1822.] on the Temperature of Mines in Cornwall, 383 



in the former, it was 87*5°, and in the latter 88°, which is by 

 much the highest temperature I have heard of in any of the 

 mines of this'county. 



For a statement of the other facts I have collected, and also 

 of the temperature of cross galleries, I must beg to refer to the 

 Transactions of the Cornwall Geological Society ; but I may 

 remark, that the latter were generally a few degrees under the 

 temperature of the galleries in the direction of the metallic veins 

 at the same level; and this small difference does not appear 

 extraordinary, when it is considered that independently of the 

 latter being sometimes more affected by extraneous causes, the 

 veins afford an easier passage to the water and vapour, than the 

 more compact ground in which they are enclosed. 



As far as my inquiries have gone, I consider the ratio of the 

 increase of temperature may fairly be estimated at about one 

 degree for every 60 or 70 feet in depth. 



M. P. Moyle states, that he found a gallery in Huel 

 Unity, 150 fathoms deep, of the temperature of 65° ; this being 

 12° above the mean temperature of our climate, taking it at 53°, 

 as I have done (which is, I beheve, rather too high than too low 

 an estimate), nearly approximates to the ratio of increase before 

 mentioned. 



In the case of Huel Trevenen Tin Mine, he describes the tem- 

 perature of the water to have been lower than that of the atmo- 

 sphere ; but as he does not say what the temperature of either 

 was, no inference, I conceive, can be drawn from this case. And 

 here I may remark, that in Tincroft, and Cook's Kitchen Mines, 

 which had been for a long period partly full of water, the tem- 

 perature was found to increase considerably in descending, 

 although in a less ratio than in other mines which were not so 

 circumstanced ; and this I attribute to the influence of evapora- 

 tion, and the accumulation of colder water from the surface. 



Huel Trumpet Tin Mine appears to present the only exception 

 which M. P. Moyle has specified. Not having visited the mine, I 

 am ignorant of the circumstances of the case ; and whether it 

 be a copious stream from the vein, or only some water accumu- 

 lated by dropping from superior strata, which is reported to 

 have been at .51°, we are not informed : if, however, it be an 

 exception, let not the cold stream of Huel Trumpet be a stronger 

 argument on one side of the question, than the hot spring of Ice- 

 land is admitted to be on the other. 



Respectfnlly thy friend, 



R.W. Fox. 



