44

H Y D R A U L I C S.

The Effect of the Common Pum p isfrom the fame Principle: For the Bucketor Sucker, raising a Column of Waterabove it in the Barrel, makes a vacuousSpace, or greatly attenuates the Air in theBarrel and Pipe below it; whence theWater must necessarily rife in the Pipe, bythe superior Pressure of the Air on the Sur-face of that in the Well. The Waterascending in the Pipe, passes through theValve in the Bottom of the Barrel, whichshutting upon the Depression of the Suc-ker, the Water is thereby forced throughthe Valve of the Sucker into the Cisternof the Pump, and discharged through theSpout. All which is clearly sliewn by theModel of a Pump in Glass (LXXVIII.)

HI-

only put a Syphon, while working, under the Receiveran Air-Pump ; for upon exhausting all the Air, th 5Syphon will cease running.

1. Or if the Syphon be equicrural, or has both th e fLegs of an equal Length, the Water will not run thr°it, because the Force of Water against the Air at eadjOrifice is equal. The fame Thing will be effectswith a Syphon of unequal Legs, though the shorterbe immersed in Water, if the Syphon be so inclist^that the Orifice of both Legs be on the fame horizo^tal Level. I need not after this give the Reason vvh/the Water will not run out of the shorter Leg, iflongest be placed in the Water. ,

(LXXVIII.) i. I shall here give the Theory 0Pump-Wori , and the Structure of such Pumps asfound to be most useful for the various Purposes ofThe Theory depends in a great Measure upon th° ®