72 THE OCEAN 



temperature in the surface waters of the 

 North Atlantic was only 0-8° F. or one-fourth 

 of that in the air resting upon them. An 

 examination of the temperatures taken by the 

 " Challenger " in other parts of the globe 

 renders it highly probable that nowhere 

 in the open ocean does the mean daily fluctua- 

 v|tion of the temperature of the surface water 

 I amount to one degree ; hence the atmosphere 

 over the ocean may be regarded as resting upon 

 or blowing over a surface, the temperature of 

 which is practically uniform at all hours of 

 the day — a generalisation which is looked upon 

 as a factor of prime importance in the study 

 of the atmosphere and of ocean meteorology. 

 The annual variation of the temperature 

 in the surface waters of the ocean at any one 

 spot may exceed 50° F. in certain regions 

 where the surface is occupied by cold waters 

 coming from polar areas at one season, and 

 by warm waters coming from tropical areas 

 at another season ; but, on the other hand, 

 there are very extensive regions both in 

 tropical and polar waters where the range 

 does not exceed a few degrees during the course 

 of the year. A map showing the annual range 

 of the surface temperature of the ocean (see 

 Plate IV.) based upon the highest and lowest 

 temperatures recorded within each two-degree 

 square throughout the ocean basins, indicates 



