134 



THE VOYAGE OF H.M.S. CHALLENGER. 



crack yielded a little and the sea water was gradually forced in, driving the contents of 

 the thermometer before it, and, taking it at a disadvantage from within, breaking the 

 shell of the large bulb, which was unsupported on account of the belt of rarefied vapour 

 between it and its outer shell. The pressure was now equalised within and without the 



instrument, and the injury went no farther. Alcohol, 

 creosote, mercury, and sea water were mixed up in the 

 outer case of the large bulb with the debris of the inner 

 bulb, and one of the steel indices lay uninjured across its 

 centre. 



As this was the deepest sounding yet taken, it was 

 desirable to try whether the dredge would still prove 

 serviceable. The small dredge was accordingly lowered at 

 10.30 a.m., with the usual bar and tangles, and from the 

 centre of the bar a Hydra sounding tube, weighted with 

 4 cwt., was suspended about 2 fathoms below the dredge. 

 A 2-inch rope was veered to 4400 fathoms ; a toggle was 

 stopped on the rope 500 fathoms from the dredge, and 

 when the dredge was well down, two weights of 1 cwt. each 

 were slipped down the rope to the toggle. Heaving in 

 was commenced about 1.30 p.m., and the dredge came up 

 at 5 p.m., with a considerable quantity of reddish -grey ooze. 

 The mud was carefully examined, but no animals were 

 detected, except a few small calcareous Foraminifera, and 

 some, considerably larger, of the arenaceous type. 



The officers of the United States Coast Survey have 

 recently obtained depths of 45G1 and 4223 fathoms about 

 50 miles to the west of this sounding of 3875 fathoms ; so 

 that this, the deepest part of the Atlantic, is probably a 

 depression of considerable extent, with its longest diameter 

 running east and west. On the 27th, 100 miles north of 

 the 3875 fathoms sounding, the depth had decreased to 

 2800 fathoms. 



On this St. Thomas-Bermuda section, twelve sound- 

 ings, five dredgings, and five serial temperature soundings 

 were obtained (see Sheet 6). 



The ocean bed rises gradually from the deep depression 

 just referred to towards Bermuda, the depth being 2475 fathoms at a distance of 50 miles 

 from that island (see Diagram 2). 



The temperature at the bottom ranged from 36°'2 to 36° - 7, the mean being 36°'4. 





Fig. 53.— Thermometer tubes broken by 

 pressure at a depth of 3875 fathoms 

 (Station 25). 



