PNEUMATICS. 141 



pipe from the pump, and set its end A into a basin 

 of water, and turn the cock e to open the pipe; 

 on which, as there is no air in the receiver, the 

 pressure of the atmosphere on the water in the 

 basin will drive the water forcibly through the 

 pipe, and make it play up in a jet to the top of the 

 receiver. 



7. Set a square phial upon the pump-plate, and 

 having covered it with a wire cage, put a close re- 

 ceiver over it, and exhaust the air out of the re- 

 ceiver; at the same time, the air will also make its 

 way out of the phial, through a small valve in its 

 neck. When the air is exhausted, turn the cock 

 below the plate to re-admit the air into the re- 

 ceiver; and as it cannot get into the phial again, 

 because of the valve, the phial will be broken into 

 pieces by the pressure of the air upon it. Had 

 the phial been of a round form, it would have sus- 

 tained this pressure like an arch, without breaking; 

 but as its sides are flat, it cannot. 



8. To show the elasticity or spring of the air : tie 

 up a very small quantity of air in a bladder, and 

 put it under the receiver ; then exhaust the air out 

 of the receiver; and the air which is confined in 

 the bladder (having nothing to act against it) will 

 expand by the force of its spring, so as to fill the 

 bladder completely : but upon letting the air into 

 the receiver again, it will overpower that in the 

 bladder, and press its sides close together. 



9. If the bladder so tied up be put into a wooden 

 box, and have 20 or 30 pounds weight of lead 

 placed upon it, and the box be covered with a 

 close receiver; upon exhausting the air out of the 

 receiver, that which is confined in the bladder will 

 expand itself so as to raise up all the lead by the 

 force of its spring. 



