126 



FIRST YEAR SCIENCE 



surface .from which it came, but a considerable part of it 

 is carried by the winds to other places and falls upon the 

 land surface, furnishing the moisture needed for the land 

 life of the world. 



62. Humidity. The condition of the air as regards the 

 moisture it holds is called its humidity. If the air contains 

 all the moisture it can hold, it is said to be saturated or to 



CUMULUS CLOUDS. 

 Typical low level clouds, indicating showers. 



have reached its dew point. The amount of vapor present 

 in the air is called its absolute humidity. The amount of 

 vapor in the air divided by the amount that it would con- 

 tain if it were saturated is called the relative humidity. 

 If the air contains much moisture, its humidity is said to 

 be high. When air which has a high humidity is .cooled, 

 it can no longer hold all the moisture which it previously 

 held, and this moisture will be deposited. 



