OX THE CONSERVATION OF FORCE. 



285 



the mouth begins to incline downwards, it flows out. The 

 buckets on the circumference are filled on the side turned to 

 the observer, and empty on the other side. Thus the former 

 are weighted by the water contained in them, the latter not ; the 

 weight of the water acts continuously on only one side of the 

 wheel, draws this down, and thereby turns the wheel ; the other 



side of the wheel offers no resistance, for it contains no water. 

 It is thus the weight of the falling water which turns the wheel, 

 and furnishes the motive power. But you will at once see that 

 the mass of water which turns the wheel must necessarily fall 

 in order to do so, and that though, when it has reached the 

 bottom, it has lost none of its gravity, it is no longer in a 



