90 THE OCEAN. 



up in the space of 60 years. Owing to their higher level, thq 

 waves of the Indian Ocean are carried into the Arabian Gulf by the 

 Straits of Babel- Mandeb ; and this flow, superficial or submarine, 

 must make itself felt with all the more force, because during eight 

 months of the year the winds blow from the north to the south, pre- 

 cisely in the axis of the lied Sea, and would thus tend to empty the 

 gulf, if the laws of gravity permitted. But whatever be the swift- 

 ness of the current coming from the Indian Ocean, a portion of its 

 water evaporates on the way, and, in consequence, the liquid mass, 

 diminished by a certain quantity from evaporation, must become 

 Salter and Salter in proportion as it advances to the north. In fact, 

 it has been established by direct analyses, that the quantity of salt 

 contained in the same volume of water increases gradually from 

 Aden to Suez. From a little more than 39 parts in a thousand at 

 the entrance to the gulf, it rises to 41 and even 43 parts in the 

 thousand at the northern extremity.* Dr Buist, a scholar of Bom- 

 bay, has calculated that if the Red Sea did not return to the ocean 

 the salt that is concentrated there in consequence of evaporation, it 

 would end in being changed into a solid mass of salt in a space of 

 time certainly less than three thousand years, and perhaps in only 

 fifteen or twenty centuries. t Now the Bed Sea has already existed 

 for thousands and thousands of years, and its waters (more salt than 

 those of other seas, it is true) are still very far from being in a state 

 of saturation. AYe therefore come to this inevitable conclusion, that 

 a very salt submarine current flows through the Straits of Babel- 

 Mandeb into the Indian Ocean, in an opposite direction, and below 

 the superficial current which supplies the Arabian Gulf. As in 

 houses, each door serves at the same time as a passage for two con- 

 trary currents, that of the warmer and lighter air which escapes 

 above, and that of the colder and heavier air penetrating below, so in 

 the seas, each strait is traversed by two streams, different in tem- 

 perature and in their saline contents. 



All these phenomena of exchange, which occur in such a striking 

 manner at the entrance to the Bed Sea, the Mediterranean, and the 

 Baltic, are reproduced in the vast space of the seas wherever the 

 equilibrium of level, warmth, or saltness, is disturbed by any cause 

 whatever. Thus the Atlantic, much better supplied than the South 

 Sea as regards rains and affluents, is nevertheless not more elevated ; 

 and on its side the Pacific does not contain a greater quantity of salt 

 than the other oceans. On all parts of the planet, seas bathing the 

 * See above, p. 23. f Maury, Geography of the Sea. 



