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ply the sum by the length, and by ; or,

instead of —j j l , multiply by •00003tt, viz.

by 3tt, for the gallons, cutting off five figuresof decimals.

Thus, taking the same example as before,where the diameters are 34 and 27, and thelength 50,

- 10000.. x x

3A=134 , 72 gallons of water displaced, beingonly two gallons more than by the precedingrules. If the circumferences are used insteadof the diameters, cut off four decimals, in-stead of five.

When casks of various sizes are collected tomake a bridge, they should be classed, andeach raft formed of vessels of nearly equal di-mensions.

As casks are not subject to be tilled likeboats or other open vessels, and their buoyancyis easily and accurately calculated, it is notnecessary to allow much excess, in determiningthe number of casks required to form a raft;but they should be placed so that the bung-holes may be easily got at, to pump out anyleakage; for which purpose small pumps shouldbe prepared, and a hole bored through the