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, what 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 which is carried in from the ocean 
is returned to the ocean again ; were it not so, the bed of that sea 
would be a mass of sohd 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. 
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 w^ater all the way from Suez to the Straits of Babelmandeb, 
which were afterward examined by Dr. Giraud, who reported the 
following results :* 
Latitude. 
Longitude. 
Spec. Gray. 
Saline Cent, 
0 
0 
1000 parts. 
No. 1. 
Sea at Suez 
1027 
41.0 
No. 2. 
Gulf of Suez 
27.49 
33.44 
1026 
40.0 
No. 3. 
Red Sea 
24.29 
36. 
1024 
39.2 
No. 4. 
do. ^ 
20.55 
38.18 
1026 
40.5 
No. 5. 
do. 
20.43 
40.03 
1024 
39.8 
No. 6. 
do. 
14.34 
42.43 
1024 
39.9 
No. 7. 
do. 
12.39 
44.45 
1023 
39.2 
* Transact, of the Bombay Geograpli. Soc, vol. ix., May, 1849, to August, 1850. 
