THE DRIFT OF SERVICE PROJECTILES, 
46 ? 
read; lie lias had the argument of the lecture submitted to him: — 
“ I am glad to find that interest is taken in the subject of the * drift 
of projectiles 5 which I re-opened about a year ago at the R.A. In¬ 
stitution. Having read over attentively what Captain Shortt says with 
respect to the cause of drift, I must confess I do not quite understand 
one or two of his propositions. In one remark I cordially concur that 
in which he says : c I believe the mathematical analysis of this problem 
to be impossible. 5 Many years ago now I pointed out, that while 
mathematics were indispensable in assisting us to arrange and compare 
the results of practice, and to obtain from them certain general prin¬ 
ciples, the facts obtained from carefully conducted experiments could 
alone afford a sound foundation for the science of gunnery; and I 
strengthened this opinion by an extract from Sir J. Herschers £ Dis¬ 
course on the Study of Natural Philosophy, 5 where he says: ‘ It was 
not till the time of d’Alembert that the method of reducing any question 
respecting the motions of fluids under the action of forces to strict 
mathematical investigation could be said to be completely understood. 
But the cases even now, in which this mode of treating such questions can 
be applied with full satisfaction, are few in comparison of those in which 
the experimental method of enquiry, as already observed, is preferable. 
Such, for example, is that of the resistance of fluids to bodies moving 
through them ; a knowledge of which is of great importance in naval 
architecture and in gunnery, where the resistance of the air acts to an 
enormous extent. 
£ ‘ Captain Shortt gives a clear account of the behaviour of the point 
of an elongated projectile when fired from a gun, which is very similar 
to that given here by myself last year, but I must notice a point in 
connection with the second quarter of the movement. He says : ‘ In 
the second quarter of a circle the point is below the line of motion, 
which will be moving still down, but to the left now. 5 It must, how- 
however, be remembered that although moving to the left, the shot wall 
still be inclined to the right, and although this inclination will be gradually 
lessening, the point will not get to the left till entering the third 
quarter. 
cc I confess I do not see why the third quarter will be passed over 
more quickly than the second. Nor do I know what Captain Shortt 
means when saying that— c If the trajectory were a straight line, there 
would be no drift. 5 Does he mean a case in which there was no such 
force as gravity to act upon the projectile? If so I agree with him. I 
also agree with him in considering that the projectile cannot assume a 
1 sleeping position 5 like a top. 
“ From an observation respecting a case where he says the projectile does 
not complete £ one revolution of its precession at all, 5 it would appear that 
Captain Shortt supposes one or more entire circle of the point occurs 
during the trajectory in most cases. This is entirely opposed to my 
ideas founded on the explanation given by Magnus, and, as I think, the 
results of practice. We must remember that even comparatively low 
velocities give but a few seconds of time for the action of the resistance 
of the air to produce the conical movement of the point, and that its re¬ 
sistance tending to produce this motion is continually decreasing during 
flight, to say nothing of the decreasing velocity of rotation of the 
projectile. I have always held that, except at very high angles of 
elevation giving long times of flight, the point does not move as far as 
