Freezing Cave of IlletzJcaya Zatchita. 361 



of the whole year, and the temperature during the three winter as 

 well as the three summer months most remarkably uniform. 



" This is precisely that distribution of temperature over time 

 which ought under such circumstances to give rise to well-defined 

 and intense waves of heat and cold ; and I have little doubt there- 

 fore that this is the true explanation of your phenomenon. 



" I should observe, that in the recorded observations of the Ca- 

 therinenburg ohservatory,the temperatures are observed two-hourly, 

 from eight a.m. to ten p.m., and not at night. The mean monthly 

 temperatures are thence concluded by a formula which I am not 

 very well satisfied with ; but the error, if any, so introduced must 

 be far too trifling to affect this argument. The works whence the 

 above data are obtained are, ' Observations Meteor ologiques et 

 Magneliques faites dans Vinl&rieur de I' Empire de Russie, ' and 

 ' Annuaire Magne'tique et Meteor ologique du Corps des Ingenieurs 

 des Mines de Russie,' works which we owe to the munificence of 

 the Russian government, and which it is satisfactory to find thus 

 early affording proofs of utility to science in explaining what cer- 

 tainly might be regarded as a somewhat puzzling phenomenon, 

 as it is one highly worthy of being further studied and being 

 made the subject of exact thermometric researches on the spot, and 

 wherever else anything similar occurs." 



Sir John Herschel then states, that since he began this letter he 

 had examined some old documents and found the paper which ac- 

 companied his letter. " The date of this manuscript," he adds, '* as 

 nearly as I can collect it from collateral circumstances, must have 

 been somewhere about the year 1829, or rather before than after. 

 " I remain, &c, 



" J. F. W. Herschel. 



" P.S. Thermometric observations in the Steppes, of the mean 

 monthly temperature of the soil at different depths from one to 100 

 feet (at Forbes's intervals), would be most interesting. At Cathe- 

 rinenburg the mean temperature of the air being 38° - 6 Fahr., no 

 permanently frozen soil would probably be reached, but a very little 

 more to the northward that phenomenon must occur. 



11 The ' thinning out' of the frozen stratum would be most inter- 

 esting to trace, but in thinning out by decrease of latitude it might 

 possibly at the same time ' dip ' beyond reach, all above it being oc- 

 cupied by soil subject to the law of periodic frost and thaw, and 

 giving room under favourable circumstances to ice-caverns, pits, or 

 galleries. What determines the distinct definition of the hot and 

 cold alternating layers is the exceedingly peculiar form of the curve 

 of the monthly temperatures as given in the tables above referred to." 



Phil. Mag. S. 3. Vol. 21. No. 139. Nov. 1842. 2 B 



