632 
MR. J. PRESTWICK ON SUBMARINE TEMPERATURES. 
and 4000 feet near the equator. Of these two and other lower isotherms in tempe- 
rate and tropical seas the older observations afford, however, very few data, and we need 
say little. We wait for those of the ‘ Challenger.’ 
Of the bathymetrical isotherms of 50°, 60°, 70°, and 80° F., the data are more 
ample. They seem respectively to set in about lat. 60°, 50°, 25°, and 12° N., and the 
first two to attain their greatest depths between lat. 40° and 20° — the isotherm of 
50° F. falling to 3000 feet, and that of 60° F. to 1200 feet. They then rise, and from 
lat. 12° N. to the equator, the isotherm of 50° F. comes within 1000 to 1200 feet of the 
surface, and that of 60° F. from 300 to 400 feet. 
In the South Atlantic, on the line of section No. 1, which now crosses over to the 
eastern area of the South Atlantic, the bathymetrical isotherms seem to be prolonged 
southward more nearly on the same level that they have near the equator — the isotherm 
of 50° lying at from 1000 to 1400 feet, between lat. 7° and 40° S., and that of 60° F. 
at 500 or 600 feet. In the western area (sect. No. 2) the isotherms of 50°, 60°, 
and 70° F. are much more irregular, sinking in lat. 10° to 20° to about 3000, 1800, 
and 500 feet, and then rising and ending, as in the other line of section, in about 
lat. 40° and 45° S. But while, on the whole, the higher isotherms range rather further 
south in the western than in the eastern area, the isotherm of 35° F. is in both prolonged 
further south, on a nearly uniform level of from 7 000 to 8000 feet, between lat. 20° and 65°. 
The Pacific Sections (Nos. 3 & 4) exhibit a much lesser number of observations, but 
still sufficient to draw some general conclusions. Starting in one case in the Arctic 
Sea north of Behring Strait, and in the other in the sea south of Behring Strait, one 
line of section (No. 3) passes through the Eastern Pacific to the equator in long. 120° W., 
and the other (No. 4) through the Western Pacific to the equator in long. 180° W. 
North of Behring Strait the sea is so shallow that the observations barely pass beyond 
the limits of diurnal variations. The width and depth (180 feet) of that strait itself 
are also so small that the intercommunication through it between the polar seas and 
the North Pacific can have little or no effect on the thermal condition of the latter; 
nevertheless it may be a question whether the submarine isotherm of 60° F. in that 
ocean extends beyond the lat. of 40° to 45° N., and the isotherm of 50° F. beyond 
about lat. 55° N., being about 5° less in either case of their northern range in the 
eastern area of the North Atlantic; while the isotherm of 35° F. disappears, as in the 
western division of the Atlantic, between lat. 60° to 70° N., instead of having the more 
indefinite northward range it has in the open North Atlantic. 
These isotherms also, instead of the remarkable rise which they present near the 
equator in the North Atlantic, exhibit in the North Pacific a gradual decline to the 
equator, where, judging from the few data we have at our disposal, they seem to lie — 
that of 60° F. at 800 to 1000 feet, of 50° F. at 2000 to 2500 feet, of 40° F. at 4000 
to 5000 feet, of 35° F. at 7000 to 8000 feet respectively, and pass the equatorial zone 
without rise or apparent change of level. 
On the other hand, in the South Pacific the conditions are much more like those of 
