100 REPORT—1857. 
Increase of 1° 
Mines. a ere Dates, Temperatures. in descending. Rocks. 
Par Consols (tin part) ...) 768 | 1837 | 74° —50=24° 32 feet | Killas. 
Botallack, C. and T.......) 1128 | 1837 | 79 —50=29 39 | »5 Killas. 
Par Consols (copper part) ni 1837 |84. —50=34 36°7 ,, Killas. 
Doleoath, C. and T....... 380 | 1822 | 75:5 —50=25°5 Be Wee Granite. 
Leyant, C. Bnd’ Te .dcdew 5. a 1853 |74 —50=24 63°7 ,, Granite. 
Levant, C. and T.......... 1530 | 1853 |87 —50=37 413,, Killas. 
Levant, C. and T.......... 1530 | 1857 |85 —50=35 AS"7 op Killas: 
Tresavean, C...sserceeseee .| 1572 | 1837 | 82-5 —50=32°5 48°4 ,, Granite. 
Doleoath, C. and T....... 1632 | 1857 | 73 —50=23 ‘fet Granite. 
Doleoath, another lode...| 1632 | 1857 | 79°5 —50=29°5 55°3 ,, Granite. 
Tresavean, C.....cccsesceees 2112 | 1853 | 90°5 —50=40°5 52°1 ,, Granite. 
On comparing the results obtained in Dolcoath in 1821-1822 and 1827, 
it appears that the temperature was increased only 4° in one level with an 
increased depth of 252 feet, giving a ratio between the stations of 1° increase 
in 63 feet; and in another level the temperature was actually 2° to 25 less 
than in 1822, although 252 feet deeper than the mine was then. These 
experiments were made with great care, and this exceptional case may pro- 
bably be due to the greater hardness and compactness of the lode in the 
deeper level, and the diminished quantity of water. 
The depth of Tresavean was increased 540 feet between 1837 and 1853, 
and the temperature 8°5 in the deepest level, or in the ratio of 1° in 63°5 
feet. 
I have not included in the Table the results recently obtained in the United 
Mines or Fowey Consols, the experiments not having been made in their 
deepest levels; but the hot spring at 116°, at the depth of 255 fathoms in 
the United Mines, gives a ratio of 1° increase in 23°2 feet, and the rock in 
another level, also 255 fathoms deep, 1° in 47 feet. 
In 1853 the bottom of the United Mines was 275 fathoms below the sur- 
face, and the rock 94°, or in the ratio of 1° in 37°5 feet. At Fowey a 
the rock, in a level 288 fathoms deep, was at 93°, or in the ratio of 1° in 
crease in 40-2 feet. 
Widely as the ratios differ from each other in different mines and in dif- 
ferent parts of the same mine, the results tend to confirm the statement that 
the temperature in general increases less rapidly in deep mines than in those 
which are of inferior depth; and this is more especially observable when ex- 
periments are made from time to time at the bottom of a mine as the depth 
increases, unless the results be modified by an increase of water coming from 
greater depths. It is not, however, to be inferred that the diminishing ratio 
of temperature in descending into the earth extends to an indefinite depth ; 
it may, on the contrary, and probably does, increase much more uniformly 
at depths where the circulating water has little or no influence. A copious 
spring of warm water gushing from a vein, is hailed by the miners as a 
favourable indication of the proximity of ore, and so is a pervious, or 
“hollow” lode; but the former clearly results from the latter, the warm 
water rising from greater depths through the lode. 
These subterranean springs are often nearly as free from saline matter as 
those occurring at the surface; in some I have found common salt and 
chloride of lime, especially in water taken from the deep levels of Poldice 
and Wheal Unity, and the hot spring at the United Mines. My friend 
William Hustler has recently examined the latter, and he reports that it 
‘still contains a large quantity of chloride of sodium, and a considerable 
quantity of chloride of calcium, with traces of the sulphates of lime and 
