on Subterranean Temperalui-e. 287 



for example, before attributing, as has been done, an absolute 

 value to these observations, it were necessary to solve this first 

 question. In a gallery, or in any other excavation, what is the 

 stratum of air whose temperature is thought to represent that of 

 the surrounding rock ? 



From all that we have hitherto related, it may be concluded 

 with certainty, that none of the observations collected on the 

 temperature of the air in mines, exactly represent the proper tem- 

 perature of the zone of rock at whose level it was made. Sup- 

 posing that, by a concurrence of extremely improbable compen- 

 sations, some of these observations having taken place at the mo- 

 ment when there existed an identity of temperature, nothing 

 could apprize us of so fortuitous an accuracy. None of them, there- 

 fore, is capable of being compared with the mean temperature of 

 the country in which it has been made. Those which have been 

 obtained at different levels in the same mine, on the same day, 

 and at not many minutes distance, are not more capable of being 

 compared with one another, although in general they are more 

 useful to be consulted than all the others. No other use, therefore, 

 can be made of this mass of observations than as mere documents. 



It must be confessed, that, even in this view, most of them 

 leave a considerable degree of uncertainty, for, in publishing them, 

 their authors have only made known a small part of the details 

 which would have been necessary for the establishm ent of their 

 real value. There is but a small number which, after being sub- 

 mitted to the scrutiny resulting from the principles exposed above, 

 could be regarded as giving a temperature either nearly the same, 

 or certainly inferior to that of the level to which they refer. The 

 observations of this kind are those which have been made during 

 cold weather, or in circumstances entirely exceptionable; for exam- 

 ple, in excavations of small extent, although deep, dry, and long 

 deserted. Now, these observations all proceeded in the same direc- 

 tion, and although they can only be considered as approxima- 

 tive, yet they positively indicate the existence of a certain in- 

 crease of heat proportional to the depths. 



We consider it useless to mention these latter observations in 

 detail, because it will be easy to distinguish them in the midst 

 of all the others of the same kind that have been published, and 

 because we shall presently discover the existence of better proofs. 

 These conclusions certainly are not without interest; but they 



