some Mines in Cornwall and Devonshire, 523 



metalliferous veins in most of the instances reported, may 

 have given a rather higher mean temperature than would 

 have been indicated by experiments confined to rocks at a di- 

 stance from " lodes." Upon the whole, however, I believe 

 that the results stated in the foregoing table are sufficiently 

 near the truth, to prove that the ratio in which the tempera- 

 ture augments in descending into the earth, is greater in 

 shallow mines than in deep ones. Moreover, 1 am persuaded 

 that we have no means at present within our reach to enable 

 us to arrive at satisfactory conclusions relative to the ratio in 

 which the temperature of the earth increases at much greater 

 depths than have yet been attained. 



It clearly appears, from what has been stated, that the con- 

 ducting power of rocks is not the immediate cause of the 

 high temperature observed in mines ; but the facts are quite 

 consistent with the hypothesis, which I have long advocated, of 

 heat being transferred from greater or less depths towards the 

 surface, in consequence of the well known tendency of warm 

 water to ascend through cooler portions of that fluid *; and 

 the anomalous results obtained at equal depths in different 

 places, often contiguous to each other, are, I conceive, mainly 

 to be attributed to the greater or less facilities afforded by 

 the rocks and veins for the circulation of the water. 



Note. — The experiments in Levant and Consolidated Mines 

 marked thus J in the table, were made by burying the bulbs 

 of long thermometers three feet deep in the rocks, and com- 

 pared with other thermometers near them buried only an 

 inch deep. Under these circumstances, the former indicated 

 about l°\ of temperature more than the latter, proving that 

 the high temperature was not due to extraneous causes, but 

 existed in the rock. Such results are, however, only to be 

 expected in the deepest parts of mines. Indeed, those ob- 

 tained in the upper levels of mines are generally unsatisfac- 

 tory and inconclusive, as it respects the native heat of the 

 earth at equal depths. 



[The details of Mr. Fox's observations on the temperature of mines 

 made from 1815 to 1823, will be found in Mr. Brayley's "Account" of 

 observations and experiments on the subject in Phil. Mag. First Series 

 vol. Ixi. p. 348, Ixii. p. 38; and in Phil. Mag. and Annals, N.S., vol. ix. 

 p. 94, appears another paper by Mr. Fox. See also Phil. Mag., First Series, 

 vol. xxxiii. p. 320, lxvii. p. 302; and Lond. and Edinb. Phil. Mag. vol. v. 

 p. 446.— Edtt.] 



* To this property of water, and its solvent power at great depths, 

 where the temperature is very high, 1 believe that many mineral deposits 

 in veins are to be referred. 1 have stated my views on this subject in the 

 Royal Cornwall Polytechnic Society's 4th Report, pp. 108 and 109, sold by 

 Trathan, Falmouth, and Simpkin and Marshall, Stationers' Court, London. 



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