Oct. 13, 1875] 
thermometer was then inserted, the hole was tightly plugged 
with clay so as to be air-tight, and was left undisturbed for half 
anhour, at the end of which time the thermometer was wit'- 
drawn and read—a mode of observation which appears well 
adapted to give reliab'e results. With respect to the tempera- 
tur_s at 161 and 290 yards (which are encivsel in brackets to 
indicate uncertanty), Mr. Bryham says that he has some 
doubt as to the correctness of the thermometer with which they 
were taken, and that they were not taken in the shaft at the 
time it was sunk, Lut in the seams at the depths named. 
Asuming the surface temperature to be 49°, we have, on the 
whole depth of 815 yards, or 2,445 feet, an increase of 45°, 
which is atthe rate of ‘o184 of a degree per foot, or a degree 
for every 54°3 feet. 
On plotting the temperature curve, including the two observa- 
tions mirked as doubtful, we find that it naturally divides itself 
into four portions, which are approximately straight lines. 
The most remarkable of these portions is the second from the 
top, extcn ling Irom the depth of 161 yards to that of 605 yards. 
It embraces 1,332 feet, and shows an increase of only 1° for every 
86 feet. 
The third portion, extending from the depth of 605 yards to 
that of 671 yards, covers only 198 feet, and shows an incre .se of 
1° for every 33 feet. 
The lowest portion extends from the depth of 671 yards to 815 
yards. It covers 432 feet, and shows an increase of I° in 54 feet. 
The topmost portion will be affected by the assumption we 
make as to surface temperature. Assuming this as 49°, it shows 
‘an increase of 1° in 31 feet. 
It is interesting to compare the Rosebridge observations with 
those previously made by Mr. Fairbairn at Astley Pit, Dukin- 
field, Cheshire, which have been described by Mr. Hull in “ The 
Coalfields of Great Britain,” and by Mr. Fairbairn himself in the 
B. A. Report for 1861. The results have been thus summed up 
by Mr. Hui] -— 
I. The first observation gives 51° as the invariable temperature 
~throuzhout the year at the depth of 17 feet. Between 231 yards 
and 270 yards the temperature was nearly uniform at 580. And 
the increase from the surface would beat the rate of 1° F. for 88 
feet. 
2. Between 270 and 309 yards, the increase was at the rate of 
1° for 62"4 feet. 
3. Between 309 and 419 yards, the increase was at the rate of 
1° for Go feet. 
4. Between 419 and 613 yards, the increase was at the rate of 
1° for 86°91 feet. 
5. Between 613 and 685 yards, the increase was at the rate of 
1° for 656 feet. 
The .esult of the whole series of observations gives an increase 
of 1° for every 83:2 feet. 
Mr. Fairbairn’s own summary is as follows :—‘‘ The amount 
of increase indicated in these experiments is from 51° to 573°, 
as the depth increases from 5% yards tu 231 yards, or an increase 
of 1° in 99 feet. But if we take the results which are more 
reliable, namely, those between the depths of 231 and 685 yards, 
we ha-e an increase of temperature from 57}° to 753°, or 17}° 
Fahrenheit. That is a mean increase of 1° in 76°8 feet.” 
Mr. Fairbairn here, by implication, throws doubt on the 
alleged invariable temperature of 51° at the depth of 17 feet, 
a de.enrination which in itself appears highly improbable, 
seeing tliat at Greenwich the thermometer, whose bulb is buried 
at a depth of 25°6 feet, exhibits an annual range of 3°'2, while 
that at the depth of 12°8 feet exhibits a range of 9°. But even 
if we assume the mean surface temperature to be 49°, we have 
still upon the whole depth an increase at the rate of 1° in 80 feet, 
as against 1° in 54°3 feetat Rosebridge. 
Mr. Fairbairn’s paper gives also the results obtained at a second 
pit at Dukinfield, which agree with those in the first in showing 
an exceptionally slow rate of increase downwards. The tempera- 
tures at the depths of 1673 yards and 467 yards were respectively 
58° and 663°, showing a difference of 8}° in 2994 yards, which 
is at the rite of 1° in 106 feet. The increase from the surface 
down to 167} yards, assuming the surface temperature as 49°, 
would be 9°, or 1” in 56 feet, and the mean rate of increase from 
the surface to the bottom would be 1° in 80 feet, the same as in 
the first pit. 
A tabular list of the strata at Rosebridge is appended to this 
report. A full account of the strata at Dukinfield is given in 
Mr. Fairbairn’s paper (B.A. Report, 1861). 
With strata so nearly similar and in two neighbouring counties, 
NATURE 
485 
we should scarcely have expected so much difference in the mean 
rates of increase downwards. In this respect, Rosebridge agrees 
well with the average of results obtained elsewhere. Dukinfield 
far surpasses all other deep mines or wells, so far as our present 
records extend, in slowness of increase. 
This implies one of two things, either that the strata of Dukin- 
field afford unusual facilities for the transmission of heat, or that 
the isothermal surfaces at still greater depths dip down in the 
vicinity of Dukinfield. 
Mr. Hull has called attention to a circumstance which favours 
the first of these explanations, the steepness of inclination of the 
Dukinfield strata. He argues, with much appearance of pro- 
bability, that beds of very various character (sandstones, shales, 
clays, and coal), alternating with each other, must offer more 
resistance to the transmission of heat across than parallel to their 
planes of bedding, as Mr. Hopkins has shown that every sudden 
change of material is equivalent to an increase of resistance; and 
it is obvious that highly inclined strata furnish a path by which 
heat can travel obliquely upwards without being interrupted by 
these breaches of continuity. 
To this suggestion of Mr. Hull’s it may be added that inclined 
strata furnish great facilities for the convection of heat by the 
flow of water along the planes of junction. It appears likely that 
surface water, by soaking downwards in this direction, may exer- 
cise an important influence in assimilating the temperature at 
great depths to that which prevails near the surface. Mr, Hull’s 
own statement of his views is given in the foot-note below. * 
Mr. McFarlane has been prevented from continuing his ob- 
servations near Glasgow during the past year by the press of 
business incident to the removal from the old to the new 
college. 
Mr. F. Amery, Druid House, Ashburton, Devon, has taken 
some observations with one of the Committce’s thermometers 
in the shaft of a mine which had been unused for a year, and 
was nearly full of water. The shaft is 12ft. x 7ft., and de- 
scends vertically for 350[t., after which it slopes to the south at 
an angle of 50°, continuing to the depth of 620.t. he water 
stood at soft. from the surface. Mr. Amery observed the tem- 
perature at every 50th foot of depth in the vertical portion, and 
found it to be 53° at all depths, except at 250ft. and 200ft., where 
it was 534 and 53:2 respectively. A copper lode crosses the 
shaft at the depth of 250.t. ; aad it appears to be generally the 
case in the Cornwall and Devonshire mines, that copper lodes 
exhibit a high temperature, a circumstance which Prof. Phillips 
explains by the conformation of the strata, which is such as to 
cause water from greater depths to make its way obliquely up- 
wards by following the course of the copper lodes. 
The nearly constant temperature observed from the surface to 
the bottom of the shaft seems to indicte a large amount of con- 
vective circulation. In this respect s:nall bores have a decided 
advantage. 
Mr. G. A. Lebour has taken observations with one of our 
thermometers in several shafts and bores near Llidsdale, 
Northumberland, made for working coal and iionstone. Mr. 
Lebour does not report the tempciatures observed, which he 
characterises as discrepant and utterly valueless, owing, he be- 
lieves, to the numerous water-bearing beds which they cut 
through, and the very varying temperature of these waters, 
Having now, however, found a dry Lore, he hopes to make a 
useful series of observations next winter. 
* Rosebridge Colliery occupies a position in the centre of a gently- 
sloping trough, where the beds are nearly horizontal ; they are terminated 
both on the west and east by large parailel faults, which throw up the strata 
on either side. The colliery is placed in what is known as ‘ the deep belt.’ 
** Dukinfield Colliery, on the other hand, is planted upon strata which are 
highly inclined. The beds of sandstone, shale, and coal rise and crop out to 
the eastward at angles varying from 30 to 35°. Now, I think we may as- 
sume that strata consisting of sandstones, shaies, clays, and coal alternating 
with each other, are capable of conducting heat more rapidly along the planes 
of bedding than across them, different kinds of rock haying, as Mr. Hopkins’s 
experiments show, different conducting powers. If this be so, we have 
an evident reason for the dissimilar results in the case before us. Assuming 
a constant supply of heat from the interior of the earth, it could only escape, 
in the case of Rosebridge, across the planes of bedding, meeting in its pro- 
gress upwards the resistance offered by strata of, in each case, varying con- 
ducting powers. On the other hand, in the case of Dukinfield, the internal 
heat could travel along the steeply-inclined strata themselves, and ultimately 
escape along the outcrop of the beds. 
“1 merely offer this as a suggestion explanatory of the results before us, 
and may be allowed to add that the strata at Monkwearmouth Colliery, the 
thermometrical observations at which correspond so closely with those obtained 
at Rosebridge, are also in a position not much removed from the horizontal, 
which is some evidence in corroboration of the views here offered."—Proc. 
Roy. Soc., Jan, 27, 1870. 
