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This bridge is constructed in an entirely novel manner, and in an eminent degree possesses the advantages of strength and lightness, together with simplicity of construction. It is a fact too well known to need any demonstration that the circle and triangle are the two most stable forms of disposing material for economy and durability, and in this invention both these forms are very prevalent. The arch is composed of a series of tubes, A, made of wrought iron plates riveted together, or cast iron. These tubes are as long as the desired width of the bridge, and they are arranged side by side as seen in Fig. 1, their length being at right angles with the roadway of the bridge. are blocks of wood or metal, but preferably of wood, fitted between the tubes at or near the ends thereof, and secured in place by long bolts, a a, pass-., ing through the whole series of tubes and zl blocks, and secured by nuts or keys at the r ( ends, or by short bolts, b, Fig. 2, passing z0 through a block and the adjacent sides of two tubes, and secured by a head on one end of the bolt, and a key on the other, or two nuts or two keys. In addition to the two series of blocks, B, there may be any number of blocks at intervals along the whole length of the tubes, so as to give the arch more rigidity. C is an arched timber or iron binder fitting over the tubes, A, and secured to the block by stirrup bolts, d d, plates, e, to keep them in position, and to retain the curve of the arch. The tubes, A, may be strengthened at the points where they are clamped between the blocks, B, by cores or disks, f, which may be fitted and keyed or cast on them. D D are sills at each end of the bridge, and are stout upright posts tenoned and secured into the said sills. The ends of the arch of tubes rest in the angle between D and E, 3 and the ends of C are tenoned into the posts. F F are tension rods of wrought iron connecting tha sills, D D, and extended by nuts, g, at the ends, so as to confine the sills longitudinally for the purpose of counteracting any thrust on the ends of the arch. H H are upright posts tenoned into the arched timbers, C. G G are diagonal braces notched and b.olted at their lower ends to the arched tim- bers, and at their upper ends to the upper part of the posts, H H, and also notched and bolted to such of the posts as they pass. F are wrought iron tension rods passing through all the posts H and E, and down to the sills, D, to which they are secured by nuts or keys. J are the roadway-bearers which may be of wood or iron, having bearings at their ends in the posts. The most important feature in this bridge is the construction of the arch of the iron tubes, the interposed blocks and arched timbers or binders. It is the arch thus constructed which constitutes the entire support of the load ; the duties of the other post being to keep the arch in shape, and to transmit to it the weight of a load passing over the bridge. The tension rods, F F, combine with the sills, D, and posts, E, to prevent the depression and longitudinal extension of the arch, and the posts, and braces, G, combine to prevent the rising of the bridge, and distribute the weight of a load from any point to the whole bridge. Thos. Durden, of Montgomery, Ala., is the inventor, and he will be happy to furnish additional particulars upon being addressed as above. The patent is dated June 1, 1858.
