191 



line ; also the increased strain then occasioned by the friction of the 

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

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

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

 and temperature must not be combined.] 



I have before this 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 the 

 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 offers 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, which 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 you 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 2700 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- 

 VOL ix. p 



