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Professor W. Chandler Roberts- Austen [March 15, 



velocity was increased beyond a certain value, a result due to a 

 superiority in the power of the face of the plate to transmit energy 

 over that possessed by the projectile, which was itself damaged, when 

 a certain rate was exceeded. At a comparatively low velocity the 

 j)oint of the shot would resist fracture, but the energy of the pro- 

 jectile is not then sufficient to perforate the plate, which would 

 need the attack of a much larger gun firing a projectile at a lower 

 velocity. 



The tendency to-day is to dispense with nickel, and to use 

 ordinary steel, " Harvey ed " ; § this gives excellent 6-inch plates, 

 but there is some difference of opinion as to whether it is advan- 

 tageous to omit nickel in the case of very thick plates, and the 



problem is now being worked out by 

 the method of trial. Probably, too, the 

 Harveyed plates will be much improved 

 by judicious forging after the process, 

 as is indicated by some recent work 

 done in America. The use of chromium 

 in the plates may lead to interesting 

 results. 



Turn for a moment to the Majestic 

 class of ships, the construction of which 

 we owe to the genius of Sir William 

 White, to whom I am indebted for a 

 section representing the exact size of 

 the protection afforded to the barbette 

 of the Majestic. [This section was 

 exhibited and is shown as reduced to 

 the diagram, Fig. 8.] Her armour is of 

 the Harveyed steel, which has hitherto 

 proved singularly resisting to chromium 

 projectiles. 



In this section A represents a 14-inch 

 Harveyed steel armour-plate, B a 4-inch 

 teak backing, C a 1^-inch steel plate, D ^-inch steel frames, and E 

 J>-inch steel linings. 



It will, I trust, have been evident that two of the rarer metals, 

 chromium, in the projectiles, and nickel in the armour, are playing a 

 very important part in our national defences ; and if I ever lecture to 

 you again, it may be possible for me to record similar triumphs for 

 molybdenum, titanium, vanadium, and others of these still rarer metals. 

 Here is another alloy, for which I am indebted to Mr. Hadfield. 

 It is iron alloyed with 25 per cent, of nickel, and Hopkinson has 

 shown that its density is permanently reduced by 2 per cent, by an 

 exposure to a temperature of — 30°, that is, the metal expands at 

 this temperature. 



A B 



Fig. 8. — Seciion of 

 Barbette of the Majestic. 



* ' Engineering,' vol. lvii. 1891, pp. 465, 530, 505. 



