ATMOSPHERIC PRESSURE 



131 



is thoroughly moistened. Then invert the tumbler. 

 The water does no.t run out because the pressure of the 



A B 



FIG. 46. The pasteboard does not fall off from the tumbler 

 because the pressure of the air on the outside of it is greater 

 than that of the water in the tumbler. In A } the air presses from 

 below ; in B, from the side. 



air outside of the pasteboard is at least equal to the 

 downward pressure of the water in the tumbler. 



If the tumbler is held so 

 that the mouth faces side- 

 wise, the water does not run 

 out, because the air also 

 presses upon the pasteboard 

 from the sides. 



Tie a piece of sheet rub- 

 ber over the large end of a 

 bell jar. Now exhaust the 

 air from the belljar by 

 means of an air pump. As !M a & i\ he we ' sht f 



FIG. 47. when air is 



pumped from the glass jar, 



