OF THE AIR-PUMP. 217 



pour some quicksilver into the cup, and exhaust the 

 receiver of air, and the pressure of the outward air, on 

 the surface of the quicksilver, will force it through the 

 pores of the hazel, from whence it will descend in a 

 beautiful shower into a glass cup placed under the re- 

 ceiver to catch it. 



9. Put a wire through the collar of leathers in the top 

 of the receiver, and fix a bit of dry wood on the end of 

 the wire within the receiver ; then exhaust the air, and 

 push the wire down, so as to immerse the wood into a 

 jar of quicksilver on the pump-plate ; this done, let in 

 the air, and, upon taking the wood out of the jar, and 

 splitting it, its pores will be found full of quicksilver, 

 which the force of the air, upon being let into tlu 

 receiver, drove into the wood. 



10. Join the two brass hemispherical cups 

 A and B together, with a wet leather between 

 them, having a hole in the middle of it ; then 

 screw the end D of the pipe C D in the plate 

 of the pump at i, and turn the cock E, so as 

 the pipe may be open all the way into the 

 cavity of the hemispheres : then exhaust the 

 air out of them, and turn the cock a quarter 

 round, which will shut the pipe C D, and 

 keep out tlie air. This done, unscrew the 

 pipe at D from the pump ; and screw the 



piece Fh upon it at D ; and let two strong men try to 

 pull the hemispheres asunder by the rings g and h, 

 which they will find it hard to do : for if the diameter of 

 the hemispheres be four inches, they will be pressed to- 

 gether by the external air with a force equal to 190 

 pounds. And to shew that it is the pressure of the air 

 that keeps them together, hang them by either of the 

 rings upon the hook P of the wire in the receiver M 

 (page 207,) and upon exhausting the air out of the re- 

 ceiver, they will fall asunder of themselves. 



11. Place a small receiver (page 207) near the hole 



