156 DISCUSSIONS IN CLIMATOLOGY. 



If the emissive power of the sun was about the 

 same during the Tertiary period as at present, and 

 there is no good grounds for supposing it was other- 

 wise, then the extra heat possessed by the northern 

 temperate and Arctic regions must have been derived 

 either from the equatorial regions or from the southern 

 hemisphere, or, what is more likely, from both. If 

 so, then the temperature either of the southern hemi- 

 sphere or of the intertropical regions, or both, must 

 have been much lower during the Tertiary period than 

 at the present day. A lowering of the temperature of 

 the equatorial regions, resulting from this transference 

 of heat, would tend to produce a more equable and 

 uniform condition of climate over the whole of the 

 northern hemisphere. As the area of the Arctic 

 Ocean is small in comparison to that of the equatorial 

 zone, from which the warm water was derived, the 

 fall of temperature at the equator would be much less 

 than the rise at the pole. Supposing there had been 

 a rise of, say, 30° at the pole, resulting from a fall of 

 10° at the equator (and this is by no means an im- 

 probable assumption), this would reduce the difference 

 between the equator and the pole by 40°, or to half 

 its present amount. We should then have a climatic 

 condition pretty much resembling that which is known 

 to have prevailed during at least considerable portions 

 of the Tertiary period. 



It is indeed very doubtful if such a climatic con- 

 dition of things as that could be brought about by a 

 high state of eccentricity with the present distribution 

 of land and water ; but, on the other hand, it is just 

 as doubtful whether the channels of communication 

 assumed by Mr. Wallace could have brought it about 

 without the aid of eccentricity. 



The very existence of so high a temperature on the 



