Royal Geological Society of Cornwall. 305 



persons, consumes monthly 3000/^5. of gunpowder, and 5000 /Z'i. 

 of candles ; is 1400 feet deep, and contains within it upwards of 

 seven millions of cu!)ic feet of excavated space. 



By Dr. F.'s calculations it appeared probable that a quantity 

 of air might be heated daily in Dolcoath by the various extra- 

 neous causes mentioned, from the teu'perature of 52 to 60 deg. 

 (which was considered the mean temperature of all the air con- 

 tained in the mine) sufficient to fill it thrice, or about 21 millions 

 of cubic feet. Applied to water, the same quantity of caloric 

 will raise, from the temperature of 52 to 77 deg. (the mean tem- 

 perature of the water in tb.e mine) only 2,300 cubic feet per day ; 

 but the j)umps of Dolcoath bring up daily upwards of 120,000 

 cubic feet of water of this temperature ! From this, therefore, it 

 is evident that the extraneous sources of caloric in mines, al- 

 though very important and more considerable than has usually 

 been allowed, entirely fail in accounting for the temperature found 

 in them. An additional, and hitherto unnoticed source of in- 

 creased temperature in mines, is that arising from the elongation 

 of the atmospheric column and consequent condensation of the 

 air; — a cause constantly operating in every mine where there is 

 a circulation of the contained atmospheric fluid, as is, indeed, 

 the case in all mines. But this, even in the deepest mines in 

 Cornwall, will only cause an increase of four degrees ; which, even 

 when added to the other adventitious causes, entirely fails to meet 

 the degree of the actual temperature. In the mines of Cornwall 

 no decomposition of pyrites, or other mineral matter, seems to 

 take place in any degree sufficient to cause any perceptible aug- 

 mentation of caloric. Whence, then, we may ask with Dr. Forbes, 

 is derived the high temperature of mines ? Notwithstanding the 

 strong arguments that can be adduced against it, must we admit 

 the existence of a constant and natural temperature of from 70 

 to SO degrees in the body of the earth at the depth of little more 

 than a thousand feet ? Or are there other adventitious causes, 

 not yet suspected, that can explain this very striking and singu- 

 lar phenomenon? Dr. Forbes considered the mean tempera- 

 ture of the whole atmosphere at the surface of the earth to be 

 about 66 degrees of Fahrenheit, and stated that this is the tem- 

 perature which he would have expected, a priori, to be found in 

 the earth at very great depths, that is, on the supposition that 

 there is no internal source of lieat. He concluded by promising 

 »ome communication on the health of miners as affected by the 

 tropical temperature of their subterranean climate. 



2. Another paper on the same sulyect by Mr. R. W. Fox, of 

 Falmouth, was also read, being the second on this interesting to- 

 pic presented by this gentleman to the Society. Mr. Fox's paper 

 was chiefly occupied in detailing observations on the tempera- 



Vol.5C. No. 270. Oct. iy20. Q q turc 



