CHAP. VIL. ] DEEP-SEA TEMPERATURES. 305 
so that we are tolerably certain by actual experi- 
ment of the amount of their error. In speaking 
of the ‘ 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 Froe 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 Féroe 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 
