GENERAL SCIENCE 



CHAPTER I 



ATMOSPHERIC MOISTURE AND EVAPORATION 



EVAPORATION 



How Moisture Gets into the Atmosphere. Wet thoroughly 

 with water a piece of cheesecloth about two feet square and hang 

 the cloth on a T-shaped stick about three feet long. Balance the 

 stick, on a prism or cylindrical 

 object, such as a piece of crayon 

 or pencil. 



Why is it necessary to re- 

 balance the stick after a minute? 



Where does the water go? 



Why can we not see water 

 which has passed off into the 

 air? 



Evaporation is the chief method of supplying the atmosphere 

 with moisture. A liquid is said to evaporate when it changes 

 into an invisible gas and is absorbed by the atmosphere. If a 

 wet cloth freezes, it will dry on the line as the ice evaporates. 

 That is, the ice will change from a solid directly into a vapor. 

 This process is called sublimation. 



Water evaporates more rapidly in some places than in others. 

 It is estimated that in the course of a year a body of water in 

 Mississippi would be lowered fifty inches by evaporation; in New 



FIG. 1. 



