1848.J 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



175 



for a wiiidlass, and everything was brought from Hynish, twelve 

 miles (lif. 



Whoever reads this book must think more highly of the labours 

 of engineers; but when we look at tlie wonderful works whicli are 

 spread o^•er this land, we cannot but wish that we liad as good 

 records of tliem. Tlie public will name many who are well able to 

 do justice to their own labours, and the fulfilment of the public 

 wish would greatly enrich our libraries. The history of the Liver- 

 pool and Manchester Railway, by Mr. George Stephenson, would 

 be a hand-book for all time. Mr. Robert Stephenson, ]M.I'., has in 

 the London and Birmingham Railway a good subject for illustra- 

 tion. l\Ir. Locke, M.P., can do no better service to the profession 

 than by the publication of an account of the Grand Junction Rail- 

 way. Mr. Brunei has spent many years upon the jierfection of 

 the broad-gauge system, and has in the Great Western Railway 

 achieved a success which should not be forgotten. Mr. Cubitt 

 has allowed his assistants to give accounts of the tunnels and 

 blasting operations on the South Eastern Railway, but a full 

 account of the whole line is wanted from his own hands. AV^e hope 

 the time is not far off when we shall see these among other contri- 

 butions to our professional literature. 



We shall now call attention to the rocks on which the Skerry- 

 vore lighthouse was raised. They form part of a long reef, 1 1 

 miles to the south of Tyree, in the outer range of the Hebrides 

 or Western Isles, so that they are in the sea-way between Scotland 

 and Ireland; and ships from seaward, if they miss the north of 

 Ireland, are often driven on Skerryvore, where many wrecks have 

 happened. In 18] 4, an act of parliament was obtained for building 

 a lighthouse, but it was not till 1834. that Mr. Alan Stevenson was 

 sent to make the first survey. 



At low tides, Skerryvore measures about 280 feet square ; but it 

 is cut up by gullies of unlooked-for depth, so that the solid part is 

 only 160 feet by 70 feet. On this a loaf of rock, about five feet 

 broad, rose to tlie height of eighteen feet above high-water level, 

 the greater part of the rest being about si.x feet above that level. 

 The rock Mr. Stevenson calls a syenitic gneiss, consisting of quartz, 

 felspar, hornblende, and mica. 



It was not till the summer of 1835 that the survey was finished, 

 and Hynish, in the wretched island of Tyree, was chosen for the 

 workyard. This is 12 miles from Skerryvore. In 1836 and 1837, 

 quarries were opened in Tyree, and in the latter year the pier at 

 Hynish was begun. Mr. Stevenson was now busy in drawing up 

 his plans, and here he came to a weighty question. 



" 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 inertiie ' In pre- 

 ferring weight to strength, we more closely follow the course painted 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 woiks, 

 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 determina- 

 tion of the mass and form of a building which may be capable of opposing 

 similar forces, as we conclude, with some reason, that the mass and form of 

 the natural rock are exponents of the amount and direction of the forces 

 they have so long continued to resist. It will readily be perceived, that we 

 are in ^ very different and less advantageous position when we attempt, from 

 such observations of natural phenomena, in which weight is solely concerned, 

 to deduce the strength of an artificial fabric capable of resisting the same 

 forces; for we must at once pass from one category to another, and endea- 

 vour to determine the s<re?;ir^A of a comparatively /;^/i< object which shall 

 be able to sustain the same shock, which we know, by direct experience, 

 may be resisted by a given weight. Another very obvious reason why we 

 should prefer mass and weight to strength, as a source of stability, is, that 

 the effect of mere inertia is constant and unchangeable in its nature; while 

 the strength which results, even from the most judiciously disposed and well 

 executed fixtures of a comparatively light fabric, is constantly subject to be 

 impaired by the loosening of such fixtures, occasioned by the almost incessant 

 tremor to which structures of this kind must be subject, from the healing of 

 the waves. It was chiefly on these grounds that the Commissioners of 

 Northern Lights, after consulting a Committee of the Royal Society of Edin- 

 burgh, and Messrs. Cubitt and Rennie, civil engineers, rejected the design of 

 Captain Sir Samuel Brown, R.N., who volunteered a proposal to build an 

 iron pillar at the time that the erection of the Skerryvore Lighthouse was 

 determined on in 1835. Mass, therefore, seems to be a source of stability, 

 the efl'ect of which is at once apprehended by the mind, as more in harmony 

 with the conservative principles of nature, and unquestionably less lial.le to 

 be deteriorated than the s<renj<A, which depends upon the careful proportion 

 and adjustment of parts," 



In fixing the quantity of matter needful to produce stability, and 

 in determining tlie shape of the tower, Mr. Stevenson had to 

 proceed empirically, for there is a want of sufficient experiments. 

 Mr. Stevenson gives, however, a full discussion of the data, which 

 are available. At this point he brings in an interesting comparison 

 of the three great lighthouses. 



Eddystone 



Bell-rock 



Skerryvore 



Height above 



lir8t entire 



course. 



Feet. 



68 

 100 

 1385 



Contents of 

 tower. 



Cubic feet. 

 13,343 

 28,530 

 58,580 



The first barrack raised was swept away by the sea, so that in 

 1839 the summer was spent in raising another, and in excavating 

 the foundation of the lighthouse tower. The difficulty of doing 

 this may be appreciated from the following account: — 



" It was commenced on the 6th of May, and was continued up to the last 

 hour of our remaining on the rock, on the 3rd of September. A more un- 

 promising prospect of success in any work than that which presented itself 

 at the commencement of our labours, I can scarcely conceive. The great 

 irregularity of the surface, and the extraordinary hardness and unworkable 

 nature of the material, together with the want of room on the rock, greatly 

 added to the other difficulties and delays, which could not fail, even under 

 the most favourable circumstances, to attend the excavation of a foundation, 

 pit on a rock at the distance of 12 miles from the land. The rock, as 

 already noticed, is a hard and tough gneiss, and required the expenditure of 

 about /(/Mr times as much labour and steel for boring as are generally con- 

 sumed 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 suflicient to contain the founda- 

 tion pit for the tower. The very rugged and uneven form of the Rock made 

 this an almost necessary precaution, in order to prevent any misconception 

 as to its real state, for it was traversed by numerous veins and bands incUned 

 at various angles, on the position and extent of which the stability of the 

 foundation in no small degree depended. That operation occupied 30 men 

 for 102 days, and required the firing of no fewer than 246 shots, chiefly 

 horizontal, while the quantity of material removed did not greatly exceed 

 2,000 tons. It was a work of some hazard ; for the small surface of the 

 Rock confined us within 30, and sometimes within a dozen yards of the 

 mines, while its form afli'orded 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 appor- 

 tion very carefully the charge of powder to the work that was to be done. 

 That was managed with great skill by Charles Barclay, the foreman of the 

 quarriers, who charged all the bores, and, along with myself, fired all the 

 shots. So completely did the simple expedient of covering the bores with 

 nets and mats check the flight of the stones, that, except on one or two 

 occasions, none of the splinters reached us, and all the damage done was a 

 slight injury to one of the cranes. Perhaps, also, our safety may, in some 

 measure, be attributed to a change which I introduced into the mode of 

 charging the horizontal shots, by which all the risk of pushing home the 

 powder in the ordinary mode with the tamping rod is avoided. That cuange 

 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 in- 

 verted 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 cbarging-rod used for great guns. The 

 amount of materials removed by blasting, as nearly as I could ascertain, was 

 only about 1,000 cubic yards; and, taking all the circumstances into account, 

 it may be doubted whether there be any instance in modern engineering of 

 an operation of so small an extent occupying so much time, and involving so 

 great risk. The blasting of the rock, however, was not the only difficulty 

 with which we had to conteiid, for it also became necessary to remove the 

 quarried materials, amounting to about 2,000 tons, into the deep water 

 round us, to prevent their being thrown by the waves upon the rock, and so 

 endangering the future temporary barrack. That was rather a laborious 

 work, and occupied two cranes, with temporary runs and trucks, during the 

 greater part of the time we spent on the rock. I am well aware that the 

 quantity of materials which I have just mentioned, will be apt to produce a 

 smile from those who have been chiefly conversant with the gigantic but 

 simple operations which generally characterise 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 slow- 

 ness 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 diw 



