THE FORCE OF

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187. The following experiment proves that the resistanceof the air to a projectile, is greater in pasting over waterthan land. In June 1764, several rounds were fired fromthe mill of Rocca Franca over the Po, from a wall-piececarrying a 3^. oz. bullet, at the elevation of 15°, with acharge that gave an initial velocity of 1770 feet the meanrange taken with the greatest accuracy was 1799 yards, thefame gun was afterwards fired in the fame manner along theroad leading to Stupinigi , and the mean range was 1863yards.

188. From the preceding comparison are deduced some ofthe corollaries in the theory of the air’s resistance (Philof. Instit.)

1. That the air’s resistance is greater in (hot of smallthan of large diameter, provided the specific gravity be thefame.

2. That in shot of equal diameters the most denseranges the farthest.

3. That when the gun and butt are in the fame plane,the elevation that will give the longest range with a givencharge is less than 45°.

4. That the less the diameter and density of the shot,the more the elevation that gives the longest range, isunder 45°.

5. That the longest range to be obtained with the largestcharge, depends on the direction of the gun, the initialvelocity of the shot, its diameter and weight, the densityof the air, and the equality or difference between theplanes of the gun and butt. Hence, (102, 103, 104,)in measuring the ranges to ascertain the charges that willimpel the shot with the greatest velocity, the results areliable to such modifications, particularly when the firstgraze of the shot is at a distance from the gun, that itrequires a series of experiments,before any one point canbe accurately determined.

189. In this compariion between the actual and potentialranges, it was supposed that the charge that gives a certaininitial velocity when the gun is laid horizontally, would givethe same at different degrees of elevation. To prove that thissupposition is true with regard to shot of small diameter, amusquet (169) was directed against a block of wood equallyporous, placed at the distance of 5 feet, it was fired horizon-tally with a charge that gave an initial velocity of 1736 feet:it was again loaded in the same manner, and fired in a ver-tical