CHAP.vui.] THE GULF-STREAM. 383 



Captain Maury writes^ that "the dynamical force 

 that calls forth the Gulf-stream is to be found in the 

 difference as to specific gravity of intertropical and 

 polar waters." " The dynamical forces which are 

 expressed by the Gulf-stream may with as much pro- 

 priety be said to reside in those northern waters as 

 in the West India seas : for on one side we have the 

 Caribbean sea and Gulf of Mexico with their waters 

 of brine ; on the other the great polar basin, the 

 Baltic, and the North Sea, the two latter with waters 

 which are little more than brackish. In one set of 

 these sea-basins the water is heavy; in the other it is 

 light. Between them the ocean intervenes ; but water 

 is bound to seek and to maintain its level ; and here, 

 therefore, we unmask one of those agents concerned 

 in causing the Gulf-stream. What is the power of this 

 agent ? Is it greater than that of other agents ? and 

 how much ? We cannot say how much ; we only 

 know it is one of the chief agents concerned. More- 

 over, speculate as we may as to all the agencies con- 

 cerned in collecting these waters, that have supplied 

 the trade-winds with vapour, into the Caribbean Sea, 

 and then in driving them across the Atlantic, we are 

 forced to conclude that the salt which the trade-wind 

 vapour leaves behind it in the tropics has to be con- 

 veyed aM^ay from the trade-wind region, to be mixed 

 up again in due proportion with the other water of 

 the sea— the Baltic Sea and the Arctic Ocean included 

 —and that these are some of the waters, at least, 

 which we see running off through the Gulf-stream. 

 To convey them away is doubtless one of the offices 

 which in the economy of the ocean has been assigned 



" Maui-y's Physical Geography of the Sea, op. cit. 



