In the consolidated mines, at a depth of 290 fathoms, thermometers sunk in a cross course of the rock (killas) indicated at the vein 92° and 88°; 10 fathoms from it, 86.3° and 85°; 24 fathoms from it, 85.3° and 84°. Here the metallic vein is the hottest part; Mr. Fox thinks, because of its allowing hot waters to ascend. The temperature 85.3° is at least 35° above that of the climate, and the ratio is consequently 1° in 49.6° feet; or, allowing 10 fathoms to the depth of variable temperature, 1° in 48 feet.
And still more lately, experiments made by Captain Oats inTresavean copper mine gave the following results.
| Rock | |||||||
| Depth. | Air. | No. 1. | No. 2. | ||||
| 26 | feet | In | granite | 53.3° | 57.0° | 52.8° | |
| 200 | lode | 77.2° | 76.0° | 75.5° | |||
| 200 | again | 77.7° | 76.0° | 75.5° | |||
| 250 | lode | 83.2° | 82.5° | 82.0° | |||
| 262 | lode | 85.5° | 82.5° | 82.0° | |||
| Ratio, | 1° in 48 feet from the surface; or, | ||||||
| 1° in 46 feet from a point 10 fathoms below surface. | |||||||
Humboldt observed, in mines near Guanaxuato (Mexico),
| At | 502 | mètres depth in | Valenciana | mine | 36.8° | centig. |
| 193 | Rayas | 33.7 | ——— | |||
| 134 | Villalpand | 29.4 | ——— |
The surface temperature is 16°. The volcanic character of the country is perhaps unfavourable for accurate inferences.
Second Class of Experiments. In Stratified Rocks.
Saussure, in the salt mines of Bex, found
| At | 108 | mètres depth the temperature | 14.4° |
| 183 | 15.6° | ||
| 220 | 17.4° | ||
| Ratio deduced, 1° centigrade for 37 mètres. | |||
Mr. Hodgkinson, at the request of the British Asso-
