Mr. R. W. Fox on the Increase of Heat in Mines. 95 



for the purpose of showing that neither the hypothesis, nor 

 the objections derived from the temperature of abandoned 

 mines, are tenable. 



I do not apprehend that a degree of pressure equal to what 

 takes place in our deepest mines would raise the temperature 

 of air many degrees, probably not more than five or six at the 

 utmost, supposing none of the heat to escape to surrounding 

 bodies ; but the water flows into some of our mines in consi- 

 derable streams at the temperature of from 80 to 90, which 

 is about 30 to 40 above that of the climate : and nearly two 

 millions of gallons are daily pumped from the bottom of Pol- 

 dice mine, which is 176 fathoms deep, at 99 to 100. This 

 being warmer than the human body, of course puts that source 

 of heat out of the question; and it often happens that streams 

 of water, the moment they gush into mines, are equal and 

 sometimes superior in temperature to the air immediately in 

 contact with them. 



Neither do the seasons seem to produce any sensible effect 

 in deep mines, which they doubtless would do if the heat 

 were in almost any degree attributable to the compression of 

 the air. 



Our mines are for the most part ventilated by shafts open- 

 ing into the levels or galleries from the surface or from a 

 higher level. These shafts are commonly numerous in ex- 

 tensive mines, and the air circulates freely and often copiously 

 through them, ascending in some shafts, and descending in 

 others. In all cases, I believe that the upward currents are 

 at a higher temperature than the downward ones ; so much so, 

 indeed, that in winter the moisture is often frozen in the latter 

 to a considerable depth, and not at all in the former. The 

 temperature of these currents has recently been ascertained 

 in some mines. 



In Dolcoath the air ascended in one shaft at 60, and de- 

 scended in another at 51 : the thermometer was placed six 

 feet down in these shafts. 



In Poldice a current came up at 61, and another went 

 down at 4-8, both having been observed at thirty feet below 

 the mouths of the shafts. 



In Tingtang mine, which is 178 fathoms deep, the thermo- 

 meter was let down fifteen feet in two shafts, and indicated a 

 temperature of 59 in the ascending, and 42 in the descend- 

 ing current. 



The inferior specific gravity of the heated air is, in fact, the 

 cause of its ascent, and consequently of the descent of fresh 

 supplies from the atmosphere at a lower temperature ; so that 



it 



