188 niYSICAL GEOGllAPHY OF THE SEA, AND ITS METEOROLOGY. 



that sets outward to the grand ocean, which this accident very 

 much demonstrates ; and, jiossibly, a great part of the water 

 which runs into the Straits retui-ns that way, and along the two 

 coasts before mentioned; otherwise this ship must, of course, 

 have been driven towards Ceuta, and so upwards. The water in 

 the Gut must be very deep ; several of the commanders of our 

 ships of war having attempted to sound it with the longest lines 

 they could contrive, but could never find any bottom." 



385. Saltness of the 3Ied{terranean. — In 1828, Dr. Wollaston, in 

 a paper before the Philosophical Society, stated that he found 

 the specific gravity of a specimen of sea water, from a depth of 

 six hundred and seventy fathoms, fifty miles within the Straits 

 to have a " density exceeding that of distilled water by more 

 than four times the usual excess, and accordingly leaves, upon 

 evaporation, more than four times the usual quantit}'- of saline 

 residuum. Hence it is clear that an under current outward of 

 such denser water, if of equal breadth and depth with the 

 current inward near the surface, would carry out as much salt 

 below as is brought in above, although it moved with less than 

 one fourth part of the velocity, and would thus prevent a per- 

 petual 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 English 

 Navj", who had collected it for Dr. Marcet. Dr. Marcet 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 fourths of the sea 

 water which runs into the Mediterranean, is evaporated from it, 

 leaving a brine for the under current having four times as much 

 salt as the water at the surface 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 under current from 

 the jVIediterranean. 



386. The escape of salt and heavy imter hy under currents. — How- 

 ever that may be, these facts, and the statements of the Secre- 

 tary of the Geographical Society of Bombay (§ 382), seem to 

 leave no room to doubt as to the existence of an under current 

 both from the Red Sea and Mediterranean, and as to the cause of 

 the surface current which flows into them. I think it a matter 

 of demonstration. It is accounted for (§ 377) by the salts of the 



