LIGHT-II0IISE (ante). Light-houses were not constructed until some advance ment was made in navigation, but beacon-fires were lighted for the guidance of the early mariners. The most celebrated ancient light-house was the Pharos (q.v.) of Alex andria, built upon a rocky point of that name which had been an islet, but was con nected by Alexander the great with Alexandria by a roadway called the seven-mile mole, or heptctstadium. The light-house was commenced by Ptolemy Soter, and finished about 280 B.C., and was regarded as one of the wonders of the world. It was about 400 ft. high, and the light which was kept burning on its top could be seen, according to Josephus, at a distance of 40 miles. It is thought to have been destroyed by an earth quake after having stood 1600 years. It was constructed in the form of the frustrum of a square pyramid, having an immense base whose dimensions are not known. The tower of Cordouan, at the mouth of the Garonne, in the bay of Biscay, is another cele brated light-house, but of modern date and still standing. It was commenced in 1584 and finished in 1610 by Louis de Foix. It stands upon a rocky ledge, which is under water except at low tide. The base is the frustrum of a cone, 135 ft. in diameter at the bottom, 16 ft. high, and 125 ft. in diameter at the top; built solid of cut stone, with the exception of a chamber in the- center, 20 ft. square and 8 ft. high, containing a water cistern. A wall 12 ft. high and 11 ft. thick stands upon the margin of the upper surface of the base. The tower is 50 ft. in diameter at its base, is 115 ft. high, and is the frustrum of a cone, surmounted by a lantern dome. The entire height from the rock is 162 ft., the whole height of the tower, including the dome, being 146 feet. The first Fresnel lens ever manufactured was placed in this light-house in 1823. The Eddystone light-house in the English channel is described under the title EDDYSTONE (ante). The Bell rock light.house, off the e. coast of Scotland, is built upon a reef or rocks in the German ocean, 11 in. from the coast, nearly opposite the Tay firth. The rock upon which it stands is a red sandstone, from 12 to 15 ft. below spring tide, with from 2 to 4 ft. exposure at low tide. The structure is also of sandstone, but the outer tiers for 30 ft. high are of granite. It was designed by the celebrated Scotch engineers, Robert Stevenson and John Rennie, and constructed by the former. The erection of the second Eddystone light-house had given Smeaton much study, :mi. his experience was taken advantage of by Stevenson in the structure at Bell rock. In form it resembles the Eddystone. The diameter at the base is 42 ft., while at the top,' beneath the cornice, it is 15 feet. The stone-work is 102i ft. high, and the whole structure, including the lan tern, 115 feet. See BELL ROCK, ante. The Skerryvore light-house, built upon the Skerryvore rocks, which lie in the tracks of vessels going around the north of Ireland or Scotland from the Clyde and Mersey, was constructed by Alan Stevenson, the son of Robert. See SKERRYVORE, ante. There are manv very fine light-houses in the United States, the most noted of which waerected upon Minot's ledge, off the town at Cohas set, Massachusetts bay, about 20 in. e.s.e. of Boston, and one of the most dangerous places in the world without a signal. The difficulties in the construction of a, light-house upon this rock were immense. An iron structure was first erected, being completed in 1849, which stood till April, 1851, when it was demolished by a terrific storm. The iron piles, 10 in. in diameter and sunk 5 ft. into the rock, were twisted off near the sur face. In 1852 money was appropriated by congress for a new light-house, and work was commenced in 1855, but it was uot till the latter part of 1857 that the first stone was laid. Four stones were laid in this year; six courses were, however, laid in 1858; and in 1859 the stone-work was-completed. The whole was finished in 1860. It is a. granite tower in the form of the frustrum of a cone, having a base 30 ft. in diameter, and a
height of stoue-work of 88 ft., the lower 40 ft. being solid. The courses are dove tailed, and are fastened together with wrought-iron dowels. The defect in the iron Minot's ledge light-house was owing to the stinted outlay. Had three or four times as much money been expended on it, so that it could have been much broader at the base as well as higher, it would doubtless have been standing to-day. The present stone structure is a fair model of engineering, and will probably resist the waves for centu ries. It possesses the advantage, which all solid or alinost solid stone structures must , have over iron framework, of a vastly greater amount of inertia, an hnportant element of resistance to the waves. Its construction is said to have offered a more difficult problem than that of Bell rock or Skerryvore, one reason being that its foundation is deeper beneath the surface. The light-house at Spectacle reef, in the northern part of lake Huron, was built not only to resist waves, but ice-fields, often covering thousands of acres and moving at the. rate of 2 or 3 in. per hour. That the structure should be able to withstand this force it was so designed as to cause the ice to be broken and piled into a protecting barrier. The tower is the frustrum of a cone, 82 ft. in diameter at the base, and 18 ft. just beneath the cornice at a height of 80 feet. The whole height of stone-work is 93 ft. above the base, which is 11' ft. bel0w the surface of the water. The tower is solid as high as 34 ft., above which it contains 5 stories, each 14 ft. in diameter. The work was commenced May 1, 1870, and the light was first used June 1, 1874. The, cost was 4375,000. The first light-house ever erected was at Point Morant, Jamaica, in 1842. The tower is built of 9 tiers of plates three-quarters of.au in. thick and 10 ft. high, held together by bolts and flanges on the inside. _The tower is filled in with masonry and concrete to the height of 27 feet. It rests upon a foundation of granite and rises to a height of 96 feet. -It is 18+ ft. in diameter at the base, and 11 ft. at the top. A modern form of light-house is constructed on what is called the " screw-pile" system, an invention of Alexander Mitchell, who, with his son, laid the foundation of the light house on Maplin sand, at the mouth of the Thames, England. Two similar structures followed, Chapman head in 1849 and Gunfieet in 1850, also near the mouth of the Thames. Other screw-pile lights were afterwards erected in different parts of the king dom. The great feature of the screw-pile is that the piles upon which it rests are in the form of screws and are driven in the sand or soil to a sufficient depth in the manner of a corkscrew. The first screw-pile light-house erected in the United States was by by col. Hartman Bach, U. S. E., at the mouth of Delaware bay, 8 m. from the ocean, in 18-17-50, where it stands at the present time iu good condition, although in an exposed place, being often acted against by immense cakes or fields of ice which come down the Delaware and move to and fro with the ebb and flow of the tide. It is surrounded' by an ice-breaker composed of screw-piles driven independently of the tower. The screw pile light-house at Sand Key, Florida reefs, is supported on 16 piles, with an auxiliary pile in the center to support the staircase, making in all 17. They are 8 in. in diameter, with a screw of 2 ft. in diameter at the lower ends, which are bored 12 ft. into the reef. The framework of the tower con'sists of cast-iron tubular columns framed together, hav ing wrought-iron tics at each joint, and braced diagonally on the faces of each tier. The keeper's house is supported by cast-iron' girders and joists 20 ft. above the founda tion. The structure is 120 ft. above the level of the water. The foundation is 50 ft. in diameter. Over 50 such light-houses have been erected in various parts of the United States.