40 DISCUSSIONS IN CLIMATOLOGY. 



then fall as snow. But Professor Newcomb actually 

 states that he cannot accept the conclusion that this 

 would lead to more snow. 



Influence of a Snow-covered Surface. — I have argued 

 that this accumulation of snow would lower the sum- 

 mer temperature, and tend to prevent the disappearance 

 of the snow, and have assigned three reasons for this 

 conclusion: — 



First. — Direct radiation. The snow, for physical 

 reasons well known, will cool the air more rapidly than 

 the sun's rays will heat it. This is shown from the fact 

 that in Greenland a snow and ice-covered country, a 

 thermometer exposed to the direct radiation of the sun 

 has been observed to stand above 100°, while the air 

 surrounding the instrument was actually 12° below the 

 freezing point. Professor Newcomb and also Mr. Hill* 

 regard the idea that this could in any way favour the 

 accumulation of snow as absurd. They think that in 

 fact it would have directly the opposite effect. They 

 have perceived only one-half of the result. It is quite 

 true, as they affirm, that the cooling of the air by the 

 snow will not prevent the melting of the snow, but the 

 reverse. There is, however, another and far more im- 

 portant result overlooked in their objection. If the 

 snow and ice-covered surface keeps the temperature of 

 the air, in summer, below the freezing-point, which it evi- 

 dently does in Greenland and in the Antarctic continent, 

 the moisture of the air will fall as snow and not as rain. 

 No doubt this is the chief reason why in those regions, 

 even in the middle of summer, rain seldom falls, the 

 precipitation being almost always in the form of snow, 

 although at that very season the direct heat of the sun 

 is often as great as in India. Were the snow and icy 



* "Geological Magazine" for January, 1880, p. 12, 



