Captain Pullen on Deep-sea Soundings. 459 



low temperature, and not Six's self- registering instrument that was 

 employed). During ray second winter at Fort Sim))Son, I, every three 

 hours throughout twelve of the twenty-four, registered twenty-one 

 thermometers, eighteen of Adie's and three of Negretti's, on glass 

 scales. I never found Adie's at any temperature to differ more than 

 a degree and a half from each other. Negretti's, when they ranged 

 low, say twenty below zero, I have found twenty, eighteen, and 

 twelve degrees lower than Adie's. Here, in a high temperature 

 (eighty degrees), I find three differing from the deck-thermometer, 

 as well as from the other three (having only sis remaining), being 

 six, seven, and ten degrees higher. The correction (but a few tenths 

 of a degree) can be allowed for certainly, but this difference may not 

 be the same at a lower temperature, therefore it occasions a serious 

 drawback to the efficiency of these instruments ; and I always feel 

 doubtful about the results. As yet I have only used those that agree 

 nearest with each other. 



My next sounding was in 10° 7' N., long. 27° 32' W., the 

 position of the Hannah Shoal, no bottom with 2000 fathoms of line. 

 There is 15 marked in some charts on this shoal. In 4° 16' N. 

 and 28° 42' W., two thermometers were sent down to 1500 and 

 1000 fathoms, the greater depth showing a minimum 39°'4, the 

 lesser 42°-5. No specimen of bottom had yet been brought up, as 

 all the soundings hitherto, except those for the Devil's Rock in the 

 Bay of Biscav, as well as the determinations of temperature, had 

 been taken from a boat with small lines ; so in the next cast I 

 sounded from the ship with a large line, — the regular deep-sea line — 

 and combined the experiments. Two thersnometers were sent down 

 on the line; and the sinker was down, by intervals, at about 1080 

 fathoms. The valve brought in a plentiful supply of bottom, and 

 the thermometers showed a minimum temperature of .38°'5 at the 

 lowest depth, and 46°- 2 at G80 fathoms. This was in latitude 

 2° 20' N., longitude 28° 44' W., 90 miles from Saint Paul's Island. 

 The specimen of bottom was a fine light greyish sand. 



Drawing now to the Equator, I determined, if possible, to get a cast 

 directly on it, and also the temperatures ; accordingly the boat took 

 the cast for bottom, while from the ship an endeavour was again 

 made to combine the experunents. It failed, however, I am sorry to 

 say, resulting in the loss of a large portion of the line, and two in- 

 struments sent down with it. From this I felt fully convinced that 

 the uncertainty of concluding when the weiglit is down, from the 

 intervals, is such, that the sounding becomes of little value, as far as 

 the true dej)th is concerned. 



[An extract of Capt. Pullcn's Journal is here given, — showing 

 the uncertainty of judging by the ' intervals' as to tlie time of reach- 

 ing the bottom, and the consequent liability to ])ay out too much 

 line ; filso the increased strain tlicn occasioned by the friction of the 

 under current on iiie over-long line, and the great risk of the latter 

 giving svay on being pulled in ; and stating the conclusion of the 

 writer, that, in order to arrive at true results, soundings for bottom 

 and temperature mast not be combined.] 



