REPORT ON OCEANIC CIRCULATION, 
37 
oceans in presenting wliat is virtually an unbroken zone of water nearly as far soutli as the 
Antarctic Circle. Now from about lat. 30° S,, where the highest atmospheric pressure of 
the southern hemisphere is massed, pressure falls from about 30'100 to 29 ’000 inches 
near lat. 63° S., from which it begins to rise as higher latitudes are reached, as siiown 
by the prevailing winds. Over this vast region, more particularly from lat. 40° to 63° S., 
the prevailing winds all the year round are nortli -westerly and westerly. As the isobai-s 
are close to each other, these are high winds, and as they blow from lower to higher 
latitudes, in other words are constantly arriving into colder climates, they are accom- 
panied with much rain, foul Aveather, and comparatively low surface specific gravities. 
The temperatures and specific gravities are further diminished liy the melting of the ice, 
and of the icebergs so frerpiently met with in these seas. 
The following table shows the mean specific gravities of the Pacific, Atlantic, and 
Indian Oceans from lat. 30° to 64° S. at depths of 100, 200, 300, 400, and 800 fathoms: — 
Pacific. 
Atlantic. 
Indian. 
No. of 
Observa- 
tions. 
M. S. G. 
No. of 
Observa- 
tions. 
M. K. G*. 
No. of 
Observa- 
tions. 
M. S. G. 
100 fathoms 
14 
1-02.57 
12 
1 0261 
5 
1 0257 
200 „ ... 
12 
1-0255 
11 
1-0257 
4 
1-0256 
300 „ ... 
12 
1 0255 
11 
1-0256 
3 
1 0254 
400 „ . . • . 
12 
1-0255 
12 
1-0256 
6 
1-0255 
800 „ ... 
10 
1 02.55 
8 
1-0257 
The mean latitude of the Pacific and Atlantic observations is lat. 36° S., but of the 
Indian Ocean lat. 55° S. The specific gravities of the three oceans from 100 to 800 
fathoms closely agree with each other, those for the South Atlantic being slightly 
greater. Here, then, there appears to be a total absence of such low specific gravities 
as have been observed by Mohn between Spitzbergen and Greenland, and by Makaroff, 
though at less depths, near the Sea of Okhotsk. The relatively high specific gravities 
maintained in the Southern Ocean, notwithstanding the heavy rainfall and extensive 
ice-melting over the surface and upper layers of the sea, must be attributed to the 
broad and powerful surface currents from the north-west, bringing with them the high 
temperature and specific gravity of sub-tropical regions, as already described. 
A map of the specific gravities at the bottom has been constructed (Map 16), a large 
number of such observations being available for the Eeport. The results for the three 
oceans south of lat. 30° S. are : — 
Number of 
Observations. 
21 
20 
i;i 
M. S. G. 
1 ■02r,S 
102f)9 
102;)G 
Pacific, 
Atlantic, 
Indian Ocean, 
