ME. J. PEESTWICH ON SUBMAEINE TEMPEEATUEES. 
631 
Indian Oceans, subject to, as the correction for pressure, the deduction of 1° Fahr. for 
every 1700 feet of depth. As the ‘Challenger’ expedition will supply ample data 
regarding the deeper temperature-soundings in the intertropical seas, the scarcity of 
them in the earlier voyages is of less importance. Those, on the contrary, collected 
on the many Arctic and Antarctic voyages under circumstances of so much difficulty, 
and which bear in so essential a manner upon the intermediate areas, are fortunately 
much more complete. The lines of Section have therefore been so selected as to 
embrace the chief observations of the several explorers in both the Arctic and the 
Antarctic seas. For this purpose two lines traverse respectively the length of the 
Atlantic and of the Pacific, and two others are run through the Indian and Southern 
Oceans. 
Section No. 1 first traverses the North Atlantic from the top of Baffin Bay to the 
equator in long. 20° W., and shows the low submarine temperatures prevailing in the 
higher latitudes on that side of the Atlantic. The bathymetrical isotherm of 35° F. 
seems on this line not to extend beyond lat. 63° N. Soundings have been made in 
Davis Strait and Baffin Bay between lat. 60° and 77° N. to the depth of 6000 feet, and 
everywhere the temperature decreases with the depth down to 29° and 28°, or even 27°, 
and in one instance so low a degree as 25 0, 75 F. has been recorded. The isotherms of 
40°, 50°, and 60° F. in the western area of the Atlantic have likewise a less northward 
extension than in the eastern area traversed by Section No. 2 ; while that of 70° F., 
which is affected by the Gulf-stream, extends further north. 
Section No. 2, which commences in the seas around Spitzbergen, exhibits, to depths 
within the annual influence, a temperature as low, if not lower, than in No. 1, while 
below that the temperature, on the contrary, down to the depths hitherto tried (not 
quite 5000 feet) increases with the depth. Owing to the great diurnal variations of 
temperature at the surface or to currents, the fluctuations in the upper strata are 
frequent and rapid. From 1000 down to 3000 feet the temperature is more uniform 
at 33° to 34°, and reaches, at 4500 to 4600 feet*, 34° to 35° F. or possibly 36°. Off 
the coast of Greenland the one experiment of Scoresby shows a decrease of tempe- 
rature to the full depth tried, viz. to 28 0, 5 (corr.) at 708 feet. 
From the Spitzbergen seas, the bathymetrical isotherm of 35° F. gradually falls until 
the latitude of about 50° N. is reached, when its depth is twice what it is in lat. 76° 
to 80°. About lat. 40° N. it appears to have attained its maximum depth of about 
11,000 feet, at which it remains to lat. 30°, from about which point it again rises gra- 
dually, lying in lat. 12° at a depth of about 8000 feet, and reaching probably still nearer 
the surface at the equatorf . The isotherm of 40° F., which, in this north-eastern part 
of the Atlantic, extends as far as lat. 72° to 73° north, reaches its maximum depth 
of about 6000 to 7000 feet between lat. 50° to 30° N., and rises to between 3000 
* Scoresbt’s deepest sounding was in 76 ° 30 ' N., 4 ° 48 ' W., 7200 feet, no bottom. 
t The depths of these isotherms in the Atlantic will no doubt require correction ; but this will not affect their 
relative position and general bearing. 
