storms are sometimes known to create; and that even the gentle trade-winds may have influence and effect upon the currents of the sea has not been denied (§ 82). But the effect of moderate winds, as the trades are, is to cause what may he called the drift of the sea rather than a current. Drift is confined to surface waters, and the trade-winds of the Atlantic may assist in creating the Gulf Stream by drifting the waters which have supplied them with vapour towards the Caribbean Sea. But admit never so much of the water which the trade-winds have played upon to be drifted into the Caribbean Sea, what should make it flow thence with the Gulf Stream to the shores of Europe? It is because there is room for it there; and there is room for it because of the difference in the specific gravity of sea-water in an intertropical sea on one side, as compared with the specific gravity of water in northern seas and frozen oceans on the other.
108. The dynamical force that calls forth the Gulf Stream to be found in the difference as to specific gravity of intertropical and polar waters.—The dynamical forces which are expressed by the Gulf Stream may with as much propriety be said to reside in those northern waters as in the West India seas; for on one side we have the Caribbean Sea, and Gulf of Mexico, with their waters of brine; on the other, the Great Polar basin, the Baltic, and the North Sea, the two latter with waters that are but little more than brackish.[1] In one set of these sea-basins the water is heavy; in the other it is light. Between them the ocean intervenes; but water is bound to seek its equilibrium as its level; and here, therefore, we unmask one of the agents concerned in causing the Gulf Stream. What is the power of this agent—is it greater than that of other agents, and how much? We cannot say how much; we only know it is one of the chief agents concerned. Moreover, speculate as we may as to all the agencies concerned in collecting these waters, that have supplied the trade-winds with vapour, into the Caribbean Sea, and then in driving them across the Atlantic—we are forced to conclude that
- ↑ The Polar basin has a known water area of 3,000,000 square miles, and an unexplored area, including land and water, of 1,500,000 square miles. Whether the water in this basin be more or less salt than that of the intertropical seas, we know it is quite different in temperature, and difference of temperature will beget currents quite as readily as difference in saltness, for change in specific gravity follows either.
