92 THE LEVER. 



174. Load between Two Supports.// a 



beam rest on two supports, and carry a load be- 

 tween them, the beam may be considered a lever 

 of the second class. The part carried by either support 

 may be found by considering it as the power,, and the 

 other support as the fulcrum. (Fig. 43.) 



FIG. 43. 



175. The Balance. The balance is essentially 

 a lever of the first class, having equal arms. Its 

 use is to determine the relative weights of bodies. Its 

 action depends upon the equality of moments explained in 

 171 and 172. The lever itself is called the beam. 

 From the ends of the beam are suspended two pans, one 

 to carry the weights used, the other to carry the article to 

 be weighed. An index needle, or pointer, is often attached 

 to the beam, and indicates equilibrium, by pointing to the 

 zero of a graduated scale, carried by a fixed support. 



(a.) That the balance may be accurate, the arms must be of the same 

 length. To make these arms exactly equal is far from an easy task. 

 That the balance may be delicate, it must turn upon its axis with 



