REPORT ON OCEANIC CIRCULATION. 
25 
north of the equator of the high specific gravities of its upper layers, so that descent of 
the higher temperature is greatly retarded. The other cause is the greater depth to 
which these currents extend that have their origin in the trade winds of the South 
Atlantic, which, of all trade winds, are the strongest and most continuous. 
The mean of twelve observations of specific gravity in the Gulf of Guinea is 1’0256, 
being thus markedly lower than the specific gravity observed to the west of the Canaries. 
In the Pacific the highest temperatures are round the Galapagos Islands and to 
the north of New Zealand, where the temperature rises to 41°, being thus 10° lower 
than the highest in the North Atlantic. These positions accord with those of the 
highest temperature at less depth. 
There is seen, just as at the 500 fathoms depth (Map 7), a local region of slightly 
lower temperature to the east of Australia between lat. 10° to 22° S. and long. 145° E. to 
178° W. A better knowledge of the contours of the bed of the ocean and some know- 
ledge of the distribution of specific gravities may be looked forward to as the explanation 
of this temperature. 
Depth q /" 700 Fathoms (Map 9 ). — The mean temperature of the ocean at this 
depth is 38 ° T , or 0°'9 lower than at 600 fathoms. The high temperature from the 
Straits of Gibraltar oceanwards is still the striking feature of the temperature. Though 
a comparatively high temperature still extends westwards to America, yet the high 
temperatures marking it out from the other oceans may be regarded as now restricted 
to the eastern half of the North Atlantic. The high specific gravity of 1'0268 has been 
recorded to the east of the Azores, whereas in the Gulf of Guinea, of the ten specific 
gravities observed by Mr Buchanan, the highest was 1'0260 and the mean of the 
whole 1 ’ 0255 , — the high specific gravity of 1’0268 near the Azores thus still pointing 
to the denser warmer waters of the Mediterranean as their source. The relative 
distribution of the temperature in the South Atlantic and the Pacific remain 
substantially the same, and as regards the South Pacific even to a comparatively low 
temperature to the north-east of Australia. 
It may be remarked that on nearing the Pacific coast of America in equatorial 
regions the temperature rises one degree, and in the Gulf of Guinea near the coast 
there is an increase of half a degree. 
Depth of 800 Fathoms (Map 10). — The mean temperature of the ocean is 37°'3, or 
0°‘8 lower than at 700 fathoms. To the west of Gibraltar temperature has now fallen 
from 51° at 700 fathoms to 46°, but this region is still the source of an abnormally 
high temperature diffused westwards over the Atlantic, the great excess apparently 
not passing to the west of long. 30° W. At this depth a large number of specific 
gravities have been observed, chiefly by the Challenger. In the area of highest 
temperatures, 1'0268 and 1'0264 have been observed. In the Atlantic, from lat. 6° N. 
to 40° S., the mean of thirteen observed specific gravities is 1’0258, and in the Gulf of 
(PHYS. CHEM. CHALL. EXP. — PART VIII. — 1895 .) 4 
