52 ELEMENTS OF SCIENCE 



order (I. Fig. 8) is one where the force or effort acts on 

 one side of the fulcrum, while the resistance is on the 

 other. 



A lever of the second order is one where both forces 

 are on the same side of the fulcrum, while the point 

 of resistance is placed between the fulcrum and the 

 effort. (II. Fig. 8). 



A lever of the third order (III. Fig. 8) is one where 

 the two forces are also both on one and the same side 

 of the fulcrum, but the effort acts between the fulcrum 

 and the point of resistance. 



FIG. 9. One of the most useful 



applications of the principle 

 of the lever is that employed 

 in thebalance, which is a lever 

 of the first order, called the 

 beam, suspended at its centre 

 and with its two arms conse- 

 quently equal. 



In the pulley, we have an 

 example of the transmission 

 of force through a cord con- 

 sidered as perfectly flexible 

 free from all friction, and 

 inextensible. 



Thus the resistance of a weight suspended at one end 

 of a cord, may be perfectly balanced by a force (such as a 

 sufficient grasp of a hand) applied at the other end of a 

 cord which has been passed over a hook and through a 

 ring (A, Fig. 9). 



Such forces must always be what is called divergent, 

 or opposed to each other, and by such an arrangement 

 the direction in which a force acts may be changed 

 without modifying its intensity, the cord being supposed 



