302 Royal Society : — 



B.D. g Professor of Applied Mathematics to the Advanced Class of 

 Artillery Officers, Woolwich. 



These experiments were undertaken with a view to determine the 

 resistance of the air to some forms of heads of elongated shot which 

 were likely to be of practical use. The chronograph used was the 

 one described in the Proceedings of the Royal Artillery Institution 

 for August 1866*, which was constructed on the plan of the Green- 

 wich instrument. Ten screens were placed in a line at intervals of 

 150 feet, the first being 75 feet from the gun. The following were 

 the forms of the heads, and ten shot of each kind were prepared : — 



(1) Hemispherical solid. 



(2) Hemispheroidal (axes as 1 : 2) solid. 



(3) Ogival (struck with a radius = 1 diameter) . . solid. 



(4) Ogival (struck with a radius = 2 diameters) . . solid. 



(5) Ogival (1 diameter) hollow. 



(6) Ogival (2 diameters) hollow. 



(3) and (5) as well as (4) and (6) had respectively the same 

 external forms, but the solid were nearly double the weight of the 

 hollow shot. The gun used was a 40-pounder M.L., and the dia- 

 meter of the shot was 4' 7 inches. 



It was found, as in the trial experiments of 1865, that, if 5 be the 

 space described in time t after passing the first screen, then, approxi- 

 mately, 



t=as+ bs 2 , 

 from which it follows that, if v be the velocity at time t 3 

 _ 1 

 ~~ a + 2bs 

 and the retarding force 



r=Z-2hv\ 



If V denote the velocity when s=0, then 



v=I, 



a 



and v = L_. 



All the hollow shot were fired, giving eighteen out of twenty suc- 

 cessful shots. Only a part of the solid shot prepared were fired ; and 

 they did not give nearly such good results as the hollow shot, pro- 

 bably in consequence of the superior angular velocity of the hollow 

 shot — because, as a 5 -lb. charge was used throughout, the lighter 

 shot had a higher initial velocity, and consequently a higher corre- 

 sponding angular velocity. 



Tables are given showing for every round: — (1) the experimental 



determination of the time of passing each screen, supposing the first 



screen to be passed when £=0; (2) the velocities at the middle 



points between successive screens ; (3) the weights of the shot ; and 



* Published separately by Bell and Daldy, 1866. 



