457 
TEE DRIFT OF SERTICE PROJECTILES. 
BY 
CAPTAIN A. G. SHORTT, R.A. 
(A Lecture delivered at the Royal Artillery Institution, Woolwich , Monday , 25th Jan., 1897.) 
Colonel E. BaiNbridge, Superintendent Royal Laboratory, 
in the Chair. 
The Chairman— Gentlemen, I have much pleasure in introducing to 
you to-night Captain Shortt, who has agreed to open a discussion on 
the subject of drift (applause), 
Captain A. G. Shortt —Colonel Bainbridge and gentlemen, what I 
have to talk to you about to-night is rather the position of the long 
axis of flight than drift, although I wish to consider it in connection 
with drift. There seems to be a great deal of difference of opinion 
about the position of this long axis and several different ideas are held 
with regard to it. One, I believe, is that, after the projectile steadies 
itself down shortly after leaving the bore, the point remains in the 
trajectory and, as the trajectory curves, the point goes down with it. 
Another theory is that in the last half of the trajectory the point is 
above the trajectory itself— i.e ., instead of keeping down in line with 
the trajectory, the point is above it. The generally received opinion, 
however, is that the point describes a spiral round the line of motion 
and this spiral completes one or two revolutions. General Owen, in 
his lecture about a year ago, said that it cannot make more than one 
revolution, if as much, because in that case the point would be alter¬ 
nately on the right and on the left and therefore the drift would be 
alternately to the right and to the left and so there would be no resul¬ 
tant drift at all. That theory I do not hold altogether, although I 
hold that the axis describes a spiral round the trajectory. Professor 
Bashforth says that because the first motion of the spiral is to the 
right and because, afterwards, the point is more to the right than to 
the left, therefore the drift is to the right by reason of the pressure of 
the air on the left side of the shell; but, although I agree that the 
point is more to the right than to the left, I do not see what the first 
initial motion being to the right has to do with it. 
The ideas that I hold are as follows :—When the shot is fired from 
a gun it is very often unsteady at starting; shortly afterwards, how¬ 
ever, it settles down into the trajectory and let us consider the forces 
that we then have on it after that. In doing so I wish to separate 
entirely the motions of translation from those of rotation—that, I think^ 
9 . Toil, XXIY, 
