234 WEATHER AND CLIMATE 



in an open space away from all trees and buildings and 

 after each rain the amount collected is measured. Snow 

 is melted before it is measured. As a rule eight or ten 

 inches of snow make an inch of rain. 



If the temperature is below the freezing point, 32 F., 

 when condensation takes place, the moisture of the air 

 will form into a wonderful variety of beautiful six-rayed 

 crystals. These gather into feathery snowflakes, which 

 float downward through the air and often cover the ground 

 with thick layers of snow. Although snow is itself cold, yet 

 it keeps in the heat of the ground which it covers, so that 



in cold regions soil 

 which is snow-covered 

 does not freeze as deeply 

 as that without snow. 

 Therefore, to keep water 

 pipes from freezing, it is 



MAGNIFIED SNOW CRYSTALS 



not necessary to bury 



them as deeply in localities where snow is abundant as in 

 places equally cold where snow seldom falls. 



If raindrops become frozen into little balls in their passage 

 through the air, they fall as hail. Hail usually occurs in 

 summer and is probably caused by ascending currents of 

 air carrying the raindrops to such a height that they are 

 frozen and often mixed with snow before they fall. Some- 

 times hailstones are more than a half inch in diameter. 

 They occasionally do great damage to crops and to the glass 

 in buildings. 



Sleet is a mixture of snow and rain. 



Rainfall of the United States. An examination of a 

 rainfall map of the United States will show that the 



