626 Prof. W. Thomson on the Voyage of the ' Challenger ' 



temperature of — o, 3 C. ; bat the weather was too boisterous to admit of 

 a serial temperature-sounding. On the 7th the sea was more moderate, 

 and we sounded in 2875 fathoms, with a botfcom-temperature of — o, 6 C, 

 and took the temperature series represented by Curve 329 (Plate 30). 

 The bottom was again a very fine grey or slightly reddish mud, almost 

 free from calcic carbonate ; samples of water were obtained for specific- 

 gravity determinations and analysis down to 2000 fathoms. 



On the 8th of March we sounded in 2440 fathoms, with a b3ttom of 

 light red mud, and a bottom-temperature of — o, 3C. ; and on the 9th, 

 somewhat to our surprise, we sounded in 1715 fathoms, with a bottom 

 of " Qlobigerina-oom" and a temperature of 1 0, 3 C. The sea was heavy, 

 and trawling-operations were consequently rather difficult ; the trawl 

 was lowered, however, on account of the remarkable shallowness of the 

 sounding ; but it unfortunately came up foul, and the observation was 

 lost. 



It seems that this sounding was on the central meridional rise which 

 separates the western from the eastern trough of the Atlantic at a depth 

 apparently nowhere much beyond 2000 fathoms, near its western edge. 

 As usual, the lower isotherm obathic lines showed a tendency to rise 

 slightly in the shallower water. 



On the 10th the morning was misty and raining, with the wind 

 northerly, shifting to the southward towards noon. We sounded in 

 2200 fathoms, " Globigerina-oom" with a bottom-temperature of + 0°-4 O. 

 The trawl was put over ; but on being recovered, it was found to have 

 been down on its back, and it contained only a few fragments of one or 

 two sponges, Crustaceans, and Echinoderms. 



"We ran on during the 11th and 12th, and on the 13th we sounded on 

 " Globigerina-ooze " at a depth of 2025 fathoms, with a bottom-tempera- 

 ture of l°-2 C. The trawl again came up empty and reversed, some frag- 

 ments adhering to the net, showing that there was a varied fauna, and 

 that much interesting material must have been got from a successful haul. 



The position of the sounding on the 14th was lat. 35° 45' S., long. 

 18° 3' W. ; the depth was 1915 fathoms, the bottom " Globigerina-ooze" 

 and the bottom-temperature l c, 5 C, the distance from Tristan d'Acunha 

 310 miles. The trawl came up again foul, with only some fragments to 

 indicate the presence of an abundant fauna. As we had already crossed 

 our outward track in 1873, and as the temperatures at depths unin- 

 fluenced by the changes of the seasons seemed to verify in every way our 

 former work, we thought it unnecessary to go further to the eastward on 

 the direct line, and we took a north-easterly course towards a point in 

 the meridian of the Island of Ascension, which was distant from us about 

 1685 miles. 



"We ran on next day, and on the 16th the position of the ship was 

 lat. 32° 24' S., long. 13° 5' W., 1470 miles almost due south of Ascension, 

 and 280 miles north bv west of Tristan d'Acunha. 



