270 OUTLINES OF NATURAL PHILOSOPHY'. 



shall be less from a great charge than from a 

 smaller. 



363. The Balistic Pendulum is an instrument 

 invented by Mr ROBINS, for determining the ve- 

 locity with which balls are projected by ordnance 

 of different kinds. The ball is made to strike a 

 heavy block of wood, suspended from a centre ; 

 the velocity is thus reduced to a quantity that is 

 moderate, and easily admitting of being measured. 

 From thence the original velocity is computed by 

 help of the principles explained, Mechanics, Sect. 7. 

 on the Rotation of Bodies, 216. 



For a particular description of this instrument, see 

 ROBINS' New Principles of Gunnery, p. 84. Also 

 Eu LEU'S Notes on ROBINS' Gunnery. The rule for 

 computing the velocity of the ball from the vibra- 

 tion of the pendulum is there investigated, as it is 

 likewise, BUTTON'S Tracts, p. 115., &c. The ini- 

 tial velocity of shot estimated in this way, varies 

 from 1600 to 2000 feet in a second. The latter is 

 nearly as great as it is ever found. 



The velocity with which the elastic fluid, disengaged 

 from the gunpowder, expands itself, is probably 

 more than double of this. Dr HUTTON estimates 

 it at 5000 feet per second. Course of Mathematics, 

 vol. in. p. 270, 



364. The 



