166 THE FITNESS OF THE ENVIRONMENT 



Water and Air Temperatures at Lesina 



According to Schott the variation of surface 

 temperature of the open ocean over the whole 

 globe is never less than 1° nor more than 15°. 

 Such variations are slight on the equator, 

 larger in the region of the trade winds, less 

 again in the northern and southern seas. 1 

 The surface temperature extends only a short 

 distance into the water, thus constituting a 

 warm surface layer. It has indeed been 

 known since the time of Aristotle that the 

 depths of the sea are cold. In the open 

 ocean the temperature increases steadily as 

 the depth increases, but more rapidly near 

 the surface, more slowly at greater depths. 

 The bottom water at great depth varies from 

 a temperature of 2° in the tropics to about 

 — 2° in the polar waters. Such low temperature 

 of the depths of the tropical oceans is almost 

 certainly due to the inflow of cold water from 

 high latitudes. 



1 Arrhenius, I.e. 



