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. [Illustration: 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.