span of 340 feet 3¾ inches; the New Hope Bridge, built in 1814 over the Delaware River, in six 175 feet combined arch and truss spans, and a considerable number of others built by the same engineer. Some of these wooden bridges, like those at Easton, Pa., and at Waterford, N. Y., remained in use for over ninety years with only ordinary repairs and with nearly all of the timber in good condition. In such cases the arches and trusses have been housed and covered with boards, so as to make what has been commonly called a covered bridge. The curious timber suspension bridge built by Theodore Burr at Schenectady was used twenty years as originally built, but its excessive deflection under loads made it necessary to build up a pier under the middle of each span so as to support the bridge structure at those points. These bridges were all constructed to carry highway traffic, but timber bridges to carry railroad traffic were subsequently built on similar plans, except that Burr’s plan of wooden suspension bridge at Schenectady was never repeated. [Illustration: MOHAWK BRIDGE AT SCHENECTADY N.Y. Built by Theodore Burr. FIG. 1.] [Illustration: PATENT BRIDGE “COLOSSUS” Across the River Schuylkill at Philadelphia. Single Arch 340 feet 3¾ inches. Built by Lewis Wernwag. FIG. 2.] =69. Town Lattice Bridge.=—A later type of timber bridge which was most extensively used in this country was invented by Ithiel Town in January, 1820, which was known as the Town lattice bridge. This timber bridge was among those used for railroad structures. As shown by the plan it was composed of a close timber lattice, heavy plank being used as the lattice members, and they were all joined by wooden pins at their intersections. This type of timber structure was comparatively common not longer ago than twenty-five years, and probably some structures of its kind are still in use. The close latticework with its many pinned intersections made a very safe and strong frame-work, and it enjoyed deserved popularity. It was the forerunner in timber of the modern all-riveted iron and steel lattice truss. It is of sufficient significance to state, in connection with the Town lattice, that its inventor claimed that his trusses could be made of wrought or cast-iron as well as timber. In many cases timber arches were combined with them. [Illustration: FIG. 3.] =70. Howe Truss.=—The next distinct advance made in the development of bridge construction in the United States was made by brevet Lieutenant-Colonel Long of the Corps of Engineers, U.S.A., in 1830-39, and by William Howe, who patented the bridge known as the Howe truss, although the structure more lately known under that name is a modification of Howe’s original truss. Long’s truss was entirely of timber, including the keys, pins, or treenails required, and it was frequently built in combination with the wooden arch. The truss was considerably used, but it was not sufficiently popular to remain in use.