Its northern front is almost perpendicular, and exposed to the most violent assaults of Ocean; on the south the declivity is less abrupt, but scarcely easier of access; and its summit is only of breadth sufficient to receive the foundation of the tower. This is 50 feet in height, and contains, besides the light-room, a sleeping chamber, a kitchen, and a store-room. At its base is built an additional store-room for the supplies of oil, charcoal, and fresh water. It is only accessible in fine weather.
The North Unst lighthouse is provided with a staff of four keepers, whose habitations are situated on the island of Unst (one of the Shetland group), about four miles distant.
It has justly been said that one of the strangest operations recorded in the history of lighthouses is, undoubtedly, the work undertaken and successfully accomplished at Sunderland in 1841. Some important improvements had been effected in its harbour; and a jetty had been constructed which rendered useless the old pier, and the lighthouse built upon it. Consequently, preparations were made for the demolition of the latter. An engineer, of the name of Murray, however, conceived the idea of transporting the monument, in one piece, to the intended site of the new lighthouse, a distance of about 475 feet. His proposal was favourably received; for the removal of great masses of masonry, in Europe at least, is an enterprise which always excites a very general curiosity. In the United States, that “go-ahead” land of bold projects and daring inventions, such enterprises are more frequent, and the process has been several times applied to houses (as recently at Chicago) and factories, for which it was desirable to secure a more convenient or a securer site. In such cases a series of openings is made in the walls, and through these openings beams are introduced, united together by cross beams so as to form a kind of flooring; then the lowest part of the base of the walls is destroyed, leaving the building to rest upon the timber platform, which is afterwards set in motion by a system of grooves.
NORTH UNST LIGHTHOUSE.
So far as concerned the Sunderland lighthouse, the enterprise was much more arduous; for its narrow base supported a burden relatively more considerable than that of a house, and one which apparently must crush all machines interposed between it and the ground. The weight of the lighthouse was 757,000 lbs.; it consisted of an octagonal tower 64 feet high, and 15 feet in diameter at the base. We must add that the new pier was 19 inches higher than the old, and that its direction was entirely different; which rendered it necessary that the building should be turned upon its axis, at the same time that it had to traverse a broken line, one of whose sections, from north to south, measured 28 feet, and the other, from west to east, 447 feet.
The accompanying illustration will afford an idea of the manner in which this difficult engineering problem was solved. By means of a series of openings made in the base of the tower, as above described, the latter was raised on a solid platform of oaken planks; while it was surrounded from base to summit by a framework of stays or props, strengthened by cross beams. The platform rested on one hundred and forty-four cast-iron wheels, grooved like those of a locomotive, and running on eight parallel rails, likewise of cast-iron, which, with their “sleepers,” were laid along the masonry of the pier and jetty. When the mass had moved a few feet, the rails were lifted, and laid down again in front of the machinery, and this process was repeated until the new site of the lighthouse was reached. Iron chains attached to the platform were wound upon windlasses, worked by a band of sturdy labourers.
The various stages of the operation were accomplished in thirteen hours and twenty-four minutes. The combined efforts of forty men were required for five hours to carry the apparatus over the 28 feet of the first section, while eighteen men sufficed to carry it in eight hours and twenty-four minutes over the 447 feet of the second.