determine the Velocities of the Rifle Bullets commonly used. 891 



3. Police carbine; length 28-75 inches; diameter 0"66 inch. 



With these guns were used the following bullets : — 



Two-yroove rifle. — 1. A Minie bullet, provided with two pro- 

 jections corresponding to the grooves of the rifle, without ' culot;' 

 weight 697 grs. 2. A sugarloaf bullet, fired point foremost ; 

 weight 669-75 grs. 3. A belted, spherical bullet ; weight 483 

 grs. 



Minie rifle. — The regulation Minie bullet, with 'culot;' 

 weight 744 grs. 



Carbine. — Spherical bullet ; weight 391 grs. 



The method employed to determine the velocity of the bullets 

 was Robins' ballistic pendulum ; and the same quantity of the 

 best gunpowder (40 grs.) was employed with each gun and bullet. 



For the erection of the pendulum, and most efficient assistance 

 afforded in the conduct of the experiments, I am indebted to 

 Mr. Joseph Harris, of the firm of Truloch and Son, Dawson 

 Street, Dublin, without whose aid I should have been unable to 

 bring these experiments to a successful issue. 



I shall first give the details of the experiments, and then men- 

 tion the principal deductions which may be obtained from them. 



The formula used in calculating the velocity is the following*: 



v=^-^xnb, (1) 



where v = velocity of bullet in feet per second. 



T = time of oscillation of pendulum. 



a = distance of centre of gravity from axis of suspension. 



CT = ratio of circumference of a circle to its diameter. 



/ = distance from axis of gun attached to pendulum to 

 axis of suspension. 



c = distance from axis of suspension to point of attach- 

 ment of tape, by which the recoil is measm-ed. 



n = ratio of weight of pendulum to weight of bullet. 



b = chord of arc of recoil, measured by tape. 



The two-groove rifle barrel being firmly strapped with iron 

 plates to the pendulum, the constants of the pendulum were 

 carefully determined, and were as follows : — 



//=32-195 feet. ^=3-14159 Weight of pend. =36-75 lbs. 

 T= 1-29 sec. /= 75 -25 in. 



a = 57-39in. c= 78-25 in. 



From these data we obtain from (1) 



r=0-12894xn6 (2) 



The following tables contain the results of the experiments 



* Poisson, Traits lie M^canique, vol. ii. p. W'J. 



