188 
MINUTES OE PROCEEDINGS OF 
with similar rotation; for instance, if a cylindro-conoidal and a flat-headed 
shot be both fired with right-handed rotation, the derivation of the former 
will be to the right and the latter to the left . 
(4) That the derivation of ordinary service shot fired from the 40-pr. 
Armstrong gun is hardly sensible at 1000 yds.; for it may be seen from 
Tables Y. and VI. that a slight breeze from left to right was sufficient to 
counteract the tendency of the shot to bear off to the right. It also appears 
from the Tables that flat-headed shot require a very much higher velocity of 
rotation than cylindro-conoidal projectiles, and that the former lose their 
velocity very much sooner than the latter* 
Various explanations have been given to account for the derivation of shot 
fired from rifled guns, but that suggested by Professor Magnus, of Berlin, is 
in all probability the true one, confirmed as it appears to be by the results 
of actual practice. In order to ascertain practically the effect produced by 
the resistance of the air upon a rotating projectile, Magnus had a gyroscope 
constructed with a small elongated shot, instead of the ordinary disc, 
suspended in such a manner that it could turn freely in any direction. The 
limits of this paper do not allow of a discussion of the principles of rotation 
as shown clearly by such a gyroscope, but the effect of the air's resistance 
tending to produce the derivation of an elongated shot may be briefly stated 
as follows.f 
In Pig. 1., the directions of the forces which act upon an ordinary 
cylindro-conoidal shot fired from a gun are shown. 
Fig. 1. 
P represents the force of projection. 
G „ „ gravity. 
It „ resultant of the air’s resistance which must he parallel to the trajectory 
AB described by g, the centre of gravity of the shot. 
The dotted lines parallel to AB represent the opposing current of air, and 
R must be midway between them. 
* False heads which will easily break up on impact have been attached to some experimental 
flat-headed shot for practice against iron plates, in order that the shot may retain a high velocity 
during flight. 
f A translation of Magnus’ pamphlet on the Deviation of Projectiles may be found in the 
“Occasional Papers” of the R.A. Institution, Vol. I. p. 443. 
