PNEUMATICS. 261 



r brium with the pressure of the atmosphere = h ; 

 the height to which the water is raised by the first 



stroke, is a+6+*-V(a + + A)--A6* . 



x2 



BOSSUT, Hydrodyn. vol. i. p. 101. 



353. The same notation being retained, and c 

 being put for a -J- b, or the greatest height to 

 which the piston ascends, b must be greater than 



c 2 



7, otherwise the water will not rise above the 

 4f ti 



piston. 



The water will cease to rise, when the air in the bar- 

 rel of the pump, which is always rarer the higher 

 the water is raised, becomes so rare, that when the 

 piston is thrust down, it is not so much condensed 

 as, by its elasticity, to open the valve in the pis- 

 "ton, or, which is the same, is not so dense as the 

 external air. This leads to the limit just as- 

 signed. 



Besides the pump just described, there is one with a 

 solid piston, without any valve, by the raising of 

 which, the water is drawn up through the valve in 

 the bottom of the pump, and on thrusting down 

 the piston, the water is forced through a pipe in 

 the side, having a valve that opens outwards, by 

 which means it can be raised to any height, if a suf- 

 ficient 



