241 
ture to be about 1 deg. Fahr. in 76 feet ; and from experiments 
made at depths from 500 to 1,000 yards, and furmsbed to me 
by Monsieur Lambert, Inspector of Mines at Cbarleroi for 
the Belgian Government, and to whom I am greatly in- 
debted for his valuable assistance, I calculate them to indicate 
an increase of 1 deg. in 125 feet, showing for our encourage- 
ment, that at increased depths the temperature does not in- 
crease at the same rapid ratio that it does at shallower 
depths, which, as we proceed under the Trias and Permian 
formations, I anticipate to become still more favourable, inas- 
much as these deposits produce little or no heat, being 
generally very cold, and in some districts very wet. At the 
same time, therefore, in working Coal at these depths, it is not at 
all improbable that this temperature in some instances may be 
considerably reduced by natural causes, such as the evapora- 
tion of water passing through the overlying strata, combined 
with the most perfect mechanical and general arrangement 
of ventilation. 
This subject of the ratio'of increase of temperature of Coal 
mines at increased depths, bears a most important and inter- 
esting part in the economy of our Coal fields in the future, 
and as it is one that chemists and engineers have somewhat 
investigated of late, I hope some member of this Society 
will contribute a paper on that subject. 
There is another insuperable barrier to pillar workings at 
increased depths, in addition to the ventilating difficulty just 
referred to, viz., the pressure of the superincumbent strata 
upon such pillars of Coal, which will necessarily increase the 
deeper we go. At the same time, in investigating this sub- 
ject, we cannot draw an infallible rule for the rate of increase, 
which is regulated a little by the material passed through ; 
for instance, if the sinkings pass through any rocks of great 
thickness and extent, the pressure might be somewhat re- 
lieved thereby. A cubic foot of rock sand weighs 156 
