128 THE PHYSICAL GEOGRAPHY OF THE SEA. 



and that the surface waters near Suez are Salter than those near 

 the mouth of the Red Sea. 



246. And, to show why there should be an outer and under 

 current from each of these two seas, let us suppose the case of a 

 long trough, opening into a vat of oil, with a partition to keep the 

 oil from running into the trough. Now suppose the trough to be 

 filled up with wine on one side of the partition to the level of the 

 oil on the other. The oil is introduced to represent the lighter 

 water as it enters either of these seas from the ocean, and the wine 

 the same water after it has lost some of its freshness by evapora- 

 tion, and therefore has become Salter and heavier. Now suppose 

 the partition to be raised, wdiat would take place ? Why, the oil 

 would run in as an upper current, overflowing the wine, and the 

 wine would run out as an under current. 



247. The rivers which discharge in the Mediterranean are not 

 sufficient to supply the waste of evaporation, and it is by a proc- 

 ess similar to this that the salt wdiich is carried in from the ocean 

 is returned to the ocean again ; w^ere it not so, the bed of that sea 

 would be a mass of solid salt. The equilibrium of the seas is 

 preserved, beyond a doubt, by a system of compensation as exqui- 

 sitely adjusted as are those by which the '' music of the spheres" 

 is maintained. (See Appendix C.) 



248. The above about under currents is theory : Now let us see 

 the results of actual observation upon the density of water in the 

 Red Sea and the Mediterranean, and upon the under currents that 

 run out from these seas. 



Four or five years ago, Mr. Morris, chief engineer of the Ori- 

 ental Company's steam-ship Ajdaha, collected specimens of Red 

 Sea water all the way from Suez to the Straits of Babelmandeb, 

 w^hich were afterward examined by Dr. Giraud, who reported the 

 following results :* 



Transact, of the Bombay Geograph. Soc, vol. ix., May, 1849, to August, 1850. 



