102 Summary Rcoiexu of the late Investigations 



temperature of the earth at all seasons, at small distances below 

 its surface, Mr. Movie gives a table of the temperatures of 

 mines, containing the results he had before communicated to 

 the Society ; and of which we have given a tabular arrangement 

 at p. 96, incorporating with them the temperatures of several 

 other mines, additionally presented in Mi'. Moyle's table. He 

 then proceeds to the following remarks on what Mr. Fox and 

 Dr. Forbes have stated, as to the progressive increase of heat 

 in the earth, in proportion to the dejith. 



" In Mr. Fox's tables, the irregular ratio of augmented tem- 

 perature is very conspicuous ; as it appears to be as hot at the 

 depth of 600 leet in Chacewater mine, as it was in Dolcoath 

 at the depth of 1440 feet, each being 82^. In the next place, 

 it is as hot at 420 feet in the United Mines, as in Dolcoath at 

 1200 feet; as hot in Chacewater at 480 as at 840 feet in Huel 

 Damsel; as hot at 780 feet in Treskerby as at 1380 in Dol- 

 coath, &c. &c., and hotter in the United Mines at the depth of 

 1080 feet than in any other mine in the county. From this 

 statement, it appears that the temperature of the earth in Chace- 

 water increases 27° in 540 feet in depth ; while Dolcoath is 

 augmented only the same in 1380 feet; and the United Mines 

 the same number of degrees in 1080 feet, or exactly double the 

 depth. These facts would induce me to look upon the pro- 

 gressive ratio of heat in a different light from those gentlemen." 



" Mr. Fox and Dr. Forbes are at variance in opinion about 



stances and in the same ratio ; but it is explained by the width of this aper- 

 ture [a natural cavernous fissure] at the mouth of the mine, which admits 

 a free passage of atmospheric air. In our Coniisk mines, ice would not be 

 preserved in a solid state at any considerable depth from the surface." — 

 p. 103. 



In Dr. Clarke's account of the Fahlun copper-mine, at p. 141 of the same 

 volume, after stating the descent of himself and companions to the depth 

 of 1 70 fathoms, he olwerves, " Here we found the heat very oppressive : 

 the miners, with the exception of their drawers and shoes, were naked at 

 their work. This high temperature, increasing always in the dii-ect pro- 

 portion of the descent from the surface of the earth, and which m.ay be 

 observed in all mines, has never been satisfactorily explained. In the great 

 mine oi Poldice, near Truro in Cornwall, which has been worked, in granite, 

 to the depth of 300 fathoms, the miners, as at FaMun, carry on their la- 

 bours naked ; and the heat is so great at the bottom of the mine, notwith- 

 standing the accumulating water, that it may be sensibly felt by any person 

 placing his hand against the sides of the rock, as the author himself ex- 

 perienced. The heat of the Fa/tlun mine is so great, that it becomes in- 

 tolerable to a stranger who has not undergone the proper degree of sea- 

 soning which enables a miner to sustain it. But then there" are causes 

 which tend greatly to increase the natural temperature: prodigious fire* 

 are frequently kindled, and at a very considerable depth in the mine, for 

 the purpose of softening the rocks previously to the application of gun- 

 powder : add to this, the terrible combustion [of pyritous matter] which 

 has taken place in the mine, threatening its destruction." 



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