The sudden irruption of an immense body of water into a mine naturally causes a compression of the air in those galleries which are cut off from all communication with the shaft. This pressure, which may rise to three or four atmospheres—or, in other words, may be three or four times greater than that of the external air—not only produces symptoms of suffocation and cerebral congestion in the unfortunate miners who are exposed to it, but, forcing its way through fissures in the roof or violently rupturing it, sometimes produces the effect of an explosion of gunpowder, throwing the earth to a distance, and even overturning houses. One of the most interesting of the accidents of this kind on record occurred in 1833, in an extensive Scotch colliery, into which the waters of the river Garnock had broken through a cavity in its bed. As the stream poured into the mine the opening gradually enlarged, until at length the whole body of the river plunged into the excavations beneath. The river was affected by the tides, and this engulfment took place at low water; but as the tide rose the sea entered with prodigious force, until the whole workings, extending for many miles, were completely filled. No sooner, however, had this taken place, than the pressure of the water in the pits became so great that the confined air, which had been forced back into the high workings, burst through the surface of the earth in a thousand places, and many acres of ground were seen to bubble up like the boiling of a cauldron. Great quantities of sand and water were also thrown up, like showers of rain, during a period of five hours, and an extensive tract of land was laid waste.
Besides the danger of being crushed to death by a fall of rock, or immured in a living tomb by an obstruction of the shaft or an irruption of water, the miner has another, and often still more formidable, enemy to encounter in the noxious gases frequently evolved in coal-pits. Thus in all well-regulated mines the greatest attention is paid to ventilation, so that no part of the workings may be left without a proper supply of air. In ordinary cases the natural currents, which set in different directions through the shafts and galleries, may sufficiently purify the atmosphere; but in the coal mines which are peculiarly subject to the evolution of foul gases, artificial or mechanical means must be resorted to for driving away the hurtful vapours as quickly as they form. To establish a proper air current, the usual method is to keep a large fire continually burning at the bottom of one of the two shafts of the pit, or of one of the two compartments of the single shaft, and the difference of temperature thus caused between the column of air of the _upcast_ shaft and the _downcast_ becomes the motive power which impels or drags the air current in obedience to it.[39] Yet this meets but half the difficulty; for the air current, which naturally tends to the shortest passage, must be forced to do its duty in every corner of the pit, and not suffered to escape through the upcast shaft before it has performed the longest circuit. For this purpose a great number of mechanical contrivances are adopted, in the shape of ‘stoppings,’ of brick, or wood, or stone, all so placed as to divert