THE ROYAL ARTILLERY INSTITUTION. 
385 
shot and rifled projectiles. With, rifled projectiles, the resistances are 
found to vary to a much greater extent than with round shot; and it 
is reasonable to suppose that where the resistance of the air is least, 
the projectiles are centred best, and less perfectly when the re¬ 
sistance of the air is greatest. Great differences are found in this 
respect ; and it is a rule that when the resistance of the air is great, 
the accuracy is not so good, and vice versa . One gun—a long B.L. 
40-pr. converted into a M.L. 47-pr.—is remarkable both for the small 
amount of resistance it gives, and for its great accuracy of fire. No 
difficulty is found in firing through ten screens with it without mishap, 
and it can be fired with accuracy at lower velocities than any of the 
other guns. The regularity of the resistance of the air is also very 
remarkable, as compared with the other guns. 
If the shot came out of the gun without any deflection of the axis, 
but rotating round an axis inclined to the longest axis, it would be 
sufficient to account for the increased resistance of the air. For many 
reasons it cannot be supposed that this is ever the case. It will not 
account for the generally inferior shooting which is found with in¬ 
creased resistance, and it is difficult to see how the small amount of 
play the projectile has in the bore of the gun can be sufficient to 
account for the great differences in resistance which are found to exist 
—sometimes as much as 25 or 30 per cent., or even more. 
The question arises, how can we suppose a sufficient amount of initial 
deflection to account for so great an amount of increased resistance ? 
But it will be admitted that there are various causes which will account 
for this. If the shot be knocking itself against the bore as it moves 
on, it may have a final knock as it leaves the gun which will have the 
effect of deflecting the axis sufficiently to account for the differences 
observed. It is possible that such a knock might be sufficient to upset 
the stability of the axis, and cause rotation round an axis inclined to 
the longest; and some people hold this view, and think that it accounts 
for a very curious fact which has been observed in the penetration of 
iron plates. On this supposition, the shot comes out of the gun rotating 
round an axis inclined to the longest axis; and thus at short ranges the 
amount of surface presented is greater than at longer ranges, when 
the shot, by virtue of the stability of its axis, has had time to centre 
itself.* A suggestion may be offered, however, which would account 
for this fact without supposing that the stability of the axis is upset. 
It is this:—-At the moment the shot is leaving the gun, we may sup¬ 
pose that it is rubbing along the bottom of the bore, and that the gas 
is rushing over the base of the shot. As soon as the lower part of the 
base is unsupported, the effect of the gas pressing downwards will be 
sufficient to give a considerable initial deflection of the point to the right. 
At first, therefore, the point of the shot will not be in the best position for 
penetration ; but as it proceeds the point will dip, and will not only con- 
* General Mayevski supposes another sort of centring 1 action different from this, and probably 
the same as that given in the text where the curve of the trajectory interferes with the gyration, 
and at one point brings about a close coincidence between the axis of the projectile and the 
trajectoi’y. This is not, however, what is here referred to. 
47 
