Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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The Same Instrument Which
In Those Caves Marks 12 Degrees, Rises In The Subterraneous Caverns
Of The Island Of Madeira,
Near Funchal, to 16.2 degrees; in
Joseph's Well, at Cairo* to 21.2 degrees (* At Funchal (latitude 32
degrees
37 minutes) the mean temperature of the air is 20.4
degrees, and at Cairo (latitude 30 degrees 2 minutes), according to
Nouet, it is 22.4 degrees.); in the grottoes of the island of Cuba
to 22 or 23 degrees.* (* The mean temperature of the air at the
Havannah, according to Mr. Ferrer, is 25.6 degrees.) This increase
is nearly in proportion to that of the mean temperature of the
atmosphere, from latitude 48 degrees to the tropics.
We have just seen that, in the Cueva del Guacharo, the water of the
river is nearly 2 degrees colder than the ambient air of the
cavern. The water, whether in filtering through the rocks, or in
running over stony beds, doubtless imbibes the temperature of these
beds. The air contained in the grotto, on the contrary, is not in
repose; it communicates with the external atmosphere. Though under
the torrid zone, the changes of the external temperature are
exceedingly trifling, currents are formed, which modify
periodically the internal air. It is consequently the temperature
of the waters, that of 16.8 degrees, which we might look upon as
the temperature of the earth in those mountains, if we were sure
that the waters do not descend rapidly from more elevated
neighbouring mountains.
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