1870.] 



Deep-sea Resea?'ches. 



207 



accounts that have been recorded of vessels sunk in the narrower part of 

 the Strait having floated up near Tangier*. But to these accounts no great 

 importance is assigned by Admiral Smyth f, who seems inclined to attribute 

 the occurrences— if they really took place as narrated — to the action of 

 the lateral Surface-outflow. 



112. The only objection that has been advanced, so far as we are aware, 

 to the hypothesis of a westerly undercurrent, is based on the existence of 

 the comparatively shallow ridge which (as already stated) crosses the 

 western end of the Gut between Capes Trafalgar and Spartel. The exist- 

 ence of this ridge, in the opinion of Sir Charles Lyell %, " has dispelled the 

 idea which was once popular that there was a counter-current at a consi- 

 derable depth in the Straits of Gibraltar, by which the water which flows 

 in from the Atlantic is restored to that ocean." — But the validity of this 

 objection has been disputed, and we think successfully, by Captain Maury, 

 who, after citing many cases in which a deep current comes up to near the 

 surface, concludes as follows : — " To my mind the proofs derived from rea- 

 son and analogy are as clear in favour of this undercurrent from the Me- 

 diterranean, as they were in favour of Leverrier's planet before it was 

 seen through the telescope at Berlin ,, §. 



113. The analogy of the Red Sea and the incurrent through the Strait 

 of Babelmandeb, which is adduced by Capt. Maury in support of this view, 

 is a very cogent one. The evaporation from the Bed Sea is well known to 

 be enormous, its annual amount being estimated by Dr. Buist as equal to 

 a sheet of water eight feet thick, corresponding in area with the whole ex- 

 panse of that sea. Of the whole amount of fresh water thus drawn off, 

 scarcely any is returned either by rivers or rains. But the level is kept 

 up by a strong current that continually sets in through the Strait of 

 Babelmandeb ; and as this current brings in salt water, there would be 

 a continual and very rapid accumulation of salt in the trough of ,the Red 

 Sea if the denser water were not carried orTby an outward current beneath. 

 Now since all the observations hitherto made upon the density of the water 

 of the Red Sea show it to be very little greater than that of the Indian 

 Ocean ||, there would seem no escape from the conclusion that such a re- 

 verse undercurrent must really exist. 



114. We shall now present, in a concise and connected form, the General 

 Results of the inquiries we have ourselves made to determine this ques- 

 tion ; the particulars having been detailed, as they presented themselves, in 

 the preceding Narrative. These results were of a twofold character. It 

 was our object, (1) to detect if possible by mechanical means any movement 

 which may be taking place in the lower stratum of water in opposition to 



* Philosophical Transactions, vol. xxsiii. p. 192. 



t Mediterranean, pp. 154-157. 



\ Principles of Geology, 10th edit. vol. i. p. 563. 



§ Physical Geography of the Sea, 1860, pp. 194-196, 



|| Transactions of Bombay Geographical Society, vol. is. p. 39. 



