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To find the quantity of timber required tofloat a given weight, the solid content must befirst known.

The rules generally used in calculating thecontent of round timber, give the result aboutJ or less than the true quantity. This is, pro-bably, intended to make allowance for squaringthe tree; but, for the purpose now under con-sideration, it will be necessary to use morecorrect methods.

Rule 1$/.—Add the areas of the two ends, andtheir geometrical mean, together; multiply one

in all his enterprises in the passage of rivers ;—of these, that ofthe Dune, in 1701, is the most celebrated

The bridges across the Vistula at Kartsiof, and near War­ saw in 1704 and 1705, were of rafts of timber. The latterwas broken by drift ice; which, had an opening been pre-pared, or an ice-guard, A. fig. 10. plate 10. constructed, wouldnot, most probably, have happened.

The passage of the Desna, in 1708, was effected on raftsmade of timber, collected from houses.

In the campaign of 1790, in Italy , the French army beingdestitute of all regular bridge equipment, a bridge of rafts oftimber was constructed on tbe Adige at Ravazone, where it isabout 120 yards wide. This bridge remained for several years,sometimes in the possession of the Austrians, and sometimes inthat of the French .

Annibal’s celebrated passage of bis elephants across theRhone on rafts is well known.