VAPOR. 69 



pp> 



157. RELATIONS OF AIR AND VAPOR. 



Does vapor rp^ Q earth is surrounded by air to the 



displace air ? 



depth of fifty miles. It is also surrounded 

 by vapor occupying the same space which the air oc- 

 cupies. But they are independent of each other. 

 Each contracts for itself, and expands for itself, accord- 

 ing to the temperature. When more vapor is produced 

 by evaporation from the sea, or other sources, it rises 

 into the air without displacing it or pushing it aside, 

 only rendering the vapor which it before contained 

 more dense. 



158. QUANTITY OF VAPOR IN THE AT- 

 ^ vapor M S P HERE - The air is always full of va- 

 in the por ; that is, where there is a cubic inch 



of air, there is a cubic inch of vapor with 

 it, occupying the same space. 



Upon what 159 ' QUANTITY OF WATER THE AIR MAY 



does the quan- CONTAIN AS VAPOR. The quantity of wa- 



tity of water . , * . . 



in the air de- ter present in the air, in the form of trans- 

 P end? parent vapor, depends on the density of the 



vapor, and this differs, as has been shown, according to 

 heat and the abundance of water. In summer, and 

 over the sea, it is commonly most dense. At a me- 

 dium summer temperature of 75 degrees, the vapor in 

 the air is sometimes so dense that every cubic yard of 

 air contains a cubic inch of water, in this form. But 

 it can never at this temperature contain more. It is 

 then said to be " saturated," and also that its capacity 

 for water is filled. 



