THE EOYAL ARTILLERY INSTITUTION. 
377 
RIFLING FOR HEAYY GUNS. 
$ 
BY 
MAJOR J. P. MORGAN, R.A., 
ASSISTANT SUPERINTENDENT ROYAL GUNPOWDER EACTORIES. 
(Reprinted, by permission, from the “Journal of the Royal United Service Institution,” 
Vol. XVII., p. 645.) 
The principles of rotation are very recondite, and have been the 
subject of some abstruse investigation ; but it is not necessary to con¬ 
sider them mathematically in order to understand their application to 
the rifling of guns. 
They may be briefly stated as follows :— 
In every rigid body there are “ three principal axes,” about which 
the body is capable of rotating permanently. 
Two of these, the greatest and the least, are “ stable axes of rotation 99 
— i.e., if the body rotate round an axis having a very small inclination 
to either of these axes, it will continue to rotate without further 
divergence. The medium principal axis is an “ unstable” axis of 
rotation— i.e., if the body rotate round that axis exactly, it will continue 
to do so ; but if the axis of rotation be inclined to it in the very least, 
the inclination will become greater and greater. With these ex¬ 
ceptions, the body will not rotate permanently round any axis, but in 
all cases the axis will change its position in the body until, at last, the 
rotation is round its shortest axis, which is the most stable of all. 
When a body rotates round a stable axis, and is not acted upon by 
impressed forces, the axis of rotation not only retains its position in 
the body, but also in space, by always remaining parallel to itself. If, 
therefore, there was no resistance of the air to an elongated projectile 
after leaving a gun, the question would be very simple ; for all that 
would be necessary would be to give a comparatively feeble rotation 
round the longest axis, and the shot, by virtue of the rotation imparted, 
would go nearly point foremost for a considerable part of its trajectory. 
It would not, however, be possible to make the projectile strike point 
foremost at very long ranges m vacuo ; and when we find, therefore, in 
practice, that it is possible to make rifled projectiles strike point fore- 
46 
