166 
ARMOUR AND ITS ATTACK BY ORDNANCE. 
Petersburg, on November 23rd and December 13th, 1892, in which the 
following plates were tested : — 
(1.) Cammell all steel hard. 
(2.) Cammed ad steel soft. 
(3.) St. Chamond ad steel. 
(4.) Ellis-Tresidder compound. 
(5.) Harvey nickel steel plate made by Vickers. 
The plates each measured 8 feet x 8 feet x 10 inches, probably 
weighing about 11*5 tons. 
The attack was made by 6-incli Holtzer forged steel projectiles, 
weighing about 90 lbs. (English) ; striking with a velocity of from 
2177 to 2205 f.s., the mean being 2188, with a striking energy of 2975 
foot-tons, and a perforation of 13*2 inches of iron or 10*5 inches of steel 
by the English formulae, and 14*8 inches of iron or 11*8 inches of steel 
by Krupp’s formula. The energy per ton of plate was 258*9 foot-tons. 
The results of the firing were as follows :— 
(1.) Cammed hard steel. The first shot penetrated 13^ inches and 
rebounded intact. The second went through and carried off a corner 
of the plate. The third shot broke the plate, bringing half of it down, 
the shot being itself fractured. 
(2.) Cammed soft steel. The first and second shots lodged. The 
third broke its head lodgiug. The fourth and fifth rebounded intact. 
A sixth shot was fired and lodged, making a crack, shown in rough 
sketch (Fig. 27) made on the ground. The penetration varied from 
Fig. 27.—C'ammell’s Soft Plate. 
11J to 21 inches. 
(3.) St. Chamond steel. The first shot broke in two and rebounded. 
The second and third rebounded intact. The fourth and fifth broke, 
