Thus it is to the salts of the sea, that we owe that feature in the system of oceanic circulation which 

 causes an under current to flow from the Mediterranean into the Atlantic, and another from the Red sea into tiie 

 Indian ocean. And it is evident since neither of these seas is salting up, — that just as much, or nearly just 

 as much salt as the under current brings out, just so much must the upper currents carry in. 



We now begin to perceive what a powerful impulse is derived from the salts of the sea in givin"- effective 

 and active circulation to its waters. 



Hence, we infer that the currents of the sea, by reason of its saltness, attain their maximum of velocity. 

 Hence, too, we infer that the transportation of warm water from the Equator towards the frozen regions of 

 the Poles, and of cold water from the Frigid towards the Torrid Zone, is facilitated ; and consequently 

 here, in the saltness of the sea, have we not an agent by which climates are mitigated, by which they are 

 softened and rendered much more salubrious than it would be possible for them to be, were the waters 0/ the^ 

 ocean deprived of this property of saltness ? 



If these inferences as to the influence of the salts upon the currents of the sea, be correct, th& same cause 

 which produces an under current from the Mediterranean, and an under current from the Red sea into the ocean, 

 should produce an under current from the ocean into the north polar basin — it being supposed merely for the 

 present that there is a surface current through Davis' Straits, always setting out of the Polar sea. In each case 

 the hypothesis with regard to the part performed by the salt in giving vigor to the system of oceanic circulation, 

 requires that, counter to the surface current of water with less salt, there should be an under current of water 

 with more salt in it. 



That such is the case with regard both to the Mediterranean and the Red sea, has been amply shown in 

 other parts of this work, and abundantly proved by other observers. 



That there is a constant current setting out of the Arctic ocean through Davis' and other straits there- 

 about, which connect it with the Atlantic ocean, is generally admitted. Lieut. De Haven, U. S. N., when in 

 command of the American expedition in search of Sir John Franklin, was frozen up with his vessels in the main 

 fhannel of Wellington straits; and during the nine months that he was so frozen, his vessels holding their 

 place in the ice, were drifted with it bodily for more than a thousand miles towards the south. 



The ice in which they were bound was of sea water, and the currents by which they were drifted were 

 of sea water— only, it may be supposed, the latter were not quite so salt as sea water generally is. 



Then since there is salt always flowing out of the north polar basin, there must be salt always flowino- into 

 it, else it would either become fresh, or the whole Atlantic ocean would be finally silted up with salt. 



It might be supposed, were there no evidence to the contrary, that this salt was supplied to the Polar seas, 

 Irom the Atlantic around North Cape, and from the Pacific through Bhering's straits, and through no other channels. 



But fortunately Arctic voyagers, who have cruised in the direction of Davis' straits, have afforded us proof 

 positive as to the fact of this other source for supplying the Polar seas with salt. They tell us of an under cur- 

 rent setting from the Atlantic towards the Polar basin. They describe huge icebergs with tops reaching high 

 up in the air, and of course the bases of which extend far down into the depths of the ocean, ripping and tearing 

 their way with terrific force and awful violence through the surface ice or against a surface current. 



