130

NEW EXPERIMENTS

TRACT 34.

3 illy. From the foregoing table, it is evident also, thatthe velocities communicated by different quantities of pow-der, are nearly in the proportion of the square roots of thosecharges.—Also, by a due computation from the quantity ofvelocity lost in the several distances, the resistance of theair to the ball of 2 - 78 inches diameter, moving with severalvelocities, will be nearly as expressed in the foregoing table,in p. 126, where the first column shows the velocity per se-cond, with which the ball moves, and the other columnsshow the corresponding resistances of the air, in ounces orpounds; that is, when a ball of that size moves with a velo*city of suppose 1700 feet per second, it is resisted by theair with a force which is equal to the weight or pressure of2472 ounces, or 154a pounds ; and so of the rest.

From this table of resistances it appears also, that there isa gradual and regular increase of resistance, as the velocityis increased, from the least to the greatest, and withoutshowing the appearance of such a very sudden or abruptchange in the nature and quantity of that resistance, as Mr.Robins suspected might obtain. But that the law of resist-ance gradually and slowly increases like the velocity itself,probably on account of the increasing partial vacuum behindthe ball in its flight, from the slowest motion, when the re-sistance changes as. the square of the velocity nearly, up toabout the velocity of 1200 or 1400 feet, when, the vacuumbeing completed, the law of increase appears to have at-tained its highest pitch, being then nearly as the 2 a powerof the velocity; after which it gradually decreases againmere and more, as the velocity increases higher, till it arriveat about the 2^ power, and perhaps still lower; which,among several others, is a law, that was unknown till it wasdiscovered by means of these experiments.

A few trials were also made with a 6-pounder gun, whichshows the practicability of using still larger pieces of ord-nance in such experiments. The dimensions of the gunwere these : the length of the bore 57 a inches, and its diam-ter 3'67. The balls on an average weighed Sib 13oz, and