on Subterranean Temperature. 37 



of Saxony, 63 feet ; and by one observation at Iluelgoet, 

 56 feet. 



The simple comparison of the numerical results of the three 

 preceding tables, will be sufficient to shew the imperfect nature 

 of the means of experiment that have been employed. Thus, 

 for example, the expressions of the increase of heat which have 

 been found in the same mine, present variations whose extent 

 infinitely surpasses that which might be admitted as resulting 

 from anomalies arising from particular circumstances of the 

 rock, or from the little inaccuracies to which observations of 

 this kind are liable. But the approximative consequences which 

 one is authorised to draw from the experiments, taken together, 

 do not the less subsist. Moreover, the inequality of the results 

 in different countries is striking, and appears to me to consti- 

 tute an entirely new consideration, to which I shall have occa- 

 sion to revert i 



I now come to examine the experiments which have been 

 made by methods more direct than those whose results have jnst 

 been discussed. Their object has been to take the temperature 

 of the rock directly, at each of the levels where they have beea 

 made. Their number is not considerable, there being only tl ? 

 following : 



1,?^, In two mines of Saxony, those of Beschert Gluck and 

 Alte Hofinung Gotes, M. de Trebra placed stationary thermo- 

 meters in galleries, situated at different levels, which were at a 

 distance from works in activity, in which there was little circu- 

 lation of air, and where people seldom passed with lights. Each 

 thermometer was inclosed in a niche, glazed on the fore part, 

 and, moreover, contained in a glass tube ; the ball was immersed 

 in a cavity, wrought directly in the rock. A wooden door co- 

 vered the glass, and was only opened when the indications were 

 to be observed. The observations were continued for a long 

 time ; and in one of the mines they were repeated so often as 

 three times a-day for two years. They were confided to the 

 working master-miners (maitres mineurs de service), and veri- 

 fied from time to time by superior officers. This system is evi- 

 dently better than those of which we have spoken, but it is not 

 imobjectionable. In mines so old, so frequented, so perfectly 

 aired, as those in question, the temperature of the walls of a 

 gallery which has not ceased to communicate with Uie r^st of 

 the works, has had time to receive great modifications, l^he 



