Page:A Treatise on Geology, volume 2.djvu/285

 CHAP. IX. {| style="font-size:85%;line-height:140%;border-style:none;text-align:left;" cellspacing="0" cellpadding="2" align="center"
 * At || the surface (as before) || 8°
 * || 180 metres || 11½
 * || 260 || 15
 * }
 * || 260 || 15
 * }
 * }

as M. Daubuisson had found in 1802.

The ratio deduced is about 1° in 37 metres in the upper part, and 1° in 22.2 metres in the lower part.

Again, under the same direction, thermometers placed in gneiss in the mine called Alte Hoffnung Gottes, gave

From these experiments it is concluded that the augmentation of temperature is 1° in 38 metres.

In the mines of Poullaouen and Huelgoat, in Brittany, M. Daubuisson found results which he considered to be partly influenced by local causes. In Poullaouen, at 140 fathoms, the augmentation was 3.1° or 1° for 45 metres. In Huelgoat, at 230 metres, the augmentation was 8.7°, or 1° in 26.4 metres.

In Cornwall, Mr. Fox's observations, at various periods, yield corresponding results. In a spring Dolcoath copper mine, 439 fathoms deep, the temperature was 27.8°, and that of the surface 10°.

In the same mine, 421 fathoms deep, the temperature of the rock of a gallery for 18 months was 24.2°.

Lately (1837) Mr. Fox communicated to the British Association some further observations, made below the lowest workings, in the Levant tin and copper mine, and the consolidated copper mine. At 230 fathoms from the surface, in the Levant mine (in granite), a thermometer, sunk 3 feet below the "sump," stood at 80; another, sunk only a few inches, was at 78.5°; and the air in the mine 67°. At 190 fathoms, the corresponding indications were 78°, 72.5°, and 67°. The general ratio is 1° Fahr. for 46 feet English; or, allowing 10 fathoms to the invariable temp., 1° in 46 feet.