text">Extremity of <span class="smcap">Kinghornness</span>—Bearing E. ¹⁄₂ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Inchkeith Lighthouse</span>—Bearing ESE. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Martello Tower</span>—Bearing SSE. ³⁄₄ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Granton Pier</span>—Bearing S. by E. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">WEST GUNNET BUOY.<span class="pagenum" id="Page400">[400]</span></td>
+<td rowspan="4" class="data">8 Feet Buoy, White.</td>
+<td rowspan="4" class="data">3³⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">Nelson’s Monument</span> just clear East of <span class="smcap">North Leith Church Spire</span>—Bearing SSW.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">North Berwick Law</span> in line with North End of <span class="smcap">Long Craig</span>—Bearing ESE. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Clump</span> of <span class="smcap">Trees</span> East of <span class="smcap">Grange House</span>
+in line with <span class="smcap">Burntisland Church Spire</span>—Bearing N. ¹⁄₂ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Inchkeith Lighthouse</span>—Bearing E. ¹⁄₂ S.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">EAST GUNNET BUOY.</td>
+<td rowspan="4" class="data">8 Feet Buoy, White.</td>
+<td rowspan="4" class="data">3¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">Notch</span> at the foot of East Brow of the <span class="smcap">Pentland Hills</span> in
+line with <span class="smcap">North Leith Church Spire</span>—Bearing SSW. ³⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Carlin’s Nose</span> clear of the North Side of <span class="smcap">Mickery Stone</span>—Bearing WNW. ³⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Kinghorn New Free Church</span> in line with <span class="smcap">Kinghornness</span>—Bearing NE. by N.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Inchkeith Lighthouse</span>—Bearing E.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">PALLAS BUOY.</td>
+<td rowspan="4" class="data">7 Feet Buoy, Striped White and Black horizontally.</td>
+<td rowspan="4" class="data">3¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">Kinghorn Free Church</span> in line with <span class="smcap">Swan’s Factory</span>—Bearing
+N. by E. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text">North Brow of <span class="smcap">Inchkeith</span> in line with the Centre of <span class="smcap">Silly
+Carr Rock</span>—Bearing ENE. ¹⁄₄ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Assembly Hall Spire, Edinburgh</span>, in line with <span class="smcap">Martello
+Tower</span>—Bearing SW. ³⁄₄ S.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Inchkeith Lighthouse</span>—Bearing ENE. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">HERWIT BUOY.</td>
+<td rowspan="3" class="data">8 Feet Buoy, Black.</td>
+<td rowspan="3" class="data">4³⁄₄ Fathoms.</td>
+<td class="text">East Brow of <span class="smcap">Pentland Hills</span>, touching West Brow of <span class="smcap">Arthur’s
+Seat</span> (half way up)—Bearing SW. ¹⁄₂ W.</td>
+</tr>
+
+<tr>
+<td class="text">East Stables (Red-tiled House) of <span class="smcap">Pettycur</span> in line with East Brow of
+<span class="smcap">Inchkeith</span>—Bearing N. by W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Inchkeith Lighthouse</span>—Bearing N. by W. ¹⁄₂ W.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">CRAIG WAUGH</td>
+<td rowspan="3" class="data">8 Feet Buoy,</td>
+<td rowspan="3" class="data">4 Fathoms.</td>
+<td class="text"><span class="smcap">Pettycur Pier</span> in line with Eastern Brow of <span class="smcap">Inchkeith</span>—Bearing N. by W. ¹⁄₂ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Assembly Hall Spire</span> just clear, West of <span class="smcap">Nelson’s Monument</span>—Bearing W. ³⁄₄ S.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Inchkeith Lighthouse</span>—Bearing N. by W. ³⁄₄ W.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">NORTH CRAIG MAST BUOY.</td>
+<td rowspan="3" class="data">12 Feet Mast Buoy, Chequered Red and White.</td>
+<td rowspan="3" class="data">3¹⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">Nelson’s Monument</span> in line with West Wing of <span class="smcap">Leith Baths</span>—Bearing WSW. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text">Summit of <span class="smcap">East Lomond Hill</span> in line with <span class="smcap">Big House Trees</span>—Bearing N. ¹⁄₂ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Carlin’s Nose</span> in line with Centre of <span class="smcap">Mickery Stone</span>—Bearing WNW.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">WEST ROCK-HEAD, OFF DYSART, BUOY.<span class="pagenum" id="Page401">[401]</span></td>
+<td rowspan="4" class="data">6 Feet Buoy, Red.</td>
+<td rowspan="4" class="data">3¹⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">Dysart Coal-Pit Chimney-Stack</span> in line with <span class="smcap">Middle</span> of
+<span class="smcap">Gable</span> of <span class="smcap">Pan Hall House</span>—Bearing N. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">North End</span> of <span class="smcap">Portbrae Church, Kirkcaldy</span>, just clear of the
+<span class="smcap">End</span> of <span class="smcap">Kirkcaldy Pier</span>—Bearing WNW. ³⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Inchkeith Lighthouse</span>—Bearing SW. by S.</td>
+</tr>
+
+<tr class="bb">
+<td class="text note">N.B.—<i>The highest part of the Rock bearing N. ¹⁄₄ E. distant about one-half cable’s length from Buoy.</i></td>
+</tr>
+
+<tr>
+<td rowspan="5" class="data">EAST ROCK-HEAD, OFF DYSART, BUOY.</td>
+<td rowspan="5" class="data">6 Feet Buoy, Black.</td>
+<td rowspan="5" class="data">3¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">Wemyss Old Castle</span> in line with <span class="smcap">Southern Houses</span> of <span class="smcap">East
+Wemyss</span>—Bearing NE. by E. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">East Wing</span> of <span class="smcap">Dysart Church</span> in line with <span class="smcap">Town-House
+Steeple</span>—Bearing NNW. ³⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Buoy</span> on <span class="smcap">West Rock-Head</span>—Bearing W. by N. ¹⁄₄ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Inchkeith Lighthouse</span>—Bearing SW. ¹⁄₂ S.</td>
+</tr>
+
+<tr class="bb">
+<td class="text note">N.B.—<i>The highest part of Rock, bearing NW. ¹⁄₄ W., distant about two cables’ lengths.</i></td>
+</tr>
+
+<tr>
+<td rowspan="6" class="data">EAST VOWS ROCK, BEACON, OFF ELIE.</td>
+<td rowspan="6" class="data">Pyramid of Iron Pillars, with open Cylindric Cage on top, painted Red.</td>
+<td rowspan="6" class="data">Rock Dry at Low Water.</td>
+<td class="text"><span class="smcap">Ruins</span> on <span class="smcap">Chapelness</span>—Bearing N. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">North End</span> of <span class="smcap">Elie Pier</span>—Bearing E. ³⁄₄ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Extremity</span> of <span class="smcap">Elieness</span>—Bearing E. by S. ¹⁄₂ S.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Isle</span> of <span class="smcap">May Lighthouse</span>—Bearing ESE. ¹⁄₄ S.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">West Vows Rock</span>—Bearing WNW. ¹⁄₂ N. distant ¹⁄₂ mile.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Buoy</span> on <span class="smcap">Thill Rock</span>—Bearing ESE. ¹⁄₈ S. distant two cables’ lengths.</td>
+</tr>
+
+<tr>
+<td rowspan="5" class="data">THILL ROCK BUOY.</td>
+<td rowspan="5" class="data">7 Feet Buoy, Black.</td>
+<td rowspan="5" class="data">3³⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">West End</span> of <span class="smcap">Millhouse Cottage</span> in line with <span class="smcap">North
+End</span> of <span class="smcap">Elie Pier</span>—Bearing NE.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Pettie Law</span> in line with <span class="smcap">West Chimney-Stack</span> of <span class="smcap">David
+Ovenstone’s House</span>—Bearing N. ³⁄₈ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Ruin</span> on <span class="smcap">Chapelness</span>—Bearing NNW. ¹⁄₂ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Beacon</span> on <span class="smcap">East Vows Rock</span>—Bearing WNW. ¹⁄₈ N.</td>
+</tr>
+
+<tr class="bb">
+<td class="text note">N.B.—<i>The Buoy lies about 35 fathoms to the SSE. of the highest part of the Rock.</i></td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">SOUTH CARR BEACON.</td>
+<td rowspan="4" class="data">Painted Red, with Cross at top.</td>
+<td rowspan="4" class="data">Rock Dry at Low Water.</td>
+<td class="text"><span class="smcap">Cairn</span> on <span class="smcap">Bass Rock</span>—Bearing N. by E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Isle</span> of <span class="smcap">May Lighthouse</span>—Bearing NE.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Dunbar Church Tower</span>—Bearing SSE. ¹⁄₄ S.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Oldham Farm-House Chimney-Stack</span>—Bearing W. ¹⁄₄ N.</td>
+</tr>
+
+<tr>
+<td class="data">NORTH CARR BEACON.</td>
+<td class="data">Beacon of Stone, with Iron Frame and Ball.</td>
+<td class="data">Rock Dry at Low Water.</td>
+<td class="text">1¹⁄₄ Mile from <span class="smcap">Fifeness</span>—Bearing from <span class="smcap">Isle</span> of <span class="smcap">May
+Light</span> NNE. distant 6 Nautic Miles.</td>
+</tr>
+
+</table>
+
+<p><span class="pagenum" id="Page402">[402]</span></p>
+
+<p class="tabhead"><span class="fsize125"><span class="gesp2">BEACONS AND BUOYS</span>.</span><br>
+DISTRICT OF FRITHS OF MORAY, CROMARTY, INVERNESS,
+AND DORNOCH.</p>
+
+<table class="beacons">
+
+<colgroup>
+<col span="2" class="w15pc">
+<col class="w10pc">
+<col class="wauto">
+</colgroup>
+
+<tr class="bb">
+<th class="br">Name of<br>Station.</th>
+<th class="br">Description<br>of Mark.</th>
+<th class="br">Depth at<br>Low Water<br>of<br>Spring<br>Tides.</th>
+<th class="br">Magnetic Bearings of Marks and of Lines<br>of Intersection Meeting at the Station.</th>
+</tr>
+
+<tr class="bb">
+<td class="data">COVESEA SKERRIES BEACON.</td>
+<td class="data">Pyramid of Iron Pillars, with open cylindric Cage, and a Cross, rising to the height of about 50 feet above High water.</td>
+<td class="data">Rock dry at Low water.</td>
+<td class="text"><span class="smcap">Covesea Skerries Lighthouse</span> on the neighbouring land of <span class="smcap">Craighead</span>—Bears
+WSW. ¹⁄₄ W. distant one mile.</td>
+</tr>
+
+<tr>
+<td rowspan="5" class="data">LONGMAN POINT BEACON.</td>
+<td rowspan="5" class="data">Cone of Iron Plates painted Black.</td>
+<td rowspan="5" class="data">Beach Dry at Low water of Spring Tides.</td>
+<td class="text"><span class="smcap">End</span> of <span class="smcap">Kessock South Pier</span>—Bearing W. by N. ¹⁄₄ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Craigtown Point</span>—Bearing NW. ¹⁄₂ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Meiklemee, East End Buoy</span>—Bearing E. ¹⁄₂ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Bogbain House</span> in line with <span class="smcap">Rigmore House</span>—Bearing S. ³⁄₄ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">End</span> of <span class="smcap">Longman Point</span>—Bearing N. ¹⁄₄ W. distant 40 Fathoms.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">MEIKLEMEE BANK BUOY.<br>East End.</td>
+<td rowspan="3" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="3" class="data">12 Feet.</td>
+<td class="text"><span class="smcap">Park’s Farm-House</span> in line with <span class="smcap">Rigmore House</span>—Bearing SSW.</td>
+</tr>
+
+<tr>
+<td class="text">Middle of space between the Houses of <span class="smcap">Scorguoy Farm-Yard</span> in line with <span class="smcap">Black
+Mill Chimney</span>—Bearing W. ¹⁄₄ S.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Chanonry Point Lighthouse</span>—Bearing ENE. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">MIDDLE BANK BUOY.<br>East End.</td>
+<td rowspan="4" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="4" class="data">12 Feet.</td>
+<td class="text"><span class="smcap">Scorguoy Farm-Yard</span> (South End), in line with <span class="smcap">Black Mill Chimney</span>—Bearing
+W. ¹⁄₂ S.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Round Clump</span> of <span class="smcap">Trees</span>, North of <span class="smcap">Ley’s House</span>,
+in line with <span class="smcap">Rigmore House</span>—Bearing SW. ³⁄₄ S.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Chanonry Point Lighthouse</span>—Bearing ENE.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Meiklemee Bank Buoy</span>—Bearing W. ⁵⁄₈ S.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">PETTY BANK BUOY.<br>North or Outer Edge.</td>
+<td rowspan="3" class="data">6 Feet Buoy. Chequered Black and White.</td>
+<td rowspan="3" class="data">12 Feet.</td>
+<td class="text"><span class="smcap">Dalcross Castle</span> in line with <span class="smcap">Fishtown Farm-House</span>—Bearing SE. ³⁄₄ S.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Extremity</span> of <span class="smcap">East Suter</span> in line with <span class="smcap">Store-house,
+Chanonry Point</span>—Bearing ENE. ³⁄₄ N.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Munlochy Buoy</span>—Bearing N.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">MUNLOCHY BUOY.<span class="pagenum" id="Page403">[403]</span></td>
+<td rowspan="2" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="2" class="data">12 Feet.</td>
+<td class="text"><span class="smcap">West Wing</span> of <span class="smcap">Avoch House</span>, now in ruins, in line with the most
+<span class="smcap">Western slated House</span> or <span class="smcap">Cottage</span> in <span class="smcap">Avoch</span>—Bearing N. ¹⁄₄ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">North End</span> of <span class="smcap">Fort-George</span> in line with <span class="smcap">Chanonry
+Point</span>—Bearing ENE. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">SKATE BANK BUOY.<br>East End.</td>
+<td rowspan="4" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="4" class="data">12¹⁄₂ Feet.</td>
+<td class="text">The <span class="smcap">East Wing</span> of <span class="smcap">Kincurdie House</span> in line with <span class="smcap">Spire</span>
+of <span class="smcap">Rosemarkie Kirk</span>—Bearing NNE. ¹⁄₂ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Flagstaff</span> of <span class="smcap">Fort-George</span> in line with the <span class="smcap">Outer End</span>
+of <span class="smcap">Chanonry Pier</span>—Bearing ENE. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Dalcross Castle</span> in line with <span class="smcap">Cottage</span> on <span class="smcap">Sea-cliff</span>—Bearing
+S. ³⁄₄ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Munlochy Buoy</span>—Bearing WSW. ¹⁄₈ W.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">CRAIGMEE <span class="allsmcap">OR</span> FORT-GEORGE BANK BUOY.</td>
+<td rowspan="2" class="data">6 Feet Buoy.<br>Chequered Black and White.</td>
+<td rowspan="2" class="data">2¹⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">High Part</span>, or <span class="smcap">West Brow</span> of <span class="smcap">Altarlie Point</span>, in
+line with <span class="smcap">Chanonry Point Lighthouse</span>—Bearing SW. ³⁄₄ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Patch</span> of <span class="smcap">Trees</span> at West End of <span class="smcap">Broomhill Wood</span>,
+called <span class="smcap">Broomhill Bush</span>, in line with <span class="smcap">Platcock House</span>—Bearing WNW. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">RIFF BANK BUOY.<br>West End.</td>
+<td rowspan="3" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="3" class="data">3²⁄₃ Fathoms.</td>
+<td class="text"><span class="smcap">Craighead Farm-House</span> in line with the most <span class="smcap">Western</span> of the <span class="smcap">Three
+Burns</span>—Bearing N. by E. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Broomhill Bush</span> (East End) in line with the <span class="smcap">Manse</span> of
+<span class="smcap">Rosemarkie</span>—Bearing W. ¹⁄₂ N.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Chanonry Point Lighthouse</span>—Bearing WSW. ³⁄₄ S.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">RIFF BANK BUOY.<br>Middle or North Angle.</td>
+<td rowspan="3" class="data">6 Feet Buoy.<br> Black.</td>
+<td rowspan="3" class="data">3¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">Three</span> remarkable <span class="smcap">Trees</span> at <span class="smcap">North End</span> of
+<span class="smcap">Craigie Wood</span>, in line with <span class="smcap">Rosemarkie Manse</span>—Bearing W. ¹⁄₂ S.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Gamekeeper’s House</span> at End of <span class="smcap">Wood</span> in line with <span class="smcap">Cave</span>
+on <span class="smcap">Sea-shore</span>, a little <span class="smcap">East</span> of the <span class="smcap">Three Burns</span>—Bearing NW. ¹⁄₂ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Chanonry Point Lighthouse</span>—Bearing WSW. ¹⁄₂ S.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">RIFF BANK BUOY.<br>East End.</td>
+<td rowspan="3" class="data">12 Feet Mast-Buoy.<br>Black.</td>
+<td rowspan="3" class="data">4¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">Castle Craig Rock</span> in line with <span class="smcap">Stack Rock</span> at foot of
+<span class="smcap">West Suter</span>—Bearing N. by E. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Store-House</span> on <span class="smcap">Chanonry Point</span>, shut in by the <span class="smcap">North</span>
+corner of <span class="smcap">Fort-George</span>, and in line with <span class="smcap">Lower</span> part of <span class="smcap">South Brow</span>
+of <span class="smcap">Ord Hill</span>—Bearing W. ³⁄₄ S.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Towrie Lumb Wood</span> in line with <span class="smcap">Craigie Wood</span> (South End)—Bearing W.</td>
+</tr>
+
+<tr class="bb">
+<td class="data">WHITENNESS BEACON.<br>(In preparation.)<span class="pagenum" id="Page404">[404]</span></td>
+<td class="data">—</td>
+<td class="data">—</td>
+<td class="text">—</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">NAVITY BANK BUOY.<br>South Edge.</td>
+<td rowspan="4" class="data">6 Feet Buoy.<br>Chequered Black and White.</td>
+<td rowspan="4" class="data">2¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">Trees</span> at end of <span class="smcap">Navity Farm-House</span> in line with <span class="smcap">East
+Bank</span> or <span class="smcap">Cliff</span> of <span class="smcap">Craighouse Burn</span>—Bearing N. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Extremity</span> of <span class="smcap">Wood</span> on <span class="smcap">Brow</span> of <span class="smcap">East
+Suter</span> in line with Lower part of <span class="smcap">Brow</span> of <span class="smcap">West Suter</span>—Bearing NE. by E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Chanonry Point Lighthouse</span>—Bearing SW. by W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Riff Bank Mast Buoy</span>—Bearing SE. ⁵⁄₈ E.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">NIGG SANDS BUOY.<br>East End.</td>
+<td rowspan="2" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="2" class="data">2 Fathoms.</td>
+<td class="text"><span class="smcap">Cromarty Gaelic Kirk Steeple</span> in line with <span class="smcap">East Wing</span> of
+<span class="smcap">Hotel</span>—Bearing S. ³⁄₄ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Face</span> of <span class="smcap">East Suter</span> apparently on a line halfway between
+<span class="smcap">Ferryhouse</span> and <span class="smcap">Stable</span>—Bearing SE. by E.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">NIGG SANDS BUOY.<br>West End.</td>
+<td rowspan="2" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="2" class="data">1²⁄₃ Fathoms.</td>
+<td class="text"><span class="smcap">Farm-House</span> of <span class="smcap">Dalney</span> in line with the <span class="smcap">Pigeon-house</span>
+East of <span class="smcap">Ballintrade</span>—Bearing NNE. ¹⁄₈ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Extremity</span> of <span class="smcap">West Suter</span> in line with <span class="smcap">Cromarty
+Lighthouse</span>—Bearing SE. ⁵⁄₈ E.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">NEWHALL BANK BUOY.<br>East End.</td>
+<td rowspan="3" class="data">6 Feet Buoy.<br>Chequered Black and White.</td>
+<td rowspan="3" class="data">2¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">Priesthill Farm-House</span> in line with <span class="smcap">Easternmost House</span> in
+<span class="smcap">Ballintrade</span>—Bearing NNE. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">East Brow</span> of <span class="smcap">West Suter</span> in line with <span class="smcap">Cromarty Gaelic
+Kirk</span>—Bearing ESE. ¹⁄₈ S.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Nigg Sands West Buoy</span>—Bearing ENE. ³⁄₈ N.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">THREE KINGS ROCKS BUOY.</td>
+<td rowspan="2" class="data">8 Feet Buoy.<br>Red.</td>
+<td rowspan="2" class="data">7¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">Eastern Trees</span> upon Top of the <span class="smcap">High Land</span>, being the most projecting and
+highest part of <span class="smcap">Sea Cliff</span>, West of <span class="smcap">Gilliam Burn</span>, in line with the
+<span class="smcap">Highest Eastern</span> part of <span class="smcap">Three Kings Rock</span>—Bearing WNW. ¹⁄₄ N.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Duke</span> of <span class="smcap">Sutherland’s Monument</span> in line with <span class="smcap">West
+End</span> of <span class="smcap">Long Storehouse</span> in <span class="smcap">Shandwick</span>—Bearing N. by E. ³⁄₈ E.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">CULLODEN ROCK BUOY.</td>
+<td rowspan="2" class="data">8 Feet Buoy.<br>Black.</td>
+<td rowspan="2" class="data">8³⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">Brucefield Farm-House</span> in line with <span class="smcap">Tarbetness Lighthouse Flag-Staff</span>—Bearing
+WSW. ³⁄₄ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Duke</span> of <span class="smcap">Sutherland’s Monument</span> in line with Lower Corner of
+<span class="smcap">Wood</span> farthest West from <span class="smcap">Dunrobin Castle</span>—Bearing NNW.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">FAIRWAY BUOY <span class="allsmcap">OFF</span> TAIN BAR.<span class="pagenum" id="Page405">[405]</span><br></td>
+<td rowspan="3" class="data">12 Feet Mast Buoy.<br>Red.</td>
+<td rowspan="3" class="data">5 Fathoms.</td>
+<td class="text"><span class="smcap">West End</span> of <span class="smcap">Bentavie Hill</span> in line with <span class="smcap">Trentham
+Farm-House</span>—Bearing NNW. ⁷⁄₈ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">West Brow</span> of <span class="smcap">East Suter</span> in line with <span class="smcap">Meiklerennie
+Farm-House</span>—Bearing SW. ³⁄₈ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Tarbetness Lighthouse</span>—Bearing SE. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">TAIN BAR INNER BUOY.<br>North Side.</td>
+<td rowspan="4" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="4" class="data">2¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">Remarkable Hollow</span> or <span class="smcap">Notch</span> in <span class="smcap">High Land</span> East
+of <span class="smcap">East Suter</span>, in line with <span class="smcap">Lochslain Castle</span>—Bearing SSW. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Lower West Brow</span> of <span class="smcap">Cambusmore Hill</span> in line with <span class="smcap">East
+End</span> of <span class="smcap">West Embo Wood</span>—Bearing N. by W. ³⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Tarbetness Lighthouse</span>—Bearing ESE. ¹⁄₂ S.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Fairway Buoy</span> off <span class="smcap">Tain Bar</span>—Bearing E. ³⁄₄ S.</td>
+</tr>
+
+<tr>
+<td rowspan="5" class="data">TAIN BAR INNER BUOY.<br>South Side.</td>
+<td rowspan="5" class="data">6 Feet Buoy.<br>Chequered Black and White.</td>
+<td rowspan="5" class="data">4²⁄₃ Fathoms.</td>
+<td class="text"><span class="smcap">Remarkable Hollow</span> or <span class="smcap">Notch</span> in <span class="smcap">High Land</span>
+<span class="smcap">East</span> of <span class="smcap">East Suter</span> in line with <span class="smcap">Meiklerennie
+Farmhouse</span>—Bearing SSW. ³⁄₈ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">West End</span> of <span class="smcap">East Embo Wood</span> in line with <span class="smcap">Embo
+Farmhouse</span>—Bearing N. ¹⁄₂ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Fairway Buoy</span> off <span class="smcap">Tain Bar</span>—Bearing E. ¹⁄₄ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Tain Bar Inner Buoy</span> (North Side)—Bearing ENE. ³⁄₈ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Dornoch Spire</span>—Bearing NNW. ³⁄₄ W.</td>
+</tr>
+
+</table>
+
+<p><span class="pagenum" id="Page406">[406]</span></p>
+
+<p class="tabhead"><span class="fsize125"><span class="gesp2">BEACONS AND BUOYS</span>.</span><br>
+FRITH OF CLYDE DISTRICT.</p>
+
+<table class="beacons">
+
+<colgroup>
+<col span="2" class="w15pc">
+<col class="w10pc">
+<col class="wauto">
+</colgroup>
+
+<tr class="bb">
+<th class="br">Name of<br>Station.</th>
+<th class="br">Description<br>of Mark.</th>
+<th class="br">Depth at<br>Low Water<br>of<br>Spring<br>Tides.</th>
+<th class="br">Bearings of Marks and of Lines<br>of Intersection Meeting at the Station.</th>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">FULLARTON ROCK BUOY.</td>
+<td rowspan="3" class="data">7 Feet Buoy.<br>Red.</td>
+<td rowspan="3" class="data">3¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">Clump</span> of <span class="smcap">Trees</span> at East side of <span class="smcap">Clachlan
+Farm</span>, just opening from the <span class="smcap">West Brow</span> of <span class="smcap">Holy Island</span>—Bearing N. by E.</td>
+</tr>
+
+<tr>
+<td class="text">Standing Stone upon <span class="smcap">Kinross Point</span>—Bearing W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text">Buoy moored upon ESE. Tail of Rock. The shallowest part of Rock has 8 Feet at Low water of Spring Tides.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">ARRANMAN’S BARRELS ROCKS BUOY.</td>
+<td rowspan="4" class="data">8 Feet Buoy.<br>Red.</td>
+<td rowspan="4" class="data">8¹⁄₂ Fathoms.</td>
+<td class="text">West End of <span class="smcap">Arranman’s Barrels Shoal</span>—Bearing W. by N.</td>
+</tr>
+
+<tr>
+<td class="text">North-East Extremity of Shoal—Bearing N. ¹⁄₂ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Ballyshare House</span> in line with the Lower East End of <span class="smcap">Dunacreein
+Rock</span>—Bearing NW. ¹⁄₂ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text">The Buoy is moored abreast of the middle of the Shoal, and is distant from the Low water Rocks about <i>half a cable’s
+length</i>.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">OTTERARD ROCK BUOY.</td>
+<td rowspan="4" class="data">8 Feet Buoy.<br>Black.</td>
+<td rowspan="4" class="data">3³⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">Clump</span> of <span class="smcap">Trees</span> at <span class="smcap">Ballaminich
+Farm-House</span> in line with the lower part of the South-eastern Brow of <span class="smcap">Island Davaar</span>—Bearing SW. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text">The remarkable Notch in distant Hill called <span class="smcap">Balavilan</span>, in line with North End of Green
+Patch on the rising ground in Field south of Long Dyke near <span class="smcap">Smerby Farm-House</span>—Bearing WNW. ³⁄₄ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Macrinnan’s Point</span>—Bearing WSW. ¹⁄₂ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text">The Buoy is moored upon ESE. Tail of Rock. The shallowest part of Rock at Low water of Springs has 12 Feet.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">MILLBEG BANK BUOY.</td>
+<td rowspan="2" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="2" class="data">2 Fathoms.</td>
+<td class="text"><span class="smcap">Campbelton Town-House Spire</span> in line with House in ruins on <span class="smcap">Trench
+Point</span>—Bearing WNW.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Crossbeg Farm-House</span> in line with Lower part or Mouth of <span class="smcap">Porter’s
+Glen</span>—Bearing N. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">CAMPBELTON HARBOUR OUTER BUOY.<span class="pagenum" id="Page407">[407]</span></td>
+<td rowspan="2" class="data">6 Feet Buoy.<br>Red.</td>
+<td rowspan="2" class="data">2¹⁄₄ Fathoms.</td>
+<td class="text">West Corner of <span class="smcap">Gaelic Church</span> in line with <span class="smcap">Trench Point</span>—Bearing
+W. by N. ¹⁄₄ N.</td>
+</tr>
+
+<tr class="bb">
+<td class="text">West End of <span class="smcap">Baraskie Farm-House</span> (dwelling-house) in line with Angle of Plantation,
+and also with the Corner of the Second Field to the South of the House—Bearing N. ³⁄₈ E.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">CAMPBELTON HARBOUR INNER BUOY.</td>
+<td rowspan="2" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="2" class="data">1¹⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">Castle Hill Church</span> in line with high water-mark on <span class="smcap">Trench
+Point</span>—Bearing WNW. ¹⁄₄ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text">North End of Higher <span class="smcap">Glenremisdil Farm-House</span> in line with Cottage at East End of
+<span class="smcap">Hetly House</span>—Bearing SW. ³⁄₄ S.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">MILLMORE BEACON.</td>
+<td rowspan="2" class="data">Pyramid of Iron Spars with Wire Ball on top.</td>
+<td rowspan="2" class="data">Beach dry at Low water.</td>
+<td class="text"><span class="smcap">Campbelton North Pier-head</span>—Bearing NW. by W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Macrinnan’s Point</span>—Bearing ENE. ¹⁄₄ N.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">TRENCH POINT BEACON.</td>
+<td rowspan="2" class="data">Pyramid of Iron Spars with Wire Ball on top.</td>
+<td rowspan="2" class="data">Beach dry at Low water.</td>
+<td class="text"><span class="smcap">Campbelton North Pier-head</span>—Bearing NW. by W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Outer</span> or <span class="smcap">Red Buoy</span> (above described)—Bearing ESE. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">LAPPOCK BEACON.</td>
+<td rowspan="3" class="data">Tower with  Stone Ball on top, painted Red.</td>
+<td rowspan="3" class="data">Rock dry at Low water.</td>
+<td class="text"><span class="smcap">Troon Harbour Light</span>—Bearing S. by W. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Beacon</span> on <span class="smcap">Lady Isle</span>—Bearing SW. ¹⁄₂ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Extremity</span> of <span class="smcap">Ardrossan Pier</span>—Bearing NNW. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">BREAST ROCK BEACON.</td>
+<td rowspan="3" class="data">Pyramid of Iron Pillars, with cylindric open Cage, painted Red.</td>
+<td rowspan="3" class="data">Rock dry at Low water.</td>
+<td class="text"><span class="smcap">Turnberry Point</span>—Bearing NE. by N. ¹⁄₈ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Pladda Lighthouse</span>—Bearing NNW.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Ailsa Craig</span> (Highest Point)—Bearing W.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">LOCH RYAN  INNER BUOY.</td>
+<td rowspan="3" class="data">7 Feet Buoy.<br>Red.</td>
+<td rowspan="3" class="data">3¹⁄₂ Fathoms.</td>
+<td class="text">Mr <span class="smcap">Moore’s Pigeon-House</span> in line with Angle of Plantation lying to the North of
+<span class="smcap">Corsewall House</span>—Bearing N. by W. ³⁄₈ W.</td>
+</tr>
+
+<tr>
+<td class="text">East End of <span class="smcap">Cairn Ryan</span> Hill Quarry, and East End of Plantation, at the foot of
+the same hill, in line with North Chimney of <span class="smcap">Mrs Begg’s Inn</span>, <span class="smcap">Cairn Ryan
+Village</span>—Bearing NE. ³⁄₄ N.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">North End</span> of <span class="smcap">Stranraer Pier</span>—Bearing SSW. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td rowspan="5" class="data">BEACON ON THE SPIT OF SCAR POINT, OFF KIRKCOLM POINT, IN LOCH RYAN.</td>
+<td rowspan="5" class="data">Cone of Iron Plates, painted Red.</td>
+<td rowspan="5" class="data">Dry at Low water.</td>
+<td class="text"><span class="smcap">Loch Ryan Lighthouse</span>—Bearing NNE. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Lochnoll Houses</span>—Bearing SE. by E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Stranraer Pier End</span>—Bearing SSW. ¹⁄₂ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Waukmill Houses</span>—Bearing SW. by W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Corsewall House</span> in line with <span class="smcap">The Scar off Kirkcolm Point</span>—Bearing
+NNW. ¹⁄₄ N.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">LOCH RYAN OUTER BUOY.<span class="pagenum" id="Page408">[408]</span></td>
+<td rowspan="2" class="data">7 Feet Buoy,<br>Black.</td>
+<td rowspan="2" class="data">3¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">Portincally Farm-House</span> in line with the Brow of <span class="smcap">Clachan Head</span>—Bearing
+NNW. ¹⁄₄ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text">Mr <span class="smcap">Charles M‘Donald’s House</span> in line with the South End of <span class="smcap">General
+Wallace’s Porter’s Lodge</span>—Bearing SE.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">LAGGAN, <span class="allsmcap">OR</span> EBBSTONE ROCK BEACON.</td>
+<td rowspan="3" class="data">Pyramid of Iron Pillars, with cylindric Open Cage on top, painted Red.</td>
+<td rowspan="3" class="data">Rock dry at Low water.</td>
+<td class="text"><span class="smcap">Corsewall Lighthouse</span>—Bearing NE. by E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Ailsa Craig</span> (Highest Point)—Bearing NE. ³⁄₄ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Laggan Point</span>—Bearing SSE. ¹⁄₂ E.</td>
+</tr>
+
+</table>
+
+<p class="tabhead"><span class="fsize125"><span class="gesp2">BEACONS AND BUOYS</span>.</span><br>
+LOCH FYNE DISTRICT.</p>
+
+<table class="beacons">
+
+<colgroup>
+<col span="2" class="w15pc">
+<col class="w10pc">
+<col class="wauto">
+</colgroup>
+
+<tr class="bb">
+<th class="br">Name of<br>Station.</th>
+<th class="br">Description<br>of Mark.</th>
+<th class="br">Depth at<br>Low Water<br>of<br>Spring<br>Tides.</th>
+<th class="br">Magnetic Bearings of Marks and of Lines<br>of Intersection Meeting at the Station.</th>
+</tr>
+
+<tr>
+<td rowspan="6" class="data">OFF ARDLAMONT POINT <span class="allsmcap">OR</span> BRADEICH ROCKS, ARGYLESHIRE, BUOY.</td>
+<td rowspan="6" class="data">8 Feet Buoy.<br>Red.</td>
+<td rowspan="6" class="data">2³⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">South-West Extremity</span> of <span class="smcap">West</span> and <span class="smcap">Eastern
+Hills</span> upon <span class="smcap">Ardlamont Point</span> in line with <span class="smcap">Extremity</span> of
+<span class="smcap">Point</span>—Bearing NW. ³⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Highest Part</span> of <span class="smcap">Bradeich Rocks</span>—Bearing NNW. ¹⁄₂ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">South End</span> of <span class="smcap">Inchmarnock Island</span>—Bearing S. ¹⁄₂ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Extremity</span> of <span class="smcap">Land South</span> of <span class="smcap">Ardlamont
+Point</span>—Bearing N. by W.</td>
+</tr>
+
+<tr>
+<td class="text">The Buoy lies about 115 fathoms distant from High water-mark upon the Point, and about 45 fathoms from the
+highest part of Bradeich Rocks.</td>
+</tr>
+
+<tr class="bb">
+<td class="text">N.B.—<i>There is a small Rock which dries at Low Spring Tides, about 10 or 12 fathoms outside of the highest main Rock.</i></td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">SKERNA SCALLAIG ROCK, <span class="smcap">OFF ENTRANCE TO</span> CRINAN CANAL, ARGYLESHIRE, BUOY.</td>
+<td rowspan="4" class="data">7 Feet Buoy.<br>Red.</td>
+<td rowspan="4" class="data">2¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">South Wing</span> of Sir <span class="smcap">John Ord’s Stables</span> in line with
+<span class="smcap">North Extremity</span> of <span class="smcap">Dunchoan Island</span>—Bearing NE. by E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Silver Craig’s Point, Island More</span>—Bearing SE. by S. ¹⁄₂ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">West Wing</span> of <span class="smcap">Ardrishaig Hotel</span> in line with
+<span class="smcap">Lighthouse</span> upon <span class="smcap">End</span> of <span class="smcap">Ardrishaig Pier</span>—Bearing N. ¹⁄₂ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text">N.B.—<i>The Buoy lies upon the South-West tail of the Shoal or Rock.</i></td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">OTTER BANK BEACON, <span class="smcap">OFF ENTRANCE TO</span> LOCH FYNE,
+ARGYLLSHIRE.<br>(Building.)<span class="pagenum" id="Page409">[409]</span></td>
+<td rowspan="3" class="data">Conical Iron Beacon.<br>To be painted Black.</td>
+<td rowspan="3" class="data">Gravel Beach.<br>Dry at Low water.</td>
+<td class="text"><span class="smcap">Auchabolonabaith House</span> (East Wing) in line with <span class="smcap">Centre</span>
+of <span class="smcap">Cottage</span>—Bearing N. by W. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Strathlachlan Hill</span> in line with <span class="smcap">Schoolhouse Point</span>—Bearing ENE.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">End of Liath Island</span>—Bearing W. ¹⁄₄ S.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">WEST OTTER BEACON, OFF CASTLE LACHLAN, LOCH FYNE, ARGYLESHIRE.<br>(Building.)</td>
+<td rowspan="3" class="data">Conical Iron Beacon.<br>To be painted Black.</td>
+<td rowspan="3" class="data">Gravel Beach.<br>Dry at Low water.</td>
+<td class="text"><span class="smcap">End</span> of <span class="smcap">Minard Point</span>—Bearing SW. by W. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">End</span> of <span class="smcap">Chapel Island</span>—Bearing ENE. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Barneycarry Farmhouse</span> in line with <span class="smcap">North-East End</span>
+of <span class="smcap">Hugh Island</span>—Bearing SE. ¹⁄₄ E.</td>
+</tr>
+
+</table>
+
+<p class="tabhead"><span class="fsize125"><span class="gesp2">BEACONS AND BUOYS</span>.</span><br>
+OBAN BAY, ARGYLESHIRE.</p>
+
+<table class="beacons">
+
+<colgroup>
+<col span="2" class="w15pc">
+<col class="w10pc">
+<col class="wauto">
+</colgroup>
+
+<tr class="bb">
+<th class="br">Name of<br>Station.</th>
+<th class="br">Description<br>of Mark.</th>
+<th class="br">Depth at<br>Low Water<br>of<br>Spring<br>Tides.</th>
+<th class="br">Magnetic Bearings of Marks and of Lines<br>of Intersection Meeting at the Station.</th>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">SKERRAT ROCK.<br>S. W. End.</td>
+<td rowspan="3" class="data">10 Feet Buoy, with Fenders.<br>Red.</td>
+<td rowspan="3" class="data">Dry at Low-water of Spring Tides.</td>
+<td class="text"><span class="smcap">Centre</span> of <span class="smcap">Oban Free Church Window</span> in line with
+<span class="smcap">North-Eastern Chimney</span> of <span class="smcap">Freemason’s Hall</span>—Bearing SE. by E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Centre of Skerry Dhu</span> or <span class="smcap">Black Rock</span> (apparently in middle of Sound
+of Kerrera) in line with <span class="smcap">Ardincaple Point</span>—Bearing WSW.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Buoy</span> on <span class="smcap">North-Eastern End</span> of <span class="smcap">Skerrat Shoal</span>—Bearing
+NE. ¹⁄₂ E. distant 105 fathoms.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">SKERRAT SHOAL,<br>N. E. End.</td>
+<td rowspan="3" class="data">6 Feet Buoy.<br>Chequered Black and White.</td>
+<td rowspan="3" class="data">12 Feet at Low water of Spring Tides.</td>
+<td class="text"><span class="smcap">Oban Free Church Steeple</span> in line with <span class="smcap">South Chimney Top</span> of
+<span class="smcap">Spring Well Cottage</span>—Bearing SE.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Ardincaple Point</span>, a little West of the Western End of <span class="smcap">Skerry Dhu</span> or
+<span class="smcap">Black Rock</span>—Bearing WSW.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Buoy on Skerrat Rock</span>—Bearing SW. ¹⁄₂ W. distant 105 fathoms.</td>
+</tr>
+
+<tr>
+<td colspan="4" class="text">N.B.—<i>No Vessel should attempt to pass between those Buoys.</i></td>
+</tr>
+
+</table>
+
+<p><span class="pagenum" id="Page410">[410]</span></p>
+
+<p class="tabhead"><span class="fsize125"><span class="gesp2">BEACONS AND BUOYS</span>.</span><br>
+LINNHE LOCH DISTRICT, ARGYLESHIRE.</p>
+
+<table class="beacons">
+
+<colgroup>
+<col span="2" class="w15pc">
+<col class="w10pc">
+<col class="wauto">
+</colgroup>
+
+<tr class="bb">
+<th class="br">Name of<br>Station.</th>
+<th class="br">Description<br>of Mark.</th>
+<th class="br">Depth at<br>Low Water<br>of<br>Spring<br>Tides.</th>
+<th class="br">Magnetic Bearings of Marks and of Lines<br>of Intersection Meeting at the Station.</th>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">CULCHENNA SPIT BUOY.</td>
+<td rowspan="4" class="data">10 Feet Mast Buoy, with Red Ball.</td>
+<td rowspan="4" class="data">4 Fathoms.</td>
+<td class="text"><span class="smcap">West End</span> of <span class="smcap">Ardgour House</span> in line with <span class="smcap">East
+End</span> of <span class="smcap">Hugh Boyd’s Cottage</span>—Bearing N. ⁷⁄₈ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">John Cameron’s Cottage</span> in line with <span class="smcap">End</span> of <span class="smcap">Culchenna
+Point</span>—Bearing NE. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Sallachan Point</span>—Bearing NNW. ¹⁄₄ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Chlavoulin Spit Buoy</span>—Bearing N. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">CHLAVOULIN  SPIT BUOY.</td>
+<td rowspan="4" class="data">7 Feet Buoy.<br>Black.</td>
+<td rowspan="4" class="data">2 Fathoms.</td>
+<td class="text"><span class="smcap">Centre</span> of <span class="smcap">Ardgour House</span> in line with <span class="smcap">Centre</span>
+of <span class="smcap">Hugh Boyd’s Cottage</span>—Bearing N. by E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">East End</span> of <span class="smcap">Second Wood</span> from <span class="smcap">Corran Point</span> in
+line with <span class="smcap">Barn</span> at <span class="smcap">East End</span> of <span class="smcap">Hugh Campbell’s Cottage</span> (Eastern
+House in Village of Chlavoulin)—Bearing NE. ³⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Corran Flat Buoy</span>—Bearing ENE. ³⁄₄ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">End of Sallachan Point</span>—Bearing W.</td>
+</tr>
+
+<tr>
+<td rowspan="3" class="data">CORRAN FLAT BUOY.</td>
+<td rowspan="3" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="3" class="data">3³⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">West End</span> of <span class="smcap">Brow</span> of <span class="smcap">Sallachan Hill</span> covered with
+Wood in line with <span class="smcap">Donald M‘Lean’s House</span>—Bearing NW. by W. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">West Chimney-Stack</span> of <span class="smcap">South Corran Ferry House</span> in line with
+<span class="smcap">White Part</span> of <span class="smcap">Rock</span> near <span class="smcap">High Water Mark</span> at the
+<span class="smcap">End</span> of a <span class="smcap">Dyke</span>—Bearing E. ³⁄₄ N.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">South Brow</span> of <span class="smcap">Stroncrigan Hill</span> in line with <span class="smcap">End</span>
+of <span class="smcap">Corran Cliff</span>—Bearing NE. by E. ¹⁄₈ E.</td>
+</tr>
+
+<tr>
+<td rowspan="2" class="data">CORRAN BANK, NORTH-WEST END, BUOY.</td>
+<td rowspan="2" class="data">6 Feet Buoy.<br>Chequered Black and White.</td>
+<td rowspan="2" class="data">2³⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">Bunrie Point</span> in line with <span class="smcap">High Water Mark</span> on <span class="smcap">Corran
+Point</span>—Bearing S. by W. ¹⁄₂ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Belfry</span> of <span class="smcap">Corran Church</span>—Bearing W. by N.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">CORRAN BANK, SOUTH-EAST END, BUOY.<span class="pagenum" id="Page411">[411]</span></td>
+<td rowspan="4" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="4" class="data">3¹⁄₂  Fathoms.</td>
+<td class="text"><span class="smcap">Culchenna Point</span> and <span class="smcap">Kintallon Point</span>, in line with
+<span class="smcap">End</span> of <span class="smcap">Cliff</span> of <span class="smcap">Corran Point</span>—Bearing SW. by S. ¹⁄₈ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Belfry</span> of <span class="smcap">Corran Church</span>—Bearing NW. by W. ⁵⁄₈ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">South Keil Farmhouse</span>, in line with <span class="smcap">Arch of Bridge on Road</span>—Bearing NNW.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Corran Bank North Buoy</span>—Bearing NNW.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">LOCHYFLAT EAST BUOY.</td>
+<td rowspan="4" class="data">6 Feet Buoy.<br>Red.</td>
+<td rowspan="4" class="data">2³⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">South End</span> of <span class="smcap">Wood</span> at <span class="smcap">Stroncrigan Point</span>,
+just clear of <span class="smcap">Cambusnagaul Point</span>—Bearing SW. by W. ³⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">East End</span> of <span class="smcap">Donald Cameron’s House</span> in <span class="smcap">Corpach</span>,
+in line with <span class="smcap">North End</span> of <span class="smcap">Old Engine House</span>—Bearing N. by W. ¹⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">South End</span> of <span class="smcap">Free Church</span> in line with <span class="smcap">North
+End</span> of <span class="smcap">Greyhouse</span>, or <span class="smcap">Old Corpach House</span>—Bearing N. ⁷⁄₈ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Entrance</span> of <span class="smcap">Caledonian Canal</span>—Bearing N. by W. ¹⁄₂ W.</td>
+</tr>
+
+<tr>
+<td rowspan="6" class="data">LOCHYFLAT MIDDLE BUOY.</td>
+<td rowspan="6" class="data">6 Feet Buoy.<br>Red.</td>
+<td rowspan="6" class="data">3¹⁄₂ Fathoms.</td>
+<td class="text"><span class="smcap">East End</span> of <span class="smcap">Henderson’s House</span> or <span class="smcap">Croft</span>
+in line with <span class="smcap">East End</span> of <span class="smcap">Schoolhouse</span> near <span class="smcap">Cambusnagaul
+Point</span>—Bearing W. ¹⁄₂ S.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Fish-house</span> in line with <span class="smcap">End</span> of <span class="smcap">Dearg
+Point</span>—Bearing N. by W. ³⁄₄ W.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Entrance</span> of <span class="smcap">Caledonian Canal</span>—Bearing N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">North End</span> of <span class="smcap">Wood</span> at <span class="smcap">Banavie</span> at
+<span class="smcap">South Side</span> of <span class="smcap">Canal</span> in line with <span class="smcap">Clump</span> of
+<span class="smcap">Trees</span> at <span class="smcap">East End</span> of <span class="smcap">John Cameron’s Cottage</span> in
+<span class="smcap">Kilcorpach</span>—Bearing NE. by E. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Buoy</span> on <span class="smcap">East End</span> of <span class="smcap">Lochyflat</span>—Bearing NE. ³⁄₄ N.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">M‘Lean’s Rock Buoy</span>—Bearing NW. by N.</td>
+</tr>
+
+<tr>
+<td rowspan="5" class="data">LOCHYFLAT  WEST BUOY.</td>
+<td rowspan="5" class="data">6 Feet Buoy.<br>Red.</td>
+<td rowspan="5" class="data">3 Fathoms.</td>
+<td class="text"><span class="smcap">Cameron’s Monument</span> in line with <span class="smcap">End</span> of <span class="smcap">Dearg
+Point</span>—Bearing N. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">North</span> or <span class="smcap">Steep Face</span> of <span class="smcap">Donnay Hill</span> in
+line with <span class="smcap">South Wing</span> of <span class="smcap">Old Castle</span> of <span class="smcap">Inverlochy</span>—Bearing E. ³⁄₈ S.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Lochyflat Middle Buoy</span>—Bearing NE.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">M‘Lean’s Rock Buoy</span>—Bearing N. by E. ¹⁄₄ E.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Fort-William Pier</span>—Bearing SSW. ¹⁄₈ W.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">MACLEAN’S ROCK, LOCHEILHEAD, BUOY.<span class="pagenum" id="Page412">[412]</span></td>
+<td rowspan="4" class="data">6 Feet Buoy.<br>Black.</td>
+<td rowspan="4" class="data">3³⁄₄ Fathoms.</td>
+<td class="text"><span class="smcap">Old Engine-House</span> in line with <span class="smcap">High Water Mark</span> on <span class="smcap">South
+End</span> of <span class="smcap">Island Creiah</span>—Bearing N. by E. ¹⁄₈ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">North Brow</span> of <span class="smcap">Donnay Hill</span> in line with <span class="smcap">Alan Kennedy’s
+Barn</span>, <span class="smcap">Southmost House</span> in <span class="smcap">Kilcorpach</span>—Bearing E. ³⁄₄ S.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Lochyflat West Buoy</span>—Bearing S. by W. ¹⁄₄ W.</td>
+</tr>
+
+<tr class="bb">
+<td class="text"><span class="smcap">Fort-William Pier</span>—Bearing S. by W. ³⁄₄ W.</td>
+</tr>
+
+<tr>
+<td rowspan="4" class="data">NEW ROCK, LOCHEILHEAD, BUOY.</td>
+<td rowspan="4" class="data">6 Feet Buoy.<br>Chequered Black and White.</td>
+<td rowspan="4" class="data">3 Fathoms.</td>
+<td class="text"><span class="smcap">Cameron’s Monument</span> in line with <span class="smcap">End</span> of <span class="smcap">Dearg
+Point</span>—Bearing N. ¹⁄₄ E.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">North End</span> of <span class="smcap">Free Church</span> in line with <span class="smcap">High Water
+Mark</span> on <span class="smcap">East End</span> of <span class="smcap">Island Creiah</span>—Bearing NE. ³⁄₄ N.</td>
+</tr>
+
+<tr>
+<td class="text"><span class="smcap">Centre</span> of <span class="smcap">Donnay Hill</span> in line with <span class="smcap">Alan Kennedy’s
+Barn</span>—Bearing E. ⁷⁄₈ S.</td>
+</tr>
+
+<tr>
+<td class="text note">N.B.—<i>Depth at Low Water of Spring Tides on Rock is 8 feet. The Buoy, moored in 3 fathoms, swings clear of the Rock
+on west side of it.</i></td>
+</tr>
+
+</table>
+
+<p class="center fsize90"><i>By order of the Board</i>,</p>
+
+<p class="right padr4 fsize90">ALAN STEVENSON, <i>Engineer</i>.</p>
+
+<p class="noindent fsize80"><span class="padl4"><i>Edinburgh</i>, <i>1st January 1848</i>.</span></p>
+
+<hr class="sec">
+
+<p class="center highline2 blankbefore2 fsize125">NOTICE TO MARINERS.</p>
+
+<p><span class="smcap">The Commissioners of Northern Lighthouses</span> <i>have resolved to publish, on 1st
+January annually, for the use of Mariners, a Descriptive List of all the Lighthouses, Beacons,
+and Buoys under their charge, giving the characteristic appearance and correct bearings of each.</i></p>
+
+<p><span class="smcap">Mariners</span> <i>are particularly requested to notice, that they should</i>
+<span class="allsmcap">NEVER PURCHASE</span> <i>any List</i>
+<span class="allsmcap">EXCEPT THAT FOR THE YEAR CURRENT</span> <i>at the time of purchase. As changes may have taken
+place, no reliance can be placed on any List which has been published for a preceding year.</i></p>
+
+<p><span class="smcap">Publishers</span> <i>are particularly cautioned not to sell any List which has been published on
+a preceding year. Arrangements have been made with the Publishers of the Board, that
+all copies remaining on hand with any Publisher, at the close of any year, will be exchanged
+for the New Issue; and all Publishers are</i> <span class="allsmcap">MOST PARTICULARLY REQUESTED</span> <i>not to retain
+on hand any copies of a past issue.</i></p>
+
+<p class="center"><i>By Order of the Board</i>,</p>
+
+<p class="right padr2">ALEX. CUNINGHAM, <i>Secretary</i>.</p>
+
+<div class="w12em padl2">
+
+<div class="split8515">
+
+<div class="left8515">
+
+<p class="noindent fsize80"><span class="smcap padl2">Northern Lights Office</span>,<br>
+<span class="smcap">Edinburgh</span>, <i>1st January 1848</i>.</p>
+
+</div><!--left-->
+
+<div class="right8515">
+
+<p class="noindent fsize175 up075">}</p>
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+</div><!--width-->
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter" id="App9">
+
+<p><span class="pagenum" id="Page413">[413]</span></p>
+
+<h3 class="nobreak"><span class="chapno">APPENDIX, No. IX.</span><br>
+<span class="chapname">REPORT TO THE COMMISSIONERS OF NORTHERN LIGHTHOUSES,
+FOR THE YEAR 1846; WITH APPENDICES.</span><br><span class="fsize90"><span class="smcap">By Alexander Cuningham,
+W.S., Secretary to the Board.</span></span></h3>
+
+</div><!--chapter-->
+
+<p>The gross amount of <span class="smcap">Duties</span> received from Shipping in the year to
+31st December 1846, as per detailed State appended hereto (<a href="#Page427">No. I.</a>, <a href="#Page429">p. 429</a>),
+is £46,001&#160;: 11&#160;: 2⁶⁄₈.</p>
+
+<p class="blankbefore75">The <span class="smcap">Commission</span> paid to Collectors in the same period is £2401&#160;: 7&#160;: 3⁴⁄₈,
+and Repayments of Duties erroneously charged, &amp;c., £218&#160;: 16&#160;: 10²⁄₈, making
+the nett amount of Duties for the year £43,381&#160;: 7&#160;: 1, as also appears
+from State, <a href="#Page427">No. I.</a>, <a href="#Page429">p. 429</a>.</p>
+
+<table class="bookkeeping">
+
+<tr>
+<td class="descr item">The nett amount of Duties in the year 1845 was</td>
+<td rowspan="3" colspan="4">&#160;</td>
+<td class="pounds">£52,391</td>
+<td class="shillings">8</td>
+<td class="pence">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr item">While that received in 1846 is</td>
+<td class="pounds bb">43,381</td>
+<td class="shillings bb">7</td>
+<td class="pence bb">1</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td class="descr subtot">Making a <span class="smcap">Deficiency</span> in the year of</td>
+<td class="pounds">£9,010</td>
+<td class="shillings">1</td>
+<td class="pence">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Whereof—</td>
+<td colspan="8">&#160;</td>
+</tr>
+
+<tr>
+<td class="descr detail">Half-year to 30th June,</td>
+<td class="pounds">£2350</td>
+<td class="shillings">9</td>
+<td class="pence">1</td>
+<td>&#160;</td>
+<td rowspan="2" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="descr detail">Ditto to 31st December,</td>
+<td class="pounds bb">6659</td>
+<td class="shillings bb">12</td>
+<td class="pence bb">2</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5">&#160;</td>
+<td class="pounds">£9,010</td>
+<td class="shillings">1</td>
+<td class="pence">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="horline">&#160;</td>
+<td colspan="8" class="horline bt bb2">&#160;</td>
+</tr>
+
+</table>
+
+<p class="blankbefore75">It is to be observed, however, that during the currency of this year, two
+reductions in the amount of Light-duties, resolved upon by the <span class="smcap">Board</span>, have
+come into operation.</p>
+
+<p class="blankbefore75">1. The first of these reductions was one halfpenny per ton (or one-half
+of the amount leviable by Statute) for the Bell Rock Light; one farthing
+per ton (or one-half of the amount leviable) for each of the Lights of
+Corsewell and Mull of Galloway; and one-eighth of a penny per ton (or
+one-fourth of the amount leviable) for Pladda Light. These reductions<span class="pagenum" id="Page414">[414]</span>
+were in operation during the first half of the year 1846. They were estimated
+to produce a deficiency in the annual Revenue of £5160, which, for
+the half-year, gives £2580. The actual deficiency in the amount levied for
+the first half of 1846, over that levied in the corresponding period of the
+preceding year, was £2350&#160;: 9&#160;: 1, being still £230 under the estimated
+amount.</p>
+
+<p class="blankbefore75">2. The <span class="smcap">Board</span> came to the resolution of making such a further reduction
+as should, including the previous one, give an aggregate abatement to
+the Coasting Trade, for each of the Lighthouses, of 50 per cent., that is,
+the amount leviable for each of the Lights being, previous to the first reduction,
+one halfpenny per ton, was reduced for the Coasting Trade to one
+farthing per ton; the amount for the Bell Rock and Skerryvore Lights,
+being one penny, was reduced to one halfpenny per ton. This reduction
+commenced on the 1st day of July 1846, and has consequently been in operation
+during the last half of that year. It was estimated to produce a deficiency
+in the annual revenue of the Board of £14,394&#160;: 14&#160;: 5, which, for
+the half-year, gives £7197&#160;: 9&#160;: 2. The actual deficiency in the amount levied
+for the last half of 1846, over that levied in the corresponding period
+of the preceding year, was £6659&#160;: 12&#160;: 2, being £540 under the estimated
+amount.</p>
+
+<table class="bookkeeping">
+
+<tr>
+<td class="descr long">It is also proper to observe, that while there is the above deficiency in Receipts of the year 1846, as
+contrasted with 1845, of</td>
+<td class="pounds">£9010</td>
+<td class="shillings">1</td>
+<td class="pence">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr long">There was a surplus Receipt of the year 1845, as contrasted with 1844, amounting to</td>
+<td class="pounds bb">6612</td>
+<td class="shillings bb">17</td>
+<td class="pence bb">8</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td class="descr detail">Making the <span class="smcap">Deficiency</span> in 1846, as contrasted with the
+<span class="smcap">Receipts</span> of 1844, upon which the calculations of the Board were founded, only</td>
+<td class="pounds">£2397</td>
+<td class="shillings">3</td>
+<td class="pence">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="horline">&#160;</td>
+<td colspan="4" class="horline bt bb2">&#160;</td>
+</tr>
+
+</table>
+
+<p class="blankbefore75">On the other hand, the greater reduction having been in operation only
+during half the year, a greater deficiency in the Revenue must be looked
+for in future years.</p>
+
+<p class="blankbefore75">The Light-Duties in 1845 were contributed by 163,174 vessels in the
+Coasting Trade, giving an aggregate tonnage of 15,566,461, and by 45,612
+vessels in Oversea Trade, giving an aggregate tonnage of 9,300,983.</p>
+
+<p><span class="pagenum" id="Page415">[415]</span></p>
+
+<p class="blankbefore75">The Light-Duties in 1846 have been contributed by 163,166 vessels in
+the Coasting Trade, giving an aggregate tonnage of 15,926,634, and by
+50,324 vessels in the Oversea Trade, giving an aggregate tonnage of
+9,577,478.</p>
+
+<p class="blankbefore75">A contrast of these statements shews an increase in the Coasting Trade
+of 1846 in tonnage of 360,173, with eight fewer vessels; and in the Oversea
+Trade an increase of 4712 vessels, with a tonnage of 276,495.</p>
+
+<p class="blankbefore75">These results (somewhat singular in their relative amounts) establish the
+important fact, that, though there is a deficiency in the revenue of the
+Board, it truly arises from the reductions in the Duties, and not from any
+reduction in the Shipping.</p>
+
+<p class="blankbefore75">For the information of the Board, there will be found appended (p. 433)
+a statement shewing the progressive increase of tonnage during the last four
+years.</p>
+
+<table class="bookkeeping">
+
+<tr>
+<td colspan="5" class="descr item">The amount of Duties received in the year 1846, as above, is</td>
+<td class="pounds">£46,001</td>
+<td class="shillings">11</td>
+<td class="pence">2</td>
+<td class="fraction">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="5" class="descr item">While the Ordinary Expenditure of the Board has been</td>
+<td class="pounds bb">32,063</td>
+<td class="shillings bb">6</td>
+<td class="pence bb">3</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="descr subtot">Giving a Surplus Receipt for the year to meet Extraordinary Expenditure of (see
+<a href="#Page439">State, No. II.</a>, <a href="#Page432">p. 432</a>)</td>
+<td class="pounds">£13,938</td>
+<td class="shillings">4</td>
+<td class="pence">11</td>
+<td class="fraction">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="horline">&#160;</td>
+<td colspan="8" class="horline bt bb2">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="descr">But the total Expenditure of the Board in the Year has been</td>
+<td class="pounds">£60,374</td>
+<td class="shillings">15</td>
+<td class="pence">9</td>
+<td class="fraction">²⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="5" class="descr">From which if there be deducted the Gross Receipts, per <a href="#Page425">page 425</a>,</td>
+<td class="pounds bb">47,895</td>
+<td class="shillings bb">8</td>
+<td class="pence bb">8</td>
+<td class="fraction bb">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="5" class="descr item">It gives a Balance superexpended beyond the surplus of the year of</td>
+<td class="pounds">£12,479</td>
+<td class="shillings">7</td>
+<td class="pence">0</td>
+<td class="fraction">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="descr">The Balance on hand at 31st March 1846 was</td>
+<td class="pounds">£42,069</td>
+<td class="shillings">6</td>
+<td class="pence">10</td>
+<td>&#160;</td>
+<td rowspan="2" colspan="4" class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">While that on hand at 31st March 1847 is</td>
+<td class="pounds">29,589</td>
+<td class="shillings">19</td>
+<td class="pence">9</td>
+<td class="fraction">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="5" class="descr subtot">Difference equal to superexpenditure,</td>
+<td class="pounds">£12,479</td>
+<td class="shillings">7</td>
+<td class="pence">0</td>
+<td class="fraction">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="horline">&#160;</td>
+<td colspan="8" class="horline bt bb2">&#160;</td>
+</tr>
+
+</table>
+
+<p><span class="pagenum" id="Page416">[416]</span></p>
+
+<p class="blankbefore75">There has been expended on the various Works in progress, prior to the
+year 1846 and in that year, as <span class="nowrap">follows:—</span></p>
+
+<table class="workexpenses">
+
+<tr class="bb">
+<th class="br">&#160;</th>
+<th colspan="4" class="br">Prior<br>to 1846.</th>
+<th colspan="4" class="br">In 1846.</th>
+<th colspan="4"><span class="smcap">Total.</span></th>
+</tr>
+
+<tr>
+<td class="descr">Skerryvore Lighthouse Works</td>
+<td class="pound">£93,576</td>
+<td class="shilling">10</td>
+<td class="intpence">0</td>
+<td class="br">&#160;</td>
+<td class="pound">£227</td>
+<td class="shilling">8</td>
+<td class="intpence">2</td>
+<td class="br">&#160;</td>
+<td class="pound">£93,803</td>
+<td class="shilling">18</td>
+<td class="intpence">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr"><span class="padl2">Add Bo-Pheg Beacon</span></td>
+<td class="pound bb">416</td>
+<td class="shilling bb">10</td>
+<td class="intpence bb">7</td>
+<td class="br bb">&#160;</td>
+<td class="pound bb">25</td>
+<td class="shilling bb">10</td>
+<td class="intpence bb">1</td>
+<td class="br bb">&#160;</td>
+<td class="pound bb">442</td>
+<td class="shilling bb">0</td>
+<td class="intpence bb">8</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="pound">£93,993</td>
+<td class="shilling">0</td>
+<td class="intpence">7</td>
+<td class="br">&#160;</td>
+<td class="pound">£252</td>
+<td class="shilling">18</td>
+<td class="intpence">3</td>
+<td class="br">&#160;</td>
+<td class="pound">£94,245</td>
+<td class="shilling">18</td>
+<td class="intpence">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Covesea Lighthouse Works</td>
+<td class="pound">9,523</td>
+<td class="shilling">17</td>
+<td class="intpence">6</td>
+<td class="br">&#160;</td>
+<td class="pound">1,109</td>
+<td class="shilling">5</td>
+<td class="intpence">4</td>
+<td class="br">&#160;</td>
+<td class="pound">10,633</td>
+<td class="shilling">2</td>
+<td class="intpence">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Cromarty Ditto</td>
+<td class="pound">2,895</td>
+<td class="shilling">18</td>
+<td class="intpence">8</td>
+<td class="br">&#160;</td>
+<td class="pound">342</td>
+<td class="shilling">9</td>
+<td class="intpence">3</td>
+<td class="br">&#160;</td>
+<td class="pound">3,238</td>
+<td class="shilling">7</td>
+<td class="intpence">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Chanonry Ditto</td>
+<td class="pound">2,832</td>
+<td class="shilling">16</td>
+<td class="intpence">1</td>
+<td class="br">&#160;</td>
+<td class="pound">405</td>
+<td class="shilling">7</td>
+<td class="intpence">8</td>
+<td class="br">&#160;</td>
+<td class="pound">3,238</td>
+<td class="shilling">3</td>
+<td class="intpence">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Ardnamurchan Ditto</td>
+<td class="pound">296</td>
+<td class="shilling">2</td>
+<td class="intpence">2</td>
+<td class="br">&#160;</td>
+<td class="pound">2,343</td>
+<td class="shilling">17</td>
+<td class="intpence">6</td>
+<td class="br">&#160;</td>
+<td class="pound">2,639</td>
+<td class="shilling">19</td>
+<td class="intpence">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Laggan Spur Beacon</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">748</td>
+<td class="shilling">10</td>
+<td class="intpence">6</td>
+<td class="br">&#160;</td>
+<td class="pound">748</td>
+<td class="shilling">10</td>
+<td class="intpence">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Island Glass New Buildings and Inclosures</td>
+<td class="pound">3,064</td>
+<td class="shilling">15</td>
+<td class="intpence">3</td>
+<td class="br">&#160;</td>
+<td class="pound">1,797</td>
+<td class="shilling">3</td>
+<td class="intpence">5</td>
+<td class="fracpence br">¹⁄₂</td>
+<td class="pound">4,861</td>
+<td class="shilling">18</td>
+<td class="intpence">8</td>
+<td class="fracpence">¹⁄₂</td>
+</tr>
+
+<tr>
+<td class="descr">Nosshead Lighthouse Works</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">1,467</td>
+<td class="shilling">6</td>
+<td class="intpence">1</td>
+<td class="br">&#160;</td>
+<td class="pound">1,467</td>
+<td class="shilling">6</td>
+<td class="intpence">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Loch Ryan Ditto</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">829</td>
+<td class="shilling">12</td>
+<td class="intpence">9</td>
+<td class="fracpence br">¹⁄₂</td>
+<td class="pound">829</td>
+<td class="shilling">12</td>
+<td class="intpence">9</td>
+<td class="fracpence">¹⁄₂</td>
+</tr>
+
+<tr>
+<td class="descr">Pentland Skerries New Works</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">3,135</td>
+<td class="shilling">17</td>
+<td class="intpence">5</td>
+<td class="fracpence br">¹⁄₂</td>
+<td class="pound">3,135</td>
+<td class="shilling">17</td>
+<td class="intpence">5</td>
+<td class="fracpence">¹⁄₂</td>
+</tr>
+
+<tr>
+<td class="descr">Ditto Dioptric Light</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">2,037</td>
+<td class="shilling">11</td>
+<td class="intpence">4</td>
+<td class="br">&#160;</td>
+<td class="pound">2,037</td>
+<td class="shilling">11</td>
+<td class="intpence">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Renewal of Fixed Lights</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">3,035</td>
+<td class="shilling">14</td>
+<td class="intpence">4</td>
+<td class="br">&#160;</td>
+<td class="pound">3,035</td>
+<td class="shilling">14</td>
+<td class="intpence">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Buoys, &amp;c.</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">1,549</td>
+<td class="shilling">14</td>
+<td class="intpence">11</td>
+<td class="fracpence br">¹⁄₂</td>
+<td class="pound">1,549</td>
+<td class="shilling">14</td>
+<td class="intpence">11</td>
+<td class="fracpence">¹⁄₂</td>
+</tr>
+
+<tr>
+<td class="descr">Campbeltown Beacons</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">17</td>
+<td class="shilling">4</td>
+<td class="intpence">10</td>
+<td class="br">&#160;</td>
+<td class="pound">17</td>
+<td class="shilling">4</td>
+<td class="intpence">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Lappock Beacon</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">8</td>
+<td class="shilling">12</td>
+<td class="intpence">5</td>
+<td class="br">&#160;</td>
+<td class="pound">8</td>
+<td class="shilling">12</td>
+<td class="intpence">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Startpoint New Works</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">5</td>
+<td class="shilling">19</td>
+<td class="intpence">4</td>
+<td class="br">&#160;</td>
+<td class="pound">5</td>
+<td class="shilling">19</td>
+<td class="intpence">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Elie or Vows Beacon</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">205</td>
+<td class="shilling">5</td>
+<td class="intpence">8</td>
+<td class="br">&#160;</td>
+<td class="pound">205</td>
+<td class="shilling">5</td>
+<td class="intpence">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Whiteness Beacon</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">152</td>
+<td class="shilling">5</td>
+<td class="intpence">8</td>
+<td class="br">&#160;</td>
+<td class="pound">152</td>
+<td class="shilling">5</td>
+<td class="intpence">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Longman’s Point Ditto</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">164</td>
+<td class="shilling">15</td>
+<td class="intpence">6</td>
+<td class="br">&#160;</td>
+<td class="pound">164</td>
+<td class="shilling">15</td>
+<td class="intpence">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Loch Ryan Ditto</td>
+<td class="blank">...</td>
+<td colspan="3" class="blank br">...</td>
+<td class="pound">152</td>
+<td class="shilling">5</td>
+<td class="intpence">9</td>
+<td class="br">&#160;</td>
+<td class="pound">152</td>
+<td class="shilling">5</td>
+<td class="intpence">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Brist Beacon</td>
+<td class="pound">734</td>
+<td class="shilling">2</td>
+<td class="intpence">9</td>
+<td class="br">&#160;</td>
+<td class="pound">8</td>
+<td class="shilling">12</td>
+<td class="intpence">5</td>
+<td class="br">&#160;</td>
+<td class="pound">742</td>
+<td class="shilling">15</td>
+<td class="intpence">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="descr">Mull of Kintyre Dykes and Road</td>
+<td class="pound">586</td>
+<td class="shilling">14</td>
+<td class="intpence">4</td>
+<td class="br">&#160;</td>
+<td class="pound">647</td>
+<td class="shilling">17</td>
+<td class="intpence">9</td>
+<td class="br">&#160;</td>
+<td class="pound">1,234</td>
+<td class="shilling">12</td>
+<td class="intpence">1</td>
+<td>&#160;</td>
+</tr>
+
+</table>
+
+<p class="blankbefore75">There has been expended on the new Steamer “Pharos,” £18,977&#160;: 6&#160;: 7.</p>
+
+<p class="blankbefore75">The <span class="smcap">Commissioners</span> have purchased a House at Crail for £105&#160;: 19&#160;: 4
+for the use of the Boatmen attending at the Isle of May.</p>
+
+<p class="blankbefore75">The attention of the <span class="smcap">Commissioners</span> is called to the circumstance that
+a complete change has been made this year in the mode of stating the Accounts.
+The Accounts are now, for the first time, concentrated in the Secretary’s
+department, and for every item entered in the subjoined <a href="#Page418">abstract</a>,
+reference is now, and will hereafter, be made to a page of the Ledger containing
+a detailed account vouching the charge. Following out this arrangement,
+the account has been branched into three heads or divisions.<span class="pagenum" id="Page417">[417]</span>
+The first head comprises the <i>ordinary</i> expenses of the Lighthouses. In
+this branch it has been thought right to state separately, under the head of
+the Isle of May, the interest on the debt to Government, being the balance
+of the price of the Island. The second head comprises the ordinary expenses
+of the Board, not in the first instance chargeable against any particular
+Lighthouse, but falling to be afterwards allocated in the final view of
+the Receipt and Expenditure of each Lighthouse. This branch is again
+subdivided so as to <span class="nowrap">shew—</span></p>
+
+<table class="standard fsize90">
+
+<tr>
+<td class="rght">1.</td>
+<td class="text">The Expense of Collection.</td>
+</tr>
+
+<tr>
+<td class="rght">2.</td>
+<td class="text">Repayments, &amp;c. of Light-Duties overcharged.</td>
+</tr>
+
+<tr>
+<td class="rght">3.</td>
+<td class="text">The Expense of the Establishment, including Salaries, Stationery, &amp;c.</td>
+</tr>
+
+<tr>
+<td class="rght">4.</td>
+<td class="text">The Shipping Establishment.</td>
+</tr>
+
+<tr>
+<td class="rght">5.</td>
+<td class="text">Beacons and Buoys—ordinary maintenance.</td>
+</tr>
+
+<tr>
+<td class="rght">6.</td>
+<td class="text">The Storehouse, Leith.</td>
+</tr>
+
+<tr>
+<td class="rght">7.</td>
+<td class="text">Charities and Superannuations.</td>
+</tr>
+
+<tr>
+<td class="rght">8.</td>
+<td class="text">Miscellaneous Payments.</td>
+</tr>
+
+</table>
+
+<p class="blankbefore75">The last division of the abstract comprises what is termed the <i>extraordinary</i>
+expenditure, that is, the expense of New Works and others not falling
+to be allocated upon the Lighthouses.</p>
+
+<p class="blankbefore75">In effecting this change, various payments which appeared in the former
+abstracts will not now be found in the present, such as Rents and Feu-duties,
+which are now charged to the respective Lighthouses for which they are
+paid; the Storekeeper’s Salary, which is stated in the Storehouse Account;
+the Office-Keeper’s, in the Office Account, &amp;c., and the Salaries of the Officers
+of the Board will be found under the head of Edinburgh Establishment.</p>
+
+<p><span class="pagenum" id="Page418">[418]</span></p>
+
+<p class="tabhead">ABSTRACT <i>of the</i> <span class="smcap">Receipts</span> <i>and</i>
+<span class="smcap">Payments</span> <i>on Account of the</i> <span class="smcap">Duties</span>
+<i>levied for the</i> <span class="smcap">Northern Lighthouses</span> <i>for the year 1846.</i></p>
+
+<table class="app9table">
+
+<colgroup>
+<col span="2" class="w015em">
+<col span="6" class="wauto">
+<col class="w03em">
+<col span="2" class="w01em">
+<col class="w015em">
+<col class="w03em">
+<col span="2" class="w01em">
+<col class="w015em">
+</colgroup>
+
+<tr>
+<td colspan="16" class="center highline075 fsize110">RECEIPTS.</td>
+</tr>
+
+<tr>
+<td class="nr highline075">I.</td>
+<td colspan="11" class="txt highline075"><span class="smcap">Gross Amount</span> of the Duties received for 1846,
+per <a href="#Page427">State, No. I.</a> <a href="#Page429">p. 429</a>,</td>
+<td class="pounds bt bl highline075">£46,001</td>
+<td class="shillings bt highline075">11</td>
+<td class="pence bt highline075">2</td>
+<td class="pence frac bt highline075">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="2" class="highline075">&#160;</td>
+<td colspan="10" class="txt highline075">Which has been received in the following proportions for each Lighthouse,
+as appears from <a href="#Page430">State, No. II.</a>, <a href="#Page430">pp. 430</a>-<a href="#Page433">3</a>,
+<span class="nowrap">viz.:—</span></td>
+<td rowspan="45" colspan="4" class="highline075 bl">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="27" colspan="2">&#160;</td>
+<td class="nr"><span class="padl2">1.</span></td>
+<td colspan="5" class="txt">Inchkeith,</td>
+<td class="pounds bt bl">£2524</td>
+<td class="shillings bt">9</td>
+<td class="pence bt">2</td>
+<td class="pence frac bt">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">2.</span></td>
+<td colspan="5" class="txt">Isle of May,</td>
+<td class="pounds bl">3825</td>
+<td class="shillings">8</td>
+<td class="pence">5</td>
+<td class="pence frac">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">3.</span></td>
+<td colspan="5" class="txt">Bell Rock,</td>
+<td class="pounds bl">5342</td>
+<td class="shillings">15</td>
+<td class="pence">5</td>
+<td class="pence frac">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">4.</span></td>
+<td colspan="5" class="txt">Girdleness,</td>
+<td class="pounds bl">2458</td>
+<td class="shillings">4</td>
+<td class="pence">5</td>
+<td class="pence frac">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">5.</span></td>
+<td colspan="5" class="txt">Buchanness,</td>
+<td class="pounds bl">1880</td>
+<td class="shillings">1</td>
+<td class="pence">3</td>
+<td class="pence frac">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">6.</span></td>
+<td colspan="5" class="txt">Kinnairdshead,</td>
+<td class="pounds bl">1744</td>
+<td class="shillings">11</td>
+<td class="pence">3</td>
+<td class="pence frac">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">7.</span></td>
+<td colspan="5" class="txt">Tarbetness,</td>
+<td class="pounds bl">329</td>
+<td class="shillings">17</td>
+<td class="pence">4</td>
+<td class="pence frac">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">8.</span></td>
+<td colspan="5" class="txt">Sumburghhead,</td>
+<td class="pounds bl">286</td>
+<td class="shillings">18</td>
+<td class="pence">2</td>
+<td class="pence frac">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">9.</span></td>
+<td colspan="5" class="txt">Startpoint,</td>
+<td class="pounds bl">1154</td>
+<td class="shillings">5</td>
+<td class="pence">4</td>
+<td class="pence frac">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">10.</span></td>
+<td colspan="5" class="txt">Pentland Skerries,</td>
+<td class="pounds bl">1370</td>
+<td class="shillings">10</td>
+<td class="pence">5</td>
+<td class="pence frac">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">11.</span></td>
+<td colspan="5" class="txt">Dunnethead,</td>
+<td class="pounds bl">1311</td>
+<td class="shillings">1</td>
+<td class="pence">10</td>
+<td class="pence frac">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">12.</span></td>
+<td colspan="5" class="txt">Capewrath,</td>
+<td class="pounds bl">1278</td>
+<td class="shillings">9</td>
+<td class="pence">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">13.</span></td>
+<td colspan="5" class="txt">Island Glass,</td>
+<td class="pounds bl">679</td>
+<td class="shillings">1</td>
+<td class="pence">10</td>
+<td class="pence frac">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">14.</span></td>
+<td colspan="5" class="txt">Barrahead,</td>
+<td class="pounds bl">1063</td>
+<td class="shillings">3</td>
+<td class="pence">2</td>
+<td class="pence frac">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">15.</span></td>
+<td colspan="5" class="txt">Skerryvore,</td>
+<td class="pounds bl">2090</td>
+<td class="shillings">11</td>
+<td class="pence">3</td>
+<td class="pence frac">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">16.</span></td>
+<td colspan="5" class="txt">Lismore,</td>
+<td class="pounds bl">239</td>
+<td class="shillings">11</td>
+<td class="pence">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">17.</span></td>
+<td colspan="5" class="txt">Rhinns of Islay,</td>
+<td class="pounds bl">1414</td>
+<td class="shillings">5</td>
+<td class="pence">8</td>
+<td class="pence frac">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">18.</span></td>
+<td colspan="5" class="txt">Mull of Kintyre,</td>
+<td class="pounds bl">1549</td>
+<td class="shillings">0</td>
+<td class="pence">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">19.</span></td>
+<td colspan="5" class="txt">Pladda,</td>
+<td class="pounds bl">2762</td>
+<td class="shillings">14</td>
+<td class="pence">3</td>
+<td class="pence frac">⁷⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">20.</span></td>
+<td colspan="5" class="txt">Corsewall,</td>
+<td class="pounds bl">2811</td>
+<td class="shillings">5</td>
+<td class="pence">3</td>
+<td class="pence frac">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">21.</span></td>
+<td colspan="5" class="txt">Mull of Galloway,</td>
+<td class="pounds bl">2823</td>
+<td class="shillings">19</td>
+<td class="pence">8</td>
+<td class="pence frac">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">22.</span></td>
+<td colspan="5" class="txt">Little Ross,</td>
+<td class="pounds bl">1187</td>
+<td class="shillings">7</td>
+<td class="pence">9</td>
+<td class="pence frac">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">23.</span></td>
+<td colspan="5" class="txt">Point of Ayre,</td>
+<td class="pounds bl">1755</td>
+<td class="shillings">17</td>
+<td class="pence">5</td>
+<td class="pence frac">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">24.</span></td>
+<td colspan="5" class="txt">Calf of Man (two Lights),</td>
+<td class="pounds bl">3839</td>
+<td class="shillings">2</td>
+<td class="pence">11</td>
+<td class="pence frac">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">25.</span></td>
+<td colspan="5" class="txt">Covesea Skerries,</td>
+<td class="pounds bl">193</td>
+<td class="shillings">7</td>
+<td class="pence">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">26.</span></td>
+<td colspan="5" class="txt">Cromarty,</td>
+<td class="pounds bl">27</td>
+<td class="shillings">14</td>
+<td class="pence">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr"><span class="padl2">27.</span></td>
+<td colspan="5" class="txt">Chanonry,</td>
+<td class="pounds bb bl">57</td>
+<td class="shillings bb">15</td>
+<td class="pence bb">1</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="8">&#160;</td>
+<td class="pounds bl">£46,001</td>
+<td class="shillings">11</td>
+<td class="pence">3</td>
+<td class="pence frac">⁷⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="2">&#160;</td>
+<td colspan="6" class="txt"><span class="smcap">Deduct</span> fractions short credited by Bankers,</td>
+<td class="pounds bb bl">0</td>
+<td class="shillings bb">0</td>
+<td class="pence bb">1</td>
+<td class="pence frac bb">¹⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="3">&#160;</td>
+<td colspan="5" class="center">As above,</td>
+<td class="pounds bbd bl">£46,001</td>
+<td class="shillings bbd">11</td>
+<td class="pence bbd">2</td>
+<td class="pence frac bbd">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr highline075">II.</td>
+<td colspan="7" class="txt highline075"><span class="nowrap"><span class="smcap">Miscellaneous Receipts</span>—</span></td>
+<td rowspan="2" colspan="4" class="bb bl">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="center bt br bb">Folio<br>in<br>Ledger.</td>
+<td colspan="6">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">32 &amp; 73</td>
+<td rowspan="12">&#160;</td>
+<td colspan="5" class="txt br">Rent of Stable behind the Office,</td>
+<td class="pounds">£18</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td rowspan="12" class="br bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">73</td>
+<td colspan="5" class="txt br">Do. of Small Houses at Arbroath,</td>
+<td class="pounds">5</td>
+<td class="shillings">5</td>
+<td class="pence">0</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">33</td>
+<td colspan="5" class="txt br">Proceeds sale of Regent Tender,</td>
+<td class="pounds">485</td>
+<td class="shillings">14</td>
+<td class="pence">3</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">32</td>
+<td colspan="5" class="txt br">Composition of 1s. 6d. per pound from the Trustee on Andrew Greig’s Bankrupt
+Estate, on a claim of £340, 11s. 8d. and Expenses arising from an evasion of Light-dues,</td>
+<td class="pounds">27</td>
+<td class="shillings">0</td>
+<td class="pence">9</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">30</td>
+<td colspan="5" class="txt br">Price of Lighter sold to Kirkcaldy Harbour Commissioners,
+<span class="pagenum" id="Page419">[419]</span></td>
+<td class="pounds">60</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">74</td>
+<td colspan="5" class="txt br">Do. do. to Leith Shipping Company,</td>
+<td class="pounds">45</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">40</td>
+<td colspan="5" class="txt br">Do. of Horse sold at Barrahead,</td>
+<td class="pounds">10</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">...</td>
+<td colspan="5" class="txt br">Do. of an Ass sold at Inchkeith,</td>
+<td class="pounds">0</td>
+<td class="shillings">9</td>
+<td class="pence">6</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">149</td>
+<td colspan="5" class="txt br">Do. of Articles sold at Skerryvore,</td>
+<td class="pounds">126</td>
+<td class="shillings">5</td>
+<td class="pence">10</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">73,75, &amp; 315</td>
+<td colspan="5" class="txt br">Fines imposed on Light-keepers, received,</td>
+<td class="pounds">13</td>
+<td class="shillings">1</td>
+<td class="pence">8</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">74</td>
+<td colspan="5" class="txt br">Sum received from the General Post-Office, for the maintenance of the Harbour
+Light at Portpatrick for the year 1845,</td>
+<td class="pounds">136</td>
+<td class="shillings">10</td>
+<td class="pence">9</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">40 &amp; 75</td>
+<td colspan="5" class="txt br">Interest received from the Royal Bank on money deposited,</td>
+<td class="pounds bb">966</td>
+<td class="shillings bb">9</td>
+<td class="pence bb">9</td>
+</tr>
+
+<tr>
+<td colspan="2" class="highline075 br">&#160;</td>
+<td colspan="6" class="right highline075"><span class="smcap">Sum</span>,</td>
+<td colspan="4" class="highline075 br">&#160;</td>
+<td class="pounds highline075 bb">1893</td>
+<td class="shillings highline075 bb">17</td>
+<td class="pence highline075 bb">6</td>
+<td class="highline075 bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="highline075 br">&#160;</td>
+<td colspan="3">&#160;</td>
+<td colspan="7" class="right br"><span class="smcap">Sums of Receipts</span> carried to
+<span class="smcap">Abstract</span>, <a href="#Page425">page 425</a>,</td>
+<td class="pounds highline075">£47,895</td>
+<td class="shillings highline075">8</td>
+<td class="pence highline075">8</td>
+<td class="pence frac highline075">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="2" class="thinline br">&#160;</td>
+<td colspan="5" class="thinline">&#160;</td>
+<td colspan="5" class="thinline btd">&#160;</td>
+<td colspan="4" class="thinline btd">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="16" class="center highline075 fsize110 bt bb">PAYMENTS.</td>
+</tr>
+
+<tr>
+<td colspan="2" class="bt br bb">Folio<br>in<br>Ledger.</td>
+<td colspan="14" class="highline075">BRANCH I.—<span class="smcap">Ordinary Expenses</span> of the
+<span class="smcap">Board</span>, being the Maintenance of the Lights for the year, <span class="nowrap">viz:—</span></td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="10" class="txt">1. <span class="nowrap"><span class="smcap">Lighthouses</span>—</span></td>
+<td colspan="4" class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">326</td>
+<td class="nr"><span class="padl2">&#8199;1.</span></td>
+<td colspan="9" class="txt br">Inchkeith,</td>
+<td class="pounds">£583</td>
+<td class="shillings">5</td>
+<td class="pence">10</td>
+<td class="pence frac">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">327</td>
+<td class="nr"><span class="padl2">&#8199;2.</span></td>
+<td colspan="5" class="txt br">Isle of May,</td>
+<td class="pounds bt">£702</td>
+<td class="shillings bt">3</td>
+<td class="pence bt">9</td>
+<td class="br bt">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td class="nr"><span class="padl2">&#8199;&#8199;&#8200;</span></td>
+<td colspan="5" class="txt br">Isle of May, Year’s Interest to Government,</td>
+<td class="pounds bb">250</td>
+<td class="shillings bb">0</td>
+<td class="pence bb">0</td>
+<td class="br bb">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="10" class="br">&#160;</td>
+<td class="pounds">952</td>
+<td class="shillings">3</td>
+<td class="pence">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">355</td>
+<td class="nr"><span class="padl2">&#8199;3.</span></td>
+<td colspan="9" class="txt br">Bell Rock,</td>
+<td class="pounds">989</td>
+<td class="shillings">1</td>
+<td class="pence">3</td>
+<td class="pence frac">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">329</td>
+<td class="nr"><span class="padl2">&#8199;4.</span></td>
+<td colspan="9" class="txt br">Girdleness,</td>
+<td class="pounds">548</td>
+<td class="shillings">18</td>
+<td class="pence">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">330</td>
+<td class="nr"><span class="padl2">&#8199;5.</span></td>
+<td colspan="9" class="txt br">Buchanness,</td>
+<td class="pounds">623</td>
+<td class="shillings">5</td>
+<td class="pence">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">331</td>
+<td class="nr"><span class="padl2">&#8199;6.</span></td>
+<td colspan="9" class="txt br">Kinnairdshead,</td>
+<td class="pounds">578</td>
+<td class="shillings">10</td>
+<td class="pence">0</td>
+<td class="pence frac">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">332</td>
+<td class="nr"><span class="padl2">&#8199;7.</span></td>
+<td colspan="9" class="txt br">Tarbetness,</td>
+<td class="pounds">574</td>
+<td class="shillings">11</td>
+<td class="pence">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">333</td>
+<td class="nr"><span class="padl2">&#8199;8.</span></td>
+<td colspan="9" class="txt br">Sumburghhead,</td>
+<td class="pounds">597</td>
+<td class="shillings">5</td>
+<td class="pence">3</td>
+<td class="pence frac">³⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">334</td>
+<td class="nr"><span class="padl2">&#8199;9.</span></td>
+<td colspan="9" class="txt br">Startpoint,</td>
+<td class="pounds">347</td>
+<td class="shillings">0</td>
+<td class="pence">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">335</td>
+<td class="nr"><span class="padl2">10.</span></td>
+<td colspan="9" class="txt br">Pentland Skerries (two Lights),</td>
+<td class="pounds">851</td>
+<td class="shillings">8</td>
+<td class="pence">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">336</td>
+<td class="nr"><span class="padl2">11.</span></td>
+<td colspan="9" class="txt br">Dunnethead,</td>
+<td class="pounds">470</td>
+<td class="shillings">19</td>
+<td class="pence">7</td>
+<td class="pence frac">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">337</td>
+<td class="nr"><span class="padl2">12.</span></td>
+<td colspan="9" class="txt br">Capewrath,</td>
+<td class="pounds">587</td>
+<td class="shillings">6</td>
+<td class="pence">11</td>
+<td class="pence frac">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">338</td>
+<td class="nr"><span class="padl2">13.</span></td>
+<td colspan="9" class="txt br">Island Glass,</td>
+<td class="pounds">515</td>
+<td class="shillings">2</td>
+<td class="pence">10</td>
+<td class="pence frac">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">339</td>
+<td class="nr"><span class="padl2">14.</span></td>
+<td colspan="9" class="txt br">Barrahead,</td>
+<td class="pounds">594</td>
+<td class="shillings">3</td>
+<td class="pence">10</td>
+<td class="pence frac">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">357</td>
+<td class="nr"><span class="padl2">15.</span></td>
+<td colspan="9" class="txt br">Skerryvore,</td>
+<td class="pounds">1122</td>
+<td class="shillings">0</td>
+<td class="pence">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">340</td>
+<td class="nr"><span class="padl2">16.</span><span class="pagenum" id="Page420">[420]</span></td>
+<td colspan="9" class="txt br">Lismore,</td>
+<td class="pounds">515</td>
+<td class="shillings">14</td>
+<td class="pence">2</td>
+<td class="pence frac">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">341</td>
+<td class="nr"><span class="padl2">17.</span></td>
+<td colspan="9" class="txt br">Rhinns of Islay,</td>
+<td class="pounds">569</td>
+<td class="shillings">12</td>
+<td class="pence">7</td>
+<td class="pence frac">³⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">342</td>
+<td class="nr"><span class="padl2">18.</span></td>
+<td colspan="9" class="txt br">Mull of Kintyre,</td>
+<td class="pounds">554</td>
+<td class="shillings">17</td>
+<td class="pence">10</td>
+<td class="pence frac">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">343</td>
+<td class="nr"><span class="padl2">19.</span></td>
+<td colspan="9" class="txt br">Pladda,</td>
+<td class="pounds">584</td>
+<td class="shillings">10</td>
+<td class="pence">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">344</td>
+<td class="nr"><span class="padl2">20.</span></td>
+<td colspan="9" class="txt br">Corsewall,</td>
+<td class="pounds">465</td>
+<td class="shillings">13</td>
+<td class="pence">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">345</td>
+<td class="nr"><span class="padl2">21.</span></td>
+<td colspan="9" class="txt br">Mull of Galloway,</td>
+<td class="pounds">517</td>
+<td class="shillings">0</td>
+<td class="pence">5</td>
+<td class="pence frac">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">346</td>
+<td class="nr"><span class="padl2">22.</span></td>
+<td colspan="9" class="txt br">Little Ross,</td>
+<td class="pounds">516</td>
+<td class="shillings">18</td>
+<td class="pence">6</td>
+<td class="pence frac">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">347</td>
+<td class="nr"><span class="padl2">23.</span></td>
+<td colspan="9" class="txt br">Point of Ayre,</td>
+<td class="pounds">409</td>
+<td class="shillings">1</td>
+<td class="pence">4</td>
+<td class="pence frac">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">348</td>
+<td class="nr"><span class="padl2">24.</span></td>
+<td colspan="5" class="txt br">Calf of Man (High Tower),</td>
+<td class="pounds bt">£394</td>
+<td class="shillings bt">4</td>
+<td class="pence bt">7</td>
+<td class="bt br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">354</td>
+<td class="nr"><span class="padl2">25.</span></td>
+<td colspan="5" class="txt br">Calf of Man (Low Tower),</td>
+<td class="pounds bb">419</td>
+<td class="shillings bb">14</td>
+<td class="pence bb">10</td>
+<td class="br bb">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="10" class="br">&#160;</td>
+<td class="pounds">813</td>
+<td class="shillings">19</td>
+<td class="pence">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">351</td>
+<td class="nr"><span class="padl2">26.</span></td>
+<td colspan="9" class="txt br">Covesea Skerries,</td>
+<td class="pounds">419</td>
+<td class="shillings">16</td>
+<td class="pence">8</td>
+<td class="pence frac">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">358</td>
+<td class="nr"><span class="padl2">27.</span></td>
+<td colspan="9" class="txt br">Cromarty,</td>
+<td class="pounds">339</td>
+<td class="shillings">17</td>
+<td class="pence">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">353</td>
+<td class="nr"><span class="padl2">28.</span></td>
+<td colspan="9" class="txt br">Chanonry,</td>
+<td class="pounds">284</td>
+<td class="shillings">7</td>
+<td class="pence">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">350</td>
+<td class="nr"><span class="padl2">29.</span></td>
+<td colspan="9" class="txt br">Loch Ryan,</td>
+<td class="pounds bb">176</td>
+<td class="shillings bb">5</td>
+<td class="pence bb">7</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="5">&#160;</td>
+<td colspan="5" class="right br"><span class="smcap">Sum</span>,—Carried to <span class="smcap">Abstract</span>, <a href="#Page425">p. 425</a>,</td>
+<td class="pounds">£16,103</td>
+<td class="shillings">0</td>
+<td class="pence">2</td>
+<td class="pence frac">³⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="thinline br">&#160;</td>
+<td colspan="6" class="thinline">&#160;</td>
+<td colspan="4" class="thinline br bbd">&#160;</td>
+<td colspan="4" class="thinline bbd">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="14" class="highline075">BRANCH II.—<span class="smcap">Ordinary Expenses</span> falling to be
+allocated upon each <span class="nowrap">Lighthouse—</span></td>
+</tr>
+
+<tr>
+<td rowspan="25" colspan="2" class="br">&#160;</td>
+<td colspan="10" class="txt">1. <span class="smcap">Expense</span> of <span class="nowrap"><span class="smcap">Collection</span>—</span></td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="9" class="txt br">To paid Commission to Collectors, per <a href="#Page427">State, No. I.</a> <a href="#Page429">p. 429</a>,</td>
+<td class="pounds bt">£2401</td>
+<td class="shillings bt">7</td>
+<td class="pence bt">3</td>
+<td class="pence frac bt">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="9" class="txt br">To paid Commission to Bankers,</td>
+<td class="pounds bb">115</td>
+<td class="shillings bb">3</td>
+<td class="pence bb">7</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10" class="br">&#160;</td>
+<td class="pounds">£2516</td>
+<td class="shillings">10</td>
+<td class="pence">10</td>
+<td class="pence frac">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="10" class="txt br">2. <span class="smcap">Repayments</span>, &amp;c., of <span class="smcap">Light-Duties overcharged</span>,</td>
+<td class="pounds">218</td>
+<td class="shillings">16</td>
+<td class="pence">10</td>
+<td class="pence frac">²⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="10" class="txt br">3. <span class="smcap">Establishment in</span> <span class="nowrap"><span class="smcap">Edinburgh</span>—</span></td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="txt br">Engineer, ³⁄₄ Salary at £900,</td>
+<td class="pounds bt">£675</td>
+<td class="shillings bt">0</td>
+<td class="pence bt">0</td>
+<td class="bt br">&#160;</td>
+<td colspan="4" class="bt br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="txt br">Engineer, ¹⁄₄ Salary at £1200,</td>
+<td class="pounds bb">300</td>
+<td class="shillings bb">0</td>
+<td class="pence bb">0</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="6" class="br">&#160;</td>
+<td class="pounds">£975</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Secretary,</td>
+<td class="pounds">500</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Accountant, Salary to 8th July, when he died,</td>
+<td class="pounds">84</td>
+<td class="shillings">12</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="txt br">Superintendent of Light-keepers, ³⁄₄ Salary at £145,</td>
+<td class="pounds bt">£108</td>
+<td class="shillings bt">15</td>
+<td class="pence bt">0</td>
+<td class="bt br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="txt br">Superintendent of Light-keepers, ¹⁄₄ Salary at £210,</td>
+<td class="pounds bb">52</td>
+<td class="shillings bb">10</td>
+<td class="pence bb">0</td>
+<td class="bb br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="6" class="br">&#160;</td>
+<td class="pounds">161</td>
+<td class="shillings">5</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="txt br">Foreman of Lightroom repairs, ³⁄₄ Salary at £110,</td>
+<td class="pounds bt">£82</td>
+<td class="shillings bt">10</td>
+<td class="pence bt">0</td>
+<td class="bt br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="txt br">Foreman of Lightroom repairs, ¹⁄₄ Salary at £140,</td>
+<td class="pounds bb">35</td>
+<td class="shillings bb">0</td>
+<td class="pence bb">0</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="6" class="br">&#160;</td>
+<td class="pounds">117</td>
+<td class="shillings">10</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Engineer’s Clerk, ¹⁄₄ Salary (formerly paid by Engineer),</td>
+<td class="pounds">32</td>
+<td class="shillings">10</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Examiner of Accounts, from 8th January to Candlemas,</td>
+<td class="pounds">17</td>
+<td class="shillings">2</td>
+<td class="pence">6</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br">First Clerk in Secretary’s Department, ¹⁄₄ Salary,</td>
+<td class="pounds">25</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Second Clerk in Secretary’s Department, ¹⁄₄ Salary,</td>
+<td class="pounds">25</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Officer (now conjoined with Housekeeper), ¹⁄₄ Salary,<span class="pagenum" id="Page421">[421]</span></td>
+<td class="pounds">5</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Payments to two Clerks in Accountant’s Department, to cease at Whitsunday in
+consequence of the appointments in Secretary’s Department,</td>
+<td class="pounds">174</td>
+<td class="shillings">6</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Interim Accountant, per minute of the Board, until Examiner of Accounts was appointed,</td>
+<td class="pounds">105</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Office, including Porter and House-Servants’ Wages, House Expenses, Taxes, Books for Library, &amp;c.,</td>
+<td class="pounds bb">910</td>
+<td class="shillings bb">10</td>
+<td class="pence bb">3</td>
+<td class="pence frac br bb">¹⁄₂</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">279</td>
+<td colspan="10" class="br">&#160;</td>
+<td class="pounds">3132</td>
+<td class="shillings">15</td>
+<td class="pence">9</td>
+<td class="pence frac">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="10" class="txt br">4. <span class="smcap">Shipping</span> <span class="nowrap"><span class="smcap">Establishment</span>—</span></td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">132</td>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Pharos Steam-Vessel,</td>
+<td class="pounds bt">£3790</td>
+<td class="shillings bt">1</td>
+<td class="pence bt">11</td>
+<td class="pence frac bt br">³⁄₄</td>
+<td rowspan="4" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">133</td>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Prince of Wales, Bell Rock Tender,</td>
+<td class="pounds">954</td>
+<td class="shillings">10</td>
+<td class="pence">2</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">135</td>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Francis, Skerryvore Tender,</td>
+<td class="pounds">920</td>
+<td class="shillings">17</td>
+<td class="pence">6</td>
+<td class="pence frac br">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">137</td>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Regent Tender (now sold),</td>
+<td class="pounds bb">259</td>
+<td class="shillings bb">3</td>
+<td class="pence bb">7</td>
+<td class="bb br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="10" class="br">&#160;</td>
+<td class="pounds">5924</td>
+<td class="shillings">13</td>
+<td class="pence">3</td>
+<td class="pence frac">³⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="10" class="txt br">5. <span class="smcap">Beacons</span> and <span class="smcap">Buoys</span>—Expense
+of Ordinary Maintenance,</td>
+<td class="pounds">91</td>
+<td class="shillings">7</td>
+<td class="pence">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="10" class="txt br">6. <span class="smcap">Storehouse, Leith</span>, including Storekeeper’s Salary,
+Taxes, Freight of Stores, &amp;c., <span class="nowrap">viz:—</span></td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2" colspan="2" class="br">&#160;</td>
+<td>&#160;</td>
+<td class="txt br">Salary, ³⁄₄,</td>
+<td class="pounds bt">£40</td>
+<td class="shillings bt">13</td>
+<td class="pence bt">0</td>
+<td rowspan="2" class="bt br bb">&#160;</td>
+<td rowspan="2" colspan="4" class="bt br bb">&#160;</td>
+<td rowspan="2" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="txt br">Salary, ¹⁄₄, at £100 per annum,</td>
+<td class="pounds bb">25</td>
+<td class="shillings bb">0</td>
+<td class="pence bb">0</td>
+</tr>
+
+<tr>
+<td rowspan="2" colspan="2" class="br">&#160;</td>
+<td colspan="6" class="br">&#160;</td>
+<td class="pounds">£65</td>
+<td class="shillings">13</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td rowspan="3" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Expenses of House, Packing Stores, &amp;c.,</td>
+<td class="pounds">145</td>
+<td class="shillings">9</td>
+<td class="pence">7</td>
+<td class="pence frac br">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">184</td>
+<td>&#160;</td>
+<td colspan="5" class="txt br">Freight of Stores,</td>
+<td class="pounds bb">133</td>
+<td class="shillings bb">4</td>
+<td class="pence bb">3</td>
+<td class="pence frac br bb">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="10" class="br">&#160;</td>
+<td class="pounds">344</td>
+<td class="shillings">6</td>
+<td class="pence">10</td>
+<td class="pence frac">³⁄₄</td>
+</tr>
+
+<tr>
+<td rowspan="8" colspan="2" class="br">&#160;</td>
+<td colspan="10" class="txt br">7. <span class="smcap">Charities</span> and <span class="smcap">Superannuations</span>
+to <span class="smcap">Retired Servants</span> of <span class="smcap">the Board</span>, <span class="nowrap">viz.:—</span></td>
+<td rowspan="7" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">1.</td>
+<td colspan="9" class="txt br">Prior to the last Act of <span class="nowrap">Parliament—</span></td>
+</tr>
+
+<tr>
+<td rowspan="5">&#160;</td>
+<td colspan="5" class="txt br">William Tweedy, one year’s Annuity,</td>
+<td class="pounds bt">£20</td>
+<td class="shillings bt">0</td>
+<td class="pence bt">0</td>
+<td class="bt br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">Mrs Leask, one year’s Annuity</td>
+<td class="pounds">10</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">Hugh Rose, one year’s Annuity</td>
+<td class="pounds">20</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">Jane Walker, one year’s Annuity (died March 13, 1847),</td>
+<td class="pounds">6</td>
+<td class="shillings">6</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">Euphemia Poole, one year’s Annuity,</td>
+<td class="pounds bb">5</td>
+<td class="shillings bb">0</td>
+<td class="pence bb">0</td>
+<td class="br bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10" class="br">&#160;</td>
+<td class="pounds">61</td>
+<td class="shillings">6</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="22" colspan="2" class="br">&#160;</td>
+<td class="nr">2.</td>
+<td colspan="9" class="txt br">Since last Act, viz.:</td>
+<td rowspan="21" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="20">&#160;</td>
+<td colspan="5" class="txt br">Robert Stevenson, Esq., late Engineer,</td>
+<td class="pounds bt">£580</td>
+<td class="shillings bt">0</td>
+<td class="pence bt">0</td>
+<td class="bt br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">Matthew Harvie, Light-keeper,</td>
+<td class="pounds">69</td>
+<td class="shillings">7</td>
+<td class="pence">6</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">John Bruce, late Officer,</td>
+<td class="pounds">13</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">George Kirk, Light-keeper,</td>
+<td class="pounds">40</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">John Watt, Light-keeper, (died Dec. 1846),</td>
+<td class="pounds">41</td>
+<td class="shillings">12</td>
+<td class="pence">6</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">William Heddle, Light-keeper,<span class="pagenum" id="Page422">[422]</span></td>
+<td class="pounds">17</td>
+<td class="shillings">15</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">Robert Selkirk, Light-keeper, (died Jan. 1847),</td>
+<td class="pounds">20</td>
+<td class="shillings">16</td>
+<td class="pence">4</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">Andrew Adamson, Light-keeper,</td>
+<td class="pounds">47</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">James Brown jun., Light-keeper,</td>
+<td class="pounds">29</td>
+<td class="shillings">11</td>
+<td class="pence">8</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">William Soutar, Light-keeper,</td>
+<td class="pounds">48</td>
+<td class="shillings">10</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">John Murray, late Boatman, Isle of May,</td>
+<td class="pounds">18</td>
+<td class="shillings">6</td>
+<td class="pence">8</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">David Lyall, Light-keeper,</td>
+<td class="pounds">43</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">Thomson Milne, Light-keeper,</td>
+<td class="pounds">64</td>
+<td class="shillings">1</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">David Laughton, Light-keeper,</td>
+<td class="pounds">47</td>
+<td class="shillings">10</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">Alexander Burnett, Light-keeper,</td>
+<td class="pounds">45</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">James Wallace,</td>
+<td class="pounds">34</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">John Miller (proportion till date of death),</td>
+<td class="pounds">11</td>
+<td class="shillings">12</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">Mrs Duncan, late Housekeeper, three-quarters,</td>
+<td class="pounds">10</td>
+<td class="shillings">10</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">John Scott, late Mate, Prince of Wales, quarter to Martinmas last,</td>
+<td class="pounds">22</td>
+<td class="shillings">10</td>
+<td class="pence">8</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">C. Cunningham, Esq., late Secretary, from 21st December to Candlemas,</td>
+<td class="pounds bb">45</td>
+<td class="shillings bb">7</td>
+<td class="pence bb">3</td>
+<td class="br bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10" class="br">&#160;</td>
+<td class="pounds">1249</td>
+<td class="shillings">9</td>
+<td class="pence">11</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="32" colspan="2" class="br">&#160;</td>
+<td colspan="10" class="txt br">8. <span class="smcap">Miscellaneous Expenses</span> not appropriated to any Particular Head,</td>
+<td class="pounds">2420</td>
+<td class="shillings">19</td>
+<td class="pence">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10" class="txt br"><span class="padl8 nowrap">Being—</span></td>
+<td rowspan="11" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;1.</td>
+<td colspan="5" class="txt br">For Educating Expectant Light-keepers, being their Travelling Charges and Subsistence,</td>
+<td class="pounds bt">£84</td>
+<td class="shillings bt">16</td>
+<td class="pence bt">0</td>
+<td class="bt br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;2.</td>
+<td colspan="5" class="txt br">Travelling Expenses of the Board,</td>
+<td class="pounds">128</td>
+<td class="shillings">18</td>
+<td class="pence">11</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;3.</td>
+<td colspan="5" class="txt br">Travelling Expenses of Officers on the Business of the Board,</td>
+<td class="pounds">513</td>
+<td class="shillings">3</td>
+<td class="pence">9</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;4.</td>
+<td colspan="5" class="txt br">Half-yearly Dinner Bills, £69, 5s., and £86&#160;: 2&#160;: 6,</td>
+<td class="pounds">155</td>
+<td class="shillings">7</td>
+<td class="pence">6</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;5.</td>
+<td colspan="5" class="txt br">Advertising Reduction of Duties,</td>
+<td class="pounds">90</td>
+<td class="shillings">10</td>
+<td class="pence">10</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;6.</td>
+<td class="txt br">Printing Expenses, viz., New Tables, Notices, Circulars, &amp;c.,</td>
+<td class="pounds bt">£173</td>
+<td class="shillings bt">5</td>
+<td class="pence bt">7</td>
+<td class="bt br">&#160;</td>
+<td rowspan="4" colspan="4" class="br">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="4">&#160;</td>
+<td class="txt br">Printing Expenses, 500 vols. Collector’s Receipt Books, &amp;c.,</td>
+<td class="pounds">146</td>
+<td class="shillings">19</td>
+<td class="pence">6</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="txt br">Printing Expenses, Annual List of Lighthouses, &amp;c.,</td>
+<td class="pounds">207</td>
+<td class="shillings">10</td>
+<td class="pence">10</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="txt br">Printing Expenses, “Stevenson on Lenses,” and Expenses connected with Lenses,</td>
+<td class="pounds bb">31</td>
+<td class="shillings bb">1</td>
+<td class="pence bb">5</td>
+<td class="br bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="br">&#160;</td>
+<td class="pounds">558</td>
+<td class="shillings">17</td>
+<td class="pence">4</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;7.</td>
+<td colspan="5" class="txt br">Making Oil Casks, and Cooperage of old do.</td>
+<td class="pounds">145</td>
+<td class="shillings">11</td>
+<td class="pence">2</td>
+<td class="br">&#160;</td>
+<td rowspan="20" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;8.</td>
+<td colspan="5" class="txt br">Postages and Carriage of Parcels,<span class="pagenum" id="Page423">[423]</span></td>
+<td class="pounds">120</td>
+<td class="shillings">18</td>
+<td class="pence">10</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;9.</td>
+<td colspan="5" class="txt br">Messrs Cuningham and Bell, W.S., Law-Agents, Account for Commissions to and Bonds by Collectors, &amp;c.,</td>
+<td class="pounds">136</td>
+<td class="shillings">4</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">10.</td>
+<td colspan="5" class="txt br">Messrs Spottiswoode and Robertson, Solicitors, London,</td>
+<td class="pounds">57</td>
+<td class="shillings">11</td>
+<td class="pence">8</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">11.</td>
+<td colspan="5" class="txt br">Gratuity to Lewis Proctor, an occasional Light-keeper, who met with a severe Accident by
+a fall from the Lighthouse at Kinnairdshead,</td>
+<td class="pounds">30</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">12.</td>
+<td colspan="5" class="txt br">Medical Attendance on Keepers’ Families at Insulated Stations,</td>
+<td class="pounds">26</td>
+<td class="shillings">17</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">13.</td>
+<td colspan="5" class="txt br">Paid for Nomination to Edinburgh Royal Lunatic Asylum for Keeper’s Wife at Chanonry Lighthouse,</td>
+<td class="pounds">12</td>
+<td class="shillings">10</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">14.</td>
+<td colspan="5" class="txt br">Gratuities voted to aged Light-keepers to meet Insurances on their Lives,</td>
+<td class="pounds">38</td>
+<td class="shillings">7</td>
+<td class="pence">1</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">15.</td>
+<td colspan="5" class="txt br">Sundry small Sums due by Light-keepers, connected with Insurances on their Lives, and Stamps for Premiums,</td>
+<td class="pounds">37</td>
+<td class="shillings">2</td>
+<td class="pence">8</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">16.</td>
+<td colspan="5" class="txt br">R. W. Swinburne and Co., Newcastle, Plate-Glass,</td>
+<td class="pounds">32</td>
+<td class="shillings">1</td>
+<td class="pence">6</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">17.</td>
+<td colspan="5" class="txt br">Paid for Temporary Lanterns during Repairs of Lighthouses,</td>
+<td class="pounds">64</td>
+<td class="shillings">17</td>
+<td class="pence">7</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">18.</td>
+<td colspan="5" class="txt br">One Dozen Stamped Receipt-Books for Keepers’ Salaries, and Fees getting same Stamped in London,</td>
+<td class="pounds">7</td>
+<td class="shillings">1</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">19.</td>
+<td colspan="5" class="txt br">Expenses incurred by Henry Banks, tailor, in visiting the different Lighthouses, and taking
+“measures” for Clothing the Keepers,</td>
+<td class="pounds">38</td>
+<td class="shillings">0</td>
+<td class="pence">2</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">20.</td>
+<td colspan="5" class="txt br">Periodicals furnished to the Keepers,</td>
+<td class="pounds">4</td>
+<td class="shillings">14</td>
+<td class="pence">7</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">21.</td>
+<td colspan="5" class="txt br">A Copper Buoy,</td>
+<td class="pounds">3</td>
+<td class="shillings">16</td>
+<td class="pence">11</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">22.</td>
+<td colspan="5" class="txt br">Repairs on Rankin Lighter,</td>
+<td class="pounds">5</td>
+<td class="shillings">2</td>
+<td class="pence">4</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">23.</td>
+<td colspan="5" class="txt br">Account connected with Skerryvore Lighters,</td>
+<td class="pounds">6</td>
+<td class="shillings">7</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">24.</td>
+<td colspan="5" class="txt br">Models of Dioptric Light,</td>
+<td class="pounds">83</td>
+<td class="shillings">13</td>
+<td class="pence">1</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">25.</td>
+<td colspan="5" class="txt br">Freight to London, Leith, Edinburgh, and Glasgow Shipping Company,</td>
+<td class="pounds">3</td>
+<td class="shillings">1</td>
+<td class="pence">5</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">26.</td>
+<td colspan="5" class="txt br">Various small items for Lithographing, &amp;c. &amp;c.,</td>
+<td class="pounds bb">35</td>
+<td class="shillings bb">7</td>
+<td class="pence bb">1</td>
+<td class="br bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="6" class="right br"><span class="padr4"><span class="smcap">Sum</span> as on preceding page,</span></td>
+<td class="pounds bbd">£2420</td>
+<td class="shillings bbd">19</td>
+<td class="pence bbd">5</td>
+<td class="br bbd">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="3">&#160;</td>
+<td colspan="7" class="right bbd"><span class="padr4">Carry forward,</span></td>
+<td class="pounds bl bt bbd">£15,960</td>
+<td class="shillings bt bbd">6</td>
+<td class="pence bt bbd">0</td>
+<td class="pence frac bt bbd">²⁄₈</td>
+</tr>
+
+<tr>
+<td rowspan="31" colspan="2" class="br">&#160;</td>
+<td colspan="10" class="center highline075 br"><span class="smcap">Ordinary Expenses</span> brought
+forward,<span class="pagenum" id="Page424">[424]</span></td>
+<td class="pounds highline075">£15,960</td>
+<td class="shillings highline075">6</td>
+<td class="pence highline075">0</td>
+<td class="pence frac highline075">²⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="10" class="center br">Which have been Allocated to each Lighthouse in the proportions following, as appears from
+State, No. II., <a href="#Page430">pp. 430</a>-<a href="#Page433">3</a>, <span class="dontwrap">viz.—</span></td>
+<td rowspan="29" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;1.</td>
+<td colspan="5" class="txt br">Inchkeith,</td>
+<td class="pounds bt">£577</td>
+<td class="shillings bt">15</td>
+<td class="pence bt">9</td>
+<td class="pence frac bt br">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;2.</td>
+<td colspan="5" class="txt br">Isle of May,</td>
+<td class="pounds">941</td>
+<td class="shillings">8</td>
+<td class="pence">6</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;3.</td>
+<td colspan="5" class="txt br">Bell Rock,</td>
+<td class="pounds">977</td>
+<td class="shillings">17</td>
+<td class="pence">9</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;4.</td>
+<td colspan="5" class="txt br">Girdleness,</td>
+<td class="pounds">544</td>
+<td class="shillings">5</td>
+<td class="pence">8</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;5.</td>
+<td colspan="5" class="txt br">Buchanness,</td>
+<td class="pounds">617</td>
+<td class="shillings">4</td>
+<td class="pence">1</td>
+<td class="pence frac br">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;6.</td>
+<td colspan="5" class="txt br">Kinnairdshead,</td>
+<td class="pounds">573</td>
+<td class="shillings">16</td>
+<td class="pence">11</td>
+<td class="pence frac br">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;7.</td>
+<td colspan="5" class="txt br">Tarbetness,</td>
+<td class="pounds">569</td>
+<td class="shillings">18</td>
+<td class="pence">1</td>
+<td class="pence frac br">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;8.</td>
+<td colspan="5" class="txt br">Sumburghhead,</td>
+<td class="pounds">591</td>
+<td class="shillings">11</td>
+<td class="pence">8</td>
+<td class="pence frac br">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">&#8199;9.</td>
+<td colspan="5" class="txt br">Startpoint,</td>
+<td class="pounds">345</td>
+<td class="shillings">4</td>
+<td class="pence">4</td>
+<td class="pence frac br">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">10.</td>
+<td colspan="5" class="txt br">Pentland Skerries,</td>
+<td class="pounds">841</td>
+<td class="shillings">17</td>
+<td class="pence">10</td>
+<td class="pence frac br">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">11.</td>
+<td colspan="5" class="txt br">Dunnethead,</td>
+<td class="pounds">467</td>
+<td class="shillings">8</td>
+<td class="pence">4</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">12.</td>
+<td colspan="5" class="txt br">Capewrath,</td>
+<td class="pounds">581</td>
+<td class="shillings">14</td>
+<td class="pence">7</td>
+<td class="pence frac br">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">13.</td>
+<td colspan="5" class="txt br">Island Glass,</td>
+<td class="pounds">510</td>
+<td class="shillings">15</td>
+<td class="pence">6</td>
+<td class="pence frac br">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">14.</td>
+<td colspan="5" class="txt br">Barrahead,</td>
+<td class="pounds">588</td>
+<td class="shillings">12</td>
+<td class="pence">7</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">15.</td>
+<td colspan="5" class="txt br">Skerryvore,</td>
+<td class="pounds">1108</td>
+<td class="shillings">19</td>
+<td class="pence">1</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">16.</td>
+<td colspan="5" class="txt br">Lismore,</td>
+<td class="pounds">511</td>
+<td class="shillings">15</td>
+<td class="pence">4</td>
+<td class="pence frac br">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">17.</td>
+<td colspan="5" class="txt br">Rhinns of Islay,</td>
+<td class="pounds">564</td>
+<td class="shillings">19</td>
+<td class="pence">6</td>
+<td class="pence frac br">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">18.</td>
+<td colspan="5" class="txt br">Mull of Kintyre,</td>
+<td class="pounds">550</td>
+<td class="shillings">3</td>
+<td class="pence">10</td>
+<td class="pence frac br">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">19.</td>
+<td colspan="5" class="txt br">Pladda,</td>
+<td class="pounds">579</td>
+<td class="shillings">15</td>
+<td class="pence">2</td>
+<td class="pence frac br">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">20.</td>
+<td colspan="5" class="txt br">Corsewall,</td>
+<td class="pounds">462</td>
+<td class="shillings">9</td>
+<td class="pence">9</td>
+<td class="pence frac br">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">21.</td>
+<td colspan="5" class="txt br">Mull of Galloway,</td>
+<td class="pounds">512</td>
+<td class="shillings">14</td>
+<td class="pence">11</td>
+<td class="pence frac br">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">22.</td>
+<td colspan="5" class="txt br">Little Ross,</td>
+<td class="pounds">512</td>
+<td class="shillings">14</td>
+<td class="pence">11</td>
+<td class="pence frac br">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">23.</td>
+<td colspan="5" class="txt br">Point of Ayre,</td>
+<td class="pounds">406</td>
+<td class="shillings">6</td>
+<td class="pence">4</td>
+<td class="pence frac br">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">24.</td>
+<td colspan="5" class="txt br">Calf of Man (two Lights),</td>
+<td class="pounds">805</td>
+<td class="shillings">8</td>
+<td class="pence">7</td>
+<td class="pence frac br">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">25.</td>
+<td colspan="5" class="txt br">Covesea Skerries,</td>
+<td class="pounds">417</td>
+<td class="shillings">3</td>
+<td class="pence">1</td>
+<td class="pence frac br">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">26.</td>
+<td colspan="5" class="txt br">Cromarty,</td>
+<td class="pounds">338</td>
+<td class="shillings">6</td>
+<td class="pence">4</td>
+<td class="pence frac br">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">27.</td>
+<td colspan="5" class="txt br">Chanonry,</td>
+<td class="pounds">283</td>
+<td class="shillings">2</td>
+<td class="pence">8</td>
+<td class="pence frac br">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">28.</td>
+<td colspan="5" class="txt br">Loch Ryan,</td>
+<td class="pounds bb">176</td>
+<td class="shillings bb">14</td>
+<td class="pence bb">1</td>
+<td class="br bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5">&#160;</td>
+<td colspan="5" class="right br bbd"><span class="padr4">As above,</span></td>
+<td class="pounds bbd">15,960</td>
+<td class="shillings bbd">6</td>
+<td class="pence bbd">0</td>
+<td class="pence frac bbd">²⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="14" class="highline075">BRANCH III.—<span class="smcap">Extraordinary Expenses</span> not Allocated to each
+<span class="nowrap">Lighthouse:—</span></td>
+</tr>
+
+
+
+
+
+<tr>
+<td colspan="2" class="ledgerno">189</td>
+<td colspan="10" class="txt br">To paid for new Steamer Pharos,</td>
+<td class="pounds bt">£7548</td>
+<td class="shillings bt">13</td>
+<td class="pence bt">7</td>
+<td class="bt">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">310</td>
+<td colspan="10" class="txt br">Expense of Harbour Light at Portpatrick,</td>
+<td class="pounds">129</td>
+<td class="shillings">17</td>
+<td class="pence">4</td>
+<td class="pence frac">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">182</td>
+<td colspan="10" class="txt br">Expense connected with Skerryvore Book,</td>
+<td class="pounds">199</td>
+<td class="shillings">18</td>
+<td class="pence">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">33</td>
+<td colspan="10" class="txt br">To paid for House in Crail for use of Isle of May Boatmen, and Fees connected with Purchase,</td>
+<td class="pounds bb">105</td>
+<td class="shillings bb">19</td>
+<td class="pence bb">4</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="10" class="br">&#160;</td>
+<td class="pounds">£7984</td>
+<td class="shillings">8</td>
+<td class="pence">3</td>
+<td class="pence frac">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="10" class="txt br"><span class="smcap">Expense of New Works</span>, <span class="nowrap">viz.:—</span></td>
+<td rowspan="24" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">150</td>
+<td rowspan="23">&#160;</td>
+<td colspan="5" class="txt br">Skerryvore,</td>
+<td class="pounds bt">£227</td>
+<td class="shillings bt">8</td>
+<td class="pence bt">2</td>
+<td class="bt br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">287</td>
+<td colspan="5" class="txt br">Bo Pheg Beacon,</td>
+<td class="pounds">25</td>
+<td class="shillings">10</td>
+<td class="pence">1</td>
+<td class="pence frac br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">284</td>
+<td colspan="5" class="txt br">Covesea,<span class="pagenum" id="Page425">[425]</span></td>
+<td class="pounds">1109</td>
+<td class="shillings">5</td>
+<td class="pence">4</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">296</td>
+<td colspan="5" class="txt br">Cromarty,</td>
+<td class="pounds">342</td>
+<td class="shillings">9</td>
+<td class="pence">3</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">298</td>
+<td colspan="5" class="txt br">Chanonry,</td>
+<td class="pounds">405</td>
+<td class="shillings">7</td>
+<td class="pence">8</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">300</td>
+<td colspan="5" class="txt br">Ardnamurchan,</td>
+<td class="pounds">2343</td>
+<td class="shillings">17</td>
+<td class="pence">6</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">314</td>
+<td colspan="5" class="txt br">Laggan Spur Beacon,</td>
+<td class="pounds">748</td>
+<td class="shillings">10</td>
+<td class="pence">6</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">316</td>
+<td colspan="5" class="txt br">Island Glass,</td>
+<td class="pounds">1797</td>
+<td class="shillings">3</td>
+<td class="pence">5</td>
+<td class="pence frac br">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">319</td>
+<td colspan="5" class="txt br">Nosshead,</td>
+<td class="pounds">1467</td>
+<td class="shillings">6</td>
+<td class="pence">1</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">322</td>
+<td colspan="5" class="txt br">Loch Ryan,</td>
+<td class="pounds">829</td>
+<td class="shillings">12</td>
+<td class="pence">9</td>
+<td class="pence frac br">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">121</td>
+<td colspan="5" class="txt br">Loch Ryan, Beacon,</td>
+<td class="pounds">152</td>
+<td class="shillings">5</td>
+<td class="pence">9</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">324</td>
+<td colspan="5" class="txt br">Pentland Skerries new Works,</td>
+<td class="pounds">3135</td>
+<td class="shillings">17</td>
+<td class="pence">5</td>
+<td class="pence frac br">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">145</td>
+<td colspan="5" class="txt br">Pentland Skerries Dioptric Light,</td>
+<td class="pounds">2037</td>
+<td class="shillings">11</td>
+<td class="pence">4</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">308</td>
+<td colspan="5" class="txt br">Renewal of Fixed Lights,</td>
+<td class="pounds">3035</td>
+<td class="shillings">14</td>
+<td class="pence">4</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">106</td>
+<td colspan="5" class="txt br">Campbeltown Beacons,</td>
+<td class="pounds">17</td>
+<td class="shillings">4</td>
+<td class="pence">10</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">...</td>
+<td colspan="5" class="txt br">Lapock Beacon,</td>
+<td class="pounds">8</td>
+<td class="shillings">12</td>
+<td class="pence">5</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">117</td>
+<td colspan="5" class="txt br">Startpoint New Works,</td>
+<td class="pounds">5</td>
+<td class="shillings">19</td>
+<td class="pence">4</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">118</td>
+<td colspan="5" class="txt br">Elie or Vow’s Beacon,</td>
+<td class="pounds">205</td>
+<td class="shillings">5</td>
+<td class="pence">8</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">119</td>
+<td colspan="5" class="txt br">Whiteness Beacon,</td>
+<td class="pounds">152</td>
+<td class="shillings">5</td>
+<td class="pence">8</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">120</td>
+<td colspan="5" class="txt br">Longman’s Point Beacon,,</td>
+<td class="pounds">164</td>
+<td class="shillings">15</td>
+<td class="pence">6</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">184</td>
+<td colspan="5" class="txt br">Brist Beacon,</td>
+<td class="pounds">8</td>
+<td class="shillings">12</td>
+<td class="pence">5</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">306</td>
+<td colspan="5" class="txt br">Mull of Kintyre Dykes and Road,</td>
+<td class="pounds">647</td>
+<td class="shillings">17</td>
+<td class="pence">9</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">286</td>
+<td colspan="5" class="txt br">Buoys,</td>
+<td class="pounds bb">1458</td>
+<td class="shillings bb">7</td>
+<td class="pence bb">11</td>
+<td class="pence frac br bb">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="6" class="right"><span class="padr4"><span class="smcap">Sum</span>,</span></td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pounds bb">20,327</td>
+<td class="shillings bb">1</td>
+<td class="pence bb">3</td>
+<td class="br bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="3">&#160;</td>
+<td colspan="7" class="right br bbd"><span class="padr4">Carried to <span class="smcap">Abstract</span> below,</span></td>
+<td class="pounds bbd">£28,311</td>
+<td class="shillings bbd">9</td>
+<td class="pence bbd">6</td>
+<td class="pence frac br bbd">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="2" class="thinline br">&#160;</td>
+<td colspan="14" class="thinline">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="16" class="center highline075 fsize110 bt bb">ABSTRACT OF THE PRECEDING ACCOUNT.</td>
+</tr>
+
+<tr>
+<td rowspan="16" colspan="2" class="br">&#160;</td>
+<td colspan="10" class="txt highline075 br"><span class="nowrap">RECEIPTS:—</span></td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="2">&#160;</td>
+<td colspan="9" class="txt br"><span class="smcap">Branch</span> <span class="dontshow">II</span>I.—Gross Amount of the Duties
+received for 1846, <a href="#Page418">p. 418</a>,</td>
+<td class="pounds">£46,001</td>
+<td class="shillings">11</td>
+<td class="pence">2</td>
+<td class="pence frac">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="9" class="txt br"><span class="dontshow"><span class="smcap">Branch</span> </span><span class="dontshow">I</span>II.—Miscellaneous
+Receipts, <a href="#Page419">p. 419</a>,</td>
+<td class="pounds bb">1,893</td>
+<td class="shillings bb">17</td>
+<td class="pence bb">6</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10" class="br">&#160;</td>
+<td class="pounds">£47,895</td>
+<td class="shillings">8</td>
+<td class="pence">8</td>
+<td class="pence frac">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="10" class="txt highline075 br"><span class="nowrap">PAYMENTS:—</span></td>
+<td rowspan="4" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="3">&#160;</td>
+<td colspan="5" class="txt br"><span class="smcap">Branch</span> <span class="dontshow">II</span>I.—Ordinary Expenses, being the
+Maintenance of Lights, &amp;c. <a href="#Page420">p. 420</a>,</td>
+<td class="pounds bt">£16,103</td>
+<td class="shillings bt">0</td>
+<td class="pence bt">2</td>
+<td class="pence frac bt br">³⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br"><span class="dontshow"><span class="smcap">Branch</span> </span><span class="dontshow">I</span>II.—Ordinary
+Expenses, falling to be allocated upon each Lighthouse, <a href="#Page424">p. 424</a>,</td>
+<td class="pounds">15,960</td>
+<td class="shillings">6</td>
+<td class="pence">0</td>
+<td class="pence frac br">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br"><span class="dontshow"><span class="smcap">Branch</span> </span>III.—Extraordinary Expenses not
+allocated to each Lighthouse, as above,</td>
+<td class="pounds bb">28,311</td>
+<td class="shillings bb">9</td>
+<td class="pence bb">6</td>
+<td class="pence frac br bb">¹⁄₄</td>
+</tr>
+
+<tr>
+<td colspan="10" class="br">&#160;</td>
+<td class="pounds bb">60,374</td>
+<td class="shillings bb">15</td>
+<td class="pence bb">9</td>
+<td class="pence frac bb">²⁄₈</td>
+</tr>
+
+<tr>
+<td rowspan="3" colspan="2">&#160;</td>
+<td colspan="8" class="txt br"><span class="smcap">Balance</span> superexpended in 1846,</td>
+<td class="pounds">£12,479</td>
+<td class="shillings">7</td>
+<td class="pence">0</td>
+<td class="pence frac">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="8" class="txt br"><span class="smcap">Balance</span> on hand at 31st March 1846,</td>
+<td class="pounds bb">42,069</td>
+<td class="shillings bb">6</td>
+<td class="pence bb">10</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="8" class="txt br"><span class="smcap">Balance</span> on hand at 31st March 1847,</td>
+<td class="pounds">£29,589</td>
+<td class="shillings">19</td>
+<td class="pence">9</td>
+<td class="pence frac">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="10" class="txt highline075 br"><span class="padl2"><span class="dontwrap"><span class="smcap">Whereof</span>—</span></span></td>
+<td rowspan="15" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td rowspan="14">&#160;</td>
+<td colspan="5" class="txt br">In the Royal Bank,</td>
+<td class="pounds bt">£28,944</td>
+<td class="shillings bt">16</td>
+<td class="pence bt">8</td>
+<td class="bt br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="txt br">In Secretary’s Account,</td>
+<td class="pounds bb">40</td>
+<td class="shillings bb">16</td>
+<td class="pence bb">11</td>
+<td class="br bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="5" class="br">&#160;</td>
+<td class="pounds">£28,985</td>
+<td class="shillings">13</td>
+<td class="pence">7</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">89</td>
+<td colspan="5" class="txt br">Balance due by Peter Grant, Superintendent, Nosshead,</td>
+<td class="pounds">203</td>
+<td class="shillings">10</td>
+<td class="pence">2</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">157</td>
+<td colspan="5" class="txt br">Balance due by Master of Prince of Wales Tender,</td>
+<td class="pounds">35</td>
+<td class="shillings">3</td>
+<td class="pence">4</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">161</td>
+<td colspan="5" class="txt br">Balance due by Steward of Pharos Steamer,</td>
+<td class="pounds">30</td>
+<td class="shillings">19</td>
+<td class="pence">2</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">164</td>
+<td colspan="5" class="txt br">Balance due by Master of Francis, Skerryvore Tender,</td>
+<td class="pounds">2</td>
+<td class="shillings">12</td>
+<td class="pence">5</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">166</td>
+<td colspan="5" class="txt br">Balance due by Superintendent of Light-keepers,</td>
+<td class="pounds">11</td>
+<td class="shillings">11</td>
+<td class="pence">2</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">168</td>
+<td colspan="5" class="txt br">Balance due by Foreman of Light-room Repairs,</td>
+<td class="pounds">5</td>
+<td class="shillings">3</td>
+<td class="pence">5</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">172</td>
+<td colspan="5" class="txt br">Balance due by Buoymaster,</td>
+<td class="pounds">5</td>
+<td class="shillings">1</td>
+<td class="pence">6</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">176</td>
+<td colspan="5" class="txt br">Balance due by Store-keeper,</td>
+<td class="pounds">7</td>
+<td class="shillings">17</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">180</td>
+<td colspan="5" class="txt br">Balance due by Thomas Hope, Superintendent, Island Glass,</td>
+<td class="pounds">87</td>
+<td class="shillings">17</td>
+<td class="pence">7</td>
+<td class="pence frac br">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">307</td>
+<td colspan="5" class="txt br">Balance due by Master of Pharos,</td>
+<td class="pounds">5</td>
+<td class="shillings">10</td>
+<td class="pence">8</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">318</td>
+<td colspan="5" class="txt br">Balance due by James Scott, Superintendent, Pentland Skerries,</td>
+<td class="pounds">188</td>
+<td class="shillings">12</td>
+<td class="pence">3</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno bt bb">Folio in Small Ledger.</td>
+<td colspan="6" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">6</td>
+<td colspan="6" class="txt br">Sum due by Robert Selkirk’s Representatives, to be paid when Insurance money is received,</td>
+<td class="pounds">10</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+<td rowspan="4" colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">8</td>
+<td colspan="6" class="txt br">Balance due by Richard Cumming, Light-keeper,</td>
+<td class="pounds">2</td>
+<td class="shillings">13</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">9</td>
+<td colspan="6" class="txt br">Balance due by James Laughton, do.,</td>
+<td class="pounds">3</td>
+<td class="shillings">0</td>
+<td class="pence">0</td>
+<td class="br">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="ledgerno">10</td>
+<td colspan="6" class="txt br">Balance due by William Kirk, do.,</td>
+<td class="pounds bb">4</td>
+<td class="shillings bb">14</td>
+<td class="pence bb">6</td>
+<td class="br bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="3">&#160;</td>
+<td colspan="7" class="right br bbd"><span class="padr4">Equal to <span class="smcap">Balance</span>,</span></td>
+<td class="pounds bbd">29,589</td>
+<td class="shillings bbd">19</td>
+<td class="pence bbd">9</td>
+<td class="pence frac bbd">¹⁄₂</td>
+</tr>
+
+<tr>
+<td colspan="2" class="thinline br">&#160;</td>
+<td colspan="14" class="thinline">&#160;</td>
+</tr>
+
+</table>
+
+<p class="noindent highline2 fsize80"><span class="padl6"><span class="smcap">Edinburgh</span>,
+<i>5th May 1847</i>.—Prepared and Reported by</span></p>
+
+<p class="right highline2 fsize90 padr10pc"><span class="padr8">(Signed)</span> ALEX. CUNINGHAM, <i>Secretary</i>.</p>
+
+<hr class="tb">
+
+<p class="right padr4 fsize80"><span class="padr4">84 George Street,</span><br>
+<i>Edinburgh, 25th May 1847</i>.</p>
+
+<p class="fsize90">In obedience to the Remit by the Honourable Board of Commissioners of Northern
+Lighthouses, I have carefully audited the Accounts of the Board for the year ending
+31st March 1847; and I have to report, that the Accounts are clearly and accurately
+stated—that they are fully vouched—and that, in my humble opinion, the Report of the
+Secretary contains a very distinct statement of the Intromissions of the Board during the
+above period.</p>
+
+<p class="right highline2 fsize90 padr10pc"><span class="padr8">(Signed)</span> KENNETH MACKENZIE, <i>Accountant</i>.</p>
+
+<p><span class="pagenum" id="Page427">[427]</span></p>
+
+<p class="tabhead">STATEMENTS ANNEXED TO THE SECRETARY’S REPORT FOR 1846.</p>
+
+<p class="tabhead fsize90">No. I.—<i>Account of Northern Light-Duties received in the Year 1846.</i></p>
+
+<table class="duties">
+
+<tr class="bb">
+<th colspan="2" class="br">&#160;</th>
+<th colspan="4" class="br">Gross<br>Receipts.</th>
+<th colspan="4" class="br">Commission<br>to<br>Collectors.</th>
+<th colspan="4" class="br">Repayments,<br>&amp;c.</th>
+<th colspan="4">Nett<br>Duties<br>Received.</th>
+</tr>
+
+<tr>
+<td class="nr">1.</td>
+<td class="lght">Aberdeen,</td>
+<td class="pnds">£2243</td>
+<td class="shllngs">3</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">£121</td>
+<td class="shllngs">11</td>
+<td class="pnc">8</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">£5</td>
+<td class="shllngs">14</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td class="pnds">£2115</td>
+<td class="shllngs">17</td>
+<td class="pnc">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">2.</td>
+<td class="lght">Alloa,</td>
+<td class="pnds">402</td>
+<td class="shllngs">6</td>
+<td class="pnc">1</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">23</td>
+<td class="shllngs">6</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">6</td>
+<td class="shllngs">17</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">372</td>
+<td class="shllngs">1</td>
+<td class="pnc">8</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">3.</td>
+<td class="lght">Arbroath,</td>
+<td class="pnds">254</td>
+<td class="shllngs">2</td>
+<td class="pnc">11</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td class="pnds">12</td>
+<td class="shllngs">17</td>
+<td class="pnc">2</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td class="pnds">3</td>
+<td class="shllngs">17</td>
+<td class="pnc">7</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">237</td>
+<td class="shllngs">8</td>
+<td class="pnc">1</td>
+<td class="frcpnc">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">4.</td>
+<td class="lght">Ayr,</td>
+<td class="pnds">158</td>
+<td class="shllngs">12</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">8</td>
+<td class="shllngs">1</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">1</td>
+<td class="shllngs">15</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">148</td>
+<td class="shllngs">15</td>
+<td class="pnc">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">5.</td>
+<td class="lght">Aberystwith,</td>
+<td class="pnds">6</td>
+<td class="shllngs">17</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">6</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">1</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">6</td>
+<td class="shllngs">9</td>
+<td class="pnc">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">6.</td>
+<td class="lght">Arundel,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">7.</td>
+<td class="lght">Banff,</td>
+<td class="pnds">467</td>
+<td class="shllngs">7</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td class="pnds">28</td>
+<td class="shllngs">17</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td class="pnds">2</td>
+<td class="shllngs">19</td>
+<td class="pnc">3</td>
+<td class="br">&#160;</td>
+<td class="pnds">435</td>
+<td class="shllngs">10</td>
+<td class="pnc">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">8.</td>
+<td class="lght">Borrowstounness,</td>
+<td class="pnds">675</td>
+<td class="shllngs">6</td>
+<td class="pnc">1</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">48</td>
+<td class="shllngs">11</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">9</td>
+<td class="shllngs">4</td>
+<td class="pnc">1</td>
+<td class="br">&#160;</td>
+<td class="pnds">617</td>
+<td class="shllngs">10</td>
+<td class="pnc">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">9.</td>
+<td class="lght">Barnstaple,</td>
+<td class="pnds">1</td>
+<td class="shllngs">7</td>
+<td class="pnc">2</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">1</td>
+<td class="pnc">4</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">1</td>
+<td class="shllngs">5</td>
+<td class="pnc">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">10.</td>
+<td class="lght">Beaumaris,</td>
+<td class="pnds">123</td>
+<td class="shllngs">17</td>
+<td class="pnc">1</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">6</td>
+<td class="shllngs">12</td>
+<td class="pnc">7</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">15</td>
+<td class="pnc">1</td>
+<td class="br">&#160;</td>
+<td class="pnds">116</td>
+<td class="shllngs">9</td>
+<td class="pnc">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">11.</td>
+<td class="lght">Berwick,</td>
+<td class="pnds">121</td>
+<td class="shllngs">0</td>
+<td class="pnc">8</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">6</td>
+<td class="shllngs">11</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">1</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">114</td>
+<td class="shllngs">7</td>
+<td class="pnc">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">12.</td>
+<td class="lght">Bideford,</td>
+<td class="pnds">8</td>
+<td class="shllngs">14</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">8</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">8</td>
+<td class="shllngs">6</td>
+<td class="pnc">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">13.</td>
+<td class="lght">Boston,</td>
+<td class="pnds">9</td>
+<td class="shllngs">15</td>
+<td class="pnc">0</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">10</td>
+<td class="pnc">7</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">5</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td class="pnds">8</td>
+<td class="shllngs">18</td>
+<td class="pnc">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">14.</td>
+<td class="lght">Bridgewater,</td>
+<td class="pnds">12</td>
+<td class="shllngs">0</td>
+<td class="pnc">7</td>
+<td class="frcpnc br">⁷⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">11</td>
+<td class="pnc">11</td>
+<td class="frcpnc br">⁷⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">2</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">11</td>
+<td class="shllngs">5</td>
+<td class="pnc">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">15.</td>
+<td class="lght">Bridlington,</td>
+<td class="pnds">26</td>
+<td class="shllngs">1</td>
+<td class="pnc">3</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">1</td>
+<td class="shllngs">6</td>
+<td class="pnc">1</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">24</td>
+<td class="shllngs">15</td>
+<td class="pnc">2</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">16.</td>
+<td class="lght">Bridport,</td>
+<td class="pnds">2</td>
+<td class="shllngs">18</td>
+<td class="pnc">0</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">2</td>
+<td class="pnc">10</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">2</td>
+<td class="shllngs">15</td>
+<td class="pnc">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">17.</td>
+<td class="lght">Bristol,</td>
+<td class="pnds">124</td>
+<td class="shllngs">12</td>
+<td class="pnc">7</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">6</td>
+<td class="shllngs">4</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">14</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">117</td>
+<td class="shllngs">14</td>
+<td class="pnc">0</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">18.</td>
+<td class="lght">Baltimore,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">19.</td>
+<td class="lght">Belfast,</td>
+<td class="pnds">2446</td>
+<td class="shllngs">1</td>
+<td class="pnc">4</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">125</td>
+<td class="shllngs">6</td>
+<td class="pnc">4</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">56</td>
+<td class="shllngs">12</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">2264</td>
+<td class="shllngs">2</td>
+<td class="pnc">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">20.</td>
+<td class="lght">Campbeltown,</td>
+<td class="pnds">82</td>
+<td class="shllngs">14</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">5</td>
+<td class="shllngs">2</td>
+<td class="pnc">1</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">1</td>
+<td class="shllngs">12</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">76</td>
+<td class="shllngs">0</td>
+<td class="pnc">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">21.</td>
+<td class="lght">Caernarvon,</td>
+<td class="pnds">25</td>
+<td class="shllngs">13</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">1</td>
+<td class="shllngs">7</td>
+<td class="pnc">7</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">8</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">23</td>
+<td class="shllngs">18</td>
+<td class="pnc">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">22.</td>
+<td class="lght">Cardiff,</td>
+<td class="pnds">110</td>
+<td class="shllngs">19</td>
+<td class="pnc">7</td>
+<td class="br">&#160;</td>
+<td class="pnds">5</td>
+<td class="shllngs">11</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">105</td>
+<td class="shllngs">8</td>
+<td class="pnc">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">23.</td>
+<td class="lght">Cardigan,</td>
+<td class="pnds">1</td>
+<td class="shllngs">7</td>
+<td class="pnc">11</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">1</td>
+<td class="pnc">7</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">1</td>
+<td class="shllngs">6</td>
+<td class="pnc">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">24.</td>
+<td class="lght">Carlisle,</td>
+<td class="pnds">84</td>
+<td class="shllngs">0</td>
+<td class="pnc">3</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">4</td>
+<td class="shllngs">7</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">10</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td class="pnds">79</td>
+<td class="shllngs">2</td>
+<td class="pnc">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">25.</td>
+<td class="lght">Chepstow,</td>
+<td class="pnds">0</td>
+<td class="shllngs">14</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">0</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">0</td>
+<td class="shllngs">14</td>
+<td class="pnc">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">26.</td>
+<td class="lght">Chester,</td>
+<td class="pnds">158</td>
+<td class="shllngs">4</td>
+<td class="pnc">5</td>
+<td class="frcpnc br">¹⁄₈</td>
+<td class="pnds">8</td>
+<td class="shllngs">1</td>
+<td class="pnc">5</td>
+<td class="frcpnc br">³⁄₈</td>
+<td class="pnds">1</td>
+<td class="shllngs">0</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">149</td>
+<td class="shllngs">2</td>
+<td class="pnc">11</td>
+<td class="frcpnc">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">27.</td>
+<td class="lght">Chichester,</td>
+<td class="pnds">2</td>
+<td class="shllngs">15</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">3</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">²⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">2</td>
+<td class="shllngs">11</td>
+<td class="pnc">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">28.</td>
+<td class="lght">Clay,</td>
+<td class="pnds">1</td>
+<td class="shllngs">2</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">1</td>
+<td class="pnc">8</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">1</td>
+<td class="shllngs">0</td>
+<td class="pnc">9</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">29.</td>
+<td class="lght">Colchester,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">30.</td>
+<td class="lght">Cowes,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">31.</td>
+<td class="lght">Coleraine,</td>
+<td class="pnds">101</td>
+<td class="shllngs">5</td>
+<td class="pnc">8</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">5</td>
+<td class="shllngs">1</td>
+<td class="pnc">7</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">96</td>
+<td class="shllngs">4</td>
+<td class="pnc">1</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">32.</td>
+<td class="lght">Cork,</td>
+<td class="pnds">70</td>
+<td class="shllngs">13</td>
+<td class="pnc">1</td>
+<td class="br">&#160;</td>
+<td class="pnds">3</td>
+<td class="shllngs">10</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td class="pnds">2</td>
+<td class="shllngs">0</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">65</td>
+<td class="shllngs">1</td>
+<td class="pnc">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">33.</td>
+<td class="lght">Dunbar,</td>
+<td class="pnds">115</td>
+<td class="shllngs">11</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">7</td>
+<td class="shllngs">1</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">11</td>
+<td class="pnc">4</td>
+<td class="br">&#160;</td>
+<td class="pnds">107</td>
+<td class="shllngs">19</td>
+<td class="pnc">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">34.</td>
+<td class="lght">Dundee,</td>
+<td class="pnds">2062</td>
+<td class="shllngs">9</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">105</td>
+<td class="shllngs">7</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td class="pnds">7</td>
+<td class="shllngs">15</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">1949</td>
+<td class="shllngs">6</td>
+<td class="pnc">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">35.</td>
+<td class="lght">Dumfries,</td>
+<td class="pnds">351</td>
+<td class="shllngs">10</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">24</td>
+<td class="shllngs">13</td>
+<td class="pnc">0</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">2</td>
+<td class="shllngs">10</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">324</td>
+<td class="shllngs">6</td>
+<td class="pnc">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">36.</td>
+<td class="lght">Dartmouth,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">37.</td>
+<td class="lght">Deal,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">38.</td>
+<td class="lght">Dover,<span class="pagenum" id="Page428">[428]</span></td>
+<td class="pnds">0</td>
+<td class="shllngs">8</td>
+<td class="pnc">0</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">0</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">0</td>
+<td class="shllngs">7</td>
+<td class="pnc">7</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">39.</td>
+<td class="lght">Dublin,</td>
+<td class="pnds">2256</td>
+<td class="shllngs">17</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">114</td>
+<td class="shllngs">0</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">9</td>
+<td class="shllngs">16</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">2133</td>
+<td class="shllngs">0</td>
+<td class="pnc">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">40.</td>
+<td class="lght">Drogheda,</td>
+<td class="pnds">149</td>
+<td class="shllngs">8</td>
+<td class="pnc">2</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">7</td>
+<td class="shllngs">9</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">141</td>
+<td class="shllngs">18</td>
+<td class="pnc">9</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">41.</td>
+<td class="lght">Dundalk,</td>
+<td class="pnds">120</td>
+<td class="shllngs">6</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">6</td>
+<td class="shllngs">0</td>
+<td class="pnc">3</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">6</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">113</td>
+<td class="shllngs">19</td>
+<td class="pnc">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">42.</td>
+<td class="lght">Exeter,</td>
+<td class="pnds">2</td>
+<td class="shllngs">17</td>
+<td class="pnc">5</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">3</td>
+<td class="pnc">0</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">2</td>
+<td class="shllngs">14</td>
+<td class="pnc">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">43.</td>
+<td class="lght">Fisherrow,</td>
+<td class="pnds">219</td>
+<td class="shllngs">0</td>
+<td class="pnc">8</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td class="pnds">13</td>
+<td class="shllngs">12</td>
+<td class="pnc">4</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">15</td>
+<td class="pnc">3</td>
+<td class="br">&#160;</td>
+<td class="pnds">204</td>
+<td class="shllngs">13</td>
+<td class="pnc">1</td>
+<td class="frcpnc">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">44.</td>
+<td class="lght">Falmouth,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">45.</td>
+<td class="lght">Faversham,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">46.</td>
+<td class="lght">Fowey,</td>
+<td class="pnds">2</td>
+<td class="shllngs">4</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">3</td>
+<td class="pnc">0</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">2</td>
+<td class="shllngs">1</td>
+<td class="pnc">10</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">47.</td>
+<td class="lght">Glasgow,</td>
+<td class="pnds">3599</td>
+<td class="shllngs">16</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">182</td>
+<td class="shllngs">14</td>
+<td class="pnc">4</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">11</td>
+<td class="shllngs">15</td>
+<td class="pnc">11</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">3405</td>
+<td class="shllngs">6</td>
+<td class="pnc">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">48.</td>
+<td class="lght">Greenock,</td>
+<td class="pnds">2671</td>
+<td class="shllngs">0</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">137</td>
+<td class="shllngs">13</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">7</td>
+<td class="shllngs">10</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td class="pnds">2525</td>
+<td class="shllngs">16</td>
+<td class="pnc">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">49.</td>
+<td class="lght">Grangemouth,</td>
+<td class="pnds">1251</td>
+<td class="shllngs">12</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td class="pnds">62</td>
+<td class="shllngs">11</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td class="pnds">2</td>
+<td class="shllngs">16</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">1186</td>
+<td class="shllngs">4</td>
+<td class="pnc">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">50.</td>
+<td class="lght">Gainsborough,</td>
+<td class="pnds">5</td>
+<td class="shllngs">19</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">6</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">5</td>
+<td class="shllngs">12</td>
+<td class="pnc">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">51.</td>
+<td class="lght">Gloucester,</td>
+<td class="pnds">61</td>
+<td class="shllngs">12</td>
+<td class="pnc">11</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">3</td>
+<td class="shllngs">1</td>
+<td class="pnc">8</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">2</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">58</td>
+<td class="shllngs">9</td>
+<td class="pnc">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">52.</td>
+<td class="lght">Goole,</td>
+<td class="pnds">31</td>
+<td class="shllngs">2</td>
+<td class="pnc">4</td>
+<td class="br">&#160;</td>
+<td class="pnds">1</td>
+<td class="shllngs">12</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">29</td>
+<td class="shllngs">10</td>
+<td class="pnc">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">53.</td>
+<td class="lght">Grimsby,</td>
+<td class="pnds">64</td>
+<td class="shllngs">11</td>
+<td class="pnc">3</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">3</td>
+<td class="shllngs">4</td>
+<td class="pnc">7</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">61</td>
+<td class="shllngs">6</td>
+<td class="pnc">8</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">54.</td>
+<td class="lght">Gweek,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">55.</td>
+<td class="lght">Galway,</td>
+<td class="pnds">38</td>
+<td class="shllngs">6</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">1</td>
+<td class="shllngs">18</td>
+<td class="pnc">3</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">6</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">36</td>
+<td class="shllngs">1</td>
+<td class="pnc">8</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">56.</td>
+<td class="lght">Hartlepool,</td>
+<td class="pnds">153</td>
+<td class="shllngs">4</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">7</td>
+<td class="shllngs">13</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">145</td>
+<td class="shllngs">10</td>
+<td class="pnc">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">57.</td>
+<td class="lght">Harwich,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">58.</td>
+<td class="lght">Hull,</td>
+<td class="pnds">1532</td>
+<td class="shllngs">8</td>
+<td class="pnc">2</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">76</td>
+<td class="shllngs">12</td>
+<td class="pnc">5</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">10</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">1455</td>
+<td class="shllngs">5</td>
+<td class="pnc">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">59.</td>
+<td class="lght">Inverness,</td>
+<td class="pnds">920</td>
+<td class="shllngs">17</td>
+<td class="pnc">1</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">56</td>
+<td class="shllngs">12</td>
+<td class="pnc">11</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">7</td>
+<td class="shllngs">1</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">857</td>
+<td class="shllngs">2</td>
+<td class="pnc">2</td>
+<td class="frcpnc">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">60.</td>
+<td class="lght">Irvine,</td>
+<td class="pnds">915</td>
+<td class="shllngs">10</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">63</td>
+<td class="shllngs">8</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">3</td>
+<td class="shllngs">8</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">848</td>
+<td class="shllngs">13</td>
+<td class="pnc">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">61.</td>
+<td class="lght">Ipswich,</td>
+<td class="pnds">17</td>
+<td class="shllngs">5</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">17</td>
+<td class="pnc">3</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">2</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">16</td>
+<td class="shllngs">5</td>
+<td class="pnc">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">62.</td>
+<td class="lght">Isle of Man,</td>
+<td class="pnds">373</td>
+<td class="shllngs">18</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">¹⁄₈</td>
+<td class="pnds">22</td>
+<td class="shllngs">15</td>
+<td class="pnc">5</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td class="pnds">1</td>
+<td class="shllngs">13</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">349</td>
+<td class="shllngs">9</td>
+<td class="pnc">6</td>
+<td class="frcpnc">³⁄₄</td>
+</tr>
+
+<tr>
+<td class="nr">63.</td>
+<td class="lght">Kirkcaldy,</td>
+<td class="pnds">745</td>
+<td class="shllngs">5</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td class="pnds">42</td>
+<td class="shllngs">16</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td class="pnds">1</td>
+<td class="shllngs">16</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td class="pnds">700</td>
+<td class="shllngs">13</td>
+<td class="pnc">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">64.</td>
+<td class="lght">Kirkwall,</td>
+<td class="pnds">131</td>
+<td class="shllngs">15</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">7</td>
+<td class="shllngs">9</td>
+<td class="pnc">0</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">9</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">123</td>
+<td class="shllngs">16</td>
+<td class="pnc">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">65.</td>
+<td class="lght">Leith,</td>
+<td class="pnds">3224</td>
+<td class="shllngs">7</td>
+<td class="pnc">3</td>
+<td class="br">&#160;</td>
+<td class="pnds">161</td>
+<td class="shllngs">4</td>
+<td class="pnc">4</td>
+<td class="br">&#160;</td>
+<td class="pnds">17</td>
+<td class="shllngs">14</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td class="pnds">3045</td>
+<td class="shllngs">8</td>
+<td class="pnc">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">66.</td>
+<td class="lght">Lerwick,</td>
+<td class="pnds">173</td>
+<td class="shllngs">1</td>
+<td class="pnc">1</td>
+<td class="br">&#160;</td>
+<td class="pnds">8</td>
+<td class="shllngs">13</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">11</td>
+<td class="pnc">1</td>
+<td class="br">&#160;</td>
+<td class="pnds">163</td>
+<td class="shllngs">17</td>
+<td class="pnc">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">67.</td>
+<td class="lght">Lancaster,</td>
+<td class="pnds">107</td>
+<td class="shllngs">0</td>
+<td class="pnc">5</td>
+<td class="frcpnc br">¹⁄₈</td>
+<td class="pnds">6</td>
+<td class="shllngs">3</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">⁵⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">18</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">99</td>
+<td class="shllngs">18</td>
+<td class="pnc">2</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">68.</td>
+<td class="lght">Leigh,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">69.</td>
+<td class="lght">Liverpool,</td>
+<td class="pnds">6780</td>
+<td class="shllngs">19</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td class="pnds">342</td>
+<td class="shllngs">8</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">9</td>
+<td class="shllngs">13</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">6428</td>
+<td class="shllngs">16</td>
+<td class="pnc">9</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">70.</td>
+<td class="lght">Llanelly,</td>
+<td class="pnds">8</td>
+<td class="shllngs">12</td>
+<td class="pnc">3</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">11</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">8</td>
+<td class="shllngs">0</td>
+<td class="pnc">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">71.</td>
+<td class="lght">London,</td>
+<td class="pnds">1943</td>
+<td class="shllngs">8</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td class="pnds">97</td>
+<td class="shllngs">3</td>
+<td class="pnc">4</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">1846</td>
+<td class="shllngs">5</td>
+<td class="pnc">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">72.</td>
+<td class="lght">Lyme,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">73.</td>
+<td class="lght">Lynn,</td>
+<td class="pnds">79</td>
+<td class="shllngs">7</td>
+<td class="pnc">7</td>
+<td class="br">&#160;</td>
+<td class="pnds">4</td>
+<td class="shllngs">15</td>
+<td class="pnc">2</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">7</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td class="pnds">74</td>
+<td class="shllngs">5</td>
+<td class="pnc">2</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">74.</td>
+<td class="lght">Limerick,</td>
+<td class="pnds">160</td>
+<td class="shllngs">2</td>
+<td class="pnc">4</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">8</td>
+<td class="shllngs">3</td>
+<td class="pnc">2</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">5</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">151</td>
+<td class="shllngs">14</td>
+<td class="pnc">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">75.</td>
+<td class="lght">Londonderry,</td>
+<td class="pnds">1058</td>
+<td class="shllngs">2</td>
+<td class="pnc">4</td>
+<td class="br">&#160;</td>
+<td class="pnds">53</td>
+<td class="shllngs">6</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">1004</td>
+<td class="shllngs">15</td>
+<td class="pnc">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">76.</td>
+<td class="lght">Montrose,</td>
+<td class="pnds">357</td>
+<td class="shllngs">13</td>
+<td class="pnc">2</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">18</td>
+<td class="shllngs">6</td>
+<td class="pnc">0</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">10</td>
+<td class="pnc">3</td>
+<td class="br">&#160;</td>
+<td class="pnds">338</td>
+<td class="shllngs">16</td>
+<td class="pnc">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">77.</td>
+<td class="lght">Maldon,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">78.</td>
+<td class="lght">Milford,</td>
+<td class="pnds">14</td>
+<td class="shllngs">4</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">19</td>
+<td class="pnc">7</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">13</td>
+<td class="shllngs">4</td>
+<td class="pnc">11</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">79.</td>
+<td class="lght">Maryport,</td>
+<td class="pnds">87</td>
+<td class="shllngs">17</td>
+<td class="pnc">1</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">4</td>
+<td class="shllngs">5</td>
+<td class="pnc">7</td>
+<td class="br">&#160;</td>
+<td class="pnds">2</td>
+<td class="shllngs">6</td>
+<td class="pnc">11</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">81</td>
+<td class="shllngs">4</td>
+<td class="pnc">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">80.</td>
+<td class="lght">Newcastle-on-Tyne,</td>
+<td class="pnds">2118</td>
+<td class="shllngs">16</td>
+<td class="pnc">8</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">75</td>
+<td class="shllngs">2</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">14</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">2042</td>
+<td class="shllngs">19</td>
+<td class="pnc">3</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">81.</td>
+<td class="lght">Newhaven,</td>
+<td class="pnds">1</td>
+<td class="shllngs">14</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">1</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">1</td>
+<td class="shllngs">13</td>
+<td class="pnc">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">82.</td>
+<td class="lght">Newport,</td>
+<td class="pnds">41</td>
+<td class="shllngs">2</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">2</td>
+<td class="shllngs">1</td>
+<td class="pnc">1</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">39</td>
+<td class="shllngs">1</td>
+<td class="pnc">6</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">83.</td>
+<td class="lght">Newry,</td>
+<td class="pnds">230</td>
+<td class="shllngs">16</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td class="pnds">13</td>
+<td class="shllngs">3</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">14</td>
+<td class="shllngs">6</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">203</td>
+<td class="shllngs">5</td>
+<td class="pnc">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">84.</td>
+<td class="lght">Perth,</td>
+<td class="pnds">275</td>
+<td class="shllngs">14</td>
+<td class="pnc">3</td>
+<td class="br">&#160;</td>
+<td class="pnds">14</td>
+<td class="shllngs">13</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">19</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">260</td>
+<td class="shllngs">0</td>
+<td class="pnc">10</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">85.</td>
+<td class="lght">Port-Glasgow,</td>
+<td class="pnds">496</td>
+<td class="shllngs">8</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td class="pnds">24</td>
+<td class="shllngs">16</td>
+<td class="pnc">3</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">15</td>
+<td class="pnc">7</td>
+<td class="br">&#160;</td>
+<td class="pnds">470</td>
+<td class="shllngs">16</td>
+<td class="pnc">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">86.</td>
+<td class="lght">Padstow,</td>
+<td class="pnds">2</td>
+<td class="shllngs">15</td>
+<td class="pnc">1</td>
+<td class="frcpnc br">³⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">2</td>
+<td class="pnc">8</td>
+<td class="frcpnc br">³⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">5</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">2</td>
+<td class="shllngs">7</td>
+<td class="pnc">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">87.</td>
+<td class="lght">Penzance,</td>
+<td class="pnds">1</td>
+<td class="shllngs">6</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">1</td>
+<td class="pnc">4</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">1</td>
+<td class="shllngs">5</td>
+<td class="pnc">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">88.</td>
+<td class="lght">Plymouth,</td>
+<td class="pnds">25</td>
+<td class="shllngs">4</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">1</td>
+<td class="shllngs">6</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">1</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">23</td>
+<td class="shllngs">17</td>
+<td class="pnc">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">89.</td>
+<td class="lght">Poole,</td>
+<td class="pnds">0</td>
+<td class="shllngs">11</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">0</td>
+<td class="pnc">7</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">0</td>
+<td class="shllngs">10</td>
+<td class="pnc">11</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">90.</td>
+<td class="lght">Portsmouth,</td>
+<td class="pnds">10</td>
+<td class="shllngs">12</td>
+<td class="pnc">4</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">10</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">4</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">9</td>
+<td class="shllngs">17</td>
+<td class="pnc">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">91.</td>
+<td class="lght">Preston,<span class="pagenum" id="Page429">[429]</span></td>
+<td class="pnds">562</td>
+<td class="shllngs">1</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">41</td>
+<td class="shllngs">14</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">520</td>
+<td class="shllngs">7</td>
+<td class="pnc">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">92.</td>
+<td class="lght">Ramsgate,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">93.</td>
+<td class="lght">Rochester,</td>
+<td class="pnds">1</td>
+<td class="shllngs">15</td>
+<td class="pnc">1</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">1</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">1</td>
+<td class="shllngs">13</td>
+<td class="pnc">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">94.</td>
+<td class="lght">Rye,</td>
+<td class="pnds">0</td>
+<td class="shllngs">18</td>
+<td class="pnc">3</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">0</td>
+<td class="pnc">10</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">0</td>
+<td class="shllngs">17</td>
+<td class="pnc">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">95.</td>
+<td class="lght">Ross,</td>
+<td class="pnds">12</td>
+<td class="shllngs">17</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">12</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">4</td>
+<td class="pnc">7</td>
+<td class="br">&#160;</td>
+<td class="pnds">12</td>
+<td class="shllngs">0</td>
+<td class="pnc">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">96.</td>
+<td class="lght">Stranraer,</td>
+<td class="pnds">90</td>
+<td class="shllngs">17</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">4</td>
+<td class="shllngs">16</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td class="pnds">1</td>
+<td class="shllngs">9</td>
+<td class="pnc">3</td>
+<td class="br">&#160;</td>
+<td class="pnds">84</td>
+<td class="shllngs">12</td>
+<td class="pnc">0</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">97.</td>
+<td class="lght">Stornoway,</td>
+<td class="pnds">56</td>
+<td class="shllngs">6</td>
+<td class="pnc">11</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">2</td>
+<td class="shllngs">16</td>
+<td class="pnc">2</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">3</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td class="pnds">53</td>
+<td class="shllngs">7</td>
+<td class="pnc">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">98.</td>
+<td class="lght">Scarborough,</td>
+<td class="pnds">8</td>
+<td class="shllngs">14</td>
+<td class="pnc">10</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">8</td>
+<td class="pnc">8</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">8</td>
+<td class="shllngs">6</td>
+<td class="pnc">2</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">99.</td>
+<td class="lght">Seilly,</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+</tr>
+
+<tr>
+<td class="nr">100.</td>
+<td class="lght">Shoreham,</td>
+<td class="pnds">0</td>
+<td class="shllngs">19</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">⁷⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">0</td>
+<td class="pnc">11</td>
+<td class="frcpnc br">⁷⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">0</td>
+<td class="shllngs">18</td>
+<td class="pnc">7</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">101.</td>
+<td class="lght">Southampton,</td>
+<td class="pnds">30</td>
+<td class="shllngs">0</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">1</td>
+<td class="shllngs">10</td>
+<td class="pnc">1</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">28</td>
+<td class="shllngs">10</td>
+<td class="pnc">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">102.</td>
+<td class="lght">St Ives,</td>
+<td class="pnds">3</td>
+<td class="shllngs">9</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">¹⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">5</td>
+<td class="pnc">2</td>
+<td class="frcpnc br">¹⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">0</td>
+<td class="pnc">1</td>
+<td class="br">&#160;</td>
+<td class="pnds">3</td>
+<td class="shllngs">4</td>
+<td class="pnc">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">103.</td>
+<td class="lght">Stockton,</td>
+<td class="pnds">226</td>
+<td class="shllngs">19</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td class="pnds">12</td>
+<td class="shllngs">0</td>
+<td class="pnc">2</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">5</td>
+<td class="shllngs">11</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">209</td>
+<td class="shllngs">7</td>
+<td class="pnc">11</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">104.</td>
+<td class="lght">Sunderland,</td>
+<td class="pnds">908</td>
+<td class="shllngs">14</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td class="pnds">47</td>
+<td class="shllngs">1</td>
+<td class="pnc">4</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">14</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">860</td>
+<td class="shllngs">18</td>
+<td class="pnc">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">105.</td>
+<td class="lght">Swansea,</td>
+<td class="pnds">28</td>
+<td class="shllngs">4</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td class="pnds">1</td>
+<td class="shllngs">12</td>
+<td class="pnc">3</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">26</td>
+<td class="shllngs">12</td>
+<td class="pnc">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">106.</td>
+<td class="lght">Sligo,</td>
+<td class="pnds">355</td>
+<td class="shllngs">0</td>
+<td class="pnc">4</td>
+<td class="br">&#160;</td>
+<td class="pnds">19</td>
+<td class="shllngs">15</td>
+<td class="pnc">10</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">10</td>
+<td class="pnc">4</td>
+<td class="br">&#160;</td>
+<td class="pnds">334</td>
+<td class="shllngs">14</td>
+<td class="pnc">1</td>
+<td class="frcpnc">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">107.</td>
+<td class="lght">Truro,</td>
+<td class="pnds">0</td>
+<td class="shllngs">11</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">0</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">0</td>
+<td class="shllngs">10</td>
+<td class="pnc">3</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">108.</td>
+<td class="lght">Tralee,</td>
+<td class="pnds">9</td>
+<td class="shllngs">7</td>
+<td class="pnc">10</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">9</td>
+<td class="pnc">4</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">2</td>
+<td class="pnc">8</td>
+<td class="br">&#160;</td>
+<td class="pnds">8</td>
+<td class="shllngs">15</td>
+<td class="pnc">10</td>
+<td class="frcpnc">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">109.</td>
+<td class="lght">Wick,</td>
+<td class="pnds">356</td>
+<td class="shllngs">17</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">20</td>
+<td class="shllngs">10</td>
+<td class="pnc">2</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">4</td>
+<td class="shllngs">9</td>
+<td class="pnc">1</td>
+<td class="br">&#160;</td>
+<td class="pnds">331</td>
+<td class="shllngs">18</td>
+<td class="pnc">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">110.</td>
+<td class="lght">Wigton,</td>
+<td class="pnds">83</td>
+<td class="shllngs">9</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td class="pnds">5</td>
+<td class="shllngs">5</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td class="pnds">1</td>
+<td class="shllngs">12</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td class="pnds">76</td>
+<td class="shllngs">11</td>
+<td class="pnc">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">111.</td>
+<td class="lght">Weymouth,</td>
+<td class="pnds">0</td>
+<td class="shllngs">15</td>
+<td class="pnc">10</td>
+<td class="frcpnc br">²⁄₈</td>
+<td class="pnds">0</td>
+<td class="shllngs">0</td>
+<td class="pnc">9</td>
+<td class="frcpnc br">²⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">0</td>
+<td class="shllngs">15</td>
+<td class="pnc">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">112.</td>
+<td class="lght">Whitby,</td>
+<td class="pnds">31</td>
+<td class="shllngs">5</td>
+<td class="pnc">10</td>
+<td class="br">&#160;</td>
+<td class="pnds">1</td>
+<td class="shllngs">11</td>
+<td class="pnc">4</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">29</td>
+<td class="shllngs">14</td>
+<td class="pnc">6</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">113.</td>
+<td class="lght">Whitehaven,</td>
+<td class="pnds">328</td>
+<td class="shllngs">1</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">18</td>
+<td class="shllngs">5</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">309</td>
+<td class="shllngs">16</td>
+<td class="pnc">4</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">114.</td>
+<td class="lght">Woodbridge,</td>
+<td class="pnds">3</td>
+<td class="shllngs">18</td>
+<td class="pnc">9</td>
+<td class="br">&#160;</td>
+<td class="pnds">0</td>
+<td class="shllngs">3</td>
+<td class="pnc">11</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">3</td>
+<td class="shllngs">14</td>
+<td class="pnc">10</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">115.</td>
+<td class="lght">Waterford,</td>
+<td class="pnds">57</td>
+<td class="shllngs">14</td>
+<td class="pnc">3</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">2</td>
+<td class="shllngs">17</td>
+<td class="pnc">10</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">54</td>
+<td class="shllngs">16</td>
+<td class="pnc">5</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="nr">116.</td>
+<td class="lght">Westport,</td>
+<td class="pnds">41</td>
+<td class="shllngs">0</td>
+<td class="pnc">6</td>
+<td class="frcpnc br">⁴⁄₈</td>
+<td class="pnds">2</td>
+<td class="shllngs">1</td>
+<td class="pnc">0</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">38</td>
+<td class="shllngs">19</td>
+<td class="pnc">6</td>
+<td class="frcpnc">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">117.</td>
+<td class="lght">Wexford,</td>
+<td class="pnds">32</td>
+<td class="shllngs">19</td>
+<td class="pnc">2</td>
+<td class="br">&#160;</td>
+<td class="pnds">1</td>
+<td class="shllngs">12</td>
+<td class="pnc">11</td>
+<td class="frcpnc br">⁶⁄₈</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">31</td>
+<td class="shllngs">6</td>
+<td class="pnc">2</td>
+<td class="frcpnc">²⁄₈</td>
+</tr>
+
+<tr>
+<td class="nr">118.</td>
+<td class="lght">Yarmouth,</td>
+<td class="pnds">49</td>
+<td class="shllngs">5</td>
+<td class="pnc">6</td>
+<td class="br">&#160;</td>
+<td class="pnds">2</td>
+<td class="shllngs">9</td>
+<td class="pnc">5</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pnds">46</td>
+<td class="shllngs">16</td>
+<td class="pnc">1</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td class="pnds bt">£46,001</td>
+<td class="shllngs bt">11</td>
+<td class="pnc bt">3</td>
+<td class="frcpnc bt br">⁷⁄₈</td>
+<td class="pnds bt">£2401</td>
+<td class="shllngs bt">7</td>
+<td class="pnc bt">3</td>
+<td class="frcpnc br bt">⁴⁄₈</td>
+<td class="pnds bt">£218</td>
+<td class="shllngs bt">16</td>
+<td class="pnc bt">10</td>
+<td class="frcpnc bt br">²⁄₈</td>
+<td class="pnds bt">£43,381</td>
+<td class="shllngs bt">7</td>
+<td class="pnc bt">2</td>
+<td class="frcpnc bt">¹⁄₈</td>
+</tr>
+
+<tr>
+<td class="paddedtop">&#160;</td>
+<td class="txt br paddedtop"><span class="smcap">Deduct</span>—Amount of fractions short credited by Bank,</td>
+<td class="pnds paddedtop">0</td>
+<td class="shllngs paddedtop">0</td>
+<td class="pnc paddedtop">1</td>
+<td class="frcpnc paddedtop br">¹⁄₈</td>
+<td colspan="4" class="blank paddedtop br">...</td>
+<td colspan="4" class="blank paddedtop br">...</td>
+<td class="pnds paddedtop">0</td>
+<td class="shllngs paddedtop">0</td>
+<td class="pnc paddedtop">1</td>
+<td class="frcpnc paddedtop">¹⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="2" class="br">&#160;</td>
+<td class="pnds bt bbd">£46,001</td>
+<td class="shllngs bt bbd">11</td>
+<td class="pnc bt bbd">2</td>
+<td class="frcpnc bt br bbd">⁶⁄₈</td>
+<td class="pnds bt bbd">£2401</td>
+<td class="shllngs bt bbd">7</td>
+<td class="pnc bt bbd">3</td>
+<td class="frcpnc bt br bbd">⁴⁄₈</td>
+<td class="pnds bt bbd">£218</td>
+<td class="shllngs bt bbd">16</td>
+<td class="pnc bt bbd">10</td>
+<td class="frcpnc bt br bbd">²⁄₈</td>
+<td class="pnds bt bbd">£43,381</td>
+<td class="shllngs bt bbd">7</td>
+<td class="pnc bt bbd">1</td>
+<td class="bt bbd">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="14" class="thinline br">&#160;</td>
+<td colspan="4" class="thinline">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td class="txt"><span class="smcap">Gross Receipts</span>,</td>
+<td colspan="8" class="br">&#160;</td>
+<td class="pnds bt">£46,001</td>
+<td class="shllngs bt">11</td>
+<td class="pnc bt">2</td>
+<td class="frcpnc bt br">⁶⁄₈</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br paddedtop"><span class="smcap">Deduct</span>—Commission,</td>
+<td class="pnds bt paddedtop">£2401</td>
+<td class="shllngs bt paddedtop">7</td>
+<td class="pnc bt paddedtop">3</td>
+<td class="frcpnc br bt paddedtop">⁴⁄₈</td>
+<td colspan="4" class="blank br paddedtop">&#160;</td>
+<td colspan="4" class="blank paddedtop">&#160;</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="5" class="txt br"><span class="dontshow"><span class="smcap">Deduct</span>—</span>Repayments, &amp;c.,</td>
+<td class="pnds bb">218</td>
+<td class="shllngs bb">16</td>
+<td class="pnc bb">10</td>
+<td class="frcpnc br bb">²⁄₈</td>
+<td colspan="4" class="blank br">&#160;</td>
+<td colspan="4" class="blank">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="10" class="br">&#160;</td>
+<td class="pnds bb">2620</td>
+<td class="shllngs bb">4</td>
+<td class="pnc bb">1</td>
+<td class="frcpnc br bb">⁶⁄₈</td>
+<td colspan="4" class="blank bb">&#160;</td>
+</tr>
+
+<tr>
+<td class="paddedtop">&#160;</td>
+<td colspan="13" class="txt paddedtop br"><span class="smcap">Nett Duties</span> received in year to 31st December 1846,</td>
+<td class="pnds paddedtop">43,381</td>
+<td class="shllngs paddedtop">7</td>
+<td class="pnc paddedtop">1</td>
+<td class=" paddedtop">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="2" class="thinline">&#160;</td>
+<td colspan="12" class="thinline br bbd">&#160;</td>
+<td colspan="4" class="thinline bbd">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="18" class="thinline">&#160;</td>
+</tr>
+
+</table>
+
+<p><span class="pagenum" id="Page430">[430]</span></p>
+
+<p class="tabhead long"><span class="smcap">No.</span> II.—<i>State shewing the Gross Receipts on
+account of each of the Northern Lighthouses, the Number of Vessels,
+and amount of Tonnage passing them;—the Particular Expenses of the Lighthouses, and their Proportions of
+the General Expenses, embracing Commissions to, and Repayments by, the Collectors; Expenses of the Shipping
+Establishment, Salaries to Officers, Experiments, and other General Expenses; also the Ordinary Expenses of
+Beacons and Buoys, for the Year 1846.</i></p>
+
+<table class="receipts">
+
+<tr class="bb">
+<th colspan="2" class="br"><span class="smcap">No. of<br>Vessels.</span></th>
+<th colspan="2" class="br"><span class="smcap">Tonnage.</span></th>
+<th rowspan="2" colspan="2" class="br">LIGHTHOUSES.</th>
+<th rowspan="2" colspan="4" class="br">&#160;</th>
+<th rowspan="2" colspan="4" class="br"><span class="smcap">Gross<br>Receipts.</span></th>
+<th rowspan="2" colspan="4" class="br"><span class="smcap">Surplus.</span></th>
+<th rowspan="2" colspan="4"><span class="smcap">Deficiency.</span></th>
+</tr>
+
+<tr class="bb">
+<th class="br">Coasting.</th>
+<th class="br">Oversea.</th>
+<th class="br">Coasting.</th>
+<th class="br">Oversea.</th>
+</tr>
+
+<tr>
+<td class="ships">15,872</td>
+<td class="ships">2,664</td>
+<td class="tonnage">1,238,057</td>
+<td class="tonnage">294,546</td>
+<td class="lightnr">1.</td>
+<td class="lightname">INCHKEITH,</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">£2524</td>
+<td class="shilling">9</td>
+<td class="penint">2</td>
+<td class="penfr br">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£583</td>
+<td class="shilling">5</td>
+<td class="penint">10</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">577</td>
+<td class="shilling bb">15</td>
+<td class="penint bb">9</td>
+<td class="penfr bb">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1161</td>
+<td class="shilling bb">1</td>
+<td class="penint bb">7</td>
+<td class="penfr bb">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound">£1363</td>
+<td class="shilling">7</td>
+<td class="penint">6</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr class="btgrey">
+<td class="ships">20,101</td>
+<td class="ships">3,349</td>
+<td class="tonnage">1,843,210</td>
+<td class="tonnage">383,516</td>
+<td class="lightnr">2.</td>
+<td class="lightname">ISLE OF MAY,</td>
+<td class="pound">£3676</td>
+<td class="shilling">18</td>
+<td class="penint">11</td>
+<td class=" br">&#160;</td>
+<td colspan="4" class=" br">&#160;</td>
+<td colspan="4" class=" br">&#160;</td>
+<td colspan="4" class="">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Add for Leading Light,</td>
+<td class="pound bb">148</td>
+<td class="shilling bb">9</td>
+<td class="penint bb">6</td>
+<td class="penfr bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound">£3825</td>
+<td class="shilling">8</td>
+<td class="penint">5</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£952</td>
+<td class="shilling">3</td>
+<td class="penint">9</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">941</td>
+<td class="shilling bb">8</td>
+<td class="penint bb">6</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1893</td>
+<td class="shilling bb">12</td>
+<td class="penint bb">3</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound">1931</td>
+<td class="shilling">16</td>
+<td class="penint">2</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr class="btgrey">
+<td class="ships">14,610</td>
+<td class="ships">4,485</td>
+<td class="tonnage">1,299,875</td>
+<td class="tonnage">632,328</td>
+<td class="lightnr">3.</td>
+<td class="lightname">BELL ROCK,</td>
+<td colspan="4" class=" br">...</td>
+<td class="pound">£5342</td>
+<td class="shilling">15</td>
+<td class="penint">5</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class=" br">&#160;</td>
+<td colspan="4" class="">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£989</td>
+<td class="shilling">1</td>
+<td class="penint">3</td>
+<td class="penfr br">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">977</td>
+<td class="shilling bb">17</td>
+<td class="penint bb">9</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
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+<td class="shilling bb">19</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
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+<td class="shilling">16</td>
+<td class="penint">5</td>
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+<td colspan="4">&#160;</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£2458</td>
+<td class="shilling">4</td>
+<td class="penint">5</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£548</td>
+<td class="shilling">18</td>
+<td class="penint">1</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound bb">544</td>
+<td class="shilling bb">5</td>
+<td class="penint bb">8</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1093</td>
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+<td class="penint bb">9</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound">1365</td>
+<td class="shilling">0</td>
+<td class="penint">8</td>
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+<td colspan="4">&#160;</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£1880</td>
+<td class="shilling">1</td>
+<td class="penint">3</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound">£623</td>
+<td class="shilling">5</td>
+<td class="penint">3</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound bb">617</td>
+<td class="shilling bb">4</td>
+<td class="penint bb">1</td>
+<td class="penfr br bb">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1240</td>
+<td class="shilling bb">9</td>
+<td class="penint bb">4</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
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+<td class="shilling">11</td>
+<td class="penint">10</td>
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+<td colspan="4">&#160;</td>
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+
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£1744</td>
+<td class="shilling">11</td>
+<td class="penint">3</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£578</td>
+<td class="shilling">10</td>
+<td class="penint">0</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">573</td>
+<td class="shilling bb">16</td>
+<td class="penint bb">11</td>
+<td class="penfr br bb">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1152</td>
+<td class="shilling bb">6</td>
+<td class="penint bb">11</td>
+<td class="penfr br bb">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound">592</td>
+<td class="shilling">4</td>
+<td class="penint">6</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="ships">273</td>
+<td class="tonnage">191,345</td>
+<td class="tonnage">18,282</td>
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+<td class="lightname">TARBETNESS,</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">£329</td>
+<td class="shilling">17</td>
+<td class="penint">4</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£574</td>
+<td class="shilling">11</td>
+<td class="penint">11</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">569</td>
+<td class="shilling bb">18</td>
+<td class="penint bb">1</td>
+<td class="penfr br bb">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1144</td>
+<td class="shilling bb">10</td>
+<td class="penint bb">0</td>
+<td class="penfr br bb">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">£814</td>
+<td class="shilling">12</td>
+<td class="penint">7</td>
+<td class="penfr">⁴⁄₈</td>
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+
+<tr class="btgrey">
+<td class="ships">279</td>
+<td class="ships">644</td>
+<td class="tonnage">32,149</td>
+<td class="tonnage">113,598</td>
+<td class="lightnr">8.</td>
+<td class="lightname">SUMBURGHHEAD,</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">£286</td>
+<td class="shilling">18</td>
+<td class="penint">2</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£597</td>
+<td class="shilling">5</td>
+<td class="penint">3</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">591</td>
+<td class="shilling bb">11</td>
+<td class="penint bb">8</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1188</td>
+<td class="shilling bb">17</td>
+<td class="penint bb">0</td>
+<td class="penfr br bb">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">£901</td>
+<td class="shilling">18</td>
+<td class="penint">9</td>
+<td class="penfr">⁴⁄₈</td>
+</tr>
+
+<tr class="btgrey">
+<td class="ships">307</td>
+<td class="ships">2,326</td>
+<td class="tonnage">33,710</td>
+<td class="tonnage">528,647</td>
+<td class="lightnr">9.</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£1154</td>
+<td class="shilling">5</td>
+<td class="penint">4</td>
+<td class="penfr br">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£347</td>
+<td class="shilling">0</td>
+<td class="penint">8</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">345</td>
+<td class="shilling bb">4</td>
+<td class="penint bb">4</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">692</td>
+<td class="shilling bb">5</td>
+<td class="penint bb">0</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound">462</td>
+<td class="shilling">0</td>
+<td class="penint">3</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4">&#160;</td>
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+
+<tr class="btgrey">
+<td class="ships">2,434</td>
+<td class="ships">2,430</td>
+<td class="tonnage">181,284</td>
+<td class="tonnage">525,582</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£1370</td>
+<td class="shilling">10</td>
+<td class="penint">5</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£851</td>
+<td class="shilling">8</td>
+<td class="penint">11</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">841</td>
+<td class="shilling bb">17</td>
+<td class="penint bb">10</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1693</td>
+<td class="shilling bb">6</td>
+<td class="penint bb">9</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">322</td>
+<td class="shilling">16</td>
+<td class="penint">3</td>
+<td class="penfr">⁶⁄₈</td>
+</tr>
+
+<tr class="btgrey">
+<td class="ships">1,911</td>
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+<td class="tonnage">139,379</td>
+<td class="tonnage">524,685</td>
+<td class="lightnr">11.</td>
+<td class="lightname">DUNNETHEAD,<span class="pagenum" id="Page431">[431]</span></td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">£1311</td>
+<td class="shilling">1</td>
+<td class="penint">10</td>
+<td class="penfr br">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£470</td>
+<td class="shilling">19</td>
+<td class="penint">7</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound bb">467</td>
+<td class="shilling bb">8</td>
+<td class="penint bb">4</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">938</td>
+<td class="shilling bb">7</td>
+<td class="penint bb">11</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound">372</td>
+<td class="shilling">13</td>
+<td class="penint">10</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="tonnage">517,333</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£1278</td>
+<td class="shilling">9</td>
+<td class="penint">9</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound">£587</td>
+<td class="shilling">6</td>
+<td class="penint">11</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="penint bb">7</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
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+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound">109</td>
+<td class="shilling">8</td>
+<td class="penint">2</td>
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+<td colspan="4">&#160;</td>
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+
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£679</td>
+<td class="shilling">1</td>
+<td class="penint">10</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound">£515</td>
+<td class="shilling">2</td>
+<td class="penint">10</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="penint bb">6</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
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+<td class="penfr br bb">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
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+<td class="pound">346</td>
+<td class="shilling">16</td>
+<td class="penint">6</td>
+<td>&#160;</td>
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+
+<tr class="btgrey">
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+<td class="tonnage">466,010</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£1063</td>
+<td class="shilling">3</td>
+<td class="penint">2</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£594</td>
+<td class="shilling">3</td>
+<td class="penint">10</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
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+<td class="shilling bb">12</td>
+<td class="penint bb">7</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1182</td>
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+<td class="penint bb">5</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">119</td>
+<td class="shilling">13</td>
+<td class="penint">2</td>
+<td class="penfr">⁶⁄₈</td>
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+
+<tr class="btgrey">
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+<td class="tonnage">52,541</td>
+<td class="tonnage">461,313</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£2090</td>
+<td class="shilling">11</td>
+<td class="penint">3</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound">£1122</td>
+<td class="shilling">0</td>
+<td class="penint">7</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound bb">1108</td>
+<td class="shilling bb">19</td>
+<td class="penint bb">1</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">2239</td>
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+<td class="penint bb">8</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">140</td>
+<td class="shilling">8</td>
+<td class="penint">4</td>
+<td class="penfr">⁴⁄₈</td>
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+
+<tr class="btgrey">
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+<td class="tonnage">159,719</td>
+<td class="tonnage">4,436</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£239</td>
+<td class="shilling">11</td>
+<td class="penint">4</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound">£515</td>
+<td class="shilling">14</td>
+<td class="penint">2</td>
+<td class="penfr br">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">511</td>
+<td class="shilling bb">15</td>
+<td class="penint bb">4</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1027</td>
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+<td class="penfr br bb">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">787</td>
+<td class="shilling">18</td>
+<td class="penint">2</td>
+<td class="penfr">⁶⁄₈</td>
+</tr>
+
+<tr class="btgrey">
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£1414</td>
+<td class="shilling">5</td>
+<td class="penint">8</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound">£569</td>
+<td class="shilling">12</td>
+<td class="penint">7</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">564</td>
+<td class="shilling bb">19</td>
+<td class="penint bb">6</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1134</td>
+<td class="shilling bb">12</td>
+<td class="penint bb">2</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound">279</td>
+<td class="shilling">13</td>
+<td class="penint">6</td>
+<td class="penfr br">²⁄₈</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr class="btgrey">
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+<td class="tonnage">357,682</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£1549</td>
+<td class="shilling">0</td>
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+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound">£554</td>
+<td class="shilling">17</td>
+<td class="penint">10</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">550</td>
+<td class="shilling bb">3</td>
+<td class="penint bb">10</td>
+<td class="penfr br bb">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1105</td>
+<td class="shilling bb">1</td>
+<td class="penint bb">9</td>
+<td class="penfr br bb">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound">443</td>
+<td class="shilling">18</td>
+<td class="penint">3</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="ships">1,937</td>
+<td class="tonnage">1,403,359</td>
+<td class="tonnage">450,849</td>
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+<td class="lightname">PLADDA,</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">£2762</td>
+<td class="shilling">14</td>
+<td class="penint">3</td>
+<td class="penfr br">⁷⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound">£584</td>
+<td class="shilling">10</td>
+<td class="penint">10</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound bb">579</td>
+<td class="shilling bb">15</td>
+<td class="penint bb">2</td>
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+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1164</td>
+<td class="shilling bb">6</td>
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+<td class="penfr br bb">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound">1598</td>
+<td class="shilling">8</td>
+<td class="penint">3</td>
+<td class="penfr br">⁵⁄₈</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="tonnage">645,447</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£2811</td>
+<td class="shilling">5</td>
+<td class="penint">3</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound">£465</td>
+<td class="shilling">13</td>
+<td class="penint">4</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound bb">462</td>
+<td class="shilling bb">9</td>
+<td class="penint bb">9</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">928</td>
+<td class="shilling bb">3</td>
+<td class="penint bb">1</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound">1883</td>
+<td class="shilling">2</td>
+<td class="penint">2</td>
+<td class="penfr br">²⁄₈</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="tonnage">531,056</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£2823</td>
+<td class="shilling">19</td>
+<td class="penint">8</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£517</td>
+<td class="shilling">0</td>
+<td class="penint">5</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound bb">512</td>
+<td class="shilling bb">14</td>
+<td class="penint bb">11</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1029</td>
+<td class="shilling bb">15</td>
+<td class="penint bb">5</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound">1794</td>
+<td class="shilling">4</td>
+<td class="penint">3</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="ships">9,195</td>
+<td class="ships">98</td>
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+<td class="tonnage">17,431</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£1187</td>
+<td class="shilling">7</td>
+<td class="penint">9</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£516</td>
+<td class="shilling">18</td>
+<td class="penint">6</td>
+<td class="penfr br">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">512</td>
+<td class="shilling bb">14</td>
+<td class="penint bb">11</td>
+<td class="penfr br bb">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1029</td>
+<td class="shilling bb">13</td>
+<td class="penint bb">5</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound">157</td>
+<td class="shilling">14</td>
+<td class="penint">4</td>
+<td class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="tonnage">843,235</td>
+<td class="tonnage">209,237</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£1755</td>
+<td class="shilling">17</td>
+<td class="penint">5</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£409</td>
+<td class="shilling">1</td>
+<td class="penint">4</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">406</td>
+<td class="shilling bb">6</td>
+<td class="penint bb">4</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">815</td>
+<td class="shilling bb">7</td>
+<td class="penint bb">9</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound">940</td>
+<td class="shilling">9</td>
+<td class="penint">8</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="ships">13,867</td>
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+<td class="tonnage">1,769,475</td>
+<td class="tonnage">546,244</td>
+<td class="lightnr">24.</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£3839</td>
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+<td class="penint">11</td>
+<td class="penfr br">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£813</td>
+<td class="shilling">19</td>
+<td class="penint">5</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">805</td>
+<td class="shilling bb">8</td>
+<td class="penint bb">7</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">1619</td>
+<td class="shilling bb">8</td>
+<td class="penint bb">0</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound">2219</td>
+<td class="shilling">14</td>
+<td class="penint">10</td>
+<td class="penfr br">⁶⁄₈</td>
+<td colspan="4">&#160;</td>
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+
+<tr class="btgrey">
+<td class="ships">1,592</td>
+<td class="ships">198</td>
+<td class="tonnage">130,026</td>
+<td class="tonnage">14,288</td>
+<td class="lightnr">25.</td>
+<td class="lightname">COVESEA SKERRIES,<a class="fnanchor" href="#Ref5">*</a><span class="pagenum" id="Page432">[432]</span></td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">£193</td>
+<td class="shilling">7</td>
+<td class="penint">0</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound">£419</td>
+<td class="shilling">16</td>
+<td class="penint">8</td>
+<td class="penfr br">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
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+
+<tr>
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+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
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+<td class="pound bb">417</td>
+<td class="shilling bb">3</td>
+<td class="penint bb">1</td>
+<td class="penfr br bb">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
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+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">836</td>
+<td class="shilling bb">19</td>
+<td class="penint bb">10</td>
+<td class="penfr br bb">²⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">643</td>
+<td class="shilling">12</td>
+<td class="penint">10</td>
+<td class="penfr">²⁄₈</td>
+</tr>
+
+<tr class="btgrey">
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="lightnr">26.</td>
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+<td colspan="4" class="blank br">...</td>
+<td class="pound">£27</td>
+<td class="shilling">14</td>
+<td class="penint">11</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£339</td>
+<td class="shilling">17</td>
+<td class="penint">3</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">338</td>
+<td class="shilling bb">6</td>
+<td class="penint bb">4</td>
+<td class="penfr br bb">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">678</td>
+<td class="shilling bb">3</td>
+<td class="penint bb">7</td>
+<td class="penfr br bb">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">650</td>
+<td class="shilling">8</td>
+<td class="penint">8</td>
+<td class="penfr">⁶⁄₈</td>
+</tr>
+
+<tr class="btgrey">
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="lightnr">27.</td>
+<td class="lightname">CHANONRY,<a class="fnanchor" href="#Ref5">*</a></td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">£57</td>
+<td class="shilling">15</td>
+<td class="penint">1</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£284</td>
+<td class="shilling">7</td>
+<td class="penint">1</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">283</td>
+<td class="shilling bb">2</td>
+<td class="penint bb">8</td>
+<td class="penfr br bb">⁶⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td class="pound bb">567</td>
+<td class="shilling bb">9</td>
+<td class="penint bb">9</td>
+<td class="penfr br bb">⁴⁄₈</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td colspan="2" class="br">&#160;</td>
+<td colspan="4" class="balance"><span class="smcap">Balance</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">509</td>
+<td class="shilling">14</td>
+<td class="penint">8</td>
+<td class="penfr">⁴⁄₈</td>
+</tr>
+
+<tr class="btgrey">
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="lightnr">28.</td>
+<td class="lightname">LOCH RYAN,<a class="fnanchor" href="#Ref5">*</a></td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Particular Expense,</td>
+<td class="pound">£176</td>
+<td class="shilling">5</td>
+<td class="penint">7</td>
+<td class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="expenses">Share of General Expense,</td>
+<td class="pound bb">176</td>
+<td class="shilling bb">14</td>
+<td class="penint bb">1</td>
+<td class="br bb">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+<td class="totexp"><span class="smcap">Total Expenditure</span>,</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound">352</td>
+<td class="shilling">19</td>
+<td class="penint">8</td>
+<td>&#160;</td>
+</tr>
+
+<tr class="btgrey">
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td class="right top">*</td>
+<td class="note" id="Ref5"><span class="smcap">Note.</span>—<span class="smcap">Covesea Skerries</span>, <span class="smcap">Cromarty</span>, and
+<span class="smcap">Chanonry</span>, were not lighted till the 15th May, to which is owing the small amount of their Revenue; and
+<span class="smcap">Loch Ryan</span> was not lighted till the 3d of March subsequent to the period embraced in this
+<span class="smcap">State</span>.</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4" class="br">&#160;</td>
+<td colspan="4">&#160;</td>
+</tr>
+
+<tr class="btgrey bb">
+<td class="ships bt">163,166</td>
+<td class="ships bt">50,324</td>
+<td class="tonnage bt">15,926,634</td>
+<td class="tonnage bt">9,577,478</td>
+<td>&#160;</td>
+<td class="right top br"><span class="padr2"><span class="smcap">Total</span>,</span></td>
+<td colspan="4" class="blank br">...</td>
+<td colspan="4" class="blank br">...</td>
+<td class="pound bt">£19,529</td>
+<td class="shilling bt">5</td>
+<td class="penint bt">1</td>
+<td class="penfr bt br">¹⁄₈</td>
+<td class="pound bt">£5591</td>
+<td class="shilling bt">0</td>
+<td class="penint bt">0</td>
+<td class="penfr br bt">²⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="22" class="thinline br">&#160;</td>
+</tr>
+
+<tr class="bt2">
+<td colspan="22" class="center highline2 fsize125">RECONCILEMENT.</td>
+</tr>
+
+<tr>
+<td colspan="18" class="txt recon">The Surplus amounts as above to</td>
+<td class="pound recon bt bl">£19,529</td>
+<td class="shilling recon bt">5</td>
+<td class="penint recon bt">1</td>
+<td class="penfr recon bt">¹⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="18" class="txt recon">And the Deficiency to</td>
+<td class="pound recon bb bl">5,591</td>
+<td class="shilling recon bb">0</td>
+<td class="penint recon bb">0</td>
+<td class="penfr recon bb">²⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="4">&#160;</td>
+<td colspan="14" class="txt recon">Actual Surplus,</td>
+<td class="pound recon bl">£13,938</td>
+<td class="shilling recon">5</td>
+<td class="penint recon">0</td>
+<td class="penfr recon">⁷⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="2">&#160;</td>
+<td colspan="16" class="txt recon"><span class="smcap">Deduct</span>—Fractions short—credited by Bank, &amp;c.,</td>
+<td class="pound recon bb bl">0</td>
+<td class="shilling recon bb">0</td>
+<td class="penint recon bb">1</td>
+<td class="penfr recon bb">¹⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="4">&#160;</td>
+<td colspan="14" class="txt recon">Surplus, as per <a href="#Page415">p. 415</a>,</td>
+<td class="pound recon bl">£13,938</td>
+<td class="shilling recon">4</td>
+<td class="penint recon">11</td>
+<td class="penfr recon">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="2">&#160;</td>
+<td colspan="16" class="txt recon"><span class="smcap">Add</span>—The Receipts derived from other sources besides Light-duties,
+per <a href="#Page419">p. 419</a>,</td>
+<td class="pound recon bb bl">1,893</td>
+<td class="shilling recon bb">17</td>
+<td class="penint recon bb">6</td>
+<td class="bb">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="18">&#160;</td>
+<td class="pound recon bl">£15,832</td>
+<td class="shilling recon">2</td>
+<td class="penint recon">5</td>
+<td class="penfr recon">⁶⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="18" class="txt recon">But there has been expended, besides the amount allocated to the different Lighthouses above,
+as per <a href="#Page425">p. 425</a>,</td>
+<td class="pound recon bb bl">28,311</td>
+<td class="shilling recon bb">9</td>
+<td class="penint recon bb">6</td>
+<td class="penfr recon bb">²⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="4">&#160;</td>
+<td colspan="10" class="txt recon">Amount superexpended, per <a href="#Page425">p. 425</a>,</td>
+<td colspan="4" class="bbd">&#160;</td>
+<td class="pound recon bbd bl">£12,479</td>
+<td class="shilling recon bbd">7</td>
+<td class="penint recon bbd">0</td>
+<td class="penfr recon bbd">⁴⁄₈</td>
+</tr>
+
+<tr>
+<td colspan="22" class="thinline">&#160;</td>
+</tr>
+
+</table>
+
+<div class="padl8 padr8">
+
+<p class="fsize90 hind02"><span class="smcap">Note.</span>—The General Expenses in the above <span class="smcap">State</span>
+are allocated to each Lighthouse in the same proportions as the Particular
+Expenses. The expense of Beacons and Buoys is equally divided by the number of Lighthouses, and the same amount allocated
+to each Lighthouse.</p>
+
+</div><!--padding-->
+
+<p><span class="pagenum" id="Page433">[433]</span></p>
+
+<p class="tabhead">No. III.—<i>Statement shewing the Increase in Tonnage during the Years 1843-44-45-46, over 1842.</i></p>
+
+<table class="tonnage">
+
+<tr>
+<th colspan="4" class="brd">&#160;</th>
+<th class="br bb">Coasting.</th>
+<th class="br bb">Oversea.</th>
+<th class="bb">Total.</th>
+</tr>
+
+<tr>
+<td class="text">The amount of the Tonnage in 1842 was</td>
+<td colspan="3" class="brd">&#160;</td>
+<td class="tons br">11,620,172</td>
+<td class="tons br">6,738,433</td>
+<td class="tons">18,358,605</td>
+</tr>
+
+<tr>
+<td class="text">The amount of the Tonnage in 1843 was</td>
+<td colspan="3" class="brd">&#160;</td>
+<td class="tons br bb">12,190,745</td>
+<td class="tons br bb">7,194,932</td>
+<td class="tons bb">19,385,677</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="3" class="text second brd"><span class="smcap">Increase</span> in 1843 over 1842</td>
+<td class="tons br bl">570,573</td>
+<td class="tons br">456,499</td>
+<td>1,027,072</td>
+</tr>
+
+<tr>
+<th>&#160;</th>
+<th class="bordered">Coasting.</th>
+<th class="bt br bb">Oversea.</th>
+<th class="bt brd bb">Total.</th>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="text">The amount of Tonnage in 1843 was</td>
+<td class="tons bl br">12,190,745</td>
+<td class="tons br">7,194,932</td>
+<td class="tons brd">19,385,677</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="text">The amount of Tonnage in 1844 was</td>
+<td class="tons bl bb br">13,425,614</td>
+<td class="tons br bb">7,737,617</td>
+<td class="tons brd bb">21,163,231</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="4" class="text second brd"><span class="padl3"><span class="smcap">Increase</span> in 1844 over 1843</span></td>
+<td class="tons bl bb br">1,234,869</td>
+<td class="tons br bb">542,685</td>
+<td class="tons bb">1,777,554</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="3" class="text second brd"><span class="smcap">Increase</span> in 1844 over 1842</td>
+<td class="tons br">1,805,442</td>
+<td class="tons br">999,184</td>
+<td class="tons">2,804,626</td>
+</tr>
+
+<tr>
+<th>&#160;</th>
+<th class="bordered">Coasting.</th>
+<th class="bt br bb">Oversea.</th>
+<th class="bt brd bb">Total.</th>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="text">The amount of Tonnage in 1844 was</td>
+<td class="tons bl br">13,425,614</td>
+<td class="tons bl br">7,737,617</td>
+<td class="tons brd">21,163,231</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="text">The amount of Tonnage in 1845 was</td>
+<td class="tons bl bb br">15,566,461</td>
+<td class="tons bb br">9,300,983</td>
+<td class="tons brd bb">24,867,444</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="4" class="text second brd"><span class="padl3"><span class="smcap">Increase</span> in 1845 over 1844</span></td>
+<td class="tons br bb">2,140,847</td>
+<td class="tons br bb">1,563,366</td>
+<td class="tons bb">3,704,213</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="3" class="text second brd"><span class="smcap">Increase</span> in 1845 over 1842</td>
+<td class="tons br">3,946,289</td>
+<td class="tons br">2,562,550</td>
+<td class="tons">6,508,839</td>
+</tr>
+
+<tr>
+<th>&#160;</th>
+<th class="bordered">Coasting.</th>
+<th class="bt br bb">Oversea.</th>
+<th class="bt brd bb">Total.</th>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="text">The amount of Tonnage in 1845 was</td>
+<td class="tons bl br">15,566,461</td>
+<td class="tons br">9,300,983</td>
+<td class="tons brd">24,867,444</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td class="text">The amount of Tonnage in 1846 was</td>
+<td class="tons bl br bb">15,926,634</td>
+<td class="tons br bb">9,577,478</td>
+<td class="tons brd bb">25,504,112</td>
+<td class="br">&#160;</td>
+<td class="br">&#160;</td>
+<td>&#160;</td>
+</tr>
+
+<tr>
+<td colspan="4" class="text second brd"><span class="padl3"><span class="smcap">Increase</span> in 1846 over 1845</span></td>
+<td class="tons br bb">360,173</td>
+<td class="tons br bb">276,495</td>
+<td class="bb">636,668</td>
+</tr>
+
+<tr>
+<td>&#160;</td>
+<td colspan="3" class="text second brd"><span class="smcap">Increase</span> in 1846 over 1842</td>
+<td class="tons br">4,306,462</td>
+<td class="tons br">2,839,045</td>
+<td class="tons">7,145,507</td>
+</tr>
+
+<tr>
+<td colspan="2" class="thinline">&#160;</td>
+<td colspan="2" class="thinline bbd brd">&#160;</td>
+<td class="thinline br bbd">&#160;</td>
+<td class="thinline br bbd">&#160;</td>
+<td class="thinline bbd">&#160;</td>
+</tr>
+
+<tr>
+<td colspan="7" class="thinline">&#160;</td>
+</tr>
+
+</table>
+
+<hr class="chap">
+
+<div class="chapter" id="App10">
+
+<p><span class="pagenum" id="Page434">[434]</span></p>
+
+<h3 class="nobreak"><span class="chapno">APPENDIX, No. X.</span><br>
+<span class="chapname">INSTRUCTIONS TO THE LIGHT-KEEPERS IN THE SERVICE OF THE
+COMMISSIONERS OF NORTHERN LIGHTHOUSES.</span></h3>
+
+</div><!--chapter-->
+
+<p>1. The Lamps shall be kept burning bright and clear every night from
+sunset to sunrise; and in order that the greatest degree of light may be
+maintained throughout the night, the Wicks must be trimmed every four
+hours, or oftener if necessary; and the Keeper who has the first watch shall
+take care to turn the oil-valves so as to let the oil flow into the Burner a
+sufficient time before lighting.</p>
+
+<p>2. The Light-keepers shall keep a regular and constant Watch in the
+Light-room throughout the night. The First Watch shall begin at sunset.
+The Light-keepers are to take the watches alternately, in such manner
+that he who has the first watch one night, shall have the second watch next
+night. The length or duration of the watch shall not, in ordinary cases,
+exceed four hours; but during the period between the months of October
+and March, both inclusive, the first watch shall change at eight o’clock.
+The watches shall at all times be so arranged as to have a shift at midnight.</p>
+
+<p>3. At stations where there is only one Light-room, the daily duty shall
+be laid out in two departments, and the Light-keepers shall change from
+one department to the other every Saturday night.</p>
+
+<p>4. <span class="smcap">First Department.</span>—The Light-keeper who has this department,
+shall immediately after the morning Watch, polish or otherwise cleanse the
+Reflectors or Refractors till they are brought into a proper state of brilliancy;
+he shall also thoroughly cleanse the lamps, and carefully dust the
+Chandelier. He shall supply the Burners with cotton, the Lamps with oil,
+and shall have every thing connected with the Apparatus in a state of
+readiness for lighting in the evening.</p>
+
+<p>5. <span class="smcap">Second Department.</span>—The Light-keeper who has this department
+shall cleanse the glass of the Lantern, lamp-glasses, copper and brass work
+and utensils, the walls, floors, and balcony of the Light-room, and the apparatus
+and machinery therewith connected; together with the Tower stair,
+passage, doors, and windows, from the Light-room to the Oil cellar.</p>
+
+<p><span class="pagenum" id="Page435">[435]</span></p>
+
+<p>6. For the more effectual cleansing of the glass of the Lantern, and
+management of the Lamps at the time of lighting, both Light-keepers shall
+be upon watch throughout the first hour of the first watch every night, during
+the winter period, between the first day of October and last day of
+March, when they shall jointly do the duty of the Light-room during that
+hour. These changes to and from the double watch shall be intimated by
+the Keepers in the Monthly Returns for October and April.</p>
+
+<p>7. At those stations where there are two Light-rooms, each Light-keeper
+shall perform the entire duty of both departments in that Light-room to
+which he may be especially appointed. But after the first hour of the first
+Watch, the Light-keeper who has charge of this watch shall perform the
+whole duty of trimming and attending the Lights of both Light-rooms till
+the expiry of his watch; and in like manner, his successor on the watch
+shall perform the whole duty of both Light-rooms during his watch.</p>
+
+<p>8. The Light-keeper on duty shall on no pretence whatever, during his
+watch, leave the Light-room and balcony, or the passage leading from one
+Light-room to another, at stations where there are two Lights. Bells are
+provided at each Light-room to enable the Light-keeper on duty to summon
+the absent Light-keeper; and if at any time the Light-keeper on duty shall
+think the presence or assistance of the Light-keeper not on duty is necessary,
+he shall call him by ringing his bell, which should be immediately
+answered by the return signal, and the Keeper so called, should repair to
+the Light-room without delay. In like manner, when the watches come
+to be changed, the bell shall be rung to call the Light-keeper next in turn.
+After which the Light-keeper on duty shall, <i>at his peril</i>, remain on guard
+till he is relieved by the Light-keeper in person who has the next watch.</p>
+
+<p>9. Should the bell of the Light-keeper whose turn it is to mount guard,
+happen to be in an unserviceable state, the other house-bell shall be used,
+and some of the inmates of that house shall call the Light-keeper not on
+duty, so as by all means to avoid leaving the Light-room without a constant
+watch during the night.</p>
+
+<p>10. The Principal Light-keeper is held responsible for the safety and
+good order of the Stores, Utensils, and apparatus of what kind soever, and
+for every thing being put to its proper use, and kept in its proper place.
+He shall take care that none of the stores or materials are wasted, and shall
+observe the strictest economy, and the most careful management, yet so as
+to maintain in every respect the best possible light.</p>
+
+<p>11. The Principal Light-keeper shall daily serve out the allowance of<span class="pagenum" id="Page436">[436]</span>
+Oil and other Stores for the use of the Light-room. The oil is to be measured
+by the Assistant, at the sight of the Principal Light-keeper.</p>
+
+<p>12. The Light-keepers shall keep a daily Journal of the quantity of Oil
+expended, the routine of their duty, and the state of the Weather, embodying
+any other remarks that may occur. These shall be written in the
+Journal-Books to be kept at each station for the purpose, at the periods of
+the day when they occur, as they must on no account be trusted to memory.
+On the first day of each month they shall make up and transmit to the
+Engineer a return, which shall be an accurate copy of the Journal for the
+preceding month.</p>
+
+<p>13. The Light-keepers are also required to take notice of any Shipwreck
+which shall happen within the district of the Lighthouse, and to enter an
+account thereof, according to the prescribed form, in a Book furnished to
+each Station for this purpose; and in such account he shall state whether
+the Light was seen by any one on board the shipwrecked Vessel and recognised
+by them, and how long it was seen before the vessel struck. A copy
+of this entry shall form the Shipwreck Return, to be forthwith forwarded to
+the Engineer.</p>
+
+<p>14. A book containing a Note of the Vessels passing each Lighthouse
+daily shall be kept; and an annual Schedule, shewing the number of vessels
+in each month, shall be sent to the Engineer in the month of January.</p>
+
+<p>15. The Monthly and Shipwreck Returns are to be written by the
+Assistant, and the accompanying letters by the Principal Light-keeper.
+The whole shall be carefully compared and signed by both Light-keepers,
+as directed by the printed form, and despatched by post to the Engineer as
+soon as possible.</p>
+
+<p>16. For the purpose of keeping up the practical knowledge of the
+“Occasional Keeper,” he shall be annually called in by the Principal
+Light-keeper to do duty for a fortnight in the month of January; and the
+same shall be stated in the Monthly Letter.</p>
+
+<p>17. The Principal Light-keeper is held responsible for the regularity of
+the Watches throughout the night, for the cleanliness and good order of the
+Reflecting or Refracting Apparatus, Machinery, and Utensils, and for the
+due performance of the whole duty of the Light-room or Light-rooms, as the
+case may be, whether performed by him personally, or by the Assistant.</p>
+
+<p>18. The Principal Light-keeper is also held responsible for the good
+order and condition of the Household Furniture belonging to the Lighthouse
+Board, as well in his own as in the Assistant’s house. This duty extends<span class="pagenum" id="Page437">[437]</span>
+also to the cleanliness of the several apartments, passages, stairs,
+roofs, water-cisterns, store-rooms, work-shops, privies, ash-pits of the dwelling-houses,
+offices, court, and immediate access to the Lighthouse.</p>
+
+<p>19. The Light-keepers shall endeavour to keep in good order and repair
+the Dykes enclosing the Lighthouse grounds, the Landing-places, and
+Roads leading from thence to the Lighthouse and the Drains therewith
+connected, together with all other things placed under their charge.</p>
+
+<p>20. When stores of any kind are to be landed for the use of the Lighthouse,
+the Light-keepers shall attend and give their assistance. The Principal
+Light-keeper must, upon these occasions, satisfy himself, as far as
+possible, of the quantity and condition of the stores received, which must be
+duly entered in the Store-book and Monthly Return-book.</p>
+
+<p>21. The Light-keepers are to make a Report of the quality of the
+Stores, in the Monthly Return for March annually, or earlier should circumstances
+render this necessary; and this Report must proceed upon
+special trial of the several Cisterns of Oil and of the other Stores in detail,
+both at the time of receiving them and after the experience of the winter
+months.</p>
+
+<p>22. At all stations where Peat Fuel is in use, there must be such a
+quantity of Peats provided, that the Stock of the former year shall be a
+sufficient supply to the end of the current year.</p>
+
+<p>23. Should the supply of any of the Lighthouse Stores at any time appear
+to the Principal Light-keeper to be getting short, so as thereby to endanger
+the regular appearance of the Light, he shall immediately intimate
+the same to the Engineer, and he must be guided by prudence in reducing
+the stated number of Burners until a supply be received.</p>
+
+<p>24. The Light-keepers are prohibited from carrying on any trade or
+business whatever. They are also prohibited from having any boarders or
+lodgers in their dwelling-houses, and from keeping dogs at the Lighthouse
+establishments.</p>
+
+<p>25. The Light-keepers are also directed to take care that no smuggled
+goods are harboured or concealed in any way in or about the Lighthouse
+premises or grounds.</p>
+
+<p>26. The Light-keepers have permission to go from home to draw their
+salaries, and also to attend church. The Assistant Light-keeper, on all occasions
+of leave of absence, must consult the Principal Light-keeper as to
+the proper time for such leave, and obtain his consent; in like manner, the
+Principal Light-keeper shall duly intimate his intention of going from home<span class="pagenum" id="Page438">[438]</span>
+to the Assistant Light-keeper;—it being expressly ordered that only one
+Light-keeper shall be absent from the Lighthouse at one and the same
+time.</p>
+
+<p>27. While the Principal Light-keeper is absent, or is incapacitated for
+duty by sickness, the full charge of the Light-room duty and of the premises
+shall devolve upon the Assistant, who shall in that case have access to
+the keys of the Light-room stores, and be held responsible in all respects
+as the Principal Light-keeper; and in the case of the incapacity of either
+Light-keeper, the assistance of the Occasional Light-keeper shall be immediately
+called in, and notice of the same given to the Engineer. Notice of
+any such occurrences to be taken in the Monthly Return, or by special letter
+to the Engineer, should circumstances render this necessary.</p>
+
+<p>28. The Light-keepers are required to be sober and industrious, cleanly
+in their persons and linens, and orderly in their families. They must conduct
+themselves with civility to strangers, by shewing the premises, at such
+hours as do not interfere with the proper duties of their office; it being expressly
+understood, that strangers shall not be admitted into the Light-room
+after sunset. But no money or other gratuity shall be taken from
+strangers on any pretence whatever.</p>
+
+<p>29. The Light-keepers are to appear in their Uniform-dress when any
+of the Commissioners or Principal Officers visit a station, and also on Sunday;—on
+which day, at noon, the weather permitting, the Lighthouse flag
+shall be hoisted by the Assistant Light-keeper, or in his absence by the
+Principal Light-keeper, when it shall remain displayed until sunset.</p>
+
+<p>30. These Instructions are to be read in the Light-room by the Principal
+Light-keeper, in the hearing of his Assistant, on the term days, before
+drawing his salary; and notice thereof taken in the Monthly Returns.</p>
+
+<p>31. In the event of any neglect occurring in the performance of any
+part of the duties required from a Light-keeper, the offending party shall,
+<i>jointly</i> with the other Light-keeper or Light-keepers at the station, send
+immediate notice of the circumstance to the Engineer; and in the event of
+one party refusing or neglecting to concur in giving this intimation, the
+others (whether Principals or Assistants) shall proceed to give the notice in
+their own names.</p>
+
+<p>32. The breach of any of the foregoing Rules and Instructions shall subject
+the Light-keepers to dismissal, or to such other punishment as the
+nature of the offence may require.</p>
+
+<p>33. It is recommended that the Principal Light-keeper, or other Principal<span class="pagenum" id="Page439">[439]</span>
+Officer at the respective Lighthouses for the time being, shall, every Sunday,
+perform the service pointed out for the inmates, by reading a portion
+of the Scriptures, and any other religious book furnished by the Board, and
+the Prayer composed for their use by the Rev. Dr Brunton, one of the
+Ministers of Edinburgh, or other Prayers in any work furnished by the
+Board. For this purpose, the Principal Light-keeper shall invite the
+families to assemble at noon in the Visiting Officer’s room.</p>
+
+<p>34. The Light-keepers are to observe that the above general Regulations
+are without prejudice to any more special Instructions which may be
+made applicable to any particular Lighthouse, or to such orders as may
+from time to time be issued by the Engineer.</p>
+
+<p class="right padr4 highline15 blankbefore75"><i><span class="smcap">Alan Stevenson</span>, Engineer<br>
+for Northern Lighthouses.</i></p>
+
+<p class="noindent fsize80 blankbefore75"><span class="smcap">Northern Lights Office, Edinburgh</span>,<br>
+<span class="padl8"><i>16th June 1847</i>.</span></p>
+
+<p class="right highline2 fsize80"><span class="smcap">Edinburgh</span>, <i>16th June 1847</i>.</p>
+
+<p><span class="smcap">The Commissioners</span> having considered the preceding <span class="smcap">Rules</span> and
+<span class="smcap">Instructions</span>, approve of the same, direct them to be substituted for those
+now in use, appoint them to be signed by the Engineer, and copies of them
+and of this Minute to be issued to the present Light-keepers; direct a copy
+to be delivered in future to each Light-keeper at the time of his appointment,
+that they may understand that they are placed under the department
+and superintendence of the Engineer, who is held responsible for the strict
+observance of the Rules and Instructions, and for their general good conduct;
+that the Engineer has power, in case of neglect or disobedience, instantly
+to suspend and remove any of the Light-keepers, and to report the
+case to the Commissioners, by whom it will be considered, and the offending
+party subjected to dismissal, or such other punishment as the offence
+may merit. In case of a punishment less than dismissal, that circumstance,
+as well as the general conduct of the Light-keeper, will always be taken into
+consideration when any application may be made for superannuated allowance.</p>
+
+<p class="right highline2"><span class="padr10"><i>Extracted from the Minutes by</i></span><br>
+<span class="padr2"><span class="smcap">Alex. Cuningham</span>, <i>Sec.</i></span></p>
+
+<hr class="chap x-ebookmaker-drop">
+
+<div class="chapter">
+
+<p><span class="pagenum" id="Page440">[440]</span></p>
+
+<p class="center highline15 blankbefore8 blankafter8 fsize80">EDINBURGH:<br>
+PRINTED BY NEILL AND COMPANY, OLD FISHMARKET.</p>
+
+<hr class="chap x-ebookmaker-drop">
+
+</div><!--chapter-->
+
+<div class="container w35emmax" id="Plate1">
+
+<p class="right"><i>PLATE</i> I</p>
+
+<img src="images/illo441.jpg" alt="Map of UK and Ireland showing Skerryvore">
+
+<p class="noindent fsize60"><i>Eng<sup>d</sup>. by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></p>
+
+</div><!--container-->
+
+<div class="illotext w20emmax">
+
+<p class="center">CHART<br>
+Shewing the Situation of the<br>
+SKERRYVORE LIGHTHOUSE</p>
+
+<p class="right fsize80 blankbefore75">Stevensons Account of Skerryvore Lighthouse</p>
+
+</div><!--illotext-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w60emmax" id="Plate2">
+
+<p class="right"><i>PLATE II.</i></p>
+
+<img src="images/illo443.jpg" alt="Water depths around Skerryvore" class="bordered">
+
+<p class="right fsize60"><i>Engraved by W. &amp; A. K. Johnston Edinburgh.</i></p>
+
+</div><!--container-->
+
+<div class="illotext w25emmax">
+
+<p class="center">CHART<br>
+of the POSITION of the<br>
+SKERRYVORE ROCKS<br>
+&amp; FOULGROUND<br>
+from a Survey made for the<br>
+COMMISSIONERS OF NORTHERN LIGHT HOUSES<br>
+JAMES RITSON SURVEYOR<br>
+1846.</p>
+
+<p class="right fsize60 blankbefore75">Stevenson’s Account of the Skerryvore Lighthouse.</p>
+
+</div><!--illotext-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="split5050" id="Plate3">
+
+<div class="left5050">
+
+<div class="container w30emmax">
+
+<p class="right"><i>PLATE</i></p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo445.jpg" alt="Low water plan" class="bordered">
+
+<p class="noindent fsize60"><i>James Andrews, Del<sup>t</sup>.</i>
+<span class="righttext"><i>William Miller, Sculp<sup>t</sup>.</i></span></p>
+
+</div><!--container-->
+
+<div class="illotext w25emmax">
+
+<p class="center">PLAN of SKERRYVORE ROCK<br>
+AT LOW WATER OF SPRING TIDES.<br>
+Shewing the site of the Lighthouse Tower, Barracks, Cranes, fresh Water Tanks, Railway &amp;c.</p>
+
+</div><!--illotext-->
+
+</div><!--left-->
+
+<div class="right5050">
+
+<div class="container w30emmax">
+
+<p class="noindent"><i>N<sup>o</sup>. III.</i></p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo447.jpg" alt="High water plan" class="bordered">
+
+<p class="noindent fsize60"><i>James Andrews, Del<sup>t</sup>.</i>
+<span class="righttext"><i>William Miller, Sculp<sup>t</sup>.</i></span></p>
+
+<div class="illotext w25emmax">
+
+<p class="center">PLAN of SKERRYVORE ROCK<br>
+AT HIGH WATER OF SPRING TIDES.</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w50emmax" id="Plate4">
+
+<p class="center">PLATE IV.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo449a.jpg" alt="Lighthouse shapes" class="bordered">
+
+<p class="noindent fsize60"><i>James Andrews, Del<sup>t</sup>.</i>
+<span class="righttext"><i>G. Aikman Sc</i></span></p>
+
+<div class="illotext w30emmax">
+
+<p class="center">CURVES FOR LIGHTHOUSE TOWERS</p>
+
+<p class="center">PARABOLA CONCHOID LOGARITHMIC HYPERBOLA</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<div class="container w40emmax">
+
+<img src="images/illo449b.jpg" alt="Marine dynamometer" class="bordered">
+
+<p class="right fsize60"><i>W. &amp; A. K. Johnston Sculp<sup>t</sup>.</i></p>
+
+<div class="illotext w30emmax">
+
+<p class="center">MARINE DYNAMOMETER, SMALL SIZE, LENGTH 18 INCHES.</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate5">
+
+<p class="center">PLATE V.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo451.jpg" alt="Temporary barrack" class="bordered">
+
+<p class="noindent fsize60"><i>Walter Ferrier Del<sup>t</sup>.</i>
+<span class="righttext"><i>G. Aikman Sculp<sup>t</sup>.</i></span></p>
+
+<div class="illotext w30emmax">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center">TEMPORARY BARRACK.</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="noindent">Barrack Room for Workmen<br>
+Engineer &amp; Foreman&#8217;s Apartments<br>
+Kitchen &amp; Provision Store<br>
+Store for Coals &amp;c.</p>
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate6">
+
+<p class="center">PLATE VI.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo453.jpg" alt="Top of support construction" class="bordered">
+
+<p class="noindent fsize60"><i>Walter Ferrier Del<sup>t</sup>.</i>
+<span class="righttext"><i>G. Aikman Scupl<sup>t</sup>.</i></span></p>
+
+<div class="illotext w15emmax">
+
+<p class="center">Elevation<br>
+Fig. 1</p>
+
+<p class="noindent blankbefore75">TEMPORARY BARRACK.<br>
+TOP FIXTURES.</p>
+
+<p class="center blankbefore75">Plan<br>
+Fig. 2</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate7">
+
+<p class="center">PLATE VII.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo455.jpg" alt="Elevation Skerryvore Lighthouse" class="bordered">
+
+<p class="noindent fsize60"><i>James Andrews, Del<sup>t</sup>.</i>
+<span class="righttext"><i>William Miller, Sculp<sup>t</sup>.</i></span></p>
+
+<div class="illotext w08emmax">
+
+<p class="center">ELEVATION.</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate8">
+
+<p class="center">PLATE VIII.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo457.jpg" alt="Section Skerrywore Lighthouse" class="bordered">
+
+<p class="noindent fsize60"><i>James Andrews, Del<sup>t</sup>.</i>
+<span class="righttext"><i>William Miller, Sculp<sup>t</sup>.</i></span></p>
+
+<div class="illotext w20emmax">
+
+<p class="center">SECTION.</p>
+
+<p class="noindent blankbefore75">84<sup>th</sup>. Course
+<span class="righttext">94<sup>th</sup>. Course</span></p>
+
+<p class="noindent blankbefore75">32<sup>d</sup>. Course
+<span class="righttext">28<sup>th</sup>. Course</span></p>
+
+<p class="noindent blankbefore75">1<sup>st</sup>. Course
+<span class="righttext">19<sup>th</sup>. Course</span></p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate9">
+
+<p class="center">PLATE IX.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo459.jpg" alt="Crane" class="bordered">
+
+<p class="noindent fsize60"><i>G. H. Slight Del<sup>t</sup>.</i>
+<span class="righttext"><i>W. H. Lizars Sculp<sup>t</sup>.</i></span></p>
+
+<div class="illotext w35emmax">
+
+<p class="center">BALANCE CRANE USED AT SKERRYVORE.</p>
+
+<p class="center blankbefore75">Elevation</p>
+
+<p class="center blankbefore75">Plan</p>
+
+<div class="split3367">
+
+<div class="left3367">
+
+<p class="center blankbefore75">Section shewing Rollers</p>
+
+<p class="center blankbefore75">Plan of Rollers</p>
+
+</div><!--left3367-->
+
+<div class="right3367">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">Plan of Pedestal &amp; Frame Circle</p>
+
+</div><!--left5050-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">End view of Crane</p>
+
+</div><!--right5050-->
+
+</div><!--split5050-->
+
+</div><!--right3367-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split3367-->
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container" id="Plate10">
+
+<p class="right"><i>PLATE X.</i></p>
+
+<img src="images/illo461.jpg" alt="Hynish facilities" class="bordered">
+
+<p class="right fsize60"><i>Engraved by W. &amp; A. K. Johnston, Edinburgh.</i></p>
+
+<div class="illotext w35emmax">
+
+<p class="center">PLAN<br>
+of ESTABLISHMENT at<br>
+HYNISH, ISLAND OF TYREE.<br>
+SHEWING THE<br>
+PIER, DOCK, RESERVOIR, LIGHTKEEPERS AND SEAMENS HOUSES &amp;c.</p>
+
+<p class="center blankbefore75">NOTE</p>
+
+<p class="left">The Soundings are marked in a fractional form thus ³²⁄₂₀ in which the
+figures in the place of the Numerator indicate the depth at high water of
+spring tides and those in the place of the Denominator the depth at low
+water of spring tides, the rise of tide being 12 feet.</p>
+
+<p class="right blankbefore75 fsize60">Stevensons account of the Skerryvore Light House</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate11">
+
+<p class="center">PLATE XI.</p>
+
+<p class="right fsize60"><i>Stevenson&#8217;s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo463.jpg" alt="Hynish dock" class="bordered">
+
+<p class="noindent fsize60"><i>Walter Ferrier, Del<sup>t</sup>.</i>
+<span class="righttext"><i>William Miller, Sculp<sup>t</sup>.</i></span></p>
+
+<div class="illotext w15emmax">
+
+<p class="center">HYNISH DOCK.</p>
+
+<p class="center blankbefore75">Elevation.</p>
+
+<p class="center blankbefore75">Section across Gates.</p>
+
+<p class="center blankbefore75">SINGLE BOOM</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate12">
+
+<p class="right"><i>PLATE XII</i></p>
+
+<img src="images/illo465.jpg" alt="First order Fresnel lens" class="bordered">
+
+<p class="noindent fsize60"><i>J. L. Kerr, del<sup>t</sup>.</i>
+<span class="righttext"><i>Eng<sup>d</sup>. by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+<div class="illotext w25emmax">
+
+<p class="right fsize60">Stevenson’s Account of Skerryvore Lighthouse.</p>
+
+<p class="center">ANNULAR LENS OF FIRST ORDER<br>
+SCALE 1¹⁄₈<sup>th</sup>.. FULL SIZE</p>
+
+<p class="center blankbefore75">PLAN</p>
+
+<p class="center blankbefore75">SECTION THROUGH A.B.</p>
+
+<p class="center blankbefore75">TABLE OF ELEMENTS OF LENS<br>
+IN MILLIMÈTRES</p>
+
+<table class="lenselements">
+
+<tr class="bb">
+<th rowspan="2" class="br">N<sup>o</sup></th>
+<th rowspan="2" class="br">RADIUS<br>OF<br>PERIPHERY</th>
+<th rowspan="2" class="brd">RADIUS<br>OF<br>CURVATURE</th>
+<th colspan="2">CO-ORDINATES TO<br>CENTRES OF<br>CURVATURE</th>
+</tr>
+
+<tr class="bbd">
+<th class="br">x</th>
+<th>y</th>
+</tr>
+
+<tr>
+<td class="br">&#8199;1</td>
+<td class="br">140.00</td>
+<td class="brd">&#8199;483.50</td>
+<td class="br">454.79</td>
+<td>&#8199;00.00</td>
+</tr>
+
+<tr>
+<td class="br">&#8199;2</td>
+<td class="br">208.15</td>
+<td class="brd">&#8199;543.60</td>
+<td class="br">488.55</td>
+<td>&#8199;13.08</td>
+</tr>
+
+<tr>
+<td class="br">&#8199;3</td>
+<td class="br">262.40</td>
+<td class="brd">&#8199;598.62</td>
+<td class="br">513.38</td>
+<td>&#8199;31.72</td>
+</tr>
+
+<tr>
+<td class="br">&#8199;4</td>
+<td class="br">309.20</td>
+<td class="brd">&#8199;659.77</td>
+<td class="br">540.71</td>
+<td>&#8199;57.00</td>
+</tr>
+
+<tr>
+<td class="br">&#8199;5</td>
+<td class="br">350.50</td>
+<td class="brd">&#8199;719.84</td>
+<td class="br">565.27</td>
+<td>&#8199;84.86</td>
+</tr>
+
+<tr>
+<td class="br">&#8199;6</td>
+<td class="br">387.44</td>
+<td class="brd">&#8199;779.48</td>
+<td class="br">588.00</td>
+<td>114.93</td>
+</tr>
+
+<tr>
+<td class="br">&#8199;7</td>
+<td class="br">422.23</td>
+<td class="brd">&#8199;846.45</td>
+<td class="br">614.35</td>
+<td>151.50</td>
+</tr>
+
+<tr>
+<td class="br">&#8199;8</td>
+<td class="br">456.23</td>
+<td class="brd">&#8199;911.30</td>
+<td class="br">636.90</td>
+<td>189.55</td>
+</tr>
+
+<tr>
+<td class="br">&#8199;9</td>
+<td class="br">490.00</td>
+<td class="brd">&#8199;980.30</td>
+<td class="br">660.11</td>
+<td>250.17</td>
+</tr>
+
+<tr>
+<td class="br">10</td>
+<td class="br">523.33</td>
+<td class="brd">1057.70</td>
+<td class="br">683.41</td>
+<td>280.60</td>
+</tr>
+
+<tr>
+<td class="br">11</td>
+<td class="br">553.33</td>
+<td class="brd">1136.01</td>
+<td class="br">712.79</td>
+<td>328.00</td>
+</tr>
+
+</table>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w30emmax" id="Plate13">
+
+<p class="right"><i>PLATE XIII</i></p>
+
+<img src="images/illo467.jpg" alt="Dioptric lantern" class="bordered">
+
+<p class="noindent fsize60"><i>G. H. Slight Del<sup>t</sup>.</i>
+<span class="righttext"><i>Eng<sup>d</sup>. by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+<div class="illotext w20emmax">
+
+<p class="right fsize60">Stevenson’s Account of Skerryvore Lighthouse.</p>
+
+<p class="center blankbefore75">REVOLVING<br>
+DIOPTRIC APPARATUS<br>
+FIRST ORDER.<br>
+ONE TWENTIETH OF FULL SIZE.</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate14">
+
+<p class="center">PLATE XIV.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo469.jpg" alt="Revolving dioptric light" class="bordered">
+
+<p class="right fsize60">G. Aikman, Sculp<sup>t</sup>.</p>
+
+<div class="illotext w30emmax">
+
+<p class="center">REVOLVING DIOPTRIC LIGHT OF THE FIRST ORDER.</p>
+
+<p class="center blankbefore75">Plan</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate15">
+
+<p class="center">PLATE XV.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo471.jpg" alt="Fixed dioptric light" class="bordered">
+
+<p class="right fsize60"><i>G. Aikman, Sculp<sup>t</sup>.</i></p>
+
+<div class="illotext w25emmax">
+
+<p class="center">FIXED DIOPTRIC LIGHT OF THE FIRST ORDER.</p>
+
+<p class="center blankbefore75"><i>Vertical Section.</i></p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate16">
+
+<p class="center">PLATE. XVI.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo473.jpg" alt="Position of concave mirrors" class="bordered">
+
+<p class="noindent fsize60"><i>J. Andrews Del<sup>t</sup>.</i>
+<span class="righttext"><i>W. H. Lizars Sculp<sup>t</sup>.</i></span></p>
+
+<div class="illotext w25emmax">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center">1<sup>st</sup>.<br>
+ORDER of LIGHTS.</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="center">CONCAVE MIRRORS.</p>
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate17">
+
+<img src="images/illo475.jpg" alt="Fixed catadoptric light" class="bordered">
+
+</div><!--container-->
+
+<div class="illotext w40emmax">
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">FIXED<br>
+CATADIOPTRIC LIGHT<br>
+OF 1<sup>st</sup>. ORDER<br>
+ONE NINETEENTH OF FULL SIZE</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">PLATE XVII.</p>
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75"><span class="padr1">REFERENCES.</span></p>
+
+<p class="left"><span class="padr1">A B C. CATADIOPTRIC ZONES.<br>
+D E F. COMPOUND DIOPTRIC BELT WITH
+DIAGONAL JOINTS C N M.<br>
+A′ B′ C′. LOWER CATADIOPTRIC ZONES ONE
+DIVISION BEING LEFT OUT FOR
+FREE ACCESS TO THE LAMP.<br>
+F. FOCUS WITH FLAME OF LAMP.</span></p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="center blankbefore75"><span class="padl1">REFERENCES.</span></p>
+
+<p class="left"><span class="padl1">X X X. DIAGONAL SUPPORTS FOR THE
+UPPER CATADIOPTRIC ZONES.<br>
+H H. SERVICE TABLE ON WHICH THE
+LAMP RESTS &amp; WHERE THE KEEPER
+STANDS TO TRIM THE BURNER.<br>
+R R. DIAGONAL FRAME FOR CARRYING
+THE APPARATUS.</span></p>
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<p class="noindent fsize60 blankbefore75"><i>James Andrews, Del<sup>t</sup>.</i>
+<span class="righttext"><i>William Miller, Sc.</i></span></p>
+
+</div><!--illotext-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate18">
+
+<p class="center">PLATE XVIII.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo477.jpg" alt="Fixed catadioptric lens positions" class="bordered">
+
+<p class="noindent fsize60"><i>G. H. Slight Del<sup>t</sup>.</i>
+<span class="righttext"><i>W. H. Lizars Sculp<sup>t</sup>.</i></span></p>
+
+<div class="illotext w20emmax">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center">1<sup>st</sup>.<br>
+ORDER of LIGHTS.</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="center">FIXED<br>
+CATADIOPTRIC<br>
+APPARATUS.</p>
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate19">
+
+<p class="right"><i>PLATE XIX.</i></p>
+
+<img src="images/illo479.jpg" alt="Catadioptric light" class="bordered">
+
+<p class="right fsize60"><i>Eng<sup>d</sup>. by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></p>
+
+<div class="illotext w15emmax">
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<p class="center blankbefore75">CATADIOPTRIC APPARATUS.</p>
+
+<p class="center blankbefore75">FOURTH ORDER</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate20">
+
+<p class="right"><i>PLATE XX</i></p>
+
+<img src="images/illo481.jpg" alt="Mechanical lamp" class="bordered">
+
+<p class="noindent fsize60"><i>Walter H. Ferrier, del<sup>t</sup>.</i>
+<span class="righttext"><i>Engraved by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+<div class="illotext w25emmax">
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<p class="center blankbefore75">MECHANICAL LAMP<br>
+for<br>
+DIOPTRIC LIGHTS<br>
+of<br>
+FIRST ORDER.</p>
+
+<p class="noindent blankbefore75">A WICK HOLDERS<br>
+B GLASS HOLDER<br>
+C SCREW TO RACK D FOR RAISING WICK<br>
+D RACK FOR D<sup>o</sup>.<br>
+E PIPE SUPPLYING OIL TO WICKS<br>
+F COLLAR SUPPORTING BURNERS<br>
+G DRIP CUP<br>
+H RETURN PIPE FOR OIL OVERFLOWING BURNER<br>
+I VALVE BOX<br>
+J CRANK RODS FOR WORKING LEATHER VALVES<br>
+K HINGE OF LID<br>
+L LID OF CISTERN<br>
+M OIL CISTERN<br>
+N SUCTION PIPE<br>
+O WINDING ARBOUR FOR MACHINE<br>
+P BOX FOR MACHINERY<br>
+Q SCREW FOR ADJUSTING LEVEL OF BURNER<br>
+R SERVICE TABLE<br>
+S COUPLING SCREW FOR OIL TUBE<br>
+T UNIVERSAL JOINTS FOR CONNECTING ROD<br>
+U CRANE FOR EMPTYING CISTERN<br>
+V CONNECTING ROD FOR CRANKS</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate21">
+
+<p class="right"><i>PLATE XXI</i></p>
+
+<img src="images/illo483.jpg" alt="Oil pumps" class="bordered">
+
+<p class="noindent fsize60"><i>Walter H. Ferrier, del<sup>t</sup>.</i>
+<span class="righttext"><i>Engraved by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+</div><!--container-->
+
+<div class="illotext w50emmax">
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<p class="left blankbefore75">MECHANICAL LAMP.<br>
+ENLARGED VIEWS<br>
+OF OIL PUMPS.</p>
+
+<p class="center blankbefore75">ELEVATION</p>
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="left blankbefore75">J SUPPORTS OF BURNER<br>
+P CRANK RODS FOR LEATHER VALVES<br>
+M N SUPPORTS FOR CRANK RODS<br>
+L COUPLING<br>
+T UNIVERSAL JOINT</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="left blankbefore75">P CONNECTING ROD FOR CRANKS<br>
+S SUCTION PIPE<br>
+O SQUARE TRAY FOR OVERFLOWING OIL<br>
+Q LID OF OIL CISTERN<br>
+I OIL TUBE</p>
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<p class="center blankbefore75">PLANS AND SECTIONS IN REFERENCE TO OPPOSITE PLATE.</p>
+
+<p class="center blankbefore75">SECTION ON LINE A. B.</p>
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">SECTION OF DISCHARGING CHEST E.</p>
+
+<p class="center blankbefore75">PLAN OF VALVES AT F. F. AND H. H.</p>
+
+<p class="center blankbefore75">PLAN AND SECTION OF PLATE K.</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">PLAN OF UPPER SIDE OF PUMP CHAMBER AT F. F.</p>
+
+<p class="center blankbefore75">SECTION ON LINE C. D.</p>
+
+<p class="center blankbefore75">PLAN OF LOWER SIDE OF PUMP CHAMBER AT H. H.</p>
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+</div><!--illotext-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate22">
+
+<p class="right"><i>PLATE XXII</i></p>
+
+<img src="images/illo485.jpg" alt="Oil pumps for mechnical lamp"  class="bordered">
+
+<p class="noindent fsize60"><i>Walter H. Ferrier, del<sup>t</sup>.</i>
+<span class="righttext"><i>Engraved by W. &amp; A. K. Johnston, Edin<sup>r</sup>.</i></span></p>
+
+<div class="illotext">
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<p class="left blankbefore75">MECHANICAL LAMP<br>
+ENLARGED VIEWS<br>
+OF OIL PUMPS.</p>
+
+<p class="center blankbefore75">ELEVATION</p>
+
+<p class="center blankbefore75">FRONT VIEW OF LEATHER PISTONS AND LEVERS WORKING INTO PUMP</p>
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="left blankbefore75">J SUPPORTS OF BURNER<br>
+P CRANK RODS FOR LEATHER VALVES<br>
+M N SUPPORTS FOR CRANK RODS<br>
+L COUPLING<br>
+T UNIVERSAL JOINT</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="left blankbefore75">R CONNECTING ROD FOR CRANKS<br>
+S SUCTION PIPE<br>
+O SQUARE TRAY FOR OVERFLOWING OIL<br>
+Q LID OF OIL CISTERN<br>
+I OIL TUBE</p>
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<p class="center blankbefore75">PLAN</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate23">
+
+<p class="right"><i>PLATE XXIII</i></p>
+
+<img src="images/illo487.jpg" alt="Clockwork" class="bordered">
+
+<p class="noindent fsize60"><i>Walter H. Ferrier Del<sup>t</sup>.</i>
+<span class="righttext"><i>Eng<sup>d</sup>. by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+<div class="illotext w25emmax">
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<p class="center blankbefore75">CLOCKWORK MOVEMENT OF MECHANICAL LAMP</p>
+
+<p class="center blankbefore75">PLAN OF CLOCKWORK</p>
+
+<p class="center blankbefore75">SIDE VIEW OF CLOCKWORK</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate24">
+
+<p class="right"><i>PLATE XXIV</i></p>
+
+<img src="images/illo489.jpg" alt="Details of mechanical lamp" class="bordered">
+
+<p class="noindent fsize60"><i>James Andrews, del<sup>t</sup>.</i>
+<span class="righttext"><i>Eng<sup>d</sup>. by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+<div class="illotext w35emmax">
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<p class="center blankbefore75">CLOCKWORK MOVEMENT AND BURNER OF MECHANICAL LAMP</p>
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">SECTION OF BURNERS</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">ELEVATION OF WICKHOLDER<br>
+ELEVATION OF INNER TUBE OF GLASS GALLERY</p>
+
+</div><!--right5050-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">PLAN OF BURNERS</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">PLAN OF THE LOWER SIDE OF BURNERS
+SHEWING THE HANDLES OF THE RACKS FOR ELEVATING THE WICKS</p>
+
+</div><!--right5050-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<p class="left blankbefore75">A. UNIVERSAL JOINT OF PUMP ROD<br>
+B. REGULATOR<br>
+C. CHAIN BARREL<br>
+D. CHAIN<br>
+E. DRIVING WHEEL<br>
+F. BEVEL WHEELS FOR HORIZONTAL MOTION<br>
+G. WHEEL WITH COGS FOR LIFTING BELL-HAMMER<br>
+H. HAMMER FOR STRIKING ALARUM BELL<br>
+I. ALARUM BELL WHICH REPEATS WHILE THE PUMP IS WORKING<br>
+K. ENDLESS SCREW ON AXIS OF REGULATOR<br>
+L. WINDING ARBOUR</p>
+
+<p class="center blankbefore75">END VIEW OF CLOCKWORK</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate25">
+
+<p class="center">PLATE XXV.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo491.jpg" alt="Burner flame" class="bordered">
+
+<p class="right fsize60"><i>G. Aikman, Sculp<sup>t</sup>.</i></p>
+
+<div class="illotext w15emmax">
+
+<p class="center">FLAME<br>
+FOR 1<sup>st</sup>. ORDER OF<br>
+DIOPTRIC LIGHTS<br>
+at full size.</p>
+
+<p class="right blankbefore75">GLASS CHIMNEY</p>
+
+<p class="center blankbefore75">PLANE OF FOCUS</p>
+
+<p class="center blankbefore75">GLASS HOLDER</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate26">
+
+<p class="right"><i>PLATE XXVI</i></p>
+
+<img src="images/illo493.jpg" alt="Lantern" class="bordered">
+
+<p class="noindent fsize60"><i>James Andrews Del<sup>t</sup>.</i>
+<span class="righttext"><i>Eng<sup>d</sup>. by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+</div><!--container-->
+
+<div class="illotext w50emmax">
+
+<p class="right fsize80"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<p class="center blankbefore75">LANTERN<br>
+1<sup>ST</sup>. ORDER OF LIGHTS.</p>
+
+<p class="center blankbefore75">PARAPET WALL</p>
+
+<div class="split5050">
+
+<div class="left5050">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">ENLARGED SECTION OF CORNICE</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">ELEVATION &amp; SIDE VIEW OF UPPER PARTS OF
+ASTRAGALS</p>
+
+</div><!--right-->
+
+</div><!--split-->
+
+</div><!--left-->
+
+<div class="right5050">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">ELEVATION &amp; PLAN OF HORIZONTAL
+PARTS OF ASTRAGALS</p>
+
+<p class="center blankbefore75">ELEVATION &amp; SIDE VIEW OF LOWER
+PARTS OF ASTRAGALS</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">ENLARGED SECTIONS OF ASTRAGALS</p>
+
+<p class="center blankbefore75">ENLARGED SECTION OF
+SOLE PLATE &amp; ASTRAGAL</p>
+
+</div><!--right-->
+
+</div><!--split-->
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+</div><!--illotext-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate27">
+
+<p class="center">PLATE XXVII.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo495.jpg" alt="Ardnamurchan lighthouse" class="bordered">
+
+<p class="noindent fsize60"><i>James Andrews, Del<sup>t</sup>.</i>
+<span class="righttext"><i>William Miller, Sculp<sup>t</sup>.</i></span></p>
+
+<div class="illotext w20emmax">
+
+<p class="center">ARDNAMURCHAN LIGHTHOUSE.</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w50emmax" id="Plate28">
+
+<p class="center">PLATE XXVIII.</p>
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<img src="images/illo497.jpg" alt="Plan of Ardnemurchan lighthouse" class="bordered">
+
+<p class="noindent fsize60"><i>H. G. Slight del<sup>t</sup>.</i>
+<span class="righttext"><i>G. Aikman Sculp<sup>t</sup>.</i></span></p>
+
+<div class="illotext w20emmax">
+
+<p class="center">ARDNAMURCHAN LIGHTHOUSE.</p>
+
+<p class="center blankbefore75">PLAN</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w60emmax" id="Plate29">
+
+<p class="right"><i>PLATE XXIX</i></p>
+
+<img src="images/illo499.jpg" alt="Construction of lightship" class="bordered">
+
+<p class="noindent fsize60"><i>James Andrews Del<sup>t</sup>.</i>
+<span class="righttext"><i>Eng<sup>d</sup>. by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+<div class="illotext w40emmax">
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">DIMENSIONS</p>
+
+<table class="standard nomargins">
+
+<tr>
+<th>&#160;</th>
+<th>F<sup>t</sup>.In.</th>
+</tr>
+
+<tr>
+<td class="text">Length between the perpendiculars</td>
+<td class="cntr">80·0</td>
+</tr>
+
+<tr>
+<td class="text">Breadth moulded</td>
+<td class="cntr">20·6</td>
+</tr>
+
+<tr>
+<td class="text">D<sup>o</sup>. extreme</td>
+<td class="cntr">21·0</td>
+</tr>
+
+<tr>
+<td class="text">Depth in hold</td>
+<td class="cntr">10·8</td>
+</tr>
+
+</table>
+
+<p class="center blankbefore75">Burthen in Tons 158⁹⁄₉₄</p>
+
+</div><!--left-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">FLOATING LIGHT VESSEL<br>
+Reduced from Drawings in possession
+of Honb<sup>le</sup>. Corporation of Trinity House
+Deptford Strond.</p>
+
+</div><!--right-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<p class="center blankbefore75">MIDSHIP SECTION</p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w35emmax" id="Plate30">
+
+<p class="right"><i>PLATE XXX</i></p>
+
+<img src="images/illo501.jpg" alt="Covesea Skerries beacon" class="bordered">
+
+<p class="noindent fsize60"><i>G. H. Slight Del<sup>t</sup>.</i>
+<span class="righttext"><i>Engraved by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+<div class="illotext w30emmax">
+
+<p class="center">ELEVATION OF COVESEA SKERRIES BEACON.</p>
+
+<p class="left blankbefore75">N. B. The Letters refer to those in <a href="#Plate31">Plate XXXI.</a></p>
+
+<p class="right fsize60 blankbefore75"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate31">
+
+<p class="right"><i>PLATE XXXI</i></p>
+
+<img src="images/illo503.jpg" alt="Details of construction" class="bordered">
+
+<p class="noindent fsize60"><i>G. H. Slight. Del<sup>t</sup>.</i>
+<span class="righttext"><i>Engraved by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+</div><!--container-->
+
+<div class="illotext w30emmax">
+
+<p class="center">COVESEA SKERRIES BEACON</p>
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">Plan on c d</p>
+
+</div><!--leftsplit-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">Plan on a b</p>
+
+</div><!--rightsplit-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">Section
+showing
+connection of
+cage with
+main Pillars</p>
+
+</div><!--leftsplit-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">Plan on e f</p>
+
+</div><!--rightsplit-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">Section
+showing
+connection
+of Pillars</p>
+
+<p class="center blankbefore75">Section showing
+attachment of Pillars<br>
+to the Sole plates
+and its connection
+with Rocks
+by Bats</p>
+
+<p class="center blankbefore75">Connecting Plate</p>
+
+</div><!--leftsplit-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">Plan on g h</p>
+
+</div><!--rightsplit-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split-->
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+</div><!--illotext-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate32">
+
+<p class="right fsize60"><i>PLATE XXXII</i></p>
+
+<img src="images/illo505.jpg" alt="Stone beacon and iron beacon" class="bordered">
+
+<p class="noindent fsize60"><i>James Andrews Del<sup>t</sup>.</i>
+<span class="righttext"><i>Eng<sup>d</sup>. by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+<div class="illotext w30emmax">
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse</i></p>
+
+<p class="center blankbefore75">STONE BEACON</p>
+
+<div class="split3367">
+
+<div class="left3367">
+
+<p class="center blankbefore75">ELEVATION</p>
+
+</div><!--left3367-->
+
+<div class="right3367">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">PLAN OF COURSE AT E&#160;E</p>
+
+</div><!--left5050-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">SECTION</p>
+
+</div><!--right5050-->
+
+</div><!--split5050-->
+
+</div><!--right3367-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split3367-->
+
+<p class="center blankbefore75">IRON BEACON</p>
+
+<div class="split3367">
+
+<div class="left3367">
+
+<p class="center blankbefore75">ELEVATION</p>
+
+</div><!--left3367-->
+
+<div class="right3367">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">PLAN OF BOTTOM PLATES</p>
+
+</div><!--left5050-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">SECTION</p>
+
+</div><!--right5050-->
+
+</div><!--split5050-->
+
+</div><!--right3367-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split3367-->
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="plates x-ebookmaker-drop">
+
+<div class="container w40emmax" id="Plate33">
+
+<p class="right"><i>PLATE XXXIII</i></p>
+
+<img src="images/illo507.jpg" alt="Types of buoys" class="bordered">
+
+<p class="noindent fsize60"><i>James Andrews Del<sup>t</sup>.</i>
+<span class="righttext"><i>Eng<sup>d</sup>. by W. &amp; A. K. Johnston Edin<sup>r</sup>.</i></span></p>
+
+<div class="illotext w25emmax">
+
+<p class="right fsize60"><i>Stevenson’s Account of Skerryvore Lighthouse.</i></p>
+
+<p class="center blankbefore75">BUOYS</p>
+
+<div class="split3367">
+
+<div class="left3367">
+
+<p class="center blankbefore75">MAST BUOY</p>
+
+</div><!--left3367-->
+
+<div class="right3367">
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">CAN BUOY</p>
+
+<p class="center blankbefore75">NUN BUOY<br>
+FOR WRECKS</p>
+
+</div><!--left5050-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">CASK BUOY</p>
+
+<p class="center blankbefore75">SPHERICAL BUOY</p>
+
+</div><!--right5050-->
+
+</div><!--split5050-->
+
+</div><!--right3367-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split3367-->
+
+<div class="split5050">
+
+<div class="left5050">
+
+<p class="center blankbefore75">NELSON BUOY<br>
+RIVER RIBBLE</p>
+
+</div><!--left5050-->
+
+<div class="right5050">
+
+<p class="center blankbefore75">FAIRWAY BUOY<br>
+RIVER TAY</p>
+
+</div><!--right5050-->
+
+<p class="thinline allclear">&#160;</p>
+
+</div><!--split5050-->
+
+</div><!--illotext-->
+
+</div><!--container-->
+
+<hr class="full">
+
+<div class="tnbot" id="TN">
+
+<h2>Transcriber&#8217;s Notes</h2>
+
+<p>Inconsistent, archaic spelling, hyphenation, typography etc. have been retained, also in proper and geographic
+names and in numbering of illustrations and plates, except as listed under Changes below. Depending on the hard- and
+software used and their settings not all elements may display as intended, and zooming and horizontal and/or
+vertical scrolling may be necessary to view the larger elements.</p>
+
+<p>The book regularly refers to a book published by the author’s father: An Account of the Bell Rock Light-House by Robert Stevenson,
+which is available at Project Gutenberg: https://www.gutenberg.org/ebooks/48414.</p>
+
+<p>Text <span class="illotext">in a dashed box</span> underneath an illustration is text that does not
+occur as such in the source document, but that has been transcribed from inside the illustration for the sake of clarity.</p>
+
+<p>Page xi: the errata have already been corrected in the text; see also under Changes made below.</p>
+
+<p>Page 149, ... the same mass of Mull stone would weigh 4252 tons ...: possibly an error for 4152 tons (which would make the calculation correct).</p>
+
+<p>Page 174: ... somewhat on the same plan as that which is described in the Appendix ...: it is not clear to which Appendix this refers;
+possibly the reference is to Plate XXXI.</p>
+
+<p>Page 252 ff.: Figures 59 and 60 are identical.</p>
+
+<p>Page 271 ff.: Figures 71 and 72 are identical.</p>
+
+<p>Page 276, See fig. 73 and the following paragraph: the description appears to refer to Fig. 71/72 rather than to fig. 73.</p>
+
+<p>Page 362, Conversely, n′ is the origin of the co-ordinates for the grinding centre O of the interior convex refracting
+surface BC, ...: in the illustration (Fig. 110) this appears to be a lower case o.</p>
+
+<p>Page 389, entries for May 14 and 15, 1844: the order as given here is the one printed in the source document; the
+reason for the inverse order is not clear.</p>
+
+<p>Page 422, item Charities &amp;c, number 2: Since last Act: there appears to be a discrepancy between the individual amounts
+paid out and the sub-total given.</p>
+
+<p class="blankbefore75">Changes made:</p>
+
+<p>Footnotes, illustrations and tables have been moved outside text paragraphs; marginalia have been moved to where they appeared to
+fit best in the paragraph concerned.
+In certain tables, Do. or do. have been replaced with the dittoed text.</p>
+
+<p>Some obvious minor typographical and punctuation errors have been corrected silently. Some minor oddities in text lay-out have been
+changed silently for easier readability.</p>
+
+<p>Repeated table and column headers, carry/brought forward, subtotals etc. on page transitions in lists and tables have been removed,
+except partly on the transition from page 423 to 424.</p>
+
+<p>Suter and Souter have been standardised to Suter.</p>
+
+<p>Page xi: the errata listed have already been corrected in the text. The amount L.93,306 : 8 : 10 does
+not occur on line 6 of page 178; the amount L.90,268, 12 : 1 that does occur on line 7 of that page has been replaced
+by L.86,977 : 17 : 7 as given in the Appendix (page 384).</p>
+
+<p>Page 61, Footnote The last column of this table ...: ... will be
+<span class="divide"><span class="num">G·M</span><span class="denom">G·M′</span></span>, by which expression ...
+changed to ... will be <span class="divide"><span class="num">G·M</span><span class="denom">G′·M′</span></span>, by which
+expression ....</p>
+
+<p>Page 231: In these figures, n n shews the reflector flame ... changed to In these figures, n n shews
+the reflector frame ....</p>
+
+<p>Page 267: François Soliel, whom I urged ... changed to François Soleil, whom I urged ...; ... the light derived from the
+accessary part ... changed to ... the light derived from the accessory part ....</p>
+
+<p>Page 281: OA = ρ . cos . OAX. changed to OA = ρ . cos OAX.</p>
+
+<p>Page 284: F is the small flame in the focus ... changed to E is the small flame in the focus ....</p>
+
+<p>Page 413, entry The Commission paid to Collectors ...: £2401 : 7 : 0⁴⁄₈ changed to £2401 : 7 : 3⁴⁄₈ cf. page 429.</p>
+
+<p>Page 430, entry 9. Startpoint, Balance: 462 0 8⁶⁄₈ changed to 462 0 3⁶⁄₈.</p>
+
+<p>Page 355: ... forming a flat parallelopepid ... changed to ... forming a flat parallelopiped ....</p>
+
+<p>Page 399, entry Drum Sand West Buoy, South Point: Bear changed to Bearing.</p>
+
+</div><!--TN-->
+
+<div style='text-align:center'>*** END OF THE PROJECT GUTENBERG EBOOK 75213 ***</div>
+</body>
+</html>
+
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diff --git a/LICENSE.txt b/LICENSE.txt
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+This eBook, including all associated images, markup, improvements,
+metadata, and any other content or labor, has been confirmed to be
+in the PUBLIC DOMAIN IN THE UNITED STATES.
+
+Procedures for determining public domain status are described in
+the "Copyright How-To" at https://www.gutenberg.org.
+
+No investigation has been made concerning possible copyrights in
+jurisdictions other than the United States. Anyone seeking to utilize
+this eBook outside of the United States should confirm copyright
+status under the laws that apply to them.
diff --git a/README.md b/README.md
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+Project Gutenberg (https://www.gutenberg.org) public repository for
+eBook #75213 (https://www.gutenberg.org/ebooks/75213)