OP THE AIR-PIMP. 



213 



3. Set the little glass A B (which is open 

 ends) over the hole i upon the pump-plateZ, L, 

 and put your hand close upon the top of it at 

 B : then upon exhausting the air out of the 

 glass, you will find your hand pressed down 



with a great weight upon it : so that you can hardly re- 

 lease it, until the air be re -admitted into the glass by turn- 

 ing the cock k ; which air, by acting as strongly up- 

 ward against the hand as the external air acted in 

 pressing it downward, will release the hand from its 

 confinement. 



4. Having tied a piece of wet bladder b 

 over the open top of the glass A (which is 

 also open at bottom) set it to dry, and then 

 the bladder will be tight like a drum. Then 



place the open end A upon the pump -plate, over the 

 hole i, and begin to exhaust the air out of the glass 

 As the air is exhausting, its spring in the glass will bt 

 weakened, and give way to the pressure of the outward 

 air on the bladder, which, as it is pressed down, will 

 put on a spherical concave figure, which will grow 

 deeper and deeper, until the strength of the bladder be 

 overcome by the weight of the air ; and then it will 

 break with a report as loud as that of a gun. If a flat 

 piece of glass be laid upon the open top of this receiver, 

 and joined to it by a flat ring of wet leather between 

 them ; upon pumping the air out of the receiver, the 

 pressure of the outward air upon the flat glass wiH 

 break it all to pieces. 



5. Immerse the neck c d of the hollow 

 glass ball e b in water, contained in the 

 phial a a ; then set it upon the pump- 

 plate, and cover it and the hole i with 

 fhe close receiver A ; and then begin to 

 pump out the air. As the air goes out 

 of the receiver by its spring, it will also 



by the same means go out of the hollow ball e b, througK 

 the neck d c , and rise up in bubbles to the surface of 



