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Extracts from a Letter addressed hy Sir J. Herschel, Bart., F.G.S., 

 to Mr Murchison, explanatory of the Phenomena of the Freezing 

 Cave of Illetzkaya Zatchita.* 



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 external air, i. e. the difference of tempera- 

 ture) 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 sum- 

 mer. And from the general course of this law I do not con- 

 sider even your Orenbm'g caves exempt, since however ap- 

 parently arid the external air at 120° Fahr. ! may be, the mois- 

 ture 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 Catherinenbourg (only 5° 

 north of Orenburg), the temperatures are given in Kuppfer's 

 reports of the returns from the Russian magnetic observato- 

 ries. If any thing similar obtains at Orenburg, I see no diffi- 

 culty in explaining your phenomenon. Rejecting diurnal fluc- 

 tuations, and confining ourselves to a single summer wave of 

 heat propagated downwards alternately with a single winter 

 wave of cold, every point at the interior of an insulated hill, 

 rising above the level plain, will be invaded by these waves in 



* From the Proceedings of the Geological Society, vol. iii. part 2 ; 

 having been read March 9. 1842. 



