A HISTORY OF SCIENCE 



of continents in temperate zones are bathed in moist 

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

 dispelling 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 cir- 

 cumscribed 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 

 Florida, 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 sub- 

 ject 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, conceived them to be. About the middle of the 

 century Lieutenant M. F. Maury, the distinguished 

 American hydrographer and meteorologist, advocated 

 a theory of gravitation as the chief cause of the cur- 

 rents, claiming that difference in density, due to differ- 

 ence in temperature and saltness, would sufficiently 

 account for the oceanic circulation. This theory 

 gained great popularity through the wide circulation 

 of Maury's Physical Geography of the Sea, which is said 

 to have passed through more editions than any other 

 scientific book of the period; but it was ably and vig- 

 orously combated by Dr. James Croll, the Scottish 

 geologist, in his Climate and Time, and latterly the old 



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