SECT. XXV. HEAT IN MINES AND WELLS. 229 



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 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 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 increased 

 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 ven- 

 tilate 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 de- 

 scending currents ; so much so, that in winter the moisture is 

 often frozen in the latter to a considerable depth ; the circula- 

 tion 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 dis- 

 cordant to furnish any conclusion as to the actual heat of the 

 earth. The high temperature of mines might be attributed to 

 the effects of the fires, candles, and gunpowder used by the 

 miners, did not a similar increase obtain in deep wells, and in 

 borings to great depths in search of water, where no such causes 



