134 ISLAND LIFE 



sun-heat warming the air or the earth much above the 

 freezing-point. This is ilhistrated by the often-quoted fact 

 that, at 80° N. Lat., Captain Scoresby had the pitch melted 

 on one side of his ship by the heat of the sun, while water was 

 freezing on the other side owing to the coldness of the air. 

 The quantity of heat required to melt ice or snow is very 

 great, as we all know by experience of the long time masses 

 of snow will remain unmelted even in warm weather. We 

 shall however be better able to appreciate the great effect 

 this has upon climate, by a few figures showing what this 

 amount really is. In order to melt one cubic foot of ice, 

 as much heat is required as would heat a cubic foot of 

 water from the freezing point to 176° F., or two cubic feet 

 to 104° F. To melt a layer of ice a foot thick will therefore 

 use up as much heat as would raise a layer of ice-cold water 

 two feet thick to the temperature of 104° F. ; and the effect 

 becomes still more easily understood if we estimate it as 

 applied to air, for to melt a layer of ice only 1-^ inches 

 thick would require as much heat as Avould raise a stratum 

 of air 800 feet thick from the freezing point to the tropical 

 heat of 104° F. 1 We thus obtain a good idea, both of the 

 wonderful power of snow and ice in keeping down tempera- 

 ture, and also of the reason why it requires so long a time 

 to melt away, and is able to go on accumulating to such an 

 extent as to become permanent. These properties would, 

 however, be of no avail if it were liquid, like water ; hence 

 it is the state of solidity and almost complete immobility 

 of ice that enables it to produce by its accumulation such 

 extraordinary effects in physical geography and in climate, 

 as we see in the glaciers of Switzerland and the ice-capped 

 interior of Greenland. 



High Land and great Moishcre Essential to the Initiation 

 of a Glacial Epoch. — Another point of great importance in 

 connection with this subject, is the fact, that this perma- 

 nent storing up of cold depends entirely on the annual 

 amount of snow-fall in proportion to that of the sun and 

 air-heat, and not on the actual cold of winter, or even on 

 the average cold of the year.^ A place may be intensely 

 cold in winter and may have a short arctic summer, yet, if 

 ^ Dr. Croll says this **is one of the most widespread and fundamental 



