SECTION VI.

ON CARRIAGE-BRIDGES ANI) SUSPENSION-BRIDGES.

Carriage- Bridges.

Carriages of burthen are useful materials formaking bridges across shallow rivers and canals.

Fig. 13, 14, 15, 16, PI. 7, are plans and eleva-tions of the Pont-roulant , mentioned in the Aide3VI<*moire. Each pair of wheels, with their axle-tree, forms, as it were, a trestle, on which thebeams and floor may be laid. The hind axletreeshifts upon the perch fig. 14, as in a commontimber-carriage. The bearers (), O, fig. 13, 14,rest upon the beds AI, M, in travelling; but maybe shifted upon the uprights N, N, at pleasure,according to the depth of water in which thebridge is to be laid.

To lay the bridge. The carriage is placed end-ways on the bank of the river, and unloaded: thefore axletree is then lashed or bolted, to preventthe carnage from turning—the pole taken ofif-th e beams and centre flooring, P, laid, and thebeams It lashed to the hind bearer O. The