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Common Science 



FIG. 157. Different forms of snowflakes. Each snowflake is a collection of 

 small ice crystals. 



In both cases water evaporates and its vapor mingles 

 with the warm air. The warm air rises and expands. 

 It cools as it expands, and when it gets cool enough the 

 water vapor begins to condense. But if the air as it 

 expands becomes very cold, so cold that the droplets 

 of water freeze as they form and gather together to 

 make delicate crystals of ice, snow is formed. The 

 ice crystals found in snow are always six-sided or six- 

 pointed, because, probably, the water or ice molecules 

 pull from six directions and therefore gather each other 

 together along the six lines of this pull. At any rate, 

 the tiny crystals of frozen water are formed and come 

 floating down to the ground ; and we call them snow- 

 flakes. After the snow melts it goes through the same 

 cycle as the rain, most of it finally getting back to the 

 ocean through rivers, and there, in time, being evapo- 

 rated on.ce more. 



Hail is rain that happens to be caught in a powerful 

 current of rising air as it forms, and is carried up so high 

 that it freezes in the cold, expanding air into little balls 

 of ice, or hail stones, which fall to the ground before 

 they have time to melt. 



Why one side of a mountain range usually has rain- 

 fall. When air that is moving along reaches a mountain 



