Page:The American Cyclopædia (1879) Volume III.djvu/281

 BRIDGE 275 Fio. 9. -New York and Brooklyn Suspension Bridge. was at Oolebrook Dale in 1779, and consists of five curved ribs, nearly semicircular in shape, and each formed of three concentric arcs, connected by radial pieces; its span is 100 ft., and rise 40 ft. The Wearmouth bridge was built in 1790, and has a striking appear- ance from its great span as well as height above the water; it is 100 ft. above high- water level, and has a span of 240 ft., with a rise of 30 ft. The pont d'Austerlitz, at Paris, has five arches, each with a span of 107 ft., and a rise of T ' T the span; it was erected in 1801-'7 by Lamande. The pont du Carrousel, in the same city, was built by Polonceau in 1838, and consists of three arches, with a span of 150 ft., and a rise of 16 ft. The largest iron arch bridge is the Southwark bridge over the Thames, built by Kennie in 1815-'19 ; it consists of three arches, 240 ft. in span, and with a rise of 24 ft. A remarkable cast-iron bridge, com- bining the purposes of viaduct and aqueduct, was designed and constructed by Oapt. M. 0. Fio. 10 Washington Aqueduct Bridge. Meigs, for the purpose of carrying the Wash- ington aqueduct over Rock creek, between Georgetown and Washington : the peculiarity of this bridge is that its arches are constructed of cast-iron pipes, which carry the roadway and the water supply at the same time ; its span is 200 ft., ite rise is 20 ft., and the diame- ter of the two pipes of which it is formed is 4 ft. in the clear. Of wronght-iron bridges, the Britannia and Con way tubular bridges, both erected by Stephenson, are widely celebrated. The Britannia bridge crosses the Menai strait at 103 ft. above high water, and consists of four spans, two of 230 ft. each, and two of 459 ft.,' forming a huge tube of wrought iron, through which passes the Chester and Holy- FIG. 11. Britannia Bridge. head railway. The Conway bridge has a sin- gle span of 400 ft., and is only 18 ft. above the level of high water; it was finished in 1848, and the Britannia bridge in 1850. The tubes were constrncted, in each instance, at a dis- tance from their respective destinations, and afterward floated to their places by pontoons, and raised by hydraulic presses, forming the most gigantic application ever made of these powerful machines. The Victoria railway bridge, over the St. Lawrence at Montreal, constructed after the plan of the Britannia bridge, is two miles long, cost over $5,000,000, and contains 10,500 tons of iron and 3,000,000 cubic feet of masonry. Since 1860 many iron viaducts have been built in the United States. Among the most notable of these are the rail-