Page:Physical Geography of the Sea and its Meteorology.djvu/75

Rh currents.—Here I am reminded to turn aside and call attention to another fact that militates against the vast current-begetting power that has been given by theory to the gentle trade-winds. In both oceans these weedy seas lie partly within the trade-wind region; but in neither do these winds give rise to any current. The weeds are partly out of water, and the wind has therefore more power upon them than it has upon the water itself; they tail to the wind. And if the supreme power over the currents of the sea reside in the winds, as Sir John Herschel would have it, then of all places in the trade-wind region, we should have here the strongest currents. Had there been currents here, these weeds would have been borne away long ago; but so far from it, we simply know that they have been in the Sargasso Sea (§ 88) of the Atlantic since the first voyage of Columbus. But to take up the broken thread:—

135. The drift matter confined to sargassos by currents.—The water that is drifting north, on the outside of the Gulf Stream, turns, with the Gulf Stream, to the east also. It cannot reach the high latitudes (§ 80), for it cannot cross the Gulf Stream. Two streams of water cannot cross each other, unless one dip down and underrun the other; and if this drift water do dip down, as it may, it cannot carry with it its floating matter, which, like its weeds, is too light to sink. They, therefore, are cut off from a passage into higher latitudes.

136. Theory as to the formation of sargassos.—According to this view, there ought to be a sargasso sea somewhere in the sort of middle ground between the grand equatorial flow and reflow which is performed by the waters of all the great oceans. The place where the drift matter of each sea would naturally collect would be in this sort of pool, into which every current, as it goes from the equator, and again as it returns, would slough off its drift matter. The forces of diurnal rotation would require this collection of drift to be, in the northern hemisphere, on the right-hand side of the current, and, in the southern, to be on the left. (See Chap. XVIII. and Plate IX.)

137. Sargassos of southern seas to the left of the southern, to the right of the great polar and equatorial flow and reflow.—Thus, with the Gulf Stream of the Atlantic, and the "Black Stream" of the Pacific, their sargassos are on the right, as they are also on the right of the returning and cooler currents on the eastern side of each one of those northern oceans. So, also, with the