204 On the Forces of Translation and Rotation in Rifled Guns. 

 £=5-9117, A=130, r=3'5, n=S, ^, = -1666, 



- =22° 30", 

 n 



whence K = -1706G (30) 



That is, on the supposition of the same pressure on the base of 

 the shot, the pressure on the driving-surface is in the latter case 

 nearly five times as great as in the former, and is, in fact, no 

 inconsiderable fraction of the propelling force. 



Let us now compare the gaseous pressures on the base of shot 

 of the same weight supposed to be fired from the guns above 

 described, and from a smooth-bored gun. From equations (28) 

 we have the pressure upon base of shot fired from 



Smooth -bored gun . . . . = G, 



First rifled gun = 1*009 G, 



Polygonal gun =1*041 G. 



In these calculations we have taken the coefficient of friction 

 =-J. It is necessary, however, to observe that very little is 

 known concerning the value of this constant at pressures so 

 high as those with which we have here to do. It is evident 

 that in the case of the contact of similar metals, when the point 

 of seizure is approached, the coefficient of friction cannot be con- 

 sidered independent of the pressure; and it is probable that 

 when the rubbing surfaces of both projectile and groove (or 

 other driving-surface) are of the same hard material, the coeffi- 

 cient of friction may be occasionally enormously increased. 



The resistance due to this cause might, under certain circum- 

 stances, be sufficient to ensure the destruction of the gun • and 

 this view is to some extent corroborated by the occasional burst- 

 ing of guns, the failure of which it is difficult to attribute to any 

 other cause; and in the instances referred to, the recovered 

 fragments of the shot were thought to exhibit decided appear- 

 ances of seizure. 



If in equation (26) we substitute 8 for — , we shall have 

 |= »*> .(3!) 



And this equation will represent the ratio of the pressures 

 B, and G in any system of rifling, 8 being the angle which the 

 radius makes with the normal to the driving- surface. Thus in 



