460 Royal Sociehj : — 



I have before tbis noticed how irregular the intervals always were 

 when getting temperatures, particularly when more than one ther- 

 mometer was on the line, but had never thoroughly considered tlie 

 cause, nor the results likely to follow from the increased weight on 

 the line ; for although the addition of the thermometer (weighing 

 about six pounds in the water-bottle) gives rapidity to the descent of 

 the weight, its bulk oifers great resistance on coming in, consequently 

 the line has more tendency to break. And when it is intended to 

 send down more than one thermometer, the line must be stopped to 

 attach the addition, Avhich at once checks the rapidity of descent, 

 and the line has then to be let off the reel with more force, impos- 

 sible to apply equably ; and the intervals become so irregular, that 

 all certainty of when the sinker is at the bottom is lost, and j'ou feel 

 at a loss when to stop. 



From this experience I think I may say we have profited, for not 

 a single fathom of line has been lost since, although going double 

 the depth ; once, too, with a fresh breeze with 2380 fathoms of line 

 out ; and it was with the greatest difficulty we could get the deck 

 engine to reel it in again, and then only by putting all the Watch on 

 to assist with their weight. I now began to observe more regularly for 

 the temperatures, and with a stouter line than that usual for sound- 

 ing, kept exclusively for the purpose. After crossing the Equator, I 

 sent the thermometers down at nearly every tenth parallel, three at a 

 time, at twelve, eight, and four hundred fathoms, reserving portions 

 of the water brought up to send home for analysis. 



In latitude 26° 46' S. and longitude 23° 52' W., nearly mid- 

 way between where Sir James Ross has sounded without getting 

 bottom, I got 2700 fathoms. A single thermometer was sent down 

 to this 2/00 fathoms depth, secured just above the sinker, and came 

 in showing a minimum temperature of 35° F. ; and the bottom brought 

 up in the valve was a very fine brown-coloured sand. 



In this case the common deep-sea line was used, and weighted 

 with 1201bs. sinker (Brook's detaching), just one-fifth of its break- 

 ing strain ; and the rapidity of descent has hardly if ever been 

 equalled in speed by smaller lines when weighted nearly up to their 

 breaking strain, as shown in the American soundings. One hour 

 from the time we let go, the intervals showed that the weight was 

 down. 



I ran the easting down between the parallels of 35° and 38° S., 

 from the Cape of Good Hope eastward outside I'llauritius in the 

 Indian Ocean, in the route of many doubtful dangers, and on ncar- 

 ing them the lead was brought into play. The first was tlie ' Bruns- 

 wick,' on which is marked 85 fathoms, deep enough certainly for any 

 ship that swims ; but to clear up all doubt, two casts were obtained not 

 far from its position, of 1410 and 1102 fathoms, without reaching 

 bottom. Then comes the ' Atalanta,' having three positions, one on 

 our Admiralty Charts, and two from Horsburgh, giving it as an ex- 

 tensive shoal under water, with pointed rocks on its v/estern part. I 

 passed from the westward between the northern position, and the 

 first in order to the southward, and got four deep casts, besides 



