94 CURRENTS IN THE OCEAN. SECT. XIII. 



the seas, which is restored by means of currents. Winds 

 and the periodical melting of the ice at the poles occa- 

 sion temporary water-courses ; but by far the most im- 

 portant causes are the centrifugal force induced by the 

 velocity of the earth's rotation, and variations in the 

 density of the sea. 



The centrifugal force may be resolved into two forces 

 one perpendicular, and another tangent to the earth's 

 surface (N. 157). The tangential force, though small, 

 is sufficient to make the fluid particles within the polar 

 circles tend toward the equator, and the tendency is 

 much increased by the immense evaporation in the 

 equatorial regions from the heat of the sun, which dis- 

 turbs the equilibrium of the ocean. To this may also 

 be added the superior density of the waters near the 

 poles, partly from their low temperature and partly 

 from their gravitation being less diminished by the ac- 

 tion of the sun and moon than that of the seas of lower 

 latitudes. In consequence of the combination of all 

 these circumstances, two great currents perpetually set 

 from each pole toward the equator. But as they come 

 from latitudes where the rotatory motion of the surface 

 of the earth is very much less than it is between the 

 tropics, on account of their inertia, they do not im- 

 mediately acquire the velocity with which the solid part 

 of the earth's surface is revolving at the equatorial re- 

 gions ; from whence it follows that within twenty-five 

 or thirty degrees on each side of the line, the ocean 

 appears to have a general motion from east to west, 

 which is much increased by the action of the trade 

 winds. This mighty mass of rushing waters at about 

 the tenth degree of south latitude is turned toward the 

 north-west by the coast of America, runs through the 

 Gulf of Mexico, and passing the Straits of Florida at 

 the rate of five miles an hour, forms the well-known 

 current of the Gulf-stream, which sweeps along the 

 whole coast of America and runs northward as far as 

 the bank of Newfoundland, then bending to the east it 

 flows past the Azores and Canary islands, till it joins 

 the great westerly current of the tropics about latitude 

 21 north. According to M. de Humboldt this great 

 circuit of 3800 leagues, which the waters of the Atlantic 



