CLIMATE AND THE POLA.lt ICE-CAP. 405 



Lai. 20° N. 





Lat. 20° S. 



Mean 



. 75 



Mean 74-5 



Range 



. 14 



Range 9 



La*. 30° N. 





Lat. 30° S. 



Mean 



. GS 



Mean 69 



Range 



. 20 



Range 12 



Lat. 40° N. 





Lat. 40° S. 



Mean 



54-5 



Mean 53*5 



Range ....... 



. 35 



Range 9 



Lat. 50° N. 





Lat. 50° S. (Falkland Islands). 



Mean 



. 39 



Mean 43 



Range 



. 46 



Range 18 



We know nothing of the winter temperatures of the Antarctic con- 

 tinent- but it seems in no way improbable that there also the 

 range is comparatively small, so that the mean temperatures are 

 not lower than those of corresponding Arctic latitudes, though the 

 summer temperatures no doubt are lower. From the fact that 

 the southern summers are cooler than the northern, it follows that 

 the mean temperature of the whole earth is lower in the southern 

 than in the northern summer. All this is generally and satisfactorily 

 referred to the law that maritime climates are less extreme than 

 continental ones, in consequence of water taking longer than land 

 to become heated and to become cooled ; and the climate of the 

 southern hemisphere is on the whole maritime, and that of the 

 northern continental. But if the relative extent and distribution 

 of land and sea were nearly the same in the two hemispheres, I 

 cannot doubt that, contrary to Mr. Croll's opinion, the southern 

 hemisphere, having a perihelion summer and an aphelion winter, 

 would have a warmer summer and a colder winter than the 

 northern. 



If, however, it is hereafter shown that the mean temperature of 

 the Arctic regions is much higher than that of the Antarctic, this 

 will be amply accounted for by the influence of the warm currents 

 of the Atlantic. Mr. Croll has shown what an enormous quantity 

 of heat they carry northward ; but there are no corresponding cur- 

 rents in the southern hemisphere. The currents that carry heat into 

 the North Atlantic and the Arctic Ocean receive their direction, first 

 from the coast of South America, which diverts the equatorial current 

 to the north-west, and afterwards that of Europe, which diverts the 

 Atlantic currents to the north-east*. Mr. Croll is probably right in 

 supposing that the glaciation of the northern hemisphere would cause 

 the north trade-wind to blow further south than at present, and that 

 this would diminish the volume of the Gulf- stream, and so tend still 

 further to lower the northern temperatures. But this cause would 



* See ' Climate and Time,' map facing p. 212. 



