PRINCIPLES OP GUNNERY. 
459 
number of foot tons required for perforation by right-angled impact 
by the square of the sine of the angle of impact. 
But if the projectile goes straight through the plate without turning 
in, the energy per inch of circumference for oblique perforation will be 
2g7rd sin 9 
This formula gives the best results for flat-headed projectiles and 
comparatively thin armour-plates. 
Chilled iron, wrought-iron, and steel have been experimented on to Material of 
ascertain their respective merits for materials to make projectiles for P r °j ectlle * 
piercing armour-plates. Chilled iron has been adopted in this country, 
on account of its easier manipulation, its great hardness, and its com¬ 
parative cheapness of production. The best material of projectile 
would be that which would neither break up on impact nor change its 
shape. Any change of shape means a loss of energy uselessly ex¬ 
pended in heating the projectile ; while if the projectile breaks up, it 
generally fails to impress all its energy on the target. Steel answers 
more to these requirements than either chilled or wrought-iron. 
Experiments carried out at Shoeburyness with 9-in. projectiles with 
ogival heads and equal weights, made of steel or chilled iron by 
different manufacturers, and fired against an armour-plate of wrought- 
iron 12 ins. thick, have shown that steel is the best material for 
armour-piercing projectiles. The chilled iron shells break up on 
impact generally, while the steel shells rarely do so; and if they break 
up it is always in large pieces, and in some cases the head only 
separates from the body. The shells made of Whitworth steel give 
the best results; it was the only sample of steel which fairly pierced 
the plate and remained perfect without any sensible alteration in shape. 
The penetration with steel projectiles which neither break up nor sen¬ 
sibly alter their shape is greater than with ordinary chilled projectiles. 
It has been found, when firing Palliser shell against armour-plates, Armour- 
that the destructive effect may be greatly modified by placing a thin jjJtery a ^ th 
armour-plate unbacked at a short distance in front of the armour- jj^ een 
plate proper. The front armour-plate is of course easily penetrated, 
but in perforation the chilled shell is broken up, and the fragments 
have but little effect on the armour-plate in rear. 
At Shoeburyness, on the 27th March, 1877, a Palliser shell was 
fired from the 38-ton gun at a 4-in. iron plate placed in front of 
another 10-in. plate at an interval of 4 ft. 7 ins. The shell passed 
through the 4-in. plate, making a hole 12*5 ins. in diameter, and 
breaking up in doing so. A quantity of it was found in a state of 
“ splash” upon the face of the 10-in. plate. The 10-in. plate was 
comparatively little injured. 
However, when firing steel projectiles which do not break up in 
perforating the thin armour-plate, this no longer holds good. A steel, 
shell fired from a 9-in. gun completely pierced an 8-in. plate placed 
4 ft. 6 ins. in rear of a 4-in. plate placed at an angle of incidence of: 
60°. It thus appears that the method of arrangement of armour- 
plates with intervals between them is useless for structures liable to* 
