124 DISCUSSIONS IN CLIMATOLOGY. 



Another Reason Assigned why the Ice does not 

 Melt. — Mr. Wallace assigns the following as an 

 additional reason why the ice does not disappear 

 during the interglacial periods when the eccentricity 

 is high: — 



" When a country is largely covered with ice, we 

 may look upon it as possessing the accumulated or 

 stored-up cold of a long series of preceding winters ; 

 and however much heat is poured upon it, its tempera- 

 ture cannot be raised above the freezing-point till that 

 store of cold is got rid of — that is, till the ice is all 

 melted. But the ice itself, when extensive, tends to 

 its own preservation, even under the influence of heat; 

 for the chilled atmosphere becomes filled with fog, and 

 this keeps off the sun-heat, and then snow falls even 

 during summer, and the stored-up cold does not 

 diminish during the year. When, however, only a 

 small portion of the surface is covered with ice, the 

 exposed earth becomes heated by the hot sun ; this 

 warms the air, and the warm air melts the adjacent 

 ice. It follows that, towards the equatorial limits of 

 a glaciated country alternations of climate may occur 

 during a period of high eccentricity, while nearer the 

 Pole, where the whole country is completely ice-clad, 

 no amelioration may take place." * 



For the past twenty years I have been maintaining 

 that, when a country is covered with ice, it becomes a 

 permanent source of cold; and however much heat 

 may be received from the sun, the temperature of the 

 surface can never be raised above the freezing-point 

 while the ice remains ; and, again, that such an ice- 

 covering tends to its own preservation, because it 

 chills the air and increases the snowfall. In short, I 

 have all along maintained this to have been one of the 



* "Island Life," p. 154, 



