REPORT ON OCEANIC CIRCULATION. 
31 
it gradually rises on proceeding southward to 75° near the Strait, outside which it 
quickly falls to 70° and 65° about long. 53° E. At this depth, in lat. 22° N., the 
specific gravity is 1-0302, immediately outside the Strait 1-0282, and off Socotra 1*0264. 
At 200 fathoms, and at greater depths, 200 fathoms being about the depth of the submarine 
ridge separating this sea from the ocean, the temperature is 71°. The specific gravity 
in lat. 22° N. is 1-0303, off Aden 1*0267, and near Socotra T0264, being thus nearly 
the same as the specific gravities at 100 fathoms. At 300 fathoms the specific gravity 
is 1*0303, and it is probable that this degree of salinity obtains down to the bottom of 
the sea. 
An undercurrent of warm water of great saltness issues from the Red Sea, just as 
happens in the case of the Mediterranean, and, as will appear, it has a marked influence 
on the temperature and specific gravity of the north-western part of the Indian Ocean. 
The Persian Gulf. 
The mean annual surface temperature at the head of the Gulf is 80°; it rises to 82° 
a little to the west of Ormuz, and outside the Gulf falls to 80° in long. 60° E. In this 
last situation the specific gravity is 1-0271, but in the Gulf itself no specific gravities 
have been observed. Its influence, therefore, on the temperature of the Arabian Sea 
adjoining will be similar, though less in degree, to that of the Red Sea. 
The Indian Ocean. 
This ocean differs essentially from the other great oceans in being completely land¬ 
locked on its north side, in comparatively low latitudes, thus putting it, as a whole, 
more fully under the influence of the Southern Ocean, as will be seen as the lower 
depths are dealt with. 
The most noticeable feature of the mean annual temperature of the surface is that 
the isothermals are more regularly distributed over the Indian Ocean than over any of 
the other oceans. From about lat. 13° S. to the north of the ocean the temperature 
exceeds 80°, except the north-west portion of the Arabian Sea, as shown on the 
map (Map 2). Over this tract temperature is lowered by the up welling produced by the 
prevailing N.W. winds of that region, which consequently blow from the land seaward, 
driving the warm surface current before them, the place of the surface water being 
taken by the colder water rising from lower depths. This lowering is continued along 
the east coast of Africa to some distance south of Cape Guardafui. To the south of 
lat. 13° S. temperature falls with characteristic regularity as the latitude increases, 
