1 82 T. C. CHAMBERLIN 



by specific comparisons of the temperature charts, the positions of 

 the isothermal hnes and the distribution of life. The general import 

 is most conveniently indicated by the fact that the thermal Equator 

 Hes 5° or 6° north of the geodetic or geographic Equator. Kriimmel 

 estimates the average surface temperature in the Northern Hemis- 

 phere to be 19.20° C, that in the Southern to be 15.97° C.; while 

 the air temperature averages 15.1° C. for the Northern Hemisphere, 

 and 13.6° C. for the Southern.^ 



For the purposes of this discussion, the nature and distribution 

 of life furnish better criteria than simple temperatures, since the 

 evidences of past climates rest almost wholly upon the fossil life, 

 and anyway life is a composite index of climate — a natural correla- 

 tion as it were — ^while temperature is only one factor. For brevity, 

 then — as well as its comprehensive significance — life, especially 

 human life, will be used mainly in the following comparisons. 

 Human life implies the concurrent presence of a highly complex 

 series of supporting t3^es of lower life, both vegetable and animal. 



COMPARISONS ON SELECTED PARALLELS OF LATITUDE 



To sweep the full range of the high latitudes, let us begin our 

 comparisons with the parallels of 50° on each side of the Equator, 

 Let us begin also at the most typical spots. The Indian Ocean has 

 a form and a placement specially well suited for showing whatever 

 warming effects in mid-latitude a great expanse of sea may have. 

 Its northern edge reaches 20° beyond the Equator and thus brings 

 in from the Northern Hemisphere a large section of equatorially 

 warmed water, while the southern edge falls more than 20° short 

 of the South Pole and thus excludes a large area that might other- 

 wise contribute polar waters. Furthermore the Indian Ocean is 

 broad and roughly rotund. Its connections and relations are 

 simpler than those of the other great oceans. Let us then start 

 our comparisons with an island lying centrally in this highly repre- 

 sentative ocean. Kerguelen Island lies a little on the equatorial 

 side of 50° S. Lat. (48°39' to 49°440, in the very heart of this ocean, 

 far away from any other land of moment. It is more than 2,000 miles 

 from Africa and a Httle farther than this from AustraHa; it is more 



' Cited from A Textbook on Oceanography, by J. T. Jenkins, London, 1921. 



