Prof. Bischoff on Hot and Tlicrrnal Springs. 133 



for, admitting the increase of temperature towards the interior 

 of the earth, the mean temperature of those waters must ne- 

 cessiarily be lower than that of the mines in their lower work- 

 ings, where the direct influence of the external heat can no 

 longer be felt. But as we are not yet acquainted with any 

 other means of ascertaining the increase of temperature to- 

 wards the interior, than by observations in mines, this diffi- 

 culty can never be avoided. Reich* justly remarks, that this 

 effect of the atmospheric waters must be greater in old mines 

 than in new ones, although in time we do not doubt it must 

 reach its limit. To this cause, as well as to the sinking of the 

 colder air into the mines, he is inclined to ascribe the less ra- 

 pid increase of temperature observed in the Erzgehirge. 



The observations in the Saxon Ei-zgeblrge furnish many 

 proofs of the cooling effect produced by the action of the 

 meteoric waters on the rock in mines. Thus, Reich t found 

 from thirty-three monthly observations, that, at a depth of 

 215 feet in the Matliusalem mine, in the Freyberg district, the 

 air had the same temperature as the rock, that the seasons of 

 the year seemed to have no effect upon it, but that after con- 

 tinued dry weather the temperature was somewhat elevated, 

 and that it suffered a depression after long continued wet. 

 This depression will of course be greater, if water brought 

 from the surface into the mines, for putting the machinery in 

 motion, should happen to pass near the points of observa- 

 tion. 



In a sounding at Rudersdorf, eight leagues from Berlin, which 

 has been carried on to a depth of 880 feet from the surface, 

 and 700 feet below the level of the sea, a continued increase of 

 temperature has, indeed, been observed in the greater depths, 

 as well as an uniformity in the temperature of the water which 

 flows out of the sounding pipe, at the bottom of the well or 

 shaft, which extends to the depth of eighty feet; however, from 

 a comparison of the continued observations of more than two 

 years, we find a considerable irregularity in the increase of 

 temperature with the depth. The most rapid increase is ob- 

 served from 200 to 225 feet deep, where, on the 4th of Decem- 



* V. rJ3. See i)age 35. t P. 58. 



