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Full text of "Account of the Skerryvore lighthouse .."

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COMMISSIONERS OF THE NORTHERN LIGHTHOUSES. 



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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. 




"rriEP • ton ■ n a n i z o m e n n n " 

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 MULL AND COMPANY, EDINBURGH. 



PEEF ACE. 



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 Sherry wre 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 unfi- 
nished 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 omis- 
sions 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 Light- 
houses, and of whose experience, as the Architect of no fewer than 
twenty-five Lighthouses, including that of the Bell Rock, I had 



PREFACE. 



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, in- 
vented by his late illustrious Brother ; but this general acknow- 
ledgment 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, en- 
titled TraitS de V Eclairage. There are, besides, many other obli- 
gations, 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 deliver- 
ances from danger, I have altogether neglected to record the re- 
markable fact, that, amidst our almost daily perils, during six sea- 
sons 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, 



PREFACE. 



v 



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 thank- 
fulness 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 — Im- 
provements in the mode of illumination — Dioptric Lights — Beacons and Buoys, . 9 

CHAPTER I. 

Topographic notice of the Skerry vore Rock, . . . . . .19 

CHAPTER II. 

Preliminary arrangements and works, including survey of the rocks, and opening of quarries 
from 1831 to 1837 — Survey of the Skerry vore 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 — Em- 
ployment 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 determin- 
ing the length of the beams, and the sites for their fixtures — Pyramid completed — Mode 
of living while erecting the barrack — Shoals of Medusas 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 — 



CONTENTS. 



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 Hog- 
ben — Proceed to Skerry vore — State in which the Rock was found — Cause of the de- 
struction 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 quar- 
rying 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 or 1840. 

Hynish workyard — Hynish pier — The Rock — Life in the barrack — Foundation-pit — Land- 
ing 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 fitting's of the Tower — Light-room appa- 
ratus, and first exhibition of the Light — Removal of the barrack from the Rock — 

Expense, .......... 169 



CONTENTS. 



ix 



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, 1SS— 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 sideral, 232— Fanal a double effet, 234— Fanal a 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 formula; 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 — Cy- 
lindric 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 — Sum- 



CONTENTS. 



mary 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 circum- 
stances, 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 Parabolo'idal 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 Skerry vore Light. 

6. Detailed Account of the Expense of the Skerry vore Lighthouse. 

7. Excerpts from Account of Experiments on the Force of the Waves of the Atlantic and Ger- 

man 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. 
XL 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 Dept- 

ford 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 XXXIL, read Plate XXX., 



PART FIRST. 



ACCOUNT OF THE SKERRYYORE LIGHTHOUSE. 



INTRODUCTION. 



In the course of preparing the account of the building of the 
Skerryvore Lighthouse, it occurred to me, that a short Introduc- 
tion should be prefixed, embracing a concise view of the constitu- 
tion 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 North- 
ern 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 
and improvements made within that period on the mode of illumi- 
nation, of which I propose, in a subsequent part of this volume, to 
give a somewhat detailed account. 

The trade of Scotland had begun to increase very soon after constitution of 
the settlement of the civil war in 1745 : but it was not till the vear ^ e Li 8 h thouse 

7 ^ Board. 

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. 

A 



10 



INTRODUCTION. 



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 ap- 
pointed for carrying this Act into execution were, the Lord Advo- 
cate 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 Commis- 
sioners, 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 as- 
sumption, the board now includes the Sheriffs of the counties of 
Ayr, Fife, Forfar, Wigtown, Sutherland, Kincardine, and Kirk- 
cudbright. 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 Id. per ton on Bri- 
tish 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 



INTRODUCTION. 



]] 



meeting, they adjourned till the 23d of January 1787. Some in- 
convenience 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 regu- 
lated 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 main- 
tenance of the several lighthouses at present under the manage- 
ment 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 Light- 
houses, 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 pass- 
ing every such lighthouse, or deriving benefit thereby, and of one 
penny per ton for each time of passing the Bell Rock Lighthouse, 



12 



INTRODUCTION. 



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 cha- 
racteristic appearance for the Lights ; but it being considered de- 
sirable to have a systematic arrangement in the three kingdoms, 
the Irish Lighthouse Board, as well as the Commissioners, are 
now required te 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 no- 
tice, signify their opinion as to the propriety of the change, or 
the utility of any new Lighthouses submitted for their considera- 
tion. The Act, however, provides, that, if the Commissioners are 
dissatisfied with the opinion of the Trinity- House, they may ap- 
peal 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 exhi- 
bited 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 Cuningpiam, the 
Secretary to the Commissioners. 

Lights established Since the Sumburgliliead Lighthouse in Zetland was lighted 

since 1821 . . 

in the year 1821, with a notice of which the account of the Bell 
Hock Lighthouse concludes, the Commissioners have been engaged 
in the establishment of seventeen new Lighthouses, and the remo- 
delling of several old ones; and they have, more particularly, 



INTRODUCTION. 



13 



effected important changes in the mode of illumination, and have 
begun to place Beacons and Buoys on the coast, They have, be- 
sides, 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 re- 
stricted 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. 

I shall not, in this place, enter on any exposition of the general improvements i 
principles which regulate the illumination of Lighthouses, and still ^ n ^° d n e of llh 
less will it be proper to discuss the advantages of the different me- 
thods of illumination by Reflection and Refraction, as I shall, in 
the sequel, find a more convenient opportunity for speaking some- 
what 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 impor- 
tant changes in Lighthouse apparatus was, unquestionably, the in- 
troduction 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 ap- 
pearance 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 advan- 
tages 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 



14 



INTRODUCTION. 



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 cha- 
racteristic 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 splen- 
did gold medal, in token of his approbation. The only other im- 
provement 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 appa- 
ratus of a fixed Light, in front of which two cylindric shades are 
alternately shut and opened by a vertical movement, so as to pro- 
duce 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 Augustln 
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 con- 
sider this subject; and under its direction a long train of experi- 
ments 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 catop- 



INTRODUCTION. 



15 



trie 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 com- 
mitted to me bv the Lighthouse Board. 

The characteristics of the two systems of illumination by Re- 
flection 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 light-room, 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 



16 



INTRODUCTION. 



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 instru- 
ments. 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 con- 
sequently acts only in a vertical direction, leaving the natural ho- 
rizontal divergence of the light unchanged, and thus distributing 
it with perfect equality in every direction. 

Those two systems of illumination possess advantages and de- 
fects 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 in- 
tensity 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 Inch- 
keith 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 



INTRODUCTION. 



17 



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 verify- 
ing M. Fresnel's results, will be found in the Appendix. The 
lenticular apparatus has been applied at the new Lighthouse sta- 
tions of the Little Ross and the Skerry vore, and, still more re- 
cently, at Covesea Skerries, Cromarty Point, Chanonry Point, 
Loch Ryan, and Girdleness. 

The establishment of a system of Beacons and Buoys on the Beacons and 
coast of Scotland for the purpose of affording additional facilities Euoys ' 
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 com- 
mittee 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 immedi- 
ately 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 con- 
nection with the Lighthouse of that name. Those works, notwith- 
standing many obstacles arising from doubts as to the powers of 
the Board, have been carried on with great vigour. In the Ap- 
pendix, 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. 

B 



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 some- 
what similar work on the Bell Bock, 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 



20 



TOPOGRAPHIC NOTICE OF THE 



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 intro- 
ducing 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 con- 
stituents should visit a reef of rocks called Sherry Vhor, where he 
thought it would be essential to have a Lighthouse. Loud remon- 
strances, 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,* and I, resolve to land upon these bare rocks, in company with 
Mr Stevenson. Pull through a very heavy swell with great diffi- 
culty, 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 

* The Sheriffs-Depute of Lanark and Edinburgh. 



SKERRYVORE ROCK. 



21 



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." 

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".* 
It is about 11 Nautic miles W.S.W I W. of the island of Tyree, 
which is the nearest land, 20 miles W.N.W § N. of the island of 
Iona, 33 miles S \ E. of the Lighthouse of Barrahead, the most 
southern of the Hebrides, and 53| 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 

* According to information for which I am indebted to Captain Yollarid, R.E., of the 
Ordnance Survey. 

c 



22 



TOPOGRAPHIC NOTICE OF THE 



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. 

The importance of the Skerry vore 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 (Skerry vore among the number) of the rough naviga- 
tion 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 ascertain- 
ing 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 pro- 
gress 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 diffi- 
cult 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 



SKERRYVORE ROCK. 



23 



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, ves- 
sels 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 en- 
deavouring to avoid hidden dangers. Thus, that which was for- 
merly 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 ima- 
ginary, 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 Skerry v ore 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. 
In 1804. A Brig, M'lver, master, lost off Hough; crew saved. 



TOPOGRAPHIC NOTICE OF THE 



1806. Ellen of Bath, Paterson, master, of 90 tons, lost off Bala- 
pliuil, 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, Eoss, 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. 



SKERRYVORE ROCK. 



25 



In 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 over- 
board 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 oppor- 



26 



TOPOGRAPHIC NOTICE OF THE 



tunity 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 
Skerry vore, 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 Skerry vore. 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, 



SKERRYVORE ROCK. 



27 



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 direc- 
tion, 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 be- 
tween 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 Macken- 
zie, Fresnel, and Stevenson. 

The rock called Boinshly lies about 3J miles from Skerryvore, 
and is of considerable extent. The origin of the names of the dif- 
ferent 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 in- 
dicative 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 



28 



TOPOGRAPHIC NOTICE OF THE 



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 ac- 
cidents 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 espe- 
cially 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 con- 
stantly surrounded, and which, in the heavy swells which some- 
times 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, 



SKERRYVORE ROCK. 



29 



although ahout 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 2| 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 re- 
spect 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 imme- 
diately 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 de- 
termined during the survey, amounting to no fewer than 130. The 

D 



30 



TOPOGRAPHIC NOTICE OF 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 2^ to 8^ fathoms at low 
water of spring tides. 

The surface of the main or principal rock, on which the Light- 
house has been placed, measures, at the lowest tides, about 280 feet 
square. It is extremely irregular, and is intersected by many gul- 
lies 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 sub- 
marine 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 ex- 
tremely 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 car- 



SKERRYVORE ROCK. 



31 



ried 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 exten- 
sive 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 sur- 
face, a feature that existed to so remarkable an extent as to have 
proved throughout the whole duration of the work, but more espe- 
cially 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 land- 



32 



TOPOGRAPHIC NOTICE OF THE 



ings 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 Skerry vore 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 shel- 
ter ; but different kinds of sea-plants grow upon it, in great abun- 
dance, at and below the low water mark. These plants are, doubt- 
less, 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 diffi- 
cult 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 spe- 
cimen 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 geo- 
logy of the rock, it may be interesting also to notice, that a con- 
siderable mass of foreign matter, somewhat resembling, in its 



SKERRYVORE ROCK. 



33 



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 contain- 
ing 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 Philo- 
sophy in King's College, Aberdeen, I received from him an ana- 
lysis of the substance, and a concurrence in the opinion I had 
formed as to its containing animal matter; and Dr Fleming, in- 
deed, expressed his belief that the matter in question is the indu- 
rated soil of birds, and had been deposited when the reef was more 
extensive, and the resort, and probably the breeding-place of sea- 
fowls.* 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, with- 
out coming to the conclusion, that the uncovered surface of Skerry- 
vore Rock must at some distant period have been much more exten- 
sive than at present, so as to permit the deposit to go on in an in- 
terior basin or lagoon, sheltered from the waves, and somewhat simi- 
lar to those which Dr Darwin has described as characteristic of the 
Coral Isles of the Pacific. This supposition seems not at all impro- 
bable, 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 

* Dr Fleming has since obtained from Ichaboe indurated bird-soil or guano, closely re- 
sembling that from the Skerryvore. 

6 



34 



TOPOGEAPHIC NOTICE OF THE 



gradually yielded to the action of the sea, leaving the harder por- 
tions 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. 

Another remarkable feature which I observed in the Skerry- 
vore 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 horse- 
bean, 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 im- 
bedded. 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 resort- 
ed to it. 

About three miles to the westward of Skerry v ore lie Macken- 
zie'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, 



SKERRYVORE ROCK. 



35 



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 light- 
houses ; 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 llynish 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 ob- 
servations 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 be- 
tween 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. 

In this chapter I shall very briefly notice those preliminary ar- Surrey of th 

\ . . Skerryvore 

rangements which may be said to have been m a great measure pre- Rocks, 
paratory to the commencement of the work itself. It has been al- 
ready 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 re- 
port 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 com- 
bining with the ordinary details required for a Chart, the minute 
accuracy in regard to surface and levels, which are always neces- 
sary for the purposes of the Engineer. 

E 



38 



PRELIMINARY WORKS. 



The first step was the measurement of a base line in the low 
lands of the adjoining Island of Tyree, which, owing to the dis- 
tance 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, be- 
came necessary, as the land objects were too distant, and their rela- 
tive positions were such as to render it difficult by observations from 
them alone to determine any stations on the sea. Buoys were there- 
fore 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 be- 
tween these buoys were afterwards used as the bases of ima- 
ginary 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.* 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 obser- 
vations 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 refer- 
ence to the high or low water of a given tide. Accurate measure- 
ments, and minute sections, were also made of the rocks in reference 
to the tide-level, and more especially of the main rock, on which 



* Vide Stevenson's Marine Surveying and Hydrometry. Edinburgh, 1842, p. 144, 



PRELIMINARY WORKS. 



39 



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. 

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 



40 



PRELIMINARY WORKS. 



nature of the bottom, accurately laid down ; and our experience 
during the course of the work, more than once shewed how es- 
sential 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 mi- 
nutely 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 parti- 
cular, 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 exist- 
ence 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 knit- 
ting stockings. 

Disadvantage* of 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 neigh- 
bouring Island of Tyree. This island is unhappily destitute of any 



PRELIMINARY WORKS. 



41 



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.* Nor is its interior 
more attractive ; for although some parts of the soil when culti- 
vated 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 pre- 
paration 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 trans- 
ported, 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. 

In the course of the survey, much attention had been bestowed Pier and work- 
upon the selection of a convenient place for a workyard in Tyree Tyree!* Hjmsh 
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, 

* A Description of the Western Islands of Scotland, &c, by M. Martin, Gent. London, 
1703. Vide 2d Edition of 1716, p. 267. 



42 



PRELIMINARY WORKS. 



however exposed it may be, if compared with creeks elsewhere 
dignified with the name of Harbour, certainly affords as good pro- 
spect 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 Skerry- 
vore 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 Another most important point of inquiry was regarding the 
materials for building the Lighthouse ; and on this subject the sug- 
gestions 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 suc- 
cess, 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 esta- 
blished 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 (techni- 
cally called dries and cutters), the frequent deceptions attending 
the opening of new quarries, the excessive hardness and unwork- 
able 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 



PRELIMINARY WORKS. 



43 



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 work- 
yard, 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 arrange- 
ments 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* 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 com- 
mittee of their number, as well as that of an Engineer specially 
entrusted with the management of the work. 

At the meeting of the Board, on the 8th December 1837, a skenyvore c m- 

•,.«.! . , ,. , •! mittee appointed. 

Committee ot their number was accordingly named, to superintend 
the erection of the Lighthouse. This Committee consisted of — 
Robert Bruce, Esq., Sheriff of Argyllshire ; Andrew Murray, 

* Blocks rough from the quarry, which are dropt or thrown promiscuously into the sea. 



44 



PRELIMINARY WORKS. 



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 Com- 
mittee, 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 esti- 
mate 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 build- 
ing 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 ex- 
pense 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 tins chapter I purpose, in the first place, to make a few ob- 
servations 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 con- 
siderations 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 command- 
ing 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 ascer- 
tained, 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 de- 

F 



46 



ON THE CONSTRUCTION OF 



termined 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 precau- 
tion of retaining additional Lightkeepers, and of having dupli- 
cates or even triplets of those parts of the apparatus that are 
liable to be injured. Of such circumstances, corresponding ex- 
tension 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 Eddy stone, the Bell Rock, and the Skerry vore 5 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, in- 
volves a corresponding increase in the supply of water, fuel and 
other provisions, requiring much additional stowage. So far, there- 
fore, 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 En- 
gineer in framing a design for a Light Tower which is exposed 



LIGHTHOUSE TOWERS. 



to the force of the waves, refers solely to the stability of the 
building. 

The first observation which must occur to any one who con- 
siders 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 in- 
ventor, 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, 



48 



ON THE CONSTRUCTION OF 



that during five summer months of 1843 and 1844, the aver- 
age 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 ob- 
served on the Bell Rock was 3013 lb., or one-fourth part less than 
that of Skerryvore. But these experiments have not been con- 
tinued long enough as yet to render them available for the En- 
gineer. 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 nu- 
merous cases which observation collects, and which reason ar- 
ranges, 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 circum- 
stances, we may carry in our recollection ; and by comparing them 
with what has been observed at places where we know that arti- 
ficial 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 



LIGHTHOUSE TOWERS. 



49 



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 deter- 
mined, 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 



50 



ON THE CONSTRUCTION OF 



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 pheno- 
mena, 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 deter- 
mine the strength of a comparatively light object which shall be 
able to sustain the same shock, which we know, by direct experi- 
ence, 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 un- 
changeable 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.* 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. 

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 al- 
ready stated, one of the utmost difficulty, and can be solved by ex- 

* It was chiefly on these grounds that the Commissioners of Northern Lights, after con- 
sulting 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 pro- 
posal to build an Iron Pillar at the time that the erection of the Skerry vore Lighthouse was 
determined on in 1835. 



LIGHTHOUSE TOWERS. 



51 



perience alone, directed by that natural sagacity which Smeaton, in 
his account of his own thoughts on the subject, with much naivete, 
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 ap- 
peal to such experience as we possess, and apply to the largest ver- 
tical 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* 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 cylin- 
der. 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 re- 
sist the force of the waves, will be almost exactly equal to the pres- 
sure 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 times. In order, there- 
fore, to endanger the stability of the solid by overturning it, the pres- 
sure, instead of being 240 tons, must be 600 tons.f 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 be- 
ing displaced by the pressure of the waves, causing it to slide along 
the surface of the Rock, owing to deficiency of friction between 

* This reduction seems to be warranted by the results of some experiments of Bossut. 
t This is the product of 240 tons, by the ratio of 2"5. 



52 ON THE CONSTRUCTION OF 

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. Redelet,* that the friction of a block of stone 
sliding on a chiselled floor of rock is equal to xoths 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.f 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, 

* L'art de batir. 

I The number 168 is x 7 <jths 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. 



LIGHTHOUSE TOWERS. 



53 



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 unreason- 
ably conclude, that, in designing such a tower, it is safe to assume 
a mass which our own judgment and recorded facts seem to con- 
cur 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. 

There are several circumstances, however, which tend to in- 
crease 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 resist- 
ance to the forces which assault the building. Thus a parallel o- 
piped 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 hav- 
ing 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 cir- 
cumstances 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, be- 
cause 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 

G 



54 



ON THE CONSTRUCTION OF 



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 sec- 
tion 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 re- 
volving 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 con- 
siderations, 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 as- 
saulted 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 



LIGHTHOUSE TOWERS. 



55 



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 out- 
line of the successive frusta composing the Tower ; and hence, we 
can hardly doubt, has really arisen in the mind of Smeaton the beau- 
tiful 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 con- 
ditions 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 suit- 
able for his great work. In that " Narrative" (§ 81), he seems 
to imply, that the trunk of an oak was the counterpart or anti- 
type of that form which his (§ 246) " feelings, rather than calcu- 
lations" 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 al- 
though 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 pro- 
perties in both. It is obvious, indeed, that Smeaton has uncon- 
sciously contrived to obscure his own clear conceptions in his at- 



56 



ON THE CONSTRUCTION OF 



tempt 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, through- 
out his reasonings on this subject, he does not appear to have re- 
garded those properties of the tree which he has most fitly charac- 
terized as " its elasticity," and the " coherence of its parts." One 
is tempted to conclude that Smeaton had, in the first place, rea- 
soned 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 concep- 
tions which a large class of minds can never receive, that he has 
misrepresented his own mode of reasoning. In the paragraph pre- 
ceding 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 ques- 
tion throughout in a masterly style. 

In a word, then, the sum of our knowledge appears to be con- 
tained in this proposition — That, as the stability of a sea-tower 
depends, cseteris 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 ap- 
proaching to parallelism with it. And this is, in fact, a general de- 
scription of the Eddystone Tower devised by Smeaton. 

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 



LIGHTHOUSE TOWERS. 



appear to have had the same conceptions of the solid of stability 
that were present to the mind of the modern Engineer of the Eddy- 
stone 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, accord- 
H ing to Egyptian conceptions. This symbol so closely and 
strikingly resembles the general appearance of the Eddy- 
flB stone, 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 circum- 
stances, 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 applica- 
tion 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 desir- 
able, 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 consider- 
able height, and that the light should command an extensive range. 
It was, therefore, from the first consideration of the subject, deter- 
mined 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 pro- 



58 



ON THE CONSTEUCTION OF 



posed 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 sup- 
pose 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 geometri- 
cal 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. View- 
ing 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 horizon- 
tal 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. 



LIGHTHOUSE TOWERS. 



59 



It so happens, that the diameter adopted is nearly the greatest 
which the Rock affords ; for, although a glance at the accompany- 
ing plan of the Rock at high water (Plate, No. III.) would lead 
one to suppose that a more extended base might have been ob- 
tained, 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 superincum- 
bent mass, and might eventually have led to the destruction of the 
Tower. 

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 1385 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 deter- 
mine the nature of the line which should connect the extremities 
of the top and bottom radii of the Pillar. As I had already con- 
cluded that this line must, as in the Eddystone and Bell Rock, be 



60 



ON THE CONSTKUCTION OF 



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 
No. 2. base of the Tower. These two points, as will be better 
pi understood by means of the accompanying diagram 

I (No. 2), are separated from each other vertically 120*25 

II feet, and are horizontally distant from each other 13 
/ j | feet, which is the excess of the bottom radius over that 

J I of the top of the shaft, or the consequent amount of 
/ I what may be called the aggregate slope of the wall. 
L.!-2i-- ' - s i 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 re- 
jected, from its too near approach to a conic frustum, and the ex- 
cessive 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 con- 
dition 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* 

* The solid, in this case, would have been formed by the revolution of the interior con- 
choid 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 



LIGHTHOUSE TOWERS. 



61 



frusta, are nearly identical in form ; and of these two curves I pre- 
ferred 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 :* 
which shews a slight superiority of the Hyperbolic over any of 
the other forms. 



Hypothetical 
Towers. 


Height 
of the 
Tower 
in feet. 

(H.) 


Diarr 

at Base 
in feet. 


teter 

at Top 
in feet. 


Volume of 
solid Tower 
in cubic 
feet. 
M. 


Distance of 
centre of 
Gravity 
from Base. 
G. 


H 

G 


Economic 
Advantage. 

G-M. 
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 



The shaft of the Skerryvore Pillar, accordingly, is a solid, ge- 
nerated by the revolution of a rectangular hyperbola about its as- 
symptote as a vertical axis. Its exact height is 120*25 feet, and 

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, 1 determined 
to adhere to my original purpose of adopting the latter curve as my guide. 

* The last column of this table is derived as follows : — Assuming that the economic advan- 
tage 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 ^^j- may be taken as an indication of the economic advantage of 

the proposed tower. Let q77^[ > 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 Q.j^, , by 
which expression, the last column in the table was calculated. 

H 



62 ON THE CONSTRUCTION OF 

its diameter at the base 42 feet, and at the top 16 feet. The or- 
dinates 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.* Immediately above this level the 
walls are 9*58 feet thick, whence they gradually decrease through- 
out 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. 

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 Skerry- 
vore, 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. 

* At the rate of 13"62 cubic feet of granite to a ton. 



- 



LIGHTHOUSE TOWERS. 63 



No. 3. 




EDDYSTONE. 



SKERRYVORE. 



BELL ROCK 



Lighthouse. 


Height of 
Tower above 
first entire 
course. 
(H) 


Contents of 
Tower. 


Diar 
at Base. 


aeter 
at Top. 


Distance of 
centre of 
gravity in feet 
from Base. 
(G) 


H 

G 


Eddystone, 
Bell Rock, 
Skerryvore, 


68 
100 
138-5 


13,343 
28,530 
58,580 


26 
42 
42 


15 
15 
16 


15-92 

2359 
34-95 


4-27 
4-24 
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 



I 



64 ON THE CONSTEUCTION OF 

contrasted figures of the three buildings, it will be at once ob- 
served 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, cceteris 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 per- 
fectly 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, pos- 
sess 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.* This ver- 



* 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 



LIGHTHOUSE TOWERS. 



65 



tical pressure operates in preventing any stone being withdrawn 
from the wall in a manner which, to my mind, is much more satis- 
factory than an excessive refinement in dovetailing and joggliiig, 
which I consider as chiefly useful in the early stages of the pro- 
gress of a work, when it is exposed to storms, and before the su- 
perstructure is raised to such a height as to prevent seas from 
breaking right over it. 

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 propor- 
tion 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 considera- 
tion 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 j oggling, 
which the adoption of a more concave outline (in which the ver- 
tical pressure could not have been so advantageously transmitted 
to the outer stones of the base), would perhaps have rendered ad- 
visable. In the case of the Bell Rock, however, whose con- 
struction, 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 corn- 
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." 



66 



ON THE CONSTRUCTION OF 



mencement of the building and the attainment of a height suffi- 
cient 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 imvards, 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 pos- 
sible 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 succes- 
sive 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 in- 
volving a greater evil. The evil has already been noticed, and 
consists in the thrust of the lowest stone (which is of course in- 
clined 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 



LIGHTHOUSE TOWERS. 



67 



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 build- 
ing 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 counter- 
act 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 prac- 
tice, 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 Eddy stone 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.* When the 

* Account of the Bell Rock Lighthouse, Plate XXI. 



68 



ON THE CONSTRUCTION OF 



great pressure of the superstructure of these Towers, however, and 
the effect of the mortar are considered, there seems little probabi- 
lity of one course being dislocated, in defiance of the friction re- 
sulting from the weight of the column. An impulse sufficient to 
produce such an effect would tend to overset the whole super- 
structure from mere deficiency in weight, and in this case the 
joggle would have little effect. But if joggles be thought neces- 
sary 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 dress- 
ing 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 in- 
serted, 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 ex- 
clude 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 to- 



LIGHTHOUSE TOWERS. 



69 



gether 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 in- 
duced 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. 



i 



CHAPTER IV. 



OPERATIONS OF 1838. 
The hazardous nature of the anchorage, and the consequent Temporary bm- 

A rack on Rock. 

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 accommoda- 
tion of the people engaged in the work, with the view of render- 
ing the operations less dependent on the state of the sea, which 
varied with every wind. So important, indeed, did this object ap- 
pear to me, that I was at times apt to look upon it as an indis- 
pensable 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 repre- 
sented in Plate No. V., and is particularly described in the Appen- 
dix 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 



72 



OPEKATIONS OF 1838. 



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 dis- 
comforts of this habitation I shall at some future time have occa- 
sion 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 accord- 
ingly 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 Ma- It was also necessary to provide a large assortment of quar- 
riers' and masons' tools of every kind ; and many cranes, crabs, 
anchors, mooring buoys and other implements were ordered, ac- 
cording to detailed specifications and drawings. These prepara- 
tions necessarily occupied the early part of the year 1838. 



OPERATIONS OF 1838. 73 

From the extent of the foul ground round the Skerryvore, and steam Tender for 
the absence of good harbours in the neighbourhood, it was fore- 
seen at the outset that the operation of landing about 6000 tons of 
materials on the Rock could not be accomplished by means of sail- 
ing 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, appli- 
cation 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 navi- 
gation. 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 build- 
ing 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 ad- 
vantages which are always derived from the use of steam-power. 
As it was, we had much to bear from the smallness of the Light- 
house 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 



74 



OPERATIONS OF 1838. 



pitching, was, to landsmen, by no means the least evil to be en- 
dured. 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 lands- 
men ; 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 About the middle of April, arrangements were made with Mr 
men ges ° ° r Charles Neilson, a builder in Aberdeen, to select granite masons 
for the works at the Skerryvore, as it was expected that the opera- 
tion 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 Aber- 
deen ; it is, at all events, expected, that they will on no account 
exceed the rate of 3s. lOd. 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 



OPERATIONS OF 1838. 



75 



the families or relatives of the workmen as may require it ; and 
that their wages shall be fully settled monthly, deducting the sub- 
sistence 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." 

Early in the month of May the preparation of the wooden bar- Progress of the 
rack for the Eock had been completed, and the whole had been set son's* operation^ 
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 ship- 
ment, 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 j anker 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 Aber- 
deen. 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 pre- 
pared for use on the Eock. 

In providing the means of efficiently carrying on so many com- 
plicated operations in a situation so difficult and remote, it is im- 
possible, 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. Ac- 
cordingly, although I had bestowed all the forethought which I 
could give to the various details of the preparation for the season (of 



76 



OPERATIONS OF 1838. 



which I found it absolutely indispensable to be personally aware, 
even to the extent of the cooking dishes), new wants were continu- 
ally springing up, and new delays occasioned, so that it was not until 
^kerrvv f re 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 sea- 
son's operations. Next morning we moored off Hynish Point about 
three o'clock, and, from the roughness of the passage, were not un- 
willing 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 build- 
ings 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 in- 
closed 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 morn- 
ing 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. 

Lny down Moor- 26th June. — Our first step was to lay down moorings for the 

ings, and try to . , 

land on the Rock, 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 



OPERATIONS OF 1838. 



77 



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. 

27 th June. — Next day also being unsuitable for attempting to Driven to Muii. 
reach the Skerry vore, 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 Midi, with the view of establishing quar- 
ries 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 land- 
ing on the Skerryvore ; but as the wind soon fell calm, we did very 
little good until evening, when some progress was made in stretch- 
ing across towards the Rock. 

28th June. — At nine this morning, we reached our moorings at First day's work 

& ' 6 on the Rock. 

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 

K 



78 



OPEKATIONS OF 1838. 



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 unac- 
countable 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 con- 
sideration, 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 



OPERATIONS OF 1838. 



79 



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 pro- 
visions, 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. 

It seldom happens that human expectations are fully realised, Shipment of an 

. i • i • • i • i the materials at 

especially m matters which excite a strong interest in the mind, Glasgow and 
and thus lead one to desire a more rapid progress than usual. Greenock - 
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 some- 
what 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 Reach Tyree. 
we landed at Hynish, in Tyree. Here I found some farther pro- 
gress 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 be- Driven to Mun. 
fore a very heavy sea to Tobermory. We immediately sailed again, 



80 



OPERATIONS OF 1838. 



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 ar- 
rival 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 

Return to Tyree. along with that vessel for Hynish, where she was immediately dis- 
charged 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. 

7th August. — We this morning took on board various tools 
and implements for the Rock, together with workmen to the num- 
ber 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 

First good day's may be called our first entire day of work on the Rock. Our 

work on the Rock. . , 1 , . 7 7 , 

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 mate- 
rials ; 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 con- 
siderable 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 3^ inches diameter, a depth of about 3 inches was bored 



OPERATIONS OF 1838. 



81 



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 Eock 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 
Eock 'was at this place a good deal lower than the site afterwards 
adopted for the barrack. The high water of spring-tides rose 2^ 
feet upon the legs or main beams ; but this site had many advan- 
tages, as it left more room for operations at or near the Tower 
itself than could have been obtained in any other position. 

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 



82 



OPERATIONS OF 1838. 



vessels. 



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 
^et^penfto the 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 con- 
sequence 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 vesssel 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 inevita- 
ble loss of the vessel and of every soul on board. In this dilemma 



OPERATIONS OF 1838. 



83 



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 occa- 
sion 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 ex- 
tent of the danger ; and to avoid confusion, they were not per- 
mitted 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 Skerry- 
vore 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 H )' nish in 
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 pro- 
tecting care of Almighty God, in preserving us through such peril. 



84 



OPERATIONS OF 1838. 



Return to the 
Rock, and have 
six days of good 
weather. 



Detained by bad It was not until Monday the 13tli that a landing was again 

weather four days ^ .it, 

at Hynish. ettected 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. 

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 1| 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. 



Erection of the 
Pyramid of the 
wooden Bai'rack. 



OPERATIONS OF 1838. 



85 



For ascertaining the exact length of each of the six beams, Mode of de- 
which formed by their union a pyramid of about 21° 30' of in- length of the 
clination, and, at the same time, for determining its exact place, SeTfor Aei? e 
in reference to the centre of the hexagon, both of which elements fixtures, 
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 



No. 4. 




a vertical rod of iron firmly batted into the rock, so as to coin- 
cide 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; //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 re- 
present the position of the beam, and, at the same time, give the 

L 



86 



OPERATIONS OF 1838. 



inclination of the surface e e, which must be at right angles to the 
axis of the beam //. In this way, bj repeated trials, the surface 
was truly dressed to its proper inclination, and the length ascer- 
tained 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 //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.* 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-hoard 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 : — 



No. 5. 




No. 6. 



No. 7. 





* 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. 



OPERATIONS OF 1838. 



87 



These holes were bored with jumpers, 3| 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 ma- 
terial, 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 out- 
side 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 erec- 
tion 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. 

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 (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 



OPERATIONS OF 1838. 



No. 8. 




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 

No. 9. 




embraced the exterior of the whole. It was obvious, that if the 
sliding-board (described on p. 85) had indicated the true inclina- 
tion of the seat on the Rock for the end of the beam to rest on, 



OPERATIONS OF 1838. 



89 



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. 

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 after- 
noon 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 suspen- 
sion, 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 



90 



OPERATIONS OF 1838. 



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 secur- 
ing 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. 

pieted id C ° m " ^ n Saturday the 18th August, the pyramid having been suc- 

cessfully erected, the men were busied for two hours, before em- 
barking for the vessel, in collecting and lashing all the loose mate- 
rials 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 During the week, while we had been engaged in fitting up the 

while erecting & ' b ° & r 

the Barrack. 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 singu- 
lar. 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 substitu- 
tion of beer for tea. Dinner occupied no longer time than break- 
fast, 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 



OPERATIONS OF 1838. 91 

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 ma- 
terials of breakfast were again produced under the name of supper ; 
but the heaving of the vessel damped the animation which at- 
tended 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 close- 
ness 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. 

One beautiful morning, during our stay of six days at the Shoals of Medusa 
Rock, we had a visit from a shoal of small fish, whose novel ap- en ' 
pearance made me take them for a fleet of some species of Nauti- 
lus. 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. 



92 



OPERATIONS OF 1838. 



Driven by a gale 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 in- 
creased 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, 

Return to Hynish, on the morning of which day we again made Hynish Bay : but the 

and are driven to ° . 

Coil. wind, which had been less violent when we started from Tober- 

mory 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 un- 
palatable 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 NW., we sailed from Loch Erin at daybreak, and 

Return to the reached the Skerryvore at ten. We now discharged all the re- 

Roclc. 

maining 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 habit- 
able part till next spring. 

%lst 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 



OPERATIONS OF 1838. 



93 



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 Driven to Tyree. 
two, in what, to landsmen, was a most distressing sea, we slipped 
and ran for Hynish Bay, which we reached at 5^ p.m. The wea- 
ther 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 unfa- Return to the 
vourable day, in remaining till three o'clock, during which time Rock 
we fixed the whole of the horizontal braces, and got everything 
which we had not been able to secure in its place firmly lashed Horizontal braces 
to the ring-bolts on the Rock, after which we were forced to leave fixed - 
it for Mall. The gale continued to blow very hard, without any Driven t0 Mull 
intermission, for some days ; and on the 6th, some wreck-timber, Heav y s ale - 

Timber cast on 

covered with goose-barnacles, came ashore among the surf at the Tyree. 

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 2^ p.m. We R eturn t0 u oc ^ t 

succeeded in getting up the mortar gallery (see Plate V.), and in and far * her p t °" 

. gress of barrack. 

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. 

10*7* 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 ob- 

M 



94 



OPERATIONS OF 1838. 



Last day's work 
on Rock this 



season 



Precaution for 
the benefit of 
shipwrecked 
seamen. 



served 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. 

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 con- 
trived 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 leav- 
ing the Rock, I climbed to the top of the pyramid, from which I 
view from top of 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 eleva- 
tion 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 



pyramid. 



OPERATIONS OF 1838. 



95 



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 im- 
mediately set sail with three cheers, rejoicing to have thus con- 
cluded our season's work. 

After spending a few days at Hynish in making various ar- 
rangements 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 dress- 
ing of the materials for the Lighthouse Tower, I left Tyree with 
the pleasing belief that the successful termination of our first sea- 
son'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 Destruction of 
Mr Hogben, the clerk and store-keeper at Tyree, the unwelcome duringTgiie. 
intelligence that the Barrack-house had been destroyed, as was sup- 
posed, by the heavy sea of the 3d November; and as his letters con- 
tain 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: — l( Sker- 
ryvore Lighthouse Works, Tyree, 5th November 1838. — Dear Sir, — Letter from 
I am extremely sorry to inform you, that the barrack erected on Mr Hogben ' 
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 Bar- 
clay, however, having gone to the top of Ben Hynish, got a mo- 
mentary glimpse of the Rock through the spray, and both were of 
opinion that the barrack was gone. This was not credited by the 



96 



OPERATIONS OF 1838. 



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 hap- 
pened, 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: — " Skerry vore 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 be- 
tween 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 dis- 
tance 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 



OPERATIONS OF 1838. 



97 



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," 

On the day on which I received this discouraging intelligence, Proceed to 
I requested a special meeting of the Committee, for the purpose of ^ errpore 
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 



98 



OPERATIONS OF 1838. 



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 Sker- 
state in which ryvore about 4 o'clock in the afternoon. The sea ran very high, 
fwnd° c waS and there was not the most remote chance of landing, but, hav- 
ing 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 de- 
scribed by Mr Hogben. The beam which lay back on the in- 
clined 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 forebod- 
ings, 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 mid- 
night. 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 inconve- 
niences 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, 



OPERATIONS OF 1838. 



99 



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. 

Various conjectures were made as to the cause of the destruc- Cause of the 
tion of the barrack. Those who saw it erected were so confident thf barrack. 
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 acci- 
dent. In this opinion they were strengthened by the total destruc- 
tion 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, pass- 
ing right over the tops a a, of the beams and h 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 enor- 
mous 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 



No. 10. 




100 



OPERATIONS OF 1838. 



to that in which it was found lying. That beam, however, al- 
though 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 These circumstances by no means shook my belief in the suit- 

a new barrack. 

ableness 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 suc- 
cess was not damped by the unhappy issue of our season's labours, 
to examine very carefully the whole details of the ties and fasten- 
ings. 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 



OPERATIONS OF 1838. 



101 



of this plate, a large spike p was driven, which produced an expan- 
sion 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 re- 
taining in its place against any tendency to move upwards, a strong 
metallic ring g, which was tightly keyed by wedges at k. Addi- 
tional ties of iron D, E, F, were also provided, which connected 
the six beams together in pairs. Each end of those ties was at- 
tached 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 

N 



No. 11. 




102 



OPERATIONS OF 1838. 



that each beam was quite enclosed by fixtures, which were thus in- 
dependent of spikes or bolts. Thin hardwood wedges were after- 
wards 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 plat- 
form 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 



OPERATIONS OF 1838. 



103 



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 store- 
house, 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 la- 
bourers whom we employed, to be permitted to purchase provi- 
sions 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. 

The quarries at Hynish, as already stated, were by no means Hynish Quarries, 
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 impreg- 
nated with clay. That stone is by no means suitable for the 



104 



OPERATIONS OF 1838. 



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 libera- 
lity, 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* or laid 
bare at Hynish, had greatly disappointed our expectations. The 
unworkable nature of gneiss rock also and its extreme uncer- 
tainty 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 

* 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. 



OPERATIONS OF 1838. 



105 



rock, of which Craigleith quarry, near Edinburgh, furnishes an ex- 
cellent 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 irre- 
gular joints, which, for the most part, are incapable of being pro- 
perly dressed. 



CHAPTER V. 



OPERATIONS OF 1839. 

During the winter months which intervened between November shipping station 
1838 and March 1839, a small detachment of men, consisting of H* n f s £ r at 
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 Hy- 
nish. The provision of accommodation for shipping at that place 
was now naturally regarded as of more urgent necessity than for- 
merly, 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 ma- 
terials to be dressed at Tyree and there reshipped in order to be 
carried to the Rockj 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 ad- 
vantage of being able, by means of a good telescope, in some mea- 
sure 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 con- 
venience of communicating with the Rock by signal, were circum- 
stances in themselves quite sufficient to determine my choice in 



108 



OPERATIONS OF 1839. 



favour of Hynisli, as the place from which the materials must be 
shipped for the Rock, even if there had been no other consider- 
ations 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 num- 
ber with the nature of the particular operations in which the men 
were occupied. 

On the afternoon of the l§th April I sailed from Greenock in 
Granite quarries the Regent, for North Bay in Mull, where the quarries were to be 
opened. We had on board the whole materials of the new Bar- 
rack, which was to supply the place of that which had been de- 
stroyed 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 



OPERATIONS OF 1839. 



109 



be engaged in preparing more permanent dwellings for the quar- 
riers 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), ar- 
rive 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 Bar- 
rack ; 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 store- 
houses 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 be- 
fore. 

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 

o 



110 



OPERATIONS OF 1839. 



rock and partly, where necessary, its inequalities were smoothed 
down by filling it with stone shivers ; and along its bed thus pre- 
pared, 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 de- 
scending 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 ope- 
ration 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* 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 quar- 
riers, 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 qua- 
lity 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, in- 



* Whether from any inflection of the Celtic Rhua, or Roy, or directly from the Italian 
Rosso, it would, perhaps, be impossible to determine. 



OPERATIONS OF 1S39. 



Ill 



to 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 quar- 
ries 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 quar- 
ried in that single spot, sufficient to supply 4300 selected blocks, 
varying in weight from f ton to 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 re- 
moved, 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 build- 
ing by a quantity which was considered sufficient to cover any 
casualty in the final dressing of the block by the masons at Hy- 
nish, and which allowance was generally equal to a film of rock 
about 1^ 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 



112 



OPERATIONS OF 1839. 



Commissioners, and sometimes in undecked boats of 16 tons, be- 
longing to the adventurous men of Tyree. The freight usually 
paid was 5s. a ton, and yet the whole of the blocks for the Light- 
house 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. l^d. per 
cubic foot, including all the expense of building barracks, opening 
quarries, freight of stones, and the expense of building and main- 
taining 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. 
Observations on As I am not aware that any professional work contains a de- 

the quarrying -i -i -i • • <■ i • 

of granite. tailed description 01 the quarrying of granite, some observations 
on that subject may not be unacceptable in this place ; and I there- 
fore 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 mat- 
ter (which operation, as I have elsewhere mentioned, is in Scot- 
land 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 shat- 
tering 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, 



OPERATIONS OF 1839. 



] 13 



be taken to keep the bore clear of cracked or unsound rock, as the 
juniper, 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 re- 
gulated 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 endea- 
vouring 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, 2| inches diameter at the 
top, diminishing to 2 inches at the bottom, may be considered a pro- 
portionate caliber. If the bore be a deep one (perhaps of 14 feet), 
its diameter will require to be 3| inches at the top, and should di- 
minish to 2§ inches at the bottom ; and the quantity of powder 



114 



OPERATIONS OF 1839. 



required for the charge will in most cases be about as much as is 
required to fill fths of the hole.* 

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 

* 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. 



OPERATIONS OF 1839. 



115 



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. 

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* 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 H 
inch diameter to the depth of 9 inches ; and if the 
plug-holes be deep, and some difficulty in driv- 
ing 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 

* The plug (tig. 12, c c'), and feathers (fig. 12. dd), are Hat 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. 




116 



OPERATIONS OF 1839. 



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 em- 
ploys 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. Hav- 
ing 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, work- 
ing with crow-bars behind the block, so as to shake it and loosen 
its hold. The two parties continue their work reciprocally, lead- 
ing 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 watch- 
ing 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. 

An opening being made in the manner above described, by 
getting one piece brought down, the same process is continued by 



OPERATIONS OF 1839. 



117 



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 posi- 
tion. 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. 

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 thick- 
ness 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 2\ inches deep, and 3| 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 2\ inches broad, 
and weigh about 7 lb. weight each. When in good order they must 
not be sharp in the mouth, but about § 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 



118 



OPERATIONS OF 1839. 



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-cut- 
ter's shed. 

As a conclusion to the above account of quar- 
rying, 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 1| 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 1^ 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 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 3| inches in diameter at 
the top (diminishing to 2§ 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 






OPERATIONS OF 1839. 



119 



No. 15. 




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 2§d. for a dozen of holes, taking light and heavy cuts 
as they come to hand. 

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 re- 
course 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 hori- 
zontally, 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. 

The dressing of the blocks for the Lighthouse Tower, as al- Dressing of the 

, .. , Pj1 .. .. .. - ,i Lighthouse blocks. 

ready mentioned, was one ot the most important operations in the 
workyard at Hynish ; and as no writer with whom I am acquaint- 
ed 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 Aber- 
deenshire, 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 



120 



OPERATIONS OF 1839. 



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 slid- 
ing 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.* 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, repre- 
senting 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 posi- 
tion of the stones in the wall, were given to the foreman of the work- 
yard, 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 1^ 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 or- 
dinary 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 

* 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. 



OPERATIONS OF 1839. 



121 



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. 

When a block has been brought to the shed, the first thing to 
be done, if it is a large stone of 1| 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 Q 
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 be- 
low 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. 

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, stand- 
ing at the higher side, commences to put on the draughts or 
guide-lines all round the edge of the face which he has just 




122 



OPERATIONS OF 1839. 




opened. For that purpose he first employs a pick of about 12 lb. 
weight, having a handle about 2 feet in length 17 
(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 be- 
tween 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 pre- 
sent the appearance of a pretty regularly dabbed 
face. Having arrived at that stage, he next pro- 
ceeds 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 3^ lb. weight ; and afterwards with the axe, he 
carefully axes a band about 2\ inches broad, so as to be 
quite out of winding, and as straight as possible all round. No ' 18 ' 
The dressing is then completed between those bands. If the a & 
block be a broad one, the mason will probably be able to i 
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 pre- 
sent 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 



OPERATIONS OF 1839. 



123 



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 fol- 
lows ; 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 <doIZ> 
that state the surface of the stone may be supposed to be 
fine enough for most kinds of work used in housebuild- 
ing 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.) 

The dressing of the first face being finished in the manner de- 
scribed, 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 No i0- 
which is left gives a good hold for the chipper or pincher $ 4 
(fig. No. 20), which is next carefully applied along the 
line, being steadily held within one hand, and with the Lj C. 
other sharply struck with a small iron mall of 3h lb. 
weight, having a short handle about 8 inches in length. While 
the chipper receives sharp strokes in succession with the mall, 




124 



OPERATIONS OF 1839. 



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 in- 
strument, 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 hit. 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 ma- 
terial between those draughts until the second face is finished ; and 
the same process is repeated for each side of the block which re- 
quires 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 thick- 
ness or height, which is regulated by means of a gauge, ^ 
known, in the technical language of the shed, as " a 
qrippers" (fig. No. 21),* from its embracing the stone Pj 
on three sides. It is simply a three-sided iron templet, | 
having one long and one short tail (at right angles 3 
to the connecting piece), the space between the two I I 1 
tails shewing the thickness of the stone. 

The practical reader will readily see, that what has been said 
above about the hewing of granite, is chiefly applicable to the dressing 

* The figure shews " a ^rippers" for a stone 14 inches thick, 



OPERATIONS OF 1839. 



125 



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 ma- 
terials 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 pre- 
vent 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 gene- 
rally 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 1\ 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 readi- 
ness 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 em- 
ployed 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 

Q 



126 



OPERATIONS OF 1839. 



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 hun- 
dred 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 cut- 
ting 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 fol- 
lows : — One dressing hammer about 16 or 18 lb. weight ; 6 dress- 
ing 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 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 opera- 
tion of putting the drafts or bands on the stones, in place of arris- 
picks, which made the workmanship clumsy, tedious and imper- 
fect, 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 shift- 
ing his position, a change, which, every one who has been long em- 
ployed 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 



OPERATIONS OF 1839. 



127 



had it not been for those changes, the actual expense of dressing the 
blocks for the Skerry vore 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 dove- 
tailed spaces of the floors out of the solid stone. 

The excavation of the foundation of the Lighthouse Tower was Excavation of 
the first operation which engaged my attention at Skerryvore Rock, Lighthouse Tower 
at the beginning of the season of 1839. It was commenced on the ™ *J e skerr - vvore 
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 pro- 
spect 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 un- 
workable 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 suf- 
ficient to contain the foundation pit for the Tower. The very rugged 
and uneven form of the Rock made this an almost necessary pre- 
caution, in order to prevent any misconception as to its real state, 
for it was traversed by numerous veins and bands inclined at va- 
rious angles, on the position and extent of which the stability of 
the foundation in no small degree depended. That operation occu- 
pied 30 men for 102 days, and required the firing of no fewer than 
246 shots, chiefly horizontal, while the quantity of material re- 
moved did not greatly exceed 2000 tons. It was a work of some 



128 



OPERATIONS OF 1839. 



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 Bar- 
clay, 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 splin- 
ters 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 engi- 
neering of an operation of s o 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, amount- 
ing to about 2000 tons, into the deep water round us, to prevent 
their being thrown by the waves upon the Rock, and so endanger- 
ing the future temporary Barrack. That was rather a laborious 
work, and occupied two cranes, with temporary runs and trucks. 



OPERATIONS OF 1839. 129 

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 men- 
tioned, 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 Al- 
mighty, 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. 



130 



OPERATIONS OF 1839. 



When the floor had been roughly levelled I again carefully sur- 
veyed 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, ap- 
parently 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 se- 
parate 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 su- 
perincumbent 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 termi- 
nating 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 be- 
fore the close of the season of 1839 about one-third of the area of 



OPERATIONS OF 1839. 



133 



the circle had been cleared, and was ready for the final pick-dress- 
ing 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 founda- 
tion 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 dress- 
ing 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 hi 
such a material. The plan employed was to bore all around the 
periphery of the circle, If 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 experi- 
ence 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. 



132 



OPERATIONS OF 1839. 



Fitting up of the The minute details given in my account of the destruction 

Second Barrack „ , , . 

on the Rock. ot the nrst 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 Bar- 
rack 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 tem- 
porary 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 situ- 
ation. That despatch, indeed, was only obtained by working (as 
we did both during the excavation of the foundation and the erec- 
tion 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, 



OPERATIONS OF 1839. 



133 



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 Micldlemiss, 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 sudden death of 

Hynish, about a fortnight after the completion of his labours on m J s rge Mlddle " 

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 ! 

No inconsiderable part of the labour of this season was de- wharf and Land . 
voted to the clearing of the landing-place, which was formed in Rock. kce 
a natural creek (see Plate III.) and in excavating the rocks in 
front of the line of wharf, so as to admit the vessels carry- 
ing 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, 

R 



131 



OPERATIONS OF 1839. 



Ring-bolts, Water 
Tanks, and Rail- 
ways. 



Incidents of the 
Season. 



Effects of a gale 
from the S.W. 



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. 

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 un- 
fortunately 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. 

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 Commis- 
sioners had engaged. 

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 



OPERATIONS OF 1839. 



135 



small pieces of timber, which we had left on the Rock when we 
were forced to leave it, came ashore in Balaphnil 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 ex- 
cavated 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 irregu- 
lar description, over which the vessel frequently drifted to a con- 
siderable 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 pro- 
gress. That circumstance also convinced us of the necessity of 



136 



OPEKATIONS OF 1839. 



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 hanting 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 Skerry vore for the season, every 
heart was full of rejoicing, and many cordial expressions of grati- 
tude 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 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 after- 
wards, the desired effect on those who remained ; but the spirit of 



OPERATIONS OF 1839. 



137 



disaffection having spread pretty widely, we had subsequently 
several other instances of sudden desertion from the service. 

In the course of my residence for four months on board the Near approach of 
tender moored off the Rock, I had opportunities of witnessing and other 
many proofs of the 2'reat necessity which existed for a Light on circumstancei ? 

J r - a J o shewing the lm- 

the Skerry vore ; and if I had ever entertained any doubt as to P ortanceof aLi s ht 

rr> o i t • on the Skerryvore. 

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 Eock ; 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 



138 



OPERATIONS OF 1839. 



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, 1 shall speak of the various departments separately, as in the 
last chapter, beginning with the workyard at Hynish. 

During the preceding winter months, the establishment at Hy- Hynish Workyard. 
nish 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 lime- 
kiln 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 re- 
inforcement 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 con- 



140 



OPERATIONS OF 1840. 



siderably, 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 in- 
roads necessarily made upon the men's time, by their being fre- 
quently required to assist in the landing of materials from Mull, a 
work for which few of the Tyree men were fit, from their awk- 
wardness 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 Eock, upwards of 20,000 cubic feet of 
granite had been dressed and fitted on the platform, when I left 
Hy irish in the end of October 1840. 
Hyuish 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 dis- 
charged at the quay, independently altogether of the ballasting of 
each vessel which discharged at the pier, and the receiving, stor- 
ing, 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 



OPERATIONS OF 1840. 



141 



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 



H2 



OPERATIONS OF 1840. 



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 re- 
mained 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 opportuni- 
ties 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, experi- 
enced 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. 

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 habi- 
tation had not been completed. During the first month we suf- 
fered 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 



OPERATIONS OF 1840. 



143 



the Rock ; and the cold and comfortless nature of our abode re- 
duced 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 despond- 
ing 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 ham- 
mock 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. To- 
wards 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 tele- 
scope 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. Imme- 
diately 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. 



144 



OPERATIONS OF 1840. 



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 ma- 
terials and Mr Charles Stewart, the foreman of the builders, and the 
other was allotted to myself. The apartments thus occupied con- 
sisted 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 gene- 
rally 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 



OPERATIONS OF 1840. 



145 



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 even- 
ing. Such protracted exertion produced a continual drowsiness, 
and almost every one who sat down fell fast asleep. I have my- 
self 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 gran- 
deur 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 bright- 
ness 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 ar- 
rested our thoughts in a situation where, with all the bustle that 
sometimes prevailed, there was necessarily so much time for reflec- 
tion. 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 re- 
sidence, on one occasion, of not less than five weeks on that desert 
Rock. 

During the first half of the season 30 men were engaged 14 hours 



146 



OPERATIONS OF 1840 



Foundation-pit. 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 exca- 
vation and the number of tools expended on it, were very great, as 
a pick seldom stood more than three strokes in the harder quartz ose 
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 in- 
convenience 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, no- 
thing 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 mate- Before we had made an actual trial of landing stones on a 
nais on the Rock. -^ 0G ^ j. ne di s t ance f 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 in- 
creasing 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 Dum- 
barton, 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 



OPERATIONS OF 1840. 



147 



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 &s 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 liohters 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 diffi- 
culty and anxiety and many narrow escapes were made ; but it- 
was managed with great prudence, and at the same time with un- 
remitting 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 



148 



OPERATIONS OF 1840. 



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 Tn e building of the Tower was commenced on the 4th July ; 

first stone. ° J 

but it was not till the 7th that the ceremony of laying the founda- 
tion-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 Skerry- 
vore 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., be- 
tween 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 occa- 
sionally set, through the activity of Mr Charles Stewart, the fore- 
man 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 gene- 
rating hyperbola. By those means we succeeded in setting, in a 



OPERATIONS OF 1840. 



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 com- 
putations 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 re- 
tain the marks left by the tools of the workmen. I had also care- 
fully compared the density of the Hynish and Mull stones, by 
weighing blocks of known dimensions, and found that it requires 
13T6 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 

T 



150 



OPERATIONS OF 1840. 



identical, in its composition, with that used by Smeaton at the 
Eddystone. Not having been able, after searching the neighbour- 
ing 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 ad- 
hesion 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 after- 
wards carefully repointed, and have never since shewn the slightest 
symptoms of leaking. 



CHAPTER VII. 



OPERATIONS OF 1841. 

The workyard at Hynish presented a very busy scene during the Hynish workyard. 
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 col- 
lected 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 Light- 
house-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 mate- 
rials and their readiness in working the cranes, made them very 
useful in directing and also in working along with the native la- 
bourers, who, partly from incapacity and partly from excessive in- 
dolence, could not be trusted for a moment to themselves. During 



152 



OPERATIONS OF 1841. 



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 testi- 
mony 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 be- 
fore ; 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 land- 
ings in the mean time, and some of them, owing to the heavy surf 



OPERATIONS OF 1841. 



153 



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 com- 
mencing 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 
oft* for a signal, and suffered so acutely during the whole night, 
that his piercing cries in the spasms which accompanied his disor- 
der, 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 win- 
ter's storms. We were not sorry, at the same time, to have an op- 
portunity 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 ap- 
paratus, which, owing to the heavy surf on the 2uth, we had not 
been able to accomplish. 

The few first days after getting fairly established in our habi- 
tation 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 



154 



OPEEATIONS OF 1841. 



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 mix- 
ing the mortar and of setting stones were begun. 

In spite of the unfavourable state of the weather and the con- 
tinual 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 pajt of the Tower to be reached ; and chain guys both in front 
and behind, secured them from falling either backwards or for- 
wards. 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 build- 
ing 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 



OPERATIONS OF 1841. 



155 



sheaves hanging from the end of beams projecting from the win- 
dows. 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. 

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 oc- 
casional application of the crane, to save them from being swept into 
the sea by the surf. Nothing struck me more than the illusive The Waves, 
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 com- 
paring their apparent height with the results of their impact on 
the rock, we were enabled to correct our notions of their magni- 
tude, 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 



156 



OPEKATIONS OF 1841. 



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 resi- 
dence 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 flat- 
tened 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 com- 
parisons, however, of the waves, with various known points of 
rock near the main Rock, and by availing myself of the observa- 
tions of some of the more intelligent of the masons, I was led to 
conclude, that the greatest elevation of an unbroken wave, mea- 
suring 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 esti- 
Coiours of break- mated 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 



OPERATIONS OF 1841. 



157 



often observed in other places, and I supposed them to be produced 
by reflection from the thin plates of water ; and took them for indi- 
cations 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. 

Amongst the many wonders of the " great deep," which we The seals, 
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 sus- 
pended for five days by a violent gale, which made it unsafe to at- 
tempt 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 previ- 
ous winter, I had caused to be constructed at Edinburgh, in the 
workshop of Mr James Dove. That apparatus, which, except as 

u 



158 



OPERATIONS OF 1841. 



to its greater size and strength, in order to suit the greater dimen- 
sions 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 bar- 
rels 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 counter- 
poise ; 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, re- 
ceding 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 posi- 
tion, 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 



OPERATIONS OF 1841. 



159 



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 direc- 
tion 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 Eock 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 satisfac- 
tion 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 pil- 
lar 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 Eock. 
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 



160 



OPERATIONS OF 1841. 



height, according to the calculated dimensions, within a fraction 
rarely exceeding T gth 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 con- 
sider 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 ap- 
pear 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 un- 
certainty 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, al- 
though many risks were run, from the breaking of warps while the 
craft lay moored to the landing quay during heavy seas. I can- 
not 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 



OPERATIONS OF 1841. 



in the lungs. Of his anxiety to forward the work, and his un- 
wearied exertion in the discharge of his harassing duty at Skerry- 
vore, 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 suc- 
cess ever since the commencement of the works on the Rock in 
1839. Mr Heddle possessed attainments superior to those gene- 
rally found among persons in his walk of life and was in every re- 
spect a most estimable man. 



CHAPTER VIII. 

OPERATIONS OF 1842. 

On the 17th of April 1842, 1 made my first landing on the Sker- State of the 

„ _ . . Rock in Spring 

ryvore, tor the season, and found traces of very heavy seas having f 1842. 
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 con- 
siderably from large stones having been thrown upon it ; and seve- 
ral 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. 

As I had resolved to keep, during the summer of 1842, a com- Commencement 
plement of about eighteen or twenty seamen on the Rock, in addi- Ji ons ° c ° pera " 
tion to the usual detachment of masons, in order to work the crabs 



164 



OPERATIONS OF 1842. 



for raising the materials to the top of the Tower by successive 
stages ; my first step was to set about preparing additional ac- 
commodation 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 addi- 
tional 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 tra- 
pezoidal, 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 sum- 
mer, dashed forcibly on the lower parts of the Barrack. Win- 
dows 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 inconve- 
niences of which few but seamen would have patiently endured. 
Those discomforts, however, were to a certain extent, counter- 
balanced 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 com- 
mencement of May we had frequent stiff gales ; and it often hap- 
pened that the men could not venture out of the Barrack, o wing- 
to the heavy sea which swept over the Rock. The crane, too, 
which had been erected at the wharf for unloading the stones, al- 
though 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 experi- 



OPERATIONS OF 1842. 



165 



ence 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 fol- 
lowing 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 mate- 
rials 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 neces- 
sary to rig from the lowest window a beam or needle (in the man- 
ner 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 con- 
tinued for about six weeks, with little interruption from the wea- 
ther, to raise the blocks of stone to the top of the Tower by suc- 
cessive 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 

x 



166 



OPERATIONS OF 1842. 



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 fea- 
ture 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 21 st 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 sea- 
son, as well as in some measure of their joy at the prospect of a 
speedy and happy termination of our arduous labours. The pro- 
cess 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 opera- 
tions, without loss of life, or even the occurrence of any serious 
accident, excepting the destruction of the first Barrack in Novem- 
ber 1839. It also gave me great satisfaction to reflect that, how- 
ever difficult a rigid adherence to scrupulous accuracy of workman- 
ship may be in such a situation as the Skerryvore, it had never- 



OPERATIONS OF 1842. 



167 



theless, 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 | 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 day after landing the last stone of the parapet, the steamer The Lantern, 
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 



168 



OPERATIONS OF 1842. 



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 op- 
portunity of pointing out to Mr Bruce the various works in pro- 
gress 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 frame- 
work 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. 

The shores of Tyree, as already often noticed in these pages, Harbour Works, 
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 at- 
tempt 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' acquaint- 
ance with Tyree, but also by Mr Thomas Stevenson, who suc- 
ceeded me in the charge of the works at Hynish, at the time 
when I was appointed Engineer to the Lighthouse Board in Janu- 
ary 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 na- 
turally 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 ves- 
sel 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 



170 



CONCLUDING OPEEATIONS 



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 accommoda- 
tion at Hynish was, for the sake of economy, laid out with refer- 
ence 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 deter- 
mined 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, com- 
posed 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 cross- 
heads 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 



AND EXHIBITION OF THE LIGHT. 



171 



compartments, protected by successive dams of rabble mason- 
ry, 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 excava- 
tion and the building of the entrance heads of the booms went regu- 
larly 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 break- 
water 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 har- 
bour, has about 60 feet of its foundation laid in a depth of water 
varying at low spring-tides from 18 inches to 3| 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 en- 
tertained by me at first ; but the most complete success has at- 
tended 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., mad« 
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 be- 
tween 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 neigh- 



172 CONCLUDING OPERATIONS 

bouring 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 en- 
trance 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 25-| 
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 \\ 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 in- 
accessible ; and but for such an arrangement, the dock must have 
remained permanently choked with sand and sea-weed. The posi- 
tion 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 vari- 
ous 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 em- 
braces 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 XL), so as to prevent their rising with the tide. 



AND EXHIBITION OF THE LIGHT. 



173 



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 mat- 
ter 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 Skerry vore, together with the dif- 
ficulty 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 com- 
munication 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 uncer- 
tain opportunities which occur at intervals, during the short days 
of winter, would often have been lost, aod 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. 

In connection with the Harbour at Hynish, I naturally no- Bo Pheg Beacon, 
tice 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 Light- 
house. From the great difficulty of landing on that small rock, 

y 



174 



CONCLUDING OPERATIONS 



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 sur- 
face 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 to- 
gether 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. 
T . , ,, , , Another necessary part of the Establishment at Hynish, was 

JLightkeepers and «/ r J ' 

Seamen's House, the provision of dwelling-houses for the families of the Light- 
keepers 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 landing on the Rock, on the 29th of March 1843, the 

on the Rock, such R es i c lent Engineer had the satisfaction of finding the whole build- 
as pointing, &c. ° t ° 

ing perfectly water-tight and saw not the slightest trace of a de- 
fective 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 



AND EXHIBITION OF THE LIGHT. 



175 



were necessary and from the care with which it requires to be 
executed, occupied a great deal of time. 

Another tedious operation was the fitting up of the interior of Jj* e ^ e ^ ttillgs 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. 

The general arrangement of the Tower, mav be seen in the Arrangement of 

00 ' •> the several apart- 

Section Plate VIII. ; and the details of its subdivision are very ments. 
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 apart- 
ment 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 apart- 
ments, 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 



.176 



CONCLUDING OPERATIONS 



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 Appa- The light of Skerry vore was exhibited to the mariner on the 
hibitiou 11 of™ the" nigh* °f tne 1st February 1844, in terms of the Statutory Notice, 
Llgit - 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 ar- 
rangement, 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 in- 
clined about 7° horizontally to the right hand, and by that devia- 
tion 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 



AND EXHIBITION OF THE LIGHT. 



177 



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 to- 
tally 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 opti- 
cal instruments employed in Lighthouses ; and as that will afford 
me a more convenient opportunity of describing the nature and pro- 
perties 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. Francois 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. 

In such a situation as the Skerryvore, new wants were dis- Removal of the 
covered every day ; and each summer brought its round of smaller ^J. ack from the 
works, which the experience of the preceding winter had sug- 
gested. The Barrack was found very useful as a place of resi- 
dence 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 out- 
lay would have made it almost as stable as at first, it was con- 
sidered inexpedient to attempt to perpetuate a structure confess- 



178 



CONCLUDING OPEKATIONS AND EXHIBITION OF LIGHT, 



edly temporary in its nature, and the sudden destruction of which 
by the waves, seemed to involve some risk of injury to the Tower 
itself. 

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.90,268, 12 : 1. 

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 pur- 
poses for which the Lighthouse was erected and records the laying 
of the foundation-stone by his Grace the Duke of Argyll, I will- 
ingly close this most defective narrative of the work. 




A . D _ O . M 



AUCTORITATE . ET . CONCILIIS 



PH A R O R U M 



.SCOTIAE.COLLECII 



HAEC. STRUCT A. FUIT. PHAROS 



CUJUS . Dl RECTI . FLA MMA 



N A UTA E 



INFAMIBUS.HIS.SCOPULIS.ADHUC. MERITO.DETERRITI 



OPTATUM- PORTUM. RECTI US. ADVENIRENT. 



JOANNES. DUX. DE . ARGYLL 
I N SULARUM . ADJACENT! U M . DOM I NUS 
LAPIDEM . AUSPICALEM . RITE. STATU IT 
DIE. IV. MENSIS.JULII.ANNO.IV. VICT. REG. 
M.D.C.C.C.X.L. 




XngrorO. Irr \CS:i:K.Mm,-<u,:,. 



PART SECOND. 



NOTES 

ON THE 

ILLUMINATION OF LIGHTHOUSES. 



PART 



SECOND. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES, WITH SHORT 
NOTICES OF THEIR EARLY HISTORY. 

The early history of Lighthouses is very uncertain ; and some Early History, 
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 hypo- 
theses drawn from the heathen mythology. Some writers have gone 
so far as to imagine, that the Cyclopes were the keepers of light- 
houses ; whilst others have actually maintained that Cyclops was in- 
tended, by a bold prosopopoeia, to represent a lighthouse itself.* 
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.f 

* 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 mytholo- 
gical 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 oppo- 
site points of Africa and Europe, at the Straits of the Mediterranean, have been unhesita- 
tingly 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. 

f "Ev#' outic, rriv vrjffov sGedoot/tiv 6<p9uXf/,oJciiv 

"Out cuv '/.v/achtcc /£U/tgu xuXivbo/Aiva ttoti yi^eov 

Odyss., ix., 146. 

Z 



182 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 suppo- 
sitions, 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 : — 

"fl£ <S' orav \% irovTMO diXag vavr'/jffi tpaveirj 
Kaio/Jjivoio vvgbg, rb h\ xukrui v^otf ogsctpi, 
1ru6(/,ui sv 6/osrdXt// rovg d' ova. 16'iXovrug ueXXai 
TIovtov W lyQuoivra p/Xwv a<xuvsv8e fiigovffiv. 

II., 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 la-Tog, merely im- 
ports a flagstaff or perch and does not at all imply the knowledge 
of beacon-lights among the Hebrews, who were not a maritime 
people. 

About 300 years before the Christian era, Chares, the dis- 
ciple 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



183 



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 ob- 
jects 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. 

Little is known with certainty regarding the Pharos of Alex- Pharos of Alex- 
andria, which was regarded by the ancients as one of the seven 
wonders of the world. It was built in the reign of Ptolemy Phi- 
ladelphus, 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 
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 call- 
ing for the establishment of a lofty and bright beacon, a sign to 
guide sailors arriving from the ocean into the entrance to the 
haven.* 

* 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: "Effr/ di %ai uvto to rr\g vneihog azgov 
Tsrga iroXvxXvarog, iyovtia irugyov 6avfJ,affrug xaTiffxivad/j/evov Xsvxov Xtdov, tfoXvogofiov, 6(jlwvv/j,ov rv\ 
vridifj' rovrov di uv'sDrixi 'SwffTgccrog Kvldiog cpiXog roov fiuaiXtoiv, rrig toiv ffXu'/fy/Aivuv awrrig/ag %ugiv, us 
<pri«iv r] Wiygafn ET/yga/^a, 2fl2TPAT02 KNIAI02 AEXI<J>ANOT2, 0EOI2 2flTHP2IN 
TnEP TON nAfllZOMENfiN. ' AXi/mvov yag ovfSqg xai raffiivrjg rrig sxaregwkv nocgaXlag, l-/over\g 
de xai ypi^&hag xai ^^dyr) nvcc, thu a^siov nvog ti-^riXov xai XafiTgov, roig ano rou TiXdyovg T|o<r- 
tXsovuiv, uo-t evaro^eiv r^g eiofioXrig tou Xifisvog. 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 Alexan- 
dria (as is abundantly testified by Josephus, Pliny, and other writers), and cannot be easily 



184 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



The accounts which have come down to us of the dimensions 
of this remarkable edifice are exceedingly various ; and the state- 
ments of the distance at which it could be seen are clearly fabu- 
lous. 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 !* 
Ammianus Marcellinusf and Pliny J are both very circumstantial 

reconciled with that of Homer (fourth Odyssey, 1. 354), who describes the island as a day's 
sail with a fair wind from the mainland. His words are as follows : — 

NJjcrog iirard rig iarl toKwAkvciru) hi irwru 
hiybirrov ir^onaooidi (<I>agov d'e e ■Ai%kr\e%o'oei) 
Toffffov (f caiivd' offffov riitavr\ix,igir\ y\a<p\)gy\ vrfig 
"Hvvffev, p \iyOg ougog iiti<7t)iur\Gi)) omffhii. 

Odyssey, iv., 1. 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 iEgypto, nunc e turri 
nocturnis ignibus cursum navium regens." Hist. Nat., v. 31 ; see also Hist. Nat., ii. 87, 
and xiii. 21. 

* Bell. Judaic, iv., cap. 10, sec. 5. (Havercamp's Josephus, torn, ii., p. 309. Am- 
sterdam, 1726.) iv device bs r) 'j^offayo^iwi/jjivri <t>agos vrjffig Kgoxarai, nu^yov ave^ovffa fieyisrov, 
ix-7rugffivovrot roig xuratfXiouffiv, stti rgiuxoffiovg ffradiovg, ug h vvxrl TroggwOev o^iAiZpivro vgog rriv duff^s^iiav 
rov xarairXou. And again, in the sixth Book of the same History (v. 4, sec. 3, torn, ii., 
p. 330), he says, xai rb /aiv <%>j///a wagtwxii ra xaru rriv <J>agov exKvgffibovri roig lit AXi^uvdgelug 
vX'souffi. The height of the Tower in the text proceeds on the idea of the observer's eye 
being ten feet above the sea. 

+ Ammianus Marcellinus, 1. xxii., c. 16. (Leipsic 1807, torn, i., p. 306.) Hoc lit- 
tus cum fallacibus et insidiosis accessibus affligeret antehac navigantes discriminibus plu- 
rimis, excogitavit in portu Cleopatra turrim excelsam, quae Pharos a loco ipso cogno- 
minatur, praelucendi navibus nocturna suggerens ministeria ; cum, quondam ex Parthenio 
pelago venientes aut Libyco, per pandas oras et patulas, montium nullas speculas vel 
collium signa ccrnentes, harenarum inlisae glutinosae mollitiae frangerentur. 

I Plinii Hist, Nat,, xxxvi. 18. (Paris, 1723, p. 739.) Magnificatur et alia turns 
a rege facta in insula Pharo portum obtinente Alexandriae, quam constitisse octingentis 
talentis tradunt ; magno animo (nequid omittamus) Ptolemai regis, quod in ea permiserit 



NOTES ON THE ILLUMINATION OE LIGHTHOUSES. 



185 



iii their notices of the Pharos as a beacon-light to guide seamen in 
approaching the coast of Egypt and port of Alexandria. The lat- 
ter adds the interesting fact, that the cost of the Tower was 
reckoned at a sum equal to about L, 390,000 of our money ;* 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 attribut- 
ing the erection of the Tower to Queen Cleopatra. Pliny mentions 
in passing, that there were also lighthouses at Ostia and Kavenna. 

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 un- 
changed, is a sufficient reason for rejecting, as erroneous, the di- 
mensions which have been assigned by most writers to the Pharos 
of Alexandria. Some have pretended that large mirrors were em- 
ployed 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 
Csesar his approach to the Pharos of Egypt on the seventh night 
after he sailed from Troy : 

Septima nox, Zepliyro imnquani laxante rudentes, 
Ostendit Phariis iEgyptia littora jlammis. 
Sed prius orta dies nocturna lampada texit, 
Quam tutas intraret aquas. 

Pharsal., ix., 1004. 

Sostrati Giiidii Architecti structurse ipsius nomen inscrilu. Usus ejus, nocturno navhim 
cursu ignes ostendere ad praenuncianda vada portusque introitum : quales, jam compluri- 
bus locis flagrant, ut Ostiae ac Ptavennae. Periculum in continuatione ignium, ne sidus 
existimetur, quoniam e longinquo similis flammarum aspectus est. 

* Supposing, as is most probable, that Pliny means the Egyptian talent ; the Attic 
talent was about one-half the value of the other. 



186 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 " jlammis" of 
which he speaks, were not so produced. The word lampada may 
however, be used metaphorically ; and jlammis 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 con- 
tinuation ignium, ne sidus existimetur, quoniam e 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 cover- 
ing the inscription with plaster, on which he carved the name of 
his royal master Ptolemy.* 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 

* Lucian, in his Treatise (Amsterdam, 1743, vol. ii., p. 68.) IIws dn iarooiav gvyygatptiv, thus 
details the merit and fraud of Sostratus. Ogag tov Kvlbiov sxeivov dgyjTiXTova, oTov smlrifftv ; 
oixobo/Aqgoig yag Ton iir'i rfi <X>agw irZ^yov, fityigTov xai xaXXigTOV egyuv diravTuv, ug irvggivoiTo air' duTov 
roig vauTiXXbfMvoig, sir! iroXv Trig SaXaggqg, xai fin xarapegoivro ilg t?)v TlagaiToviav, irayydXiirov, ug 
pamv, r ouaav xai dtpuXTov, h Tig epmgoi hg rot, eg/tara. Olxobo^gag bvv to igyov, evdodtv jU.sk, xara 
r'M Xidwv, to dvTou ovofJia Wiyqa~\>iv. Wiriyj/tgag be r/ravw xai eirixaXii^ag, eireyga-^/e to bvofLa tov 
Ton (3agiX'evovrog, iibojg, itfiTig xai eyevsro, irdvu oXiyov %fovov, avvexirisov^va /j,sv tuj ^id^a-Ti ra yga/x,- 
fj.at.TOi, expavriffo/JMvov be 2f!2TPAT02 AEXI<PANOY2 Kvibiog. koig ffwTngaiv wrtg tuv irXw'i'fy/Aiuv, x.t.X. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



187 



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 Cesar's Commentaries, Valerius Flaccus, and Pomponius 
Mela.* At Alexandria, there is a modern lighthouse called the 
Pharos, which is maintained by the Pacha of Egypt. 

Mr Moore, in his History of Ireland, vol. i., p. 16, speaks of Coruna Tower, 
the Tower of Coruna, which he says is mentioned in the tradition- 
ary history of that country, as a lighthouse erected for the use of 
the Irish in their frequent early intercourse with Spain. In con- 
firmation of this opinion, he cites a somewhat obscure passage from 
^Ethicus, 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 Lu- 
pus, an architect of the city of Aqua Flavia, the modern Chaves. f 

* Csesar 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 serena 
Arce Pharon praeceps subiit : 

Argonaut, vii., v. 84. 

Pompon. Mela, ii. cap. 7. 

f " 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 Coruna, 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 JEthieus, 
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. ' iEthicus in Hispaniae descriptione altissimi cujusdam Fari meminit.' " The pas- 
sage in Strabo above referred to is on page 179 of the first volume of the Oxford folio edi- 
tion of 1807, where the geographer speaks of Cape Neg/ov, which Casaubon distinctly iden- 
tifies with the Cabo de Finisterra of modern seamen. 



188 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



A Lighthouse has lately been established on this headland, for 
which Dioptric apparatus was supplied from the workshop of M. 
Letourneau of Paris. 
Lighthouse at the There is also a record in Strabo of a magnificent lighthouse of 

mouth of the Gua- 3 

daiquivir. stone at Capio, or Apio, near the Harbour of Menestheus (the mo- 
dern 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 iden- 
tical with those used by him in speaking of the Pharos of Alexan- 
dria. 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.* 

Ancient Phari in j n Camden' s Britannia, a passing notice is taken of the ruins 

Britain. 1 ° 

called Ccesar's Altar, at Dover, and of the Tour oV Ordre, at Bou- 
logne, 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.f 

Such seems to be the sum of our knowledge of the ancient his- 
tory 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 



* The words of Strabo are (Oxon. 1807, p. 184), Kai 6 rov Kairiwvo; (vel Kntmwg) 
nwyog 'tdgurou liti vr'ergug o\fi(pKhv6rov, &a\j/jjU.<Siu)g xuriffxivaff/Aivog, StCirig 6 <J>a^og rqg ruv •rrXia'iZp- 
/Aivwv Goir'^iag yjz^iv, Ti Ti y a £ sK^aXXofiiivr) yj>vg xnro rov irorapbov figaytot irom xai yotga,hoihr\g sariv 
o ir%b dvrov roitog wffri ha ffri/Miov ring siri<pavovg. 

t Gough's Camden's Britannia, vol. i., 318, and vol. ii., p. 198; Batcheller, in his 
Dover Guide (1845, p. Ill), says, that the Dover Pharos was buiit " during the lieu- 
tenancy of Aulus Plautius and Ostorius Scapula, the latter of whom left Britain, a. d. 53." 
— Pennant's History of Whiteford and Holywell, p. 112. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 189 



of what is afterwards stated is the result of my own observation, 
during my visits to the most important lighthouses of Europe. 

The first lighthouse of modern days that merits attention, is Tour de Cor- 
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 Langue- 
doc 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 1Y. It is minutely described in Belidor's Architec- 
ture 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 coni- 
cal 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 case- 
mates. This wall is an outwork of defence, and receives the chief 
shock of the waves. The tower itself contains a chapel, and va- 
rious apartments ; and the ascent is by a spacious staircase. The 
first light exhibited in the Tour de Corduan was obtained by burn- 
ing 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 sub- 
stitute parabolo'idal 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 Aca- 
demician. 

The history of the famous Lighthouse on the Eddystone Rocks Eddystone. 
is well known to the general reader, from the narrative of 
Smeaton the Engineer. Those Rocks are 9^ miles from the Ram- 
Head, on the coast of Cornwall ; and from the small extent of the 

2 a 



190 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



surface of the chief Rock and its exposed situation, the construc- 
tion 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 acci- 
dent ; for not long after the destruction of Mr Winstanley's light- 
house, 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, be- 
fore the Trinity-House of London could obtain a new Act of Par- 
liament, 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



191 



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 diame- 
ter 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 com- 
posed 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 em- 
ploying 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 lay- 
ing, in circular trenches or grooves cut in the stones which 
form the outside casing, tie-belts of chain, which were heated be- 
fore 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 paraboloidal reflectors of silvered cop- 
per, were substituted for the chandelier of candles. 



1.92 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 re- 
markable 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 ob- 
jects. 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, how- 
ever, 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 Robebt Steven- 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



193 



son, the Engineer to the Lighthouse Board, after being submitted 
to the late Mr Rennie, was at length adopted ; and it was deter- 
mined to construct a tower of masonry, on the principle of the 
Eddystone. On the 17th of August 1807, Mr Stevenson ac- 
cordingly 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 trans- 
porting 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 exca- 
vated, 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 Ac- 
count of the work, published at the expense of the Lighthouse 
Board in 1824, to which I would refer for more minute information 



194 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 dia- 
meter 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 apart- 
ments, 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 
paraboloidal mirrors, arranged on a quadrangular frame, whose al- 
ternate 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 paraboloidal 
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 de- 
scribed, 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. 



I 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 195 

It must therefore be sufficient to say, that the principal Light- 
houses on this plan (those of the Maplin, Fleetwood, and Belfast 
Lough) consist of piles or of hollow pillars of cast-iron, grouped to- 
gether 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 Light- 
house (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. 

Having thus hastily described the most interesting and cele- Early modes of 
brated 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 Com- 
missioners of the Northern Lights in 1786, was of that kind ; and, 
even in England, the art of illumination had made so little pro- 
gress, that the magnificent Tower of the Eddystone, for about forty 
years after it came from the hands of Smeaton, could boast of no 



196 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 an- 
other, an object which, on a difficult and rugged coast, maybe con- 
sidered 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 inflamma- 
ble 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 sub- 
stance 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 sup- 
plied 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 diop- 
tric 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 ren- 
dered less variable, and could be more easily regulated, and the in- 
convenience 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



197 



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 conse- 
quences 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, 1 was enabled 
to report the results to the Commissioners of Northern Light- 
houses 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 B 



198 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

" 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 sperma- 
ceti oil, being in the ratio of I - 05 6 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 steadi- 
ness 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 Ar- 
gand, 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 sper- 
maceti 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 in- 
troduce the use of the colza oil into all the dioptric lights, except 
that of Skerry vore, 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



199 



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 circum- 
stances 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 de- 
crease its horizontal volume. The elongated form of flame in- 
creases 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."* 

The application of the Drummond and Voltaic lightsf to light- Drummond and 
house purposes is, owing to their prodigious intensity, a very de- Voltaic Ll s hts - 
sirable consummation ; but it is surrounded by so many practical 
difficulties that, in the present state of our knowledge, it may safe- 
ly 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 

* Since the above report was written, the price of colza oil has risen ; and other cir- 
cumstances have occurred to justify the caution as to the universal adoption of that oil. 

] The Drummond light is produced by the ignition or combustion of a ball of lime 
(| 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 paraboloid 
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. 



200 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 ex- 
periments 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 Cor- 
duan Light, the flashes would last only 1^ second, and would not, 
therefore, be seen in such a manner as to suit the practical pur- 
poses 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 insur- 
mountable difficulties, would, in any case, render the maintenance 
of the light precarious and uncertain in the last degree. 
Mr Gumey's l n 1835, Mr Gurney proposed the combination of a current of 

Lam P- oxygen with the flame of oil, in order to obtain a powerful light 

of sufficient size to produce the divergence required for the illumi- 
nation of lighthouses. The Trinity-House of London entertained 
the proposal, and made some experiments on this important sub- 
ject ; but the plan was finally rejected as disadvantageous in prac- 
tice. 

Until the invention by Argand (about the year 1784), of the 

Argand Burners. J # v ... 

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, 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



201 



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.* 

* 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, 
Traite de PEclairage, 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 ap- 
pearance 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 succes- 
sively developed, we shall form a cone whose length will depend on the ratio of the velo- 
cities 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 ve- 
locities, 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 



202 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 there- 
by 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 veloci- 
ties 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 ar- 
rangement 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 ac- 

films succeeding each other, each of them would give rise to the same series of coloured 
rings ; and as thei - e 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, Traite de V Eclair age, p. 51. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



203 



tion. The wick has its lower edge fixed to a metallic ferule or 
ring, called a wickholder, which (by means of a peculiar arrange- 
ment, to be afterwards described) gives the power of raising or de- 
pressing 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 cur- 
rent 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 tem- 
perature than can ever be attained in the thick solid wick or the nar- 
row 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. 

Great as the improvement of Argand undoubtedly was, the 
value of the lamp alone as a means for the illumination of light- 
houses 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 



204 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

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 intercep- 
tion 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 up- 
wards into the sky, or downwards below the plane in which sea- 
men 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 eflicient sea-light could ever be ob- 
tained. 

CATOPTRIC* SYSTEM OF LIGHTS. 

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 absorb- 
ing more and some less of the incident light. Perhaps the earliest 



* From the Greek xumrTPov, a mirror ; a compound of xara, opposite to, and o-xrofiui, 
I see. 



NOTES ON THE ILLUMINxYTION OF LIGHTHOUSES. 205 

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 illu- 
mination. 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. 

The name of the inventor of parabolo'idal mirrors and the date Application of 
of their first application to Lighthouses, have not been accurately TOw^toLi^h^ 11 '" 
ascertained. The earliest notice which I have been able to find, is houses- 
that by Mr William Hutchinson, the pious and intelligent author 
of a quarto volume on " Practical Seamanship" (published at Liver- 
pool in 1791), who notices (at p. 93) the erection of the four lights at 
Bidstone and Hoylake, in the year 1763, and describes large para- 
bolic 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 ha^ first in- 
vented the parabolo'idal mirror and applied it to use in a Light- 
house ;* but, in the absence of any statement as to the date when 

* Mr Hutchinson seems also (" Practical Seamanship, 11 p. 198) to have tried specu- 
lum metal as a material for Lighthouse reflectors. 

2 c 



206 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

the mirrors were really adopted, the merit of the improvement 
must, in justice, be awarded to others. 

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 paraboloidal reflectors ; and he is said, in 
a memoir dated the 26th June 1783, to have proposed their com- 
bination 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 car- 
ried into effect at Corduan, under the directions of the Chevalier 
Borda ; and to him is generally awarded the merit of having con- 
ceived the idea of applying paraboloidal 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 Scot- 
land, 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 paraboloidal moulds of plaster, according to 
the designs of the late Mr Thomas Smith, the Engineer of the Board, 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



207 



who (as appears from the article Reflector, in the Supplement to the 
third edition of the Encyclopsedia 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 where- 
ever lighthouses are known. 

To enable us to enter on the subject of the proper forms of re- Reflei tiou. 
Sectors, 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* 

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 enume- 
rated, 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 direc- 
tion as if they had come from a point as much behind the mirror 

* 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 perpendi- 
cular 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 A OB, 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 reflec- 
tion ; but in cases where the reflecting sur- 
face is curved, it is more convenient to refer 
the angles to the normal BO. 



Pig. 22. 



H 



A 




208 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 lumi- 
nous body from its surface, and diminishes with the degree of con- 
vexity of the mirror. 3d, A concave surface diminishes the diver- 
gence 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 pro- 
duce 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 mathe- 
matical point at a moderate distance; and, as this is a case which 
can hardly occur in the practice of Lighthouse illumination, I con- 
tent myself with observing that this object may be attained ap- 
proximately by placing the lamp in front of a spherical mirror at 
any distance greater than half the radius of the curve surface, or ac- 
curately 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 cir- 
cular space on the horizon equal in diameter to the mirror em- 
ployed ; this object will be rigorously attained only by placing the 
light in the focus of a paraboloklal 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



209 



subtend only a small angle at the centre of curvature. The para- 
boioidai mirror, on the contrary, has the property of converging to 
the focus parallel rays falling upon every point of its surface, how- 
ever extended it may be. 

Any one practically acquainted with this subject, must at once Paraboioidai 

• IVtirrors 

perceive that the paraboioidai 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 mo- 
tion ; 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 azi- 
muths 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 paraboioidai 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 there- 
fore embraces in its action the greatest number of the whole rays 
coming from the focus, and, cwteris pai^ibus, 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 



210 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



be rigorously fulfilled by placing an infinitely small flame in a per- 
fect paraboloidal' 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 ob- 
tain 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 parabolo'idal 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* 

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 

* 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 e, bounded by the curve at either end, would then 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



211 



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. 



Fig. 23. 




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 per- 
pendicular 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. 

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 d of the line 
a b from the directrix AB, a circle cutting the line 
a 6 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 ob- 
tained, x 

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 = V 4 m x. 




212 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Divergence of We have already seen that a perfect paraboloidal mirror, with 

Paraboloidal . „,.,.«• i n T T • n n . * • 

Mirrors. a point oi light infinitely small placed in the locus, 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 in- 
strument 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 light- 
house, it would be completely useless, as will appear from the fol- 
lowing simple considerations. Let us suppose that a true para- 
boloidal 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 ver- 
tical 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 dis- 
tance 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 7 ^d part of a se- 
cond, a space of time far too short to make a perceptible impres- 
sion 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 ascer- 
tained 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 Tggth 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 dia- 
meter 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, 



NOTES OX THE ILLUMINATION OF LIGHTHOUSES. 213 



being repeated by reflection, gives the effective divergence of each 
side of the mirror at that point.* 



* This is easily understood by reference to the accompanying figure (No. 25.), in which 
A OB is a central section of a paraboloidal mirror. 



PF = distance from the focus F to a point in the 
curve P, and PG a tangent drawn from P to the sur- 
face 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 di- 
vergence of the mirror at that cross section. 

Now sin GPF = — ? 

PF 

or the sine of the divergence from each point 
Radius of flame. 




Distance from focus to point of reflection. 
It is obvious that this quantity which varies in- 
versely 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 paraboloid. 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 bv the limits 
of this minimum divergence ; for the faint light which first reaches the eve of a distant 
ob server, in the revolution of a reflector, is not that which is reflected bv the sides or ed°"e<. 
as might at first be supposed, but proceeds from the centre. The light, in fact, graduallv 
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 minimiun 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 finallv 
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 there- 
fore, 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 anv given position of the 
mirror. This will be more easilyunderstood by referring to the accompanving diagram Fig. 26. 
in which e a e is the principal section of a paraboloidal mirror, F its focus, a FA its axis, and 
FK the radius of the flame. If the reflector revolve round a vertical axis at O, an observer 

2D 



214 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



It is still more obvious that a perfect paraboloidal figure, and 
a luminous point mathematically true, would render the illumina- 

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 26 ' 
c' to his eye as parallel), would re- 
ceive the first ray of light in the di- 
rection 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 re- 
flected at a, from a single point on 
the opposite margin of the flame ; 
and hence, as above, the greatest di- 
vergence is measured by the angle 
which the flame subtends at the 
vertex a of the mirror, being the sum 
of the angles a and «'. We shall 
next suppose the mirror to move a 
little, so that the observer may re- 
ceive at G a ray of light from some 
other point in the flame which is re- 
flected at 6 ; while another ray from 
an opposite point reflected at V would be seen in the parallel direction V G', thus indicating 
the boundary of a circular portion of the mirror b a 6', 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 d 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 drrection a D', which is the opposite limit of the extreme diver- 
gence 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 re- 
mind the reader that every portion of the flame radiates light, which, being reflected, conduces 
to the effect. Some rays also arc 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 




NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 215 



tion 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 fol- 
low, 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 
parabolo'idal 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 be- 
nighted seamen. 

In order to obtain a mirror capable of producing a given diver- 
gence 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 dis- 
tance of a given point on the surface of the mirror from the focus. 
The best proportions for paraboloidal mirrors depend on the ob- 
jects 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 

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', eE, 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 Illu- 
mination of Lighthouses in the London Transactions for 1837, p. 218. 



216 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



have a short focal distance ; while those mirrors which are de- 
signed to produce a nearer approach to parallelism (as in the case 
of revolving lights which illuminate but a few degrees of the ho- 
rizon 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 assump- 
tion, that the penumbral portion of the light on each side of the 
strongest beam (which is confined within the limits of the least di- 
vergence, 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 parabolo'idal 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 imper- 
fectly 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 difficultv which 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



217 



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 ad- 
mit 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 Parabo- 

The maximum luminous effect of the reflectors ordinarily em-io^ai minors, 
ployed 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, agree- 
ably 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 diver- 
gence 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 arrang- 
ing reflectors on the frame of a fixed light, however, it is advisable 



218 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



to calculate upon a less amount of effective divergence, for be- 
yond 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 Parabo- The measure of the illuminating power of a paraboloidal mirror 
i s . es timated as the quotient of the surface of the circle which 

cuts it in the plane of its greatest double ordinate, divided by the sur- 
face 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 inaccu- 
rate, 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 con- 
dition of having its surface equal to that of the greatest cross sec- 
tion 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 paraboloid. 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 say- 
ing, that such a line will be found to be a mean proportional be- 
t ween the greatest and least focal distances of the mirror. * The large 
mirrors used in the Northern Lights have about jfths of the whole 
light of the lamp incident on their surface ; the rest escapes in the 
comparatively useless state of naturally radiating light. 
Manufacture of 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 paraboloidal form, by 

* This subject is treated in detail in M. Barlow's Paper already noticed. (London 
Transactions for 1837, p. 212.) 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



219 



a delicate and laborious process of beating with mallets and ham- 
mers of -various forms and materials, and are frequently tested dur- 
ing 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 altera- 
tion of the figure of the reflector. Polishing powders are then ap- 
plied, and the instrument receives its last finish. The details of 
this manufacture are given in the Appendix. 

Two gauges of brass are employed to test the form of the re- Testing of 

* irrors 

flector. 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 inten- 
sity 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 co- 
incident 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. 



220 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Argand Lamps 
used in Reflectors 



we shall have b = as the distance to which the object must be 

removed outwards from the true focus on the line of the axis.* 

The flame generally used in reflectors, is from an Argand foun- 
tain-lamp, whose wick is an inch in diameter. Much care is be- 
stowed upon the manufacture of the lamps for the Northern Light- 
houses, 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 /, by which it can be 



* The truth of this equation may be easily ascertained as follows (See fig. 27) : — 
Let AP he the mirror, F its principal 



focus, and PH the line of reflection of the 
ray FP ; then an object at I will be re- 
flected at P to the conjugate focus 0, 
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 

PF 2 

FO : PF : : PF : FI, and FI = " ; and 

r O 

substituting the letters in the text, we get 



Fig. 27. 




NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 221 

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 



Fig. 28. Fig. 29 Fig . 30 . 




(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 hh, is soldered to the brass band I, 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 h\ and oil-cup I, 
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/the guide-rod, con- 

2 E 



222 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 




nected with the perforated sockets on which the checking-handle g 
slides. The oil-cup I (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 pre- 
pare 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 com- 
munication 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. 
Arrangements for would needlessly occupy much time and space to describe the 

Raising or lower- ^ 1 <* A 

ing the Argand various means (many of them sufficiently clumsy) which have been 
employed, and in many places are still in use, for raising and de- 
pressing the wick ; it will be enough to say, that they all involve 
some application of the rack and pinion. I shall, therefore, only de- 
scribe 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 sur- 
face. 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



223 



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 



Pig. 33. 



Fig. 34. 



Pig. 32. 




req 



V 



9 




; i l 



Pig. 35. 
WicR 



Pig. 36. 










TV 






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. 

An important point in the economy of the Argand lamp, is the Fiowm 
level at which the outlet for the oil, in its passage from the fountain to Lamp ' 
the burner, should be cut. The cutting of this hole (generally called 



224 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Fig. 37. 



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 pro- 
per level of the burner, before the wick is put in. A more ready 
and accurate method of accomplishing this object and at once deter- 
mining 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 Light- 
houses. Its nature will be readily understood by a reference to the 
accompanying diagram, No. 37 : 
The hatched surface represents 
a metallic ruler , with a spirit-level 
at L ; C is the cup in which the bot- 
tom of the fountain / (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 al- 
lowed to fall until a notch in it at 
sf 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 w' x indi- 
cates 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 




NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



225 



coincides with y) measures the length y x = y' «f ; 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 (de- 
scribed 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 syste- 
matic 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 stat- 
ing, that it is generally found that the sperm oil should stand in 
the empty burner at about § inch below its top. For colza oil § 
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 be- Fi g- 3 s. 
fore extinguishing the lights in the morning. 

The arrangement for cutting off the oil is very sim- 
ple, 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 Y 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 ver- 
tical axis, while the valve V, which rests in a notch 
in the cup of the lamp, remains still, and sliding over 
T, opens the floio-hole. S is the screw-plug which re- 
tains the oil in the fountain, and which is unscrewed 
and removed when the fountain is to be filled. 



226 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Placing the Lamp 
in the Focus. 



Tig. 39. 




In the reflecting apparatus of the Northern Lighthouses, the fo- 
cal position of 
the lamp is not, 
as we have al- 
ready seen, lia- 
ble to derange- 
ment, by the re- 
moval of the 
burner for the 
purpose of clean- 
ing, as the slid- 
ing gear describ- 
ed at p. 221 in- 
sures 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 ver- 
tex, 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 P P, and 



Fig. 40. 




NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



227 



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 inte- 
rior of the mirror. If the tube of the burner ascends into the cir- 
cular 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 po- 
sition ; 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 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. 

The great advantage derived by seamen from the establish- Distinctions of 
ment of lights on a coast, soon makes the calls for additional lights Catoptne Llgh1 
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 distinc- 
tive character, which shall effectually prevent the possibility of its 
being mistaken for any other. 



228 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Catoptric lights are susceptible of nine separate distinctions, 
which are called fixed, revolving white, revolving red and white, re- 
volving red with two whites, revolving white with two reds, flashing, 
intermittent, double fixed lights, and double revolving ivhite 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 revolv- 
ing 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 gra- 
dually 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 dis- 
tinctions, 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 construc- 
tion 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 strik- 
ing effect, totally different from that of a revolving light, and pre- 
senting 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 distin- 
guished by bursting suddenly into view and continuing steady 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 220 

for a short time, after which it is suddenly eclipsed for half a 
minute. Its striking appearance is produced by the perpendicu- 
lar 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, suscep- 
tible 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 neces- 
sary, 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 de- 
sired. 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 fths to |ths 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 

2f 



230 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



only ftlis of the light ; but its colour produces, as might be expect- 
ed, 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 After what has been already said on the subject of diver- 
Frame, gence, it will at once be seen, that in revolving lights the reflec- 
tors are placed with their axes parallel to each other, so as to con- 
centrate their power in one direction ; whilst in fixed lights it is 
necessary, in order to approach as near as possible to an equal dis- 
tribution 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, 

Fig. 41. 
O 




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 
0, are made to span the faces of the reflectors, one of which is 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



231 



moved about till its edges are in close contact with the flat sur- 
face of one of the arms of the gauge. 

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 flame or chandelier ; o o, the reflectors with their oil- 
fountains pp. 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 tt ; 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 ; I 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. 




Pig. 43. 




232 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Fig. 44 shews a plan of one tier of reflectors arranged in the 
manner employed in a fixed catoptric light ; n n shews the chan- 
delier, q the fixed shaft in the 
centre, which supports the whole, 
o o the reflectors, and pp the foun- 
tains of their lamps. In this 
figure (in order to prevent con- 
fusion) only one tier of reflectors 
is shewn ; the other tiers are so 
arranged, that their axes divide 
into equal angles the arcs inter- 
cepted between the axes of the 
adjoining reflectors on the first tier, 
thereby producing the nearest ap- 
proach to an equal distribution of the light, which is attainable by 
this arrangement. 

In lighthouses of moderate height, the proper position for the re- 
flector itself is perfect horizontality of its axis, which may be ascer- 
tained 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 be- 
comes 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. 

BorcHer Marcet's 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 illumina- 

Fanai siderai. tion of lighthouses and the streets of towns. Amongst many other 
ingenious combinations, he has invented and constructed an appa- 
ratus which is much used in harbour-lights on the French coast, 




NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



233 



where it is known by the fanciful name of Fanal* sidSral. 
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 dia- 
meter. A perfect idea of the construction and effect of this instru- 
ment 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 perpen- 
dicular 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 gene- 
rated 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 / 1 are 
small pillars, which connect the two 
reflecting plates, and give strength to the apparatus. 



Fig. -15. 




* Fanal, from <pa.vov, a lantern. 



234 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

M. Bordier Marcet has also prepared an ingenious modifica- 
tion of the paraboloidal mirror, which he has described under the 
name of fanal a 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 
paraboloidal mirrors, generated by the revolution of two para- 
bolas 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 inter- 
cepted 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 conoidal 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 ac- 
tion 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 re- 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



235 



fleeted 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 Heve 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 for- 
gotten, that the divergence which is obtained by means of it is 
not confined to the horizontal direction in which only it is want- 
ed ; 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 Aegand him- 
self, in 1806, and also in 1808, by M. Haudry, Ingenieur des Fonts 
et ChaussSes. 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 re- 
flected to it by means of the ellipsoidal surface from the lamp placed 
in the anterior focus. From the optical focus thus obtained, some 
rays would fall on the parabolo'idal surface and produce, by reflec- 
tion, 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 parabolo'idal 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 Ar- 
gand's apparatus. 

It would occupy much time to exhibit all the disadvantages of 
the arrangements in the /anal a double effet of M. Bordier Marcet, 



236 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

and also in those of Argand and Haudry ; and I shall therefore dis- 
miss the subject by observing, that the loss of light due to the posi- 
tion of the flame in the apparatus of Argand, is so great as to in- 
duce 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 parabo- 
loid, with a short focal distance, which has the double advantage of 
increasing the divergence which is due inversely to the focal dis- 
tance, and, at the same time, subjecting to the action of the mirror 
a larger portion of the luminous sphere proceeding from the flame. 
Fanai a double Lastly, I shall notice M. Bordier Marcet's fanal a double face, 
which consists of two paraboloidal 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 

Fig. 46. 




the central or cono'idal mirror MN will fill the interior of one of those 
luminous rings with a cone of rays, whose intensity will be in the in- 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



237 



verse ratio of MN 2 to a b 2 (or FM 2 to F a 2 ), which latter surface re- 
presents 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 con- 
siderable 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 ap- 
paratus with all the satisfaction generally felt by inventors ; but it 
is no difficult matter to identify its effect with that of the common 
paraboloidal 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, conse- 
quently, 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 advan- 
tage to be derived from this arrangement as insignificant.* 

Spherical mirrors have been employed in Lighthouses chiefly Mr Barlow's 
when they can be introduced to aid the effect of refracting appara- s i ,herical Mirrors, 
tus ; 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,! who suggests placing in front of the flame a small spherical 
reflector, whose centre is coincident with the focus of a paraboloid, 

* See Peclet's Traite de TEclairage, p. 302, from which fig. 46 is copied, 
"j" In an excellent paper above noticed, on the Illumination of Lighthouses, in the London 
Transactions, for 1837. 

2g 



238 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 paraboloidal 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 inci- 
dent on the spherical surface, but at the same time to diminish it 
by intercepting a portion of the light reflected from the paraboloid. 
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 light- 
houses ; 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. 
Captain Smith s Captain Smith of the Madras Engineers, has described in the 
ofTparaboiic f0rm " Professional papers of the ' Corps of Eoyal Engineers,'* a new 
* pinflle 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 rota- 
tion 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 op- 
posite azimuths, would, therefore, be sufficient to illuminate the 
whole horizon. The author of the paper, however, appears to con- 
template the employment of a series of those mirrors ranged one 
above another and breaking joint vertically, somewhat in the man- 
ner already described in speaking of the arrangement of the para- 



* Vol. v., p. 56. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 230 

boloidal 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 ex- 
tinction 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 cer- 
tain situations, where no regular establishment of trained light- 
keepers is maintained, that security may be an object of more im- 
portance 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. 

dioptric* system of lights. 

One of the earliest notices of the application of lenses to light- 
houses is that recorded by Smeaton in his Narrative of the Eddy- 
stone 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 parti- 
cular 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 



* Most probably directly derived from the Greek an optical instrument with holes 

for looking through, whose name is a compound of hia, through, and 1-ttoij.ou, I see. 



240 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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."* 

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 bach 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 refract- 
ing 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 toler- 
able success, about the year 1780, by the Abbe 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 in- 
strument ever constructed in this manner, is that which was made 
by Messrs Cookson of Newcastle-upon-Tyne, for the Commis- 
sioners of Northern Lighthouses. 

The merit of having first suggested the building of lenses in se- 
parate 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 de- 

* Hutchinson's Practical Seamanship, p. 200. See also the notice of the spherical mirrors 
made by Messrs Francois and Letourneau of Paris in a subsequent part of this volume. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



241 



scribed this mode of building lenses in 1811, in the Edinburgh 
Encyclopaedia; and in 1822, the late eminent Fresnel, unac- 
quainted with the suggestions of Condorcet or the description by 
Sir David Brewster, explained, with many ingenious and inte- 
resting 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 aber- 
ration 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 de- 
termining the radius and centre of the curvature of the generating 
arcs of each zone, having contented themselves with simply depress- 
ing 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.* After mature consi- 
deration, he finally adopted crown glass, which, notwithstanding its 
greenish colour, he preferred to flint glass, as being more free from 

* 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. 



242 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



striw. 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.* The instru- 
ments have received the name of annular lenses, from the figure 
of the surface of the zones. 

A ray of light, in passing obliquely from one transparent body 
into another of different density, experiences at the point of the in- 
tersection 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 pheno- 
menon, 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 atten- 
tion to the laws which regulate the change of direction in the inci- 
dent light, which are three in number. 

1. Incidence and refraction, in uncrystallized media of homo- 
geneous structure such as glass, always occur in a plane perpendicu- 
lar to that of the refracting surface. 

2. In the same substances, the angle formed with the perpen- 
dicular by the ray at its entering the surface of the second me- 
dium, 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 nor- 
mally 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 refer- 

* 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, 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



243 




ence 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. 

The diagram (fig. 47) will serve to render those laws more in- 
telligible. Let a raj of light a meet a 
surface of water n m at 0, it will be imme- 
diately bent into the direction a ; and if, 
from the centre 0, we describe any circle, 
and draw a line b b\ perpendicular to 
n m; then a b 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 bO a, and of the angle of refraction b' a', and the 

ratio of those sines to each other, or 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 

/. ,i n \ • p • • j sine of refraction 

(in the case ot emergent rays) sine ot incidence = ; 

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. 



2U 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 




Tims, if a ray proceed from a point (fig. 48), within a piece 
of glass, to a point C, at its surface 
A B ; and if C b, its incidence, be 
less than 41° 49', it will be refract- 
ed in some direction Of ; but if 
this angle be greater than 41° 49', 
as C b\ the ray will be reflected 
back into the glass in the direction 
C 0'. 

The material hitherto employed in the construction of lighthouse 
apparatus is crown glass, which, although it possesses a lower refrac- 
tive 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 ex- 
posed 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 maimer above de- 
scribed, as to the truth of the following general propositions result- 
ing 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 inci- 
dent ray, and the refractive power and thick- 
ness of the plate. The effect of this displace- 
ment is merely to give the ray an apparent 
point of origin different from the true one. 
This will be easily understood by the diagram jjl 
(fig. 49), in which a b is a normal to the 
plate, whose surfaces x x and x' x' are parallel, 
rrrr shews the path of the ray, r r the dis- 
placement, and r' the apparent point of origin 
resulting from its altered direction. 



Fig. 49. 

a 




NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 24-5 



Pig. so. 





2. When a raj passes through a triangular prism a b c, the in- 
clination 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. 

3. When parallel rays fall on a concave lens, they will, at their 
emergence, be divergent. The sec- 
tion of the diaphanous body abed 
may be regarded as composed of in- 
numerable frusta of prisms, having 
their apices directed towards the 
centre line x r ; and the rays which 
pass through the centre, being nor- 
mal to the surface, will be un- 
changed 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. 

4. Lastly, when divergent rays fall on a convex lens a 6, from 
a point /, 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.* This 
effect, which is the opposite 
of that caused by the concave 
lens, may be explained in a similar manner, by conceiving the sec- 
tion a b of the convex lens to be composed of innumerable frusta of 
prisms, arranged with their bases towards the centre of the lens. 

* It is, of course, to be understood that only rays incident near the axis of the lens 
are refracted accurately to a focus. 

2 H 




246 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Now, it is obvious, that we can derive no assistance, in econo- 
mising the rays of a lamp for Lighthouse purposes, from concave 
lenses, whose property is to increase the dispersion of the rays in- 
cident on them. With concave lenses, therefore, we have no con- 
cern ; 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 gene- 
rally 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. 

Let Q q be a section of a lens, and / 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 diver- 
gent 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 po- 
sition of this point depends partly on the refractive power of the 
substance of which the lens is composed and partly on the curva- 
ture of the surface or surfaces which bound it. 




NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



247 



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 ad- 
vance, step by step, to the practical application of refracting instru- 
ments, 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 con- 
tent to refer, where needful, to those works, and shall confine my- 
self simply to what concerns Lighthouse lenses and their use. It 
would also be superfluous to determine the position of the prin- 
cipal focus of a plano-convex lens, in terms of the refractive in- 
dex and radius of curvature,* 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 direc- 
tion ; 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 

F= — - — - in which r is the radius of curvature, and m is the refractive index. — 
m— 1 

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. 



248 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 formulae used by his lamented 
predecessor, in determining the elements of those instruments which 
have so greatly improved the lighthouses of modern days. 

Spherical lenses, like spherical mirrors, collect truly into the focus 
those rays only which are incident near the axis ; and it is, there- 
fore, of the greatest importance to employ only a small segment of 
any sphere as a lens. The experience of this fact, among other con- 
siderations, led Condorcet, as already noticed, to suggest the build- 
ing of lenses in separate pieces. Fresnel, however, was the first 
whovactually constructed a lens on that principle; and he has subdi- 
vided, 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 tabu- 
lar 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 millimetres, or 36*22 inches, is about 11 inches in 
diameter; and the annular rings which surround it vary slightly in 
breadth from 2| to 1| 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 cor- 
rect the excessive aberration produced by refraction through a 
hemisphere or great segment, whose edge would make the parallel 
rays falling on its curve surface cod verge to a point much nearer 
the lens than the principal focus, as determined for rays near the 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 249 

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 incon- 
veniences in telescopic lenses have been devised ; and the sugges- 
tions 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 de- 
prived us of the advantages which would result from the use of 
telescopic lenses entirely free from spherical aberration. In Light- 
house 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 de- 
termining 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 doioels 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 | 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 com- 
posed 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 formulae employed by Fresnel, to de- 
termine the elements of the compound lens,* in the calculation of 



* It may be proper to mention that, while the formulae given in the text are those of 
M. Fresnel, I am responsible for the investigations in the Notes ; I have, at the same 



250 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Fig. 5i. 



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. 

I begin with the case of the central disc or lens round which 
the annular rings are arranged. Its principal section is a mixti- 
linear figure (fig. 54) composed of a segment 
b a c, resting on a parallelogram bcde, whose 
depth b d or ce is determined by the strength 
which is required for the joints which unite 
the various portions of the lens. Those par- 
ticulars 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 re- 
mains to be done by others. 

Referring to fig. 55, we have, for obtaining the radius of the 
central disc, the following formulae, in which 




Pig. 55. 



r = AB, half the aperture of the lens 
r = AB' 

= AF, the focal distance 
t' —Aa, the thickness of the lens at the ^ 

vertex v* \ 

t" = Bb, the thickness of the joint 
/U = the index of refraction 
|0 = the radius of curvature. 

Then for the radius of curva- 
ture near the axis we have : 



and for that near the margin we 
have : 




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. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



251 



tan i' — 



sra e = - 



sin i 



r' = r — t". tan e 

tan i=—r 




sin 6=- 



sm ^ 



and, finally p=^ ^J* * 



* The following steps lead to the formulse 
given in the text. Let APQB (fig. 56) re- 
present 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 he the centre of curva- 
ture, 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. 




Then fj. 



mii PCG 



PG 
CG 



and also p.— 



sin QFG 



QG 
QF 



sin GPC CG ^ sinQGF' 
Now, as P approaches A, we have ultimately PG = AG,QG = BG, and QF = BF ; 
Therefore, putting AG = and AC = p' 
_AG_ J9_ _ BG _ d-f 
^~ CG~ 6 — p"^~ BF — (p ' 
from which, fl 6— ]xp'=d; and// <p = d—t? and eliminating (9, we have p 2 (p + p. p' = 



p<p + t', whence, as above, p' = (p.— l) ((p + — 



But as this value of the radius of curvature, as already stated, is calculated for rays 
near the axis, it would produce a notable aberration for rays incident on the margin of 
the lens. In order, therefore, to avoid the effects of aberration as much as possible, a 
second radius of curvature must be calculated, so that rays incident on the margin of the 
lens may be refracted in a direction parallel to the axis. This second value of the radius 
is called p ' 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 me- 
dium is produced in the directions AB, a! b'. 



252 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



I come next to the second case, which concerns the calcula- 



Let C be the centre of curvature (see fig. 57) 
a = A C b the angle of emergence 
rf = W b C the second angle of refraction 
6 = B b B' the first angle of refraction 
i = B'F A the first angle of incidence 
*'=BFA 
e = b'Bb 

AB =r 

AB'-r' 

B b — f the thickness of the lens at the edge 

AY = (f) the focal distance. 

., r . sin i' 

l hen tan i = —r : sin e = 

(p fx 

whence bb' = t" tan e becomes known. 
Now, since BB' = b U nearly, AB' = AB - bb' 
or r' — r—t" tan e. 
From this is obtained the angle of in- 
cidence and the first angle of refraction e ; 

~ v 1 , . sin i 

tor tan i = -j- and sin € = - 



Fig. 57. 




Next B'bC=BbC-BbB' or r) = a-e 
and sin a = / u sin rf=jj. sin (a -e) 

from which, sin a cos e — cos a sin e = 



sin a 



sin ? 



cos- e— 



whence sin a^cos € -~j^ = cos a sin e ; and 

+ =cos 2 a sin 2 e = (l-sin 2 a) sin 2 e = sin 2 e-sin J a 



2 cos e 



Then transposing we have 

sin 2 a f (cos 2 € + sin 2 e) - l^if + -1 ) = sin 2 e 
L jJ. p. 2 ) 

and because (cos 2 £ + sin 2 c) = 1 we have, by dividing, 



sin- a = — 



sin- € 



f , 2 cos £ 11 



yll 2 sin 2 £ 



and sin a = 



p. 2 — 2/x cos £ + 1 
/z sin 6 



Next, since b C 



a'b 



sin AC b sin a 
we have p" — 



V 1 — 2 yu cos £ + yu 3 

, putting Cb = p", and substituting 

■\//U 2 — 2 /i cos € + 1 



yu sin e 

and, taking for the radius of curvature, the mean of p' and p" the values calculated 
central and marginal rays, we have finally p = ^ — 



for the 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 253 



Fiff. 58. 



tion of the elements of a concentric ring. The section abcde 
(fig. 58) of one of those rings includes a mixti- 
linear triangle a be, and a rectangle bee d, the 
thickness b c being the same as that of the edge 
of the central disc ; and the elements to be deter- 
mined are the radius of the curve surface, and 
the position of the centre of curvature, with re- 
ference to the vertex of the lens. 

The radius of curvature of the zone may be calculated by 




the following formuhe, in which 
(see fig. 59) 

r x =3 AB the distance of the outer margin 
of the zone from the axis of the lens 
r. — AE the distance of the inner margin 
from the axis 
/ = BE the breadth of the zone — r l — r s 
p — the radius of curvature = b C = m C 
(p = focal distance AF 
t= thickness of the joint B b 
t" = B b 

// = refractive index of the glass 
i x — BFA 
i 2 = EFA 

Y 

Then tan i', — tan 

1 (p 2 (p 



sin t 



; sin e„ = 



sm a' 



r\ = r 1 — t" sin e l ; 



r'=r. 



•t sine,. 



tan i ; tan i a — *~f- 
1 (p 2 (j) 



sm € = - 



sm i. 



sin € =- 



sm a = 



sm e 



sin a = 



2/jl cos e + 1 
sin 

vV~2/z cos e' + l ; 77 = 
and lastly p = , 



Fig. 59. 




2 cos e' 



2 cos {r; + i(a — a') } sin £ (a — a') 

which is Fresnel's value of the radius of curvature.* 



The following steps will conduct us to this expression 



2x 



254 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

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—p . sin a — a b — p . sin a — r, 
CQ = |0 . cos a — qQ = p . cos a — f 



Fig. 60. 



Let B 6/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'6 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 = /- i; KB' = r\; Cb = p 
AE=r 2 ; AE' = / 2 ; B b=t" ; BE = r^ -r a =1 
e = the first angle of refraction b B' k 
7] = the second angle of refraction B' b C 
€' = the first angle of refraction e E k 1 
7)' = the second angle of refraction e m C 
a = the angle of emergence b C q 
a' — the angle of emergence m C q 
i'j =BFA ; i' s =EFA ; 8 1 = B'FA ; » a =ETA 
e^BbB'; e s =EeE'. 

Proceeding exactly as in the case of the cen- 
tral lens we shall have 

BA r. , EA r„ 

tan 1 1 = ; tan * 2 = _ = ^- 



sin i 



sm i 



sin e, — 



sm e. = 



a 



/j = — t" sin e x ; 



tan i, =-r L ; tan i — 



= r„ — t" sin e , 

>"'n 



sin 6 = - 



<P 
sin i 



sm e = 



Sin 6 



0' 
sin f 



and sin a' ■ 



sm U ~Vp?-2p, cos e-1' ' \Zp. 2 -2ficos e' + l 

Now, the angle 6 Cm= a— a' from which (since the triangle bmC is 



isosceles) bmC — 90° 



£ (a — a!) ; also, in the triangle b m e, the angle 
bme = bmC—emC=90° — £(a — a'}—r) 
and 6 e m=k' e E' = 90 c — e' 




/a sin e 



We have therefore in the triangle b in e 
b e sin b e in I cos €' 



sin 6 e cos {77 + £ (a — a')} 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



255 



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 dia- 
meter, and 10 concentric rings, all of which have a common prin- 
cipal 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 con- 
jugate focus of the entire surface of the compound lens, differs in 
a very small degree from that obtained by calculation in the man- 
ner described below.* 



and in b m C 



a') 



^Q_bm sin b m C _ I cos e' cos |- (a - 

sin bG in ~~ cos (77 + &(a — a') sin (a - a') 

I cos e' cos A (a — a') 
~cos {77 + i- (a — a')} 2 sin i (a— a') cos ^ (a- 
from which, putting bC = p 



a') 



P = < 



I cos e' 



'2 cos {77 + i (a — a')} sin £ (a — a') 

* The tests generally applied for examining the lenses used in Lighthouses, is to find the Testing Lenses, 
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 



Fig. 61. 




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 i*ight 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 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 prin- 
cipal 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 is formed, or will be the con- 
jugate 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. 

We shall suppose QA (fig. 61) to represent the half of a lens, and remembering the 



256 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Divergence of An- 
nular Lenses. 




In the combination of lenses with the flame of a lamp, similar 
considerations must influence us in making the necessary arrange- 

conditions described in reference to the last figure, we shall at once perceive the truth of the 
following analogy (fig. 62) : — 

OA : AF : : AQ : FR : : AI : FI, Fig . 62 . 

and putting OA = 8, AI = <p', and : - ; 
AF = (jf), we have 8 : <p : : (p' : <p'—(p, 
and, consequently, 8 (p' —8 (p = (p (p' ; 
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 : 

1st, To find the principal focal distance of a lens from the measured position of its ob- 

8 d>' 

ject and its image refracted through it, we have, (p — ^ A p' 

2<1, For the distance of the object, when that of the image is known, we have, 8 = . 

8 (b 

'3d, For the position of the image, when that of the object is known, we have, <p' = ^ — 

In testing lenses, of course, it is this last equation which we use, because the value of (p or 
the principal focus is always known, and is that whose accuracy we wish to try, while 8 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 (p' due to 
50 yards, which in this case is 
equal to AF', OA being equal 
to 8; and move a screen of white 
paper backwards and forwards 
until you receive on it the small- 
est 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 l'ecede 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 <p', is an indication 
of the accuracy of the workmanship of the lens. When the measured distance is greater 
than the calculated (p', we know that the lens is too flat ; and it is on this side the error 
generally falls. On the other hand, when (p' is greater than the measured distance, we 
know that the lens has too great convexity. I have only to add, that an error of on 
the value of <p' may be safely admitted in Lighthouse lenses ; but I have had many in- 



Pier. 63. 




NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 257 

ments, as in the case of reflectors. We have already seen that the 
size of the flame and its distance from the surface of reflecting in- 
struments have an important practical bearing on the utility of 
the instrument, and that the divergence of the resultant beam ma- 
terially 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 iden- 
tical with those which determine the divergence of a paraboloidal 
mirror illuminated by a lamp in its focus. The divergence, in the 
case of lenses, may be described as the angle which the flame sub- 
tends at the principal focus of the lens, the maximum of which, pro- 
duced at the vertex of Fresnel's great lens by the lamp of four 
concentric wicks, is about 5° 9'.* 

On the subject of the illuminating power of the lenses, it seems illuminating 
enough to say, that the same general principle regulates the estimate Pmver of Le 
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 illu- 
minating effect of the great lens, as measured at moderate distances, 

struments made by M. Francois Soleil, whose error fell below g 1 ^ of (p' . Owing probably 
to the mode of grinding, the surfaces of all the lenses I have yet examined are somewhat 
too Hat. 

* This will be easily seen by examining the annexed figure (64), in which Q q represents 



258 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Arrangement of 
the Lenses in a 
Lighthouse. 



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 pro- 
duced a considerably greater effect. 

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.,* 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 



the lens, A its centre, F the principal focus, b F and b'F the radius of the flame ; then is the 

Fi K . 64. 




psr. 



6F 



angle b A V equal to the maximum divergence of the lens. Sin b A F = = sin 6'AF = 

"^ a( ^ °^ — ame ; and twice b AF = the whole divergence at A. Then for the divergence at 
Focal distance ' 

the mai-gin of the lens, or at any other point, we have, FQ = \/(AQ- + AF 2 ) and Q x 

I . Fa; 

= \Z(QF 2 + F« 2 ) ; and for any angle at Q, we have sin FQ« = |Tq. 

* 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. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



259 



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 ser- 
vice of the mariner, by means of two very simple expedients, the 
light which would otherwise have uselessly escaped above and be- 
low the lenses. 

For intercepting the upper portion of the light, Fresnel em- p j 
ployed 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 ad- 
visable 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 de- 
fect 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 formulae as those given 
for the great lenses. In fixing the focal distance and inclination 
of those subsidiary lenses, Fresnel was guided by a considera- 



260 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Curved Mirrors. 



tion of the necessity for keeping them sufficiently high to prevent in- 
terference 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. 

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 Light- 
house; and any attempt to subject it to lenticular action, so as 
to add it to the periodic flashes, would have led to a most incon- 
venient 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 diop- 
tric 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.* 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 



Fief. 65. 




-11 



* 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 0, and draw Nf 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 261 

screws, which are attached to the backs of the brass cases, and 
which afford the means of adjusting them to their true inclina- 
tion, so that they may reflect objects on the horizon of the Light- 



parallel to a tangent of the curve, or topP, then PO 
or p O is the radius required. Now, we have similar tri- 
angles 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 

Hence compounding those 
ratios (in which Pd = Nn 
nearly) 

Ne 
also N e 

(for O P p and N o e are si- 
milar triangles) 

PH 2 : PN 2 

then PN 2 -PH 2 = HN 2 
and PO-NO = NP, 
therefore HN 2 : PN 2 : : NP : PO. 

PN 3 



Fig. 66. 



Pp 



PH 2 : PN 2 
NO : PO, 



NO : OP, 




and finally, PO: 



HN 2 " 



Then put FP = HC = FN = / o ; SN='p-s- then as FP 2 -FH 2 = PH 2 = 
PN 2 = PH 2 + HN 2 = (p* - 2 ) + (pa -2pz + z 2 ) 
= 2p 2 -2pz 
?2S = V2p(p-z) 

Therefore PO = ^ 2 P & ~ 
{p-zf 



:p 2 -Z 2 



0« 
»3 



and finally, PO = 2*/2 \/ -Bl 

p-z 



2k 



262 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



house to an observer's eye, placed in the common focus of the 
system.* 



To find the versed sine of the curvature (which may be use- 
ful in the examination of the mirrors by a mould) we may pro- 
ceed (see fig. 67) to 

put AG=/; BE = C; AC = R 

then BG 2 = AG . GD 
4BG 2 = BE 2 = 4AG . GD 
C 2 = 4/. (2R-/) 
C 2 = 8/R-4/ 2 

From which equation, 

,C 2 




2/- 2R = riV4R 2 - C 2 = - 2R + 

4 R 



64 R ; 



&c. 



2/= 



C 2 

4R " 
J 8R 



C* 
6411 3 

C* 
128R 3 



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, /, which is arbitrarily placed in front of the mirror ; and 6 = 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. 
fW = a 
SW = b 

OM'=:R 

Then (because / MS is bisected by 
OM, and for points near the vertex 
of the mirror at M') 

SM' : fW : : SO : 6/ 
or 6:a::R — b : a — R 
a b— Ra = R6 — ab. 

R ct 

From which b = 2 a _R ' tue Stance required, in which an error of (of its whole 
length) may be safely admitted. 



Fig. 68. 



— -(KHSi 




* See note on next page. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 263 



Having once contemplated the possibility of illuminating Light- Cylindric Refrac- 
houses by dioptric means, Fresnel quickly perceived the advan-^g^ Flxed 
tage 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 consider- 
ing 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 pos- 
sesses the property of simply refracting the rays in one plane co- 
incident 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 refract- 
ing an equally diffused zone of light round the horizon. The dif- 
ficulty, however, of forming this apparatus appeared so great, that 
Fresnel determined to substitute for it a vertical polygon, coni- 



* 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 determin- 
ed as follows : Draw a line from the focus F 
through the point 0, where the centre of the mir- 
ror is to be, producing it beyond that point to a con- 
venient distance at I ; through draw HOH, pa- 
rallel 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. 



Fig. 69. 



n 




264 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

posed 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 suffi- 
cient 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 man- 
ner, than by any combination of the parabolic mirrors used in the 
British Lighthouses. 
Application of An ingenious modification of the fixed apparatus is also due to 

crossed prisms to . . . . „ 

cause occasional the inventive imnd oi r resnel, who conceived the idea ot 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 cylin- 
dric pieces have the property of refracting all the rays which they 
receive from the focus, in a direction perpendicular to the mixtili- 
near section which generates them, it is obvious that if two re- 
fracting 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 revo- 
lution of cylindric refractors with vertical axes, ranged round the 
outside of the fixed light apparatus already described. 
True Cylindric Having been directed by the Commissioners of the Northern 
Refractors 1 ami 116 Lighthouses to convert the fixed catoptric light of the Isle of May, 
menL^^hdr a dioptric light of the first order, I proposed, that an attempt 

Construction. should be made to form a true cylindric, instead of a polygonal belt 
for the refracting part of the apparatus ; and this task was success- 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



265 



fully 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 be- 
comes at the same time more easy. One other variation from the 
mode of construction at first contemplated for the Isle of May re- 
fractors, was forced upon me by the repeated failures which oc- 
curred 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 manu- 
factory of Messrs Cookson. I also, at a subsequent period, greatly 



266 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

improved the arrangement of this apparatus, by giving to the me- 
tallic frames which contain the prisms, a rhoniboidal,* 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 inter- 
ception is confined to a small rhomboidal space, whose area is in- 
versely proportional to the sine of the angle of inclination ; and if 
the helical j oints be formed between the opposite angles of the old 
rectangular frames, the amount of intercepted light becomes abso- 
lutely equal in every azimuth.f 

Such an apparatus is shewn in Plate XVII. ; and the accom- 
panying diagram (fig. 70) shews an elevation ABCD, a section 



Pig. 70. 




BD, and a plan ABD, of a single pannel of this improved com- 
pound belt. AC and BD are the diagonal joints above described. 
Time and perseverance, and the patience and skill of Monsieur 

* The form would not be exactly rhomboidal, but would be a portion of a flat helix in - 
tercepted between two planes, cutting the enveloped cylinder at right angles to its axis, 
f Sec my Report on the Refractors of the Isle of May Light, 8th October 1836. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 267 



Francois Soeiee. 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. 

The loss of light bv reflection at the surface of the most perfect Catadioptnc 

, * . . Zones. 

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 Fres- 
nel, to whose friendship (as I have often, with much pleasure, ac- 
knowledged) 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 com- 
putations : but put me in possession of various important sug- 
gestions, 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 greatlv abridged the 
labours of computation. Mr Fresnel agreed with me in antici- 
pating a considerable increase of the light derived from the acces- 
sary 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 quan- 
tity of light acted upon by the curved mirrors : and. although the 
difficulties of grinding were somewhat similar to those which had 
alreadv been encountered in forming the cylindric belt for the Isle 
of May apparatus, there were also some special difficulties attend- 



268 



NOTES OX THE ILLUMINATION OF LIGHTHOUSES. 



ing 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 
1| inch), which is the distance traversed by the ray between its im- 
mergence into and its emergence out of the zones of the small ap- 
paratus ; and having had it carefully polished, with both faces pa- 
rallel, 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 fths of the inci- 
dent light. According to the experiments of Bougeur, the loss 
by the two refractions may be assumed at ^th. ; so that we could not 
sensibly err in concluding that the whole loss due to the transmis- 
sion of the light through the zones would not much exceed fths of 
the incident light. In the lights of the first order, the loss by re- 
flection from the surface of the mirrors, and by the escape of light 
through the interstices which separate them, is not less than |ds 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 imper- 
fections 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 im- 
portant to be readily renounced, more especially when it was 
considered that the fixed lights, to which it chiefly applies, are 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 269 

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 millimetres 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 iso- 
sceles 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 fromM. Leonor F resnel, 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 at- 
tempts 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 ho- 
rizon, so that none might be lost. He, at the same time, informed 
me of the success of M. Francois 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. Fres- 
nel 's Table afresh, with results differing from his only in one or 

2 L ' 



270 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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. Francois 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 appa- 
ratus 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 cylin- 
der 6 feet in diameter, and 30 inches high ; below it are six trian- 
gular 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 de- 
termined ; and this, I fear, I cannot do without considerable pro- 
lixity of detail. Referring to Plates XV., XVI., XVII., and XVIIL, 
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 A 2 B 2 C 2 (fig. 71, on page 
271), whose action on the divergent rays of the lamp causes the 
rays FC, FB and FC 2 , FB 2 to emerge horizontally, by refracting 



NOTES OX THE ILLUMINATION OF LIGHTHOUSES. 



271 



them at the inner surfaces BC, B 2 C 2 , reflecting them at AB, A 2 B 2 , 
and a second time refracting them at AC, A 2 C 2 . 

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 an- 
nular 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 fol- 
low the horizontal direction CH. 



Fig. 71. 




272 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 corol- 
laries. 

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 horizon- 
tally 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 ne- 
glecting 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 inci- 
dence 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 273 

directions backwards through the zones to the focus. This method, 
however, depends entirely upon accurate protraction, and is there- 
fore 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. 

Eeferring to fig. 72, which shews the first and second zone of 



Fig. 72. 




the upper series, we have 



Tan LCF = 



FL 

CL : 



and if we make 



the known angle, SCF = a 



OCF = f = the complement of BCF = the angle of incidence 



for FC. 



DC0 = 7 = angle of refraction. 
LCF = 6 = (HCF - 90°) = (2 a - 90 c ) 
SCD=(a + 7 -£) 



And m= the index of refraction for crown glass. 



we obtain the means of determining the angles 7 and f in two equa- 
tions, which are based upon the relation between the angles of inci- 



274 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



dence and refraction, and on the interdependence of the various 
angles about C. These primary equations are : 

sin £=m . sin 7 
and 

* y = 2£-6 (making 2 a-90° = <9) 
Eliminating 7 between these two equations we obtain : 

sin £=m. sin (2 £— #) 

an expression, which, after various transformations of circular 
functions, assumes the form 

sin 4 £-i sin 6 . sin 3 £+ (_L--l\ . sin 2 £ + _L sin0. sin£+i sin 2 = Ot 



* The truth of the first of these equations (sin £ = m . sin y) 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 per- 
ceive the truth of the second. I therefore subjoin the steps by which I reached it. It is ob- 
vious (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 = (a— y) = (OL + 7 — £;)> and, therefore, ACB, which is twice ACW or 
SCD= (2 a + 2 y — 2 £). Now, by construction OC is a normal to the refracting surface CB 
and its production C g gives AC g — y. But 7 = ACB — g CB = (2 a + 2 7 — 2 £) — g CB 
= (2 a + 2 7- 2 £) - 90°, hence 

7={2 a + 27-2 0-90°, 
and 7 — 27= — 7= — 2£ + (2 a— 90°) by transposition, and finally 
changing signs, we have as above : 
7 = 2£-(2a-90°) 
=2 £-6. 

f 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 £=m sin (2 £—6) 

sin j~ = m sin (2 6) 

= m{sin 2 £ . cos 6 — cos 2 £ sin 6} 
= m cos 6 . sin 2 £ — to sin 6 . cos 2 £ 
= to cos (9 . 2 sin £ . cos £—m sin . {1 — 2 sin 2 £} 
= 2 m cos 6 . sin £ . cos £ — m sin a + 2 m sin 6 . sin 2 
Therefore, to sin + sin £—2 m sin sin 2 £=2 to cos . sin £ . cos £ 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



275 



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 neces- 
sarily lies between zero and unity ; and as the protraction, if con- 
ducted with due care in the manner already described, affords the 
means of at once assuming a probable value of f 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 notwith- 
standing 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 £— m sin (2 £-0)=o (see page 274) be regarded 
as an expression for the error, when the true value of £ which 
would satisfy the equation has been introduced into its first mem- 
ber, we may consider any error in the value of £ as expressed by 
the equation : 

sin £— m . sin (2 £— 6) = e 

and differentiating this expression we have : 

</e = cos £ . d£-2m cos (2 £-0) . d £ 
= {cos £-2 m cos (2 £-0)} . <*£ 



Then : 

m 2 sin 2 6 + 2 m sin 6 . sin £ — 4 wr sin 2 6 sin 2 £ f sin 2 £— 4 m sin . sin 3 £ + 4 m 2 sin 2 6 . sin 1 £ 
= 4 m 2 cos 2 6 sin 2 £ (1 — sin 2 £) = 4 m 2 . cos 2 6 . sin 2 £—4 m 2 cos 2 6 sin 4 £. 
Hence we have : 

m 2 sin 2 6+ 2 m sin 6 . sin£+(l — 4 »i 2 ) . sin 2 £—4 m sin 6 . sin 3 £+4 m' 1 sin 4 £=0 
Then dividing bv 4 m 2 and arranging according to powers of £, we have as above: 

sin 4 ?— —sin 6 . sin 3 £ + (_L_— 1^ . sin 2 £ + _!_ . sin . sin £ + - sin 2 0=0 
m • \4 m- / s 2 m 4 



276 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Then dividing by the differential coefficient we obtain 

dp= il 

^ cos £- 2 m cos (2 £—0; 

But when £ becomes d e will also become e + d e ; but 
e+d€=0 
therefore d e = — € 
hence by substitution we have 

d y_ — C 

* cos £-2 m cos (2%-d) 

_ — {sin £— m sin (2^—0,)} 
cos £—2 m cos (2 0) 

£_ — sin £+m sin (2 £ — 0) 
^ cos £— 2 m cos (2 £— 0) 

By substituting, therefore, in this last equation the known values 
of m and 0, and the assumed value of £, a correction is obtained, 
which being applied to £ and the same process repeated, new cor- 
rections may be found until the value of d £ 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 £ 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 ob- 
tuse 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° + 7=90° +.2J-0. 
We next proceed to consider the form of BA, the reflecting side 
>f 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



277 



resulting direction of the reflected rays. The conditions of the 
question require, that every ray EW, after reflection at the surface 
AB, shall, like AVI, 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 con- 
dition of the problem, may, however, be produced by a curvature 
of AB, such that all the rays shall have a degree of convergence be- 
fore 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 inclina- 
tion required for causing the ray BF finally to converge to F ; and 
the line j oining B and A must be a curve, every point of which has 
its tangent inclined so as to serve the same purpose. 

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 form- 
ing an angle CAU, which is, 
of course, equal to the inclina- 
tion of the extreme rays re- 
fracted by CB at C, with rays / 
2 m # 




278 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 6, 
which must be so inclined that the ray F b will, after refraction 
at 6, be reflected into the direction, b C ; but as the rigorous deter- 
mination of this is difficult, I shall describe two approximations sug- 
gested 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 sup- 
position 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 inclina- 
tion 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, 

b FC 

according to the assumption, equal to -o-— s which may be expressed 

by \ 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 /3 of the secant of the reflecting arc over its radius the 
following expression : 

B(3 = i AB . tan * BFC* 



* The following steps will shew the mode of obtaining this expression : Suppose (tig. 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 re- 
fracted in the direction n 0, and draw nri parallel to CA, the ray which is refracted at C, then 
will n' nO — m.b FC = § b FC. But the tangent AZ should make with the tangent b Z an angle 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



279 



The value of B b gives, of course, the direction of the second 
tangent Zb (which must be equal in length to AZ), whence we 
easily deduce the chord of the reflecting side A b. 

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=?/ / , and finally reflected in 
the direction BC, must make the angle YBZ = MBC. I shall de- 



equal i 6 FC, or one-half the inclination of the rays refracted at b and C, which are after- 
wards 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), 

Av; „„- b FC bFC , 
or AX b = B Z b = — — = — — — nearly. 

2 m 3 

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 J- BFC. Then 

AB 2 = B/3 (B(3 + 2 AX) Pig. 74. 



= B/3 2 + 2B/3 . AX 




tan | BFC V 

X 

hence we have, as in the text, 

B/3=i- BA . tan J BFC 



280 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



scribe it as follows : In the an- 



Fig. 75. 



nexed figure (fig. 75) MBZ is 
a tangent to the reflecting sur- 
face at B, and KBF is the 
angle of incidence of the ray 
BF before its refraction at B. 




If KBF=^ / , and the angle of 



incidence of FC=ECF=£*, we 
have BFC (which is the incli- 
nation of those rays to each 
other, and must be equal to 



the difference of their angles of n e c k y t 

incidence to the same surface) =x—x', whence knowing x, we 
easily find a value of af corresponding to the length of BC. Then 
for finding the angle of refraction KBYrr?/' we have : 



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 =/x, we have the right angle NBZ made 
up of /x+f/' + NBK. But NBK clearly equals /u, because it is the in- 
clination of the normals to BC and BZ, and hence y' + 2 ^=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 ^ is easily found, for M = CB A + ABM = CB A + BAM- CB A + 
(MAC-BAC) = CBA + i(180°-^)-BAC. Thus knowing M and y\ 
we have only to see whether 



We have now only to find the length of the radius AX or h 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 



(y-2^)-90°=0 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



281 



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 

AC . sin AC b 



Ab = 



and, as above, 



sin b CA ' 

AX6 = *fr-y): 



Fig. 76. 



. , Ab . sin £(180° — (b) , AJ , , 

And AX=6X = p = A~ Xi =*A6 . cosecU <p. 

' sin r 

And, lastly, for the co-ordinates to X, the centre of curvature 
for the reflecting arc, we have 

OX = p . sin OAX 
and OA = jO . cos . OAX.* 

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 quanti- 
ties AH, HC, and BK, to Cy or Civ, 
and by deducting CK from Cy; 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 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° - (H AU + *CAU) . 




282 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 pro- 
duced 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 find- 
ing those co-ordinates is, of course, similar to that already given ; 
and, the radii being assumed at 4000 millimetres, the co-ordinates 
are respectively proportional to the sine and cosine of the inclina- 
tion of the radius at A to the vertical line, which inclination de- 
pends 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 C 2 of the second zone, 
which is at the intersection of the horizon GAG. 2 with the ray 
FBC 2 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. Theodoke 
Letourneau, who now manufactures the apparatus for the Northern 
Lights Board, in the room of M. Francois Soleil, who is en- 
gaged 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 them- 
selves, 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, 
oqual and similar to the cross section of the zone. The horizontal 
motion of this arm would, of course, detect the inaccuracies of the 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



283 



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 re- 

. , 1 Fiff. 77. 

presents the prism, with one angle 
inclosed between the arms AC and 
AB, moveable round a centre 0, 
and RR the graduated limb. This 
instrument is inconvenient and de- 
fective, as the convexity of the sides 
AB and BC of the zone requires 
some skill in getting the arms to 
be tangents to them. 

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 mea- 
suring 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 tele- 
scope, 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 maimer as to be capable of sliding on the rod, I observed the cut- 
ting 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 direc- 
tion 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 




284 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 verti- 
cal 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. F is the small 

Fig. 78. 




' 1 

flame in the focus ; ABC is the zone ; TT is the telescope ; and R 
a graduated limb, on which is read the angular deviation 6 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 suc- 
ceeded by this method in detecting the inaccurate position of some 
of the zones in the frame ; and the error has been reduced by care- 
fully 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 prefer- 
ence to that just described, was to measure the vertical inclination 
(given in the Table in the Appendix), of each surface of the zone, 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



285 



Fig. 79. 




Pig. 80. 




and more especially the reflecting surface, by means of the instru- 
ment, 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 se- 
cond (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 f 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 sur- 
faces 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 alter- 
ing 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.* 

Pig. 81. 



* In connection with the use of the clinome- 
ter, 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 inclina- 
tions (fig. 81) are shewn by the angles BNO, 
BON, and CPF ; and are given in the Table of 
the Zones in the Appendix. 

2 N 




286 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 
Framing of The mode of framing the greater zones is shewn in Plate XVIII. 

Zones. . & ° 

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 distri- 
bution of whose light, the whole of the apparatus, above described, 
is applied. Fresnel immediately perceived the necessity of combin- 
ing 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 prac- 
tical 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 sup- 
ply of oil, which is thrown up from a cistern below by a clock- 
work 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 carbon- 
isation 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



287 



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. 

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) 



Pig. 82. 



Fig. 83. 





shews a section of this burner. C, C, C", C w 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 chim- 
ney 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 



Pig. 84. 



m 



288 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 ba- 
lancing a weight placed at the opposite end of a lever. The mo- 
ment 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 ad- 
justed 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. Dela- 
veleye 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 289 

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 inge- 
nious artist whom M. Fresnel employed to carry some of his im- 
provements 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. 

The most advantageous heights for the flames in dioptric lights Height of the 



Those heights of flame can be obtained only by a careful ad- 
justment 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 millimetres (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 



are as follows : — 



flame of the Me- 
chanical Lamp. 



Inches. 



1st Order, 
2d Order, 
3d Order, 



10 to 11 centimetres = 3 94 to 4-33 

8 to 9 = 315 to 3-54 

7 to 8 = 2-76 to 3-15 



290 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 be- 
comes whiter and purer ; while by diminishing its aperture, the con- 
trary 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 horizon- 
tal plane the chimney is shut, when in a vertical plane it is open ; 
and each intermediate inclination increases or decreases the aper- 
ture. 

Position of flame I need scarcely add, that in order to produce the proper effect 
&oiwQf appara- °f a system of lenses or refractors, the vertical axis of the flame 
tus - should coincide with their common axis ; and it is further neces- 

sary, 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 millimetres = 1'10 inches. 

.... 2d order, 26 ••• =1-02 

- 3d order, 24 ••• =0-95 - 

For the purpose of placing the lamp in the centre of the appa- 
ratus, 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 spheri- 
cal segment, which acts in every azimuth. Its application to 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



291 



this purpose is due, I believe, to M. Letourneau, the successor 
of M. Francois 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 the air- 
bubble ; and e shews circles of equal altitudes en- 
graved on the glass. After the first application of 
this level, the adjustment of the burner as to its a 
central position is carefully repeated by means of 
a centre gauge (shewn at fig. 90, p. 295), with re- 
ference to the vertex of each lens, or to many points on the inter- 
nal 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 con- 
necting-rod that works the valves of the oil-pumps. 

The pumps of the lamp should raise, in a given time, four times Working of the 
the quantity of oil actually consumed by burning during that time. Lamp! ° f ^ 
Their hourly produce should be, 

lb. avoirdupois. 

For the lamp with four wicks, . . 6"615 

three wicks. . . 4*410 

two wicks, . . 1675 

This surplus of three times what is burned is necessary to pre- 
vent 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 XXIL, 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 




292 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Choice of Focal 
Point for various 
parts of the appa- 
ratus. 



and replace them by fresh ones, is a very simple process, more espe- 
cially 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.* 
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 import- 
ant 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 millimetres above the focus of 
the lenses, so that all the light be- 
low that point necessarily falls be- 
tween the horizon and the Light- 
house ; but for the lower zones, it 
was necessary, owing to their ar- 
rangement for convenience in a 
cjdindric form, to adopt a separate 
focus for each zone in the direc- 
tion 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 up- 
wards from a to / 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 rector round some point 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. 



Pi?. 86. 



PLANE OF FOCUS OF LENSES 



0i 



v// 



e 

J. 



* See also M. Leonor Fresnel's Instructions sur V organisation ct la surveillance du 
service des Phares ct Fanaux de France. Paris, 1842, pp. 12, 13, 14, and 15. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



293 



In the arc next the land, in fixed lights, a great loss of light Application of 
ensues from the escape of the rays uselessly in that direction. So ta^^Lm^So 
far back as 1834, I suggested the placing a segment of a spherical Llghts - 
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, Fig . 87 . 

mightbethrownback v "_ 

through the focal 
point and finally re- 
fracted into such a 



M 



■r 



direction as to contri- 
bute to the effect of r" 

the lens QA q in sea- M 
ward 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 dis- 
tance of the lenses, between which and the focus, the reflecting seg- 
ment 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. Francois ground some beautiful mirrors of three feet radius, 
which were afterwards tinned by his successor, M. Letourneau, 
by a new process discovered by himself;* 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" 1 " 1 - 
(5 feet 10 inches), which subtend a vertical arc of about 40°. 

The arrangements of the dioptric apparatus in the lightroom Arrangement of 
will be more fully understood by referring to the Plates. raS" PPa 

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 ; 

* See notice of a similar process practised about the year 1750 by Mr Rogers of London, 
ante, p. 240. 

2 o 



294 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 ; I/I/, 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 1/ I/, and so in- 
clined as to project the beams reflected from them in planes parallel 
to the horizon ; Z, Z are the lower zones, first used at Skerry vore, 
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 circu- 
lates, with the clockwork which give 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 cylin- 
dric 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 expla- 
Arran ementof na ^i° n of the arrangement of all the parts. 

the Dioptric Appa- p r the purpose of arranging the various parts of the dioptric 

ratus in the Light- , , . . . 

room. apparatus in their proper positions, three gauges are employed. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



295 




Pig. 89. 



The first (fig. 88) is for ascertaining that the lenses /, I, meet at the 
proper horizontal angle, 
so that their axes shall 
meet with the proper in- 
clination in F the focus. 
This is done by means of 
two arms, whose project- 
ing points r, r, r, r touch 
the backs of the lenses, 
while the graduated arc 
c indicates the inclination 
of I, I, to I, I, or the com- 
plement of that inclina- 
tion at F. 

Again, for ascertaining the verti- 
cally of the main lenses, or for setting 
the subsidiary lenses or mirrors shewn 
in Plates XIII. and XIV., at the re- 
quired angle of inclination, recourse 
is had to a clinometer (fig. 89) touch- 
ing 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. 

Lastly, to test the true 
position of the lamp it- 
self, with reference to the 
lenses thus properly ar- 
ranged, 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 





290 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



lens 1,1; at B is a graduated slide, which admits of the trainer be- 
ing 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 in- 
dicate the proper level for the burner which is noticed at page 290, 
in speaking of the lamp. The dotted line F & B' A' shews the 
position of the trainer in reference to an adjacent lens. 

The elegant apparatus invented by Augustin Fresnel for Har- 
bour 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 pro- 
ject all the light derived from the focus in a direction parallel to 
the other rays by total reflection. 

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 sec- 
tion and plan. F is the focal point in f%. 91. 
which the flame is placed ; r, r cylindric Zip ppj§^ 
refractors, forming by their union a cy- 
linder with a lamp in its axis, and pro- 
ducing a zone of light of equal intensity 
all round the horizon ; x, x are catadiop- 
tric prismatic rings acting by total re- 
flection, and giving out zones of light of 
equal intensity at every point of the ho- 
rizon. The dotted lines shew the course 
traversed by the rays of light which pro- 
ceed from the lamp, and are acted upon 
by the rings of glass. The letters r' r' shew the external prisms, 




NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 297 

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 de- 
scribed 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 con- 
venient 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 millimetres (about 19^ 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 millimetres; 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 Appen- 
dix :— 



298 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Number 
of Zone. 


Radii of 
curvature. 


Horizontal 
distance 
from the 

axis of the 
system. 


Vertical 
distance 
from the 
outer arris. 


Number 
of Zone. 


Radii of 
curvature. 


Horizontal 
distance 
from the 

axis of the 
system. 


Vertical 
distance 
from the 
outer arris. 






Reflecting Surfaces (Convex). 






I. 


1094-5 


723-5 


833-78 


V. 


1222-9 


523-6 


1169-1 


II. 


10457 


652-8 


89101 


VI. 


1249-4 


544-0 


11921 


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). 







T 

-I. 


1 9^0-0 


1290-7 


30319 


V. 


125000 


1 1 00-99 
1 IUU _ — 




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 


11730 


717-71 


VIII. 


125000 


1251-90 


557-22 






Inner Refracting Surfaces (Convex). 






I. 


12500 


150-67 


1211-90 


V. 


1250.00 


452-23 


1184-20 


II. 


12500 


228-19 


120880 


VI. 


1250 00 


453-07 


1185-20 


III. 


1250-0 


30510 


1203-35 


VII. 


125000 


374-60 


119600 


IV. 


1250-0 


381-00 


1195-30 


VIII. 


125000 


294-35 


1203-80 



Power of Dioptric The effect of an annular lens, in combination with the great 

Instruments. i • i it 

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 The dioptric lights used in France are divided into four orders, 

in relation to their power and range ; but in regard to their cha- 
racteristic appearances, this division does not apply, as, in each of 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



299 



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 de- 
scribed as follows : — 

1st, 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 con- 
centric wicks, consuming 570 gallons of oil per annum. 

2d, 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. 

3d, Lights of the third order, lighted by a lamp of two con- 
centric wicks, consuming 183 gallons of oil per annum. The in- 
struments 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 ')- 

4th, 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.* 

Those four orders are not intended as distinctions ; but are Distinctions of the 
characteristic of the power and range of lights, which render them loptnc Llghts - 
suitable for different localities on the coast, according to the dis- 
tance at which they can be seen. This division, therefore, is ana- 
logous 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. 

* An apparatus of O^'ISS 01 " - 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 cra- radius is styled the Sixth order. Those minute subdivisions I consider to be 
unnecessary. 



300 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

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, 1st, 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 ; 2d, Lights flashing once in every half minute, and com- 
posed of sixteen half lenses. Those lights may have the subsidiary 
parts simply catoptric, or diacatoptric ; and, 3d, Fixed lights, com- 
posed 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 cylin- 
drical 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 em- 
ployed 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 distinc- 
tions based upon colour have been discarded in the French lights. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



301 



The distinctions are, in fact, only four in number, viz. : Fixed ; 
Fixed, varied by flashes ;* 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 jive 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 expe- 
rience 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. 

Having thus fully described the nature of the catoptric and Comparison of 
dioptric modes of illuminating lighthouses, I shall next comparetoptriclpparatus 
the merits of both systems, with a view to determine their eligi-L^g* olvilie 
bility 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 em- 
ployed in the revolving lights on the Scotch coast. It may be 
said, however, that the dia-catoptricf 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 re- 
membered that in the French lights, this additional power is used 
only to compensate for one of the defects of the system by length- 
ening 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 

* The " Feu fixe, varie par des eclats," or " Feu fixe, a courtes eclipses," of Fresnel. 
t I use this word to designate the arrangement of pyramidal lenses and plane mirrors, 
by which the light is first refracted, and then reflected. 

2 r 



302 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



adopt the horizontal deviation of 7° for the upper lenses, with a 
view to remedy this defect. Assuming, therefore, that it were re- 
quired 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 reflec- 
tors 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 expe- 
rience at the Isle of May and Inchkeith, that the quantity of sper- 
maceti 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 consump- 
tion 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 con- 
sumed by ten reflectors, or 400 gallons in the year, against the 
Scotch system. But in order fully to compare the economy of pro- 
ducing 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. 

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 ap- 
paratus, may be estimated at L.1459, and the annual maintenance 
at L.354, 10s. 4d. It therefore follows, that to establish and after- 
wards 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



303 



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 re- 
volving lights on either system, may be estimated as follows : — 
In a revolving light, like that of Skerry vore, 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 Inch- 
keith, having seven sides of one reflector, each lighting with its 
greatest power a sector of 4 0, 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 -=- 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. 

I shall now speak of fixed lights, to which the dioptric method Comparison of 
is peculiarly well adapted. The effect produced by the consump-optr/rApprratus 
tion of a gallon of oil in a fixed light, with twenty-six reflectors/ 01 Flxed Llghts ' 
which is the smallest number that can be properly employed, may 
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 ag- 
gregate effect of 62,640, which, divided by 1040 (the number of 



304 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 aggre- 
gate 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 com- 
bustion 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.* The luminous cones, or pyramids of which 

* A similar arrangement can also he made in revolving lights hy making the radius 
of the mirrors somewhat less than that of the inscribed circle of the octagon hounded hy the 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



305 



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 sea- 
ward, by nearly one-third of the light which would otherwise be 
lost. 

The expense of establishing a fixed light composed of twenty- 
six reflectors, may be estimated at L.950, and its annual mainte- 
nance, 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 ho- 
rizoB, is four times greater. 

The comparative views already given of the catoptric and diop- 
tric 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 in- 
sures 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. 

A few general considerations, serving briefly to recapitulate the 
arguments for and against the two systems, may not be out of 

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. 



306 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



place. And, first, regarding the fitness of dioptric instruments for 
revolving lights, it appears from the details above given, — 
summary of con- \ s f That by placing eight reflectors on each face of a revolving 

siderations as to . . . . 

the fitness of the frame, a light may be obtained as brilliant as that derived from the 
RevoMng Lights, 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. 

2d, 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. 

36?, 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, al- 
ready so well known to British mariners ; and any change of exist- 
ing 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. 

4th, That the uncertainty in the management of the lamp ren- 
ders it more difficult to maintain the revolving dioptric lights with- 
out risk of extinction, an accident which has several times oc- 
curred at Corduan and other lighthouses both in France and else- 
where. 

5th, 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 tchole horizon is to- 
tally 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, 
b^iderations'as to In comparing the fixed dioptric, and the fixed catoptric appara- 
two s^stemffor 6 tus, the results may be summed up under the following heads : — 

Fixed Lights. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



307 



1st, It is impossible, by means of any practicable combination of 
paraboloidal 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. 

2d, The average light produced in every azimuth by burn- 
ing 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. 

3d, 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. 

4th, 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 com- 
bination of paraboloidal reflectors. 

5th, The inconveniences arising from the uncertainty which at- 
tends 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. 

6th, 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 result- 
ing from the extinction of the single lamp of the dioptric light, 
which deprives the whole horizon of light. 

7th, There may also, in certain situations, be some risk arising 
from irregularity in the distances at which the same fixed catoptric 



308 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Advantages and 
disadvantages of 
both systems un- 
der certain cir- 
cumstances. 



light can be seen in the different azimuths. This defect, of course, 
does not exist in the dioptric light. 

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 con- 
ducted 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 im- 
portant view ; but the consideration of vertical divergence must 
not be altogether overlooked. Now, while it is obvious that ver- 
tical 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 prac- 
tically 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 circum- 
stances. The powerful beam of light transmitted by the lens, pecu- 
liarly 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 incon- 
venience 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 309 

than the reflector, because, while the duration of its least diver- 
gent 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 ho- 
rizon ; and, while its least divergent beam is much less power- 
ful 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 exten- 
sive 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 practi- 
cal inconvenience ; but this defect may be partially remedied by giv- 
ing 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 sea- 
man's head. For the purpose of leading lights, in narrow chan- 
nels, on the other hand, and for the illumination of certain nar- 
row seas, there can be no doubt that reflectors are much more suit- 
able and convenient. In such cases, the amount of vertical diver- 
gence below the horizon, forms an important element in the ques- 
tion, 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 

2 Q 



310 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



whole or the greater part of the horizon, the use of dioptric instru- 
ments 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 re- 
venue 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 diver- 
gence in certain azimuths, than dioptric instruments afford, I have 
found it convenient and economical to add to the fixed refracting 
apparatus a single paraboloidal reflector, in order to produce the 
desired effect, instead of adapting the whole light to the more ex- 
pensive 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 illu- 
mination in the immediate vicinity of the lighthouse, we might, 
perhaps, advantageously adopt a variation of the form and dimen- 
sions 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 posi- 
tion between the parameter and the vertex, and slightly elevated 
above the axis of the instrument, so as to throw the greater por- 
tion of the beam resulting from this second burner below the ho- 
rizontal plane of the focus. Such an expedient is no doubt some- 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 311 



what 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 light- 
houses ; 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 conies before us, before selecting that instru- 
ment, or combination of instruments, which appears most suitable. 

The mode of distinguishing lights in the system of Fresnel, Distinctions of the 
depends more upon their magnitude and the measured interval of the ^ th^appfka--' 
time of their revolution, than upon their appearance ; and no other coloured 
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 appear- 
ance 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 con- 
cerned, 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 Map- 
lin Light at the mouth of the Thames, and Cromarty Point Light 
at the entrance to the Cromarty Frith, and in both instances suc- 
cessfully. 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 



312 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 rajs ; but the 
appearance of the light, at a distance, is much less marked than that 
produced by the glasses used in Britain.* Such deficiency of cha- 
racteristic colour might lead to serious consequences, as the trans- 
mission of white rays, through a hazy atmosphere, too often pro- 
duces, by absorption, a reddish tinge of the light, for which the less 
marked appearance given by the paler media might be easily mis- 
taken. 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 tchite light for a white 
light revolving at half the velocity. Such a mistake might per- 
haps 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 accord- 
ingly. All other coloured media except red have been found use- 
less 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 avail- 
able at the distance of a few cables' lengths. 



* See page 229, ante. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



313 



It seems to be a natural consequence of the physical distribution 

Captain Basil 

of light, that fixed lights, which illuminate the whole horizon, ^ r AL p L ^™ p ° s t t e 
should be less powerful than revolving lights which have their ef- appearance of 

* . Fixed Lights by 

feet concentrated within narrow sectors of the horizon. Any at- rapid movement, 
tempt 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 con- 
sideration 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 interme- 
diate between the lenses passes over his eye ; and this succession 
of bright flashes alternating with dark intervals, produces the cha- 
racteristic 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 per- 
fect 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, with- 



314 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



out 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 pos- 
sibility of causing a continuous impression on the retina by inter- 
mittent 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 consider- 
ably less than the duration of the impression itself ; for the con- 
tinuity of effect must, of course, be caused by fresh impulses suc- 
ceeding each other before the preceding ones have entirely faded. 
If it were otherwise, and the time required to make the impres- 
sion 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 
Lame, 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 315 



times may be in themselves, the one is yet 10,000 greater than the 
other. 

It has been ascertained by direct experiment,* 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 in- 
versely as the time required to make an impression. 

From this property which bright bodies passing rapidly before Effects of rapid 

■ i P 'j' i- • , ,i motion on the 

the eye possess or communicating a continuous impression to the power of Ll v hts 
sense of sight, Captain Hall conceived the idea, not merely of ob- 
taining all the effects of a fixed light, by causing a system of lenses 
to revolve with such a velocity as to produce a continuous impres- 
sion, but, at the same time, of obtaining a much more brilliant ap- 
pearance, 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 refract- 
ing zones at present used in fixed dioptric lights, or attempt to ob- 
tain 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 

* Lame, Cours de Physique, p. 424. " L'impression peut subsister encore lorsque la 
tmivante a lieu." 



316 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 si- 
milar and equal to that received by any other stationed at a differ- 
ent 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 hy- 
pothesis, 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 cu- 
rious physiological observations regarding the sensibility of the re- 
tina, 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 317 

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 se- 
ries of continuous impressions being weakened by a blending of 
the dark with the bright intervals, the eye would in reality be sti- 
mulated by the contrast of light and darkness, so as thereby to re- 
ceive 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 ap- 
peal 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 identi- 
cal 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 appa- 
rently continuous impression on the eye. To this experiment I 
added that of comparing the beam thrown out by the central por- 
tion 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 compa- 
risons at the short distance of 100 yards ; and in order to obtain 

2 R 



318 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

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 cir- 
cumstances, but with very different results. I shall not, how- 
ever, 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 dis- 
tance of 14 miles ; but shall briefly notice the more important re- 
sults which were obtained by the distant view. They are as fol- 
lows : — 

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 ef- 
fect was bv 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 sepa- 
rated by an interval of darkness ; and even when the nearest ap- 
proach 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



319 



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 warrant- 
able to draw the following general conclusions : — 

1. That our expectations as to the effects of light, when distri- 
buted according to the law of its natural horizontal divergence, are 
supported by observed facts as to the visibility of such lights, con- 
trasted with those whose continuity of effect is produced by col- 
lecting the whole light into bright pencils, and causing them to re- 
volve 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 vo- 
lume of the light and, consequently, cwteris 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 experi- 
ments warrant us in drawing; and the practical result, in so far as 
lighthouses are concerned, is sufficient to discourage us from at- 
tempting 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. 



320 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Connection of the This decrease in the volume of the luminous obiect caused by 

experiments with ... 

irradiation. 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. Pla- 
teau, in his elaborate essay on this subject, after a careful examina- 
tion of all the theories of irradiation, states it to be his opinion, 
that the most probable mode of accounting for the various ob- 
served 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 numer- 
ous 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 de- 
gree 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 ac- 
celerated, 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, 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



321 



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 neces- 
sary, of course, to make allowance for this penumbral arc by in- 
creasing 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 adop- 
tion, 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.* 

Those quantities may therefore serve to guide the Lighthouse 
engineer to approximate more rapidly to his object, as he will ge- 
nerally 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. 

* 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 (3 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 trian- 
gulation next day, and half the difference between the observed angle (which is always the 
lesser of the twoj and the computed subtense of the masked sector of the lantern, is, in 
each case, the amount of the allowance stated in the text. 



322 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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, there- 
fore, 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 cha- 
racteristic appearance. In many cases it is not necessary (but it is 
certainly always desirable) that the lights should, from the first mo- 
ment 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 ex- 
tent, 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.* But the effect of irradiation, to which I have al- 
ready alluded, tends to blend together the images of the lights long 
before their distance apart has become so low a fraction of the ob- 

* 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 visibi- 
lity, 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 fa- 
miliar to every one accustomed to view distant objects, that vertical length is an important 
constituent in their visibility. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



323 



server'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. 

Adopting this as the smallest angle which the two lights should 
subtend at the observer's eye, we may find the least vertical dis- 
tance between them which will cause them to appear as separate 
objects by the following formula: 

H = 2A . tan 6 

in which A is the observer's distance in feet ; 6, half the sub- 
tense, = 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 tri- 
angles, increase, of course, in an arithmetical series : 



Distance of the 

observer in 
Nautic Miles. 


Vertical distance 
in feet between 
the Lights. 


Distance of the 

observer in 
Nautic Miles. 


Vertical distance 
in feet between 
the Lights. 


1 


602 


11 


66-22 


2 


12-04 


12 


72-24 


3 


1806 


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 

. 1 


120-40 



Akin to the subject of Double Lights, is that of Leading Lights, Leading Lights. 



324 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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, ac- 
cording 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 in- 
dicate 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 doable 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 draw- 
ing the lines on an accurate chart of the locality. In some few 
situations, the configuration of the coast does not admit of a sepa- 
ration 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 intersec- 
tion, the distance between the lights, wherever attainable, should 
be not less than one-sixth of the distance between the more sea- 
ward of the two Towers and that point at which the seaman be- 
gins 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 se- 
parated, so as in some measure to compensate for their horizontal 
nearness, by rendering their intersection more sharp and striking 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



325 



than it can be where the observer must draw from the upper light 
an imaginary perpendicular in his mind, and then estimate the se- 
paration of the lights by the sine of an angle, which decreases as 
the difference of their apparent elevations increases. 

The considerations which enter into the choice of the position Distribution of 

p -i t • -i t o .,, ,1 Lights on a Coa 

and character ot the Lights on a line or 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 con- 
veniently 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 dis- 
covered 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 in- 
stances in which the distance separating lights of the same character 

2 s 



326 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

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 pos- 
sible, for sea-lights, exceed 200 feet ; and about 150 feet is suffi- 
cient, under almost any circumstances, to give the range which is 
required. Lights placed on high headlands are subject to be fre- 
quently 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 project- 
ing cliffs, which, while they subject the lights placed on them to 
occasional obscuration by fog, would also entirely and perma- 
nently 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 con- 
flicting, 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 ne- 
glected 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 327 



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 measure- 
ment 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 re- 
quire 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 distinc- 
tion from any neigbouring lights. 

14. Floating lights, which are very expensive and more or less 
uncertain from their liability to drift from their moorings, as well 



328 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



as defective in power, should never be employed to indicate a 
turning point in a navigation in any situation where the conjunc- 
tion of lights on the shore can be applied at any reasonable expense. 
Height of Light- The spheroidal form of the Earth requires that the height of a 
andTts relation to Lighthouse Tower should increase proportionally to the difference 
range of Light, between the Earth's radius and the secant of the angle intercepted 
between the normal to the spheroid 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 accord- 
ance 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 : — 
Referring to the accompanying 
figure (No. 92), in which S' d L' is a \ j / 

segment of the ocean's surface, the \ j / 

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, 

H'=i|- (1.) 

in which I = the distance in English miles L' d at which the light 
would strike the ocean's surface. We then reduce this value of IT 
by the correction for mean refraction, which permits the light to be 

2 I 2 

seen at a greater distance, and which =-^p' ( 2 -) 

2/2 2 I 2 At 2 
So as to get, H = — — - = — y- (3.) 

an expression which at once gives the height of the tower required, 




V 




NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



320 



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 earth. We must, therefore, in the first instance, 
find the distance d S = V, 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 : — 



Deducting this distance from SL, the whole effective range of the 
light, we have L d - I, and operating with this value in the former 
equation, 




we find the height of the tower which answers the conditions of 
the case.* From the above data the following Table has been 
computed. 



H 

Heights 
in 
Feet. 


A 

Lengths 
in English 
Miles. 


A' 

Lengths 
in Nautical 
Miles. 


H 

Heights 
in 
Feet. 


A 

Lengths 
in English 
Miles. 


A' 

Lengths 
in Nautical 
Miles. 


H 

Heights 
in 
Feet. 


A 

Lengths 
in English 
Miles. 


A' 

Lengths 
in Nautical 
Miles. 


5 


2-958 


2-565 


70 


11-067 


9-598 


250 


20-916 


18-14 


10 


4-184 


3-628 


75 


11-456 


9-935 


300 


22-912 


19-87 


15 


5123 


4-443 


80 


11-832 


10-26 


350 


24-748 


21-46 


20 


5-916 


5-130 


85 


12-196 


10-57 


400 


26-457 


22-94 


25 


6-614 


5-736 


90 


12-549 


10-88 


450 


28-062 


24-33 


30 


7-245 


6-283 


95 


12-893 


1118 


500 


29-580 


25-65 


35 


7-826 


6-787 


100 


13-228 


11-47 


550 


31-024 


26-90 


40 


8-366 


7-255 


110 


13-874 


12-03 


600 


32-403 


28-10 


45 


8-874 


7-696 


120 


14-490 


12-56 


650 


33-726 


29-25 


50 


9-354 


8112 


130 


15083 


13-08 


700 


35-000 


30-28 


55 


9-811 


8-509 


140 


15-652 


13-57 


800 


37-416 


32-45 


60 


10-246 


8-886 


150 


17-201 


14-91 


900 


39-836 


34-54 


65 


10-665 


9-249 


200 


18-708 


16-22 


1000 


41-833 


36-28 



* In the above expressions I and V are given in English miles, which in Scotland may he 
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. 



330 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 to- 
gether the two numbers in the column of lengths A or A' (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 dis- 
tance is required, we must seek first for the number in A or A' cor- 
responding to the height of the observer's eye, and deduct this 
from the whole proposed range of the light, and opposite the re- 
mainder in A or A' 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 con- 
structed for the Scotch Lighthouses, consists in the vertical direc- 
tion of the astragals, which, of course, tend to intercept the whole 
or a great part of the light in the azimuth which they subtend.* 
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 

* I must also except the small pier light at Kirkcaldy, erected (I believe in 1836) 
by my friend Mr Edward Sang. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



331 



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. 

Great care is bestowed on the glazing of the lantern, in order Glazing of the 

Lantern. 

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 gene- 
rally 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 \ inch wide, capable of holding a 
good thickness of putty, are provided in the astragals for receiving 
the glass, which is \ 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 com- 
posed. 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 use- 
ful 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. 

The ventilation of the lanterns forms a most important element ventilation of the 

Lanterns. 

in the preservation of a good and efficient light. An ill-ventilated 
lantern has its sides continually covered with the water of condensa- 
tion, which is produced by the contact of the ascending current 



332 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 plea- 
sure, so as to admit from without a supply of air when required, are 
provided in the parapet-wall on which the lantern stands ; the lan- 
tern roof also is surmounted by a cover which, while it closes the 
top of an open cylindric tube against the entrance of rain, and de- 
scends over it only so far as is needful for that purpose, still leaves 
an open air-space between it and the dome. This arrangement per- 
mits 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 in- 
ternal 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 ex- 
tremely bad ventilation in Lighthouses, Dr Faraday thus de- 
scribes his apparatus :* 

" 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 \\ inch 

* Minutes of Institution of Civil Engineers, vol. i., p. 207. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 333 

is opened out into a conical form, about 5| inches in diameter at 
the lowest part. When the chimney is put together, the upper 
end of the bottom piece is inserted about | 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 \ 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 ven- 
tilating flue is to carry up every portion of the products of com- 
bustion 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 junc- 
tions in no way interfere with the tube in carrying up all the pro- 
ducts 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 de- 
scribed 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 

2 T 



334 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



derangement from sudden gusts of wind from the roof in the man- 
ner noticed above. 

Arrangements and All the Lighthouses in the district of the Commissioners are 

ment of a Light- 

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 instruc- 
tions, 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 di- 
rectly 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, an- 
swers 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 manage- 
ment 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 light- 
keepers. 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



335 



the instructions already alluded to, which will be found in the Ap- 
pendix. 

Each of the two lightkeepers has a house for himself and fami- 
ly, both being under a common roof, but entering by separate doors, 
as shewn in Plates XXVII. and XXVIII., which exhibit the build- 
ings 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 light- 
keepers 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, there- 
fore, in situations such as Skerryvore, where it is unavoidable, the 
dwelling's 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 cleanli- 
ness in everything connected with a Lighthouse, the optical appara- 
tus 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. 

If, in all that belongs to a lighthouse, the greatest cleanliness Cleansing of Ap- 
be desirable, it is in a still higher degree necessary in every part f paratl,s - 
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 



336 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



Mode of measur- 
ing the relative 
iutensitj and 
power of Lights. 



freed from dust before being either washed or burnished ; and with- 
out 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 ap- 
plied, 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 care- 
fully 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 neces- 
sary 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. 

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 mea- 
surement of the intensity of lights by the method of shadows. 

The intensity of light decreases as the observer recedes from 
the luminous body, in proportion to the square of his distance. 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



337 



Suppose a beam of light to proceed from a 

radiant at F, and we shall have the rajs e 
which, of course, move in straight lines, 
gradually receding from each other, as F 
b, b\ b" , b"\ and c, c\ c", c'" ', so that the sec- 
tion of the beam will increase with the 
distances F b, and F c ; and the same num- 
ber 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 por- 
tions of a vertical screen of paper, we may, by repeatedly com- 
paring the luminousness of those surfaces, and moving one of the 
lights farther from, or nearer to the screen, at length cause the se- 
parate portions of the paper to become equally luminous. This ar- 
rangement, 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 posi- 
tion at (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 to cast a sha- Pig 94 

dow 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 EE 
by one of the lights, while every other por- 





338 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



tion 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 S S ; and we shall have the ratio of the 
intensity of the light at F to that of the light at F', as (F S') 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 pre- 
cautions 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. 
More accurate com- The difficulties of estimating the deepness or sharpness of the 
teniit n <rf SgMs" 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 Traite de V eclair age, 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 varia- 
tions 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 in- 
creased. 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 com- 
pared be placed on a table, in such situations as to spread pretty 
far apart on the screen the shadows of a vertical rod placed be- 
tween 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 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



339 



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.* " 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 centimetres, 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. 

" 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. 

" Let A B (fig. 95) be a white opaque surface, a, a luminous 
body, and m, a black opaque body, then the Fig. 95. 

shadow V cast on A B, will appear deeper 
when observed from P, than as seen from 
Q. This is a fact which may be easily veri- 
fied, and the cause of which is easily con- 
ceived. In fact, the surface A B, although 
it disperses the light, must still reflect more a. 1 
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 h' must appear deeper from the 
point P than from Q. Pi 96 

" If we now place (fig. 96) two lights a B 
in front of the screen AB, at such distances q J 

that the two shadows a' and b' should have 

equal intensities, it is evident that if the Z^i* 
eye be placed at P, the shadow V must ap- 6 ^ J 

* Traite de 1'eclairage, p. 214. 




340 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

pear 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 ob- 
served, 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 V is illumi- 
nated 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 sha- 
dows 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 pro- 
portion 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). 



XOTES ON THE ILLUMINATION OF LIGHTHOUSES. 341 



" 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 per- 
ceive the differences ( of the intensity in the shadows) to be in op- 
posite directions. The distances of the lamps may then be consi- 
dered 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 per- 
fectly equal also.* 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 sufiiciently 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 penum- 
brae 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. 

" "When we wish to make a great manv observations, it is verv 
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 

* 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, 
bowever quick Iv taken. 

2u 



3-t2 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

generally use a table CC DD (fig. 97), about two metres long 
(6 feet 6 inches), by 80 centimetres wide (2 feet 8 inches). At one 
end I place the screen AB, covered with white paper, dull (or not 

Fig. 97. 




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 / 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 ob- 
serving which you wish to follow. These lines M/, Mg I divide 
into decimetres and centimetres, starting from the points a\ b\ and 
over these lines I place the centres of the flames ; the distance be- 
tween 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 lat- 
ter for the former, without causing any sensible error. That dis- 
tance 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 plum- 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 343 



met, whose point will touch some division and indicate the dis- 
tance 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 in- 
tensity. 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 ( nettete J of the 
shadows, and to make them more distinct when they are viewed 
from the point x"* 

1 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 con- 
venient 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 /M, and carrying the divided scales of 
centimetres. This affords the means of making any slight change 
in the position of the lamps so easily, as entirely to avoid the dis- 
turbance of the flame which ensues from lifting the lamp and re- 
adjusting 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 observa- 
tions 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 

2 Those who feel a curiosity to look farther into this subject may consult Count Rum- 
ford's elaborate paper in the Phil. Trans, for 1794, p. 67. 



344 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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 com- 
parison of the intensity, and not of the aggregate poicer of two 
flames, is to be made, it is necessary to adopt the precaution of in- 
closing 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 quo- 
tient 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 : — 



Trials. 


Distance. 


Squares of Distances. 


Illuminating Power, or 
Quotient of Squares. 


Lamp A. 


Lamp B. 


Lamp A. 


Lamp B. 


Lamp A. 


Lamp B. 


1 

2 


143 
117 


140 
114 


20,449 
13,689 


19,700 
12,996 


1-00 
100 


0-958 
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 ve- 
rified 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 extin- 
guished, without touching the wick, and its clockwork movement 
was stopped. One hour afterwards, I set the clockwork in mo- 
tion and relighted the lamp, but without touching the wick. It 
was found in the same state as at the first comparison, and I mea- 
sured its intensity in reference to the first. Those experiments 



NOTES ON THE ILLOILNATIOX OF LIGHTHOUSES. 



34-5 



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 conti- 
nuance of the (successive) observations." 



r~ — — — 

Time; of 
Observation. 




Lamp. >~o. 1. 


Lamp. Xo. 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 tem- 
perature 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 employ- 
ing a gas-burner, supplied from a gasometer under a constant pres- 
sure ; but I found it very difficult to obtain satisfactory proof of the 
constancy of the pressure: and in a large town, where there are 
manv burners around one, their lighting: or extinction is found to 



346 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



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. 

K There are various dangers on the shores of Britain, more espe- 
cially 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 fol- 
lowing brief sketch of the nature and peculiarities of Floating 
Lights which was communicated to me by Mr Herbert, the se- 
cretary of the Corporation : — 

" The annual expense of maintaining a Floating Light, includ- 
ing the wages and victualling of the crew, who are eleven in num- 
ber, 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 para- 
bolic 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). 



NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 



347 



" The Corporation's light-vessels are moored with chain- 
cables of 1^ 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, con- 
sisting of 100 fathoms of chain to each arm, and a mushroom an- 
chor 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.) 

Still lower in the scale of " signs and marks of the sea," are Beacons and 

Buoy~ 

Beacons and Buoys, which are used to point out those dangers 
which, either owing to the difficulty and expense that would at- 
tend 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 prefer- 
red 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 uncom- 
pleted 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 XXXII., for about L.640. In less exposed places, where 
the bottom is gravel or hard sand, a conical form of Beacon, com- 
posed 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 



348 NOTES ON THE ILLUMINATION OF LIGHTHOUSES. 

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 ex- 
clusively 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 heat- 
ing 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 



NOTES ON THE rLLOILXATIOX OF LIGHTHOUSES. 



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 can- 
not add that any practically useful result has been obtained. 

In laying do^n Beacons or Buoys, their position is fixed, as 
may be seen in the Table in the Appendix, either by the intersec- 
tion of two lines drawn through two leading objects on the shore 
(the magnetic bearings of which are given for the sake of easy re- 
ference 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 Buov from which thev are 
measured by means of a sextant. In the latter case, the angles are 
always measured around the whole horizon, thus affording a check 
bv the difference of their sum from 360°. The magnetic bearing 
of one of those lines is afterwards carefullv ascertained, bv 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 
IvXXITL. bv means of chains and iron sinkers, with a sufficient 
allowance in the length of the chain to permit them to ride easily. 



APPENDIX. 



353 



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), af is the height of the co- 
lumn, a c and fh the radii of its base and top ; and we have to determine the par- 
ticular hyperbola which will pass through the points c, h. 

Putting be = x ; e y=y, the equation to the curve, referred to its asymptotes, is 



in which the value of the constant is to be found. For this purpose we have the 

conditions a c = 21 ; / A = 8 ; and a /= 120*25. Let the co- 
ordinates of the point c be x 1 , y', and of h, x", y", then Fig- 98. 
y' = 21 ; y" = 8 ; x" = x' + 120-25. f | — /' 




And since 



a' 

x' y' = - ?r =x" y' 



we have 



21 z'=8(>' + 120-25) 
^=74 



e 



9 



from which 



and 



|-=^y=74x 21 = 1554. 




Therefore a;y = 1554. 

Transferring the origin to a, x becomes x—x' — x — 74, 
and y (x — 74) = 1554, and the required equation by which 





b 



d 



the following Table was computed is, y — — - 



2 Y 



354 APPENDIX, No. I. 



Table of the Radii of the Hyperbolic Column at each foot of its 

Height. 



Height. 


Radius. 


Height. 


Radius. 


Height. 


Radius. 


Height. 


Radius. 





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 


9195 


3 


20-182 


34 


14-389 


65 


11180 


96 


9141 


4 


19-923 


35 


14-257 


66 


11-100 


97 


9-088 


5 


19-671 


36 


14127 j 


67 


11021 


98 


9035 


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 


13170 


75 


10-430 


106 


8-633 


14 


17-659 


45 


13059 


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 


10157 


110 


8-446 


18 


16-891 


49 


12-634 


80 


10091 


111 


8-400 


19 


16-710 


50 


12-532 


81 


10-026 


112 


8-355 


20 


16-532 


51 


12-432 


82 


9962 


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 


8222 


23 


16021 


54 


12141 


85 


9 774 


116 


8179 


24 


15-857 


55 


12046 


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 


8010 


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 







355 



APPENDIX, No. II. 

NOTES ON THE MANUFACTURE OF PARABOLOIDAL REFLECTORS, 
from Information furnished by Mr James Murdoch, of the Northern Lights 
Service. 

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 

Pig. 99. 




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, 



356 



APPENDIX, No. It 



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 



Fig. 100. Pig. 101. 




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 pro- 
cess of smoothing the reflector all over, the workman bestrides the horse. 

During the process of raising with the peened side of the mallet, an ex- 
ternal mould FGHF (fig. 101), with a needle-point P, at its vertex, is ap- 
plied, to indicate its proper position with reference to the mould ; and allow- 
ance is made on the height and diameter of the reflector to meet the ex- 
pansion 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 re- 
moved 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 parabo- 
loid to the proposed size. 



ON THE MANUFACTURE OF PARABOLOID AL REFLECTORS. 357 



The reflector is next hard-hammered all over (or planished, as it is tech- 
nically 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. 

Fig. 102. Fig. 103. Fig. 104. 




Fig. 105. 



This is a tedious process, and the workman requires continually to have re- 
course 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, 




358 



APPENDIX, No. II. 



Fig. 106. 



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. 

When thus finished from the hammer, the reflector is put into the appa- 
ratus shewn in fig. 106, which is placed at the end of a long dark cor- 
ridor. R R 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 al- 
ways 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 ad- 
mit of perfect adjustment to the point which- ought to be the focus of the re- 
flector. 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 ap- 
pear 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 P P (which is 
worked by means of the arms A A, 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 P P, cross-arms F F, which are provided with sockets H H, 




ON THE MANUFACTURE OF PARABOLOIDAL REFLECTORS. 359 



which slide over the rods G G, G G, are added to prevent any lateral shake 
or derangement. The whole frame is stiffened by the cross-head in which 
the screw S works. 

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. Af- 



Fig. 107. Fig. 108. 




ter this the reflector is ready for being finally polished; for which purpose, 
it is placed in a chaise percee, padded round the edges, and is first scoured 
all over with a piece of pure charcoal of hard wood, and next with a mix- 
ture 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 



360 



APPENDIX, No. II. 



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 re- 
flector-making are generally as follows : — 

Raising the plate to the curve, with the wooden mallet, L.O 10 

Hammering and smoothing to the mould, . . 15 

Finishing in the die, and putting on bizzle and back-belt, G 

Polishing, . . . . . . 12 

L.2 13 

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. 



361 



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 rub- 
bers 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 Catadiop- 
tric 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 sur- 
faces 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 Ap- 
pendix, No. IV.) 

The pieces must be 
placed end to end on the \ / 

horizontal plane or table of 71 \~ o 

the lathe at A A (fig. 110), f 

and must rest on the exterior arris A of the reflecting side, on which arris 

2 z 



Pig. 110. 

i 




362 



APPENDIX, No. III. 



there is ground a narrow plane whose width is proportionate to the projec- 
tion 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 0, the grinding centre for the exterior concave refracting sur- 
face AC, are measured, and e AC the arc swept by the grinding surface. Con- 
versely, n' is the origin of the co-ordinates for the grinding centre 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 mo- 
tion 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 de- 
ranged 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° centi- 
grade. 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 pre- 
cisely 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 cir- 
cular 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 millimetres (or about T Vth inch) 
between the ends of each of the two adjacent segments. Without this inter- 
val the heat evolved during the polishing would cither dilate the glass so 



GRINDING OF DIOPTRIC APPARATUS. 



363 



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 con- 
sequence of which would be the fracture of the pieces. Those intervals be- 
tween 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 there- 
fore 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 consi- 
derably 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. Ill), the outer edge of this nar- 
row 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 l 

AC and BC, combine to fix an accurate starting point for the rubber, in 
grinding the reflecting surface AB. 



Fie;. 111. 




364 



APPENDIX, No. III. 



Dressing off the rough, part of the Ring. 

The ring is generally reduced from the rough state by means of fixed rub- 
bers, the adjustment of which is more easily regulated than that of the move- 
able beam or radius of the arc, which is used to give the exact curvature of 
the surface. Those fixed rubbers are 150 millimetres (nearly 6 inches) wide, 
by 200 millimetres (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 pre- 
vent 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 free- 
stone 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 inequa- 
lities 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 grind- 
ing 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-ordi- 
nates (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 di- 
rect contact of the cast-iron rubber with the glass. Splintering or scratch- 



GEINDING OF DIOPTRIC APPARATUS. 



365 



ing, which cannot be easily effaced, may result from the neglect of this pre- 
caution. 

Practice alone, and an eye duly trained by continual experience, can de- 
termine the point of time at which each kind of emery must be discontinued. 
The celerity of the work depends on circumstances very difficult to appre- 
ciate, 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 milli- 
metres (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 inop- 
portunely 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 commence- 
ment of the polish ; and that the carpet-cloths should be brushed and washed 



366 



APPENDIX, No. III. 



twice rather than once. In all cases, the quality of the carpet forms an im- 
portant 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 fiat copper-wheel, one-half millimetre 
(gVth 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. 



GRINDING OF DIOPTRIC APPARATUS. 



367 



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. 

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 pre- 
vents 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). 

It is essential for the production of good cement, that the mixture of 
the ingredients be complete. 

Prices of the varioris parts of the Dioptric Apparatus. 

The expense of the various parts of the Dioptric apparatus is as fol- 
lows : 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; ap- 
paratus of sixth order, for whole horizon, L.44. The expense of the me- 
chanical lamp of the first order with four wicks, as made for the Scotch 
Lighthouses by Mr John Milne of Edinburgh, is L.30. 





368 



Diagrams illustrative of the Table, Appendix, No. IV. 

Fig. 114. 




[JSTIN FRESNEL. 



the construction of the grinding apparatus, at once to refer the whole of the grinding machinery to the axis of the 
^allax which the distance of the radiant points from the origin of the co-ordinates would occasion, it is necessary to 

1 Focus of the Lenses, and each y of this series, therefore, requires a reduction of that quantity ; while the x remains 
sector round a point between them. In this way, the xs remain unaltered ; but the tfs will be lengthened successively 
applicable to the existing protractions of that system. It is only necessary to add, that the conversion of millimetres 



AC, Outer Refracting 


Surfaces (concave). 


BC, Inner 


Refracting 


Surfaces (convex). 


A 




Radius 
of 

Curvature 
in Milli- 
metres. 


Horizonta 

distance oi 
centre of 

curvature 
from the 

axis of the 
System 
in Milli- 
metres. 


^ Vertical 
. distance oi 
centre 
of curva- 
ture above 

LUC UULCl 

arris of the 
Zone at A 
in Milli- 
metres. 


Inclination 
of the 
Radii in 
A and C. 


TtipI in n t.iAn 

of the Outer 
Radius at 
A to the 
Vertex. 


T? nriiiie 

1 i ! 1 1 i Llo 

of 

Curvature 
in Milli- 
metres. 


TTAri 7 fin f n 

distance of 
centre of 

curvature 
from the 

axis of the 

System 
in Milli- 
metres. 


distance of 

centre 
of curva- 
ture below 
the outer 
arris of the 
Zone at A 
in Milli- 
metres. 


Inclination 

of the 
Radii in 
C and B. 


lnr*lmfiTinn 

of the Outer 
Radius in 
C to the 
Vertex. 


Distance 
of C from 

tnp r ripn a 

LU4.C JL UL/UU 

for the 
Zones, 
in Milli- 
metres 
= FC. 

(Fig. 114.) 


J.MO. 

of 
Zone 


4000 00 


3825-31 


2817-77 


1 ii 

1 21 50 


O ' II 

45 12 56 


4000-00 


2021-19 


3777-07 


1 II 

1 19 24 


15 58 47 


1054-34 


i 




3923-65 


2683-55 


1 19 56 


47 51 52 




1918-37 


3797-40 


1 17 34 


14 48 41 


1069-02 


2 




4015-06 


2542-31 


1 18 34 


50 32 14 




1813-60 


3815-77 


1 16 16 


13 39 01 


1087-52 


3 




4098-54 


2394-23 


1 17 42 


53 14 00 




1707-55 


oool oo 


1 15 26 


12 30 46 


1J-W OO 






4173-08 


2239 64 


1 17 18 


55 57 02 




1599-72 


3846 04 


1 15 04 


11 23 47 


1136-14 


5 




4237-70 


2078-82 


1 17 20 


58 41 15 




1489-62 


3858-14 


1 15 08 


10 17 59 


1166-57 


6 




4291-45 


191218 


1 17 48 


61 26 32 




1376-71 


3868-30 


1 15 36 


9 13 16 


1201-46 


7 




4333-30 


174012 


1 18 44 


64 12 46 


... 


1260-38 


3876-59 


1 16 32 


8 09 30 


124116 


8 




4362-26 


156310 


1 20 06 


66 59 50 




1139-94 


388303 


1 17 56 


7 06 33 


128615 


9 




4377-24 


1 381-63 


1 21 53 


69 47 36 




1014-67 


3887-66 


1 19 48 


6 04 19 


1336-99 


10 




4376 72 


1194-94 


1 22 00 


72 37 06 




884-95 


3893-00 


1 19 56 


5 03 46 


1394-36 


11 




4360-70 


1009-41 


1 21 12 


75 22 58 




752-78 


3897-32 


1 19 56 


4 05 38 


1457-22 


12 




4329-31 


828-19 


1 21 46 


78 03 02 




618-37 


3901-10 


1 19 56 


3 10 00 


1525-43 


13 


4000-00 


3855 83 


2785-60 


' u 

1 21 28 


45 51 40 


4000-00 


2002-52 


3781-91 


1 19 04 


15 42 08 




1 




3983-21 


264416 


1 21 28 


48 37 15 




1918-55 


3801-51 


1 19 04 


14 27 22 




2 




4104-84 


2494-82 


1 21 24 


51 24 46 




1836-22 


3818-93 


1 19 04 


13 14 29 




3 




4218-56 


234002 


1 21 20 


54 11 48 




1756-33 


3834-20 


1 19 04 


12 04 07 




4 




4322-95 


218217 


1 21 12 


56 56 18 




1679-85 


3847 38 


1 19 04 


10 57 02 




5 




4416-91 


2023-99 

I 


1 21 04 


59 36 09 




1607-39 


385856 


1 19 04 


9 53 43 








369 



APPENDIX, No. V. 



NOTICE TO MARINERS.— SKERRY VORE 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 there- 
after, 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 Coun- 
cil, 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 navi- 
gated 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) 




Edinburgh, 23c? December 1843. 



3 A 



370 



APPENDIX, No. V. 



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. ^ E., 
distant 33 nautic miles ; from Hynish Point, in Tyree, AVSAV. ^ W., 
distant 10^ miles ; from lona Island, WNW. ^ N., distant 20 miles ; 
from Rhinns of Islay Lighthouse, N. \ E., distant 44 miles; and from 
Innistrahull Lighthouse in Ireland, NE. by N., distant 53^ 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 atten- 
tion is called to the prefixed Chart,* 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. \ S. from 
the Lighthouse ; Stevenson's, 2\ miles W. \ 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. 

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 ob- 
server, in favourable circumstances, the Light will not wholly disappear 
between the flashes. 



* A copy of the Chart referred to will be found at Plate II. at the end of this volume. 



371 



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 Tip the joiner 
work, .... £2996 7 7 

Timber, pavement, bricks, ironmongery, glass, 

&c, &c., used in the erections, . . 1376 16 9i 

Slater, plaster, and plumber work of the 

houses, . . . . . 436 1 

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 

£4822 5 4£ 



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. 



Carry forward, £4822 5 4j 



372 



APPENDIX, No. VI. 



Brought forward, £4822 5 4* 

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 6j- 

A smith's forge, bellows, anvil, and smith's 
tools used at Rock in erecting the bar- 
rack, . . . . 32 19 14- 



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 con- 
tractor 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 bar- 
rack, 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 6* 



790 8 2f 



1479 1 m 



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 win- 



Carry forward, £378 11 9 £7922 14 8| 



EXPENSE OF ERECTING SKERRYVORE LIGHTHOUSE. 



373 



Brought forward, £378 11 9 £7922 14 8| 
dows, including furnishings required for 
erecting the habitable part of Skerryvore 
Barrack at North Bay as a temporary ac- 
commodation for the workmen, and sun- 
dry other charges, . . . 361 4 7 

Sundry furnishings — such as utensils for pro- 
vision store, smithy, &c, . . 13 2 5 

752 18 9 



Quarries at North Bay. 

Cost of rails and timber for railway and timber, &c, for ship- 
ping-pier at North Bay, . . £131 5 ] 

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 
Rook. 

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 rail- 
way, 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 3h 

A portable forge, and other smith's tools, 

used at the rock for this work, . 21 15 10 



Carry forward, £630 18 U £10,817 2 



374 



APPENDIX, No. VI. 



Brought forward, £630 18 1* £10,817 2f 
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, Glas- 
gow, for part of the sill of platform, . 24 14 

763 8 6i 



Dressing Lighthouse Blocks. 

"Wages of masons, including the assistance of labourers, car- 
ters, &c, in dressing the blocks for ' the Lighthouse 
Tower at Hynish, . . . £8589 8 1\ 

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 



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 6i 

Wages of the smiths and their hammermen 
keeping these tools in repair and making 
others, . . . . 908 16 5 

2085 5 lli 

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 



Carryforward, £1605 15 9 £25,099 5 \\ 



3 E>~SE OF ERECTING SEESEYTOEE LIGHTHOUSE. 375 



Brought forward, £1605 15 9 £25,099 5 li 
Large balance crane used in buildins the Light- 
house Tower. . . . 533 10 Oj 
Hoisting beams or needles, and a pair of strong 
sheer-poles, used in building the Light- 
house Tower, . . - 42 11 2 

2181 16 lli 



Cabtage Accoott. 

Cost of 3 large draught horses and a pony, for the use of 

the works, .... £127 9 lOi 

Carts and stable utensils, . . 65 14 24 
Harness and other furniture, and keeping them 

in repair, . - . . 52 2 3i 

Provender for the horses for seven vears. 555 14 5 



Mobtak Accotts*. 

Cost of the lime which was used for all the departments of 
the works, .... £331 9 5 

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 

^"ages of labourers grinding and sifting Pozzo- 
lano at Hynish. and burning and sifting 
a portion of the lime, . . 121 15 5 

Packages to contain Pozzolano. to prevent its 
aittixtttre with :t*_et :-it-r: :;^ri 
ship, . . . . 20 1 



SlGSAL TOWZB AT HY51SH. 

Expense of (marrying, 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 



1104 1 m 



85? 11 7 



Carry forward, £513 19 7 £29 ; 274 1 8j 



376 



APPENDIX, No. VI. 



Brought forward, £513 19 7 £29,274 14 8£ 
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 

Plumber work of roof, . . . 35 9 6 

A 5 feet achromatic telescope, with stand, &c, 

for Signal Tower, . . . 35 10 

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 

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 Skerry- 
vore, . . . £5930 11 

Alteration on the engines, by raising the 

shafts, &c, . . . . 423 5 

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 Hy- 
nish), and sundry other minor charges, 5538 10 111 

12,949 1 01 

" Queen" Tender. 

First cost and complete outfit of the " Queen" Ten- 
der, ..... £935 13 3 
Sailing expenses and other charges, . 1010 7 9 

Repairs on the hull, rigging, sails, &c, . 77 12 8| 

2023 13 8} 



Carry forward, 



£45,462 12 2f 



EXPENSE OF ERECTING SKERRYVORE LIGHTHOUSE. 



Brought forward, £45,462 12 

Stone Lighters. 

First cost and outfit of four lighters for transporting the 
Lighthouse blocks, &c, from Hynish to the Skerryvore 
Rock, .... £1666 15 6i 

Hawsers for towing, mooring-ropes, heaving- 
lines, &c, used in the course of transport- 
ing the stones to the Rock, . . 249 1 6 

Upholding the lighters in repair, and sundry 



other charges, 

Expense transporting the lighters on various 
occasions to different places, 

Expense shifting and attending upon the 
lighters when lying at Leith, and adver- 
tising them for sale, 



178 9 9+ 



58 15 10 



19 



2172 12 



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, hedging, 
&c, . . . . . 48 16 1 

Chains and shackles for do., <fcc, . 354 2 7 

Upholding and keeping in repair the buoys, 4 17 1 



766 4 



Boats and Attendance. 

Cost of 8 boats, with oars, sails, tackling, &c, £207 19 ll£ 

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 

355 19 

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 



Carry forward, £50,058 3 
3 B 



378 



APPENDIX, No. VI. 



Brought forward, £50,058 3 6| 

Freight and Sailing Expenses. 

Freights and other charges paid the owners of hired vessels, 
for the materials which were imported for the use of 
various departments of the works, exclusive of the Light- 
house blocks from North Bay, .... 4045 9 1\ 

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 con- 
nected 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 7£ 

Cost of the blasting powder used for the purpose of quarrying 

stones, excavating rocks, &c .... 375 14 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 depart- 
ments 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 



Carry forward, £3837 7 £58,587 11 11 1 



EXPENSE OF ERECTING SKEREYVORE LIGHTHOUSE. 379 



Brought forward, £3837 7 £58,587 11 llf 
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, gaug- 
ing -rods for do., . . 276 10 7 

Cast-iron water-tanks and coal-boxes, for in- 
terior of Tower, .... 160 13 9 

A large cooking apparatus for kitchen of 
Tower, a stove to heat the lower apart- 
ments, 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 

Cast-iron permanent railway on the Skerry - 
vore 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 land- 
ing 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 ex- 
tra time, .... 454 2 6 



Carry forward, £6459 14 10 £58,587 11 llf 



380 



APPENDIX, No. VI. 



Brought forward, £6459 14 10 £58,587 11 llf 
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 

Premiums of the landing master at Rock, fore- 
man of masons, &c, .. . . 96 12 

Cost of the furniture, bedding, utensils, books, 

&c, for the Lighthouse Tower, . . 304 6 10 

Sundry furnishings connected with the build- 
ing of the Lighthouse Tower, — the wages 
of workmen quarrying stones at Hynish 
for Lighthouse Tower, previous to open- 
ing quarries at North Bay, and the wages 
of workmen, and furnishings for the gene- 
ral purposes of the works, . . 1386 18 5% 

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 10* 



Cost of the iron and steel which were used for all the depart- 
ments of the works, . . ... . 1299 3 h\ 



LlGIlTROOM AND APPARATUS. 

Cost of the lantern of cast-iron, with facings of bell-metal, 
in cludingthe cleaning andtrimming paths, and bell-metal 
ladder outside of lantern, and the wages of the contrac- 
tor'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, 



Carry forward, £1131 18 £68,438 15 3* 



EXPENSE OF ERECTING SKERRYVORE LIGHTHOUSE. 381 
Brought forward, £1131 18 £68,438 15 3 



handles, air-tubes, rain-water pipe?, a 
platform outside of dome for cleaning the 
vents, with the wages of the contractor's 
workmen fitting them up at Skerry vore, 348 16 9 

Machinery of the revolving apparatus, and 
brass case for do. complete ; three ma- 
chines 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 Skerry vore, . . . . 1244 10 6£ 

The charge of Mr Francois 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, 



Cost of two bells, and one spare do., used 
during foggy weather, . £107 6 3 

Shafting for do. ; bevel wheels, 
levers, hammers, &c., con- 
necting with the machinery 
of apparatus, . . 63 14 11+ 



£762 



Expense of transporting the whole 
apparatus to Leith, 



79 7 10 



841 7 10 



171 1 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 



Carryforward, £3820 14 10 £68,438 15 3£ 



382 



APPENDIX, No. VI. 



Brought forward, £3820 14 10 £68,438 15 3£ 
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 ad- 
joining Islands, . . . £3262 10 5 

Agency of the Agent at Aberdeen, who made 
the monthly payments to the workmens' 
relatives, and for some time superintend- 
ing 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 

LlGHTKEEPEKS' 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 


13 


6 


Bricks for partitions, lining of external walls, 








<fcc, . 


73 


10 





Pavement for floors, water-cisterns, &c, 


51 


16 





Workmanship, executing the plastei'-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 



Carry forward, £3504 15 7 £76,255 3 8& 



EXPENSE OF ERECTING SKERRYVORE LIGHTHOUSE. 383 



Brought forward, £3504 15 7 £76,255 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 4 

3915 4 4 



Pier at Hynish. 

Wages of masons, quarriers, cai'ters, labourers, &c, quarry- 
ing, dressing, and building the stones of a pier at Hy- 
nish for the landing and shipping of materials, 

£2300 17 U 

Iron rails for the works of building the pier, 53 10 1 
Timbers for fenders of pier, and other pur- 
poses connected with the building of it, 130 19 4 
Cost of a pont for building the pier, . 106 8 11 



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 ; quaiTying, 
dressing, and building the stones of boom-heads and 
walls of dock ; excavating reservoir and forming em- 
bankment 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 

Cost of two sluices, and of the machinery, &c, 

complete for working them, . . 81 14 

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 



2591 15 54 



Carry forward, £7034 18 9 £82,762 3 6 



384 



APPENDIX, No. VI. 



Brought forward, £7034 18 9 £82,762 3 6 



Cost of silt-pumps, and furnishings of leather, 
&c, for making others, and keeping them 
in repair, .... 

Compensation paid the tenant of the farm of 
Hynish, for liberty to cut drains for a sup- 
ply of water for a reservoir, 

Two signal lamps, two torches, turpentine, &c, 
for signalizing when the tender enters the 
dock at night, .... 



10 



5 



5 14 8 



7055 3 5 



Total, £89,817 6 11 



Deductions — 

Price of steamer " Skerryvore," sold, . £1616 6 

Do. of sloop " Queen," sold, . . 200 

Do. of 4 Stone Lighters, sold, . . 225 

Do. of Horses and Carts, sold, . . 60 

Implements sold or afterwards used at other 

works of the Board, . . . 738 8 10 



2839 9 4 



£86,977 17 7 



385 



APPENDIX, No. TIL 

excerpts from ax account of experiments upon the force 
of the waves of the atlantic and german" ocean's. by 

Thomas Stevenson. F.R.S.E., Ctvil-Engineeb. Edinbtjkgh. 

(From the Transactions of the Royal Society of Edinburgh. Tol. XV J 

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 experi- 
ments 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 everv in- 
stance they were found equidistant from the bottom of the cylinder ; prov- 
ing 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 improperlv termed a 
Marine Dynamometer, is, therefore, a self-registering apparatus which in- 
dicates the maximum force of the waves. In the graduation of the instru- 
ment, the power of the spring is ascertained by carefully loading the disc 
with weights, so that when the quantity that the spring has vielded bv 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 

3 c 



386 



APPENDIX, No. VII. 



generally 6 inches, and the powers of the springs varied from 10 lb. to about 
50 lb. for every £ inch of elongation. Their respective effects were after- 
wards 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 situa- 
tions 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 fol- 
lowing 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 shel- 
tered 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 Skerry- 
vore 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 



EXPERIMENTS UPON THE FORCE OF WAVES. 



387 



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 ob- 
served, is that of the Atlantic at Skerry vore, 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 any- 
thing 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 con- 
sidered 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 im- 
pact of a hard body. The near coincidence, or indeed almost perfect agree- 
ment 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 1841, 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 de- 
veloped ; 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 



388 



APPENDIX, No. VII. 



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, can- 
not, from the unusual fineness of the weather at the time, be regarded as afford- 
ing 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 com- 
plicate the Tables by inserting these, excepting in one or two instances. 



EXPERIMENTS UPON THE FORCE OF WAVES. 



389 



Dates. 



lbs. to a 
Square Foot. 



Dates. 



lbs. to a 
Square Foot. 



Observations at Little Ross. 



1842 




• 1 

• 


1842 






April 


25 


15 


June 


25 


458-0 




28 


51 


July 


25 


380 


June 


1 


36 


Aug. 


2 


570-0 




4 


81-5 




5 


665-0 




20 


86-5 




6 


380-0 




24 


840-0 




9 


380-0 



April 
May 



June 



July 



24 
25 
7 
11 
12 
16 

20 

3 
4 
7 

8 
9 
2 



The Observations at the Skerryvore Rock, 
neighbouring Island of Tyree, distant 13 miles 
Skerryvore, are as follows : — 

1843. 1843. 

455 Aug. 
707 
243 

182 Sept. 
243 

364 Oct. 
J 495 

1 476 Nov. 
182 
519 
428 

855 Dec. 
173 
476 
/723 
(866 
433 



3 
30 



9 
22 
30 

5 
21 

5 

6 
18 
19 
27 
29 

5 



14 

26 



and the 
from the 



346 

723 

389 

866 

952 
1535 
1606 
1711 
1497 
1497 
2353 
2674 
3421 
At least 
2460 
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 
2353 
357 



1844. 
Jan. 9 

10 



Both instruments set parallel. 

1844. I 11 1844. 

Jan 16 ' 424 Jan. 16 



1925 
1000 
826 
1000 



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 



1844. 
Feb. 



429 
457 



Dates. 


lbs. to a 


Date?. 


lbs. to a 




Square Foot. 




Square Foot. 


1 Q A A 

10-14. 




1 oil. 




Feb. 3 


429 
457 


April 19 


800 
535 


13 


214 




481 




228 


22 


913 


15 


321 

280 




482 
962 




321 


24 


1942 


16 


428 




1604 
1370 




343 


25 


1283 


24 


1284 
1364 




343 
321 




boo 


27 


457 


26 


2032 




481 


c . . • • • 


2068 


- -1 


+ N !s ht 800 
tide 




399 


I 


27 


321 




642 




321 


30 


229 




342 




241 


March 4 


3316 


May 1 5 


343 




3369 


14 


481 




3427 


June 6 


571 


7 


1069 


15 


1828 




963 


July 11 


1028 




913 


13 


457 


10 


1925 


18 


914 





1925 


23 


1532 




1713 


25 


571 


11 


535 


26 


971 




481 


27 


457 




456 


28 


1142 


12 


3316 


29 


286 




4011 


30 


914 




2970 


31 


1028 


13 


1142 


Aug. 1 


571 




1283 


7 


914 




1283 


13 


914 


April 10 


457 


14 


914 




428 


21 

... ~ i 


ftnn 
oxjyj 




481 


30 


1713 


11 


800 


Sept. 12 


1028 


12 


343 


14 


914 




321 


20 


457 


14 


571 


23 


1142 




535 


25 


685 


16 


571 


... 30 


1599 




G42 


Oct. 2 


2399 




481 


3 


1485 


... 17 


800 


4 


1828 




856 


11 


3427 1 




862 


14 


1599 


18 


571 


19 


1599 




481 


20 


2513 



1 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 1£ 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 l 1 ton = 
2800 1b. 6 6 4 



390 



APPENDIX, No. VII. 



Dates. 


lbs. to a 
Square Foot. 


Dates. 


lbs. to a 
Square Foot. 


Dates. 


lbs. to a 
Square Foot. 


Dates. 


lbs. to a 
Square Foot. 


1844. 




1844. 




1844. 




1844. 




Oct. 22 


800 


Nov. 10 


1028 


Nov. 23 


3427 


Dec. 10 


1825 


... 24 


1827 


... 14 


1257 


... 27 


3199 


... 13 


1925 


... 28 


1485 


... 15 


2056 


... 28 


4112 


... 14 


1027 


... 29 


457 


... 16 


2056 


Dec. 7 


1369 


... 15 


1764 


Nov. 2 


1942 


22 


2627 


9 


2738 







A more exposed point of the Skerryvorc 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. IT.). 
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 Dynamo- 
meter 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. 



Date. 


Remarks. 


No. of 
Instrument. 


Pressure in lbs. 
per 
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 




f Waves supposed about 


II. 


3041 




{ 10 feet high. 


11 


Short sea. 


I. 


1028 


... 24 


Heavy sea. 


I. 


2281 




| Waves supposed about 


II. 


4562 




1 20 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, 








J and the spray rose 


II. 


6083 




about 70 feet. 







EXPERIMENTS UPON THE FORCE OF WAVES. 391 



Register of Observations on the force of the Sea, made at the Bell Bock, German 

Ocean. 



\ Dates. 


lbs. to a 
totjuare Foot. 


Dates. 


1 

lbs. to a 

S(J 113,1*6 l^OO t. 


1844. 




1845. 




Sept. 15 


853 


Jan. 27 


1199 


... 20 


2260 


... 30 


2879 


Oct. 9 


3013 


... 31 


1559 




2562 


Feb. 6 


2999 


... 26 


1142 


... 24 


1199 


... 27 


958 


... 25 


959 


Nov. 12 


1680 


... 27 


839 


... 13 


1920 


... 28 


1319 


Dec. 13 


1560 


March 4 


959 


... 26 


1439 


7 


1079 






11 


1919 


1845. 




... 20 


2519 


Jan. 7 


1559 


... 21 


2759 


i ... 10 


1439 


... 24 


1319 


... 11 


1439 


... 25 


959 


... 15 


1559 


... 28 


599 


... 25 


959 


... 30 


1079 


... 26 

1 


719 







APPENDIX. Ho. Tin. 



IIST OF NORTHMEN IIGHTHOISES. EEACOXS 

AND BIOTS. 

FOE 1S48. 



3d 



394 



APPENDIX, No. VIII. 



Name of Light. 



INCHKEITH. 



ISLE OF MAY. 



DO. LEADING LIGHT... 



BELL ROCK. 



GIRDLENESS 



BUCHANNESS. 



KINNAIRDIIEAD. 



COVESEA SKERRIES. 



CHANONRY POINT. 



CROMARTY POINT. 



TARBETNESS. 



NOSSHEAD. 



DUNNETHEAD , 



PENTLAND SKERRIES. 



START POINT. 



Situation of Light. 

J Highest Land on the Island of Inchkeith, ) 
\ in Fifeshire J 

Highest Land on Isle of May, in Fifeshire.. 

J Placed about 130 feet below the High 
{ Light, and to the NE. by N. of it 

Bell Rock, a sunk reef, 11 § miles S. by E. ] 
^ E. off Arbroath, in Forfarshire........ J 

Girdleness, Kincardineshire 

Buchanness, Aberdeenshire 

Kinnairdhead, Aberdeenshire. 

Craighead, Morayshire 

Chanonry Point, Ross-shire 

Cromartyshire 

Tarbetness, Cromartyshire 

Nosshead, Caithness-shire (building) 

j Dunnethead, most northern point of the 
I Mainland of Scotland, Caithness-shire... 

Pentland Skerries Island, Orkney 

| Start Point, Sanday Island, the most cast- 
le ern point of Orkney 



Number of 
Lights. 



One 



One 



One 



One 



Two 



One 



One 



One 



One 



One 



One 



One 



Two 



One 



Appearance of Light. 



Revolving, and appearing in its brightest state 
once every minute 



Fixed. 



Fixed. 



Revolving, and shewing alternately a red and 
white light every 2 minutes 



Fixed Lights, one above the other. 



Flashing once every 5 seconds. 



Fixed - 



I Revolving, and appearing in its brightest state 
j once every minute. From W. by N. i N. 

to SE. by E. J E. the light is of the natu- 
1 ral appearance; but from SE. by E. \ E.l 



Fixed. 



Fixed and red 



/Intermittent, suddenly bursting into view, and 
continuing in sight 2\ min., then suddenly 
| eclipsed for half a minute. But within the 
Moray Frith, in Southerly and South-wester- 
ly directions from Tarbetness, the light does 
not intermit, but is permanently visible 



Fixed. 



Fixed, and 100 feet apart. 



Revolving, and appearing in its brightest state "1 
once every minute J 



LIGHTHOUSES. 



395 



Distance visible in 
Nautic Miles. 


Points of Compass within which Light is Visible. 


Height of Lantern 
in feet above High- 
water Spring Tides. 


North Latitude. 


West Longitude. 


Date of 
tirst rjxni- 
bition. 


18 




220 


56° 2' 


3° 8' 


1804 


21 




240 


56° 11' 


2° 33' 


1816 


15 


/ When seen in one line with the High Light, \ 
1 these two .Lights bear JNL. by IN. ^ JN., and 1 
J SW. by S. J 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 j 


110 






1844 


14 




90 


56° 26' 


2° 23' 


1811 


19 & 16 


("From NNE. to WSW. -J- W. Easterly and 1 
\ Southerly ..J 


185 & 115 


57° 8' 


2° 3' 


1833 


16 


From N. by E. to SW. by W. Easterly 


130 


57° 28' 


1° 46' 


1827 


15 


From WNW. to SE. Northerly 


120 


57° 42' 


2° 0' 


1787 


18 


From W. by N. J N. to SE. J S. Northerly 


160 


57° 43' 


3° 20' 


1846 


11 


From W. 1 N. to N. by E. Southerly 


40 


57° 35' 


4° 5' 


1846 


9 


From WNW. to SE. by E. \ S. Northerly 


50 


57° 41' 


4° 2' 


1846 


18 


From SW. J W. to W. -J- N. Easterly 


175 


57° 51' 


8° 48' 


1830 














23 

i 


From SE. 1 E. to W. Northerly 


346 


58° 40' 


3° 21' 


- 

1831 


16 & 18 




140 & 170 


58° 41' 


2° 55' 


1794 


15 




100 


59° 17' 


2° 23' 


1806 



396 APPENDIX, No. VIII. 



Name of Light. 



SUMBURGH-HEAD. 



CAPE WRATH 



ISLAND GLASS. 



BARRAHEAD. 



ARDNAMURCHAN. 



LISMORE 



SKERRYVORE*. 



RHINS OF ISLAY, 



MULL OF KINTYRE . 



PLADDA. 



CORSE WALL. 



LOCH RYAN 



MULL OF GALLOWAY 



LITTLE ROSS. 



POINT OF AYRE 



(ALF OF MAN. 



Situation of Light. 



Number of 
Lights. 



The most southern Headland of Zetland . 



| Cape W rath, north-western Headland of 
( Sutherlandshire 



One 



One 



Island Glass, one of the Harris Isles, Inver- 
ness-shire 



Highest land on Bernera Island, Inverness- 
shire 



Ardnamurchan Point, Argyleshire (building) 



Mouscdale, small Island off Lismore, Ar- ) 
gyleshire J 



Skerry vore Reef, 12 miles WSW. ^ W. 
from Tyree Island, with foul ground all 
round it 



Oversay, small Island off Islay, Argyleshire. 



South-western Headland of Argyleshire. 



j Pladda Isle, off south-east point of Arran, 
\ county of Bute 



f Western side of entrance to Loch Ryan, in ) 
I Wigtonshire J 



f Cairn Ryan Point, within Loch Ryan, 
\ Wigtonshire 



Southern extremity of the Mainland of] 
Scotland, Wigtonshire j 



Little Ross Island, Kirkcudbrightshire. 



Northern extremity of Isle of Man . 



J West side Calf Island, at the southern ex- ( 
) extremity of Isle of Man J 



One 



One 



One 



One 



One 



One 



Two 



One 



One 



One 



One 



One 



Two 



Appearance of Light. 



Fixed , 



f Revolving, and shewing alternately a red and 
[ white light every 2 minutes 



Fixed 



f Intermittent, suddenly bursting into view, and 
I continuing in sight 2-i- min., then suddenly 
[ eclipsed for half a minute 



Fixed 



Revolving, and appearing at its brightest once | 
every minute J 



Flashing once every 5 seconds. 



Fixed 



Fixed, the one above the other. 



Revolving, and shewing alternately a red and 
white light every 2 minutes 



Fixed , 



Intermittent, suddenly bursting into view, and 
continuing in sight 2i min , then suddenly 
eclipsed for half a minute .' 



Flashing once every 5 seconds. 



f Revolving, and shewing alternately a red and 
{ white light every 2 minutes 



f Revolving, and shewing white lights every 2 
\ minutes 



xpected to 



At Hynish Point in Tyree Island, two fixed Lights are shewn from the Pier, but only when the Vessel which attends the Lighthouse is 
enter the Dock at Hynish. In the Trinity House Chart, Skerryvore Light is erroneously described as " Intermittent." 



LIGHTHOUSES. 



397 



Distance visible in 
Nautic Miles. 


Points of Compass within which Light is Visible. 


Height of Lantern 
in feet above High- 
water Spring Tides. 


« 

North Latitude. 


West Longitude. 


Date of 
first Exhi- 
bition. 


22 


j From NE. by E. | E. to NW. by N. J N. ] 

{ Southerly 


• 


300 


59° 51' 


1° 16' 


1821 


25 


From SE. £ E. to SW. by W. Northerly 


400 


58° 37' 


5° 0' 


1828 


16 


From W. by S. to ENE. J E. Southerly 


130 


57° 52' 


6° 33' 


1789 


32 


f From N. by E. to ENE. "Westerly and South- ] 

1 er] y 




680 


56° 48' 


7° 38' 


1833 














15 


From E. to NE. by E. \ E. Westerly.... 




103 


56° 30' 


5° 38' 


1833 


18 




150 


56° 19' 


7° 7' 


1844 


17 


From NNE. to SE. Southerly '. 


150 


55° 41' 


6° 29' 


1825 


22 


From NNE. \ E. to S. by W. \ W. Southerly 


297 


55° 1' 


5° 49' 


1787 


13 & 16 


From NW. by W. to NE. by E. Southerly 




77 & 130 


55° 26' 


5° r 


1790 


15 


From NE. by E. to SW. Northerly 


112 


55° V 


5° & 


1817 


10 


From S. by W. \ W. to N. \ E. Westerly 


30 


54° 58' 


5° 2' 


1847 


23 


From NE. to NW. \ W. Southerly 


325 


54° 38' 


4° 51' 


1830 


18 


From N. by E. to NW. by W. Southerly 


175 


54° 46' 


4° 5' 


1843 


15 


From S. by W. to W. by N. Northerly 




106 


54° 25' 


4° 22' 


1818 


22 & 24 


From NE. \ E. to SW. \ W. Southerly 


275 & 368 


54° 3' 


4° 49' 


1818 



398 APPENDIX, No. VIII. 

BEACONS AND BUOYS. 



FRITH OF FORTH DISTRICT. 



Name of Station. 


Description of 
Mark. 


Depth at Low 

Water of 
Spring Tides. 


Bearings of Marks and of Lines of Intersection 
Meeting at the Station. 


MIDDLE BANK, 
WEST END, 
BUOY. 


6 Feet Buoy, 
Red. 


H Feet. 


Alloa Tower in line with the Centre of Clack- 
mannan Pier — Bearing N. by E. 

Clackmannan Church Spire in line with High 
Chimney-Stack of Park-Farm House — Bearing 

"NTT? 1 V 

Middle Bank Buoy, East End — Bearing SE. 

hy S. 


MIDDLE BANK, 
EAST END, 
BUOY. 


6 Feet Buoy, 
Red. 


± Feet. 


Tullyallan House in line with Tullyallan 
Old Church Spire, in ruins — Bearing ESE. \ S. 

Remarkable Clump of Trees on distant high land 
m line with Airth Church spire — Hearing W. by 
N. i N. 

Buoy off Inch Brake Rock — Bearing S. by E. ' 


INCH BRAKE 
BUOY. 


6 Feet Buoy, 
Black. 


5 Feet. 


Flagstaff on the Ferry Pier, 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 — Bear- 
ing N. by W. 

Long Annat Buoy — Bearing SSE. -1- E. 


LONG ANNAT 
BUOY. 


6 Feet Buoy, 
Black. 


9 Feet. 


Sands House, West Wing, in line with West 
Face of Annat Quarry — Bearing NNE. \ E. 

Binns Monument in line with the Middle of Bo'- 
ness Pier — Bearing bE. by S. 

Hen and Chicken's Buoy — Bearing SE. by E. 

is. 


HEN AND 
CHICKEN'S 
BUOY. 


6 Feet Buoy, 
Black. 


12 Feet. 


The East Wing of Culross Abbey in line with 
Eastmost House in Culross Village — Bearing 
NNE. 1 E. 

Airth Castle, in line with High- Water Mark 
on Long Annat Point — Bearing NW. i W. 

Buoy on East End of Dods' Bank — Bearing 
SSE. \ E. 



BEACONS AND BUOYS. 399 



Name of Station. 


Description of 
Mark. 


Depth at Low- 
Water of 
Spring Tides. 


Bearings of Marks and of Lines of Intersection 
Meeting at Stations. 


DODS' BANK 
BUOY. 


7 Feet Buoy, 
Red. 


15 Feet. 


Berry-Law Trees in line with the 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. | w. 

Comary House, East Wing, in line with the 
West Wing of the Factor's House — Bearing N. 
by E. a 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. J E. 

The Buoy of Hen and Chicken's Rock — Bear- 
ing NNW. i W. 


BEAMER 
BEACON. 


Painted Black, 
with Spherical Ball 
at top. 


Rock Dry at Low 
Water. 


Bo'ness Pier — Bearing NW. by W. 

Charleston Pier, Outer End — Bearing NW 
by N. 

South- West Extremity of the Point at North 
Queensferry — Bearing ESE. i E. 

The Halls, or principal South Queensferry 
Pier — Bearing SSE. |- E. 


DRUM SAND 
EAST BUOY. 


7 Feet Buoy, 
Red. 


12 Feet. 


Newbigging House in line with East Edge of 
Carcraig Rock — Bearing NE. i E. 

Oxscare Beacon — Bearing E. § N. 

Inchkeith Lighthouse — Bearing ESE. A E. 

Highest Point of Arthur's Seat in line with 
Nelson's Monument — Bearing S. by E. | E. 


DRUM SAND 
WEST BUOY. 


8 Feet Buoy, 
Red, with Fenders. 


Fathoms. 


South Point of Inchkeith inline with Centre of 
Opening of Mickery Stone — Bear ESE. i E. 

Inchkeith Lighthouse — Bearing ESE. 1 E. 

Fordel House in line with Centre of Doni- 
bristle House — Bearing N. + E. 

Chimney-Stack of Castle Landhill Farm- 
House in line with End of Lazarett Pier — Bear- 
ing NW. f N. 


OXSCARE 
BEACON. 


Painted Red, 
with Flat Cone at top. 


Rock Dry at Low 
Water. 


South Point of Carlin's Nose — Bearing W. § N. 
Burntisland Pier — Bearing ENE. 
Extremity of Kinghornness — Bearing E. | N. 
Inchkeith Lighthouse — Bearing ESE. i E. 
Martello Tower — Bearing SSE. § E. 
Granton Pier — Bearing S. by E. \ E. 



400 



APPENDIX, No. VIII. 



Name of Station. 


Description of 
Mark. 


Depth at Low- 
Water of 
Spring Tides. 


Bearings of Marks and of Lines of Intersection 
Meeting at Stations. 


WEST GUNNET 
BUOY. 


8 Feet B1107, 
White. 


3f Fathoms. 


Nelson's Monument just clear East of North 
Leith Church Spire — Bearing SSW. 

North Berwick Law in line with North End of 
i-iONG L/Raig — Hearing i^oiii. £ hi. 

Clump of Trees East of Grange House in line 
with Burntisland Church Spire — Bearing N. \ W. 

Inchkeith Lighthouse — Bearing E. \ S. 


EAST GUNNET 
BUOY. 


8 Feet Buoy, 
White. 


3£ Fathoms. 


Notch at the foot of East Brow of the Pentland 
Hills in line with North Leith Church Spire — 
Bearing SSW. £ W. 

Carlin's Nose clear of the North Side of Mickery 
otone — jjcarmg vv in w . w . 

Kinghorn New Free Church in line with King- 
hornness — Bearing NE. by N. 

Inchkeith Lighthouse — Bearing E. 


PALLAS BUOY. 


7 Feet Buoy, 
Striped White and 
Black horizontally. 


3J Fathoms. 


Kinghorn Free Church in line with Swan's 
Factory — Bearing N. by E. f E. 

North Brow of Inchkeith in line with the Centre 
of Silly Carr Rock — Bearing ENE. \ N. 

Assembly Hall Spire, Edinburgh, in line with 
Martello Tower — Bearing SW. f S. 

Inchkeith Lighthouse — Bearing ENE. -| E. 


HERWIT BUOY. 


8 Feet Buoy, 
Black. 


4f Fathoms. 


East Brow of Pentland Hills, touching West 
Brow of Arthur's Seat (half way up) — Bearing 
SW. J- 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. ^ W. 


CRAIG WAUGH 
BUOY. 


8 Feet Buoy, 
Red. 


4 Fathoms. 


Pettycur Pier in line with Eastern Brow of 
Inchkeith — Bearing N. by W. -J- W. 

Assembly Hall Spire just clear, West of Nel- 
son's Monument — Bearing W. f S. 

Inchkeith Lighthouse — Bearing N. by W. f- 
W. 


NORTH CRAIG 
! MAST BUOY. 




12 Feet Mast Buoy, 
Chequered Red and 
White. 


3£ Fathoms. 


Nelson's Monument in line with West Wing of 
Leith Baths — Bearing WSW. \ W. 

Summit of East Lomond Hill in line with Bio 
House Trees — Bearing N. £ E. 

Carlin's Nose in line with Centre of Mickery 
Stone — Bearing WNW. 



BEACONS AND BUOYS. 



401 



Name of Station. 


Description of 
Mark. 


Depth at Low 

Water of 
Spring Tides. 


Bearings of Marks and of Lines of Intersection 
Meeting at the Station. 


WEST ROCK- 
HEAD, OFF 
DYSART, BUOY. 


6 Feet Buoy, 
Red. 


31 Fathoms. 


Dysart Coal-Pit Chimney-Stack in line with 
Middle of Gable of Pan Hall House — Bearing 
N. \ E. 

North End of Porterae Church, Kirkcaldy, 
just clear of the End of Kirkcaldy Pier — Bearing 
WNW s W 

Inchkeith Lighthouse — Bearing SW. by S. 

N.B. — The highest part of the Rockbearing N. j- E. 
distant about one-half cable's length from 
Buoy. 


EAST ROCK- 
HEAD, OFF 
DYSART, BUOY. 


6 Feet Buoy, 
Black. 


3£ Fathoms. 


Wemyss Old Castle in line with Southern 
Houses of East Wemyss — Bearing NE. by E. \ E. 

East Wing of Dysart Church in line with 
Town-House Steeple — Bearing NNW. J W. 

Buoy on West Rock-Head — Bearing W« by N 

Inchkeith Lighthouse — Bearing SW. J S. 

N.B.— The highest part of Rock, bearing NW. 
1 W., distant about two cables' lengths. 


EAST VOWS 
ROCK, BEACON, 
OFF ELIE. 


Pyramid of Iron 
Pillars, with open 
Cylindric Cage on top, 
painted Red. 


Rock Dry at Low 
Water. 


Ruins on Chapelness — Bearing N. 3 E. 

North End of Elie Pier — Bearing E. § N. 

Extremity of Elieness — Bearing E. by S. J S. 

Isle of IVIay Lighthouse Bearing ESE. \ S. 

West Vows Rock — Bearing WNW. £ N. dis- 
tant \ mile. 

Buoy* on Thill Rock — Bearing ESE. \ S. dis- 
tant two cables' k-ngths. 


THILL ROCK 
BUOY. 


7 Feet Buoy, 
Black. 


3f Fathoms. 


WESt End of Millhouse Cottace in line with 
North End of Elie Pier — Bearing NE. 

Pettie Law in line with AVest Chimney-Stack 
of David Ovenstone's House — Bearing N. -| W. 

Ruin on Chapelness — Bearing NNW. ^ W. 

Beacon on East Vows Rock — Bearing WNW. 
A N. 

N.B. — The Buoy lies about 35 fathoms to the 
SSE. of the highest part of the Rock. 


SOUTH CARR 
BEACON. 


Painted Red, with 
Cross at top. 


Rock Dry at Low 
Water, 


Cairn on Bass Rock — Bearing N. by E. 

Isle of May Lighthouse— Bearing NE. 

Dunbar Church Tower — Bearing SSE. |- S. 

Oldham Farm-House Chimney^Stack — Bearing 
W. 1 N. 


NORTH CARR Beacon of Stone, 
BEACON. with Iron Frame and 
Ball. 


Rock Dry at Low 
Water. 


Mile from Fifeness — Bearing from Isle of 
May Light NNE. distant 6 Nautic Miles. 



3 E 



402 



APPENDIX, No. VIII. 



BEACONS AND BUOYS. 



DISTRICT OF FRITHS OF MORAY, CROMARTY, INVERNESS, 

AND DORNOCH. 



Name of Station. 


Description of 
Mark. 


Depth at Low- 
Water of 
Spring Tides. 


Magnetic Bearings of Marks and of Lines of Intersection 
Meeting at the Station. 


COVESEA 
SKERRIES 
BEACON. 


Pyramid of Iron Pil- 
lars, with open cy- 
lindric Cage, and a 
Cross, rising to the 
height of about 50 
feet above High wa- 
ter. 


Rock dry at Low 
water. 


Covesea Sk.ek.kies Lighthouse on the neigh- 
bouring land of Craighead — Bears WSW. J W. 
distant one mile, 


LONGMAN 
POINT BEACON. 


Cone of Iron Plates 
painted Black. 


Beach Dry at Low 
water of Spring 
Tides. 


End of Kessock South Pier — Bearing W. by 
N. -]- N. 

Craigtown Point — Bearing NW. 4- W. 

Meiklemee, East End Buoy — Bearing E. ^ N. 

Bogbain House in line with Rigmore House — 
Bearing S. § E. 

End of Longman Point — Bearing N. \ W. dis- 
tant 40 Fathoms. 


MEIKLEMEE 
BANK BUOY. 
East End. 


6 Feet Buoy. 
Black. 


12 Feet. 


Park's Farm-House in line with Rigmore House 
—Bearing SSW. 

Middle of space between the Houses of Scorguoy 
Farm-Yard in line with Black Mill Chimney — 
Bearing W. -\- S. 

Chanonry Point Lighthouse — Bearing ENE. 
IE. 


MIDDLE BANK 
BUOY. 
East End. 


6 Feet Buoy. 
Black. 


12 Feet. 


ioCORGUOi -TARM-XAK-O [ Ajliuy, in luie wim 

Black Mill Chimney — Bearing W. £ S. 

Round Clump of Trees, North of Ley's House, 
in line with Rigmore House — Bearing SW. § S. 

Chanonry Point Lighthouse — Bearing ENE. 

Meiklemee Bank Buoy — Bearing W. § S. 


PETTY BANK 
BUOY. 
North or Outer Edge. 


6 Feet Buoy. 
Chequered 
Black and White. 


12 Feet. 


Dalcross Castle in line with Fisiitown Farm- 
House — Bearing SE. J S. 

Extremity of East Suter in line with Store- 
house, Chanonry Point — Bearing ENE. £ N. 

Munlociiy Buoy — Bearing N. 



BEACONS AND BUOYS. 



403 



Same of Station. 



MUNLOCHY 
BUOY. 



SKATE BANK 
BUOY. 
East End. 



CRAIGMEE or 
FORT-GEORGE 
BANK BUOY. 



RIFF BANK 
BUOY. 
West End. 



RIFF BANK 

BUOY. 
Middle or North 
Angle. 



Description of 
Mark. 



6 Feet Buoy. 
Black. 



6 Feet Buoy, 
Black. 



6 Feet Buoy. 
Chequered 
Black and White. 



Depth at Low 

Water of 
Spring Tides. 



12 Feet. 



12* Feet. 



2\ Fathoms. 



6 Feet Buoy. 
Black. 



RIFF BANK 
BUOY. 
East End. 



6 Feet Buoy. 
Black. 



12 Feet 
Mast-Buoy. 
Black. 



34 Fathoms. 



3i Fathoms. 



4-|- Fathoms. 



Magnetic Bearings of Marks and of Lines of Intersection 
Meeting at the Station. 



West Wing of Avoch House, now in ruins, in 
line with the most Western slated House or Cot- 
tage in Avoch — Bearing N. \ W. 

North End of Fort-George in line with Cha- 
nonry Point- — Bearing ENE. |- E. 



The East Wing of Kincurdie House in line 
with Spire of Rosemarkie Kirk — Bearing NNE. 

h E. 

Flagstaff of Fort-George in line with the 
Outer End of Chanonry Pier — Bearing ENE. 
i E- 

Dalcross Castle in line with Cottage on Sea- 
cliff — Bearing S. J E. 

Munlochy Buoy — Bearing WSW. J g W. 



High Part, or West Brow of Altarlie Point, 
in line with Chanonry Point Lighthouse — Bearing 
SW. f W. 

Patch of Trees at West End of Broomhill 
Wood, called Broomhill Bush, in line with Plat- 
cock House — Bearing WNW. J W. 



Craighead Farm-House in line with the most 
Western of the Three Burns — Bearing N. by E. 
IE. 

Broomhill Bush (East End) in line with the 
Manse of Rosemarkie — Bearing W. £ N. 



Chanonry Point Lighthouse- 
i S. 



-Bearing WSW. 



Three remarkable Trees at North End of 
Craigie Wood, in line with Rosemarkie Manse — 
Bearing W. i S. 

Gamekeeper's House at End of Wood in line 
with Cave on Sea-shore, a little East of the Three 
Burns — Bearing NW. i W. 



Chanonry Point Lighthouse — Bearing WSW. 
i S. 



Castle Craig Rock in line with Stack Rock at 
foot of West Suter — Bearing N. by E. £ 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 — Bear- 
ing W. $ S. 



Towrie Lumb Wood in line with Craigie Wood 
(South End)— Bearing W. 



404 



APPENDIX, No. VIII. 



Name of Station. 


Description of 
Mark. 


Depth at Low 

Water of 
Spring Tides. 


Magnetic Bearings of Marks and of Lines of Intersection 
Meeting at the Station. 


WHITENNESS 

BEACON. 
(In preparation.) 








NAVITY BANK 
BUOY. 
South Edge. 


6 Feet Buoy. 
Chequered 
Black and White. 


2\ Fathoms. 


Trees at end of Navity Farm-House in line with 
East Bank or Cliff of Craighouse Burn — Bear- 
ing N. | E. 

Extremity of Wood on Brow of East Sitter 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. f E. 


- 

NIGG SANDS 
BUOY. 
East End. 


6 Feet Buoy. 
Black. 


2 Fathoms. 


Cromarty Gaelic Kirk Steeple in line with 
East Wing of Hotel — Bearing S. | E. 

Face of East Suter apparently on a line half- 
way between. Ferryhouse and Stable— Bearing 
SE. by E. 


NIGG SANDS 
BUOY. 
West End. 


6 Feet Buoy. 
Black. 


If Fathoms. 


Farm-House of Dalney in line with the Pigeon- 
house East of Balustrade — Bearing NNE. ^ E. 

Extremity of West Souter in line with Cro- 
marty Lighthouse — Bearing SE. § E. 


NEWHALL 
BANK BUOY. 
East End. 


6 Feet Buoy. 
Chequered 
Black and White. 


21 Fathoms. 


Priesthill Farm-House in line with Eastern- 
most House in Ballintrade — Bearing NNE. f E. 

East Brow of West Suter in line with Cro- 
marty Gaelic Kirk — Bearing ESE. J S. 

Nigg Sands West Buoy — Bearing ENE. | N. 


THREE KINGS 
ROCKS BUOY. 


8 Feet Buoy. 
Red. 


7| Fathoms. 


Eastern Trees upon Top of the 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 — 

n • TK7" XT ATE T 1 XT 

Bearing WJN W. J- JN. 

Duke of Sutherland's Monument in line with 
West End of Long Storehouse in Shandwick — ■ 
Bearing N. by E. f E. 


CULLODEN 
ROCK BUOY. 


8 Feet Buoy. 
Black. 


8|- Fathoms. 


Bruckfield Farm-House in line with Tarbetness 
Lighthouse Flag-Staff — Bearing WSW. f W. 

Duke of Sutherland's Monument in line with 
Lower Corner of Wood farthest West from Dun- 
robin Castle — Bearing NNW. 



BEACONS AND BUOYS. 



405 



Name of Station. 


[ 

Description of 
Mark. 


Depth at Low 

Water of 
Spring Tides. 


Magnetic Bearings of Marks and of Lines of Intersection 
Meeting at the Station. 


FAIRWAY 
BUOY off TAIN 
BARR. 


12 Feet Mast Buoy. 
Red. 


5 Fathoms. 


West End of Bentavie Hill in line with 
Trentham Farm-House — Bearing NNW. f W. 

West Brow of East Suter in line with Meikle- 
rennie Farm-House — Bearing SW. |- W. 

Tarbetness Lighthouse — Bearing SE. § E. 


TAIN BAR 
INNER BUOY. 
North Side. 


6 Feet Buoy. 
Black. 


21 Fathoms. 


Remarkable Hollow or Notch in High Land 
East of East Suter, in line with Lochslain Castle 
—Bearing SSW. J W. 

Lower West Brow of Cambcjsmore Hill in line 
with East End of West Embo Wood — Bearing N. 
by W. | W. 

T AT?"RFTNFSS Ti TfJRTHflTI^F— T^PH T1T1 O* R'S"R 1 ft 

X ■ 1 I > 1 > 1 1 " 1 1 J }'■<)• Jill 1^1, 1 I 1 J 1 1 I 1 _ 1 . 1 _■ t t y KJt 

Fairway Buoy off Tain Bar — Bearing E. J S. 


TAIN BAR 
INNER BUOY. 
South Side. 


6 Feet Buoy. 
Chequered 
Black and White. 


4f Fathoms. 


Remarkable Hollow or Notch in High Land 
East of East Souter in line with Meiklerennie 
Farmhouse — Bearing SSW. § W. 








West End of East Embo Wood in line with 
Embo Farmhouse — Bearing N. i W. 

Fairway Buoy off Tain Bar — Bearing E. -\ N. 

Tain Bar Inner Buoy (North Side) — Bearing 
ENE. f N. 

Dornoch Spire — Bearing NNW. £ W. 



406 



APPENDIX, No. VIII. 



BEACONS AND BUOYS. 



FRITH OF CLYDE DISTRICT. 



Name of Station. 


Description of 
Mark. 


Depth at Low 

W ater of 
Spring Tides. 


Bearings of Marks and of Lines of Intersection 
Meeting at the Station. 


FULLARTON 
ROCK BUOY. 


7 Feet Buoy. 
Red. 


Fathoms. 


Clump of Trees at East side of 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 

BARRELS 
ROCKS BUOY. 


8 Feet Buoy. 
Red. 


8J Fathoms. 


West End of Arranman's Barrels Shoal — 
Bearing W. by N. 

North-East Extremity of Shoal — Bearing N. } E. 

Ballyshare House in line with the Lower East 
End of Dunacheein Rock — Bearing NW. 1- 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. 


OTTER ARD 
ROCK BUOY. 


8 Feet Buoy. 
Black. 


3J Fathoms. 


Clump of Trees at Ballaminich Farm-House in 
line with the lower part of the South-eastern Brow 
of Island Davaar — Bearing SW. |- W. 

The remarkable Notch in distant Hill called Ba- 
lavilan, in line with North End of Green Patch 
on the rising ground in Field south of Long Dyke 
near Smerby Farm-House — Bearing WNW. £ N. 

Macrinnan's Point — Bearing WSW. i 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 
BUOY. 


6 Feet Buoy. 
Black. 


2 Fathoms. 


Campbelton Town-House Spire in 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. \ W. 



BEACONS AND BUOYS. 



407 



Name of Station . 


Description of 
Mark. 


Depth at Low 

Water of 
Spring Tides. 


Bearings of Marks and of Lines of Intersection 
Meeting at the Station. 


CAMPBELTON 

HARBOUR 
OUTER BUOY. 


6 Feet Buoy. 
Red. 


Fathoms. 


West Corner of Gaelic Church in line with 
Trench Point — Bearing W. by N. |- N. 

West End of Bakaskie Fakm-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. -| E. 


CAMPBELTON 

HARBOUR 
INNER BUOY. 


6 Feet Buoy. 
Black. 


1} Fathoms. 


Castle Hill Church in line with high water- 
mark on Trench Point — Bearing WNW. \ W. 

North End of Higher Glenremisdil Farm-House 
in line with Cottage at East End of Hetly House 
—Bearing SW. f S. 


MILLMORE 
BEACON. 


Pyramid of Iron 
Spars with Wire 
Ball on top. 


Beach dry at 
Low water. 


Campbelton North Pier-head — Bearing NW. 
by W. 

Macrinnan's Point — Bearing ENE. |- N. 


TRENCH POINT 
BEACON. 




Pyramid of Iron 
Spars with Wire 
Ball on top. 


Beach dry at 
Low water. 


Campbelton North Pier-head — Bearing NW. 
by W. 

Outer or Red Buoy (above described) — Bearing 
ESE. i E. 


LAPPOCK 
BEACON. 


Tower with Stone 
Ball on top, 
painted Red. 


Rock dry at 
Low water. 


Troon Harbour Light — Bearing S. by W. |- W. 
Beacon on Lady Isle — Bearing SW. A W. 
Extremity of Ardrossan Pier — Bearing NNW. 

i w. 


BREAST ROCK 
BEACON. 


Pyramid of Iron 
Pillars, with cylin- 
dric open Cage, 
painted Red. 


Rock dry at 
Low water. 


Turnberry Point — Bearing NE. by N. ^ E. 
Pladda Lighthouse — Bearing NNW. 
Ailsa Craig (Highest Point) — Bearing W. 


LOCH RYAN 
INNER BUOY. 


7 Feet Buoy. 
Red. 


o-i Fathoms. 


Mr Moore's Pigeon-House in line with Angle of 
Plantation lying to the North of Corsewall House 
■ — Bearing N. by W. f 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. J N. 

North End of Stranraer Pier — Bearing SSW. 

i w. 


BEACON ON THE 
SPIT OF SCAR 
POINT, OFF 
KIRKCOLM 
POINT, IN LOCH 
RYAN. 


Cone of Iron 
Plates, pai nted Red. 


Dry at Low water. 


Loch Ryan Lighthouse — Bearing NNE. 1 E. 

Lochnoll Houses — Bearing SE. by E. 

Stranraer Pier End — Bearing SSW. -J- W. 

Waukmill Houses — Bearing SW. by W. 

Corsewall House in line with The Scar off Kirk- 
colm Point — Bearing NNW. i N, 



408 



APPENDIX, No. VIII. 



Name of Station. 


Description of 
Mark. 


Depth at Low 

Water of 
Spring Tides. 


Bearings of Marks and of Lines of Intersection 
Meeting at the Station. 


LOCH RYAN 
OUTER BUOY. 


7 Feet Buoy, 
Black. 


3 J Fathoms. 


Portincally Farm-House in line with the Brow 
of Clachan Head — Bearing NNW. \ W. 

Mr Charles M'Donald's House in line with the 
South End of General Wallace's Porter's Lodge 
— Bearing SE. 


LAGGAN, ok 
EBBSTONE 
ROCK BEACON. 


Pyramid of Iron 
Pillars, with cylin- 
dric Open Cage on 

top, painted Red. 


Rock dry at 
Low water. 


Corsewall Lighthouse — Bearing NE. hy E. 

Ailsa Craig (Highest Point; — Bearing NE. 
f N. 

Laggan Point— Bearing SSE. \ E. 


BEACONS AND BUOYS. 

LOCH FYNE DISTRICT. 


Name of Station. 


Description of 
Mark. 


Depth at Low 

"Water of 
Spring Tides. 


Magnetic Bearings of Marks and Lines of Intersection 
Meeting at the Station. 


OFF ARDLAMONT 
POINT or BRA- 
DEICH ROCKS, 
ARGYLESHIRE, 
BUOY. 


8 Feet Buoy. 
Red. 


2f Fathoms. 


South-West Extremity of West and Eastern 
Hills upon Ardlamont Point in line with Extre- 
mity of Point — Bearing NW. | W. 

Highest Part of Bradeich Rocks — Bearing 
NNW. i W. 

South End of Lnchmarnock Island — Bearing S. 
i 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 Bock. 


SKERNA SCAL- 
LAIG ROCK, 

OFF ENTRANCE TO 

CRINAN CANAL, 
ARGYLESHIRE, 
BUOY. 


7 Feet Buoy. 
Red. 


2\ Fathoms. 


SouTn Wing of Sir John Ord's Stables in line 
with North Extremity of Dunchoan Island — 
Bearing NE. by E. 

Silver Craig's Point, Island More — Bearing 
SE. by S. i E. 

West Wing of Ardrishaig Hotel in line with 
Lighthouse upon End of Ardrishaig Pier — Bear- 
ing N. | E. 

N.B. — The Buoy lies upon the South- West tail 
of the Shoal or Bock. 



BEACONS AND BUOYS. 



409 



Name of Station. 


Description of 
Mark. 


Depth at Low 

Water of 
Spring Tides. 


Magnetic Bearings of Marks and Lines of Intersection 
Meeting at the Station. 


OTTER BANK 
BEACON, 

OFF ENTRANCE TO 

LOCH FYNE, 
ARGYLLSHIRE. 
(Building.) 


Conical Iron 
Beacon. 
To be painted Black. 


Gravel Beach. 
Dry at Low water. 


Auchabolonabaith House (East Wing) in line 
with Centre of Cottage — Bearing N. by W. J W. 

Strathlachlan Hill in line with Schoolhouse 
Point — Bearing ENE. 

End of Liath Island — Bearing W. \ S. 


WEST OTTER 

BEACON, 
OFF CASTLE 
LACHLAN, 
LOCH FYNE, 
ARGYLE SHIRE. 
(Building.) 


Conical Iron 
Beacon. 
To be painted Black. 


Gravel Beach. 
Dry at Low water. 


.ejND oi MiNARD roiNT — .Bearing o vv . Dy vv . \ vv . 

End of Chapel Island — Bearing ENE. f E. 

Barneycarry Farmhouse in line with North- 
East End of Hugh Island — Bearing SE. \ E. 


BEACONS AND BUOYS. 

OBAN BAY, ARGYLLSHIRE. 


Name of Station. 


Description of 
Mark. 


Depth at Low 

Water of 
Spring Tides. 


Magnetic Bearings of Marks and Lines of Intersection 
Meeting at the Station. 


SKERRAT ROCK. 
S. W. End. 


10 Feet Buoy, 
with Fenders. 
Red. 


Dry at Low-water 
of Spring Tides. 


Centre of Oban Free Church Window in line 
with North-Eastern Chimney of Freemason's 
Hall — Bearing SE. by E. 

Centre of Skerry Dhu or Black Rock (appa- 
rently in middle of Sound of Kerrera) in line with 
Ardincaple Point — Bearing WSW. 

Buoy on North-Eastern End of Skerrat Shoal 
— Bearing NE. h E. distant 105 fathoms. 


SKERRAT 
SHOAL, 
N. E. End. 

N.B. — No Vessel s 


6 Feet Buoy. 
Chequered 
Black and White. 

hould attempt to pass i 


12 Feet at Low 
water of Spring 
Tides. 

tetioeen those Buoys. 


Oban Free Church Steeple in line with South 
Chimney Top of Spring Well Cottage — Bearing 
SE. 

Ardincaple Point, a little West of the Western 
End of Skerry Dhu or Black Rock — Bearing 
WSW. 

Buoy on Skerrat Rock — Bearing SW. \ W. 
distant 105 fathoms. 



3 F 



410 APPENDIX, No. VIII. 

BEACONS AND BUOYS. 



LINNHE LOCH DISTRICT, ARGYLLSHIRE. 



Name of Station. 


Description of 
Mark. 


Depth at Low 

Water of 
Spring Tides. 


Magnetic Bearings of Marks and Lines of Intersection 
Meeting at the Station. 


CULCHENNA 
SPIT BUOY. 


10 Feet Mast Buoy, 
with Red Ball. 


4c Fathoms. 


West End of Ardgour House in line with East 
End of Hugh Boyd's Cottage — Bearing N. £ E. 

John Cameron's Cottage in line with End of 
Culchenna Point — Bearing NE. f E. 

Sallachan Point — Bearing NNW. \ W. 

Chlavoulin Spit Buoy — Bearing N. £ E. 


CHLAVOULIN 
SPIT BUOY. 


7 Feet Buoy. 
Black. 


2 Fathoms. 


Centre of Ardgour House in line 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. f E. 

Corran Flat Buoy — Bearing ENE. f E. 

End of Sallachan Point — Bearing W. 


CORRAN FLAT 
BUOY. 


6 Feet Buoy. 
Black. 


3| Fathoms. 


West End of Brow of Sallachan Hill covered 
with Wood in line with Donald M'Lean's House 
—Bearing NW. by W. \ 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. | N. 

South Beow of Stroncrigan Hill in line with 
End of Corran Cliff — Bearing NE. by E. \ E. 


CORRAN BANK, 
NORTH-WEST 
END, BUOY. 


6 Feet Buoy. 
Chequered 
Black and White. 


2£ Fathoms. 


Bunrie Point in line with High Water Mark 
on Corran Point — Bearing S. by W. £ W. 

Belfry of Corran Church — Bearing W. by N. 



BEACONS AND BUOYS. 



411 



Name of Station. 


Description of 
Mark. 


Depth at Low 

Water of 
Spring Tides. 


Magnetic Bearings of Marks and Lines of Intersection 
Meeting at the Station. 


CORRAN BANK, 
SOUTH-EAST 
END, BUOY. 


6 Feet Buoy. 
Black. 

-i 


3£ Fathoms. 


Culchenna Point and Kintallon Point, in line 
with End of Cliff of Corran Point — Bearing SW. 
by S. £ W. 

Belfry of Corran Church — Bearing NW. by 
W,|W. 

8 T 

South Keil Farmhouse, in line with Arch of 
Bridge on Road — Bearing NNW. 

Corran Bank North Buoy — Bearing NNW. 


LOCHYFLAT 
EAST BUOY. 


6 Feet Buoy. 
Red. 


2f Fathoms. 


South End of Wood at Stroncrigan Point, 
just clear of Cambusnagaul Point — Bearing SW. 
by W. | W. 

East End of Donald Cameron's House in Cor- 
pach, in line with North End of Old Engine 
House — Bearing N. by W. J W. 

South End of Free Church in line with North 
Lnd oi (jreyhouse, or Old Corpach House — 
Bearing N. ■§• E. 

Entrance of Caledonian Canal— Bearing N. 
by W. i W. 


LOCHYFLAT 
MIDDLE BUOY. 


6 Feet Buoy. 
Red. 


3-i- Fathoms. 


East End of Henderson's House or Croft in 
line with East End of Schoolhouse near Cambus- 
nagaul Point — Bearing W. ^ S. 

Fish-house in line with End of Dearg Point — 
Bearing N. by W. f 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. \ E. 

Buoy on East End of Lochyflat — Bearing NE. 

f- N. 

M' Lean's Rock Buoy — Bearing NW. by N. 


LOCHYFLAT 
WEST BUOY. 


6 Feet Buoy. 
Red. 


3 Fathoms. 


Cameron's Monument in line with End of Dearg 
Point — Bearing N. £ E. 

North or Steep Face of Donnay Hill in line 
with South Wing of Old Castle of Inverlochy — 
Bearing E. § S. 

Lochyflat Middle Buoy — Bearing NE. 

M'Lean's Rock Buoy — Bearing N. by E. \ E. 

Fort- William Pier — Bearing SSW. | W. 



412 



APPENDIX, No. VIII. 



Name of Station. 


Description of 
Mark. 


Depth at Low 

Water of 
Spring Tides. 


Magnetic Bearings of Marks and Lines of Intersection 
Meeting at the Station. 


MACLEAN'S 
ROCK, LOCHEIL- 
HEAD, BUOY. 


6 Feet Buoy. 
Black. 


3f- Fathoms. 


Old Engine-House in line with High Water 
Mark on South End of Island Creiah — Bearing 
N. by E. i E. 

North Brow of Donnay Hill in line with Alan 
Kennedy's Barn, Southmost House in Kilcorpach 
—Bearing E. f S. 

Lochyflat West Buoy — Bearing S. by W. £ 
W. 

Fort- William Pier — Bearing S. by W. f W. 


NEW ROCK, 
LOCHEILHEAD, 
BUOY. 


6 Feet Buoy. 
Chequered 
Black and White. 


3 Fathoms. 


Cameron's Monument in line with End of Dearg 
Point — Bearing N. } E. 

North End of Free Church in line with High 
Water Mark on East End of Island Creiah — 
Bearing NE. f N. 

Centre of Donnay Hill in line with Alan Ken- 
nedy's Barn — Bearing E. £ 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, 1 
Edinburgh, 1«£ January 1848. J 



413 



APPENDIX, No. IX. 

REPORT TO THE COMMISSIONERS OF NORTHERN LIGHTHOUSES, 
FOR THE YEAR 1846; WITH APPENDICES. By Alexander Cuning- 
ham, 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 : 21. 

The Commission paid to Collectors in the same period is £2401 : 7 : 0$, 
and Repayments of Duties erroneously charged, &c, £218 : 16 : 10-f , mak- 
ing 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 1 845 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 



414 



APPENDIX, No. IX. 



were in operation during the first half of the year 1846. They were esti- 
mated 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 Boaed came to the resolution of making such a further reduc- 
tion 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 reduc- 
tion, 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 ope- 
ration during the last half of that year. It was estimated to produce a defi- 
ciency 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 le- 
vied 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 Re- 
ceipts 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. 



REPORT ON NORTHERN LIGHTHOUSES. 



415 



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 Over- 
sea 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 2f 

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 -i llf 



But the total Expenditure of the Board in the Year has been £60,374 15 9| 

From which if there be deducted the Gross Receipts, per page 425, 47,895 8 8| 

It gives a Balance superexpended beyond the surplus of the year of £'12,479 7 0* 

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 9| 

Difference equal to superexpenditure, . . £12,479 7 Of 



416 



APPENDIX, No. IX. 



There has been expended on the various Works in progress, prior to the 
year 1846 and in that year, as follows : — 



J 

- 


Prior to 


1846. 




In 1846. 


Total. 


Skerryvore Lighthouse Works.. 


£93,576 


10 







o 
o 


o 


/->f\ O O A O 

£y3,b03 


18 


2 




416 


10 


7 


ZD 


10 


-i 
I 


A A CI 

442 





8 




f QO QQQ 


U 


7 


£252 


18 


3 


£94,245 


18 


10 




Q fiOQ 




a 
O 


1,109 


5 


4 


10,633 


2 


10 




Z,Oi)0 


1 Q 


o 
O 


342 


9 


3 


3,238 


7 


11 




Z,ooZ 


1 R 

Id 


1 


405 


7 


8 


3,238 


3 


9 




296 


2 


2 


2,343 


17 


6 


2,639 


19 


8 










748 


10 


6 


748 


10 


6 


Island Glass New Buildings "V 


3,064 


15 


3 


1,797 


3 


5J 


4,861 


18 


8* 










1,467 


6 


1 


1,467 


6 


1 


Loch Ryan Ditto 








829 


12 


y 2 


829 


12 


9* 


Pentland Skerries New Works . . . 








3,135 


17 




3,135 


17 


5* 










2,037 


11 


4 


2,037 


11 


4 


Renewal of Fixed Lights 








3,035 


14 


4 


3,035 


14 


4 










1,549 


14 


1H 


1,549 


14 


ii* 










17 


4 


10 


17 


4 


10 










8 


12 


5 


8 


12 


5 


Startpoint New Works 








5 


19 


4 


5 


19 


4 










205 


5 


8 


205 


5 


8 










152 


5 


8 


152 


5 


8 










164 


15 


6 


164 


15 


6 










152 


5 


9 


152 


5 


9 




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 Ac- 
counts. The Accounts are now, for the first time, concentrated in the Se- 
cretary'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 con- 
taining a detailed account vouching the charge. Following out this ar- 
rangement, the account has been branched into three heads or divisions. 



REPORT ON NORTHERN LIGHTHOUSES. 



417 



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 ex- 
penses of the Board, not in the first instance chargeable against any parti- 
cular 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 extraor- 
dinary expenditure, that is, the expense of New Works and others not fall- 
ing 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 Offi- 
cers of the Board will be found under the head of Edinburgh Establishment. 



3g 



418 



APPENDIX, No. IX. 



ABSTRACT of the Receipts and Payments on Account of the Duties 
levied for the Northern Lighthouses for the year 1846. 



EECEIPTS. 

I. Gross Amount of the Duties received for 1846, per State, No. I. p. 429, 

Which has been received in the following proportions for each Light- 
house, as appears from State, No. II., pp. 430-3, viz. : — 



1. Inchkeith, 

2. Isle of May, 

3. Bell Rock, 

4. Grirdleness, 

5. Buchanness, 

6. Kinnairdshead, 

7. Tarbetness, 

8. Sumhurghhead, 

9. Startpoint, 

10. Pentland Skerries, 

11. Dunnethead, 

12. Capewrath, 

13. Island Glass, 

14. Barrahead, 

15. Skerryvore, 

16. Lismore, 

17. Rhinos of Islay, 

18. Mull of Kintyre, 

19. Pladda, 

20. Corsewall, 

21. Mull of G-alloway, 

22. Little Ross, 

23. Point of Ayre, 

24. Calf of Man (two Lights), 

25. Covesea Skerries, 

26. Cromarty, 

27. Chanonry, 



Deduct fractions short credited by Bankers, 
As above, 
II. Miscellaneous Receipts — 



Rent of Stable behind the Office, 

Do. of Small Houses at Arbroath, . 
Proceeds sale of Regent Tender, 
Composition of Is. 6d. per pound from 
the Trustee on Andrew Grreig's Bank- 
rupt Estate, on a claim of £340, lis. 
8d. and Expenses arising from an 
evasion of Light-dues, 



£2524 


9 


2f 


3825 


8 


6# 




1 5 

J. O 


54 


2458 


4 


H 


1880 


1 


3* 

8 


1744 


11 


H 


329 


17 


4s. 


286 


18 


H 


1154 


5 


4f 


1370 


10 


5f 


1311 


1 


lOf 


1278 


9 


9 


679 


1 


lOf 


1063 


3 


H 


2090 


11 


H 


239 


11 


4 


1414 


5 


8f 


1549 





1 


2762 


14 


3* 


2811 


5 


3s- 


2823 


19 


8f 


1187 


7 


H 


1755 


17 


H 


3839 


2 


lis- 


193 


7 


o 8 


27 


14 


11 


57 


15 


1 


£46,001 


11 


H 








n 


£46,001 11 


2f 




£18 








5 


' 5 





485 


14 


3 


27 





9 



Carried forward, 



£46,001 11 2f 



£46,001 11 Of 



REPORT OX NORTHERN LIGHTHOUSES. 



419 



RECEIPTS — Continued. 



Folio in 
Ledger. 



30 

74 

40 

149 
/ 3,/ 5. 
& 315 
74 



40&75 



Miscellaneous Receipts — Brought forward, 



Price of Lighter sold to Kirkcaldy Harbour 
Commissioners, 
Do. do. to Leith Shipping Company, 
Do. of Horse sold at Barrahead, 
Do. of an Ass sold at Inchkeith, 
Do. of Articles sold at Skerryvore, 

Fines imposed on Light-keepers, received, . 

Sum received from the General Post-Office, 
for the maintenance of the Harbour Light 
at Portpatriek for the year 1845, 

Interest received from the Royal Bank on 
money deposited, ..... 



Sum, 



£60 








45 








10 











9 


6 


126 


5 


10 


13 


1 


8 


136 


10 


9 


966 


9 


9 



Sums of Receipts carried to 
Abstract, page 425, 




PAYMENTS. 



Folio in 
Ledger. 



326 
327 



BRANCH I. — Oedixaet Expenses of the Board, being the Maintenance of the 

Lights for the year, viz ■ — 



355 


3. 


329 


4. 


330 


5. 


331 


6. 


332 


7. 


333 


8. 


334 


9. 


335 


10. 


336 


11. 


337 


12. 


338 


13. 


339 


14. 


357 


15. 



Lighthouses — 

1. Inchkeith, ...... 

2. Isle of May, 

Do. Year's Interest to Government, 

Bell Rock, . 
Girdleness, 
Buchanness, . 
Kinnairdshead, 
Tarbetness, 
Sumburghhead, 
Startpoint, 

Pentland Skerries (two Lights 
Dunnethead, . 
Cape wrath. 
Island Glass, . 
Barrahead, 
Skerryvore, 



£702 3 9 
250 



£583 


5 


10* 


952 


3 


9 


989 


1 


3i 


548 


18 


1 


623 


5 


3 


578 


10 


0* 


574 


11 


11" 


597 


5 


Q3 

°I 


347 





8 


851 


8 


11 


470 


19 




587 


6 




515 


2 


101 


594 


3 


10* 


1122 








Carried forward. 



£9935 4 1U 



420 



APPENDIX, No. IX. 



PAYMENTS — Continued. 



Folio in 
Ledger. 



340 


16 


341 


17 


342 


18 


343 


19 


344 


20 


345 


21 


346 


22 


347 


23 


348 


24 


354 


25 


351 


26 


358 


27 


353 


28 


350 


29 



BR ANCH I. — Ordinary Expenses of the Board — Continued. 
1. Lighthouses — Brought forward, 



Rhinns of Islay, 
Mull of Kintyre, 
Pladda, . 
Corse wall, 



Little Ross, 
Point of Ayre, 



Do. 



(Low Tower), 



Sum, — Carrie 



£394 


4 


7 


419 


14 


10 



to Abstract, p. 425, 



£9935 


4 


11* 


515 


14 


24 


569 


12 


n 


554 


17 


101- 


584 


10 


10 


465 


13 


4 


517 





51- 


516 


18 


61 


409 


1 


4-1 


813 


19 


5 


419 


16 


8* 


339 


17 


3 


284 


7 


1 


176 


5 


7 



£16,103 2* 



BRANCH II. — Ordinary Expenses falling to he allocated upon each Lighthouse — 



1. Expense of Collection — 

To paid Commission to Collectors, per State, No. I. p. 429, 
Do. do. to Bankers, .... 



2. Repayments, &c, of Light-Duties overcharged, 

3. Establishment in Edinburgh — 



Engineer, f Salary at £900, £675 
Do. I do. at £1200, 300 

Secretary, ...... 

Accountant, Salary to 8th July, when he died, 

Superintendent of Light-keep- 
ers, f Salary at £145, 
Do. i do. at £210, 



£108 


15 





52 


10 






£82 


10 





35 









Foreman of Lightroom re- 
pairs, £ Salary at £110, 
Do. I- Salary at £140, . 

Engineer's Clerk, \ Salary (formerly paid hy 
Engineer), ..... 

Examiner of Accounts, from 8th January to 
Candlemas, ..... 

First Clerk in Secretary's Department, 
\ Salary, ... 

Second do., J Salary, . 

Carried forward, 



£975 
500 
84 12 



161 5 



117 10 
32 10 

17 2 6 



£2401 7 
115 3 7 



3| 



£2516 10 10f 
218 16 lOf 



25 
25 



£1937 19 6 



£2735 7 8& 



REPORT OX NORTHERN LIGHTHOUSES. 



421 



PAYME XTS — Co a tin ued. 



Folio in 
Ledger. 



279 

132 
133 
135 
137 



184 



BRANCH II. — Ordinary Expenses falling to be" allocated upon each Lighthouse- 

Continued. 



Brou slit forward, 



Establishment in Edinburgh — Continued. 

Officer (now conjoined with Housekeeper), 
} Salary, 

Payments to two Clerks in Accountant's De- 
partment, to cease at "Whitsunday in con- 
sequence of the appointments in Secretary's 
Department, ..... 

Interim Accountant, per minute of the Board, 
until Examiner of Accounts was appointed, 

Office, including Porter and House-Servants' 
Wages, House Expenses, Taxes, Books for 
Library, &c, . 

, Shipping Establishment — 
Pharos Steam- Vessel, .... 
Prince of Wales, Bell Rock Tender, 
Francis, Skerryvore Tender, . 
Regent Tender (now sold), 



£1937 19 6 

5 

174 6 

105 

910 10 3* 



5. Beacons and Buoys — Expense of Ordinary Maintenance, 

6. Storehouse, Leith, including Storekeeper's Salary, Taxes, 

Freight of Stores, &c, viz : — 



Salary, f , ... 
Do. J, at £100 per annum, 



£40 13 
25 



Expenses of House, Packing Stores, &c. 
Freight of Stores, . 



Charities and Superannuations to Retired Servants of 

the Board, viz. : — 
1. Prior to the last Act of Parliament — 
William Tweedy, one year's Annuity, 
Mrs Leask, do. 
Hugh Rose, do. 
Jane Walker, do. (died 

March 13, 1847), 
Euphemia Poole, do., 



2. Since last Act, viz. : 

Robert Stevenson, Esq., late Engineer, 

Matthew Harvie, Light-keeper, 

John Bruce, late Officer, 

George Kirk, Light-keeper, 

John Watt, do. (died Dec. 1846), 



Carried forward, 






£3790 


1 


HI 


954 


10 


2 


920 


17 


6* 


259 


3 


7 



£65 13 
145 9 1\ 
133 4 3* 



£20 








10 


|| 





20 








6 


6 





5 










£580 








69 


7 


6 


13 





' 


40 








41 


12 


6 


£744 









£2735 7 



3132 15 9i 



5924 13 3f 
91 7 



344 6 lOf 



61 6 



£12,289 16 8| 



422 



APPENDIX, No. IX. 



PAYMENT S — Continued. 




BRANCH II. — Ordinary Expenses falling to be allocated upon each Lighthouse- 

Continued. 



Brought forward, 



7. Charities, &c. — Continued. 

William Heddle, Light-keeper, 

Robert Selkirk, do. (died Jan. 1847), 

Andrew Adamson, do., 

James Brown jun., do., 

"William Soutar, do., 

John Murray,late Boatman, Isle of May, 

David Lyall, Light-keeper, 

Thomson Milne, do. 

David Laughton, do. 

Alexander Burnett, do. 

James Wallace, .... 

John Miller (proportion till date of 
death), 

Mrs Duncan, late Housekeeper, three- 
quarters, .... 

John Scott, late Mate, Prince of Wales, 
quarter to Martinmas last, 

C. Cunningham, Esq., late Secretary, 
from 21st December to Candlemas, 



£744 








17 


15 





20 


16 


4 


47 








29 


11 


8 


48 


10 





18 


6 


8 


43 








64 


1 





' 47 


10 





45 








34 








11 


12 





10 


10 





22 


10 


8 


45 


7 


3 



New Tables, Notices, 
Circulars, &c, 
Do. 500 vols. Collector's 

Receipt Books, &c, 
Do. Annual List of Light- 
houses, &c, 
Do. "Stevenson on Lenses," 
and Expenses connected 
with Lenses, 



£173 


5 


7 


146 


19 


6 


207 


10 


10 


31 


1 


5 



7. Making Oil Casks, and Cooperage of old do. 



Carried forward, 



Miscellaneous Expenses not appropriated to any Particular 
Head, ......... 

Being — 

1. For Educating Expectant Light-keepers, 

being their Travelling Charges and 
Subsistence, .... 

2. Travelling Expenses of the Board, 

3. Do. do. of Officers on the 
Business of the Board, . 

4. Half-yearly Dinner Bills, £69, 5s., and 

£86 : 2 : 6, 

5. Advertising Reduction of Duties, 

6. Printing Expenses, viz., 



£84 


16 





128 


18 


11 


513 


3 


9 


155 


7 


6 


90 


10 


10 



558 
145 



17 
11 



£1677 5 6 



£12,289 16 



8£ 

°8 



1249 9 11 
2420 19 5 



£15,960 6 Of 



REPORT ON NORTHERN LIGHTHOUSES. 



423 



PAYMENT S — Continued. 




BRANCH II. — Ordinary Expenses falling to be allocated upon each Lighthouse- 

Continued. 



Brought forward, 



Miscellaneous Expenses, &c. — Continued, 

8. Postages and Carriage of Parcels, 

9. Messrs Cuningham and Bell, W.S., Law- 

Agents, Account for Commissions to and 
Bonds by Collectors, &c, 

10. Messrs Spottiswoode and Robertson, So- 

licitors, London, .... 

11. Gratuity to Lewis Proctor, an occasional 

Light-keeper, who met with a severe 
Accident by a fall from the Lighthouse 
at Kinnairdshead, 

12. Medical Attendance on Keepers' Families 

at Insulated Stations, 

13. Paid for Nomination to Edinburgh Royal 

Lunatic Asylum for Keeper's Wife at 
Chanonry Lighthouse, 

14. Gratuities voted to aged Light-keepers to 

meet Insurances on their Lives, 

15. Sundry small Sums due by Light-keepers, 

connected with Insuranceson their Lives, 
and Stamps for Premiums, 

16. R. W. Swinburne and Co., Newcastle, 

Plate-Glass, ..... 

17. Paid for Temporary Lanterns during 

Repairs of Lighthouses, 

18. One Dozen Stamped Receipt-Books for 

Keepers' Salaries, and Fees getting same 
Stamped in London, 

19. Expenses incurred by Henry Banks, tailor, 

in visiting the different Lighthouses, 
and taking " measures" for Clothing 
the Keepers, ..... 

20. Periodicals furnished to the Keepers, 

21. A Copper Buoy, .... 

22. Repairs on Rankin Lighter, 

23. Account connected with Skerryvore 

Lighters, ..... 

24. Models of Dioptric Light, 

25. Freight to London, Leith, Edinburgh, 

and Glasgow Shipping Company, 

26. Various small items for Lithographing, 

&c. &c, 

Sum as on preceding page, 



£1677 5 6 
120 18 10 



136 4 

57 11 8 

30 

26 17 

12 10 

38 7 1 

37 2 8 

32 1 6 

64 17 7 

7 1 



38 2 

4 14 7 
3 16 11 

5 2 4 

6 7 
83 13 1 

3 1 5 

35 7 1 



£2420 19 5 



Carry forward, 



£15,960 -6 Of 



£15,960 6 04 



424 



APPENDIX, No. IX. 



PAYMENTS — Continued. 




BRANCH II. — Ordinary Expenses falling to be Allocated upon each Lighthouse- 

Continued. 



Ordinary Expenses brought forward, 

Which have been Allocated to each Lighthouse in the proportions fol- 
lowing, as appears from State, No. II., pp. 430-3, viz. — 



189 
310 
182 
33 



150 

287 



1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
22. 
23. 
24. 
25. 
26. 
27. 
28. 



Inchkeith, 
Isle of May, 
Bell Rock, 
Clirdleness, 
Buchanness, 
Kinnairdshead, 
Tarbetness, 
Sumburghhead, 
Startpoint, 
Pentland Skerries, 
Dunnethead, 
Cape wrath, 
Island Olass, 
Barrahead, 
Skerryvore, 
Lismore, 
Bhinns of Islay, 
Mull of Kintyre, 
Pladda, 
Corsewall, 
Mull of Calloway, 
Little Ross, 
Point of Ayre, . 
Calf of Man (two Lights) 
Covesea Skerries, 
Cromarty, . . 
Chanonry. 
Loch Ryan, 



As above, 



£577 


15 


9* 


941 


8 


6 


o t i 




q 


544 


5 


8 


617 


4 


If 


573 


16 


Hf 


569 


18 


^8 


591 


11 


8f 


345 


4 


4f 


841 


17 


10f 


467 


8 


4 


581 


14 


72. 
1 8 


510 


15 


6a 

°8 


588 


12 


7 


1108 


19 


1 


511 


15 


AA 
^8 


564 


19 


6f 


550 


3 


lOf 


579 


15 


2f 


462 


9 


QA 
^8 


512 


14 


Hf 


512 


14 


Hf 


406 


6 


4t 


805 


8 


7a 

' 8 


417 


3 


14 


338 


6 


4f 


283 


2 


8f 


176 


14 


1 



BRANCH III. — Extraordinary Expenses not Allocated to each Lighthouse :- 



To paid for new Steamer Pharos, ...... 

Expense of Harbour Light at Portpatrick, .... 

Do. connected with Skerryvore Book, .... 

To paid for House in Crail for use of Isle of May Boatmen, and 
Fees connected with Purchase, ...... 



Expense of New Works, viz. 
Skerryvore, 
Bo Pheg Beacon, 



Carry forward, 



£227 8 2 
25 10 1 



£252 18 3 



£7548 13 7 

129 17 4J 

199 18 

105 19 4 



£7984 8 3-1- 



£7984 8 31 



REPORT ON NORTHERN LIGHTHOUSES. 



425 



PAYMENTS — Continued. 



Folio 
in 

Ledger. 



BRANCH III. — Extraordinary Expenses not Allocated to each Lighthouse — 

Continued. 





Brought 


forward, 




Expense of New Works— brought forward, 


£252 


18 


3 


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 




319 


Nosshead, ...... 


1467 


6 


1 


322 


Loch Ryan, ...... 


829 


12 




121 


Do. Beacon, ..... 


152 


5 


9 


324 


Pentland Skerries new Works, 


3135 


17 


5£ 


145 


Do. Dioptric Light, 


2037 


11 


4 


308 


Benewal of Fixed Lights, 


3035 


14 


4 


106 


Campbeltown Beacons, .... 


17 


4 


10 




Lapock Beacon, ..... 
Startpoint New Works, .... 
Elie or Vow's Beacon, .... 


8 


12 


5 


117 


5 


19 


4 


118 


205 


5 


8 


119 


Whiteness do., .... 


152 


5 


8 


120 


Longman's Point do., .... 


164 


15 


6 


184 


Brist Beacon, ...... 


8 


12 


5 


306 


Mull of Kintyre Dykes and Road, 


647 


17 


9 


286 


Buoys, ....... 


1458 


7 


m 



Smr, 

Carried to Abstract below, 



£7984 8 34 



20,327 1 3 



£28,311 9 6i 



ABSTRACT OF THE PRECEDING ACCOUNT. 



RECEIPTS :— 

Branch I. — Gross Amount of the Duties received for 1846, 

P- 418, 

II. — Miscellaneous Receipts, p. 419, .... 



PAYMENTS :— 



Branch I. — Ordinary Expenses, being the 
Maintenance of Lights, &c. 
p. 420, .... 

II. — Do. do. falling to be 

allocated upon each Light- 
house, p. 424, 

III. — Extraordinary Expenses not 

allocated to each Light- 
house, as above, 



£16,103 2| 



15,960 6 01 



28,311 9 64. 



Balance superexpended in 1846, 
Balance on hand at 31st March 1846, 

Balance on hand at 31st March 1847, 

Carry' forward, 



£46,001 11 2f 
1,893 17 6 



£47,895 8 8f 



60,374 15 9 1 



£12,479 7 Of 
42,069 6 10 



£29,589 19 9i 



£29,589 19 9* 



3 H 



426 



APPENDIX, No. IX. 



ABSTRACT OP THE PRECEDING ACCOUNT — Continued. 



Folio in 
Ledger. 



89 

157 
161 
164 
166 
168 
172 
176 
180 

307 
318 



Folio in 
Small 
Ledger. 



9 
10 



Brought forward, 



PAYMENTS- 
Whekeof — 



-Continued. 



In the Royal Bank, 
In Secretary's Account, 



Balance due hy Peter Grant, Superintendent, 
Nosshead, ...... 

Do. by Master of Prince of "Wales Tender, 
Do. by Steward of Pharos Steamer, . 
Do. by Master of Francis, Skerryvore Tender, 
Do. by Superintendent of Light-keepers, 
Do. by Foreman of Light-room Repairs, 
Do. by Buoymaster, .... 

Do. by Store-keeper, .... 

Do. by Thomas Hope, Superintendent, Island 
Glass, ...... 

Do. by Master of Pharos, .... 

Do. by James Scott, Superintendent, Pent- 
land Skerries, 



Sum due by Robert Selkirk's Representatives, 
to be paid when Insurance money is 
received, ...... 

Balance due by Richard dimming, Light- 
keeper, 

Do. by James Laughton, do., 
Do. by William Kirk, do., 

Equal to Balance, 



£28,944 16 
40 16 


8 
11 


£28,985 


13 


7 


203 


10 


2 


35 


3 


4 


30 


19 


2 


2 


12 


5 


11 


11 


2 


5 


3 


5 


5 


1 


6 


7 


17 





87 


17 


7- 1 - 

' 2 


5 


10 


8 


188 


12 


3 


10 








2 


13 





3 








4 


14 


6 



£29,589 19 



9* 



29,589 19 94 



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. 



REPORT ON NORTHERN LIGHTHOUSES, 



427 



STATEMENTS ANNEXED TO THE SECRETARY'S REPORT FOR 1846. 



No. I. — Account of Northern Light-Duties received in the Year 1846. 



Gross Keceipts. 



Commission 
to Collectors. 



Repayments, &c. 



Nett Duties 
Received. 



1. Aberdeen, 

2. Alloa, 

3. Arbroath, 

4- Ayr, 

5. Aberystwith, 

6. Arundel, 

7. Banff, 

8. Borrowstouriness, 

9. Barnstaple, 

10. Beaumaris, 

11. Berwick, 

12. Bideford, 

13. Boston, 

14. Bridgewater, ... 

15. Bridlington, 

16. Bridport, 

17. Bristol, 

18. Baltimore, 

19. Belfast, 

20. Campbeltown, ... 

21. Caernarvon, 

22. Cardiff, 

23. Cardigan, 

24. Carlisle, 

25. Chepstow, 

26. Chester, 

27. Chichester, 

28. Clay, 

29. Colchester, 

30. Cowes, 

31. Coleraine, 

32. Cork, , 

33. Dunbar, , 

34. Dundee, 

35. Dumfries, , 

36. Dartmouth, 

37. Deal,...'. 



S 
6 
2 

158 12 11 
6 17 



£2243 
402 
254 



9* 



467 7 5 

675 6 If 

1 7 2* 

123 17 U 
121 8f 

8 14 11 

9 15 Of 
12 1\ 
26 1 3f 

2 18 Of 

124 12 7f 



2446 
82 14 



1 

84 



1 4f 

9a 

25 13 10 8 

110 19 7 

7 Hf 

3f 

14 11 



15S 
2 
1 



4 
15 
2 



1 1 



101 5 8f 
70 13 1 
115 11 11 
2062 9 10 



351 10 



Carryforward, j £10,253 10 8f £562 1 9| 



£121 11 8f 
23 6 8 
12 17 2f 
8 1 10 
O 6 9| 



28 17 6 
48 11 H 
1 4f 
6 12 7* 
6 11 9f 
8 9 
10 7f- 

11 11| 

1 6 1 
2 10| 
6 4 6f 



125 6 4f 

5 2 lf 

1 7 7 

5 11 

1 7f 

4 7 9f 

9 

8 1 

3 

1 



5| 



5 1 
3 10 
7 1 
105 7 



24 13 Of 



£5 14 5 
6 17 9 
3 17 7f 
1 15 10 
10 



2 19 3 
9 4 1 

'6"ti"l 
18 

6""5 "*6 
2 10 



14 

56 i'2' 10 

1 12 8 

8 



10 5 

1 



2 9 
11 4 
7 15 10 
2 10 8 



£105 11 6| 



£2115 17 
372 1 
237 

148 15 
6 9 



8f 
8 If 
3 
9 



435 10 
617 10 
1 

116 
114 



3 
10 
5 
3 
2 



5 
9 
7 

8 6 

8 18 11 
11 5 10 
24 15 2 

2 15 2 
117 14 



2264 2 2 
76 
23 18 3 
105 8 

1 6 
79 2 

14 
149 2 llf 

2 11 9 

1 9f 



96 
65 



4 n 
1 10 



107 19 5 
1949 6 10 
324 6 10 



£9585 17 5 



428 



APPENDIX, No. IX. 



Gross Receipts. 



Brought forward, . . . 

38. Dover, 

39. Dublin, 

40. Drogheda, 

41. Dundalk, 

42. Exeter, 

43. Fisherrow, 

44. Falmouth, 

45. Faversham, 

46. Fowey, 

47. Glasgow, 

48. Greenock, 

49. Grangemouth, ... 

50. Gainsborough, ... 

51. Gloucester, 

52. Goole, 

53. Grimsby, 

54. Gweek, 

55. Galway, 

56. Hartlepool, 

57. Harwich, 

58. Hull, 

59. Inverness, 

60. Irvine, 

61. Ipswich, 

62. Isle of Man, 

63. Kirkcaldv, 

64. Kirkwall, 

65. Leith, 

66. Lerwick, 

67. Lancaster, 

68. Leigh, 

69. Liverpool, 

70. Llanelly, 

71. London, 

72. Lyme, 

73. Lynn, 

74. Limerick, 

75. Londonderry, 

76. Montrose, 

77. Maldon, 

78. Milford, 

79. Maryport, 

80. Newcastle-on-Tyne, 

81. Newhaven, 

82. Newport, 

83. Newry, 

84. Perth, 

85. Port-Glasgow, 

86. Padstow, 

87. Penzance, 

88. Plymouth, 

89. Poole, 

90. Portsmouth,. 



Commission 
to Collectors. 



£10,253 


10 


8f 


£562 


1 


9* 





8 


Of 








5 


2256 


17 


10 


114 





9 


149 


8 


2£ 


7 


9 


5 


120 


6 


6| 


6 





3f 


2 


17 


H 





3 


Of 


219 





8| 


13 


12 


4* 



Repayments, &c. 



Carry forward, 



2 


4 


11 





3 


0* 


3599 


16 


10 


182 


14 


4* 
8 


2671 





9 


137 


13 


1251 


12 


5 


62 


11 


6 


5 


19 


8 





6 


9 


61 


12 


11* 


3 


1 


8f 


31 


2 


4 


1 


12 


2 


64 11 


3# 


3 


4 


7 


38 


6 





1 


18 


3f 


153 


4 





7 


13 


2 


1532 


8 


2* 


76 


12 


5£ 


920 


17 


If 


56 


12 


Hf 


915 


10 


10 


63 


8 


11 


17 


5 








17 


3 


373 


18 




22 


15 


5f 


745 


5 


5 


42 


16 


2 


131 


15 


6* 


7 


9 


0| 


3224 


7 


3 


161 


4 


4 


173 


1 


1 


8 


13 





107 





6* 


6 


3 


6| 


6780 


19 


5 


342 


8 


9 


8 


12 


3 





11 


9 


1943 


8 


9f 


97 


3 


4f 


79 


7 


7 


4 


15 




160 


2 


4* 


8 


3 


2* 


1058 


2 


4 


53 


6 


6 


357 


13 


2f 


18 


6 


Of 


14 


4 


6* 





19 


7 


87 


17 


If 


4 


5 


7 


2118 


16 


8| 


75 


2 


9 


1 


14 


10 





1 


9 


41 


2 


8 


2 


1 


If 


230 


16 


2 


13 


3 


9 


275 


14 


3 


14 


13 


6* 


496 


8 


6 


24 


16 


3 


2 


15 


If 





2 


8f 


1 


6 


10 





1 


4 


25 


4 


9 


1 


6 


2 





11 


6 








7 


10 


12 


4# 





10 


6* 



£42,719 1 7|- £2223 2 10| 



£105 11 6f 

9 Te i9 

6 8 
015 3 



11 15 llf 
7 10 6 
2 16 10 



2 



6 



10 

7 1 11 

3 8 8 

2 

1 13 9 
1 16 2 
9 9 

17 14 2 

11 1 

18 8 



Nett Duties 
Received. 







9 13 11 



7 2 
5 

10 3 



2 6 llf 
14 8 



14 6 11 

19 10 

15 7 

5 



1 

4 9 



£203 18 8# 



£9585 17 
7 
2133 
141 18 
113 19 
2 14 
204 13 



5 

7* 
4 

7 
5 



2 

3405 
2525 16 
1186 4 
5 
58 

29 10 
61 6 



1 10| 

6 6 
7 

4 1 
12 11 

9 3 
2 

8| 



36 1 8| 
145 10 10 



9 

2f 

3 

9 

6f 
1 



1455 5 

857 2 

848 13 
16 5 

349 9 

700 13 

123 16 9 
3045 8 9 

163 17 
99 18 2f 

6428*16 9 
8 6 
1846 5 5 



74 5 2| 
151 14 2 
1004 15 10 
338 16 11 



13 
81 



2042 19 



13 
1 



1 

39 
203 
260 

470 16 
2 7 
1 5 



7 

°t 
1 

H 

5 6 
10f 



5 
6 

23 17 7 
10 11 
9 17 1 



£40,302 



REPORT ON NORTHERN LIGHTHOUSES. 



429 



Gross Receipts. 



Commission 
to Collectors. 



Repayments, &c. 



Nett Duties 
Received. 



Brought forward, 

91. Preston, 

92. Ramsgate, 

93. Rochester, 

94. Rye, 

95. Ross, 

96. Stranraer, 

97. Stor noway, 

98. Scarborough,... 

99. Seilly, 

100. Shoreham, 

101. Southampton,.. 

102. Stives, 

103. Stockton, 

104. Sunderland, 

105. Swansea, 

106. Sligo, 

107. Truro, 

108. Tralee, 

109. Wick, ' 

110. Wigton, 

111. Weymouth, , 

112. Whitby, 

113. Whitehaven,..., 

114. Woodbridge,.... 

115. Waterford, , 

116. Westport, 

117. Wexford, 

118. Yarmouth, 



Deduct — Amount of 
fractions short cre- 
dited by Bank, 



£42,719 1 7-j 
562 1 11 



£2233 2 10$ 
41 14 10 



1 15 



1 

18 3f 
12 17 10 
17 9 



90 
56 



6 llf 
14 10$ 



19 
30 

3 9 
226 19 
908 14 



28 
355 



11 

9 7 
356 17 

83 9 



6* 
9 

n 

2 

57 8 
Q6. 
^8 

4 

10* 

H 



15 10* 



31 

328 
3 



5 
1 
18 



57 14 
41 -0 
32 19 

49 5 



10 
9 
9 

3* 
6* 
2 
6 



£46,001 11 3i 



11 



£46,001 11 24 



1 10 
10$ 
12 11 
4 16 6 
2 16 2f 
8 8* 



llf 

1 10 1 

5 2i 
12 2$ 
47 1 4| 

1 12 3 

19 15 lOf 
9 
9 4f 

20 10 2$ 
5 5 5 



1 11 
18 5 

3 11 

2 17 10$ 
2 10 

1 12 llf 

2 9 5 



9£ 

4 

5 



£2401 7 3# 



£2401 7 3* 



£203 18 8* 



4 7 
19 3 
3 6 



1 

5 11 

14 9 

6 10 4 

o' 2 8 

4 9 1 

1 12 11 



£40,302 1 llf 
520 7 1 



£218 16 104 



£218 16 104 



Gross Receipts, 



Deduct— Commission, 

Repayments, &c. 



£2401 7 3* 
218 16 lOt 



Nett Duties received in year to 31st December 1846,.. 



£46,001 11 2* 



2620 4 If 



1 13 3 

17 5 

12 4 

84 12 

53 7 3 

8 6 2 



18 
28 10 
3 4 
209 7 
860 18 
26 12 
334 14 
10 



/ 
8 
6 



331 18 
76 11 
15 
29 14 
309 16 
3 



6 

1 8 

3 

15 lOf 



6 
I 

1 

6 
4 

14 10 

5 



54 16 
38 19 
31 6 
46 16 1 



6* 
2f 



£43,381 



9.x 



1* 



£43,381 7 1 



43,381 7 1 



430 



APPENDIX, No. IX. 



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 j—the Particular Expenses of the Lighthouses, and their Proportions o f 
the General Expenses, embracing Commissions to, and Repayments by, the Collectors ; Expenses of the Shipping 
Establishment, Salaries to Officers, Experiments, and other General Expenses j also the Ordinary Expenses of 
Beacons and Buoys, for the Year 1846. 



No. or Vessels. 


Tonnage. 


LIGHTHOUSES. 




Gross Receipts. 


Coasting. 


Oversea. 


Coasting. 


Oversea. 








15,872 


2,664 


1,238,057 


294,546 


1. INCHKEITH, . 

Particular Expense, 
Share of General Expense, 
Total Expenditure, 


£583 5 104 
577 15 9f 


£2524 9 
1161 1 


n 










Balance, 
















20,101 


3,349 


1,843,210 


383,516 


2 TST/TC OF MAY 

Add for Leading Light, . 


£3676 18 11 
148 9 64 


£3825 8 
1893 12 


H 










Particular Expense, 
Share of General Expense, 
Total Expenditure, 


£952 3 9 
941 8 6 


3 










T£ AT, A Nf!P 


















14,610 


4,485 


1,299,875 


632,328 


3. BELL ROCK, . 

Particular Expense, 
Share of General Expense, 
Total Expenditure, 


£989 1 3| 
977 17 9 


£5342 15 
1966 19 


5f 
Of 










"Rat* 'MPT? 
















7,915 


3,978 


788,947 


587,977 


4. GIRDLENESS, 

Particular Expense, 
Share of General Expense, 
Total Expenditure 


£548 18 1 
544 5 8 


£2458 4 
1093 3 


H 

9 










"Rata wpt? 


















5,293 


4,012 


419,988 


590,453 


5. BUCHANNESS, 

Particular Expense, 
Share of General Expense, 

TnTAT. "P.V P'FNTiTTTTT} V 


£623 5 3 
617 4 If 


£1880 1 
1240 9 


3! 

4« 












*s 
















4,829 


2,819 


390,166 


546,856 


6. KINNAIRDSHEAD, 

Particular Expense, . 
Share of General Expense, 
Total Expenditure, 


f'P'TQ 1 A (\± 

±,5/o 10 Of 
573 16 llf 


£1744 11 
1152 6 


3£ 
Hf 










Balance, 
















2,256 


273 


191,345 


18,282 


7. TARBETNESS, 

Particular Expense, 
Share of General Expense, 
Total Expenditure, 


£574 11 11 
569 18 If 


£329 17 
1144 10 


4f 
Of 










Balance, 
















279 


. 644 


32,149 


113,598 


8. SUMBURGHHEAD, 
Particular Expense, 
Share of General Expense, 
Total Expenditure, 


£597 5 3f 
591 11 84 


£286 18 
1188 17 


Of 










Balance, 


















307 


2,326 


33,710 


528,547 


9. STARTPOINT, 

Particular Expense, 
Share of General Expense, 
Total Expenditure, 


£347 8 
345 4 4| 


£1154 5 
692 5 


4f 
Of 










Balance, 
















2,434 


2,430 


181,284 


525,582 


10. PENTLAND SKERRIES, 
Particular Expense, 
Share of General Expense, 
Total Expenditure, 


£851 8 11 
841 17 10| 


£1370 10 
- 1693 6 


6f 
91 










Balance, 


















73,896 


26,980 


6,418,731 


4,221,685 


Carry forward, 









SUBPLCS. 



£1363 7 64 



1931 16 24 



3375 16 5f 



1365 84 



639 11 10# 



592 4 6# 



Deficiency. 



462 8# 



£9329 18 1 



£814 12 74 



£901 18 94 



322 16 3S 



£2039 7 8j 



REPORT ON NORTHERN LIGHTHOUSES. 



431 



No. of Vessels. 



Coasting. 



73,896 
1,911 



1,700 



1,734 



669 



555 



2,430 



3,152 



5,023 



12,372 



12,453 



12,884 



9,195 



9,733 



13,867 



Oversea. 



26,980 
2,267 



2,231 



1,153 



1,821 



1,788 



34 



1,550 



1,440 



1,937 



161,574 



Tonnage. 



Coasting. 



2,776 



2,458 



98 



1,034 



2,559 



50,126 



6,418,731 
139,379 



131,138 



137,060 



9,517 



52,541 



159,719 



385,786 



509,914 



1,403,359 



1,407,921 



1,648,915 



729,918 



843,235 



1,769,475 



Oversea. 



4,221,685 
524,685 



517,333 



226,941 



466,010 



461,313 



4,436 



382,841 



357,682 



450,849 



645,447 



531,056 



17,431 



209,237 



546,244 



15,796,608 



LIGHTHOUSES. 



9,563,190 



Brought forward, . 

11. DCJNNETHEAD, . 
Particular Expense, 
Share of General Expense, 
Total Expenditure, 



12. CAPEWRATH, 

Particular Expense, 
Share of General Expense, 
Total Expenditure, 



13. ISLAND GLASS, . 
Particular Expense, 
Share of General Expense, 
Total Expenditure, 



14. BARR AHEAD, 

Particular Expense, 
Share of General Expense, 
Total Expenditure, 



15. SKERRYVORE, 

Particular Expense, . 
Share of General Expense, 
Total Expenditure, 



16. LISMORE, 

Particular Expense, 
Share of General Expense, 
Total Expenditure, 



17. RHINNS OP ISLAY, 
Particular Expense, 
Share of General Expense, 
Total Expenditure, 



18. MULL OP KINTYRE, . 
Particular Expense, 
Share of General Expense, 
Total Expenditure, 



19. PL ADD A, 

Particular Expense, 
Share of General Expense, 
Total Expenditure, 



20. CORSEWALL, 

Particular Expense, 
Share of General Expense, 
Total Expenditure, 



21. MULL OP GALLOWAY, 
Particular Expense, 
Share of General Expense, 
Total Expenditure, 



22. LITTLE ROSS, 

Particular Expense, . 
Share of General Expense, 
Total Expenditure, 



23. POINT OP AYRE, . 
Particular Expense, 
Share of General Expense, 
Total Expenditure, 



24. CALF OP MAN (2 Lights), 
Particular Expense, 
Share of General Expense, 
Total Expenditure, 



Carry forward, 



£470 19 1% 
467 8 4 



Balance, 



£587 6 llf 
581 14 7| 



Balance, 



£515 2 10-| 
510 15 64 



Balance, 



Gross Receipts. 



£1311 1 10? 



938 7 11| 



£1278 9 9 

1169 1 6| 

£679 1 lOf 

1025 18 4S 



£594 3 10|- 
588 12 7 



Balance, 



£1122 7 
1108 19 1 



Balance, 



£515 14 2f 
511 15 4* 



Balance, 



£569 12 7f 
564 19 6? 



Balance, 



£554 17 10J 
550 3 lOf- 



Balance, 



£584 10 10 
579 15 2# 



£1063 3 2* 



1182 16 54 



£2090 11 34. 
2239 19 8 



£239 11 4 
1027 9 6f 



£1414 5 8# 



1134 12 24 



£1549 1 



1105 1 9# 



£9,329 18 1 



372 13 101 



109 8 24 



Balance, 



£465 13 4 
462 9 9| 



Balance, 



£517 54 
512 14 llf 



Balance, 



£516 18 6f 
512 14 11# 



Balance, 



£409 1 44 
406 6 44 



Balance, 



£813 19 5 
805 8 74 



Balance, 



£2762 14 31 



1164 6 0# 



£2811 5 3| 
928 3 14 



£2823 19 8f 
1029 15 5 



£1187 7 94 



1029 13 54 



£1755 17 5 | 
815 7 9 



£3839 2 llf 
1619 8 04 



Deficiency. 



279 13 6| 



443 18 3g 



1598 8 34 



1883 2 2# 



1794 4 31 



157 14 4 



940 9 84 



2219 14 101 



£2,039 7 



£19,529 5 14 



346 16 6 



119 13 



140 8 44 



787 18 2| 



£3434 4 Of 



432 



APPENDIX, No. IX. 



No. of Vessels. 



Coasting. Oversea. 



161,574 
1,592 



163,166 



50,126 
198 



50,324 



Tonnage. 



Coasting. 



15,796,608 
130,026 



15,926,634 



Oversea. 



9,563,190 
14,288 



9,577,478 



LIGHTHOUSES. 



Brought forward, . 

25. COVESEA SKERRIES * . 
Particular Expense, 
Share of General Expense, 
Total Expenditure, 



26. CROMARTY* . 

Particular Expense, 
Share of General Expense, 
Total Expenditure, 



27. CHANOKRY* . 
Particular Expense, 
Share of General Expense, 
Total Expenditure, 



28. LOCH RYAN* 

Particular Expense, 
Share of General Expense, 
Total Expenditure, 



* Note.— Covesea Skerries, Cromar- 
TT, 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, 



£419 16 8| 
417 3 1| 



Balance, 



£339 17 3 
338 6 4J- 



Balance, 



£284 7 1 
283 2 8# 



Balance, 



£176 5 7 
176 14 1 



Gross Receipts. 



£193 7 
836 19 lOf 



£27 14 11 

678 3 7f 



£57 15 1 
567 9 94 



SCRPLUS. 



£19,529 5 1| 



£19,529 5 H 



Deficiency. 



£3434 4 Of 



.643 12 lOf 



650 8 8# 



509 14 8£ 



352 19 8 



£5591 0# 



RECONCILEMENT. 

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, 



£19,529 


5 


1* 


5,591 





Of 


£13,938 


5 


o* 










£13,938 


4 


Hf 


1,893 17 


G 


£15,832 


2 


5f 


28,311 


'9 


6# 


£12,479 


7 





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 allo- 
cated to each Lighthouse. 



REPORT ON NORTHERN LIGHTHOUSES. 



433 



No. III. — Statement shelving the Increase in Tonnage during the Years 1843—44-45-46, over 1842. 











Coasting. 


Oversea. 


Total. 


The amount of the Tonnage in 1842 was 








11,620,1/2 


6,/ 38,433 


18,358,605 


in 1843 








12,190,745 


7,194,932 


19,385,677 




Increase in 1843 over 


1842 


570,573 


456,499 


1,027,072 




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 
















1,234,869 


■ 542,685 


1,777,554 












Increase in 1844 over 


1842 


1,805,442 


999,184 


2,804,626 




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 
















2,140,847 


1,563,366 


3,704,213 












Increase in 1845 over 


1842 


3,946,289 


2,562,550 


6,508,839 




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 
















360,173 


276,495 


636,668 




Increase in 1846 over 


1842 


4,306,462 


2,839,045 


7,145,507 

















3 i 



434 



APPENDIX, No. X. 



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. Fiest Depaetment. — The Light-keeper who has this departmen , 
shall immediately after the morning Watch, polish or otherwise cleanse the 
Reflectors or Refractors till they are brought into a proper state of bril- 
liancy ; 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 Depaetment. — 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 ap- 
paratus and machinery therewith connected ; together with the Tower stair, 
passage, doors, and windows, from the Light-room to the Oil cellar. 



INSTRUCTIONS TO LIGHT-KEEPERS. 



435 



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, dur- 
ing the winter period, between the first day of October and last day of 
March T 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 neces- 
sary, 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 



436 



APPENDIX, No. X. 



Oil and other Stores for the use of the Light-room. The oil is to be mea- 
sured 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, embody- 
ing 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 recog- 
nised 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 ves- 
sels 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 Light- 
house Board, as well in his own as in the Assistant's house. This duty ex- 



INSTRUCTIONS TO LIGHT-KEEPERS. 



437 



tends also to the cleanliness of the several apartments, passages, stairs, 
roofs, water-cisterns, store-rooms, work-shops, privies, ash-pits of the dwell- 
ing-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 he landed for the use of the Light- 
house, the Light-keepers shall attend and give their assistance. The Prin- 
cipal Light-keeper must, upon these occasions, satisfy himself, as far as 
possible, of the quantity and condition of the stores received, which must he 
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 cir- 
cumstances 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 ap- 
pear to the Principal Light-keeper to be getting short, so as thereby to en- 
danger 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 oc- 
casions 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 



438 



APPENDIX, No. X. 



to the Assistant Light-keeper ; — it being expressly ordered that only one 
Light-keeper shall be absent from theLighthouse 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 pre- 
mises 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 imme- 
diately 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 let- 
ter 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 con- 
duct 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 ex- 
pressly 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 Sun- 
day ; — 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 sub- 
ject the Light-keepers to dismissal, or to such other punishment as the 
nature of the offence may require. 

33. It is recomended that the Principal Light-keeper, or other Principal 



INSTRUCTIONS TO LIGHT-KEEPERS. 



439 



Officer at the respective Lighthouses for the time being, shall, every Sun- 
day, 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 Regula- 
tions 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 
far 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 appoint- 
ment, 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 con- 
duct ; that the Engineer has power, in case of neglect or disobedience, in- 
stantly 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 offend- 
ing 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 in- 
to consideration when any application may be made for superannuated allow- 
ance. 

Extracted from the Minutes by 

Alex, Cuningham, Sec. 



EDINBURGH : 

PRINTED BY NEILL AND COMPANY, OLD FISHMARKET. 



I' LATE I 



.-•7 



& 



• 1 r wl 



C ft A IT 

Skewing the Situation of the 



■a. 

ZETLAND 



^I'&ffc ISLANDS 



0*. 



Sumlwylt Haid 



i) Fair Kb 



5* 



ORKNEY 



lfkaniiur Isles 
or rHunti-rs 



ISLANDS 

Thmrao" 




SI KU.bi l' 1 



& E ffi M A F 



A T 1L ■ A 1ST T 1 C 



ThJtixtrahulLJs^ 3 




TrrisIIriuL 



Cape Clear ^ 



Lands End 
Seillv Isles w 



Xry' ty It &J,X. Johnston Vetin r 



1° Meridian. a£ Greenwich. l| 



PLATE II. 



Ben ll i ■/ 




mm 



i s h a n b 




RE FE1EICES 
always above water 
covered, every tide 
locks 

locks on which the .sea breetks 
outings are marked in Fathoms 



Stevenionls account of the Skaiyvon Light House 



JZiwray'il- Try W &ATCJdlwstmi F.i!i:dwrph 



PLATE II. 



HAM T 

SIT ION oi the 




OlI-OKOrND 

trvey made for ///<■ 
NORTHERN LIGHT HOUSES 



RITSON SURVEYOR 




| 1 § L A H S 



'0 F 




m m m » 

Bo-theq above water 

E 



1EFE1MCES 
> Rocks always above water 
% Rocks covered every tide 
+ Slink Roclcs 

$ A(7(/.- 2focfo o;i vc/ziV-^ tlie sea breaks 
TIw Soimdinas are marked in Fathoms 



Strvcnsonb account of the Skenyvore liyla House 



Engrarei ir ir.iA7CJolins!mi E&n/nayk. 



PLAN OF SKERRYVORE ROCK 

AT IOTV WafflR OF SFJilMr T/DFS. 




. — — ■ — ' William MiUa: Sculp? 

•nKt/fruiinr.r. /M l 



W9T/I. 



Stevenson's -drawn £ o r ,.) ferrif wre Zu/h&wi/se. 

PLAN of SKEKEYVORE ROCK 



ATfflGH WZWR OF HD£S. 




Scale, of Jfeet 

10 5 O lO 20 30 40 50 OO 70 SO 9p J0O 



Jumes-gndrzHs. Bel c 



PLATE IV. 

Stev&ison'sJLccmoib of Skerryiwr&JjujJi&ioiise 



CURVES FOR LIGHTHOUSE TOWERS 




PARAB OZA COJVCIfOJJ) LOGARITHMIC HYPPRB OZA 

Jamp,$ Andrews del ? GrAzkmasi Sc 



XARTXE DYXAMXMIE'TER . SHALL SIZE. LESG-TH 18 I5TCHES. 




J 'JCJbhm-ton Sculp- 




±j±l 



JO 



Scale of^ feet 

20 



SO 



Ja7nz?dJuiraK. Bel' 



WiZlzamJliiZltr S 



PLATE IX. 

* ■5V/'iy/;.iv>/fo- .darounf o/\Y/.rriy/v;/rf Lighthouse 






r i a j 

of ESTABLISHMENT at 

HYHIEH, I8LAID 01 TTREE. 

SKEWING I EE 

PIER, DOCK, RESERVOIR. LIGHTKEEPERS AND SEAMENS HOUSES Sc. 




StevensoyS-Accciisit of SlietTuvtrre-Z-ighJrJwijse- 

HYNISH DOCK. 




1 Q 987C54321 o 20 2pjFeet 



Section across Gat&s\ 




WultErFerwr. Z>elf 



Witiurni JdLller. Sculp 



rum xk 



StBrensons Jlccount of Skentyrotv lAtfhthouse 



ANNULAR LENS of FIRST ORDER 

SCALE i] H FULL SIZE 
PLAN 




SECTION THROUGH A.B. 



N?H N?I0 N°9 N°8 N?7 H°6 N?5 N°4- N°3 N?2 



. 

N°2 

N?3 

N?4 

N?5 

N?6 [ 

N°7 

N°8 

N?9 

N°I0 

N° II 



TABLE of ELEMENTS of LENS 

IN MILLIMETRES 



N» 


RADIUS 
F 


RADIUS 
OF 


1 1 

CO-ORDINATES TO 

CENTRES OF CURVATURE 




PE RIPHERY 


CURVATURE 


as 


y 


1 


LIO 


. 00 


485 


50 


454 


• 79 


oo 


OO 


2 


208 


. 16 


S45 


60 


188 


. 55 


15 


08 


3 


282 


. 40 


598 


62 


515 


. 58 


51 


72 


+ 


309 


. 20 


659 




540 


. 71 




00 


5 


550 


. 50 


713 


84 


565 




84 


88 


6 


587 


. 44, 


779 


48 


588 


.00 


Hi 


85 


7 


432 


. 25 


846 


45 


614 


. 55 


151 


50 


8 


456 




9XL 


30 


056 


. 90 


189 




9 


490 


. 00 


!)80 


30 




. 11 


250 


17 


10 






1057 


70 


683 


. 41 


280 


60 


II 






U56 


01 


712 


. 79 


S28 


00 



■ FOC U S 



J%? by V.irJS-JohmtlonEdinr 



Dm! J C AffAlAfii 

ONE TWENTIETH OF FULL SIZE. 



» 



V 



( 



PLATE XIV. 



Sm 'eruon's JlecourU. or' Skerryvore IzgTtihou. 



REVOLVING DIOPTRIC LIGHT OF THE FIRST ORDER. 

Flan 




., , Scdle- o f Fe&t 

Inches 



C O I 2 3 / 



PLATE XV. 

- an -i v nag ■ r, ----- Z g 5 a 

FIXED DIOPTRIC LICHT OF THE FIRST ORDER. 

Ve7ticaJ Section. 




PLATE. XVI. 



St/'vcrusoruv Account t>t' Skerry voj-e Lighthoiuse 




FIXED 
C ATA DIOPTRIC LIGHT 

OF I st ORDER 



ONE NINETEENTH OF FULL SIZE 




SteraisonXjccoit/zb of Skerry \-ore LzgJuTwzcse 

PLATE XVI I . 




PLATE Will. 




/ 



StevewLtons JLexunirtbofSkenyvare lighthouse 



CATADIOPTRIC APPARATUS. 



FOURTH ORDER 




I i / SCALE ONE HALF 

Tina 3 , bv W. X-J Ju Johnston Jidin'' 



T1A1EJXL 



Stevaisons -Account ofSharyron lujlidiouye 



01' Oil PT^IPS, 



E LEV AT I ON 




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 

SQUARE TRAY FOR OVERFLOWING OIL 
Q LID OF OIL CISTERN 

1 OIL TUBE 



PLANS AND SECTIONS IN REFERENCE TO OPPOSITE PLATE. 



SECTION ON LINE A.B 



SECTION OF DISCHARGING CHEST I. 
I 



PIAN OF UPPER SIDE OF PUMP CHAMBER AT F.F. 



• • • 



PLAN OF VALVES AT HE AND HH. 



SECTION ON LINE CD. 



G • O O • O 



PLAN AND SECTION OF PLATE K. 













PLAN OF LOWER SIDE OF PUMP CHAN 


iER AT H H. 


• • 

1' 


• • 


# 


• < 


> * 




••• 



PEC" I P 3 1 



SCALE 



9 10 INCHES 



Walter R. Terrier, deC 





SIDE VIEW OF CLOCKWORK 



SCALE 

DECifJO 5 0_ 1 2_ 3 -1 INCHES 



PLATE XXW 



Stevens m us' JLccaimt of STc.exyyvoT'e Litiliiltounc 



CLOCKWORK MOVEMENT AND BURNER OF .MECHANICAL LAMP 





PLATE XXV. 



Stet-'ensoiiA? ArcoLisit or' Skertywr? Zu}hrhoiu?e . 



FLAME 

FOR P. 1 ORDER OF 

DIOPTRIC LIGHTS 

at Ml size. 




G-dihtian.. Sculpt 



PLATE IXVJ 



Sltvensoris Accatml of Slccrryvom LwhjtJuoux 




r 



j 



PLATE XXVI II 



tfWMM'HWSltrottn/. ofSko-lviorf Lliiltl7tiiu.rr 



AlfflJMMUltCtfAlf LIGHTHOUSE 



TZA N 




10 5 O 10 20 30 Fe^t 

l^-. ■■ I — I - I — I - I 



'JI.G.SUght Aa 



I 

GiAiJoTunb sculpt 



'1 



J'LITK xxz a 

Sleemwrv UTiihlltoiurr ' 




IRON BEACON 




n:JZ 12 3 I 1 

hrtrj— T "i | . i i 



SCALE 

5 6 7 8 3 



Jiimi'.v^htillfww Del'. 



J 




■TmrutA Jhvircws Del'. Eiia-'l.v .i-J.Jt . 'ohn,?t,m Kdiit'.