330 ON THE CONSERVATION OF FORCE. 



is precisely similar. Let a b. Fig. 40, be a simple lever, 

 supported at c, the arm c b being four times as long as the 

 other arm a c. Let a weight of one pound be hung at 6, 

 and a weight of four pounds at a, the lever is then in equi- 

 librium, and the least pressure of the finger is sufficient, 

 without any appreciable exertion of force, to place it in 

 the position a' b\ in which the heavy weight of four 

 pounds has been raised, while the one-pound weight has 

 sunk. But here, also, you will observe no work has 

 been gained, for while the heavy weight has been raised 



Fig. 40. 



through one inch, the lighter one has fallen through 

 four inches ; and four pounds through one inch is, as work, 

 equivalent to the product of one pound through four 

 inches. 



Most other fixed parts of machines may be regarded as 

 modified and compound levers ; a toothed-wheel, for in- 

 stance as a series of levers, the ends of which are repre- 

 sented by the individual teeth, and one after the other of 

 which is put in activity, in the degree in which the 

 tooth in question seizes, or is seized by the adjacent 

 pinion. Take, for instance, the crabwinch, represented in 

 Fig. 41. Suppose the pinion on the axis of the barrel of 



