THE ROYAL ARTILLERY INSTITUTION. 
417 
Pressure on driving surface = - 
2ttpV1 + F 
G, 
where 
? — /*i) Hh 2t 7p 3 (p, 1 £ + 1) 
77 = 8-14159, p = rVl = 2-475, £ = 13-3697, £ = 294, 
r = 8*5, = *1666, 
whence we obtain 
£ = *0375 G t , 
.(29) 
In the second case from (26), 
Pressure = ■ 
27rp 2 
_^== (2,rpH -rh) +-- 
V1 + *- A 
(27rp 2 sin - + rhJc) 
where 
77 = 3*14159, 
p = -i- c 3 . 
P 12 
O . 277 
2 + cos — 
_ n _ 
277 
: 2'350 (c = length of side of polygon), 
whence 
1 — cos - 
n 
£=5-9117, £=130, r= 35, ft= 8, = • 
- = 23° 33', 
ft 
£ = •1706 £.....(30) 
That is, on the supposition of the same pressure on the base of the shot, the 
pressure on the driving-surface is in the latter case nearly five times as great 
as in the former, and is, in fact, no inconsiderable fraction of the propelling 
force. 
Let us now compare the gaseous pressures on the base of shot of the 
same weight supposed to be fired from the guns above described, and from 
a smooth-bored gun. Prom equations (28) we have the pressure upon base 
of shot fired from 
Smooth-bored gun.= Cr, 
Pirst rifled gun... ...= 1'009 G , 
Polygonal gun ........=1*041 
In these calculations we have taken the coefficient friction = -J. It is 
necessary, however, to observe that very little is known concerning the value 
of this constant at pressures so high as those with which we have here to 
do. It is evident that in the case of the contact of similar metals, when 
the point of seizure is approached, the coefficient of friction cannot be 
