OF THE AIR-PUMP. 



221 



20. Pour some quicksilver into the small 

 bottle A, and screw the brass collar c of the 

 tube B C into the brass neck b of the bottle, 

 and the lower end of the tube will be immersed 

 into the quicksilver, so that the air above the 

 quicksilver in the bottle will be confined 

 there, because it cannot get out about the 

 joinings, nor can it be drawn out through the 

 quicksilver into the tube. This tube is also 

 open at top, and is to be covered with the 

 receiver G and large tube E F, which tube 

 is fixed by brass collars to the receiver, and 

 is close at the top. This preparation being 

 made, exhaust the air both out of the re- 

 ceiver and its tube ; and the air will, by the 

 same means, be exhausted out of the inner 



tube B C, through its open top at C ; and as the re- 

 ceiver and tubes are exhausting, the air that is confined 

 in the glass bottle A will press so by its spring upon 

 the surface of the quicksilver, as to force it up in the 

 inner tube as high as it was raised in the ninth experi- 

 ment by the pressure of the atmosphere : which demon- 

 strates that the spring of the air is equivalent to its 

 weight. 



21. Screw the end C of the 

 pipe C D into the hole of the 

 pump-plate, and turn all the 

 three cocks d, G, and H, so as 

 to open the communications be- 

 tween all the three pipes E, F, 

 D C, and the hollow trunk A B. 

 Then, cover the plates g and h 

 with wet leathers, .which have 

 holes in their middle where the 



pipes open into the plates : and place the close receiver 

 / upon the plate g : this done, shut the pipe F by turn- 

 ing the cock H, and exhaust the air out of the receiver 



LECT 

 VI 



