ON THE TEMPERATURE OF DEEP MINES IN CORNWALL. 99 
lode was worked, the level extending to about fourteen fathoms to the west- 
ward of the engine-shaft.. There the granite was found to be at 795, and 
the water, which was much more abundant than in the other level, 79°-5, 
while the air was at 78°. Two men at a time worked near each of the 
stations in both levels. The pumps discharged only about 190 gallons of 
water per minute from the mine. 
In 1821-1822 the deepest level in Dolcoath was 230 fathoms from the 
surface, and I. then had an accurate thermometer, 4 feet long, kept im it 
more than a year and a half, with the bulb sunk 3 feet in the lode, and 
it varied from 75° and 75°5 to 76°5 and 77°; an occasional influx of water 
haying caused a temporary rise of the mercury to the extent of a degree or 
more. This temperature being from two to three degrees higher than the 
rock, was lately found by H. Peters to be at an increased depth of 42 fathoms : 
I begged Captain Charles Thomas, the manager of the mine, to have a ther- 
momneter left for some days in a hole in the rock near one of the ends of the 
deepest level on the north lode. This he has done, and he reports that 
the temperature did not vary from 73°, although the thermometer was left 
there a week, and the top of the hole was well closed, thus confirming 
H. Peters’ observations. 
The water near the bottom of the engine-shaft in 1822 was at 82°, at 239 
fathoms below the surface, and this year (1857) it was at 82°5, at 278 
fathoms deep. 
Levant copper and tin mine, in St. Just parish, is nearly twenty miles to 
the west of Dolcoath, and is close to the sea. Its deepest level is 255 
fathoms below the surface of the ground, and nearly 230 fathoms beneath 
the sea-level, having been horizontally extended under it through killas. 
The temperature of the rock near the end of this level was 84°-7 on one side 
of the latter, and 85°-5 on the other; the water 85°°5, and the air 85°. No 
men had been employed in this level for some time. There was very little 
water there, and indeed only about 60 or 70 gallons were discharged per 
minute from the mine. 
In 1853 the temperature of the rock in this level, when it was not ex- 
tended so far westward under the sea, was reported to me to be 87°, and the 
granite rock at the same level, eastward of the shaft, ‘74°. 
Botallack copper and tin mine is situated at the north-western extremity 
of Cornwall, in the parish of St. Just, and the engine-house is built on a 
rock which is washed by the sea. The western levels have been worked 
through killas far under the Atlantic, one of them extending more than half 
-a mile from the shore. ‘Two men and a boy were employed in the deepest 
level, which was less advanced from the shore. It was 188 fathoms below 
the ground, and about 180 fathoms under the sea-level. The rock near the 
end of the level was 79° on one side of it, and ’79°5 on the other, the air 81°: 
no water at that station, and but little comparatively in the mine. 
The foregoing results exhibit great differences in the rates of increase in 
the temperature in different mines, and also in different parts of the same 
mine. If we arrange the mines in the order of their respective depths, in- 
cluding those only in which experiments were made in the rocks or lodes at 
their deepest levels, the following will be the ratios in feet, in descending 
from the surface, in which the temperature was augmented one degree Fahr, 
from 50°, the mean temperature of the climate. 
HQ 
