538 MILITARY PROJECTILES. 



tion which affects the course of the ball in a manner 

 which depends on the direction in which this rotatory 

 motion takes place. Now this will evidently depend on 

 the side of the barrel on which the ball accidentally 

 rubbed on issuing from the gun. It is for this reason 

 that if a barrel is bent in any direction, the ball which 

 issues from it, will, as it is said, be deflected in the con- 

 trary quarter. There will always be, from this cause, a 

 deviation from a straight line, in the direction of the ball, 

 as the axis of rotation will always be perpendicular to 

 the axis of the gun. 



In order to remedy this difficulty the idea was con- 

 ceived of giving the ball a rotatory motion, whose axis 

 should be coincident with the axis of the gun. This 

 would prevent effectually any other rotation, while it 

 would itself occasion no deflection. This object is ac- 

 complished by cutting spiral grooves on the interior of 

 the barrel, which made one turn from the breech to the 

 muzzle, so that the ball, in passing through the barrel, 

 revolves once, on that axis which coincides with the axis, 

 of the barrel. It will of course continue in this state 

 of revolution through its whole flight. In order that the 

 ball should so adapt itself to the grooves of the gun, it 

 must be driven down with considerable force. Its fric- 

 tion, consequently in passing out will be much greater, 

 and to guard against the increased danger of bursting, 

 which this will occasion, the barrel must be made thick- 

 er and stronger. 



The nature of the motion of projected balls has been 

 an object of very assiduous inquiry, especially by the na- 

 tions of Europe, who have been ambitious of great mili- 

 tary power. For many centuries the art of gunnery 

 was founded entirely upon practice. The little devia- 

 tion from a straight line which the path of the arrow or 

 the spear presented, could be easily estimated after re- 

 peated trials, and an allowance sufficiently accurate for 

 ordinary purposes, was easily made. And in regard to 

 those great engines which the ancients constructed, in 



