Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/78

 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.