28 DISCUSSIONS IN CLIMATOLOGY. 



sun's rays, and thus allow the water of the ocean to 

 stand at a higher temperature than it would otherwise 

 do. Again, the slowness with which the ocean thus 

 parts with its heat enables it to maintain that com- 

 paratively high temperature during the long winter 

 months. And again, it is to the mobility of the 

 particles of water, the depth to which the heat 

 penetrates, and the rapidity with which it is absorbed, 

 that those great currents of warm water become pos- 

 sible. Were the waters of the ocean like the land, 

 not mobile, and were only a few inches at the surface 

 reached by heat from the sun, there could be no Gulf- 

 stream, or any great transference of heat from the 

 southern to the northern hemisphere, or from equa- 

 torial to temperate and polar regions, by means of 

 oceanic circulation. 



Second. — ' The air is probably heated more rapidly 

 by contact with the ground than with the ocean ; but 

 on the other hand, it is heated far more rapidly by 

 radiation from the ocean than from the land. The 

 aqueous vapour of the air is to a great extent diather- 

 manous to radiation from the ground, while it absorbs 

 the rays from water, and thus becomes heated.' 



To this Professor Newcomb objects, as follows: — "If, 

 then, the air is really heated by contact with the ground 

 more rapidly than by contact with the ocean, it can only 

 be because the ground is hotter than the ocean, which 

 is directly contrary to the theory Mr. Croll is main- 

 taining." What I maintained was that, were it not 

 for certain causes, the mean annual temperature of 

 the ocean would be higher than that of the land. 

 During the day and also during the summer the sur- 

 face of the ground is hotter than that of the ocean ; 

 and the air, of course, will be heated more rapidly by 

 contact with the former than with the latter. But 



