ON THE MOTION 
OF 
ELONGATED PROJECTILES. 
BY 
G. T. WALKER, B.A., B.Sc. 
The latest work on the subject of projectiles from a practical 
standpoint is that of Rev. F. Bashforth on the “ Bashforth Chrono¬ 
graph.” In the Chapter devoted to elongated projectiles he gives 
an explanation of the origin of ‘ drift ’ and points out that it will be 
vertical as well as horizontal: when calculating a trajectory he allows 
an increase of elevation on account of the vertical drift, but observes 
(§ 146) that this is not quite satisfactory. The author gives (p. 125) 
several references to mathematical treatises on the subject, but appears 
to regard them as of no value for calculation. 
The only mathematical work on the subject that I have succeeded 
in finding is that of Greenhill in the Minutes of Proceedings of the 
Royal Artillery Institution, xi., pp. 124—130. By dint of identifying 
the axis of the shot with the tangent to the trajectory (p. 126 
at the top) and taking one variable fr to represent the inclination to 
the horizon of each, his work is greatly simplified, but deprived, as 
it appears to me, of most of its value: it is the difference between 
these directions that gives rise to drift, and there is no reason given 
for the identification but the existence of a couple in the required 
direction. But since the magnitude of this couple is not proved to 
be what is required, and since there are considerations of energy, 
angular momentum about a vertical axis through the origin &c., 
which he neglects, the reasoning on (p. 126) is not adequate. These 
objections may be illustrated by the results that Greenhill gets. On 
p. 127, is initially finite, in reality it is initially zero if yjr be 
the angle between the axis of the shot and the horizon. 
5 . VOL. XIX. 
26 
