J. Croll—Geological Climatology. 263 
“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 sup- 
porting 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, whi 
18 in contact with vegetation, The two phenomena, therefore, 
by no means counterbalance or counteract each other, as it is 
So constantly and superficially asserted that they do.”—Jsland 
ufe, p. 140. : 
he Fundamental misconception —I come now to a misap- 
prehension which more than any other has tended to prevent 
& proper understanding of the causes which lead to the con- 
servation by snow. Whatever 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. Conse- 
exactly as much more in summer. More snow would therefore 
formed in the one half of the year, but exactly as much 
more be melted in the other half. The colder winter and the 
armer summer would exactly neutralize each other’s effects, 
and on the average of years no accumulation could begin. 
rma facie, therefore, high eccentricity will not account for 
glacial periods.”* In the language of Professor Newcomb it. 
Is as follows: ¢“ During this perihelion summer the amount of 
heat received from the sun by every part of the northern hem- 
‘sphere would suffice to melt from four to six inches of ice per 
Y over its entire surface ; that is, it would suffice to melt 
the whole probable accumulation in three or four days. The 
reader can easily make a computation of the incredible reflect- 
ng power of the snow and of the unexampled transparency of 
the air required to keep the snow unmelted for three or four 
months,” 
* Geological Magazine, January, 18890, p. 12. 
