304 Royal Geological Society of Cornwall. 



of the climate. As the existence of so great a temperature as 

 this so near the surface, and still more the speiniiigly progressive 

 and nic;;t rapid increase of it in descending, are at first sight 

 circumstances vcrv startling to oiw prc-conceived notions, and 

 still more so when traced to the conclusions to which they neces- 

 sarily lead ; the author of the memoir, previously to coming to 

 any opinion as to the site or source of this high temperature, dis- 

 cussed the many hypothetical ohjectious that cau he advanced 

 against the existence of an internal source of heat in the body of 

 the earth, We have not space to notice all these, nor to notice 

 any of them fully. The following, among others, w ere particu- 

 larlv adduced and insisted on: 1. The fact that the degree of 

 elevation above the sea does not affect the temperature of mines ; 

 mountain-uiines, at equal depths below the surface, being as 

 warm as those at the sea level. 2. The difference of tempera- 

 turs ill mines of the same depth under the surface. 3. if so high 

 a temperature existed at so comparatively small depths, ought 

 not tlie law of the e(iuilibrium of caloric to render this percepti- 

 ble at the very surface of the earth? Ought not the tempera- 

 ture of our deep wells and copious springs to be the mean of tliis 

 internal temperature and the external ur atmospheric tempera- 

 ture conjoined, and not of the latter only, as is the fact ? 4. Be- 

 sides noticing the fact of the very low temperature of deep seas 

 and lakes, as bearing on the same point, Dr. Forbes brought 

 proofs that the temperature of several abandoned mines filled with 

 water fo>- vears, to the depth at least of several hundred feet, is 

 not greater than the mean temperature of Cornwall. These and 

 many other considerations naturally led the author to inquire 

 into the various possible sources of extraneous temperature that 

 SM-e found in mines, and to tlie examination of how far these will 

 go in accounting for their high temperature: an inquiry, more- 

 over, rendered more natural and necessary by the fact, fully 

 proved bv the author of the memoir, of the presence or absence 

 of miners occasioning a difference often of 6, S, or 10 degrees of 

 temperature in the same mine, or in different mines similarly 

 circumstanced in other respects. The various sources of extra- 

 neous temperature noticed by Dr. Forbes were: I. candles; 

 2, gunpowder; 3. friction and percussion; 4. the bodies of the 

 miners; 5. the dinvnished capacity of air for caloric, in deep 

 mines, in consequence of the condensation caused by the in- 

 creased height of the atmos))heric column. In estimating the 

 effect of the four first sources, the author entered into mitmte cal- 

 culations, founded on the experiments of various philosophers, 

 and illijstrated tlie whole by apjjlication to the case of a single 

 mine. The mine chosen for this purpose was the magnificent 

 copper mine of Dolcoath, \yhich employs (under-ground) 750 



persons. 



