IMPOKTANCE OF SNOW. 207 



and important influence on the atmosphere by diminishing its 

 humidity.* How fai* similar results woidd be obtained by ex- 

 periments continued through the year can only be conjectured, 

 but it is certain that the action of snow upon the atmosphere, 

 even in om* chmate, is an element of great meteorological im- 

 portance. Whenever the humidity of the atmosphere in contact 

 with snow is above the point of satm*ation at the temperature to 

 wliich the air is cooled by such contact, the superfluous moisture 

 is absorbed by the snow or condensed and frozen upon its sur- 

 face, and of com-se adds so much to the winter supply of water 

 received from the snow by the ground. This quantity, in all 

 probabihty, much exceeds the loss by evaporation, for during the 

 period when the ground is covered with snow, the proportion of 

 clear, dry weather favorable to evaporation is less than that of 

 humid days with an atmosphere in a condition to yield up its 

 moisture to any bibulous substance cold enough to condense it.f 

 The cloud which so often caps snowy Alpine peaks is usually 

 due to the condensation of atmospheric humidity by the snow, 

 rather than to vapor borne up from below. The snow is at all 

 times either giving off moisture by evaporation, or condensing 

 and absorbing it. Thus the water of precipitation, which, if 

 deHvered by the cloud in the form of rain, would run off or be 

 absorbed by the earth, when it takes the form of snow is saved 

 and returned again to the atmosphere. 



In our Northern States, irregular as is the climate, the first 

 autumnal snows pretty constantly fall before the ground is frozen 

 at all, or when the frost extends at most to the depth of only a 

 few inches.:}: In the woods, especially those situated upon the 



* The condensation of moisture is also an important agent in the conversion 

 of flocculent snow into neve. The heat disengaged in condensation partially 

 melts the flakes, and, in freezing again, they contract and assume the globular 

 form which characterizes neve. 



f The hard snow-crust, which in the early spring is a source of such keen 

 enjoyment to the children and youth of the North — and to many older persons 

 in whom the love of nature has kept awake a relish for the simple pleasures 

 of rural life — is doul»tless due to the congelation of the vapor condensed by 

 the snow rather than to the thawing and freezing of the superficial stratum ; 

 for when the surface is melted by the sun, the water is taken up by the ab- 

 sorbent mass beneath before the temperature falls low enough to freeze it. 



J The hard autumnal frosts are usually preceded by heavy rains which 



