292 On the Ventilation of Coal-Mines. [APRIL, 
sons appointed to explore the workings for this purpose, before the. 
passages, /, J, were fully charged. 
Such an accumulation of fire-damp, however, supposing both 
passages full, though very inconsiderable when compared with 
what frequently takes place in mines ventilated on different prin- 
ciples, would certainly be fatal to the miner who should heedlessly 
or unfortunately set it on fire. But it is probable that the mischief 
would not extend further. Having plenty of room to expand in 
every direction without meeting with resistance, it is certain that 
the force of such an explosion would be speedily diminished, and 
that, at a very short distance, it would be perfectly harmless. Its 
immediate effects would be confined to the blowing open a few of 
the slight doors which might be nearest to it, and which the return 
of the air would shut again by, breaking the suspending string or 
fastening ; and its ultimate effects would only amount to a tem- 
porary derangement of the atmospheric currents in the immediate 
neighbourhood. 
‘The evolution of fire-damp in mines is in general gradual and 
slow: but not unfrequently great discharges of it are made into 
the workings, from what are called blowers. A blower is a fissure, 
or small opening, through which a stream of fire-damp rushes into 
the mine, in great quantity, and with considerable noise; as if the 
reservoir from which it comes were under the pressure of a head of 
water, which may in some instances be the case. Blowers are said 
in general to proceed from the roof, but are sometimes also ob- 
served to issue from the floor of the mine. The stream of gas 
issues from a blower in much less quantity after it has blown for 
some time than at the beginning; and is generally found to diminish 
gradually, until it ceases altogether. 
When the discharge of fire-damp from a blower is so large as to 
be dangerous, there is no choice of the measures to be adopted ; as 
there is only one which can be effectual, and that is, to lead the 
fire-damp the nearest way to the upeast shaft. This may be done 
in different modes, as may best suit the circumstances of the case. 
If, for instance, a dangerous blower issues in a place which is no 
common thoroughfare, as at N, the simplest mode of directing it 
to the upcast shaft, is to let it have the whole passage to itself, by 
shutting the lateral doors, 0, 0, and p, p, on each side, and leaving 
an opening in the lower one at R, to admit a sufficient supply of 
air to float the products of the blower to the upcast shaft. 
But when a blower occurs in a part of the mine, through which 
it is absolutely, necessary to pass, and that frequently, the mode ot 
cure is more difficult, and consequently more expensive. 
Let Fig. 3 represent a section of a passage, in which a blower, 
A, issues from the roof, and has formed an excavation in it. To 
carry off the fire-damp as fast as it issues, it will only be necessary 
to fix the tube, B, along the roof of the passage, so that its upright 
part, C, may open into the highest part of the excavation, which 
may be enlarged and deepened for this purpose. The other end of 
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