/ 
in tilt Coal Mines of Great Britain. 137 
appears to have its origin in a constant natural internal heat in 
the physical constitution of the earth. 
It has been asserted by those who have considered the tem- 
perature of mines, that the heat found there arises from the 
workmen, and from the lights and horses employed in the mines. 
These causes, how'ever, cannot produce more than a degree or two 
of temperature, as the air is necessarily kept in constant cir- 
culation for the safety of the workmen. 
Others have asserted, that the increased temperature arises 
from the decomposition of pyrites, which abounds in coal and the 
accompanying strata, and that this is the cause of the high tem- 
perature of hot springs. This opinion, however, does not 
seem to be well founded. Although in the very extensive coal 
mines of Great Britain, pyrites abounds in great quantities, yet 
in no instance was pyrites ever found decomposed in situ, al- 
though the coal abounds with water, and gives out carbonic 
acid gas and carburetted hydrogen, but never atmospheric air, 
and the pyrites only decomposes when exposed to the action of 
oxygen. Had pyrites been liable to decompose in situ, the 
greater part of the coal-fields in the world would have been de- 
stroyed by spontaneous ignition ; but this spontaneous ignition 
only takes place in coal mines where the pyrites is throvvii in- 
to the waste, and exposed to the action of atmospheric air, and 
the moisture of the strata. If pyrites is the cause of the high 
temperature of hot springs, these springs would vary continually, 
both in temperature and composition, according to the extent 
of surface exposed to the decomposing action. 
The celebrated traveller M. Humboldt has stated, that the 
temperature of the silver mine of Valenciana in New Spain, is 
11® above the mean temperature of Jamaica and Pondicherry ; 
and that this temperature is not owing to the miners and their 
lights, but to local and geological causes.'’ He also remarks, 
that the health of the miners is greatly injured by working in a 
temperature which ranges from 71® to 80® Fahrenheit. Many 
of the miners in Great Britain, however, are daily exposed to a 
temperature within that range, namely, from 70® to 77 
Edinburgh, April 1819. 
