SPECIFIC GRAVITIES AND OCEANIC CIRCULATION. 329 



Thus, the Keel Sea serves as a reservoir from which a constant current of water of a 

 high salinity and temperature flows into the deeper waters of the Arabian Sea. There 

 is only one observation of the salinity of the Arabian Sea at a depth exceeding 200 

 fathoms. This was made by Admiral Makakoff in lat. 12° 48' N., and long. 45° 55' E. at a 

 depth of 437 fathoms, and was 1*0266, which is still a high salinity, being 0*0010 above 

 the average of the whole ocean at this depth. 



There have, however, been a comparatively large number of temperatures observed in 

 this part of the ocean at various depths, and as shown by the maps of temperatures 

 published in the Challenger Report the temperature of this part of the Arabian Sea off 

 the Arabian Coast is higher than elsewhere down to at least 1000 fathoms. This out- 

 flowing under-current from the Red Sea, after passing the Strait of Bab-el-Mandeb, takes an 

 approximately horizontal direction during the first part of its course, but, as it advances, 

 sinks to greater depths, thus imparting a higher temperature and specific gravity to the 

 deeper waters in the north-west of the Arabian Sea. 



But this mode of circulation is exemplified on a more extensive scale by the Medi- 

 terranean Sea in its relations to the Atlantic Ocean. To the west of the Strait of 

 Gibraltar the salinity of the surface is a little higher than 1*0270, but it quickly increases 

 in advancing eastward till about long. 10° E. it rises to 1*0280, and over the eastern 

 basin it is 1*0290, showing thus a salinity higher than ever occurs in the open sea, and 

 only exceeded by the confined waters of the northern half of the Red Sea. Thus, the 

 water of the Mediterranean, even on the surface, is much Salter than that of the Atlantic, 

 due to the dry climate of the region, where the loss from evaporation is not nearly com- 

 pensated for by the fresh water additions from the rainfall and by the rivers which empty 

 themselves into its basin. 



Carpenter's and subsequent observations and discussions have established the im- 

 portant fact that in the Strait of Gibraltar there are, after allowing for tidal influence, 

 two currents, one superimposed over the other. The upper-current is an inflowing one, 

 carrying with it the surface water of the Atlantic ; and the under-current is an outflowing 

 one, carrying out with it into the Atlantic the warmer and denser underlying water of 

 the Mediterranean. 



The submarine ridge at the strait separating the deep water of the Atlantic from that 

 of the Mediterranean is not quite 200 fathoms from the surface, and hence all direct 

 communication between the seas is confined within that depth. A little way to the east 

 of the strait the temperature of the Mediterranean at 100 fathoms is about 55°, varying 

 about a degree either way, in all probability according to the mildness or severity of the 

 preceding winter ; it increases to 58° to the east of Malta, and rises to a little above 60° 

 in the Levant. At this depth the salinity in the Atlantic to the west of the strait is 

 1*0267, but to the east of it it rises to 1*0284. 



At 200 fathoms east of the strait the temperature is 55°, and on proceeding eastward 

 it rises to 57° about long. 20° E. and to 58° in the Levant. The salinity a little to the 

 west of the strait is 1*0268 ; a little to the east of it, 1*0287 ; and in the Levant, 1*0290. 



