CHAP, Vill] THE GULF-STREAM. 883 
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 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. 
