CtlBEENTS OF THE EED SEA. 



89 



ever increasing layers. In order that the equilibrium of saltness 

 between the two seas should not be interrupted, it is necessary that 

 the Mediterranean should send its saltest waters to the Atlantic. 

 This is, in fact, what takes place. Besides the lateral eddies that 

 occur along the shores on each side of the current coming from the 

 Atlantic, a Mediterranean counter-current flows below the lighter 

 superficial waters, and takes its direction towards the ocean. This 



Fig. 25.— Profile of the Straits of Gibraltar. 



submarine river, which passes the Straits of Gibraltar to be lost in 

 the open sea, is, as chemical analyses have shown, a current of heavy 

 water, almost saturated with salt. Thus, an exchange is accomplished 

 through that narrow passage ; the Atlantic gives to the Mediterranean 

 the waters which it needs, and receives in return its superfluity of 

 salt to difl'use through the ocean. The sea endeavours incessantly to 

 re-establish its constantly disturbed equality at the boundary of the 

 two marine basins, at a depth of about 546 fathoms. 



This harmony of the forces of nature is shown in a still more 

 striking manner at the entrance to the Red Sea. This elongated gulf, 

 which is nearly 1480 miles in length from the Strait of Babel- 

 Mandeb to Suez, receives from the atmosphere and the bordering coun- 

 tries so slight a quantity of water that it may be considered as absolutely 

 nothing. It rains but very rarely over the sheet of water lying be- 

 tween the two deserts of Egypt and Arabia, and not a single torrent 

 brings down its waters to it. The Red Sea is therefore only an im- 

 mense basin of evaporation, and the annual loss is all the greater 

 that the rays of the sun shine almost always from a cloudless sky. 

 The portion of fluid transformed into vapour is estimated at about 

 eight-tenths of an inch per 24 hours ; that is to say, nearly 23 feet 

 per year, so that if the gulf was completely closed, the water, whose 

 mean depth does not exceed 220 fathoms, would be entirely dried 



