Page:Physical Geography of the Sea and its Meteorology.djvu/77

 Rh the Gulf Stream, its progress to the north is arrested. It now turns to the east with the Gulf Stream, and, yielding to the force of the westerly winds of this latitude, is (§ 107) by them slowly drifted along: losing temperature by the way, these waters reach the southward flow on the east side with their specific gravity so altered that, disregarding the gentle forces of the wind, they heed the voice of the sea, and proceed to unite with this cool flow, and to set south in obedience to those dynamical laws that derive their force in the sea from differing specific gravity.

142. The resemblance between the currents in the North Atlantic and the North Pacific.—The Thermal Charts of the North Atlantic afford for these views other illustrations which, when compared with the charts of the North Pacific now in the process of construction, will make still more striking the resemblance of the two oceans in the general features of their systems of circulation. We see how, in accordance with this principle (§ 132), the currents necessary for the formation of thickly-set sargassos are generally wanting in southern oceans. How closely these two seas of the north resemble each other; and how, on account of the large openings between the Atlantic and the Frozen Ocean, the flow of warm waters to the north and of cold waters to the south is so much more active in the Atlantic than it is in the Pacific. Ought it not so to be?

143. A cushion of cool water protects the bottom of the deep sea from abrasion by its currents.—As a rule, the hottest water of the Gulf Stream is at or near the surface; and as the deep-sea thermometer is sent down, it shows that these waters, though still far warmer than the water on either side at corresponding depths, gradually become less and less warm until the bottom of the current is reached. There is reason to believe that the warm waters of the Gulf Stream are nowhere permitted, in the oceanic economy, to touch the bottom of the sea. There is everywhere a cushion of cool water between them and the solid parts of the earth's crust. This arrangement is suggestive, and strikingly-beautiful. One of the benign offices of the Gulf Stream is to convey heat from the Gulf of Mexico, where otherwise it would become excessive, and to dispense it in regions beyond the Atlantic for the amelioration of the climates of the British Islands and of all Western Europe. Now cold water is one of the best non-conductors of heat, and if the warm water of the