368 
MINUTES OF PROCEEDINGS OF 
29. I shall now put these results in actual figures, and shall again 
take for illustration the 10-in. gun, supposed (as before) to be rifled, 
1st, on the uniform, 2nd, on the parabolic or service twist. 
With the uniform twist, G (see table) = 1547 tons; and using 
equation (28) and the values of the constants given in 22, 
G'= G — -245i2 
= •989(7..(29) 
Hence the decrement of pressure due to the suppression of rifling is 
only about 1 per cent.; that is, the total pressure on the base of the 
shot is reduced from 1547 tons to 1530 tons, or the bursting pressure 
is reduced from 19*7 tons per square inch to 19 *5 tons per square inch. 
At the muzzle of the gun, in the same manner, we find that the total 
pressure is reduced from 205 tons to 202*8 tons, and the pressure per 
inch in a corresponding proportion. 
30. Similarly, from equation (26) and the values of the constants 
given in 25, the values of G' at the point of maximum pressure and at 
the muzzle of the gun are obtained; and I find that with the parabolic 
twist the pressure on the base of the shot would be reduced from 
1547 tons to 1541 tons, or the bursting pressure would be reduced 
from 19*7 tons to 19*62 tons per square inch. 
At the muzzle the corresponding reductions are from 205 tons total 
pressure, to 196 tons, or from 2*61 tons to 2*49 tons per’square inch. 
31. For the sake of clearness, I recapitulate the results at which I 
have arrived. They are as follow :— 
1st. That the pressures actually exerted at all points of the bore to 
give rotation to the 10-in. British service projectile, compared with 
the pressures which would be exerted were the gun rifled on a uniform 
twist, are very approximately exhibited in the diagrams on the Plate. 
2nd. That in the 10-in. gun (and other guns similarly rifled) the 
pressure on the studs due to rifling is but a small fraction (about 
2J per cent.) of the pressure required to give translation to the shot. 
3rd. That the substitution of the parabolic for the uniform rifling 
has reduced by about one-half the maximum pressure on the studs. 
4th. That the increment of the gaseous pressure, or the pressure 
tending to burst the gun, due to rifling is exceedingly small,* both in 
the case of the uniform and parabolic rifling. This result is entirely 
confirmed by the experiments of the Explosive Committee, who have 
found no sensible difference of pressure in the 10-in. gun fired in the 
rifled and unrifled states. 
5th. That, small as the increment in gaseous pressure due to rifling 
is, it is still less in the parabolic than in the uniform system of rifling. 
Elswick Works, 
February 15,1873. 
* Although the increase of strain due to rifling is inconsiderable, yet the decrease of the strength 
of the structure of a gun inseparable from rifling may be, and in many systems is, considerable; 
but the discussion of this question is outside of the scope of my paper. 
