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. Now 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 ? 
