224. CAUSES OF DRIFT. 
circular motion of the point will gradually cease; but in ordinary 
practice* during the few seconds of flight which generally elapse, as the 
velocity is pretty high throughout, there is probably sufficient time and 
pressure not only to turn the point to the right, but to bring it down on 
to the trajectory. Practically, however, on account of the drooping of 
the point, the longer axis may throughout a considerable portion of 
the time of flight approximate very nearly to a tangent to the trajectory 
as in Fig. 7. 
Professor Magnus said—“ We deduce then from these experiments 
with the gyroscope, that the deviation of elongated projectiles arises 
from the fact that the resistance of the air has a tendency to raise their 
points. It is true that this raising is hardly sensible to the eye, because 
the forces which act upon the mass of the projectile are combined in 
such a way that the point, instead of being lifted, only moves on one 
side, and always to the right in the case of right-handed rotation. 
Consequently, the projectile assumes an oblique position to the 
direction of the air’s resistance, and is thereby in its further progress 
depressed on the side towards which the apex is turned, while the air’s 
resistance acts against it as against an inclined plane, and thus produces 
the deviation.t 
The instrument made for me by Mr. Colbrook,{ shows these effects 
very clearly. When the projectile is fired without rotation, it turns 
over in flight, a pointed head being turned upwards, and a flat-head 
downwards. 
When fired with rotation, the shot is prevented from turning over, 
and the velocity being very low, the axis remains parallel to its original 
direction. 
There is however enough resistance to turn the head of the pointed 
shot to the right, and that of the flat-head to the left, with right-handed 
rotation, the range being too short to allow of the drooping of the point. 
It will be found that the results of experiments on the practice 
ground, fully bear out the explanation given above of the chief cause 
of drift, and of the drooping of the point of an elongated projectile 
fired from a rifled gun, with a high velocity. The following experi- 
* \Vhen the velocities are high and the angles of elevation low. 
+ Magnus on the Deviation of Projectiles, Berlin (1860), Second edition, 
- ft See Appendix I. 
