CHAP. II. ] TENERIFFE TO SOMBRERO. 197 
bottom water, amounting to about two litres, was brought up 
on each occasion, except on the one already mentioned where 
the instrument was lost, and on two others where the valves 
did not completely close: its specific gravity was determined, 
and the water was either subjected to further analysis or re- 
tained for future investigation. 
In thirteen cases a dredge, measuring 54 inches in length of 
opening and 15 in width, and weighing 137 pounds, or in very 
deep water one somewhat smaller, was lowered; and in nine 
instances, notwithstanding the great depths and the extreme 
difficulty of the operation, brought up a sample of the bottom 
usually weighing one hundred-weight or more, and what we 
could scarcely doubt was a fair representation of the fauna of 
the ground which it had gone over at the bottom. 
At almost every station a serial temperature sounding was 
taken, the temperature being ascertained at certain stated in- 
tervals, usually at intervals of 100 fathoms from the surface to 
1500. In many eases samples of water were brought up from 
intermediate depths for examination, and in every case the sur- 
face temperature of the sea was taken, the temperature of the 
air with dry and wet bulb thermometers, and the amount of 
atmospheric pressure. 
Every single operation, whether of sounding or dredging, 
was conducted from beginning to end by Captain Nares, and 
in every case the conditions required were determined with an 
amount of care which left no reasonable doubt of their accu- 
racy within very narrow limits of error. I should therefore 
say, with reference to this first section, that the results were 
thoroughly satisfactory. 
In the length of the section at the foot of Plate V. one cen- 
timetre division represents 100 nautical miles, so that 1 mm. 
corresponds with 10 miles. In order to make the differences 
in depth perceptible, and at the same time to avoid too great 
an amount of exaggeration, this proportion has been multiplied 
