Natural History, are certain noxious ex- halations issuing from some parts of the earth, and which prove almost instantly fatal to those who breathe them.

These damps are chiefly observed 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 the miners and colliers the choke and fire-damps; and both go under one general name of foul air. The choke-damps, known in modern chemistry by the name of fixed air, or carbonic acid gas, usually infest those places which have been formerly worked, but long neglected, and are called by the miners wastes. No place, however, can be reckoned safe from this kind of damps, except where there is a due circula- tion of air; and the procuring of this is the only proper means of preventing accidents from damps of all kinds. The choke-damp suffocates the miners suddenly, with all the appearances found in those that are suffocated by fixed air. Being heavy, it 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 inflammable air, or hydrogen gas, rises to the roof of the workings, as being specifically lighter than the common atmosphere; and hence, though it will suffocate as well as the other, it seldom proves so dangerous in this way as by its inflammable property, by which it often takes fire at the candles, and 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. First, Those who are in the place where the vapour is fired sud- denly find themselves surrounded with flames, but hear little or no noise; though those who are in places adj- acent, or above ground, hear a very great one. Secondly, 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 often thrown with great force out at the mouth of the pit; nor are the heaviest machines found able to resist the impetuosity of the blast. Thirdly, No smell is perceived before the fire, but a very strong one of brimstone is af- terwards perceptible. Fourthly, The vapour lies towards the roof; and is not perceived if the candles are held low; but when these are held higher, the damp descends like a black mist, and catches hold of the flame, lengthening it to two or three handfuls; and this appearance ceases when the candles are held nearer the ground. Fifthly, The flame continues in the vault for several minutes after the crack. Sixthly, Its colour is blue, something inclin- ing to green, and very bright. Seventhly, On the explo- sion of the vapour, a dark smoke like that proceeding from fired gunpowder is perceived. Eighthly, Damps are gene- rally observed to come about the latter end of May, and to continue during the heat of summer. They return sev- eral times during the summer season, but observe no cer- tain rule.

Besides these kinds of damps, which are very common, we find others described in the Philosophical Transactions, concerning the nature of which we can say nothing. In- deed the account seems somewhat suspicious. They are given by Mr Jessop, from whom we have the foregoing observations concerning the fire-damp, and who had these from the miners in Derbyshire. After describing the common damp, which consists of fixed air, "They call the second sort," says he, "the peas-bloom damp, be- cause, 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 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-trefill flowers, by them called honeys- uckles, 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 is broke by any acci- dent, as the splinter of a stone, or the like, disperseth it- self immediately, and suffocates all the company. There- fore, to prevent casualties, as soon as they have espied it, they have a way, by the help of a stick and long rope, of Damsel 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 Safety Lamp.)