56 



LIVING IN AN OCEAN OF AIR 



If you had seven bricks piled one upon the other, how 

 will the pressure under the third brick from the top com- 

 pare with the pressure under the bottom brick? Just 



Observe that the matter in the pillows at the bottom of the pile is crowded into a 



smaller space, thus making it denser. In this respect which is more like the 



conditions in the atmosphere, the bricks or the pillows ? 



as seven bricks exert more pressure than three bricks be- 

 cause they have more weight, for that same reason air at 

 the level of the ocean will exert more pressure than air on 

 top of a mountain. We would then expect the pressure 

 at a seaport like New York to be greater than at a moun- 

 tain city like Denver. The pressure at seaport towns is 

 14.7 pounds per square inch, or enough to hold a column of 

 mercury 29.92 inches. It is common practice to regard 

 30 inches for the barometer or 15 pounds per square inch 

 as standard atmospheric pressure at sea level. 



How the Atmos- 



Imile phere Holds Things 



Together. If you lay 

 one square of glass 

 upon a second glass, 

 you can easily pick 

 the first one off from 

 the second. But if 

 you wet the two pieces 

 of glass and place 

 them together, the 



Does the air press down with as much force at Watei> takeS the P laCG 

 the top of this mountain as it does at the bottom ? of the air between the 



4 mile/ 



