288 PRESSURE IN THE AIR, 



of elevation: instead of swelling and dilating, 

 it is found, in the descent, to contract and col- 

 lapse into a smaller volume. There can be no 

 doubt that the condensation? which has thu& 

 taken place, has been produced by the pres- 

 sure of the external air, having overcome the 

 resistance of the rarified air, which the bladder 

 contained, 



2. In like manner, if two hollow hemispheres^ 

 whose cavity is equal to one cubic foot, after 

 having had the air which they contained, ex- 

 hausted out of them, had the same quantity of 

 this rarified air introduced within them ; it is 

 very obvious that the external air would press 

 against the hemispheres, as it did against the 

 bladder, and keep them together in close COG^ 

 tact. 



3. If this rarified air were introduced within 

 an exhausted receiver, to which the external 

 air could not obtain access, it is very clear that 

 the external pressure of the air must fix the re- 

 ceiver to the pump-plate. 



4. That if this rarified air were introduced 

 into an exhausted cylinder, covered over with 

 a bladder ; that the bladder would be pressed 

 upon by the external air, and depressed into 

 the cylinder. 



5. That if this rarified air Were introduced 

 into an exhausted tube, which was placed upon 

 any fluid whatever, whether water or mercury, 



