134 



FERGUSON'S LECTURES. 



plunger is raised to its 

 greatest height. Therefore, 

 as the water between the 

 plunger g and box H can 

 neither get through the plun- 

 ger upon its descent, nor 

 back again into the lower 

 part of the pump Le, but 

 has a free passage by the 

 cavity around H into the pipe 

 M" M, which opens into the 

 air-vessel K K at P ; the 

 water is forced through the 

 pipe M M by the descent of 

 the plunger, and driven into 

 the air-vessel ; and in run- 

 ning up through the pipe at 

 P, it opens the valve a ; 

 which shuts at the moment 

 the plunger begins to be 

 raised, because the action o^ 

 the water against the under 

 side of the valve then ceases. 



The water, being thus forced into the air-vessel K K 

 by repeated strokes of the plunger, gets above the lower 

 end of the pipe G HI, and then begins to condense the 

 air in the vessel K K. For, as the pipe G // is fixed 

 air-tight into the vessel below F, and the air has no way 

 to get out of the vessel but through the mouth of the 

 pipe at 7, and cannot get out when the mouth / is co- 

 vered with water, and is more and more condensed as 

 the water rises upon the pipe, the air then begins to act 

 forcibly by its spring against the surface of the water at 

 H : and this action drives the water up through the 

 pipe I H G F, from whence it spouts in a jet & to a 

 great height ; and is supplied by alternately raising and 

 depresssing of the plunger g, which constantly forces 



