\ ai:i:ativk OF THE OET7ISE. 



421 



.surface st.rat.uiri of '.17 "'2 and < In- cold stratum at 80 fathoms of 32° , 5 I they W&tt unable 



to record any alteration between tlio.se, temperatures at, greater depths. 



The bottom thermometers showed the temperature of immersion on their maximum 



side, and 32 0, 2 and 32°'0 on the minimum. As this is a colder result, than any other 



instrument showed between the surface and .ooo fathoms, it, is probably justifiable 



to assume the mean (82*1) to be tie- correct, bottom tem|>cra.l.urc at this p". it ion. 

 The result of the foregone' ob. erva.tions may lie briefly Stated thus: — 

 On the passage towards Cape Otway the cold intermediate stratum was traced as 



far north as 54° S.. where its temperature was 32°"5 at a depth of 80 fathoms. 



Farther south it decreased until in hit. GO" S. it, was 29° from immediately below the 



surface to a, depth of 200 I'll horns, or nearly as low as the freezing point of salt, water. 



The. warmer stratum of oceanic water underlying it also gradually decreased in 



temperature as higher latitudes were reached, and it is possible, that farther south the 

 temperature of the water from the surface to the bottom will be found nearly uniform 

 at probably 29" or no"; but in that case it, is somewhat difficult to account for the rise in 

 temperature of the bottom water to 33 0, 5 in lat. 50" S., long. 123° E., only about 1200 

 miles from its source, as it is known that this temperature is retained with little altera 

 lion for 3000 miles, for Captain Shortland obtained bottom temperatures of 33 \" in the 

 Arabian Sea with unprotected thermometers. This will be referred to again when dis- 

 cussing the specific gravity of the, sea water of the Southern Ocean. 



During the winter season the ice at the surface urns! oeceSSarily be colder than flu- 

 water underlying it ; it seems therefore highly probable that flic cold wedge of water 

 found near the surface is merely the remains of the winter-cooled sea, which has not 

 sufficient time during tic- short, summer to recover its temperature; it is also probable 

 that during winter the solar heated surface belt is entirely removed, and that the sea as 

 far north, at, least, OS the c,:',n\ parallel of south latitude becomes frozen over, the frequent 

 gales breaking Up the field ice and converting it, into pack. It is noticeable that the 



temperature of the underlying tratum was on each occasion found to be warmer than 

 the surface water. This fact is also confirmed by the observations of Cook, Ross, and 

 Will 



The fact that the cold wedge above referred to extended north just as far as the 



icebergs did in March I H74 points to there being some conned ion between the temp 

 hue and the presence of melting icebergs. The lowest bottom temperature registered 



between the 'ape of Good Mope and Melbourne) north of the 54th parallel, was 88 

 at tin- ;, )th parallel it was 32"'), and at, all Station farther south of this, it cannot be 

 said with absolute certainty what the bottom temperature was, as the thermometers below 

 300 fathoms came op with exactly the same readings as at that depth. 



hiiiing the time, the, ship was near the edge, of the pack ice the surface temperature 

 from 28° to 29*, and remained uniform to a depth of upwards of 200 fathoms, 



