HYDROSTATICS. 



123 



(a.) Pascal contrived a neat experiment to verify this principle. 

 The apparatus consists of a wooden support carrying a ring into 

 which may be screwed any one of three vessels, one cylindrical, one 

 widening upward and one narrowing upward, straight or bent. On 

 the lower side of the ring is a plate a, supported by a thread from 



FIG. 73. 



one end of an ordinary balance. The other end of the balance 

 carries a scale-pan. Weights in the scale-pan hold the plate a, 

 against the ring with a certain force. Water is carefully poured 

 into M until the pressure forces off the plate and allows a little 

 of the water to escape. A rod o marks the level of the liquid 

 when this takes place. Repeating the experiment with the same 

 weights in the scale-pan, and either P or Q in the place of M, 

 the plate will be detached when the water has reached the same 

 height although the quantity of water is much less. 



226. Rule for Downward Pressure. When 

 the cylindrical vessel, mentioned in the last paragraph, is 

 filled, it is evident that the downward pressure is equal to 

 the weight of the contained liquid. It is further evident 



