THE DRIFT OF SERVICE PROJECTILES. 
\Us 
or at any rate beyond, tlie second quarter of the circle, and that the left 
side of the projectile is consequently exposed during most of its flight 
to more pressure than the right side, as the shot proceeds with its 
point more or less to the right during the whole time of flight, and 
is therefore deflected to the right (with right-handed rotation). 
“ This is the simple explanation borne out, I think, by the results of 
practice and by the motion of the gyroscope, as I endeavoured to explain 
last year, with very high angles approaching 70°, shells fired from a 
6" howitzer deflected to the left; and at first sight one might suppose 
that, in this case, the third quarter of the circle had been passed by the 
point of the shell during^the longer time of flight; but it is plain on 
examination that these shells were unsteady during a large portion of 
their flight, the velocity of rotation not being high enough to prevent 
them turning on their longer axes. Besides this, some shells fired from 
a 9" gun at 70° had right deflections. Perhaps I may have not 
understood Captain Shortt’s remarks, and I am sorry not to be able to 
be present to hear his explanations, which would, doubtless, be more 
satisfactory than judging them by reading over a short printed slip.” 
The Chairman —Professor Smith, will you help us in this matter? 
Professor P. J. Smith, E.E.S.—I have really nothing to say, sir, upon this 
subject—which is not mine at all—but I should like to ask a question, whether any 
data have been gathered as to the position of the shot at different points, photograph¬ 
ically. I w T orked, as Professor Boys has, on the early photographs of shots in 
flight and it struck me that rather more definite light might be thrown upon the 
question of drift by getting successive photographs showing what the shot is 
really doing. Probably the process may be thoroughly well known here; I am 
speaking in entire ignorance of w 7 hat has been done in these buildings on the 
subject. I do not know whether it has been done at present, but it strikes me 
that it might throw light upon the position of the shot in flight. 
Major P. A. MacMaiion, P.E.S.—Captain Shortt has considered the question 
from a great many data, but he has not brought to consideration at all the position of 
the centre of gravity of the shot with respect to the figure of the shot—it seems 
to me that that is a very important point. It is a matter of common experience 
that the more forward the centre of gravity the greater the tendency for the shot 
to keep tangential to the path. 
There is another point I should like to ask Captain Shortt about in connection 
with the remark he made that “ if the path of the projectile were a straight line 
there would be perfect symmetry of motion of the point of the shot about the line 
of flight,” because he said there was perfect symmetry and he did not see any 
reason why there should be any difference on one side or the other—to the right 
or to the left. It seems to me that there is a want of symmetry really, because, 
as the projectile advances along its path, supposing the path to be a straight line, 
the pressure of the air upon the shot diminishes and, therefore, during the second 
half of the revolution of the point there will be a less pressure than during the 
first half of the revolution. This seems to me. to destroy that symmetry upon 
which Captain Shortt relied when he said that he thought that if the path of the 
projectile were a straight line there would be perfect symmetry of motion of the 
point about the path. 
Captain Shortt made another remark to the effect that with a very high velocity 
gun the drift was very much less. It is almost obvious that this must be so from 
the fact that the time comes into the question, and that with a high velocity gun 
the projectile has really less time to deflect from its path. 1 was thinking, when 
c Captain Shortt was speaking, of what happens in billiards. It is well known that 
