124 
ON THE DERIVATION, OR DRIFT, OF ELONGATED RIFLED 
PROJECTILES. 
BY 
A. G. GREENHILL, M.A. 
{Professor of Mathematics to the Advanced, Class of Artillery Officers.) 
The principles of the preceding paper afford an explanation of the 
drift of an elongated projectile to the right of the plane of fire. 
If a projectile were fired in a vacuum, the axis would remain parallel 
to itself during the trajectory; no rifling would be required, and 
there would be no drift. 
But it is observed that a projectile fired in air, with, proper spin, has 
its axis in the tangent to the trajectory (very nearly), and that after it 
has reached a distance, short in comparison to ordinary ranges, from 
the muzzle, all “ wabbling” ceases, being destroyed by the friction of 
the air, and the shot may be said, like a top, to “ go to sleep.” 
Closer observation reveals that the point of the shot is a little above 
and to the right of the exact tangent to the trajectory; this deviation 
becoming more marked at the end of the trajectory. 
A shot, even if perfectly centred, on issuing from the muzzle, has 
after the first instant its axis inclined to the tangent to the trajectory, 
in consequence of the curvature of the path of the centre of gravity 
due to the action of gravity. 
Elevation. 
