233 
THE EFFECT OF THE ROTATION OF THE 
EARTH ON THE MOTION OF PROJECTILES. 
BY 
E. T. DIXON, (late R.A.). 
Trinity College, Cambridge. 
A moment’s consideration will show that the rotation of the earth 
must have some effect on the flight of a projectile—that, in fact, the 
common theory of a parabolic path is only an approximation, even if 
the resistance of the air is neglected. If, for example, a gun were fired 
from the north pole, as soon as the shell left the muzzle it would cease 
to be affected by the rotation of the earth, and would therefore drift to 
the right as many minutes as the earth had rotated during the time of 
flight. It follows easily that at any other latitude there will be a 
similar drift, to the right in the northern hemisphere and to the left in 
the southern, the amount only being less, in the ratio of the sine of the 
latitude. This drift however would not concern practical artillerists, 
even if it were much larger than it is, for being constant for any given 
range, in any given latitude, it is naturally absorbed in the correction 
for drift due to rifling. But if the rotation of the earth produced any 
considerable effect depending upon the azimuth of the line of fire, it 
would be otherwise. It will be shown below that it does produce such 
an effect, of sufficient magnitude to be of theoretical interest, and 
which might even be made visible by careful experiments, though it is 
too minute compared with other sources of error to be worth taking 
into account in practice. 
In the following dynamical discussion it will be assumed that the 
attraction of the earth on the projectile is constant in magnitude, and 
in direction with reference to the station from which the gun is fired, 
throughout the flight of the projectile. A consideration of the resulting 
equations will show that this approximation may be relied on to the 
order adopted for the deflection of the projectile, and also for its range, 
when the latter is not extreme. 
5. VOL. XX. 
