﻿552 Astronomical Theory of Ice Ages and Genial Ages. 



ocean currents seem a sufficient answer, but happily the 

 objection can be entirely disposed of. For the transference 

 of heat from ocean currents to lat. 54° at present depends on 

 the excess of temperature of the ocean over what I may call 

 the sun-heat temperature of 54°. Hence the objection sup- 

 poses that the present midwinter excess of ocean temperature 

 at 54° over the sun-heat temperature at 54° is greater than 

 the excess of ocean temperature at 50° over the sun-heat 

 temperature at 50° was in the epoch of great eccentricity. 

 But since the present midwinter sun-heat temperature at 54° 

 is the same as that at 50° in the earlier epoch, this supposition 

 requires the midwinter ocean temperature to be now higher 

 at lat. 54° than it was at lat. 50° in the epoch of great eccen- 

 tricity. But since the sun-heat temperature of the ocean at 

 lat. 50° at the earlier epoch was the same as that at lat. 54° 

 now, there is nothing which could tend to make the winter 

 temperature of the ocean at 50° in the earlier epoch lower than 

 that at 54° now, while the far greater summer heating the 

 water then underwent in the lower latitudes must have made 

 its winter temperature higher than it is now. Hence the 

 supposition that the winter temperature of the ocean would 

 be lower is disposed of for Great Britain at least *. 



Of course the foregoing argument proceeds on the sup- 

 position that the configuration of the land, and with it the 

 general character of the ocean currents and air currents was 

 the same at the epoch of great eccentricity as it is now. It 

 then supplies a satisfactory proof that there is nothing in the 

 astronomical causes which would alter those currents, or at 

 least nothing of the nature required by CrolFs theory. 



If, instead of taking the radiation proportional to the 

 absolute temperature, we take Stefan's law, published in 

 1881, giving it as proportional to the 4th power of the 

 temperature, we should reduce CrolPs result by one fourth. 

 Thus his 45°'3 F. would come down to 11° F.; and if we further 

 consider that ocean and air currents are twice as effective as 

 winter sun-heat in maintaining the temperature we should get 

 a lowering of about 4°F. at midwinter, about the same as 

 the amount I arrive at otherwise. This is not quite accurate, 

 for we ought to take the 4th power from zero, not from 

 — 239, and also we ought to take the percentage diminution, 

 not of the solar heat, but of the total heat. Still the calcula- 

 tion may help in a rough way to show the reasonableness of 

 the results obtained in the paper. 



* Of course in strict accuracy we should use in the argument not 54° 

 but the somewhat lower latitude whose midwinter sun-heat temperature 

 at present is the same as that of 50° in the period of great eccentricity. 



