46 



LIVING IN AN OCEAN OF AIR 



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there is no air. Air is found in water, as can easily be 

 shown by bringing a glass flask of water nearly " to a 

 boil." Bubbles of air will be seen to form on the inside 



of the flask. Air is also 

 found in the soil, as can 

 be seen by packing a 

 tumbler about half full 

 of soil and then adding 

 water. Notice what hap- 

 pens when the water 

 soaks into the soil. We 

 can easily show that air 

 fills the space in a vessel 

 we call "empty." The 

 simplest experiment is to 

 push an inverted glass 

 into a vessel of water and 

 see if anything keeps the 

 water from filling the 

 glass. A more interesting 

 way of showing the same 

 principle is used in the 

 demonstration on page 45. 



How our atmosphere tapers off. It is 30 Xhe Atmosphere Ex- 



times as dense at sea level as it is 15 ^ rm 



miles above. erts Pressure. The 



atmosphere is the entire 



body of air which surrounds the earth; the term "air" 

 is commonly used when we refer to any small part of 

 the atmosphere. Since the atmosphere gets thinner and 

 thinner as one rises in it, a cubic foot of space at the 

 earth's surface must have more air in it than a cubic 

 foot of space several miles above the surface. While 

 some people say that the air reaches a distance of 200 miles 

 or more above the earth, about half of it is below the tops 

 of mountains 3^ miles high. But wherever we are, the 



Sea level 



