384 
MINUTES OF PROCEEDINGS OF 
this, because greater spin thus involves greater deflection of axis, 
and consequently greater resistance of the air; and that this reasoning 
is sound, is proved by the fact that guns with a rapid twist, if they are 
accurate shooting guns, and do not deflect at one time to the right and 
at another to the left, as did the Lancaster gun, always deflect more to 
the right than those with a less twist.* 
These principles have been dwelt on at some length, because it is 
necessary to know exactly what we have got to do in rifling guns. It 
is a mistake to suppose that giving a very great twist is all that is 
required. What is required is to limit the extent of the gyrations as 
much as possible, so as to keep the point as close as may be to the 
trajectory, and thus occasion less resistance of the air during the 
whole flight of the projectile, and the greatest penetration at any 
point; and what is of still greater importance, to ensure that the 
gyrations, whatever they may be, shall be regular, so that they may be 
allowed for and we may have accurate shooting. This last can only be 
obtained by proper centring; for if the projectile be not properly centred, 
there is always an initial cause to interfere with the after regularity of 
the deflection. There can be no doubt, however, that a rapid twist is 
the best thing that will compensate for want of centring; because, in 
the first place, it is not so easy to deflect the point of the shot as it 
comes out of the gun when the twist is great; and, in the second 
place, any initial deflection which may exist becomes more readily 
absorbed in the larger and more stable gyration which afterwards 
ensues. It is better, however, to do with a less rapid twist and more 
perfect centring, not only because it strains the gun and the projectile 
less, but also because it in reality gives more accurate shooting. 
No one will doubt the fact that some rifled guns shoot better than 
others, though some may be disposed to question whether the better 
shooting is due to more perfect centring. The results given in 
Reports of Experiments with the Bashforth Chronograph 99 to deter¬ 
mine the resistance of the air, may be therefore stated, in further 
support of the view here advocated. This instrument gives a very 
accurate measurement of the resistance of the air, both with round 
* The following table, taken from “ Reports of Experiments with the Bashforth Chronograph,” 
(p. 168), shows the co-efficients of the resistance of the air with Whitworth and service projectiles:— 
Velocity. 
Whitworth 
flat-headed shot. 
Ogival radius 
= If diameter. 
Hemispherical 
head. 
Spherical shot. 
! f.s. 
; 1140 
J -0001396 
•0001079 
•0001329 
•0001534 
1060 
•0001246 
•0000972 
— 
•0001473 
1 928 
| -0001384 
•0000659 
— 
•0001385 
This shows that, with Whitworth shot, the co-efficient of resistance does not decrease with the 
velocity of translation in the same manner as service rifled and spherical shot; and no doubt the 
greater spin with Whitworth shot is the cause of this, as explained in the text. 
