Page:Collier's New Encyclopedia v. 02.djvu/205

LEFT BRIDGE 175 BRIDGE is 300 yards long, paved with stone for the passage of carriages and horses. The so-called flying bridge is rather a ferry than a bridge of boats. The longest floating bridge in the world, probably, is the pontoon bridge across the river Hooghly, at Calcutta, ends. They are each of the great length of 160 feet, made of such considerable length in order to obviate pitching motion in rough weather. The roadway plat- form is of 3-inch planks of teakwood from Burma, forming a roadway 48 feet wide, with a footpath at each side 7 feet ^ „.™^ ^ ^^ ^ 1 1 ^^s&^^K^^^ "^^ 5^ -z:: - HELL GATE BRIDGE OVER EAST RIVER, NEW YORK designed and constructed by Sir Bradford Leslie. The bridge is 1,530 feet long be- tween the abutments, and is carried on 14 pairs of pontoons, which are held in position by means of chain cables, 1% inches thick, and anchors weighing three tons each, laid on the up stream and down stream sides, 900 feet asunder. By wide. An opening 200 feet wide, for the passage of ships, is made by removing, when occasion requires, four of the pon- toons with their superstructure, and sheering them clear of the opening. The floating bridge is connected with the shore at each end by adjusting ways hinged to the shore. ROLLING LIFT BRIDGE their great length, the cables afford the necessary spring to allow for the or- dinary rise and fall of the river, the stress on each cable varying from 5 tons to 25 tons, according to the stage of the weather and of the tide, the maximum velocity of which is 6 miles an hour. The pontoons are rectangular iron boxes, hav- ing rounded bilges and wedge-shaped Military Bridges are temporary con- structions to facilitate the passage of rivers by troops, to restore a broken arch, or cross a chasm of no very great width. Those over a river are either floating or fixed. The former are made of pontoons, boats, casks, rafts of timber, or anything that will give sufficient buoyancy; and the latter of piles, trestles, or other timber