THE GULF STREAM. 37 



velous things in the ocean — we can do little more than conjec- 

 ture. But we have two causes in operation which we may safely 

 assume are among those concerned in producing the Gulf Stream. 

 One of these is in the increased saltness of its water after the 

 trade-winds have been supplied with vapor from it ; and the other 

 is in the diminished quantum of salt which the Baltic and the 

 North Sea contain- The waters of the Baltic are nearly fresh ; 

 they contain only about half as much salt as sea water does gen- 

 erally (§ 248). 



Now here we have, on one side, the Caribbean Sea and Gulf of 

 Mexico, with their waters of brine ; on the other, the Baltic and the 

 North Sea, w^ith w^aters 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 intervenes ; but water is bound 

 to seek and to maintain its level ; and here, therefore, we unmask 

 one of the agents concerned in causing the Gulf Stream. What 

 is the influence of this agent — that is, how great is it, and to what 

 extent does it go — we can not say ; only it is at least one of the 

 agents concerned. Moreover, speculate as we may as to all the 

 agencies concerned in collecting these waters, that have supplied 

 the trade-winds with vapor, into the Caribbean Sea, and then in 

 driving them across the Atlantic, of this w^e may be sure, that the 

 salt which the trade-wind vapor leaves behind in the tropics has 

 to be conveyed away from the trade-wind region, to be mixed up 

 again in due proportion with the other water of the sea — the Baltic 

 included — and that these are the waters which we see running off 

 through the Gulf Stream. To convey them away is one of the 

 offices which, in the economy of the ocean, has been assigned to it. 



37. As to the temperature of the Gulf Stream, there is, in a 

 winter's day, off Hatteras and even as high up as the Grand Banks 

 in mid ocean, a difference between its waters and those of the 

 ocean near by of 20^, and even 30°. Water, we know, expands 

 by heat, and here the difference of temperature may more than 

 compensate for the difference of saltness, and leave, therefore, the 

 waters of the Gulf lighter by reason of their warmth. 



38. Being lighter and adhesive, they should therefore occupy a 

 higher level than those through which they flow. Assuming the 

 depth off Hatteras to be one hundred and fourteen fathoms, and 

 allowing the usual rates of expansion for sea water, figures show 



