

176 PKESSURE UPON THE BASE OF VESSELS. 



A weight of 40^ being placed in the scale-pan, water is 

 poured cautiously into the vessel, up to the mark. With 

 proper care no water will escape. The weight of 40 gr 

 in the scale-pan on the right hand balances the pressure 

 of the water upon the base of the vessel ; but if a very 

 small quantity of water be added, the plate which re- 

 presents the base will be pressed downwards by the 

 additional weight, and the water will escape. The 

 pressure of 40 gr of water upon the base is hence not 

 less than 40 gr . In consequence of the escape of water, 

 drops will attach themselves to the plate and the other 

 portions of the apparatus; these must be carefully re- 

 moved before the next experiment is commenced, since 

 they interfere with the correct estimation of the weights 

 which are really employed. 



When the same quantity of water is now poured into 

 vessel 2, which may be fixed in the manner described 

 further on, it will be found that 40^ of water do not in 

 this case exert a pressure of 40 gr upon the base of the 

 vessel. The pressure is less, for a quantity of water 

 may be added considerably exceeding the height of the 

 mark, but the plate is not pressed down, and no water 

 escapes. This will not happen until the height of the 

 water in vessel 2 is exactly the same as that which 

 it had in vessel 1, when the water commenced to 

 escape. This shows, not only that the pressure upon 

 the base of a vessel which gradually widens from the 1 

 base towards the top is less than the weight of the con- 

 tained liquid, but also that the pressure is the same as 

 that upon the basd of a vessel with perpendicular sides, 

 when the area of the base and the height of the liquid 

 are equal in both vessels. W r hen vessel 3 is used, the 





