REPORT ON OCEANIC CIRCULATION. 
13 
round to east, south, and, finally, to the south-west as they sweep over the West Indian 
Islands and past the east coasts of the States. The result is that a generous rainfall is 
deposited over the Eastern States, and on the western portion of the Atlantic adjoining. 
Thus, the specific gravity there is reduced, and it is still further reduced by the upwell- 
ing set in along that coast by the south-westerly winds blowing seawards from the land. 
These south-westerly winds pass northwards over the Atlantic, more particularly 
its eastern half, at all seasons, carrying with them their higher temperature and specific 
gravity. This is seen in the most impressive manner by the extraordinary protrusion 
northwards of the specific gravity line of 1*0260 which reaches the latitude of about 
72° N. In the North Pacific the northern extension of this line stops at lat. 34° N., 
or nearly 40° short of its position in the Atlantic. 
In the closed basin of the Gulf of Mexico, which is virtually cut off from the great 
wind system of the North Atlantic, the specific gravity of its eastern half is 1*0271. 
Again, in the closed area of the Mediterranean the specific gravity rises to 1*0280 in 
the western basin, and to 1*0290 in the eastern basin. Further, in the Red Sea, 
which is more effectually closed to the ocean than either of the above seas, the specific 
gravity rises from 1*0275 at the Straits of Bab-el-Mandeb successively to 1*0310 near 
Suez, being the highest known mean specific gravity anywhere observed on the surface 
of the sea. 
Of all the great oceans, the North Pacific shows by far the lowest specific gravity 
on the surface. The two regions of highest specific gravity, and they are comparatively 
of small extent, are marked off by the line of 1*0265. During the whole year, but 
especially the summer months, the rainfall over the western half of this great ocean 
is large, being occasioned both by the many high islands that the prevailing winds 
meet in their course, and by the Tow barometric gradients characterising this region, 
resulting in calms and light winds, to which this ocean owes its name, and a larger 
rainfall and less evaporation than would otherwise be observed. Further, as this ocean 
on its northern side is really a closed basin, neither the prevailiug winds nor the ocean 
currents they generate cross into the Arctic Ocean, but re-curve round on the coast of 
America from lat. 50° N. southward. Hence over the whole of that part of the North 
Pacific skies are more clouded, rainfall larger, and evaporation and specific gravity 
therefore less. 
In the South Pacific the area of high specific gravity is large, extending from 
South America across the whole breadth of the ocean. The region of highest specific 
gravity, 1*0270, is confined to the eastern half of the ocean, the specific gravity of the 
western half being reduced from like causes to those which lower 'the specific gravity of 
the western half of the North Pacific. 
The Indian Ocean exhibits several marked peculiarities of its own. Owing to the 
arid climates of Arabia and adjoining regions, and the high specific gravity of the Red 
