424i Scientific Intelligence, — Hydrology. 



HYDROLOGY. 



7. Submarine Currents, — The temperature of the lower 

 depths of the ocean, between the tropics, is from ^2° to 25° 

 Cent, below the lowest point at which seamen have observed 

 the thermometer at the surface. Thus, this very cold bed at 

 the bottom is not maintained by the precipitation of the super- 

 ficial layers ; and it hence seems impossible not to admit that 

 submarine currents transport the watfer of the icy ocean to 

 beneath the equator. 



The consequence of this is important ; and its reality is 

 confirmed hy the experiments which have been made in the 

 Mediterranean. This inland sea cannot receive the cold cur- 

 rents which proceed from the polar regions in any other way 

 than through the narrow Strait of Gibraltar. Hence, in the 

 Mediterranean, the temperature of the greatest depths is never 

 so low, aeteris paribus, as in the wide ocean. We may go 

 further, and state that in no situation does the temperature 

 of the bottom of the Mediterranean appear to descend lower 

 than the mean temperature of the place. If this last cir- 

 cumstance be confirmed, it will follow that no portion of the 

 icy stream coming from the poles enters the tln-eshold, so to 

 speak, of the Strait of Gibraltar. When Captain Durville 

 sailed, some years since, in the first voyage of V Astrolabe, I 

 conceived it would be useful to examine if the phenomena of 

 the ocean, as to the temperature of great depths, exhibited them- 

 selves in all their purity immediately to the westward of the 

 Straits. The Academy then seconded my views ; and upon this 

 recommendation some observations of the required nature were 

 made at a short distance from Cadiz. The result was an entire 

 correspondence with those performed in the Mediterranean. 



This curious fact seems to admit of two different explana- 

 tions. It may be supposed either that the polar current is com- 

 pletely repelled by the submarine current which proceeds from 

 the Mediterranean to the ocean, the existence of which seems 

 scarcely doubtful. Or, it may be supposed also, that the bold 

 projection of the southern coast of Portugal does not permit the 

 current of cold water coming from the north to sweep round 

 almost at a right angle to reach the parts which approach the 

 mouth of the Guadalquiver. In this state of the question, the 



