254 THE PHYSICAL GEOGRAPHY OF THE SEA. 



part its heat ? The temperature of sea water from the tropics in 

 which ice is forming is invariably (§ 442) 28°. Does not the cir- 

 cumstance of De Haven's invariably finding this to be the tem- 

 perature below the ice on which he drifted tend to confirm the 

 conjecture (§ 479) about the ice and the 'river water? 



484. This under polar current water, then, as it rises to the top, 

 It comes to the sur- and is brought to the surface by the agitation of the 

 ^''^'^^- sea in the arctic regions, gives out its surplus heat 

 to warm the atmosphere there till the temperature of this warm 

 under current water is lowered to the requisite degree for going 

 out on the surface. Hence the water-sky of those regions. And 

 the heat that it loses in falling from its normal temperature, 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 miti- 

 gate the climate there. Now is not this one of those modifications 

 of climate which may be fairly traced back to the eftect of the 

 saltness of the sea in giving energy to its circulation? Moreover, 

 if there be a deep sea in the polar basin, which serves as a recep- 

 tacle for the waters brought 5bt5 it by this under current, which, 

 because it comes from toward the equatorial regions, comes from 

 a milder climate, and is therefore warmer, we can easily imagine 

 why there might be an open sea in the polar regions — why Lieu- 

 tenant De Haven, in his instructions (§ 428), was directed to look 

 for it ; and why both he and Captain Penny, of one of the En- 

 glish searching vessels, and afterward Dr. Kane, found it there. 

 And in accounting for this polynia, we see that its existence is not 

 only consistent with the hypothesis with which we set out, touching 

 a perfect system of oceanic circulation, but that it may be ascribed, 

 in a great degree at least, if not wholly, to the effect produced by 

 the salts of the sea upon the mobility and circulation of its waters. 

 Here, then, is an office which the sea performs in the economy of 

 the universe by virtue of its saltness, and which it could not per- 

 form were its waters altogether fresh. And thus philosophers 

 have a clew placed in their hands which will probably guide them 

 to one of the many hidden treasures that are embraced in the true 

 answer to the question, " Why is the sea salt?" 



485. Sea Shells. — We find in sea water other matter besides 

 Sea Shells— their common Salt. Lime is dissolvcd by the rains and 



influence upon cur- , . , • i • , j • ^ • • . j.i 



rents. the Hvcrs, and emptied in vast quantities into the 



