542 MILITARY PROJECTILES. 



the incipient velocity of a cannon or musket ball, or the 

 elastic force of various kinds of powder. We shall de- 

 scribe one, which is called the eprouvette. We must first, 

 however, state that when gunpowder explodes, the ex- 

 pansive force is exerted in every direction. It acts not 

 only against the ball, but against the sides and back of 

 the gun. The force which it exerts each side is extin- 

 guished by the strength of the metal, but by the force 

 exerted against the back or breech of the gun, the gun 

 is thrown backward as much as the ball is thrown for- 

 ward. We do not mean as far or as siviftly, but that 

 the whole amount of motion is as great. That is, if the 

 cannon or gun weighs one hundred pounds and the ball 

 one, the cannon will be thrown back one hundredth part 

 as far. This is called the recoil, and upon the well 

 known mathematical principle that the action and reac- 

 tion are equal, it is the same in amount as the motion of 

 the ball. 



The eprouvette measures the recoil. It is an instru- 

 ment contrived for the purpose of comparing the strength 

 of different kinds of gunpowder. It consists of a 

 small brass gun, about two and a half feet long, suspend- 

 ed by a metallic stem or rod, turning by an axis on a 

 firm and strong frame, by means of which the piece 

 moves round in a circular arch. A little below the axis, 

 the stem divides into two branches, reaching down to the 

 gun, to which the lower ends of the branches are fixed, 

 the one near the muzzle, the other near the breech of 

 the piece. The upper end of the stem is firmly attach- 

 ed to the axis, which turns very freely by its extremities 

 in the sockets of this supporting frame ; by which means 

 the gun and stem vibrate together in a vertical plane, 

 with a very small degree of friction. The piece is charg- 

 ed with a small quantity of powder, (usually about two 

 ounces,) without any ball, and then fired ; by the force 

 of the explosion the piece is made to recoil or vibrate, 

 describing an arch or angle, which will be the greater or 

 less, according to the quantity or strength of the powder. 



To measure the quantity of recoil, and consequently 

 the strength of the powder, a circular brazen or silvered 

 arch of a convenient extent, and of a radius equal to ita 



