470 
THE DRIFT OF SERVICE PROJECTILES. 
railway train running round a curve for the gyro static domination of the wheels 
to overcome the centrifugal force, so that the train is occasionally found to have 
run off the inside of the curve. 
Captain Shortt might, in my opinion, have elaborated one detail in his argu¬ 
ments by referring the various curves which he lias drawn for us to a moving 
plane which is taken to pass through the centre of gravity of the projectile and to 
be always normal to the trajectory; so as not to refer the motion to a fixed 
vertical plane. I think that his arguments concerning the longer time taken by the 
point of the projectile in describing the part of its path to the right than that to 
the left, by reason of having to overtake the descending tangent, would have been 
more convincing if it had been exhibited by curves—the same figures, of course, 
would serve—but if it were referred to a moving plane normal to the tangent. 
Captain Mansell’s arguments which he brought before us at General Owen’s 
lecture were very ingenious ; he described there, I think, if I remember rightly, 
the deviating effect due to the vortex that was carried forward by the projectile, but 
according to my calculations that vortex would have the effect of causing a difference 
of pressure tending to set the projectile to the left, and such an effect is certainly 
discernible with golf balls and tennis balls ; and also in throwing at the American 
game of baseball. Another simple apparatus on the table can be made to illustrate 
this effect and certainly, I think, it is observed, (so I have read) that there is a 
tendency for a certain amount of drift to the left of the plane of fire at the outset, 
but that the drift on the whole is more and more to the right, and that is shown 
in the apparatus. We have a wire to imitate the trajectory with the projectile at 
the end of it; the wire is passed up the bore of a small model cannon and by 
twisting the wire we imitate, to a certain extent, the spin of the projectile, and 
we see that the projectile tends slightly to the left at the first, but afterwards 
swerves more and more to the right. 
Captain Shortt has, in my opinion, sir, performed very valuable service in 
bringing before us again this very difficult subject of Drift. 
The Chairman —Captain Mansell, have you anything to say ? 
Captain J. H. Mansell —I am placed in a somewhat difficult position"in 
following after all this talent, sir, but with regard to Captain Shortt’s lecture to¬ 
night, I cannot quite see why he does not agree, as he says at the beginning of 
his argument, with one point. lie says : “ The first motion of the point being 
to the right therefore is not the reason for drift.” I do not follow that argument 
at all. I think Captain Shortt himself acknowledges that the reason for drift is 
because the first motion of the point is to the right. Supposing a quarter pre¬ 
cession was never completed during the time of flight, the point of the shot would 
then be to the right the whole time. Whatever the cause of drift may be, we 
should have the point to the right and certainly longer to the right than 
to the left, because it never gets to the left. This question of continuous 
precession going on is, of course, a matter of opinion—I do not myself 
think that it happens—but that is only my opinion. As to the cause 
of drift, I think I follow Major Mac Mahon. He said that the time'bad a great 
deal to do with the question with high velocity guns. 1 think the time has a 
great deal to do with the question myself (1 do not quite know how to put this) 
and also, I think, that the angle at which the shot is thrown across the trajec¬ 
tory has a tremendous lot to do with the amount of drift. 
I cannot help thinking that Captain Shortt rather confuses J the [terms 
4 ‘rapidity of spin” and “rapidity of precession.” The rapidity of preces¬ 
sion has a great deal to do with the drift, because of the angle at which 
we get the shot thrown across the trajectory. This angle, in .my opinion, 
has more to do with the question than the mere comparative times that 
the point of the shot is to the right or to the left, supposing we get 
