THE GULF STREAM. 39 



It is safe to assume that the trade-winds, bj their constant force, 

 do assist to skim the Atlantic of the water that has supplied them 

 with vapor, driving it into the Caribbean Sea, whence, for causes 

 unknown, it escapes loy the channel of the Gulf Stream in prefer- 

 ence to any other.* 



37. In the present state of our knowledge concerning this won- 

 derful phenomenon — for the Gulf Stream is one of the most mar- 

 velous things in the ocean — we can do little more than conjecture. 

 But we have two causes in operation which we may safelj 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 v/ith vapor from it, be it much or little ; 

 and the other is in the diminished quantum of salt which the Bal- 

 tic and the Northern Seas contain. The waters of the Baltic are 

 nearly fresh ; they are said to contain only about half as much 

 salt as sea water does generally. 



38. Now here we have, on one side, the Caribbean Sea and 

 Gulf of Mexico, with their waters of brine ; on the other, the great 

 Polar basin, the Baltic and the North Sea, the two latter with 

 waters that are but little more than brackish, f In one set of 

 these sea-basins the water is heavy ; in the other it is light. Be- 

 tween 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 in- 

 fluence 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 



* The fact is familiar to all concerned in the manufacture of salt by solar evapora- 

 tion, that the first show of crystallization commences at the surface. 



+ The Polar basin has a known water area of 3,000,000 square miles, and an unex- 

 plored area, including land and water, of 1,500,000 square miles. Whether the water 

 in this basin be more or less salt than that of the inter-tropical seas, we know it is quite 

 different in temperature, and difference of temperature will beget currents quite as 

 readily as difference in saltness, for change in specific gravity follows either. 



