140 
ISLAND LIFE. 
[part I. 
doubt warm the vapour in the atmosphere, but this heat would 
be carried off to other parts of the earth, while a considerable 
portion of the whole would be lost in space. It must also be 
remembered that an enormous quantity of heat is used up in 
melting snow and ice, without raising its temperature; each 
cubic foot of ice requiring as much heat to melt it as would 
raise nearly six cubic feet of water 30° F. It has, however, 
been argued that because when, water is frozen it evolves just 
as much heat as it requires to melt it again, there is no loss of 
heat on the whole ; and as this is adduced as a valid argument 
over and over again in every criticism of Dr. Croll’s theory, it 
may be well to consider it a little more closely. 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 sa< constantly and superficially 
asserted that they do. 
Effect of Clouds and Fog in cutting off the Sun’s heat. — Another 
very important cause of diminution of heat during summer in 
a glaciated country would be the intervention of clouds and 
fogs, which would reflect or absorb a large proportion of the 
sun-heat and prevent it reaching the surface of the earth ; and 
such a cloudy atmosphere would be a necessary result of large 
areas of high land covered with snow and ice. That such a 
prevalence of fogs and cloud is an actual fact in all ice-clad 
countries has been shown by Dr. Croll most conclusively, and 
he has further shown that the existence of perpetual snow often 
