44 VELOCITY OF PF.OJECTILE9, 



The time fup- One thing may naturally fuggeft itfelf, which is, that the 



fo allow"* mea- tIme ° f the ba,,,S P affin S fr0m 0ne dilk t0 the ° ther » throu g h a 

 furablc arc ? fpace of three or four yards, muft be lefs than -j-^ of a fecond 5 



and it is difficult to conceive, that in fo (hort a fpace the dilk 

 could defcribe an arc capable of being meafured. 

 But Jt did not But this difficulty is eafily folved by the faft. When the 

 motion became uniform, the wheel and axle commonly made 

 0*833 of a turn in a fecond ; and every turn of the wheel pro- 

 duced 7*875 turns of the axis of the difks, which confequently 

 made 6'56 turns in a fecond. Thus a point on the dilk three 

 feet from the axis would move about 41 yards in a fecond, 

 and in T %-$ of a fecond ^fc of a yard, or nearly 15 inches, a 

 length more than fufficient for the moil accurate meafurement. 

 The fire-arms The experiments were made with a foldier's firelock and a 

 experimented horfeman's carbine, the lengths of which in the bore were 

 . 3 f. 8 in, and 2 f . 5 in. The balls were accurately weighed, 

 found to be on a medium 332 grains troy, and ea,ch wa.s im- 

 pelled by half its weight of powder. 

 Formula for cal- The following formula was employed for calculating the 

 Jechy"^ £ VC " velocity of the balls. Putting «r for the femiperiphery, when ra- 

 dius is unity se 3.141 ; k for the ratio between the turns made 

 by the wheel and axle and the arbor of the difks ; / the time 

 employed by the wheel and axle to make a number of turns 

 n; r the diftance of the hole in the fecond difk from the centre; 

 a the arc defcribed by this hole while the ball pafles from one 

 dilk to the other; b the diftance between the difks; and Y lh$ 

 velocity of the ball : we mall have the equation 



v^m. j-b. 



hi a 



Mean velocity The mean velocity deduced from ten experiments with the 

 •with a carbine, rb - e was j 2 69 feet and a half in a fecond ; that from the ex- 



1209 r. per lee. ' 



withamulket, periments with the mufket, 1397 feet. Thefe being in the 

 *397» ratio of J l' to 10 nearly, it would appear, that the length of 



the foldiers's firelock might be reduced without much diminifh- 

 ing its range*: but there are other circumftances in a military 

 view, by which the length of the weapon ufed by the infantry 

 requires to be regulated. 



* The differences of the range are much lefs than thofe of the 

 velocity. See Dr. Hut ton. — T, 



The 



