on Subterranean Temperature. 281 



If the identity of the temperatures in question cannot occur in 

 such a mine as we have imagined, still less possible is it in com- 

 mon mines, to which the air has continual access, in which the 

 filtering waters incessantly act as a cause of variation, and where 

 the lights and workmen daily disengage large quantities of heat. 

 Let us examine the effects which these three disturbing causes 

 produce upon the temperature of the air contained in mines. 



Theexternal air, by continually mixing with the air contained in 

 a mine, acts in the ratio of the temperature which it brings to each 

 point, and of the mass which is introduced at this point in a given 

 time. Now, these two elements are continually varying, and their 

 influence necessarily extends to the most distant excavations. I 

 estimate the velocity of the draught which takes place by means 

 of the shafts that serve for ventilating mines, as being sometimes 

 four times and even six times as great when it is very cold as it is 

 in ordinary weather. The temperature of the air which enters 

 varies every^day, every hour, or it may be said every moment. 

 This temperature is lowered more or less, from the effect of the 

 more or less abundant evaporation which the air produces, by rea- 

 son of its dryness and original heat, in proportion as it circulates 

 along the humid surface of the iexcavations. At the same time 

 it is subjected to a very feeble cause of augmentation, which sel- 

 dom compensates the preceding, and which depends upon the in- 

 creasing influence of the atmospherical pressure, in proportion as 

 the air introduced penetrates into deeper cavities. This cause, 

 the effect of which has been exaggerated by some persons, could 

 only augment the temperature of the introduced air, about five 

 or six tenths of a degree of Fahrenheit for a depth of 180 feet. 



These data justify the proposition which precedes them. Fur- 

 ther, there results from them a curious fact, which it is of import- 

 ance to establish ; namely, that the mean temperature of the mass 

 of air which has been introduced into a mine in the course of a 

 year, is certainly inferior to the mean temperature of the country 

 for the same year. According to various researches, which it 

 would occupy too much time to relate, I estimate the difference 

 as being from three to five degrees Fahrenheit, in most of the 

 mines of our climates. Thus, not only does the introduction of 

 <?xternal air into a mine increase and diminish incessantly, and in 



