THE GULF STREAM. $5 



marvel is, fbat they in tlicir violence do not, by mingling the 

 Gnlf and littoral waters together (§ 70), sooner break np and 

 obliterate all marks of a division between them. But the waters 

 of the Gnlf Stream differ from the inshore waters not only in 

 colour, transparency, and temperature, but in specific gravit}^ 

 in saltness (§ 102), and in other properties, I conjecture^, also. 

 Tlierefore they may have a peculiar viscosity, or molecular 

 arrangement of their own, which further tends to prevent 

 mixture, and so preserve their line of demarkation. 



101. Action on copper. — Observations made for the purpose in 

 the navy show that ships cruising in the West Indies suffer in 

 their copper sheathing more than they do in any other seas. 

 This would indicate that the waters of the Caribbean Sea and 

 GuK of Mexico, from which the Gulf Stream is fed, have some 

 peculiar property or other which makes them so destructive 

 upon the copper of cruisers. 



102. Saltness of the Gulf Stream. — The story told by the copper 

 and the blue colour (§ 71) indicates a higher point of saturation 

 with salts than sea-water generally has; and the salometer 

 confirms it. Dr. Thomassy, a French savant, who has been ex- 

 tensively engaged in the manufacture of salt by solar evaporation, 

 informs me that on his passage to the United States he tried the 

 saltness of the water with a most delicate instrument: he found 

 it in the Bay of Biscay to contain 3-^ per cent, of salt ; in the 

 trade-wind region 4yV per cent. ; and in the Gulf Stream, off 

 Charleston, 4 per cent., notwithstanding the Amazon and the 

 Mississippi, with all the intermediate rivers, and the clouds of the 

 West Indies, had lent their fresh water to dilute the saltness of 

 this basin. 



103. Agents ' concerned. — Now the question may be asked. 

 What should make the waters of the Mexican Gulf and Caribbean 

 Sea Salter than the waters in those parts of the ocean through 

 which the Gulf Stream flows ? There are physical agents that 

 are known to be at work in different parts of the ocean, the 

 tendency of which is to make the waters in one part of the ocean 

 Salter and heavier, and in another part lighter and less salt than 

 the average of sea-water. These agents are those employed by 

 sea-shells in secreting solid matter for their structures ; they are 

 also heat* and radiation, evaporation and precipitation. In the 



* According to Dr. Marcet, sea-water contracts down to 28° ; my ovrn to 

 alDout 25.G. 



D 2 



