CHOKE-BORES. 



311 



this motion of rotation is opposed the friction of the 

 atmosphere, which on the hemisphere D, A, B may 

 all be represented by the line a A tangentional to 

 the surface, and in like manner the line b C may be 

 taken to represent the total friction on the hemi- 

 sphere D, C, B. The total friction on both hemi- 

 spheres then will be equal to a A + b C. Now, it 

 is evident that the pressure of the atmosphere from 

 its resistance to the forward motion of the pellet 

 must be far greater on the hemisphere D, A, B than 

 on the hemisphere D, C, B ; therefore the force a A 

 must be greater than the force h C, and in accordance 

 with the laws of motion, this gives rise to another 

 force equal to a A— b C, and tending to give to the 

 pellet a motion of translation in the direction of the 

 line a A and toward the centre of the charge. 



To each of the rotating pellets this law applies, the 

 intensity of the force we have represented by a A— 

 b C varying with the inequalities of their surfaces and 

 the velocities of their rotation, and this it is that 

 chiefly determines the character and extent of their 

 divergence from the line of fire. This force will vary 

 also in accordance with the amount of the constric- 

 tion, the size of the shot, and the velocity with which 

 they are propelled ; and it may at times be sufficient 

 to carry certain pellets across the centre of the charge 



