﻿Astronomical Theory of Ice Ages and Genial Ages. 547 



of our year as the corresponding standard latitudes received in 

 the 199 coldest days of their year in the epoch of great eccentricity, 

 that is, of course, in their winter (of course 90° cannot be 

 brought into this comparison). In other words, the same 

 daily average of sun-heat is received during the 199 days by the 

 corresponding latitudes in the present and former epochs. 



But it is quite evident that the present midwinter tempe- 

 ratures of 44°* 2, 54°, &c. must, so far as the direct effect of 

 sun-heat is concerned, be lower than the midwinter tempera- 

 tures of the standard latitudes in the epoch of great eccen- 

 tricity. For if the actual daily sun-heat received by latitude 

 44 0, 2 at present were the same for each of the 199 days 

 as that received on the corresponding day by latitude 40° 

 in the former epoch, then we could affirm that, so far as 

 sun-heat alone was concerned, the temperatures of the two 

 latitudes ought to be equal. But since 44°* 2 receives far 

 more than this amount of daily heat in the beginning of the 

 199 days, its temperature will be higher at first, and there- 

 fore, since the total heat received up to midwinter is the 

 same in both cases, the temperature of the 44°* 2 must be 

 lower at midwinter — otherwise it would be higher all the time, 

 which is impossible. For if it were higher all the time, it 

 would be constantly losing more heat by radiation; wherefore, 

 as it only receives the same quantity of heat, its finnl tempe- 

 rature must be lower, not higher. Thus the supposition that 

 the midwinter temperature of 44°'2, so far as direct sun-heat 

 is concerned, is higher than that of 40° in the epoch of great 

 eccentricity, involves an absurdity. 



So far 1 have only dealt with the effect of the winter sun- 

 heat. Consider now the annual sun-heat. First, the present 

 summer sun-heat on lat. 44°* 2 in the remaining 166 days of 

 our year is far less (9 per cent, less) than the sun-heat received 

 by lat. 40° in its summer of 166 days in the period of great 

 eccentricity. Hence, so far as summer sun-heat is concerned, 

 latitude 44°*2 now begins its 199 days at an appreciably 

 lower temperature than 40° began its 199 days in the former 

 epoch, and therefore, on this account as well, its present 

 midwinter temperature should be lower than the midwinter 

 temperature of 40° was in the supposed glacial winter. 



Of course all the foregoing applies equally to the other 

 latitudes. 



Hence we conclude that, other things equal, the direct 

 effect of the altered sun-heat in the epoch of great eccentricity 

 was probably to place latitudes 40°, 50°, 60°, 70°, and 80° in 

 about the same conditions as to midwinter temperature as 

 43°'3, 52°-4, 61 c -7, 71°*3, and 81° are at present, and that 



