268 ANNUAL OF SCIENTIFIC DISCOVERY. 



perceive that at the end of the fiftieth day it would not be so high, by 

 10 inches, as it was the first day it commenced to flow. The top of 

 this sea, therefore, is probably an inclined plane. But the salt water, 

 which has lost so much of its freshness by evaporation, becomes 

 salter, and therefore heavier. The lighter water at the straits cannot 

 balance the heavier, colder, and salter water at the isthmus, and there- 

 fore the heavier water must either run out as an under-current, or it 

 must deposit its surplus salt, and thus gradually make the bottom of 

 the Red Sea a salt bed. As we know that this latter process is not 

 going on, we infer that there is from the Red Sea an under or outer 

 current, as from the Mediterranean through the Straits of Gibraltar. 

 The rivers which discharge into the Mediterranean are not sufficient 

 to supply the waste of evaporation, and it is by this under-current that 

 the salt carried in from the ocean is returned to it again ; were it not 

 so, the bed of that sea would be a mass of solid salt. Thus it is that by 

 a system of compensations the equilibrium of the seas is maintained. 



Lieut. Maury said that he had noticed this fact, that, inasmuch as 

 the Gulf Stream was a bed of warm water, lying between banks of 

 cold water, the warm water was lighter, and therefore the surface 

 of the Gulf Stream was in the shape of a double inclined plane, like 

 the roof of a house, down which there was a shallow surface or roof 

 current, from the middle, towards either edge of the stream. This 

 fact had been confirmed in a singular way ; a person who had been 

 engaged on the Coast Survey, with observations on the Gulf Stream, 

 had noticed that, when he tried the current in a boat, he found it some- 

 times one way and sometimes another, but scarcely ever in the true 

 direction ; whereas the vessel, which drew more water, showed it con- 

 stantly in one direction. 



Lieut. Maury also called attention to this remarkable fact, that, 

 though there be well-known currents which bring immense volumes of 

 water into the Atlantic, we know of none which carry it out again, and 

 which, according to the principle before stated, ought to be found run- 

 ning back from that ocean. The La Plata, the Amazon, the Missis- 



O ' ' 



sippi, and St. Lawrence, with many other rivers, run into this very 

 small ocean, and it is not probable that all of these waters are taken 

 up from it again by evaporation; "yet the sea is not full." Where 

 does the surplus go? The ice-bearing current, from Davis's Straits, 

 which is counter to the Gulf Stream, moves an immense volume of 

 water down towards the equator. The ice-bearing current which runs 

 from the Antarctic regions, and passes near Cape Horn into the Atlan- 

 tic, and the Lagullas current which sweeps into it around the Cape 

 of Good Hope, both move immense volumes of water, and bear it 

 along also towards the equator. This water must get out again, or the 

 Atlantic would be constantly rising. A part of the Gulf Stream runs 

 around North Cape into the Arctic Ocean. The thermal charts now 

 in process of construction, under the direction of Lieut. Maury, at the 

 National Observatory, prove this, as also do the charts of Prof. Dove, 

 of Berlin. But this current probably performs its circuit of the Arctic 

 Ocean, and returns to the Atlantic with increased volume. The great 

 rivers of Northern America, Asia, and Europe, that empty into the 



