194 THE PHYSICAL GEOGRAPHY OF THE SEA. 



seas, and the temperature of the surface water is always 28°. At 

 least Lieutenant De Haven so found it in his long imprisonment, 

 and it may be supposed that, as it was with him, so it generally 

 is). Assuming, then, the water of the surface current which runs 

 out with the ice to be all at 28°, we observe that it is not unrea- 

 sonable to suppose that the water of the under current, inasmuch 

 as it comes from the south, and therefore from warmer latitudes, 

 is probably not so cold ; and if it be not so cold, its temperature, 

 before it comes out again, must be reduced to 28°, or whatever be 

 the average temperature of the outer but surface currelit. Dr. 

 Kane found the temperature of the open sea in the Arctic Ocean 

 (§ 486) as high as 36°. Can water flow in the depths below from 

 the mild climate of the temperate zones to the severe climates of 

 the frigid zone without falling below 36° ? To what, in the depths 

 of the sea, can a warm current of large volume impart its heat ? 



539. Moreover, if it be true, as some philosophers have suggest- 

 ed, that there is in the depths of the ocean a floor or plane from the 

 equator to the poles along which the water is of the same temper- 

 ature all the way, then the question may be asked. Should we not 

 have in the depths of the ocean a sort of isothermal floor, as it 

 were, on the upper side of which all the changes of temperature 

 are due to agents acting from above, and on the lower side of 

 which, the changes, if any, are due to agents acting from below ? 



540. This under Polar current water, then, as it rises to the 

 top, and is brought to the surface by the agitation of the sea in 

 the Arctic regions, gives out its surplus heat and warms the at- 

 mosphere there till the temperature of this warm under current 

 water is lowered to the requisite degree for going out on the sur- 

 face. Hence the water-sky of those regions. 



541. And the heat that it loses in falling from its normal tem- 

 perature, be that what it may, till it reaches the temperature of 

 28°, is so much caloric set free in the Polar regions, to temper the 

 air and mitigate the climate there. Now is not this one of those 

 modifications of climate which may be fairly traced back to the ef- 

 fect of the saltness of the sea in giving energy to its circulation ? 



542. Moreover, if there be a deep sea in the Polar basin, which 

 serves as a receptacle for the waters brought into it by this under 



