MECHANICAL PARADOXES 



For in whichever barrel it stands a little higher 

 it weighs more, since they are of the same 

 diameter. It therefore presses harder on the 

 water near the bottom, and this greater pressure 

 is transmitted across and upwards in the other 

 tube, lifting the water in this latter tube till 

 it is at the same level, and therefore has the 

 same weight, and makes the same pressure, 

 in both. 



But it is not merely the pressure from the 

 water that is transmitted in every direction. On 

 each water-surface there is a weight of nearly 

 fifteen pounds of air, and the pressures from 

 these weights of air are also transmitted, and 

 balance each other. To prove that this is so, 

 it is only necessary to fit pistons into each 

 barrel, above the water. Then if the piston 

 in A be lifted a little, it lifts the weight of air 

 from the water in A, while the equal weight 

 of air still pressing the piston on to the water 

 in B has its pressure transmitted so as to lift 

 up the water in A and make it follow the 

 piston. 



On the other hand, if the piston in A be 

 forced down a little, the extra pressure is trans- 

 mitted down, across, and up, so as to lift the 

 piston in B with the fifteen pounds of air rest- 

 ing upon it. 



If now the tap C be opened, any of these 

 actions upon A will have exactly the same kind 

 of influence upon the five barrels B, D, E, F, 



80 



