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An Essay on the principles and construction of military bridges, and the passage of rivers in military operations / by Howard Douglas
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wine countries for holding wine. Two sacks tobe fastened to each saddle, and inflated whenrequired. In this way, Folard observes,* cavalry may pass rivers, however wide andrapid they may be, without risk or difficulty.

A proposition was submitted to the Institute of France , a few years ago, by Captain Williac,for making rafts for bridges, of inflated bagsformed of animal skins sewed together, or ofcanvass bags lackered over with a solution ofgum-elastic, (indian rubber, page 105,) by whichthe seams and pores may be made imperviousto water. The bags with which the experimentswere made,f were of elliptical shape, 6 feet long,2 feet wide in the centre, and 2 feet deep. Theupper surface was fastened to a frame 7 feetlong, and 2 feet 3 inches wide, with sides a fewinches high, forming, consequently, a shallow,light case, in which the bags, when not inflated,might he packed for travelling. The contentof each hag was about 18 ^ cubic feet,capable,consequently, of displacing about 1,150 lbs. ofwater; but allowing for compression and im-perfect inflation, it may be rated at 1,190 lbs.To inflate the vessel, two or three men standingon planks attached to the lower surface of the

* Folards Polybius, vol. iv. p. G9.

f Encyclopedic , art . Militaire, tom. iv. p. 833.