PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 529 



tlon is that in iron we get a perfect metal tliroughont, but this is not so, we 

 can never get a mass of matter homogeneous; so after much generalization 

 it was concluded that a revolving motion given to the ball would obviate 

 this unequal gravity or crystalization of the iron. With regard to a ball 

 turning and pointing its lightest end forward it is found to be true, but 

 only so in small arms, which the rifling motion now given to the ball may 

 be said to remedy, the ball being made to rotate on its axis is constantly 

 changing its specific gravity, by which the ball is kept in the line that it 

 received from the barrel of the gun. 



Mr. T. D. Stetson. — AVith regard to the form of balls it is a little singular 

 that the first balls we know of were long. The Arabians had guns that 

 fired arrows of iron, and some that used other materials ; and simple as 

 it now appears, the man who conceived the idea of making balls round 

 accomplished a wonderful thing in his day It was a tremendous i«ven- 

 tion, it could roll in the gun, and in the air, or on the ground. The first 

 rifling we know of was in straight grooves, and tliis was to allow leakage, 

 and is now adopted to a certain extent in firing shells, which leaves a place 

 for the gas to ignite the fuse. It was found that by using spiral grooves, 

 a ball would rotate on its shortest axis, and tiie end which would strike 

 first could be known precisely, so the rifling makes a gun nearl}' perfect. 

 The minie ball is the result of a long list of experiments. The rear end 

 being made hollow, when fired swells and fits into the grooves, and on this 

 account, the ball must be made a trifle smaller, in order to let it go into the 

 barrel. In the minie ball the powder spreads the hollow centre of the rear 

 end into the grooves, which brings the ball coincident with the bore of the 

 gun. Balls that use a sabo in the rear, to fill the grooves, have not thus 

 far acted well, as the sabo flies off from the ball as soon as it leaves the 

 muzzle, and therefore there is very little rifling motion given to the ball, 

 and the tendency will be to go outside of the line desired. The minie ball 

 being in one piece makes it preferable, but it has this drawback, "the thin 

 sharp edges of the hollow rear end at times fly off ragged, which leaves 

 one side rough and lighter than the other, and tends to destroy its accu- 

 racy. At the present time we want long range and accuracy ; and this is 

 the reason why rifles are used in the government service. We want them 

 to reach half a mile instead of the old 200 3'ards. Compound balls have 

 failed to meet the favorable attention of government oflBcers. But the idea 

 of using a sabo at the back of the ball is quite old. At present there is 

 nothing so well established in the government service as the minie ball for 

 rifles. There is what is called the Shankle projectile, a ball with a papier 

 raache sabo ; this has some very good qualities, but there is one objection 

 to it, and that is, the thickness of the paper or the swelling of it with the 

 hygrometric changes of the atmosphere. On this account the paper has to 

 be made very thin, but in a dry atmosphere the paper contracts and fits the 

 bore of the 'gun very loosely, and consequently there is a leakage of the 

 gases from the powder, but this style of ball is now going out of use. It 

 is generally believed that lead is better than iroji for balls, because it is 

 denser ; but why not use it in cannon ? This cannot well be done, for if we 

 fire a leaden ball of large size, it will squash or act like so much putty . 



[Am. Inst,] I* 



