126 Mr. J. Croll on the Excentricity of the Earth's Orbit, 



the sun • and, as a consequence, in a country like Greenland, 

 covered with an icy mantle, the temperature of the air, even 

 during summer, seldom rises above the freezing-point. 



Were it not for the ice, the summers of North Greenland, 

 owing to the continuance of the sun above the horizon, would be 

 as warm as those of England ; but, instead of this, the Greenland 

 summers are colder than our winters. Cover India with an ice- 

 sheet, and its summers would be colder than those of England, 



If at the glacial epoch the heat of the sun during the short 

 summer in perihelion, for reasons already stated, would fail to 

 melt the total quantity of snow accumulated during the long 

 and intensely cold winter — which no doubt it would — then the 

 snow and ice would accumulate year by year till the surface of 

 the entire country would be covered. After this the mean 

 temperature of the summers, no matter what the intensity of 

 the sun's rays might be, could not rise far above the freezing- 

 point. The rays which fell upon the ice-covered ground would 

 have no tendency whatever to raise the temperature ; they would 

 simply melt the ice ; and as the ice-covered surface would cool 

 the air more rapidly than the sun would heat it, the summers 

 could not possibly be warm. 



"At those periods of extreme excentricity when the winter oc- 

 curred in perihelion, there would be a short and warm winter and 

 a long and moderately cold summer. The winters would pro- 

 bably be about as warm as the summers, and an equable and 

 uniform condition of climate would prevail over the whole year. 

 The midsummer temperature 850,000 years ago, did the winter 

 occur in perihelion, would be about 75°, according to the mode 

 of calculation adopted. At the periods 950,000 and 750,000 

 years ago the temperature would be 60° and 63° respectively. 

 But there are certain modifying circumstances which might pro- 

 bably prevent the temperature of the winters from rising much 

 above perhaps 50° or 60°. 



In the arctic regions there would be an absence of the sun for 

 several months during winter, and the cold from stellar space 

 would no doubt be intense. This would tend to lower the tem- 

 perature of the winters in temperate and subarctic regions to a 

 certain extent. But, on the other hand, there is one powerful 

 agent which would now come into play, that would prevent the 

 possibility of a low temperature in arctic regions even in the 

 absence of the sun. I refer to the enormous quantity of warm 

 water which at this period would be flowing into those regions. 



The midsummer temperature determined according to the 

 sun's distance at the periods 950,000, 850,000, and 750,000 

 years ago, were the winter then in perihelion, would be 39°, 

 27°-4, and 36° respectively. But, again, there are here also mo- 



