Page:Physical Geography of the Sea and its Meteorology.djvu/281

Rh the water of the under current, inasmuch as it comes from the south, and therefore from warmer latitudes, is 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 current. Dr. Kane found the temperature of the open sea in the Arctic Ocean (§ 429) as high as 36°. Can water in the depths below flow from the mild climate of the temperate zones to the severer 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? The temperature of sea water from the tropics in which ice is forming is invariably (§ 442) 28°. Does not the circumstance of De Haven's invariably finding this to be the temperature below the ice on which he drifted tend to confirm the conjecture (§ 479) about the ice and the river water?

484. It comes to the surface.—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 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 mitigate the climate there. Now is not this one of those modifications of climate which may be fairly traced back to the effect 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 receptacle for the waters brought into it by this under current, which, because it comes from towards 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 Lieutenant De Haven, in his instructions (§ 428), was directed to look for it; and why both he and Captain Penny, of one of the English searching vessels, and afterwards 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