218 CAUSES OF DRIFT. 
know how much you have gone into this, but I think that so far as 
regards what I want to bring before you it is pretty simple, and I think 
I shall be able to make out my case by the results of experiments. 
In the ‘Text Book of Gunnery, 1887,” written by Major G. Mackinlay, 
R.A., the question of the Drift of projectiles fired from rifled guns is 
treated in rather an unsatisfactory way, the subject being summed up 
as follows :— 
“Tn the present state of our knowledge it is impossible to give reasons 
for drift which will be received by all, as different explanations have 
been given by various authorities.” Itis said in the preface (second 
edition) that the Text Book is not only used at the R.M. Academy, but that 
it has been “adopted for use in the Royal Artillery, and has also had 
a considerable circulation elsewhere.” Itisin fact the accepted Text 
Book of the service, as my “ Modern Artillery ” was for some years, the 
only difference being that the later Text Book is a strictly official work, 
while mine was an independent publication accepted officially. This 
being the case, it is somewhat surprising, that what was considered 
well-establised by competent authorities should be ignored in the Text 
Book, and that no notice whatever is taken of the experiments carried 
out by Professor Magnus, of Berlin, or of those by myself; also of the 
results of practice made independently, which serve to confirm what 
had been ascertained from the former. 
On visiting Shoeburyness not long ago I was informed by an 
Officer in authority there, that, although I might not credit it, the drift 
was due to the projectile rolling on a dense layer of air below it. That 
this rolling may have some effect is probable,* but when projectiles 
with right-handed rotation deflect in certain cases to the left, it is 
obvious that we must look elsewhere for the chief cause. The writer 
of the Text book recognizes the inadequacy of the theory, for he 
says :—“ But this simple explanation will hardly account for the facts 
that rifled projectiles are not overturned in flight, and that their axes 
are kept nearly tangential to the trajectory.” Why then does he make 
no allusion to the ample evidence given in “ Modern Artillery,” and in 
other works and papers to the /eft deflection or drift of cylindrical or 
flat-headed projectiles, fired with right-handed rotation ? not the so- 
called flat-headed shot having rounded shoulders, with which it was 
attempted to show that truly cylindrical shot drift in the same direction 
as pointed projectiles having right-handed rotation. 
It may also be asked, who are the various authorities who have given 
different explanations ? No trustworthy experiments have been made 
since my own; nor has any theory of any value been established, which 
could, in any way, affect the explanations of Professor Magnus, 
confirmed by many experiments.f 
The only attempt, in this direction, as far as I know, was the sugges- 
tion of Lieutenant-Colonel Sladen in his “Principles of Gunnery,’— 
“that the axis of the projectile makes one or more complete gyrations 
round the trajectory, and that the drift with service projectiles is always 
to the right, because the first movement of gyration is in that direction ;” 
* T shall show further on that the rolling may produce effect on drift, when very low 
charges and high angles are employed. 
+ The subject was treated mathematically by General Mayevski in a paper entitled— 
“De VInfluence du Movement de Rotation sur la Trajectoire des Projectiles oblongs 
dans lair,” in ‘“ Revue de Technologie militaire,” tom. v., 1865, Paris et Liége. 
