in Mining, certain noxious exhalations or gases issuing from some parts of the earth, and which prove almost instantly fatal to those who breathe them.

These damps occur chiefly in mines and coal-pits, though vapours of the same kind often issue from old lavas of burning mountains; and, in those countries where volcanoes are common, it is said that they fill the houses, and destroy people suddenly without the least warning of their approach. In mines and coal-pits they are chiefly of two kinds, called by miners and colliers the choke-damp and fire-damp. The choke-damp, known in modern chemistry by the name of fixed air, or carbonic acid gas, usually infests those places which have been formerly worked, but long neglected, and are known among miners as wastes. No place, however, can be reckoned safe from this kind of damp, except where there is a due circulation of air; and the procuring of this is the only proper means of preventing accidents from damps of all kinds. The choke-damp being heavy descends towards the lowest parts of the workings, and thus is dangerous to the miners, who can scarcely avoid breathing it.

The fire-damp, which is carburetted hydrogen, rises to the roof of the workings, as it is specifically lighter than common atmospheric air; and hence, though it will suffocate like the other, it seldom proves so dangerous in this way as by its inflammable property; for when exposed to the flame of the miners' candle it explodes with extreme violence.

In the Philosophical Transactions (No. 119), there is an account of some explosions by damps of this kind, on which the following observations have been made:—

1st. Those who are in the place where the vapour is fired find themselves suddenly surrounded with flames, but hear little or no noise; while those who are in places adjacent, or above ground, hear a very great one.

2d. Those who are surrounded by the inflamed vapour feel themselves scorched or burnt, but are not moved out of their places; though such as unhappily stand in the way of it are commonly killed by the violence of the shock, and are sometimes ejected from the mouth of the pit. Nor are the heaviest machines able to resist the impressiveness of the blast.

3d. No smell is perceived before the fire, but a very strong one of brimstone is afterwards perceptible.

4th. The vapour lies towards the roof, and is not perceived when the candles are held low; but when held higher, the damp descends like a black mist, and catches hold of the flame, increasing it to two or three handlengths; and this appearance ceases when the candles are held nearer the ground.

5th. The flame continues in the vault for several minutes after the report.

6th. Its colour is blue, something inclining to green, and very bright.

7th. On the explosion of the vapour, a dark smoke like that proceeding from fired gunpowder is perceived.

8th. Damps are generally observed to come about the latter end of May, and to continue during the heat of summer. They return several times during the summer season, but observe no certain rule.

Besides these damps other kinds are described in the Philosophical Transactions by Mr Jessop, who derived his information from the miners in Derbyshire. After describing the common damp, he says, "They call the second sort the peas-bloom damp, because, as they say, it smells like peas-bloom. They tell me it always comes in the summer time; and those grooves are not free which are never troubled with any other sort of damps. I never heard that it was mortal—the scent, perhaps, freeing them from the danger."

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1 The nature of the fire-damp was first accurately examined by Dr Henry of Manchester, in a paper published in Nicholson's Journal, xix., in the year 1806. of a surprise; but by reason of it many good grooves lie idle at the best and most profitable time of the year, when the subterraneous waters are the lowest. They fancy it proceeds from the multitude of red-trefoil flowers, by them called honey-suckles, with which the limestone meadows in the Peake do much abound. The third is the strangest and most pestilential of any, if all be true which is said concerning it. Those who pretend to have seen it, for it is visible, describe it thus: In the highest part of the roof of those passages which branch out from the main groove, they often see a round thing hanging, about the bigness of a foot-ball, covered with a skin of the thickness and colour of a cobweb. This, they say, if it be broke by any accident, as the splinter of a stone, or the like, disperses itself immediately, and suffocates all the company. Therefore, to prevent casualties, as soon as they have espied it, they have a way, by the help of a stick and long rope, of breaking it at a distance; which done, they purify the place well with fire before they dare enter it again. I dare not avouch the truth of this story in all its circumstances, because the proof of it seems impossible, since they say it kills all that are likely to bear witness to the particulars; neither do I deny but such a thing may have been seen hanging on the roof, since I have heard many affirm it." See Lamp, Safety.