OCEAN CURRENTS TEMPERATURE AND VELOCITY The great distinction between currents and the other movements of the sea is—that the former alone effect an actual transference of the water from one part of the ocean to another. Both wind-waves and tides are mere undulations, leaving the water, as regards temperature, almost exactly the same. Ocean-currents, on the contrary, are the chief agents in the distribution of solar heat. Surface currents convey the heated waters of the tropics north and south to temper the rigorous cold of remote polar regions ; while the iceberg-laden polar cur rents, and icy-cold underflow, moderate the otherwise unbear able heat of the tropics. The temperature of currents, there fore, depends primarily on their origin. Thus the Peruvian current, derived from the Antarctic drift, is 47° F. colder than the overlying air, and 10° F. colder than the adjacent open sea ; while the equatorial current in the Atlantic has an average temperature of 75° F., or 6° above the water on either side. The Gulf Stream, as it leaves the Narrows, has a tem perature of 80° F. ; and in mid-ocean, before its final dispersion, it is still 8° or 10° higher than the adjoining water ; while in winter, off Newfoundland, it is as much as 30° F. higher than the water through which it flows.
The velocity of ocean currents depends on several con ditions, being modified by the configuration of the coast and depth of the water. The velocity of some currents decrease
rapidly ; others gradually flow faster. Thus the Gulf Stream rushes through the Straits of Florida at the rate of 4 miles an hour ; but its velocity gradually decreases, being off Cape Hatteras 3 miles, and off Newfoundland 1 miles an hour, gradually merging into the slow north-easterly drift of the Atlantic of 5 miles a day. In the Pacific, on the contrary, the Japanese current, with a velocity of only 10 miles a day off Formosa, flows past the southern coasts of Japan at the rate of 50 miles a day. The great equatorial currents flow at the rate of 20 to 30 miles a day in the Atlantic, 15 to 24 miles in the Pacific, and 15 to 50 miles in the Indian Ocean. Currents generally attain their maximum velocity when passing through narrow channels,—e.g., the Gulf Stream at the Narrows—or when rounding the extremities of continents, e.g., Cape Horn current, Agulhas current, &c. Generally speaking, warm cur rents flow much faster than cold ones ; thus both the Arctic and Antarctic currents are very slow, scarcely exceeding 15 miles a day, while the Gulf Stream and other warm currents sweep on at a rate of 50, or even 100, miles a day.