chap, viii.] THE GULF-STREAM. 383 



Captain Maury writes 1 that "the dynamical force 

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

 difference as to specific gravity of intertropical and 

 polar waters." " The dynamical forces which are 

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

 priety he said to reside in those northern waters as 

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

 Carihhean 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 away 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 



1 Maury's Physical Geography of the Sea, op. cit. 



