Of the Air-Pump. 115

5 . Immerse the neck cd of the hollow glafs ball eb in water, con- Fig. 7 .tained in the phial aa-, then set it upon the pump-plate, and cover it

and the hole i with the dose receiver A ; and then begin to pumpout the air. As the air goes out of the receiver by its spring, it willalso by the fame means go out of the hollow ball eb, through theneck dc t and rife up in bubbles to the surface of the water in thephial ; from whence it will make its way, with the rest of the air inthe receivety through the air-pipe GG and valves a and b, into theopen air. When it has dbne bubbling in the phial, the ball is sufficient-ly exhausted; and then, r upon turning the cock k, the air will get intothe receiver, and preis so upon the surface of the water in the phial,as to force the water up into the ball in a jet, through the neck c d ;and will 611 the ball almost füll of water. The reafon why the ball isnot quite 611ed, is becaufe all the air could not be taken out of it; andthe fmall quäntity that was lest in, and had expanded itfelf so as tofill the whole ball, is now Condensed into the fame state as the out-Ward air, and remains in a fmall bubble at the top of the ball; andso keeps the water from filling that part of the ball.

6. Pour forne quicksilver into the jar D, and fet it on the pump-plate Fig. s. ,near the hole t ; then fet on the tall open receiver A B, so as to beoverthejar and hole;'and cover the receiver with the brass piate C.

Screw the open glafs tube fg (which has a brass top on it at h) intothe syringe H, and putting the tube through a hole jn the middle ofthe plate, so as to immerse the lower end of thelübe e in the quick-silver at Z), serew the end h of the syringe into the plate. This done,draw up the piston in the syringe by the ring I, which will makea vacuum in the syringe below the piston; and as the upper end ofthe tube opens into the syringe, the air will be dilated in the tube, be-caufe part of it, by its Ipring, gets up into the syringe ; and the springof the undilated air in the receiver acting upon the surface of the quick-silver in the jar, will force part of it up into the tube: for the quick-silver will follow the piston in the syringe, in the same way, and forthe same reafon, that water follows the piston of a common pumpwhen it is raifed in the pump-barrel; and this, according to some, isdone by suction. But to refute that erroneous notion, let the air bepumped out of the receiver A B, and then all the quicksilver in thetube will fall down by its own weight into the jar; and cannot beagain raifed one hair's breadth in the tube by working the fyringe:which ihews that suction had no hand in raising the quicksilver; and,to prove that it is done by presture, let the air into the receiver by the<ock k (Fig. i.) and its action upon the surface of the quicksilver in the

0^2 jar