190 



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 six 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 Biscay, 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 thermometers 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 680 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 experiments. 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 weight is down, from the 

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

 the true depth is concerned. m 



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

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

 ing the bottom, and the consequent liability to pay out too much 



