Page:The fairy tales of science.djvu/198

 his mouth with hot porridge and expressed his surprise at the slowness with which it cools, without being able to assign the philosophical reason of the phenomenon.

The currents that exist in the ocean are produced by convection, and are quite as easily accounted for as the currents in the heated water of our tea-kettle. The oceanic currents are of great constancy and regularity, but they are modified in their direction by the general distribution of land and water on the earth's surface. That part of the ocean which is immediately under the tropics, and between the eastern and western hemispheres, for example, becomes highly heated. The water being greatly expanded, flows off on either side towards the poles, acquiring a westerly direction as it passes south of the coast of Guinea, and striking the promontory of Cape St. Roque, on the South American coast, is split into two streams. The smaller one continues southwards towards Cape Horn; while the larger current maintains a north-westerly course into the Gulf of Mexico, where it receives further accessions of heat, and is gradually changed in its direction. It now passes along the southern shores of North America, and finally emerges northward in the narrow channel between the peninsula of Florida and the Bahama Islands,where it assumes the name of the Gulf Stream. The temperature of this current is found to be nine or ten degrees higher than that of the neighbouring