On the Low Temperature of Particular Caverns, IIS' 
is calculated to throw some light on the subject, though we are 
by no means disposed to admit that the conclusion he has drawn 
from it is altogether free from objection. At the ice-cave of 
Brezon, in the Alps, a current of cold air wa^ observed to issue, 
with considerable force, from several crevices near the cavern, 
which depressed a thermometer exposed to its influence from 
51° to S8|°. In applying this fact to the solution of the cause 
of the phenomenon in question, M. Pictet cites the observations 
of Saussure on the air rushing from the cavities of Monte Tes- 
taceo, near Rome ; where a little hill, composed of the fragments 
of urns, and other vases of earthen ware, produces an effect simi- 
lar to that of the calcareous sides of these icy caverns. Round 
the base of this artificial mound several caves have been dug, in 
the back walls of which a number of perforations have been 
formed, running upwards like chimneys, and through which a 
current of cold air constantly descends in summer. On the 1st 
of July 1776, the external air being at 78°.l Fahrenheit, the 
thermometer stood at 44|° in one of the caverns, and at 44° 
in another. It is certainly a very singular phenomenon,” says 
Saussure, “ that, in the middle of the Compagna of Rome, where 
the air is always burning-hot and suffocating, there should be 
found a little insulated hill, from the base of which should issue, 
on all sides, currents of air of an extreme coolness.” Saussure 
mentions several other places, where he observed that a current 
of air rushing from crevices in the rocks, v/hich formed the sides 
of caves, was accompanied with a great degree of cold. The 
caverns in which the cold was the most remarkable, were gene- 
rally situated in calcareous rocks, at the foot of a mountain. In 
short, these grottoes appear, in many instances, to be the mouths 
of natural galleries, communicating with upright shafts, through 
which a stream of air flows downward, when the temperature of 
the external air exceeds that of the cavern. The current of air 
thus determined, must acquire, during its descent, the tempera- 
ture of the vertical portion of the crevices through which it 
passes ; and that temperature must in general be at least as low 
as the mean temperature of the place. Professor Pictet supposes 
that the air descending through these fissures in the strata must 
be still further cooled by the refrigerating effect of evaporation,- 
from the moistened materials which it encounters in its progress 
VOL. X. NO. 19. JAN. 1824 
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