Scientific Intelligence. — Geology. I95 



of free carbonic acid ; I found its temperature 80°.25, from 

 wliich, I was told by the captain of the mine, it never va- 

 ried all the year round. Indeed, it had lately become more 

 copious in quantity, which had been accompanied with a 

 slight elevation of temperature. Air of gallery, in vicinity of 

 spring, 77°.22, being heated by radiation from the water. — 

 As the value of these observations is greatly enhanced by the 

 precision and accuracy with which they are conducted, I shall 

 briefly describe to you the thermometers with which, and the 

 manner in which, they are made. The bulb, and more than 

 8 feet of the tube, which is altogether about 4 feet long, are 

 enclosed in a brass cylinder about half an inch in diameter, and 

 closed at the lower extremity. The upper part only of the 

 tube, which projects scarcely a foot out of the cylinder, is gra- 

 duated, but very delicately, so that ^^^jth of a degree of Reau- 

 mur is clearly distinguishable, and smaller fractions may be cor- 

 rectly estimated. The space between the non-graduated part 

 of the tube and the brass case is filled with fine sand, so as to 

 exclude completely the action of the external air. With these 

 precautions, the brass tube is sunk its whole length into a hole 

 bored obliquely into the soUd gneiss rock, forming the walls of 

 the galleries, (in which little chambers have been previously 

 hewn, closed by a door, the key of which is only in the hands 

 of thesteiger), leaving only the graduated scale above the surface, 

 on which the temperature may be observed. The bulb of the 

 thermometer is thus sunk 3 feet into the solid rock, and completely 

 excluded from the air, both by the sand between the tube of the 

 thermometer and the inside of the brass cylinder, and another 

 layer of sand with which the interval between the outside of the 

 cylinder and the walls of the bore is filled up. These thermo- 

 meters are so delicate, that, notwithstanding these precautions, 

 they are affected momentarily by passing currents of air, and 

 even by the too long proximity of the observer. M. Keich 

 proposes publishing his observations when he has collected a 

 sufficient number. He observed to me, pn our conversing on 

 the subject, that he suspected many of the observations pub- 

 lished on subterranean temperature were very deficient in tlie 

 precautions taken to ensure accurate results. He places very 

 little reliance on the observations of Professor Kuppfer of Kasan, 



