FREEZING CAVERN AT ILLETZKAYA-ZASTCHITA. 
187 
adhered to this statement, and the expression of the peasants was, that in winter 
they could sleep in the cave without their sheepskins. 
In our hurried visit we could do no more than request the authorities to look 
carefully to this point during ensuing winters, and to preserve thermometric re- 
gistration of the changes in the cave, in relation to the external air. In the mean 
time, the simple fact which was presented to our senses was quite sufficient to 
create the utmost surprise. 
Our first attempt to afford an explanation of the phenomenon , was by sup- 
posing, that the chief fissure opening downwards, communicated with a floor of 
rock-salt, the saliferous vapours of which might be so rapidly evaporated or changed 
in escaping to an intensely hot and dry atmosphere, as to produce ice and snow. 
If this or some such subterranean process were admissible, then the apparent 
connexion between the intense cold within the cave and the great heat without, 
might, we thought, be explained. Finding, however, that our geological chemistry 
was doubted by some persons, we submitted the case to Sir John Herschel, and 
he kindly endeavoured to solve the problem by reference to ordinary climatological 
causes only. The following is an extract from a letter addressed by him to Mr. 
Murchison : 
“ That the cold in ice-caves (several of which are alluded to in a part of this 
letter not published) does not arise from evaporation, is, I think, too obvious to 
need insisting on. It is equally impossible that it can arise from condensation of 
vapour, which produces heat not cold. When the cold (by contrast with the ex- 
ternal air, i. e. the difference of temperature) is greatest, the reverse process is 
going on. Caves in moderately free communication with the air are dry and (to 
the feelings) warm in winter, wet or damp and cold in summer. And from the 
general course of this law I do not consider even your Orenburg caves exempt ; 
since however apparently arid the external air at 120° Fahr. may be, the moisture 
in it may yet be in excess and tending to deposition, when the same air is cooled 
down to many degrees beneath the freezing-point. 
“ The data wanting in the case of your Orenburg cave are the mean temperature 
of every month in the year of the air, and of thermometers buried, say a foot deep, 
on two or three points of the surface of the hill, which, if I understand you right, is 
of gypsum and of small elevation. I do not remember the winter temperature of 
Orenburg, but for Ekaterinenburg (only 5° north of Orenburg) , the temperatures are 
given in Kuppfer’s reports of the returns from the Russian magnetic observatories. 
