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new experiments

TRACT 34v

of the arch, was this : The radius was made just 10 feet: Itherefore prepared a smooth and straight deal rod, uponwhich was set off a length of 10 feet; I then divided eachfoot into 10 equal parts, and each of these into 10 partsagain ; by which means the whole rod or radius was dividedinto 1000 equal parts, being 100th parts of a foot. Ithen transferred the divisions of the rod to the face of thearch in this manner, namely ; the first division of the rodwas applied to the side of the arch at the beginning of it,and made to turn round there as a centre; then, in thatposition, the rod, when turned vertically round that point,always touched the side of the arch, and the divisions of itwere marked on the edge of the arch, successively as theycame into coincidence with it.

17. In fig. 2, plate v, g shows the leaden weights placedabout the trunnions ; h a screw for raising or depressingthe breech of the gun, by means of the piece i embracingthe cascable, and moveable along the perpendicular armKi, to suit the different lengths of guns, and held to it bya screw passing through the slit made along it. The ma-chines and operations for finding the ranges will be de-scribed hereafter.

On the Centres of Gravity aud Oscillation.

18. It being necessary to know the position of the centresof gravity and oscillation, without which, the velocity can-not be computed ; these were commonly determined everyday as follows:

The centre of gravity was found by one or both of thesetwo methods. First, a trian-gular prism of iron A b, beingplaced on the ground with oneedge upwards, the pendulumor gun-frame was laid across it,and moved backward or for-ward, on the stem or block, as

the case required, till the'two parts exactly balanced each