MECHANICS AND PHYSICS 



191 



" If we take a rectilinear lever divided by a fulcrum 

 into two unequal arms to the ends of which two 

 unequal masses hang ; when the lever turns round its 

 fulcrum, the two weights will move with different 

 velocities, the one which is farthest from the fulcrum 

 will describe in a given time a greater arc than the one 

 which is nearest to it ; the velocities with which the 

 two weights move have the same ratio to each other 

 as the lengths of the arms of the lever. 



When, therefore, we wish to compare the forces of 



Fig. 31. 



the two weights, we must find, for each of them, the 

 product of the weight by the length of the arm of the 

 lever ; that one which corresponds to the greater pro- 

 duct will outweigh the other ; and if the two products 

 are equal, the two weights will remain in equilibrium." * 

 By an intuition of genius, Aristotle extended to 

 other mechanisms his theory of the lever; he shows 

 that the various operations of these mechanisms can 

 be explained merely by considering the velocities with 

 which certain circular arcs are described ; hence he 

 1 11 Duhem, Origines, I, p. 7. 



