Equinoctial Regions of America, vol 2 | Page 9

to a
chain of mountains with abrupt declivities; and we know that even the
sea is generally deepest where the coast is elevated, rocky, or
perpendicular.
The temperature of the lake at the surface during my abode in the
valleys of Aragua, in the month of February, was constantly from 23 to
23.7 degrees, consequently a little below the mean temperature of the
air. This may be from the effect of evaporation, which carries off
caloric from the air and the water; or because a great mass of water
does not follow with an equal rapidity the changes in the temperature of
the atmosphere, and the lake receives streams which rise from several
cold springs in the neighbouring mountains. I have to regret that,
notwithstanding its small depth, I could not determine the temperature
of the water at thirty or forty fathoms. I was not provided with the

thermometrical sounding apparatus which I had used in the Alpine
lakes of Salzburg, and in the Caribbean Sea. The experiments of
Saussure prove that, on both sides of the Alps, the lakes which are from
one hundred and ninety to two hundred and seventy-four toises of
absolute elevation* (* This is the difference between the absolute
elevations of the lakes of Geneva and Thun.) have, in the middle of
winter, at nine hundred, at six hundred, and sometimes even at one
hundred and fifty feet of depth, a uniform temperature from 4.3 to 6
degrees: but these experiments have not yet been repeated in lakes
situated under the torrid zone. The strata of cold water in Switzerland
are of an enormous thickness. They have been found so near the surface
in the lakes of Geneva and Bienne, that the decrement of heat in the
water was one centesimal degree for ten or fifteen feet; that is to say,
eight times more rapid than in the ocean, and forty-eight times more
rapid than in the atmosphere. In the temperate zone, where the heat of
the atmosphere sinks to the freezing point, and far lower, the bottom of
a lake, even were it not surrounded by glaciers and mountains covered
with eternal snow, must contain particles of water which, having during
winter acquired at the surface the maximum of their density, between
3.4 and 4.4 degrees, have consequently fallen to the greatest depth.
Other particles, the temperature of which is +0.5 degrees, far from
placing themselves below the stratum at 4 degrees, can only find their
hydrostatic equilibrium above that stratum. They will descend lower
only when their temperature is augmented 3 or 4 degrees by the contact
of strata less cold. If water in cooling continued to condense uniformly
to the freezing point, there would be found, in very deep lakes and
basins having no communication with each other (whatever the latitude
of the place), a stratum of water, the temperature of which would be
nearly equal to the maximum of refrigeration above the freezing point,
which the lower regions of the ambient atmosphere annually attain.
Hence it is probable, that, in the plains of the torrid zone, or in the
valleys but little elevated, the mean heat of which is from 25.5 to 27
degrees, the temperature of the bottom of the lakes can never be below
21 or 22 degrees. If in the same zone the ocean contain at depths of
seven or eight hundred fathoms, water the temperature of which is at 7
degrees, that is to say, twelve or thirteen degrees colder than the
maximum of the heat* of the equinoctial atmosphere over the sea, I

think it must be considered as a direct proof of a submarine current,
carrying the waters of the pole towards the equator. (* It is almost
superfluous to observe that I am considering here only that part of the
atmosphere lying on the ocean between 10 degrees north and 10
degrees south latitude. Towards the northern limits of the torrid zone,
in latitude 23 degrees, whither the north winds bring with an extreme
rapidity the cold air of Canada, the thermometer falls at sea as low as
16 degrees, and even lower.) We will not here solve the delicate
problem, as to the manner in which, within the tropics and in the
temperate zone, (for example, in the Caribbean Sea and in the lakes of
Switzerland,) these inferior strata of water, cooled to 4 or 7 degrees, act
upon the temperature of the stony strata of the globe which they cover;
and how these same strata, the primitive temperature of which is,
within the tropics, 27 degrees, and at the lake of Geneva 10 degrees,
react upon the half-frozen waters at the bottom of the lakes, and of the
equinoctial ocean. These questions are of the highest importance, both
with regard to the economy of