458 
TIIE DRIFT OF SERVICE PROJECTILES. 
we can always do. Let us consider the case of a pointed projectile and 
then., supposing it starts point first, with no rotation at all due to 
rifling, the shot will soon find itself broadside on; 1 think there can 
be no doubt about that—it is the same in everything in nature. If a 
ship is moving through the water it has to be kept to its course by 
the man at the wheel constantly, otherwise it would find its nose get¬ 
ting further and further from its original direction. If a shilling is 
dropped into the water edgeways, instead of going down perfectly 
straight, it will turn flat and afterwards it will zig-zag down chiefly in 
a nearly horizontal position; if this were not so the Aden diving boys 
would never be able to get the threepences and sixpences that one 
throws overboard for them. And quite irrespective of what the action 
of the air is on the projectile, or where the resultant resistance will 
act, whether in front or in the rear of the centre of gravity, the actual 
result is that the point of the projectile is driven away from the direc¬ 
tion of motion ; that, I think, is pretty certain. Accordingly we have 
a force of rotation acting in some way to take the point away from 
the line of motion in the plane which contains the long axis of shot 
and the tangent to the trajectory for that instantaneous position of 
the shot, so that, as regards motions of rotation, we have the rotation 
round the centre of gravity tending to take the point away from the 
line of motion and also we have the initial rotation which we give 
from rifling. 
Now the effect of these I want to illustrate and I think it is best 
illustrated by an ordinary top. If Fig. 1 be a top, supposing it to have 
Fig. 1. 
no spin round its long axis, it will simply fall to the ground by the 
action of gravity acting through its centre of gravity; that causes it 
to rotate round its point in the direction represented by the arrow A. 
It is exactly similar to the force acting on the projectile tending to 
turn the point away from the line of motion. Now let us consider this 
motion of the top. It has two rotations—the spin given to it by the 
string and the force of gravity tending to turn it round in the direc¬ 
tion shewn. If we combine these two (and we may combine them very 
simply by the ordinary theorem in dynamics of combining the two axes 
