1895.] on the Barer Metals and their Alloys. 513 



the American Civil War in 1866. It was found to be necessary, in 

 order to pierce the plates, to employ harder and larger projectiles 

 than those then in use, and the chilled cast-iron shot with which 

 Colonel Palliser's name is identified proved to be formidable and 

 effective. The point of such a projectile was sufficiently hard to 

 retain its form under impact with the plate, and it was only necessary 

 to impart a moderate velocity to a shot to enable it to pass through the 

 wrought-iron armour (A, Fig. 7). 



It soon became evident that in order to resist the attack of such 

 projectiles with a plate of any reasonable thickness, it would be 

 necessary to make the plate harder, so that the point of the projectile 

 should be damaged at the moment of first contact, and the reaction to 

 the blow distributed over a considerable area of the plate. This 

 object could be attained by either using a steel plate in a more or 

 less hardened condition, or by employing a plate with a very hard 

 face of steel, and a less hard but tougher back. The authorities in 

 this country during the decade, 1880-90, had a very high opinion of 

 plates that resisted attack without the development of through- 

 cracks, and this led to the production of the compound plate. The 

 backs of these plates (B, Fig. 7) are of wrought iron, the fronts are of 

 a more or less hard variety of steel, either cast on, or welded on by a 

 layer of steel of an intermediate quality cast between the two plates. 

 Armour-plates of this kind differ in detail, but the principle of their 

 construction is now generally accepted as correct. 



Such plates shown by the plate B, resisted the attack of large 

 Palliser shells admirably, as when such shells struck the plate they 

 were damaged at their points, and the remainder of the shell was 

 unable to perforate the armour against which it was directed. An 

 increase in the eize of the projectiles led, however, to a decrease in 

 the resisting power of the plates, portions of the hard face of which 

 would at times be detached in flakes from the junction of the steel 

 and the iron. An increase in the toughness of the projectiles by a 

 substitution of forged chrome-steel for chilled iron (see lower part of 

 plate B), secured a victory for the shot, which was then enabled to 

 impart its energy to the plate faster than the surface of the plate 

 itself could transmit the energy to the back. The result was that 

 the plate was overcome, as it were, piecemeal ; the steel surface was 

 not sufficient to resist the blow itself, and was shattered, leaving the 

 projectile an easy victory over the soft back. The lower part of 

 plate B (in Fig. 7) represents a similar plate to that used in the 

 Nettle trials of 1888.* It must not be forgotten, in this connection, 

 that the armour of a ship is but little likely to be struck twice by 

 heavy projectiles in the same place, although it might be by smaller 

 ones. 



Plates made entirely of steel, on the other hand, were found, 

 prior to 1888, to have a considerable tendency to break up com- 



* Proceedings Institution of Civil Engineer;*, 1889, vol. xcviii. p. 1 et seq. 



