154 NATURE STUDY 



column of water vapor rising from below. Oftener, how- 

 ever, the water vapor which makes the clouds above us 

 has travelled a great distance, sometimes in the form of 

 clouds, it is true, but sometimes as invisible water 

 vapor. 



Rain : 



If these clouds encounter a cold wind, more and more 

 of the water is condensed, and the line particles of water 

 dust by the law of cohesion are attracted toward each 

 other. They unite, forming drops, which are drawn down 

 to the ground in the form of rain by attraction of gravi- 

 tation. 



Effects of Rain : 



Directly or indirectly all the inequalities of the sur- 

 face of the earth may be traced back to the action of rain. 

 Hills, slopes, plains, valleys, gorges, ravines, all are due 

 to the action of water, and of water ceaselessly flowing 

 back to the ocean only to be reprecipitated again as rain. 



Rain makes the greater part of the food of all vegeta- 

 tion, and is absolutely essential to both animal and vege- 

 table life. 



Sxow : 



If the water vapor reaches freezing air before conden- 

 sation takes place, then small ice needles, white because 

 they contain air, are formed and are attracted toward 

 each other by a regular rule Avhich results in the forma- 

 tion of many beautiful figures, all of which are built up 

 on the plan of six. 



Vegetation is protected by the blankets of snow which 

 cover the colder parts of the country in the winter. 



