82

THE FORCE OF

diameter and less weight have a still greater initial velo-city.

170. The following experiments made under a mean stateof the atmosphere, strew the initial velocities of shot impelledby different charges of fine war powder.

Initial Velocities,

Feet.

Weight of Powder.

JJracbms.

Mufquet, length ofbore 3 ft. 6 in.

Wall-piece, weightof bullet 2s oz.

J 399

1736

1984

1504

2056

2060

A mufquet fired with the ordinary charge of 7 drachms ofpowder does not range so far, as if the charge were larger; butas the barrel would soon become too hot, the smaller charge ispreferred. From the experiments made with the mufquet(167, 168, 169,) it will be easy to deduce by analogy, the velo-cities of other fire-arms discharged in very moist or very dryweather. For example, to know the initial velocity of a shotfrom a wall-piece fired in very dry weather, with a charge of 25drachms of fine war powder: as its initial velocity under a meanstate of the atmosphere is 2060 feet, and that of the mufquet1736 feet; and the initial velocity of the same mufquet in verydry weather is 1829 feet, by making a proportion of these values1736 : 2060 :: 1829 - 2245 feet, which is the velocity of thewall-piece in very dry weather.

171. Since the initial velocity of fire-arms of all lengths maybe thus found, it will be easy to ascertain the scale of prestureswhich the elastic fluid exerts upon the Ihot in different pointsof the bore of the gun. For this purpose, fire three or fourguns differing in length but equal in calibre, charged withthe fame quantities of powder: having measured the initialvelocities of the shot, set off from A to R (Fig. 20.) on theline A R the lengths of the guns taken from the part of thecylinder where the shot is lodged to the mouth of the piece ;and supposing A C to be the length of the shortest gun ; A Dthat of the second, and A B that of the longest ; make the per-pendiculars C E, D F, B G equal to the initial velocities ofthe respective shot; then a line pasting through the pointsA, E, F, G will be the scale of velocities in the spaces A C,

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