i14 Analysis, §-c. of Cordier’s Essay upon the 
breath. In some mines, all these causes of error exist ; in 
mines long abandoned, very few of them are found; bué 
making every possible allowance, with all the accuracy that 
the present state of our knowledge admits, the general fact 
of the increase of heat in proportion as we descend from the 
surface, remains untouched. : 
the depth corresponding to an increase of one degree o 
centigrade thermometer. On these experiments he makes 
the following remarks : Bee 
_ “1. The imperfection of the: thermometers; ‘from origirial 
inaccuracy, and from inaccuracy proceeding from the effect of 
time on the renee a and on the bulb. On the necessity of a pre- 
vious verification of the mercurial scale. 
es, S may arise on the absolute depths of the mines 
» Doubt 
subjected to observation. The openings of mines ‘are usu ly be- 
w the medium level of the count 
a mill at their first exit, ‘may be used, provided care be taken’ 
to\observe whether they are not influenced by surrounding moun-' 
‘tainous regions, and other local circumstances. 
_ 6. Phe old opinion of the effect of decomposing pyrites, is 
now abandoned by those who possess the modern geological i 
i 
. 
formation. . Pyr tes is not so abundant any where, even in the. 
roofs of coal measures, as to produce any notable effect: nor is the 
decomposition of pyrites easily effected, unless they be broken 
in pieces ; for their decomposition proceeds by one surface after 
' another.” j eal wi 
« He instances this, from the pyrites in the coal mine of St. 
eorge Lavencas in Aveyron. ise 
en then proceeds to the conclusions that may reason- 
be drawn ion the experiments passed under review. 
