75 



and durability, combined with a moderate amount of wear. That the 

 breech-loaders are most properly abandoned is now an admitted fact. 

 The cost of the old 8 -inch cast iron guns was abont £100, while the 

 cost of a similar breech-loader is about £800, while the initial velocity 

 has been proved by H. M. S. " Excellent's" practice to be very inferior 

 to that of the muzzle-loaders. The mean velocity of a 49 lb. shell, 

 fired from a 32-pounder rifled service gun was shown to be 1120 feet 

 per second, with a range of 1600 yards, while 826 feet per second is 

 the mean initial velocity of a breech-loading field service gun. Guns, 

 it must be admitted on all sides, will have an advantage over ships, as 

 there is no absolute restriction to the size of the gun, though there is to 

 the size and weight of the armour-plates of the ships. That great 

 desideratum — "stability" — seriously affects all our iron-clads, and is a 

 fault that can only be rectified by the loss of a great portion of that 

 armour plate that renders them " invulnerable" (?). 



In the calculation of the effect of any explosive agent, due regard 

 Mr. Longridge observes, must be given to the evolution of the perma- 

 nent gases. Captain Boxer, R. A., in his valuable treatise on Artillery, 

 computes the gases evolved from one cubic foot of gunpowder when re- 

 duced to ordinary temperature to be 



Nitrogen, 79*4 cubic feet, 



Carbonic acid, . . . 238*0 ,, 



or, according to Mariotte's law, a pressure of 317*4 atmospheres. This 

 pressure may indeed be estimated by this law, represented by the equa- 

 tion to an adiabatic curve — 



1 p fv'\k 



p oc_, or £_= _ . 



v k p \v J 



Here p and p' are the pressures before and after compression ; v and v' } 

 the volumes corresponding; the ratio of the specific heat at constant 

 volume to that at constant pressure. In the case of air, k= 1*41; and 

 if this be the same for carbonic acid and nitrogen, the pressure after 

 compression = 317*4 atmospheres, 

 = 3-367 



= 22*17 tons per square inch. 



In estimating the initial force of gunpowder from the velocity as ascer- 

 tained by the ballistic pendulum, the usual method is that of Dr. Hutton, 

 to find the value of n in the formula : — - 



\/ nhd 2 . _ h 



v = 47'i Log-', 



p + w ° a 



from which we obtain 



n = (p + iv)v 2 

 ^TlHtfLog 



b 



