190 Mr. Mallet on the Physical Conditions 



2 r C 

 Gun-metal, . . 924 x 15 x 898, 

 Cast-iron, . . 1005 x 90 x 374. 

 ur, as 



124-46 : 338-28. 



105. The cast-iron gun of the same size and in the same conditions will cool, 

 therefore, nearly three times as fast as the gun-metal one, taking no regard to the heat 

 lost in both cases by evection. 



106. 6°. The softness and flexibity of gun-metal, as compared with cast- 



iron, enables its form in guns to be distorted partially by internal 



forces locally applied, which in cast-iron, are diffused in virtue 



of its stiifness, through the other parts of the mass, and which thus 



cause the whole to yield (if at all) without alteration in form, or 



unsymmetrically. 



M. Ardent, of the French Corps de Genie, has shown also that in bodies 



possessing the physical properties of bronze or gun-metal, when elongation due 



to any tractile force shall have nearly reached the maximum, consistent with 



immediately unimpaired elasticity, very slight additions of force are sufficient 



to produce greatly increased elongations ; the cohesive forces are no longer 



in a state of stable equilibrium. When, therefore, a gun is strained by unequal 



expansion up to a given point, very slight additional strains suffice to destroy 



its form completely. 



Thus it -will be perceived that, as compared with those of gun-metal, cast- 

 iron guns possess properties giving a minimum distortion by unequal heating, 

 and the power of complete recovery from the small distortion that they do 

 sustain, which is scarcely ever possible in gun-metal, owing to the great range 

 indicated by its coefficient T^- 



107. The great extent of local distortion to which heavy brass ordnance is 

 liable is instructively shown by observation of the state of the upper side, at the 

 muzzle, of the chase of the French howitzer in St. James's Park: where the shells 

 appear to have grazed hardest, on leaving the gun, all projectiles (as is well 

 known) being thrown from side to side on passing through the chase, by the play 

 of windage {ballottage). The inner arris of the muzzle in this case is quite beaten 

 out, and elevated in an angular ridge above the level of the flat terminal of the 



