140 



ISLAND LIFE. 



[part I. 



doubt warm the vapour in tlie 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 helow 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 meltirtg 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 constantly and superficially 

 asserted that they do. 



Effect of Clouds and Fog in cutting off the Suns 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 



