THE ROYAL ARTILLERY INSTITUTION. 
365 
the values of the constants in (19) being in the case of the 10-in. gun 
as follows:— 
p = ’312 ft., 1c = 12*732, h = 33-383 ft., / = *417 ft., ^ = -167. 
Hence 
R = *04426 . G .(20) 
23. But the values of G are known with very considerable exactness 
from the investigations of the Explosive Committee under the pre¬ 
sidency of Colonel Younghusband. The following table gives the value 
of G (that is, the total pressure in tons acting on the base of the 
projectile) for a charge of 70 lbs. of pebble powder at various points of 
the bore, and the corresponding values of R. It will be remarked how 
high the pressure on the studs is when that on the base of the shot is a 
maximum, and how rapidly the strain decreases as the shot approaches 
the muzzle. 
Table showing the 'pressure on the studs in a 10 -in. British service gun rifled ivith 
a uniform twist , calculated from (17). 
Travel of shot. 
Total pressure Cr¬ 
on base of shot. 
Value of C. 
Value of B, 01 - 
total pressure 
on studs. 
ft. 
tons. 
tons. 
0*000 
0 
•04426 
0 
0-333 
1547 
// 
68-5 
0-945 
1077 
n 
47-7 
1-834 
781 
a 
34-6 
2-723 
621 
a 
27-5 
3-612 
610 
n 
22-6 
4-500 
424 
a 
18-7 
5-389 
356 
n 
15-8 
6-278 
305 
a 
13-5 
7-167 
268 
n 
11-8 
8-055 
240 
a 
10-6 
8-944 
220 
n 
9-7 
9-833 
205 
n 
9-1 
24. The results in the table show the pressures required to give 
rotation, if the 10-in. gim be rifled on a uniform twist. I turn now to 
the rifling as it actually exists, and which is defined to be a parabolic 
twist, commencing with one turn in 100 calibres and terminating at 
the distance of 9'833 ft. with a twist of one turn in 40 calibres; and 
first to determine the equation to the parabola. 
Let the origin be at the point where the twist vanishes when the 
curve AB is sufficiently prolonged—that is, at the vertex of the para¬ 
bola. Let Oz and Oy! be the axes of co-ordinates; let OA! — z i3 
44 
