270 
GEXEItAL TEJtPEItATl'ItE. 
for instance, that of Wimelburg, which communicates with 
the cavern of Cresfielcl. 
The determination of the temperature of grottoes pre- 
sents a field for interesting observation. The cavern of 
Caripe, situated nearly in the latitude of 10° 10', consequent- 
ly 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 mouth of September, 
the temperature of the internal air was between IS’4° and 
18-9° of the centesimal thermometer ; the external atmos- 
phere being at 16‘2 0 . At the entrance of the cavern, the 
thermometer in the open air was at 17 - 6°; but when im- 
mersed in the water of the little subterranean river, it 
marked, even to the end of the cavern, 16'8°. These ex- 
periments are very interesting, if we reflect on the tend- 
ency to equilibrium of heat, in the waters, the air, and the 
earth. \\ hen 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 suc- 
cess, to solve the grand problem of Subterranean meteor- 
ology. The stony strata that form the crust of our planet, 
are alone accessible to our examination ; and wc now know 
that the mean temperature of these strata varies not only 
with latitudes and heights, but that, according to the po- 
sition of the several places, it performs also, in the space 
of a year, regular oscillations round the mean heat of 
the neigbouring 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°, rises in the subterra- 
neous caverns of the island of Madeira, near Funchal, to 
16'2° ; in Joseph’s Well, at Cairo* to 21'2°; in the grot- 
toes of the island of Cuba to 22° or 23°.+ This increase 
is nearly in proportion to that of the mean temperature 
of the atmosphere, from latitude 48° to the tropics. 
* At Funchal (lat. 32° 37’) the mean temperature of the air is 20’4°, 
and at Cairo (lat. 30° 2'), according to Nouet, it is 22'4°. 
t The mean temperature of the air at the Havannah, according to 
Mr. Ferrer, is 25' 6°. 
