GAEFOETH: FIEE-DAMP DETECTOE. 
401 
be done), still there are other serious difficulties to contend with, in 
consequence of the increased depth at which coal will in the future 
have to be won. Fortunately, large quantities of water (which in 
some shallow pits has been the chief drawback to the mine being 
worked profitably) are seldom met with at great depths ; and fire- 
damp, which might naturally be expected to be given off in greater 
proportions, owing to the increased weight of the the superincumbent 
strata, is found to be Uttle, if any more, than in mines lying nearer 
the surface. The cost of actually raising the coal is not seriously 
felt, on account of the various improvements which have been made 
in ropes, compensating winding drums, regulating valves, and the 
more economical use of fuel in both engines and boilers. The 
improved manufacture and reduced price of steel has contributed 
very materially to these and other advantageous results. 
The principal difficulties of deep mining are, increase of temper- 
ature, and the effects of the weight of the superincumbent strata. 
With reference to the former, it was thought, about the time the 
Royal Commission was appointed to enquire into the probable 
duration of the English coal-fields, that the temperature of the strata 
increased about one degree for every fifty feet, (after sixty feet 
from the surface) ; but recent sinkings have proved the increase is 
not so great, being only one degree for every seventy-six to seventy- 
nine feet. At Ashton Moss Colliery, near Manchester, the deepest 
shaft in England, and at Dukinfield Collieries, Cheshire (with both 
of which the writer is well acquainted), the temperature at 2,880ft. 
deep is eighty-four to eighty-five degrees. 
The natural temperature of the strata has been much reduced 
in some mines, by passing large volumes of air at a low temperature 
along the roadways ; but as deep mines will have to work extensive 
areas to save the cost of sinking additional pits, it follows that 
in an increased length of air-way, the air will become warmer, and 
less able to absorb the heat given off by the surrounding strata. To 
obtain sufficient air for cooling purposes, in addition to the ordinary 
requirements connected with the men, horses, lights, and diluting 
the noxious gases, a great increase of motive power will be required. 
The greatest help to obtain this increased quantity is by a larger 
