242 HEAT IN MINES AND WELLS. SECT. XXVI. 



serves as an origin whence the effects of the external 

 heat are estimated on one side, and the internal temper- 

 ature of the globe on the other. 



As early as the year 1740, M. Gensanne discovered 

 in the lead mines of Geromagny, three leagues from 

 Befort, that the heat of the ground increases with the 

 depth below the zone of constant temperature. A vast 

 number of observations have been made since that time 

 in the mines of Europe and America, by MM. Saussure, 

 Daubuisson, Humboldt, Cordier, Fox, Reich, and others, 

 which agree, without an exception, in proving that the 

 temperature of the earth becomes higher in descending 

 toward its center. The greatest depth that has been 

 attained is in the silver mine of Guamaxato in Mexico, 

 where M. de Humboldt found a temperature of 98 at 

 the depth of 285 fathoms ; the mean annual temperature 

 of the country being only 61. Next to that is the Dal- 

 coath copper mine in Cornwall, where Mr. Fox's ther- 

 mometer stood at 68 in a hole in the rock at the depth 

 of 230 fathoms, and at 82 in water at the depth of 240 

 fathoms, the mean annual temperature at the surface 

 being about 50. But it is needless to multiply exam- 

 ples, all of which concur in showing that there is a very 

 great difference between the temperature in the interior 

 of the earth and at its surface. Mr. Fox's observations 

 on the temperature of springs which rise at profound 

 depths in mines, afford the strongest testimony. He 

 found considerable streams flowing into some of the 

 Cornish mines at the temperature of 80 or 90, which 

 is about 30 or 40 above that of the surface; and also 

 ascertained that nearly 2,000,000 gallons of water are 

 daily pumped from the bottom of the Poldice mine, 

 which is 176 fathoms deep, at 90 or 100. As this is 

 higher than the warmth of the human body, Mr. Fox 

 justly observes that it amounts to a proof that the in- 

 creased temperature cannot proceed from the persons of 

 the workmen employed in the mines. Neither can the 

 warmth of mines be attributed to the condensation of 

 the currents of air which ventilate them. Mr. Fox, 

 whose opinion is of high authority in these matters, 

 states that even in the deepest mines, the condensation 

 of the air would not raise the temperature more than 



