REMARKS ON TEMPERATURE OF THE EARTH IN MINES. 13- 



In the observations which have been made on this matter, 

 the British mining engineer or manager takes a prominent place, 

 although he is not alone in drawing attention to it. Inform- 

 ation on such subjects is, however, generally made available to 

 the English reader in whatever language it may have been 

 originally written. 



In the history of the coal trade by Matthias Dunn, pub- 

 lished in 1844, it it stated that "the temperature of coal mines 

 is now pretty well known to be in proportion to their depth. A 

 single instance from my minutes of January, 1820, will shew 

 the eii'ect in different situations of Jarrow Colliery : Temperature 

 at surface, 40 degs. ; temperature at bottom of shaft, 14G fathoms 

 deep, 61 degs." The other observations do not affect the present 

 question ; the mean ratio here is nearly 10 fathoms of depth to 1 

 deg. of temperature. The observation is made at the surface, 

 however, in winter ; whereas in summer the surface tempera- 

 ture would have been higher than that taken at the bottom of 

 the shaft without the temperature at that point being materially 

 altered, as the air would have become of the normal temperature 

 of the strata through which it had passed. This observation 

 therefore proves nothing, but it illustrates the principle which 

 appears to affect all the observations which have been taken, 

 which is, that whilst in nearly all cases there is an increment of 

 heat in a lower over that of a higher level, that increment is 

 almost, if not altogether, due to local and exceptional circum- 

 stances, and not to any general principle of internal heat, uni- 

 formly or otherwise affecting the crust of the earth in proportion to 

 the depth from the surface or from any other point, wdiether a 

 plane of invariable temperature, the surface of the ocean or the 

 neiglibouring plain ot earth. 



Mr. W. J. Hemwood, F.R.S., F.G.S., &c., &c., gives the 

 result of forty-five observations in the principal mining districts 

 of Cornwall and Devon. Mean depths, 112 fathoms ; mean 

 temperature, 66-88 ; ratios, 6'8 fathoms, or about 40 feet 

 descent for each degree of temperature. Now the mean 

 between this and the ratio of increment given by Dunn, which 

 is also given by "Wardle in his " Reference Book on Practical 

 Coal Mining," will give 50 feet for each degree; and Hopton in 



