THE ROYAL ARTILLERY INSTITUTION. 
397 
intersects its axis (which he terms the “ centre of resistance ”), not 
being exactly opposite to the centre of gravity, the force of projection 
and that of resistance act so as to form a couple BC which tends to 
deflect the head of the shot. This being opposed by the centrifugal force 
due to rotation and the effect varying continually, the axis of the pro¬ 
jectile constantly describes in space a form approaching a cone, the 
path of its centre of gravity being a helix or spiral. 
General Maievsky arrives at the conclusion that the helix becomes 
wider and wider as the projectile proceeds further and further on its 
path. 
Facts seem to contradict this, and though General Maievsky gives 
reasons in support of his conclusions, it seems likely that the conditions 
of the question are affected by the velocity of translation (and hence 
the disturbing cause—viz. the resistance of the air) decreasing much 
more rapidly than the velocity of rotation. 
The small diminution of the velocity of rotation, as compared w T ith 
that of translation, is a fact that has been frequently overlooked, and 
the strong reasons there are for believing that the flight of the pro¬ 
jectile increases in steadiness suggest the doubt whether General 
Maievsky has sufficiently considered these disproportionate rates of 
decrease in his investigations. 
Mr. Mallet on Partial Penetration of Armour . 
Mr. Mallet in his paper discusses the actual effects which are pro¬ 
duced by various forms of projectiles in piercing armour, on the 
supposition that it is “ a homogeneous plate of parallel thickness of a 
malleable material,” which is not completely penetrated by a rigid pro¬ 
jectile. 
The greatest resistance is made by tough and moderately soft wrought- 
iron, but even this behaves as a more or less brittle body whenever the 
velocity of impact reaches about 560 ft. per second. The entrance of 
projectiles into armour, Mr. Mallet considers then as accompanied by a 
certain amount of direct fracture and a certain amount of lateral displace¬ 
ment, the metal behaving to some extent as a plastic and flexible body. 
The ogival form of head is specially adapted to perform this work 
effectually. 
Probably the direct punching of the flat-headed shot compares better 
with the wedging open of the ogival head if the plates are very hard. 
The cylindro-ogival shot, if the angle of incidence be greater than 
that made with the axis of the shot by a tangent to the curve of the 
head at the point, digs its point in at once and “ the centre of gravity 
of the shot at the same time goes forward, turns round more readily 
at first than the flat-ended shot upon an equatorial axis, and slides in 
the direction of a line making an angle, more or less, towards the 
internal side of the face struck. The forward part of the shot thus cuts 
out and partly pushes before it, normally to the face towards which it 
slides, the plastically distorted part of the iron, and bulges or not the 
opposite face in an umbo , whose conditions are such as referred to in 
fig. below.” 
