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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Gilbert And Ilsen, Is Only 578 Feet In Length; The Cavern
Of Scharzfeld 350; That Of Gaylenreuth 304; That Of
Antiparos 300.
But according to Saussure, the Grotto of Balme is 1300 feet.) Owing
to the different degrees of solubility
In rocks, it is generally
not in calcareous mountains, but in gypseous formations, that we
find the most extensive succession of grottoes. In Saxony there are
some in gypsum several leagues in length; for instance, that of
Wimelburg, which communicates with the cavern of Cresfield.
The determination of the temperature of grottoes presents a field
for interesting observation. The cavern of Caripe, situated nearly
in the latitude of 10 degrees 10 minutes, consequently in the
centre of the torrid zone, is elevated 506 toises above the level
of the sea in the gulf of Cariaco. We found that, in every part of
it, in the month of September, the temperature of the internal air
was between 18.4 and 18.9 degrees of the centesimal thermometer;
the external atmosphere being at 16.2 degrees. At the entrance of
the cavern, the thermometer in the open air was at 17.6 degrees;
but when immersed in the water of the little subterranean river, it
marked, even to the end of the cavern, 16.8 degrees. These
experiments are very interesting, if we reflect on the tendency to
equilibrium of heat, in the waters, the air, and the earth. When I
left Europe, men of science were regretting that they had not
sufficient data on what is called the temperature of the interior
of the globe; and it is but very recently that efforts have been
made, and with some success, to solve the grand problem of
subterranean meteorology. The stony strata that form the crust of
our planet, are alone accessible to our examination; and we now
know that the mean temperature of these strata varies not only with
latitudes and heights, but that, according to the position of the
several places, it performs also, in the space of a year, regular
oscillations round the mean heat of the neighbouring atmosphere.
The time is gone by when men were surprised to find, in other
zones, the heat of grottoes and wells differing from that observed
in the caves of the observatory at Paris. 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.
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