VELOCITY OF PROJECTILES. 45 



The commiffioners made fome experiments with half charges With J of pow. 

 or with powder only to the quantity of one fourth of the weight £* 2 \ and^o 

 of the hall. In thefe the mean velocities were, for the fire- 

 lock 829 feet, for the carbine 822§. Thefe velocities do 

 not differ fo much from each other, and confiderably exceed 

 the half of thofe given by the full charge, which may be 

 afcribed chiefly perhaps to the more complete firing of the 

 powder. 



The commiffioners were defirous likewife of making fome Tne refinance 

 experiments on the refinance of the air to the motion of the ds diminiihe4 

 ball, the diameter of which was from 15 to. 16 millemetres the velocity 

 (5-8755 lines to 6-2672.) For this purpofe the mouth of the nearly one - fift k 

 gun-barrel, which at firft was 7 f. 9 in. from the neareft fixed 

 fcreen, was removed to the diftance of 67 f. 9 in. In this 

 fituation the mean velocity of the mufket-ball was 1127 f. in- 

 jftead of 1397, fo that it was diminifhed nearly in the ratio of 

 4-2 to 34. The experiments of this kind however were few 

 in number. 



There is no doubt but the dimenfions of Col. Grobert's ap- The apparatus 

 paratus may be enlarged, fo as to adapt it to experiments with w^a withad- 

 cannon balls ; though it is not eafy to fay without trial what vantage. 

 dimenfions would be compatible with accuracy of experi- 

 ment. 



The Colonel likewife propofes an alteration in it, for mea- Mode ofadapt- 

 furing the velocity of projectiles at different elevations, as far ^ l \ t ° at -^ i " 

 as 45°. The following is his contrivance for this purpofe. 

 Each of the difks has a feparate axis. The wheel and axle 

 has a wheel at each end, with an endlefs chain, one turning 

 the arbor of one difk, the other that of the other. Thus the 

 rotatory motion imparted by the defcending weight is com- 

 municated equally to both difks at the fame time, the wheels 

 and arbors being made exactly of correfponding dimenfions. 

 The ftand of the difk fartheft from the gun is moveable in a. 

 vertical direction, fo that it may be raifed to the neceffary 

 elevation ; a few links being added to the endlefs chain for 

 every different height. As the difk is raifed indeed, it be- 

 comes inclined to the path of the ball ; but as the greateft 

 diminution that can take place in this way is in the ratio of 

 about 7 to 5, a fufficient field is ftill left for pointing with 

 precifiou. 



To 



