ciiAP. v.] GENERAL CONCLUSIONS. 279 



directly continuous, layer for layer, with the water of the Ant- 

 arctic basin, it must be looked upon, not as being in connection 

 with that basin only, but as being a portion of the great ocean 

 of the water hemisphere ; and over the central part of the wa- 

 ter hemisphere precipitation is certainly greatly in excess of 

 evaporation, while the reverse is the case in its extensions to 

 the northward. The water is, therefore, carried off by evapora- 

 tion from the northern portions of the Atlantic and of the Pa- 

 cific, and the vapor is hurried downi toward the great zone of 

 low barometric pressure in the southern hemisphere, the heavy, 

 cold w'ater welling up from the southward into the deepest 

 parts of the northward-extending troughs to which it has free 

 access to replace it. It is unfortunate that we have as yet 

 scarcely sufficient data to estimate the relative amount of rain 

 and snow in the northern and southern hemispheres; but the 

 broad fact that there is very much more in the southern is so 

 patent as scarcely to require proof. This excess becomes still 

 more apparent wdien we include, as we must do, in this source 

 of supply of water to the north, the tropical region of the Soutli 

 Pacific, wdiicli forms part of the great ocean. 



To recapitulate briefly the general facts and conclusions with 

 regard to the distribution of ocean temperature in the Atlantic, 

 it seems to me : 



1. That the Atlantic must be regarded in the light of an 

 inlet or gulf of the general ocean of the water hemisphere, 

 opening directly from the Southern Sea. 



2. That the water of the Southern Sea simply wells up into 

 the Atlantic, and that all the temperature bands of the Atlantic 

 are essentially continuous with like temperature bands in the 

 Southern Sea, w^ith these modifications : That [a) above a certain 

 line, which maj^ be roughly represented by the isothermobathic 

 lines of 5° and 4° C, the temperature of the water is manifestly 

 affected by direct radiation and by the very complicated effects, 

 direct and indirect, of wind -currents; and {I)) that the whole 



