Page:Physical Geography of the Sea and its Meteorology.djvu/337

Rh and that, consequently, the twine to be used must be strong; it was therefore subjected to a test which required it to bear a weight of at least sixty pounds freely suspended in the air. So we had to go to work anew, and make several hundred thousand fathoms of sounding-twine especially for the purpose. It was small, and stood the test required, a pound of it measuring about six hundred feet in length. The officers intrusted with the duty soon found that the soundings could not be made from sailing vessels with any certainty as to the depth. It was necessary that a boat should be lowered, and the trial be made from, it; the men with their oars keeping the boat from drifting, and maintaining it in such a position that the line should be "up and down "the while. That the line would continue to run out after the cannon-ball had reached bottom, was explained by the conjecture that there is in the ocean, as in the air, a system of currents and counter currents one above the other, and that it was one or more of these submarine currents, operating upon the bight of the line, which caused it to continue to run out after the shot had reached the bottom. In corroboration of this conjecture, it was urged, with a truth-like force of argument, that it was these under currents, operating with a "swigging" force upon the bights of the line—for there might be several currents running in different directions, and operating upon it at the same time—which caused it to part whenever the reel was stopped and the line held fast in the boat.

570. Evidence in favour of a regular system of oceanic circulation.—A powerful train of circumstantial evidence was this (and it was derived from a source wholly unexpected), going to prove the existence of that system of oceanic circulation which the climates, and the offices, and the adaptations of the sea require, and which its inhabitants (§ 465) in their mute way tell us of. This system of circulation commenced on the third day of creation, with the "gathering together of the waters," which were "called seas;" it will probably continue as long as sea water shall possess the properties of saltness and fluidity.

571. Method of making a deep-sea sounding.—In making these deep-sea soundings, the practice is to time the hundred fathom marks (§ 568) as they successively go out; and by always using a line of the same size and "make," and a sinker of the same shape and weight, we at last established the law of descent.