MECHANICAL PARADOXES. 



If the shorter end be placed in a beaker of 

 water, as at D, the difference of pressures in 

 the two legs is increased from the start, since 

 to the height F E of the column of water, 

 which causes the movement by neutralising 

 part of the atmospheric pressure upwards in the 

 left leg, is to be added the height of the water 

 column G F between the water level in the 

 beaker and the bottom of the right leg. The 

 pressure of this column, transmitted in all 

 directions, presses upwards in the lower end 

 of the right leg, and so its effect is added to 

 that of the atmosphere, which presses upwards 

 in the same way, its pressure now being not 

 direct, but on the surface of the water in the 

 beaker, which transmits it to the tube as well 

 as everywhere else. 



The total moving force, then, is measured 

 by the height of the water column E F, which 

 shows the excess by which the weight of water 

 in the left leg diminishes the upward atmo- 

 spheric pressure in that leg as compared with 

 the corresponding diminution in the right, 

 plus the height of the water column G F, whose 

 pressure is added to the atmospheric pressure 

 in the right leg. The two together make the 

 height G E, between the delivery point and the 

 surface of the water in the beaker. This force 

 obviously lessens as the level in the beaker falls, 

 whereas, when we had to do with water in the 

 tube alone, the moving force went on increasing. 



90 



