34 THE PHYSICAL GEOGRAPHY OF THE SEA. 



for a period of ten years ; and it is said the fact has been estab- 

 lished, that the copper on the bottom of ships cruising in the 

 Caribbean Sea and Gulf of Mexico suffers more from the action 

 of sea water upon it than does the copper of ships cruising in 

 any other part of the ocean. In other words, the salts of these 

 waters create the most powerful galvanic battery that is found in 

 the ocean. 



27. Now it may be supposed — other things being equal — that 

 the strength of this galvanic battery in the sea depends in some 

 measure upon the proportion of salts that the sea waters hold in 

 solution. 



If, therefore, in the absence of better information, this sugges- 

 tion be taken as a probability, we may go a step farther, and draw 

 the inference that the waters of the Gulf Stream, as they rush out 

 in such volume and with such velocity into the Atlantic, have not 

 only chemical affinities peculiar to themselves, but, having more 

 salts, they are therefore specifically heavier than the sea water 

 through which they flow in such a clear and well-defined channel. 



28. The affinities of which I speak, and which are manifested 

 in the reluctance of the Gulf Stream to mingle its waters with 

 those of the ocean (§ 2), may be the resultant of their galvanic 

 properties, higher temperature, and greater degree of saltness, all 

 combined. 



29. If the story told by the copper (^ 26) be taken to mean a 

 higher point of saturation with salts, and, consequently, a greater 

 specific gravity for the waters of the Gulf and Caribbean Sea 

 than for the waters of the broad ocean at the same temperature, 

 then we should have as a source for the initial velocity of the 

 Gulf Stream, not, indeed, a higher level of the waters in the Gulf, 

 but a greater density. 



30. Mow a greater density, implying, of course, a greater specific 

 gravity, would serve, as well as a higher level, to impart an initial 

 velocity, but with this difference : the heavier waters would, by 

 reason of their greater pressure, be ejected through the most con- 

 venient aperture out into the ocean of lighter waters by a sort of 

 squii'ting force. But what, it may be asked, should make the 

 waters of the Mexican Gulf and Caribbean Sea Salter than the 

 waters of like temperature in those parts of the ocean through 

 which the Gulf Stream flows ? 



