418 THE VOYAGE OF H.M.S. CHALLENGE!*. 



viz., that by all three observers the temperature at 100 fathoms was either the same or 

 lower than that at the surface, and was at or below the freezing point of fresh water, 

 whilst at 150 fathoms the mean temperature was only on one occasion less than that of 

 the surface, or below 32°, the mean of the sixteen observations at that depth being 34° - 3, 

 aud higher than the temperature of the surface. The coldest submarine temperature 

 obtained was by Wilkes, who registered 27^° at a depth of 320 fathoms, 1 but as serial 

 temperatures were not obtained there is no reason for believing that this temperature 

 existed at the depth of 320 fathoms, as the thermometer might, and probably did, pass 

 through a stratum of water at that temperature before it reached the depth of 100 fathoms. 



During the voyage of the Challenger from Kerguelen to Australia five serial tem- 

 perature observations were obtained south of the 60th parallel ; and as these observations 

 are highly important, a full notice of them is appended in order to afford every possible 

 facility for future discussion, and also to indicate the data still required as well as the kind of 

 instrument necessary to obtain those data. The general result of the observations seems to 

 show that from the most southerly Station a wedge of cold water stretches northwards 

 for more than twelve degrees of latitude, underlying and overlying strata at a higher 

 temperature than itself. The temperature of the water below the lower warm stratum is 

 uncertain, because it lies between the maximum and minimum observed at lesser depths. 

 These results receive confirmation from the imperfect observations of Cook, Ross, and 

 Wilkes (see Diagram 9). 



On the 14th February 1874, in lat. 65° 42' S., long. 79° 49' E., the most southerly 

 Station at which temperature observations were obtained, the temperature of the surface 

 water was 29°*5 and that of the air 33°. The ship was about 1^ miles from the edge of 

 the pack ice with many icebergs around, forty-eight being counted within a horizon of 4 

 miles; the average height of the bergs out of the water was 150 to 200 feet, most of 

 them were tabular, and had changed little from their virgin state, they must, therefore, 

 have extended to a depth of from 200 to 300 fathoms below the surface. The tempera- 

 ture of the water at 50, 100, 200, 300, 500, and 1675 fathoms (bottom) was determined. 

 For this purpose two thermometers, Nos. 66 and 67, were sent successively to each of 

 these depths, having been cooled to a temperature of 30° - 2 before immersion. At 50 

 and 100 fathoms each thermometer registered a slight change in the maximum index, 

 which is probably due either to an error in reading off or to a slight defect in the 

 instruments, as it has been frequently found that the maximum indices alter their 

 positions slightly on entering cold water. 2 The minimum index of each fell to 29° 

 proving that they had entered or passed through a stratum of cold water. At the 

 greater depths of 300, 500, and 1675 fathoms the thermometers registered a decidedly 



1 Wilkes* U. S. Expl. Exp., vol. ii. p. 299, 1845. 



2 Or this may be due to the glass contracting suddenly before the temperature has reached the spirit in the bulb 

 of the thermometer, and so forcing the index up slightly. 



