involved in the Construction of Artillery. 187 



15. — Numerical Example. 



100. If we apply this to a 32-pounder brass gun, of 9 feet iii lengtli, in 



which — 



I = 54: inches, 



c = 6'5 inches nearly ; and 



e — '017 inches, 

 we shall find that with the difference in temperature of 300° between the 

 two opposite sides, the radius of curvature will be 267^ feet, and the versed 

 sine, 0'46 inches, that is to say, the gun will be bent nearly half an inch from a 

 straight line. 



The cause assigned is sufficient, therefore, to account for the extent of the 

 phenomena. 



1 6. — Belation as to Distortion., of Gun-Metal and of Iron Guns. 



101. It may be questioned, then, why does "drooping at the muzzle" occur 

 in gun-metal guns, and never in cast-iron guns. It does occur in cast-iron guns, 

 but in a degree so much diminished, as to be in them, imperceptible; and, 

 furthermore, after cooling again to an uniform temperature, the cast-iron gun 

 will, under all practical conditions (as to the extent to which it can be heated 

 unequally), recover its form, which the gun-metal one may not. 



The following are the chief reasons, however, why this distortion is so much 

 greater in guns of gun-metal than of cast-iron of equal sizes, forms, and charges : — 



1°. The gun-metal is much more heated by each discharge, in the ratio by 

 which it is a better conductor of heat than cast-iron, or as about 

 89 : 37, and, therefore, takes up more heat during the moment of 

 the flash. This is modified also in the inverse proportion to their 

 respective specific heats, so that the same quantity of heat that 

 would raise the temperature of the cast-iron gun 110° will raise 

 that of the gun-metal gun 134°. The gun-metal gun, therefoi'e, 

 takes up from each discharge, of the same weight of gunpowder, 

 about tliree times as much heat as the cast-iron gun. 



2". Gun-metal is much more ductile and less elastic than cast-iron, and 

 possesses a much longer range through which its form may be 

 altered, before its elasticity is finally overcome, though with a 



