ON THE CONSERVATION OF FORCE. 



289 



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 instance as 

 a series of levers, the ends of which are represented by the in- 

 dividual teeth, and one after the other of which is put inactivity 

 in the degree in which the tooth in question seizes or is seized 



FIG. 41. 



by the adjacent pinion. Take, for instance, the crabwinch, re- 

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

 of the winch has twelve teeth, and the toothed-wheel, HH, 

 seventy-two teeth, that is six times as many as the former. The 

 winch must now be turned round six times before the toothed- 

 wheel, H, and the barrel, D, have made one turn, and before the 

 rope which raises the load has been lifted by a length equal to 

 the circumference of the barrel. The workman thus requires 

 six times the time, though to be sure only one-sixth of the exer- 

 i. u 



