THE STORY OF NINETEENTH-CENTURY SCIENCE 



But the superheated equatorial air, becoming chilled, 

 descends to the surface in temperate latitudes, and con- 

 tinues its poleward journey as the, anti-trade-winds. 

 The trade- winds are deflected towards the west, because 

 in approaching the equator they constantly pass over 

 surfaces of the earth having a greater and greater veloc- 

 ity of rotation, and so, as it were, tend to lag behind 

 an explanation which Hadley pointed out in 1735, but 

 which was not accepted until Dal ton independently 

 worked it out and promulgated it in 1793. For the 

 opposite reason, the anti-trades are deflected towards 

 the east ; hence it is that the western borders of con- 

 tinents in temperate zones are bathed in moist sea- 

 breezes, while their eastern borders lack this cold-dis- 

 pelling influence.. 



In the ocean of water the main currents run as more 

 sharply circumscribed streams veritable rivers in the sea. 

 Of these the best known and most sharply circumscribed 

 is the familiar Gulf Stream, which has its origin in an 

 equatorial current, impelled westward by trade-winds, 

 which is deflected northward in the main at Cape St. 

 Roque, entering the Caribbean Sea and Gulf of Mexico, 

 to emerge finally through the Strait of Flor-ida, and 

 journey off across the Atlantic to warm the shores of 

 Europe. 



Such, at least, is the Gulf Stream as Humboldt under- 

 stood it. Since his time, however, ocean currents in 

 general, and this one in particular, have been the subject 

 of no end of controversy, it being hotly disputed whether 

 either causes or effects of the Gulf Stream are just what 

 Humboldt, in common with others of his time, con- 

 ceived them to be. About the middle of the century, 

 Lieutenant M. F. Maury, the distinguished American 



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