AND ITS DISTRIBUTION. 45 



By a thorough discussion of all the observations, Mid- 

 dendorff obtained, as the general rate of increase of 

 temperature, ( 48 ) 1 of Reaumur for between 100 and 

 117 English feet, or 1 Pahr. for from 44-4 to 52'1 

 English feet. This is a more rapid rate of increase than 

 is given by several very accordant results from different 

 excavations in Middle Europe (see above, p. 37). The 

 mean annual temperature of lakutzk is considered to 

 be -813 Reaum., or 13'71 Pahr. Neveroff's observa- 

 tions, continued during fifteen years (1829 1844), give 

 the variation of temperature between winter and summer 

 so great, that sometimes the temperature of the air, for 

 14} successive days in July and August, is from 20 to 

 23-4 Reaum., or from 77 to 84-6 Eahr. ; while for 

 120 successive days in winter (November to February) 

 the cold fluctuates between 33 and 44*8 Reaum., 

 or 42-25 and 6S'S Fahr. The depth beneath 

 the surface of the earth at which the lower limit of the 

 frozen ground, or the temperature of Reaum. and Cent.,, 

 or 32 Fahr., would be met with, is calculated approxi- 

 mately from the increase of temperature found in piercing 

 the icy stratum so far as lias yet been done. Middendorff's 

 estimate, from his observations in the Schergin Shaft, in 

 accordance with the much earlier one of Erman, assigns from., 

 612 to 642 French, or 652 to 684 English, feet. On the 

 other hand, the increase of temperature in the excavations 

 of Mangan, Schiloff, and Davydoff (scarcely four miles 

 from lakutzk, in the chain of hills on the left bank of 

 the Lena), which, however, are not quite sixty feet deep, 

 would place the temperature of (or 32 Fahr.), at a 

 depth of little more than 300 feet.( 4 ?) Is this great 



