in Geological Climatology. 255 
The influence of fogs on the summer temperature is a fact 
so well established by observation that it seems strange that 
anv one should be found arguing against it. 
Heat Evolved by Freezing. — There is one objection to -which 
I may here refer, and which has been urged by nearly all my 
critics. It is said, correctly enough, that as water in freezing 
evolves just as much heat as is required to melt it, there is on 
the whole no actual loss of heat ; that whatever heat may be 
absorbed in the mechanical work of melting the snow, just 
as much was evolved in the formation of the snow. Conse- 
quently it is inferred, in so far as climate is concerned, the 
one effect completely counterbalances the other. This infer- 
ence, sound as it may at first sight appear, has been so well 
proved to be incorrect by Mr. Wallace that I cannot do 
better than quote his words : — 
" In the act of freezing, no doubt water gives up some of 
its heat to the surrounding air, but that air still remains below 
the freezing-point or freezing would not take place. The heat 
liberated by freezing is therefore what may be termed low- 
grade heat — heat incapable of melting snow or ice; while 
the heat absorbed while ice or snow is melting is high-grade 
heat, such as is capable of melting snow and supporting 
vegetable growth. Moreover, the low-grade heat liberated 
in the formation of snow is usually liberated high up in the 
atmosphere, where it may be carried off by winds to more 
southern latitudes : while the heat absorbed in melting the 
surface of snow and ice is absorbed close to the earth, and is 
thus prevented from warming the lower atmosphere, which is 
in contact with vegetation. The two phenomena therefore 
by no means counterbalance or counteract each other, as it is 
so constantlv and superficiallv asserted that thev do " ('Island 
Life." p. 140). 
The Fundamental Misconception. — I come now to a mis- 
apprehension which more than any other has tended to pre- 
vent a proper understanding of the causes which lead to 
the conservation by snow. TVhatever the eccentricity of the 
earth's orbit may be, the heat received from the sun during 
summer is more than sufficient to melt the snow of winter. 
Consequently it is assumed no permanent accumulation of 
snow can take place. This objection, as expressed by Mr. 
Hill, is as follows : — '"' TTe have no reason to suppose that at 
present, in the northern hemisphere, more snow or ice is any- 
where formed in winter than is melted in summer. With 
greater eccentricity less heat than now would be received in 
winter, but exactly as much more in summer. More snow 
would therefore be formed in the one half of the year, but 
