ADDRESS. 29 



of the necessary ductility and toughness. The cases have to stand a 

 pressure at the moment of firing of as much as twenty-five tons to the 

 square inch — a pressure which exceeds the ordinary elastic limits of the 

 steel of which the gun itself is composed. 



There is nothing more wonderful in practical mechanics than the 

 closing of the breech openings of guns, for not only must they be gas- 

 ti«^ht at these tremendous pressures, but the mechanism must be such 

 that one man by a single continuous movement shall be able to open or 

 close the breech of the largest gun in some ten or fifteen seconds. 



The perfect knowledge of the recoil of guns has enabled the reaction 

 of the discharge to be utilised in compressing air or springs by which guns 

 can be raised from concealed positions in order to deliver their fire, and 

 then made to disappear again for loading ; or the same force has been used 

 to run up the guns automatically immediately after firing, or, as in the 

 case of the Maxim gun, to deliver in the same way a continuous stream 

 of bullets at the rate of ten in one second. 



In the manufacture of shot and shell cast iron has been almost super- 

 seded by cast and wrought steel, though the hardened Palliser projectiles 

 still hold their place. The forged-steel projectiles are produced by methods 

 very similar to those used in the manufacture of metal cartridge-cases, 

 though the process is carried on at a red heat and by machines much more 

 powerful. 



In every department concerned in the production of warlike stores 

 electricity is playing a more and more important part. It has enabled 

 the passage of a shot to be followed from its seat in the gun to its 

 destination. 



In the gun, by means of electrical contacts arranged in the bore, a time- 

 curve of the passage of the shot can be determined. 



From this the mathematician constructs the velocity-curve, and 

 from this, again, the pressures producing the velocity are estimated, and 

 used to check the same indications obtained by other means. The velocity 

 of the shot after it has left the gun is easily ascertained by the Boulange 

 apparatus. 



Electricity and photography have been laid under contribution for 

 obtaining records of the flight of projectiles and the effects of explosions 

 at the moment of their occurrence. Many of you will recollect Mr. Vernon 

 Boys' marvellous photographs showing the progress of the shot driving 

 before it waves of air in its course. 



Electricity and photography also record the properties of metals and 

 their alloys as determined by curves of cooling. 



The readiness with which electrical energy can be converted into heat 

 or light has been taken advantage of for the firing of guns, which in their 

 turn can, by the same agency, be laid on the object by means of range- 

 finders placed at a distance and in advantageous and safe positions ; while 

 the electric light is utilised to illumine the sights at night, as well as to 

 search out the objects of attack. 



