ON THE TEMPEliATURE OF MINES. 467 
verses the works, and imparts its heat to the strata ; it then 
ascends, and is succeeded by a fresh portion of air from 
the surface, which in the same way becomes heated, and 
imparts its heat to the strata, and they, in turn, communi- 
cate it all around. Thus, in a long course of working in a 
deep mine, the air at the bottom is heated, and also the 
rocks to a considerable depth; and when the working 
ceases, the mine takes a long time to lose its temperature ; 
and this is found to be the case, particularly when the mine 
becomes full of water, the water being found at first of a 
high temperature, and gradually to lose its heat, which is 
in consequence of the strata imparting theirs to the water, 
and as soon as they have given out all their heat, the water 
indicates the mean temperature nearly of the place. 
The reverse takes place in an old mine when reworked ; 
in that case, the temperature rises gradually as the work- 
ing continues : and in those mines which are not worked, 
but in which the ventilation still goes on, I believe it will 
be found that they do not lose more of their temperature 
than can be placed to the abstraction of the other causes of 
heat in working mines, such as that produced by the men, 
and the lights. 
The exact quantity of heat given out by air, in propor- 
tion to its condensation, it is difficult to ascertain, but every 
day's experience proves it to be very considerable ; and, I 
believe, this, added to the other obvious sources of heat in 
mines in a state of working, will be found sufficient to ac- 
count for their high temperature. 
