44S 72* railing [Book VlT. 



pump A B fhould be entirely under the fur face of the 

 water A A. 



Now if the pifton I is raifed by lowering the extre- 

 mity Y of the lever Y Z X, fo that the lever may 

 affume the podtion y Z , the pifton will rife in the 

 body of the pump, where it will create an imperfect 

 vacuum equal to the diftance X #, and confequently 

 the water beneath will raife the fucker s, and will 

 pafs out of the bafon into the pump. When the 

 pifton is lowered again, this prerTurc caufes the fucker 

 s to clofe, and the fucker S to rife up ; hence the 

 water which was below the pifton is then above it. 

 By a fecond exertion of the pifton, this quantity of 

 water is elevated, and by the fame mechanifm a frefh 

 quantity is permitted to pafs into the pump, and after- 

 wards to rife above the pifton, in the fame manner 

 as the firit portion was raifed ; fo that by a certain 

 number of exertions of the pifton, the railing pipe 

 AT is filled. When this is accomplimed, at every 

 exertion or ftroke of trie pifton there is ejected at the 

 fpout or difcharging pipe T a mafs of water equal 

 to a cylinder, the bafe of which is equal to the width 

 of the pifton, and of a height equal to the fpace 

 through which the pifton pafles in the body of the 

 pump. This fpace is commonly called the play of 

 the pifton. 



It is not difficult to eftimate the weight of the co- 

 lumn of water with which the pifton is charged, when 

 the raifmg pipe is full, and confequently the force 

 which is neceffary to be exerted at Y in order to 

 work the pump. It has been obierved before, that 

 fluids prefs in proportion to their perpendicular height, 

 and the width of the bafe which oppofes their defcent. 

 In a pump, this bafe is the pifton, and the perpendi- 

 cular 



