CAUSES OF DRIFT. 219 
but it is difficult to conceive that this reason for drift can be the correct 
one ; for if a complete gyration were made during flight, the projectile 
would be inclined, and therefore present more surface to the resistance 
of the air, first on one side and then on the other, and the consequent 
effects would be neutralized at the end of the range, but should show 
intervening right and left deviations. That the deflections are in one 
direction, and increase with the time of flight, is shown by ordinary 
practice tables.* 
In dealing with the question, I will first restate the results of experi- 
ments, and the deductions from them, which it was generally 
acknowledged some few years ago, both at home and abroad, had 
sufficed to establish the correctness of the explanations of the cause of 
“drift,” offered by Professor Magnus. After this I will givean account 
of some very unsatisfactory experiments, made with the object of 
proving that all shot, whether flat or round-headed, deviate in the 
direction of their rotation; and my letter to the Secretary of the 
department of the Director of Artillery, exposing the fact of the so- 
called flat-headed shot fired, not being cylindrical in form, and the 
consequent worthlessness of the results; and lastly, I will refer to the 
great effect upon drift, produced probably by the so-called rolling of the 
shot upon the dense air below it, in high angle fire. 
It is known that elongated projectiles turn over in flight, when fired 
with high velocities without rotation, unless the centre of gravity be in 
or near the head ; and it was supposed for some time after the introduc- 
tion of such projectiles for rifled arms, that the longer axis of the shot 
remained, during flight, parallel, or nearly so to its primary direction. 
This would be so with very low velocities, but it was found that with 
high velocities, such as those obtained from small arms, or ordnance, 
the point drooped during flight, that is, the longer axis assumed a 
position tangential, or nearly so to the trajectory. ‘To show these effects 
of the turning over of elongated shot fired without rotation, of their 
steadiness with rotation, and the maintenance of the longer axis nearly 
in its original direction with very low velocities, an insirumentt was 
made for me by Mr. Colbrook, Modeller of the R.M. Academy, and these 
effects were shown, by using light wooden. or paper shot, constantly to 
the Cadets of the R M. Academy, also at the R.U.S. Institution, and at 
the R.A. Institution. 
Spherical bullets were used for some years with rifled small arms, 
but they were superseded by elongated projectiles, which presented so 
much less surtace to the resistance of the air during flight. It was 
found that with either form there was a constant deviation to the right 
or left, according as the gun had a right-handed or left-handed twist, 
giving right or left-handed rotation. This peculiar deviation has been 
called ‘ derivation” by the French, and “ drift” latterly in our service. 
The Tables{ given below will serve to show the direction of the drift 
with guns giving right and left-handed rotation respectively. 
* This may be clearly seen in Table xiv., page 309, Text Book. 
{This instrument is described in Appendix J. Major Mackinlay had a similar 
instrument made, and told me in a letter, that it answered its purpose very well, and 
asked if he should give it my name. 
{ From a paper on ‘‘The Derivation of Elongated Projectiles,’ by Major C,H. Owen, B.A. 
Proceedings of the Royal Artillery Institution. Vol. iv., page 180, 
