473. Quantity of salt in the sea.—If all the salts of the sea were precipitated and spread out equally over the northern half of this continent, it would, it has been computed, cover the ground one mile deep. What force could move such a mass of matter on the dry land? Yet the machinery of the ocean, of which it forms a part, is so wisety, marvellously, and wonderfully compensated, that the most gentle breeze that plays on its bosom, the tiniest insect that secretes solid matter for its sea-shell, is capable of putting it instantly in motion. Still, when solidified and placed in a heap, all the mechanical contrivances of man, aided by the tremendous forces of all the steam and water power of the world, could not, in centuries of time, move even so much as an inch this matter which the sunbeam, the zephyr, and the infusorial insect keep in perpetual motion and activity.
474. Deductions.—If these inferences as to the influence of the salts upon the currents of the sea be correct, the same cause which produces an under current from the Mediterranean (§ 471), and an under current from the Red Sea into the ocean, should produce an under current from the ocean into the north polar basin; for it may be laid down as a law, that whenever two oceans, or two arms of the sea, or two sheets of water, differing as to saltness, are connected with each other, there are currents between them, viz., a surface current from, and an under current into the sea of lightest water. In every case, the hypothesis with regard to the part performed by the salt, in giving vigour 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 (§ 471), and abundantly proved by other observers. That, in obedience to this law, there is a constant current setting out of the Arctic Ocean through Davis' and other straits thereabout, which connect it with the Atlantic Ocean, is generally admitted. Lieutenant De Haven, United States Navy, when in command of the American expedition in search of Sir John Franklin, was frozen up with his vessels—the Advance and the Rescue—in mid-channel near Wellington Straits; and during the nine months that he was so frozen, his vessels, like H.B.M. ship Resolute and the Fox (§ 431), each holding its place in the ice, were drifted with it bodily for more than a thousand miles towards the south.
