78 



WELLS'S NATURAL PHILOSOPHY. 

 Fig. 49. 



Until quite recently, the muskets placed in the hands of soldiers were usu- 

 ally aimed so that the line of sight was parallel to the barrel, and directed to 

 the object, as in Fig 49. So long as the range of the musket was of limited 

 extent, and great precision was not expected, the deviation of the ball from 

 a straight line was not taken into account ; but with the introduction of rifles 

 throwing a ball to a great distance, the drop of the ball occasioned by the 

 curvature of the path of the projectile, was found to deprive the weapon of 

 the necessary precision. On all modem guns, therefore, a double sight is 

 provided, by which the elevation necessary to secure accurate aim can always 

 be given to the barrel This is exhibited in Fig. 50, where one of the sights, 

 B, is fixed, in the usual manner, at one extremity of the barrel, while the 

 other is located nearer the breach. This last sight is often graduated and 

 provided with an adjustment, by which it can be adapted to objects at dif- 

 ferent distances, so as to hit them exactly. 



Fig. 50. 



What is Cir- 

 cular Motion? 



163. 

 duced 

 central point. 



164. 



Circular Motion is the motion pro- 

 by the revolution of a body about a 



Hoir if Circn. 

 lar Motion pro- 

 duced} 



Circular Motion is a species of com- 

 pound motion, and is caused by the continued 

 operation of two forces ; — one the force of 

 projection, which gives the body motion, tends to cause 

 it to move in a straight line ; while the other is continually 

 deflecting it from a straight course toward a fixed point. 



ninstrate the '^^ ^^^^ ^^ illustrated by the common sling, or by swinging 



production of a heavy body attached to a string round the head. The body, 

 in this case, moves through the influence of two forces, the 

 force of projection, and the string which confines it to the 

 hand. These two forces act at right angles to one another, and according to 



Circular 

 tion. 



