ON THE CONSERVATION OP FORCE. 



831 



the winch has twelve teeth, and the toothed-wheel, H H, 

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

 former. The winch must now be tm-ned 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 



Fig. 41. 



time, though to be sure only one-sixth of the exertion, 

 which he would have to use if the handle were directly 

 applied to the barrel, D. In all these machines, and parts 

 of machines, we find it confirmed that in proportion as 

 the velocity of the motion increases its power diminishes, 

 and that wlien the power increases tlie velocity diminishes, 

 but that the amount of work is never thereby increased. 



In the overshot mill-wheel, described above, water acts 

 by its weight. But there is another form of mill-wheels, 



