On the Prtnv'iplcs of Pump-Jj'urk. ?()7 



in A(y" or IS Inches per second, if a lever be worked with 

 its natural motion. But in the descent of tlic piston no 

 water is raised ; therefore only IS inches of water is raised 

 bv one piston in two seconds, or the water raised in a sinole 

 pimip is not more than nine inclics per second, which is' 

 about 3*6 gallons, or 2lG per minute, whicli is short of a 

 ton by 36 gallons, 



64. But if the pump be so constructed with two pistons, 

 that while one descends, the other ascends, the water will, 

 in that case, always keep risino- in the pipe; and the water 

 delivered by such a pump would be 1 8 inches per second, 

 or 432 gallons, or 1| ton per minute. 



63. Such would be the state of pump-work in its utmost 

 perfection if men could act like a ueiglit, viz. always with 

 the same tenor of force ; but though the force of two men 

 may be equivalent to t'OOlb. for a few efforts at first work- 

 ing, yet this human force will soon abate and decrease, and 

 it IS found by experience, that Ibr working a pump without 

 ceasing but 10 or 1 j minutes, one man can raise no more 

 than about 30 lb. of water to his share ; therefore six men, 

 at least, must be employed for raising the above-mentioned 

 tpiantity of 43'2 gallons of water per minute. 



QG. But such perfection is not to be expected in common 

 pumps, for two reasons : first, they are subject to great 

 friction between the piston and pipe, and other parts of the 

 mechanism; and this is scarce ever so little as a third part 

 o[ the charge of the whole machine, and therefore will re- 

 quire nine or ten men to raise that quantity of water instead 

 of six. 



67. But, secondly, the great imperfection of all common 

 pumps working with a single piston is, that the water risci 

 ptr vicetrr, or by fits ; for while the piston is descending, 

 the watery coknnn AG is quiescent, and only moves when 

 ttie piston rises ; therefore every tiuic the stroke is repeated, 

 a new or additi(^nal force is required to give motion to the 

 water, over and above, what is necessary to continue that 

 motion when produced. 



68. Again, thirdly, the motion of the water by a single 

 piston can never he equable. For suppose the jet B VV 

 (fig. 5.) was produced by the pressure of the atmospl)ere or 

 weight of the water BD (in lig. a.), then the velocity of 

 the jet at the fir=t instant will be as \^BD — ^/BT{, and 

 Ihc jet will thereby rise to V. 



n<J. But the velocity of the jet nuist increase bv the con- 

 ti'Hic-d pressiu-c of the colunm KD, and at last will be as 



v/KD, and thereby produce the uniform jet BW. Ami 

 3 suuiclijino; 



