274 



Mr. Mallet on the Physical Conditions 



out of the graphite, is rapidly swept away by the blast of each successive 

 discharge. Copper vents, or, still better, red gun-metal (copper with about 

 3 per cent, of tin), bouched into the gun, appear to remedy this to a great 

 extent. The French experiments at La Fere, however, gave some ground to 

 suspect a weakening of the gun by the excess of expansion of the copper plug. 

 It would seem that a far better method than " tapping" or screwing in the vent- 

 plug might be adopted, giving the power of renewal, and of rendering the gun 

 unserviceable or serviceable again in a few seconds, without the necessity of 

 s])iking and unspiking, and preventing the possibility of the latter being effec- 

 tually performed. 



31. — Of the Position of the Trunnions upon the Strength of the Gun. 



257. The mass of the shot, whose diameter is Z>, being J/, and its initial 

 velocity v, and the mass of the gun M', neglecting that of the powder, the vis viva 

 of its explosion is (Eq. 58) 



Mv' + M'v'\ 

 and that of the recoil M'v''\ Tlue latter, transferred as a pressure against the 

 interior of the breech, is propagated as a force tending to stretch the metal 

 of the gun from the section rj in line of the axis towards the muzzle z ; the 

 rate of propagation, being (Eq. sect. 134) extremely rapid; — most so in steel; 

 least so in gun-metal ; in either so rapid that, to the senses, the whole gun recoils 

 together and as one mass, and at the same instant; yet in reality the first 

 effect of the recoil is to elongate the gun, pushing out the breech part like one 



