THE SALTS OF THE SEA. 247 



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 in- 

 sect that secretes solid matter for its sea-shell, is capable of put- 

 ting it instantly in motion. Still, when solidified and placed in a 

 heap, all the mechanical contrivances of man, aided by the tre- 

 mendous 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 pei-petual 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 Ked Sea into the ocean, should 

 produce an under current from the ocean into the north polar ba- 

 sin ; for it may be laid down as a law, that whenever two oceans, 

 or two arms of the sea, or two sheets of water, dififering as to salt- 

 ness, are connected with each other, there are cuiTents 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 Ai'ctic Ocean through Davis' and other 

 straits thereabout, which connect it with the Atlantic Ocean, is 

 generally admitted. Lieutenant De Haven, United States Xavy, 

 when in command of the American expedition in search of Sir 

 John Franklin, was frozen up with his vessels — the Advance- and 

 the liescue — in mid-channel near Wellington Straits ; and during 

 the nine months that he was so frozen, his vessels, like H.B.M. 

 ship Eesolute 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. 



