144 HEAT OP LOWEST STRATUM OF AIR. 



surface of the ground as is beyond the reach 

 of the changes of external temperature; that 

 is to say, in such latitudes there must be a 

 certain depth, at which the ground is in a state 

 of perpetual congelation. In northern Asia and 

 in America, between 58° and 62° N. L., the 

 ground is found to be frozen at the depth of 

 fifteen or sixteen feet even in the hottest days 

 of summer. At Bogoslousk (mean tempera- 

 ture 0°-6 C. = 33°-l Fahr.) nearly under latitude 

 60° north, Humboldt found the earth, in the 

 middle of summer, thawed only to the depth of 

 six feet. At Yakutsk (8°-l C. = 46°-6 Fahr.) 

 under 62° N. L., where in the months of July and 

 August it is very warm, there is found neverthe- 

 less, at the depth of only three or four feet, a 

 stratum of perpetual ice, the bottom of which, 

 according to the experiments of Schergin, a mer- 

 chant of that place, was not reached at a depth of 

 three hundred and fifty-eight Parisian feet. It 

 may easily be conceived, remarks Humboldt, how 

 rapidly the thickness of the frozen stratum must 

 increase from 62° to 72° N. L., from Yakutsk to 

 the mouth of the Lena. Natural springs cannot 

 therefore exist in these regions; and to obtain 

 well water, it must be necessary to bore through 

 the whole thickness of the layer of ice-bound 

 earth. 



Wrangel found in Siberia, near the coast of 



