36 
THE VOYAGE OF H.M.S. CHALLENGER. 
bergen falls to 29°. The deepest sounding made was 2005 fathoms in lat. 68° 21' N. 
and long. 2° o' W., where the temperature observed was 29°'5. There are five positions, 
at depths exceeding 1500 fathoms, at which Molin observed the temperature and specific 
gravity. They range from 1547 to 1861 fathoms, with a mean of 1688 fathoms; their 
mean position was lat. 69° 20' N. and long. 3° 27' E., and the mean temperature was 
29°‘8, and mean specific gravity 1 '0259. This temperature found in the deepest parts 
of the Arctic Ocean is only from 2° to 3 higher than the freezing-point of sea-water 
of the above specific gravity. All the five positions underlie the region of the warm 
area, and it will be seen that the specific gravity there observed is closely approximate 
to that of the surface. 
The area enclosed by the surface isothermal of 30° has virtually the same tempera¬ 
ture down to the bottom, except that at the greater depths it falls to 29°, and the same 
area appears to have a lower specific gravity than the rest of this ocean, judging from 
the small number of observations of specific gravity taken. The important inference 
follows that the great volume of the warm dense current from the Atlantic does not 
contribute the water forming the north-easterly current that fills the cold area, but 
that it overspreads the region around where it terminates and thereafter descends 
downwards to greater depths, cooling as it descends till at about 1000 fathoms it 
becomes nearly as cold as the rest of the Arctic Ocean. The different specific gravities 
no doubt play an important part in delaying the mixture of these two great bodies of 
water placed side by side in the region enclosed between Norway, Iceland, Greenland, 
and Spitsbergen. The high specific gravities observed at the bottom doubtless play an 
important part in maintaining the fluidity of the bottom water of the Arctic Ocean. 
The Southern Ocean. 
Under this head all portions of the ocean to the south of lat. 40° S. are included. 
Everywhere in this extensive region the temperature of the surface falls below 60°. 
The lowest isothermal is 40°, which may be taken as the annual mean about lat. 55° S. 
all round the globe. To the south of lat. 55° S. no observations have been taken for any 
two or four months of the year, such as January and July, or February, May, August, 
and November, &c., from which a fairly good annual mean could be calculated. It is 
probable, however, that, reasoning from the positions of the isothermals of the air and 
the temperatures at 100 fathoms, an annual mean of about 30° encircles the globe 
near lat. 63° S. The specific gravity is under 1*0260 all round, falling to 1*0241 
about lat. 65° S., this being the lowest specific gravity observed by the Challenger. 
As regards the atmospheric pressure and the prevailing winds which necessarily 
result from the manner of its distribution, this ocean differs essentially from all other 
