In the Atlantic, on the contrary, communication with the Arctic is comparatively open, by Davis' Strait to the north-west, and the vast channel—divided into two unequal portions by Iceland—extending from the eastern shores of Greenland to Norway. That there is a " set " of the colder Arctic waters into the Atlantic, even along the surface, is proved by the fogs off Newfoundland, formed by the impact of the polar currents, from Baffin Bay and East Greenland Channel, on the still warm waters of the Gulf Stream. That this cola northern water presses south along the eastern coasts of North America, is proved by the "cold wall," which is so distinctly marked off Massachusetts that a vessel may have her bow in warm, and her stern in cold, water. The sur face waters of the channel between Iceland and Norway are apparently a north-easterly drift of comparatively warm water, probably a continuation of the Gulf Stream ; but even here the " cold and warm " areas, found side by side, show that a cold stream from the Arctic moves not only along the surface, but also along the bottom, into the Atlantic. But while the average bottom temperature of the North Atlantic is 35.3 F., that of the South Atlantic is 32.9 F. ; so that, while the Arctic influx is in some measure impeded by the ridges which form the northern boundaries of the North Atlantic, the South Atlantic communicates more freely with the Antarctic, and thus receives a greater inflow of the South Polar waters.
A remar' ab'e fact in connection with the temperature of the ocean is, ti at the temperature of the water in enclosed basins is uniformly the same as that of the water at the sum mits of the surrounding ridges. Thus, in the Sulu Sea, the temperature decreases from 84° F. at the surface to 50.5° F. at 200 fathoms. In the adjacent China Sea the surface tem perature and that at 200 fathoms is the same—viz., 84° and 50.5° F. But while the Sulu Sea preserves a uniform tem perature of 50.5° F. from 200 fathoms to the bottom (1780 fathoms), the temperature of the China Sea falls from 50.5° F. at 200 fathoms to 37° F. at the bottom. This uniformity of temperature is probably limited to the minor tropical basins, no such invariableness being found in the larger oceanic basins ; and is evidently due to the fact that the water in such enclosed basins, having no contact with water colder than that overly ing them, must, sooner or later, acquire the same temperature.