12 
any other way available, it is quite at your service for that 
purpose. 
P.S. — Water at 120° Fahr., or even much higher, would, 
I fear, afford but an inefficient moving power unless some 
means could be devised (without the expense of more power 
than the gain expected) of concentrating the heat of a large 
quantity of warm water into a smaller. This might perhaps 
be done through the intervention of air alternately rarefied 
and condensed. 
Mr. Binney, F.R.S., F.G.S., said that at the present time 
little is known as to the difficulties we should experience in 
working coal mines at a depth of 4,000 feet from the surface. 
The exact increase of temperature in deep mines is not by any 
means well ascertained. All we can say is that no great diffi- 
culties have been found in working at a depth of 2,100 feet. 
It must always be borne in mind that the deeper a mine is the 
greater will be the natural ventilation, that is the current 
caused by the air of the mine, at say a temperature of 
80° Fahr., ascending the upcast shaft, while the air at the 
surface, of 40°, descends by the downcast shaft. No doubt a 
mine might be cooled by the expansion of compressed air, 
but it could not, so far as at present known, be done econo- 
mically. In most deep mines a considerable cooling of the 
air takes place by the expansion of the compressed gas (light 
carburetted hydrogen) as it escapes from the coal, where it 
has been long imprisoned under great pressure ; and this has 
not always been allowed for by observers of temperature in 
such places. In newly-opened mines this pent-up gas forces 
off large pieces from the face of the coal, and it sometimes 
makes a noise like water rushing over a weir. In sinking a 
deep shaft at Wigan some years since the compressed gas 
in the coal forced up about four yards of strong bind and 
made its way through it into the shaft. The rising of the 
roof of the coal as the shaft approaches it is well known to 
sinkers in deep and newly-opened coal fields. 
