46 COSMOS. 



surface at which the ice exhibits the temperature of 32 F., 

 and which is consequently the nearest to the lower limit of 

 the frozen soil ; according to MiddendorfTs results which 

 entirely agree with those that had been obtained much earlier 

 by Erman, this point was found in Schergin's shaft to be 652, 

 or 684 feet below the surface. It would appear, however, 

 from the increase of temperature which was observed in the 

 mines of Mangan, Shilow and Dawydow, which are situated 

 at about three or four miles from Irkutsk, in the chain of 

 hills on the left bank of the Lena, and which are scarcely 

 more than 60 feet in depth, that the normal stratum of perpe- 

 tual frost seems to be situated at 320 feet below the surface. 47 

 Is this inequality only apparent in consequence of the un- 

 certainty which attaches to a numerical determination, based 

 on so inconsiderable a depth, and does the increase of tem- 

 perature obey different laws at different times ? Is it 

 certain that if we were to make a horizontal section of 

 several hundred fathoms from the deepest part of Schergin's 

 shaft into the adjoining country, we should find in every 

 direction and at every distance from the mine frozen soil, in 

 which the thermometer would indicate a temperature of 4. 5 

 below the freezing point ? 



Schrenk has examined the frozen soil in 67 30' N. L. in 

 the country of the Samojedes. In the neighbourhood of 

 Pustojenskoy Gorodok, fire is employed to facilitate the 

 sinking of wells, and in the middle of summer ice was found 

 at only 5 feet below the surface. This stratum could be 

 traced for nearly 70 feet, when the works were suddenly 

 stopped. The inhabitants were able to sledge over the 

 neighbouring lake of Usteje throughout the whole of the 

 summer of 1813. 48 During my Siberian expedition with 

 Ehrenberg and Gustav Rose, we caused a boring to be made 



4 7 Middendorff, Bd. i, s. 160, 164, 179. In these numerical data and 

 conjectures regarding the thickness of the frozen soil, it is assumed 

 that the temperature increases in arithmetical progression with the 

 depth. Whether a retardation of this increase occurs in greater depths 

 is theoretically uncertain, and hence there is no use in entering upon 

 deceptive calculations regarding the temperature of the centre of the 

 earth in the fused heterogeneous rocky masses which give rise to 

 currents. 



48 Schrenk's Reise durck die Tundern der Samoje.den, 1848, Th. i, 

 B. 597. 



