A PUZZLE EXPLAINED. 



203 



the tube, B, be now filled to an equal height, the same 

 force will be exerted against the other side. To prove 

 this, let the stop-cock be opened, when the two columns 

 of water will remain at an exact level. 



If enough water be now poured into the tube, B, to fill 

 it to the top, it will immediately settle down on a level 

 with the water in A, raising the whole surface in the lat- 

 ter. This result has seemed strange to many, who can 

 not conceive how a small column of water can be made to 

 balance a large one, and it has been therefore termed the 

 Hydrostatic Paradox. But the difficulty entirely vanish- 

 es, and ceases to appear a paradox, when we remember 

 that the water in the larger vessel rises as much more 

 slowly than it descends in the smaller, as the large one 

 exceeds the smaller ; thus acting on the principle of vir- 

 tual velocities in precisely the same manner that a heavy 

 weight on the short end of a lever is upheld by a small 

 weight on the long end. The great mass of water is sup- 

 ported directly by the bottom of A, in the same way that 

 nearly all the weight on the lever is supported by the 

 fulcrum. A man who was seeking a solu- 

 tion to the absurd mechanical problem of 

 perpetual motion, and who supposed that 

 the large mass in A would overbalance the 

 small column in B, and drive it upward, 

 constructed a vessel in the form shown in 

 fig. 230, so that the small column, when 

 forced upward, would flow back into the 

 larger vessel perpetually. He was, how- 

 ever, greatly surprised to sec the fluid in 

 both divisions settle at the same level. 



This principle may bo further explained by the following 

 experiment : A B (fig.231) represents the inside of a metallic 

 vessel, with a bottom, C, which slides up and down, water- 

 tight. If water be poured in to fill the lower or larger 

 part only, it will be found to press on the sliding bottom 



Attempted Perpetual 

 Motion. 



