The following instances, taken from the many made on different voyages of discovery, will suffice to illustrate this fact : —
Temperatures of the Atlantic.
Latitude.
° 42 0 N.
29 0 N.
7 21 N.
4 25 N.
15 3 S.
25 10 S.
29 33 S.
32 20 S.
38 12 S.
Longitude (corrected to Greenwich).
°
34 40 W.
34 50 W.
20 40 W.
26 6
23 14 W.
7 59 E.
10 57 E.
43 50 E
54 80 W.
Depth.
ft.
4688
8399
3030
6037
7200
5315
6310
6444
2000?
Temperature. Surface. Bottom.
62.0 44.0 F.
76.0 43.0
80.0 36.0
80.8 37.9
77.0 39.5
67.4 37.6
66.4 35.8
71.0 36.5
62.4 37.6
Observer & Date.
Chevalier 1837.
" "
Lenz 1832.
Tessan 1841.
" "
" "
" "
Lenz 1832.
Tessan 1841.
In the Antarctic regions Sir James Ross made a considerable
number of observations in 1839-43. Whatever the temperature of
the surface, he found the temperature from 2800 to 3600 feet to
be from 38° to 39.8°, the higher temperature being at the lower
depth. He concluded that below 1800 feet there was very little
variation in temperature, and inferred that in lat. 56° 14' S. there
is an ocean belt, the temperature of which from top to bottom is of
39.5°. This conclusion seems to have been based on an erroneous
idea of the specific gravity of sea-water, and is possibly in some
degree attributable to errors of the instruments used. Captain
Willis, however, came to the same conclusion with respect to a belt
of uniform temperature. I cannot find that there is any sufficient
foundation for this hypothesis, which is in no way confirmed by the
observations of others. As the other observations were not generally
known, this hypothesis has unfortunately been too often accepted.
Later experience has shown that in many instances there is an
error in the earlier observations, in consequence (where proper
precautions were not used) of the pressure on the thermometer at
great depths. Dr. Carpenter has determined this to amount to as
much as 2° or 3°, or even more. Consequently a deduction to this
extent has often to be made in order to get a true reading of some
of the older observations. In many of the French expeditions,
however, great care was taken to guard against the influence of
pressure.
If we turn to the Pacific, we shall find similar low temperatures prevailing at great depths both in the temperate and torrid zone. I again take merely a few cases in illustration.
