278 HEAT IN MINES AND WELLS. [SECT. xxvr. 



240 fathoms, the mean annual temperature at the surface 

 being about 50. But it is needless to multiply examples, 

 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 tem- 

 perature 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 sur- 

 face, 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 increased temperature 

 cannot proceed from the persons of the workmen employed 

 in the mines. Neither can the warmth of mines be attri- 

 buted to the condensation of the currents of air which venti- 

 late them. Mr. Fox, whose opinion is of high authority in 

 these matters, states that, even in the deepest mines, the con- 

 densation of the air would not raise the temperature more 

 than 5 or 6 ; and that, if the heat could be attributed to this 

 cause, the seasons would sensibly affect the temperature of 

 mines, which it appears they do not where the depth is great. 

 Besides, the Cornish mines are generally ventilated by 

 numerous shafts opening into the galleries from the surface 

 or from a higher level. The air circulates freely in these, 

 descending in some shafts and ascending in others. In all 

 cases, Mr. Fox found that the upward currents are of a higher 

 temperature than the descending currents ; so much so, that 

 in winter the moisture is often frozen in the latter to a con- 

 siderable depth; the circulation of air, therefore, tends to 

 cool the mine instead of increasing the heat. Mr. Fox has 

 also removed the objections arising from the comparatively 

 low temperature of the water in the shafts of abandoned 

 mines, by showing that observations in them, from a variety 

 of circumstances which he enumerates, are too discordant to 



