MILITARY PROJECTILES. 543 



distance below the axis, is fixed against the descending 

 branches of the stem, and graduated into divisions, 

 according to the purpose required to be answered by the 

 machine. 



The divisions in these scales are pointed out by an in- 

 dex, which is carried on the arch during the vibration, 

 and then stopping there, shows the actual extent of the 

 vibration. 



Another contrivance which has been resorted to, to 

 measure the force of a ball thrown by gunpowder, is call- 

 ed the Ballistic pendulum. It measures the force, not 

 by the recoil, but by the force given to a heavy body sus- 

 pended like a pendulum, and against which the ball is 

 thrown. 



* The block of wood which is struck by the ball, in- 

 stead of being left at liberty to move straight forward in 

 the direction of the ball's motion, is suspended like the 

 weight of the vibrating pendulum of a clock, by a strong 

 iron stem (with adequate braces,) having a horizontal 

 axis at the top, on the ends of which it vibrates freely 

 when struck by the ball. This large pendulum, after re- 

 ceiving the blow, is penetrated by the ball to a small 

 depth, and by reason of the motion communicated, os- 

 cillates round its axis, describing an arch, which is 

 greater or less according to the magnitude of the impul- 

 sion. From the extent of the arch described by the vi- 

 brating pendulum, the velocity of any point of the block 

 can be readily computed. 



' Several blocks of this kind, varying in weight, from 

 COO pounds up to about twentyfive hundred pounds, were 

 constructed and employed under the direction of Dr Hut- 

 ton, for the purpose of ascertaining the initial velocities, 

 as well as the velocities at different distances from the 

 mouth of the piece, of balls weighing from one to sixteen 

 pounds.' 



We have thus presented to our readers the prominent 

 facts in regard to this branch of human skill. The sub- 

 ject of war is at best a very melancholy one. It is never 

 pleasant to consider the efforts which human ingenuity 

 has made to facilitate the destruction of property and 



