1823.] Mr.Moyle on the Temperature of Mines. 41 



Secondly, it is necessary to make a few remarks on what Mr. 

 Fox and Dr. Forbes have stated, trusting that those gentlemen 

 will excuse the liberty which I have taken. 



In Mr. Fax's tables, the irregular ratio of augmented tempera- 

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

 of6(J0feet in (Jhacewater mine, as it was in Dolcoath at the 

 depth of 1440 feet, each being 82°. In the next piece, it is as 

 hot at 420 feet in the United Mines, as in Dolcoath at 1200 

 feet; as hot in Chacevvater at 480 as at 840 feet in Huel Damsel; 

 as hot at 780 feet in Treskerby as at 1:380 in Dolcoath, &c. Sec. ; 

 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 Chacewater 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 progressive ratio of heat in a 

 different light from those gentlemen. 



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

 a limit as to the precise point below the surface, for the com- 

 mencement of augmented temperature : an examination of an 

 experiment or two will prove the confidence we may place in the 

 conclusions of either. 



Mr. Fox commences at 50 feet, and Dr. Forbes at 200 feet, 

 below the surface ; and from the extreme temperature observed 

 in our deepest mines, would deduct b° for artificial and extra- 

 neous causes of heat, thus reducing the actual degree at about 

 1300 or 1400 feet from 72° to 74°; and after the ratio of 1° for 

 every 50 feet, it would be at the depth of 1044 feet, 68°. Now 

 reverse the order of calculation, and we shall find Mr. Fox to 

 make it 69^-°, and Dr. Forbes, Gb'-^- for the same depth. This 

 is the precise depth of the lowest of the three levels driven under 

 Trenoweth from Crenver, the temperature of which is actually 

 only 58°, although a spot not in the course of working, yet has 

 a distant communication with the mine in general, and at a 

 working spot on the same level, the temperature is but 68°, after 

 being exposed to all the extraneous sources in common. 



Dr. Forbes remarks (and Mr. Fox in his last communication 

 Kays the same), " hence it follows, that the natural temperature 

 of the earth in the mines in Cornwall, at the depths mentioned, 

 must be considerably above that of the mean of the climate. 

 This conclusion is equally deducible from many facts which 

 have been observed in mines. The most conclusive of these is 

 the high temperature of extensive collections of water in aban- 

 doned mines, or in parts of mines that have been lo lg since 

 abandoned. In cases of this kind, it is impossible to believe 

 that the temperature can have been derived from any other 

 source than the rocky walls of the cavity in which it is con- 

 tained ; and as these walls could not derive their temperature 



