16 Extracts explanatory of the Phenomena, ^c. 



I should observe that, in the recorded observations of the 

 Gather in enbourg Observatory, the temperatures are observed 

 trv'o-hourly, from 8 a.m. to 10 p.m , and not at night. The 

 mean monthly temperatures are thence concluded by a for- 

 mula which I am not very well satisfied with ; but the error, 

 if any, so introduced, must be far too trifling to affect this ar- 

 gument. The works whence the above data are obtained are — 

 Observations Meteorologiques et Magiittiqiies faites dans Vintc- 

 rieur de V Empire de Russie, and Ammaire Mapnetiqiie et Me- 

 teorologique 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 aflx)rding proofs 

 of utility to science, in explaining what certainly 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 accompanied his letter. " The date of this manu- 

 script," 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. Hehschel. 



P-S. — Thermometric observations in the Steppes^ of the mean monthly 

 temperature of the soil at different depths, from 1 to 100 feet (at Forbes' 

 intervals'), would be most interesting. At Catherinenbourg, the mean 

 temperature of the air being 33°. 6 Fahr., no permanently frozen soil would 

 probably be reached, but a very little more to the northward that pheno- 

 menon must occur. 



The " thinning out " of the frozen stratum would be most interesting 

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

 the same time " dip" beyond reach, all above it being occupied by soil 

 subject to the law of periodic frost and thaw, and giving room, under 

 favourable circumstances, to ice caverns, pits, or galleries. What deter- 

 mines 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. 



