THE PROBLEMS OF THE DEEP SEA. '465 



iEgean Seas. The western pool is less deep, though it reaches some 

 10,000 feet. And, just as the western end of the eastern pool com- 

 municates by a shallow passage, not a sixth of its greatest depth, 

 with the western pool, so the western pool is separated from the 

 Atlantic by a ridge which runs between Capes Trafalgar and Spartel, 

 on which there is hardly 1,000 feet of water. All the water of the 

 Mediterranean which lies deeper than about 150 fathoms, therefore, 

 is shut off from that of the Atlantic, and there is no communication 

 between the cold layer of the Atlantic (below 1 ,000 fathoms) and the 

 Mediterranean. Under these circumstances, what is the temperature 

 of the Mediterranean ? Everywhere below 600 feet it is about 55 

 Fahr. ; and consequently, at its greatest depths, it is some 20 warmer 

 than the corresponding depths of the Atlantic. 



It seems extremely difficult to account for this difference in any 

 other way than by adopting the view so strongly and ably advocated 

 by Dr. Carpenter, that, in the existing distribution of land and water, 

 such a circulation of the water of the ocean does actually occur, as 

 theoretically must occur, in the universal ocean, with which we started. 



It is quite another question, however, whether this theoretic circula- 

 tion, true cause as it may be, is competent to give rise to such move- 

 ments of sea-water, in mass, as those currents, which have commonly 

 been regarded as northerly extensions of the Gulf Stream. I shall not 

 venture to touch upon this complicated problem ; but I may take occa- 

 sion to remark that the cause of a much simpler phenomenon the 

 stream of Atlantic water which sets through the Straits of Gibraltar, 

 eastward, at the rate of two or three miles an hour or more, does not 

 seem to be so clearly made out as is desirable. 



The facts appear to be that the water of the Mediterranean is very 

 slightly denser than that of the Atlantic (1.0278 to 1.0265), and that 

 the deep water of the Mediterranean is slightly denser than that of 

 the surface ; while the deep water of the Atlantic is, if any thing, 

 lighter than that of the surface. Moreover, while a rapid superficial 

 current is setting in (always, save in exceptionally violent easterly 

 winds) through the Straits of Gibraltar, from the Atlantic to the Med- 

 iterranean, a deep under-current (together with. variable side-currents) 

 is setting out through the Straits, from the Mediterranean to the At- 

 lantic. 



Dr. Carpenter adopts, without hesitation, the view that the cause 

 of this indraught of Atlantic water is to be sought in the much more 

 rapid evaporation which takes place from the surface of the Mediter- 

 ranean than from that of the Atlantic ; and thus, by lowering the 

 level of the former, gives rise to an indraught from the latter. 



But is there any sound foundation for the three assumptions in- 

 volved here : Firstly, that the evaporation from the Mediterranean, 

 as a whole, is much greater than that from the Atlantic under cor- 

 responding parallels ; secondly, that the rainfall over the Mediterra- 



VOL. III. 30 



