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side of the sinkers, and on these were placed,in succession, 16 half-cwts.—viz. 8961bs. Pigsof iron ballast were then laid on the surface ofthe beam. When the weight had been in-creased to 42601bs. the scantling, after somestanding, sprung, at 12 feet from one end, fromthe upward strain occasioned by the powerfulleverage of the weight acting over the block Eas a fulcrum, underneath which the chainpassed to the point of the beam: as this lever-age may be reduced, by diminishing the dis-tance between the block and the point at whichthe chain is fastened to the beam; and as,moreover, in case of being applied as for abridge, the beams would be equally loaded,throughout, it appears that this method oftrussing beams may be extremely useful onmany occasions.

In restoring, by carpentry, communicationsacross broken arches, and, (as in following upa retreating army,) when only one side of theimpediment can be got at, the great difficultyis to get the first beam across the gap. Themethod of effecting this, shown in fig. 23,plate 10, was frequently resorted to in thePeninsula. For this a pair of wheels and anaxle-tree, are sufficient; and the process is soincapable of injuring them, that gun or waggon