Page:Physical Geography of the Sea and its Meteorology.djvu/237

Rh decreased as Rodgers approached the shore, yet the specific gravity decreased also, because the saltness decreased by reason of the increasing proportion of river water as he neared the shore. And thus we have in our own waters an illustration and an example of how water that is cool and light—because not so salt—may be made to cover and protect as with a mantle, a sheet of warmer, but Salter and heavier water below.

427. An under current of warm but salt and heavy water.—The mean specific gravity of the Arctic Ocean water as observed by Rodgers, and reduced to the freezing-point (27°.2) of sea water, was 1.0263. The specific gravity of the Gulf Stream water, as observed by him, and reduced to the same temperature (27°.2), was 1.0303. If these be taken as fair specimens of the water of the torrid and frigid zones, it would appear that the waters of intertropical seas have 15 per cent, more salt in them than the surface water of the Arctic Ocean has. It is to be regretted that the hydrometer has not been more frequently used in the Arctic Ocean, for a careful series of observations upon the specific gravity of the water there at the surface and at various depths would indicate to us not only the extent to which the water there is diluted by the rivers and the rains, but it would yield other highly interesting results. Now this salt and heavy water, whose specific gravity at 27°.2 would have been 1.0303, is the very water which Rodgers observed in the Gulf Stream on its way to the arctic regions. This is the water which, after passing the Grand Banks and meeting the diluted water as an ice-bearing current from the north, dips down, but continues its course as an under current. It is protected from farther loss of heat, after the manner of our own littoral waters, by the colder but lighter and upper current from the north, until it enters the Arctic Ocean, there to rise up like a boiling spring in the centre of an open sea.

428. De Havens water sky.—Relying upon a process of reasoning like this, and the deductions flowing therefrom. Lieutenant De Haven, when he went in command of the American expedition in search of Sir John Franklin and his companions, was told in his letter of instructions, to look, when he should get well up into Wellington Channel, for an open sea to the northward and westward. He looked, and saw in that direction a "water sky." Captain Penny afterwards went there, found open water, and sailed upon it. The open sea in the Arctic Ocean is probably not