THE GULF STREAM. 
37 
velous things in the ocean — we can do httle 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, with waters 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 we 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 
