PRINCIPLES OP GUNNERY. 
365 
The number of gyrations depends upon the velocity of the projectile : 
a projectile fired with a high velocity will make several gyrations,, while 
a projectile fired with only a low velocity and at a high angle of eleva¬ 
tion would only make a part of one gyration. 
Pig. 2. 
Fig. 2 represents a horizontal projection of an ogival-headed pro¬ 
jectile at the end of the first quarter-revolution of its axis round the 
tangent to the trajectory— i.e., during the first quarter of gyration. 
G represents the position of the centre of gravity in its longer axis, 
GA. The direction of motion of the projectile in the horizontal plane 
is represented by GT. The axis, GA, of the projectile is deflected to 
the right of this line. RC represents the direction of the resultant 
of the resistance of the air. The resolved part of this resultant 
resistance perpendicular to GT causes the projectile itself to drift bodily to 
the right; it also tends to rotate the projectile round its shorter axis 
through the centre of gravity, G. The combination of this rotation 
with the rotation impressed on the projectile round its longer axis 
causes the axis of the projectile to dip, and thus to commence the 
second quarter-gyration. Fig. 2, then, represents a vertical projection 
at the end of the second quarter of gyration. 
The resolved part of the resultant resistance perpendicular to GT 
now drives the projectile bodily downwards, and at the same time 
tends to produce rotation by deflecting the axis of the projectile from 
the direction of motion. This rotation, combined with the rotation of 
the projectile, causes the axis of the projectile to deflect to the left 
(Fig. 1 may now be taken as the horizontal projection under these 
conditions) \ and the resolved part of the resultant in the third quarter 
of gyration drives the projectile bodily to the left, and tends to cause 
rotation, which, combined with the rotation of the projectile, causes 
the axis of the* projectile to rise, and thus to commence the fourth 
quarter of gyration. 
A gyroscope, with an elongated shot with a rounded head, serves to illustrated 
explain this motion. If the elongated shot is made to rotate in the ofjTg^o. 
direction of the hands of a clock— i.e., with a right-handed rotation— scope, 
and a pressure applied by means of a pencil-point on the head of the 
shot below its axis, then the axis of the shot will deflect to the right, 
with reference to an observer looking at it from the rear. If now the 
pressure is applied on the left front, the axis of the shot will dip; if 
