CHAP, vii.] DEEP-SEA TEMPERATURES. 305 



so that we are tolerably certain by actual experi- 

 ment of the amount of their error. In speaking 

 of the 6 Lightning ' temperatures, I mean, therefore, 

 the actual temperatures taken by the ordinary ther- 

 mometers, corrected approximately to the standard 

 of the Miller- Casella thermometers, afterwards used 

 in the ( Porcupine.' 



Leaving Stornoway in the ' Lightning/ on the 

 llth of August, 1868, and directing our course 

 towards the Faeroe banks, we sounded in 500 fathoms 

 about 60 miles to the north-west of the Butt 

 of the Lews, and took a bottom temperature of 

 9'4 Cent, with the ordinary Six's thermometer 

 the only form of the instrument in use at the time. 

 This, when corrected for pressure, gives about 7'8 C. 

 We were surprised to find the temperature so high, 

 and we were at the time inclined to think that the 

 observation, which was taken in a breeze of wind, 

 was scarcely to be depended upon. Subsequent 

 observations, however, in the same locality, con- 

 firmed its accuracy. On the Fseroe Banks, at a 

 depth under 100 fathoms, the bottom temperature 

 averaged 9 C., while that of the surface was about 

 12 C. ; temperature indications on this bank were, 

 however, of little value, as the water is no doubt 

 affected to some extent through its entire depth by 

 direct solar radiation. The next observation was 

 in lat. 60 45' N. and long. 4 49' W., at a depth 

 of 510 fathoms, with a bottom temperature of 

 0-5 C., about 140 miles nearly directly north 

 of Cape Wrath. Then followed a series of sound- 

 ings, Nos. 7, 8, 10, and. 11 of the chart (Plate I.), 

 taken while traversing the northern portion of the 



x 



