TRACT 37.

OP GUNNERY.

293

drical bore of the piece. This indeed cannot amount tomuch: but, whatever it is, there does not appear to be anyexact method of computing it. Another cause of diminu-tion, is the loss of force by the elastic fluid escaping by thevent and windage of the gun ; and this is likely to be veryconsiderable, as the fluid will issue out by the vent, and bythe sides of the ball, with its whole velocity, which is at arate vastly more than that of the ball itself. Some estimateof the loss of velocity by this cause, might be deduced fromsome of the earliest part of our experiments; butamore ac-curate calculation of it must be deferred, till we come to de-termine with what velocity it is that the elastic fluid expandsitself.

165. Other causes of diminution in the velocity are, thegradual firing of the powder, also the unequal motion anddensity of the elastic fluid behind the ball, and lastly theweight of the powder itself, which must require part of theforce to give it so violent a motion. The investigation ofthe theorem proceeds on the supposition that all the powderis fired the first instant. But, though the time of firing ismanifestly very small, yet it must be acknowledged that it isnot all inflamed in an instant, both from the circumstance, inthe higher charges, of many grains of powder being blownout unburnt, and the velocity of the ball being very sensiblybelow what it ought to be, on the supposition of the totaland instantaneous inflammation. A considerable diminutionmust therefore result on this account, without admitting of atheoretical investigation, and without the means of an esti-mation, except from the defect of its due force in the ex-periments.

16G. Again, the motion qf the inflamed fluid is slowestnext the breech, and gradually quicker all the way, fromthence to the ball, where it is the quickest. For the samereason also, the fluid is densest and strongest next the breech,and all the way rarer and weaker to the ball, where it is theweakest. Besides, the fluid is supposed to act upon the ball,