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unequal powers of floatation; but when smallboats of different capacities are used in thesame bridge, the intervals should be reducedand regulated, severally, accordingly.

In rivers exposed to much agitation from windor floods, the construction of a floating bridgeshould be such as to allow something for theindividual motion of each boat, so that thebridge may have sufficient flexibility to undulatea little with the swell, and thus yield to a forcewhich might otherwise break, or strain the beams.

If beams, doubly keyed or bolted to eachother, be thus prolonged, as if forming one piece,and rest on both gunwales of large boats exposedto roll, rise, or fall into the positions A B, C D,E F, fig. 4, plate 2, by a heavy swell, it is evi-dent that a force will be exerted to break thebeams, if the motion impressed upon the vesselsbe too much restrained; and if, on the otherhand, the beams be disconnected and laid fromthe side of one boat, to the nearest gunwale ofthat adjoining, a small boat or vessel would becaused to dip, or heel, very much, under thepressure of any concentrated weight.

To remedy this, a trestle, A B, fig. 5, plate 2,should be fixed longitudinally in each boat, theupper surface of the ridge-beam raised a littleabove the gunwales, and the length of the trestle