84 THE PHYSICAL GEOGRAPHY OF THE SEA. 



106. Whatever be the cause that enables these trade-wind wa- 

 Amount of salt left ^ers to remain on the surface, whether it be from the 

 by evaporation. ^^^^ j^g^ Stated, and in conscqucnce of which the 

 waters of the Gulf Stream are held together in their channel ; or 

 whether it be from the fact that the expansion from the heat of 

 the torrid zone is sufficient to compensate' for this increased salt- 

 ness ; or whether it be from the low temperature and high'satura- 

 tion of the submarine waters of the intertropical ocean ; or wheth- 

 er it be owing to all of these influences together that these waters 

 are kept on the surface, suffice it to say, we do know that they go 

 into the Caribbean Sea (§ 103) as a surface current. On their 

 passage to and through it, they intermingle with the fresh waters 

 that are emptied into the sea from the Amazon, the Orinoco, and 

 the Mississippi, and from the clouds, and the rivers of the coasts 

 round about. An immense volume of fresh v/ater is supplied 

 from these sources. It tends to make the sea water, that the 

 trade- winds have been playing upon and driving along, less briny, 

 warmer, and lighter ; for the waters of these large intertropical 

 streams are warmer than sea water. This admixture of fresh wa- 

 ter still leaves the Gulf Stream a brine stronger than that of the 

 extra-tropical sea generally, but not quite so strong (§ 102) as that 

 of the trade-wind regions. 



107. The dynamics of the sea confess the power of the winds in 

 Currents created by thosc trcmcudous currcuts which storms are some- 

 ^'°™^* times known to create; and that even the gentle 

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

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

 as the trades are, is to cause what may be called the drift of the 

 sea rather than a current. Drift is confined to surface waters, and 

 the trade-winds of the Atlantic may assist in creating the Gulf 

 Stream by drifting the waters which have supplied them with va- 

 por toward 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 of the differ- 

 ence in the specific gravity of sea water in an intertropical sea on 

 one side, as compared with the specific gravity of water in north- 

 ern seas and frozen oceans on the other, that they so flow. 



108. The dynamical forces which are expressed by the Gulf 



