190 
MINUTES OF PROCEEDINGS OF 
to turn to tlie left instead of to tlie right, and the deviation will therefore be 
in the same direction, viz. to the left; these principles are clearly shown by 
the gyroscope, and fully confirmed by the results of the practice before 
given. 
The grazes of the greater number of the flat-headed shot fired on the 9th 
and 18th April were also inclined to the left , and that some were not so 
inclined no doubt arose from the unsteadiness of the shot during flight. 
A popular theory frequently advanced to account for the derivation of 
projectiles from rifled guns is,—that a shot rotating rapidly and at the same 
time falling in the air will experience a greater pressure underneath than 
above, and will therefore roll as it were upon the denser air below. Were 
this the real cause a flat-headed shot having right-handed rotation would 
deviate to the right, like a shot of any other form, and the derivation would 
increase with the rapidity of the rotatory motion imparted to the projectile, 
which is not the case. 
As a projectile having a pointed or rounded head deviates in one direction 
and a flat-headed shot in the opposite direction, it is probable that by making 
experiments with shot having heads of different shapes, a form might be 
discovered which would show no derivation .* Derivation may be decreased 
by increasing the velocity of rotation of the shot. 
It may be as well to point out in conclusion, that if an ordinary cylindro- 
conoidal shot maintained its velocity for a very long range, so that great 
resistance would continue to be exerted by the air upon the shot, the point 
of the latter, with right-handed rotation, would not only turn to the right, 
but would gradually droop, then turn to the left, and in fact describe a 
circle, and after a certain time the direction of the derivation of the shot 
would change. In practice, however, although the resistance during flight 
is doubtless sufficient not only to turn the point of a shot but also to cause 
it to droop, yet the resistance decreases so rapidly with the velocity, that at 
the end of any ordinary range the derivation is still in the direction at first 
given. 
* See “Motion of Projectiles,” by Major Owen, R.A., p. 49. 
