288 Professor Bertram Hopkinson [Jan. 26, 



compression, such as results from the blow of the colliding rods, of 

 more than 300 tons per square inch. If it were ductile it would 

 flow so rapidly under this pressure that there would be appreciable 

 deformation even in the very short time during which the pressure 

 lasts. If it were very hard it would be instantly shattered. In both 

 cases the circumstances of pressui-e transmission would be completely 

 altered. It is, however, fairly certain that in neither would the 

 pressure exceed that calculated on the hypothesis of perfect elasticity, 

 and that in both it would be greater than that calculated (as for the 

 lead rifle bullet) on the hypothesis of no elasticity. 



I am afraid, therefore, that at present our theories can throw but 

 little light on the interesting question of the pressure developed when 

 a hard steel armour-piercing shell strikes a hard steel plate with a 

 velocity of 2000 feet per second. But a consideration of the visible 

 effects of such a blow is suggestive in many ways, and by the kind- 

 ness of Sir R. Hadfield I am able to describe and show some of them 

 to you to-night. 



You see before you specimens of modern armour-piercing shot, 

 and their essential features are shown on the drawing. The shell 

 is made of a special steel of great strength and considerable ductility, 

 and after manufacture the point is hardened by thermal treatment, 

 the base and most of the body of the shell remaining more or less 

 ductile. In recent years it has become the practice to fit a cap of 

 soft steel over the hardened point. I will speak of the functions of 

 this cap later, and for the present we will consider the shell with- 

 out it. 



I first show the effect of firing an uncapped shell at a plate of 

 wrought iron or mild steel (Fig. 8). In this case the metal of the 

 plate is so soft that pressures that are quite without effect on the 

 hardened point of the shell are able to make it flow very rapidly. 

 The shell simply ploughs its way through, pushing out the wrought 

 iron before it, and emerges quite unscathed. It will be noticed that 

 on the striking side there is a rim or lip of wrought iron which has 

 ])een squeezed out in a direction opposite to the movement of the 

 shell. A similar lip is formed if a hole is blown in a lead plate by 

 means of a gun-cotton primer, and there seems to be a good deal of 

 analogy between the two cases. 



Completely to stop a 14-inch shell, such as that which you see 

 l)efore you, would require a thickness of at least 2^ feet of wrought- 

 iron, and almost as great a thickness of mild steel. I believe that 

 some ships twenty-five years ago were fitted with armour of this sort of 

 thickness, but, of course, the weight is almost prohibitive. Modern 

 improvements in armour, whereby the same effective resistance is 

 obtained with less than half the thickness, are based on the use 

 of special steel having sufficient ductility to enable it to be worked 

 and fixed in place on the ship while possessing greater strength than 



