The full details which we have given of the erection of the Bell Rock Lighthouse will render unnecessary any elaborate account of the mode of construction of later edifices. There are some, however, which we are unwilling to pass over without at least a cursory notice, owing either to their romantic position or to their special interest as examples of engineering skill. One of the most important of these is the Lighthouse of the Skerryvore, situated on a reef which, in all leading features, is a counterpart of the Bell Rock. It is placed in the same parallel of latitude, and occupies the identical position on the west coast of Scotland which the latter occupies on the eastern. Nor was it of old less fatal or less ominous to the mariner, but annually exacted its tribute of precious lives and wrecked vessels. A few minutes sufficed for the total loss of any unfortunate ship which dashed against the gneiss crags of the Skerryvore, and its rent and shattered timbers were quickly carried by the tide to the fishermen of the island of Tyree. Not that this formidable memorial of past volcanic convulsions was totally submerged—some of its higher points rose above the level of the highest tides: but the extent of its foundations was considerable; and even in the summer season latent dangers beset the difficult channel between its eastern extremity and the island of Tyree, which lies about eleven miles distant.[44]
For various reasons the attention of the Commissioners of Northern Lights had been early directed to this formidable reef; and in 1814 they had determined to mark its locality by the erection of a lighthouse. It was visited in this same year by some of the members of the Commission, accompanied by one whose name alone is sufficient to render the visit ever memorable—Sir Walter Scott. He was much struck with the desolateness of the situation, which he thought infinitely surpassed that of the Bell Rock or the Eddystone.
Owing, perhaps, to the difficulty of the enterprise, it was deferred until the autumn of 1834, when Mr. Alan Stevenson was authorized to commence a preliminary inspection, which he did not complete until 1835. This difficulty proceeded not only from the position, but from the nature of the reef itself.
It is true that the distance from the mainland was three miles less in the case of Skerryvore than in that of the Bell Rock; but the barren and over-populated island of Tyree did not offer the resources of the eastern coast, nor a safe and commodious port like that of Arbroath. The engineers were therefore compelled to erect, at the nearest and most favourable point of Tyree, a quay and a small harbour, with temporary cabins for the workmen, and storehouses of every kind; all whose materials, excepting only stone—and even the supply of that failed after awhile—required to be transported from distant parts.
The first and most embarrassing, perhaps, of the numerous questions which present themselves to the engineer when entering upon the construction of a lighthouse, are those of the height and the mass. In the days of Smeaton, when the best light in use was that of common candles, the elevation beyond a certain point could not be of any utility; while in 1835 the application of the reflector and the lens, by assisting in the extension and diffusion of the light, rendered, on the contrary, a considerable elevation both necessary and desirable.
It was therefore decided that the height of the Skerryvore should be 135 feet above the highest tides, so as to command a horizon visible for a radius of eighteen miles. The diameter of the base was fixed at 42 feet, and that of the topmost story at 16 feet; consequently the masonry of the tower would be double that of the Bell Rock, and four and a half times that of the Eddystone.
Another peculiarity distinguishes the Skerryvore from the Bell Rock. The sandstone of the latter is wave-worn, and broken up into a thousand rugged inequalities: the action of the sea on the igneous formation of the Skerryvore has, on the contrary, communicated to it the appearance and polish of a mass of dark-coloured crystal. It is so compact and smooth that the foreman of the masons, when he landed on it, said it was like climbing up the neck of a bottle. Moreover, notwithstanding its durability, the gneiss of Skerryvore is excavated into caverns, which considerably limit the area adapted for building operations. One of these caverns, we are told, terminates in a narrow spherical chamber, with an upper opening; through which, from time to time, springs a bright, luminous shaft of water, 20 feet high, and white as snow, except when the sun wreathes it with a thousand rainbows.
Mr. Alan Stevenson commenced actual operations in 1838 by the erection of a provisional barrack on piles, at such a height as to be beyond the reach of all average tides. This was designed to shelter the men at night, saving them the voyage to and from the mainland; and also to accommodate them when their work was suspended by bad weather. The first erection was swept away in a great gale on the night of November 3; but happily the labours of the season were then ended, and there were no occupants. On this occasion the grindstone was deposited in a hole 36 feet deep; the iron anvil was transported 13 yards from the place where it had been left; the iron stanchions were bent and twisted like corkscrews; and, finally, a stone weighing half a hundred-weight, lying at the bottom of an excavation, was carried to the highest surface of the rock.