38 rnrsicAL geography of the sea, and its sieteorology. 



storms are sometimes known to create ; and that even tlie gentle 

 trade-winds may have influence and effect npon the currents of 

 the sea has not been denied (§ 82). But the effect of moderate 

 vrinds, as the trades are, is to cause what may he called the 

 drift of the sea rather than a current. Drift is confined to sur- 

 face waters, and the trade-winds of the Atlantic may assist in 

 creating the Gulf Stream by drifting the waters which have 

 supplied them with vapour towards the Caribbean Sea. But 

 admit never so much of the water which the trade-winds have 

 played upon to be drifted into the Caribbean Sea, what should 

 make it flow thence with the Gulf Stream to the shores of 

 Europe ? It is because there is room for it there ; and there is 

 room for it because of the difi"erence in the specific gravity of 

 sea- water in an intertropical sea on one side, as compared with 

 the specific gravity of water in northern seas and frozen oceans 

 on the other. 



108. Tlie dynamical force that calls forth the Gulf Stream to he 

 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 propriety be said to reside in those 

 northern waters as in the West India seas ; for on one side w^e 

 have the Caribbean Sea, and Gulf of Mexico, with their waters 

 of brine ; on the other, the Great Polar basin, the Baltic, and the 

 Xorth Sea, the two latter with waters that are but 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 inter- 

 venes ; but water is bound to seek its equilibrium as its level ; 

 and here, therefore, we unmask one of the 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 knov^ it is one of the chief agents con- 

 cerned. Moreover, speculate as we may as to all the agencies 

 concerned 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 



* Tlie Polar basin has a known -svatcr area of 3,000,000 square miles, and an 

 unexplored area, including land and water, of 1,500,000 square miles. Whetlier 

 the water in this basin be more or less salt than that of the intertropical seas, 

 we know it is quite different in temperature, and difference of temperature will 

 beget currents quite as readily as difference in saltness, for change in specific 

 gravity follows either. 



