a q 2 - 
4 
f 
; 
REPORT ON SUBTERRANEAN TEMPERATURE. 315 
The first Table contains results obtained in the deepest 
galleries or accessible parts of mines, a few only excepted, in 
which cases the experiments were made with great care in the 
rock at superior levels, and at a distance from other excava- 
tions. Some of the reasons for preferring the former to the 
generality of results derived from the upper parts of mines 
have been stated on previous occasions, and they appear to be 
so obvious as to render repetition needless. 
The rate of increase of temperature, as it respects the rock 
or rubbish, and the water and air, appears to have been 
tolerably consistent. The mean is 16°46 at 100 fathoms deep, 
and 27°:03.at 200 fathoms deep; the augmented temperature 
of the first hundred fathoms being to that of the second hun- 
dred fathoms, as 16°43 to 10°60. 
Some of the results from which these means are deduced 
are rather uncommonly high, and probably the general mean 
temperature observable in our mines would be more nearly 
represented by their omission, thus reducing both the above 
means a little; but if this were done, it does not appear that 
their relations to each other would be essentially altered. 
In the last columns are included all the results obtained in 
the rock, water, and air, with the exception of a few which seem 
to be in unusual excess, and they give, in round numbers, 
A temperature of 60° at 59 fms. below the surface. 
S 70° at 132 ,, Ms 
and 80° at 239 ,, A 
Being an increase of 
10° at 59 fis. deep, or 1° in 35-4 feet, 
1 of 10 more at 73 fms. deeper, or 1 in 48°8 feet, 
} andof10 ,, 114 fms. still deeper, or 1 in 64:2 feet. 
_ The second Table shows the temperature observed in the 
_ rock or rubbish, water, and air, in various mines at different 
depths, but not in the lowest excavations. It will not there- 
fore, perhaps, be considered to possess much value beyond 
what is derived from the great number of the results, and the 
probability that the mean which they indicate may be an ap- 
proximation to the truth. The figures only are given, without 
any details, and are to be found in my papers inserted in the 
Transactions of the Cornwall Geological Society, and in the 
Philosophical Magazine. 
__ Many of the observations, even in the first Table, may per- 
haps now be considered very imperfect, having been obtained 
_ when the inquiry was in its infancy. The method which I 
mnave more recently adopted, of having the bulbs of different 
_ thermometers buried at different depths at the bottom of a 
_ mine, appears to be as unexceptionable as the circumstances 
_ of the case will admit of; but, in fact, I have always considered 
