C si )

rapid part of the current, so as to admit of thenavigation of the river being opened, and of thepassage of any floating bodies, which mightotherwise endanger the bridge. The moveablepart, A B, fig. 5, plate 3, is constructed on two,and sometimes on three or more boats, accordingto the magnitude of the river, and formed into aseparate portion, of length sufficient to fill,exactly, the requisite space, C D. The beams,E E, of the moveable part, project about one footover the outside gunwales of the outward boats;the beams, F F, of the adjoining boats on eachside, likewise project over their sides; and theends of the beams are covered, G G, so thatthey may not hitch in each other, in re-formingthe bridge. The planks, or floor, are fasteneddown to the beams, throughout the bridge,by curb pieces, clamped down with wedges,excepting on the projecting parts, of one footeach, at the junctions of the standing andmoveable portions, which are usually coveredby planks of corresponding width, attached tothose adjoining, by hinges. The moveable por-tion of the bridge is provided with two largeanchors, laid upwards in the stream, and astrong hawser fastened to each standing end ofthe intended interval. The boats forming themoveable portion are likewise provided with