38 



HEAT OF THE EAKTH. 



miners, had not, however, been regularly observed 

 before the middle of the last century. But since 

 that time observations on this head have been 

 carefully made at many places : in Germany espe- 

 cially in the mines of the Erzgebirge, in Switzer- 

 land, in Prance, in England, in Sweden, in Italy, 

 and even in several mines of Mexico and Peru. At 

 several places they were continued for a long time, 

 and at some have been followed up till very lately. 

 The temperature has been found everywhere to 

 increase with the depth. No trustworthy statements 

 have been made tending to disprove the univer- 

 sality of this fact. In the north of Siberia at 

 Yakutsk, where the frozen soil, even in the 

 middle of summer, is thawed only to the depth of 

 three feet, it was found in digging a well that the 

 cold became gradually less, and that at last at a 

 depth of three hundred and eighty feet the ground 

 was soft. I subjoin the numbers obtained in this 

 remarkable experiment, which was begun in 1830, 

 but not finished before 1837. 



Depth in 

 feet. 



Degrees of Temperature. 



Centigrade. 



Fahrenheit. 







82 



127 



221 



407 



___ Q / (Mean of 

 y X the year.) 



-7 



— 5 



— 25 



— 0-6 



15-8 



19-4 



23 



27'5 



30-92 



Nor less decisive of this question is the fact, 



