MODE OF DETERMINING VELOCITY OF PROJECTILE. 185 



stroke is easily deduced from the chord of the arch, through 

 which it ascends by the blow ; for it is a well-known pro- 

 position, that all pendulous bodies ascend to the same height 

 by their vibratory motion, as they would do if they were 

 projected directly upwards from their lowest point with the 

 same velocity they have in that point; wherefore, if the 

 versed sine of the ascending arch be found (which is easily 

 determined, from the chord and radius being given), this 

 versed sine is the perpendicular height to which a body 

 projected upwards with the velocity of the point of oscil- 

 lation would arise ; and consequently what that velocity is 

 can be easily computed by the common theory of falling 

 bodies. 



" To determine the velocity with which the bullet im- 

 pinged on the centre of the wood, when the chord of the 

 arch described by the ascent of the pendulum, in con- 

 sequence of the blow, was 17 inches as measured on the 

 ribbon, no more is necessary than to multiply 3^ by 505, 

 and the resulting number (1641) will be the feet which the 

 bullet would describe in 1" if it moved with the velocity 

 it had at the moment of its percussion. The velocity 

 of the foot of the pendulum on which the bullet struck is 

 determined to be 3 feet in V by the following calcula- 

 tion : The distance of the ribbon from the axis of sus- 

 pension being 711 inches, reduce 17^ in the ratio of 71 J to 

 66; the resulting number, which is nearly 16 inches, will 

 be the chord of the arch through which the centre of the 

 plate ascended after the strike : now, the versed sine of an 

 arch whose chord is 16 inches and its radius 66 inches, is 

 1 -93939; and the velocity which would carry a body to 

 this height, or, which is the same thing, what a body would 

 acquire by descending through this space, is nearly that of 

 3J feet in 1"." 



Velocity, or its equivalent, penetration, is measured by 

 English military authorities in a much more practical 

 manner, but at the same time, in a way which is open to 

 serious objections, as will be hereafter shown. Their machine 

 is composed of a series of twenty elm planks half an inch 

 thick, with an inch between them. These are made to slide 

 into the grooves of a metal frame, and after being soaked in 



