CUBBENTS OF THE SEA. 181 



equal breadth and depth with the ciuTent invfard near the surface, 

 would carry out as much salt below as is brought in above, although 

 it moved ^vith less than one fomih part of the velocity, and would 

 thus prevent a perpetual increase of saltness in the Mediterranean 

 Sea beyond that existing in the Atlantic." The doctor obtained 

 this specimen of sea water from Captain, now Admiral Smyth, of 

 the Enghsh Navy, who had collected it for Dr. Marcet. Dr. Mar- 

 cet died before receiving it, and it had remained in the admiral's 

 hands some time before it came into those of Wollaston. It may, 

 therefore, have lost something by evaporation ; for it is difficult to 

 conceive that all the river water, and three fom^ths of the sea water 

 which rmis into the Mediterranean, is evaporated from it, lea^dng 

 a brine for the under cmTent having /owr times as much salt as the 

 water at the smface of the sea usually contains. Very recently, 

 M. Coupvent des Bois is said to have shown, by actual observation, 

 the existence of an outer and mider cmTent from the Mediterranean. 

 386. However that may be, these facts, and the statements of 

 The escape of salt the Secretary of the Geogi'aphical Society of Bombay 

 ^der currents. (§382), secm to Icavo uo room to doubt as to the 

 existence of an under cmTent both fi'om the Bed Sea and Mediter- 

 ranean, and as to the cause of the sm-face current which flows into 

 them. I think it a matter of demonstration. It is accounted for 

 (§ 377) by the salts of the sea. Writers whose opinions are 

 entitled to great respect differ with me as to the conclusiveness of 

 this demonstration. Among those wTiters are Admiral Smyth, of 

 the British Navy, and Sir Charles Lyell, who also differ with each 

 other. In 1820, Dr. Marcet being then engaged in stud^dng the 

 chemical composition of sea water, the admiral, with his usual 

 alacrity for doing " a kind tmii," undertook to collect for the doctor 

 specimens of Mediterranean water from various depths, especially 

 in and al^out the Straits of Gibraltar. Among these was the one 

 (§ 385) taken fifty miles within the Straits from the depth of six 

 hundred and seventy fathoms (four thousand and twenty feet), 

 which, being four times Salter than common sea water, left, as we 

 have jiLst seen, no doubt in the mind of Dr. Wollaston as to the 

 existence of this under cmTent of brine. But the indefatigable 

 admiral, in the com'se of his celebrated smwey of the Mediterranean, 

 discovered that, while inside of the Straits the depth was upwards of 

 nine hmidred fathoms, yet in the Straits themselves the depth 

 across the shoalest section is not more than one hundred and sixty* 



* " The Mediterranean."' 



