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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 ***