SALINITY OF THE GULF-STEEAM. 69 



tlie Gulf- stream like a wall of ice.* Sometimes the line of demarcation 

 between tlie two liquid masses is so precise that it is appreciable to 

 the sight, and the exact moment when a ship leaves one current, to 

 cleave the other with its prow, may be distinguished. The water of 

 the Gulf-stream is of a beautiful azure, that of the counter-current is 

 greenish ; the first is saturated with salt, the latter contains it in a 

 much less proportion. The one is tepid, the other cold, and the thermo- 

 meter, when plunged alternately in the two liquids, instantly marks 

 the difference of temperature. On the boundary line of the currents, 

 the friction of the two masses of water flowing in opposite directions 

 produces a series of eddies, whirlpools, and short waves, which give 

 to these ocean-rivers an aspect similar to that of continental rivers. 

 Sometimes one can even hear like a dull roaring the noise of the 

 waters contending on the surface of the sea. Floating plants and 

 other fragments are whirled round on the ever-changing boundary of 

 the two contending streams. f 



The Gulf-stream, like all other currents, finally mingles with the 

 sea, and thus tends to equalize the proportion of salt and all other 

 substances contained in the liquid mass. The normal salinity of the 

 Caribbean Sea is from 36 to 37 thousandths, except in the neighbour- 

 hood of the mouths of great rivers. After having received the fresh 

 waters of the Mississippi and the visible and subterranean rivers of 

 Florida, the Gulf-stream does not contain quite 36 thousandths of 

 saline substances ; but this is gradually increased as it advances 

 towards the north. Off Newfoundland, where the waters of the St. 

 Lawrence and many other rivers, as well as the melted ice, fogs, and 

 hea\y rains, have rendered the waves of the sea more fresh, the Gulf- 

 stream contains less than 34 parts in 1000 of saline matter, but 

 it gradually increases the proportion to 35 thousandths as it shapes 

 its course towards the coasts of western Europe, and the polar 

 regions. The currents of cold water which serve as its bed are all 

 less rich in saline substances, as Forchhammer and other chemists 

 have proved. But in consequence of the incessant mixture of the 

 waters, an equalization of saltness between the currents is produced in 

 the various latitudes.:!: 



Another effect of the Gulf- stream, no less important in the 

 economy of our planet, is that which it accomplishes in concert with 



* Franklin Bache, JJnited States Coast-Survey. 



t KoW. Fitzroy, Adventure and Beagle., Appendix to Vol. II. 



X Forclihammer, FJiilosojoMcal Transactions, part I., p. 241, 1865. 



