MILITARY PROJECTILES. 



541 



the path of a projectile, through a resisting medium like 

 the air. The practice of gunnery, therefore, depends al- 

 most entirely upon the skill which the gunner acquires 

 by repeated trials. Some experiments have, however, 

 given important and useful results. The following table 

 presents the reader with the comparative effects produc- 

 ed by different charges, and different degrees of eleva- 

 tion. The ball used was of one pound weight. 



By this tabla it appears that with two ounces of pow- 

 der, the ball moved with a velocity of 860 feet per second, 

 whereas with twelve ounces, which is six times as much 

 powder, it moved only 1680, or about twice as fast. 

 With the two ounces, its range, or the distance to which 

 it went was 4100 feet, and with six times as much pow- 

 der, only 6700, which is not nearly twice as far. The 

 reason is, that with great velocities the resistance increases 

 very rapidly. The resistance is as the square of the 

 velocity, as it is mathematically expressed ; that is, doub- 

 ling the velocity, the resistance is increased fourfold ; and 

 three times the velocity, gives nine times the resistance. 

 Indeed it can be proved that with a certain velocity, 

 which can without much difficulty be given, a ball, will 

 move on so fast that the air will not close over it instant- 

 ly, but there will be a vacuum behind it. In this case 

 the ball will be resisted at the rate of fifteen pounds to 

 the square inch, which would make in a ball, four inches 

 in diameter, bctioecn 150 and 200 pounds. Such a load 

 as this must soon stop any ball ; and it is found that 

 whenever a ball is thrown with such a velocity, it almost 

 instantly becomes retarded, until it is reduced to a much 

 smaller velocity, so that the resistance will be less. 



Various instruments have been devised for measuring 



