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diff --git a/75213-0.txt b/75213-0.txt new file mode 100644 index 0000000..19c1d30 --- /dev/null +++ b/75213-0.txt @@ -0,0 +1,19539 @@ + +*** 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 *** |