EEPORT ON OCEANIC CIRCULATION. 
21 
united ocean stream drifts westwards past the West Indian Islands and thereafter joins 
the great Atlantic north-easterly current. In these circumstances, the source of supply 
to meet the drain caused by these west-going currents cannot be found in the North 
Atlantic off the coast of Africa, that part of the ocean being filled with a strong flowing 
current which is generated and maintained by the northerly and north-easterly winds 
prevailing there, but is to be sought for in the South Atlantic near the place where the 
northern section of the south-east trades are weakest. And there it is located with the 
upwelling and characteristic low temperature of 53° which accompanies it. It may be 
pointed out that, while the temperature of the Gulf of Guinea is greater than it is over 
the ocean to westward enclosed by the isothermal of 55°, it is to the east of the area 
of lowest temperature, 53°, that the highest temperature of 59° is found on the Guinea 
coast. 
The lowest temperatures yet observed at the depth of 100 fathoms are 29°'0 by the 
Challenger in lat. 65° 42' S. and long. 79° 49' E ; 29°’2 by the Dundee whaling vessels 
off Graham’s Land; 29°‘7 by the Norwegian Expedition in lat. 75° 16' N. and long. 
0° 54' W. ; and 29°'8 by Admiral Makaroff off Okhotsk — all, it wfill be observed, closely 
approximate to each other. 
Specific Gravities at depth q/* 100 Fathoms . — In the Pacific Ocean, between lat. 
40° N. and 40° S. and long. 150° E. to 130° W., the following are the results of the specific 
gravities : — 
North Pacific. 
South Pacific. 
Number of Observations, 
23 
22 
Highest, 
1 0260 
1-0271 
Lowest, 
1-0253 
1-0260 
Mean, . . . . 
1-0256 
1-0264 
thus showing a marked difference in the specific gravities of the ocean at this depth. 
Over the region of highest temperature, which is south of the equator, the specific 
gravities are all high, but over the North Pacific they are low. They are low also in 
the region of lowest temperature, 50°, being only 1’0257. It may be added that the 
same low specific gravity occurs in lat. 15° S. and long. 94° W., where, in respect of the 
south-east trades, upwelling is to be expected, but to the west of this point, where high 
temperatures rule, it rises to 1‘0269. Hence the high specific gravities of the South 
Pacific convey down to this depth a temperature much greater than is done in the 
North Pacific, where the specific gravity is much less. 
In the North Atlantic, from lat. 12° to 40° N. the mean of the fifteen specific gravities 
observed over the whole breadth of the ocean is 1‘0270, the lowest being 1‘0264 and 
the highest 1'0278. This part of the ocean, is therefore remarkable for its high specific 
gravity, higher, indeed, than any other part of the ocean from which we have observa- 
tions. In the South Atlantic, from Cape St. Eoque to Monte Video to long. 30° W. on 
the east, there are eight observations, giving a mean specific gravity of 1'0268, which 
