in natural history, (from the Saxon word damp, signifying vapour or exhalation), are certain noxious exhalations 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 or burning mountains; and, in those countries where volcanos are common, will frequently enter houses, and kill 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-damp is very much of the nature of fixed air; and usually infects those places which have been formerly worked, but long neglected, and are known to the miners by the name of wafters. No place, however, can be reckoned safe from this kind of damps, 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 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 scarce avoid breathing it. The fire-damp, which seems chiefly to be composed of inflammable air, 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 Phil. Trans. no. 119, there is an account of some explosions by damps of this kind, on which we have the following observations. 1. Those who are in the place where the vapour is fired, suddenly find themselves surrounded with flames, but hear little or no noise; though those who are in places adjacent, or above ground, hear a very great one. 2. 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. 3. No smell is perceived before the fire, but a very strong one of brimstone is afterwards felt. 4. 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. 5. The flame continues in the vault for several minutes after the crack. 6. Its colour is blue, something inclining to green, and very bright. 7. On the explosion of the vapour, a dark smoke like that proceeding from fired gunpowder is perceived. 7. 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 kind of damps, which are very common, we find others described in the Philosophical Transactions, concerning the nature of which we can say nothing. Indeed 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 pease-bloom damp, because, as they say, it smells like pease-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 surprize: 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 tomesuckle, with which the limestone meadows in the Peake do much abound. The third is the strangest and most perilous 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 accident, as the splinter of a stone, or the like, disperseth 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 dare I deny, but such a thing may have been seen hanging on the roof, since I have heard many affirm it."—Some damps, seemingly of the same nature with those last mentioned, are noticed by the author of the Chemical Dictionary, under the word Damps. Damps. Damps. "Amongst the noxious mineral exhalations, (says he), we may place those which are found in the mines of sal-gem in Poland. These frequently appear in form of light flecks, threads, and spider's webs. They are remarkable for their property of suddenly catching fire at the lamps of the miners with a terrible noise and explosion. They instantly kill those whom they touch. Similar vapours are found in some mines of fossil coal."

With regard to damps, it is a question well worth deciding, whether they are occasioned by a stagnation of the common atmosphere in the pit, impregnating itself by degrees with various noxious effluvia; or whether they are occasioned by some imperceptible operation of nature within the bowels of the earth itself?—As the choke-damp is often to be met with in old wastes, it would seem, that the air in those places becomes noxious merely from stagnation. But from some accounts given by those who are conversant in coal-mines, it appears that these damps, the inflammable ones especially, issue from particular places in great quantity, and often very suddenly; and that very dangerous effects will follow from merely beating on those places with a hammer. It cannot be denied, however, but that these accounts must be suspicious; for philosophers seldom visit those regions, at least with a design to take up their abode in them; and the workmen are no doubt apt to indulge the natural passion for the marvellous, in all their accounts of such phenomena. In the Phil. Trans. No. 136, we have the following account of a fire-damp which seemed plainly to issue from the earth. "This work is upon a coal of five yards in thickness, and hath been begun upon about six or eight and thirty years ago. When it was first found, it was extreme full of water, so that it could not be wrought down to the bottom of the coal; but a witchet, or cave, was driven out of the middle of it, upon a level for gaining room to work, and drawing down the spring of water that lies in the coal to the eye of the pit. In driving of which witchet, after they had gone a considerable way under ground, and were fanned of wind, the fire-damps did begin by little and little to breed, and to appear in crevices and flits of the coal, where water had lien before the opening of the coal, with a small bluish flame, working and moving continually; but not out of its first seat, unless the workmen held their candles to it; and then being weak, the blaze of the candle would drive it with a sudden fizz, away to another crevice, where it would soon after appear blazing and moving as formerly. This was the first knowledge of it in this work, which the workmen made but a sport of; and so partly neglected, till it had grown some strength; and then upon a morning, the first collier that went down, going forwards in the witchet with his candle in his hand, the damp presently darted out so violently at his candle, that it struck the man clear down, singed all his hair and clothes, and disabled him from working for a while after. Some other small warnings it gave them, insomuch that they resolved to employ a man on purpose that was more resolute than the rest, to go down a while before them every morning, to chase it from place to place, and so to weaken it. His usual manner was to put on the worst rags he had, and to wet them all in water, and when he came within the danger of it, then he fell down groveling upon his belly, and so went forward, holding in one hand a long wand or pole, at the head whereof he tied candles burning, and reached them by degrees towards it; then the damp would fly at them, and, if it missed of putting them out, would quench itself with a blast, and leave an ill-scented smoke behind. Thus they dealt with it till they had wrought the coal down to the bottom, and the water following, and not remaining as before in the body of it, among sulphurous and brassy metal that is in some veins of the coal, the fire-damp was not seen nor heard of till the latter end of the year 1675, which happened as followeth.

"After long working of this coal, it was found upon the rising grounds, that there lay another roach of coal at the depth of 14 yards under it, which proved to be 3½ yards thick, and something more sulphureous. This encouraged us to sink in one of the pits we had formerly used on the five-yards coal.—As we sunk the lower part of it, we had many appearances of the fire-damp in the watery crevices of the rocks we sank thro', flashing and darting from side to side of the pit, and shewing rainbow-like colours upon the surface of the water in the bottom; but upon drawing up of the water with buckets, which stirred the air in the pit, it would leave burning, till the colliers at work, with their breath and sweat, and the smoke of their candles, thickened the air in the pit, and then it would appear again; they lighted their candles at it sometimes when they went out; and so in this pit it did no further harm."

In another pit, however, it soon appeared, and at last produced a most terrible explosion. This was occasioned by one of the workmen going imprudently down with a lighted candle, after a cessation of work for some days, and the force exerted by it seemed equal to that of gunpowder.—Many very terrible accidents are also daily known to happen from vapours of this kind; but from any histories of these cases which can yet be obtained, no certain theory of the formation of these vapours can be established. Doctor Priestley hath indeed shewed, that inflammable air may be produced artificially in a great number of ways. It arises from a mixture of iron-filings and oil of vitriol or spirit of salt; and therefore the fire-damp hath been thought to proceed from large quantities of pyrites. But it is also produced from vegetable and animal substances in great quantities by distillation; and even from several metals by heat only, without any acid. From a letter by Doctor Franklin to Doctor Priestley, it appears, that inflammable vapours rise up even from the bottom of ponds of water in some places, take fire on the surface, and will burn for two or three seconds.—It doth not appear that these artificial methods of procuring inflammable air can throw the smallest light upon the natural processes by which it is produced in mines, or at the bottom of the waters above-mentioned. The supposition of its being produced by pyrites in a manner analogous to that from oil of vitriol and iron-filings can by no means be admitted; for the pyrites produce no acid capable of acting upon iron, unless after long exposure to the air; neither do they contain any iron in its metallic form, which is absolutely necessary to the success of the experiment. Though a mixture of iron-filings and brimstone will take fire from being exposed to the air, or even if slightly covered with earth, yet if covered with water, though the mixture swells and turns black, it does not generate the least quantity of inflammable vapour.

The difficulty is still greater with regard to fixed air. This is well known to have issued from many parts of the earth, for a number of ages together; particularly the Grotto del Cani in Italy. Now, though we know that this kind of air is discharged in great quantity from fermenting and putrefying substances, and also from earthly ones when calcined by heat, it seems altogether impossible, upon these principles, to account for such a constant and regular production of this kind of air in the cavern above-mentioned.—The greatest quantity of fermenting or putrefying substances we can imagine, must in time have finished their fermentation or putrefaction, and then ceased to discharge this kind of air; and the like must have happened with any quantity of calcareous matter we can suppose to be subjected to the action of subterraneous heat. It seems probable, therefore, that nature hath some method of producing these kinds of air which hath not yet been imitated by any artificial processes; and, in all probability, both fixed and inflammable air answer some purposes in the natural operations which are as yet unknown to us.—Concerning this, the author of the Chemical Dictionary offers the following conjecture. “Almost all chemists and metallurgists agree in believing, that mineral exhalations contribute to the production of metals. This opinion is so much more probable, that, as phlogiston is one of the principles of metals, (if it be be true that these mineral exhalations are nothing else than phlogiston), and as this principle is then in a state of vapour, and consequently much divided, perhaps reduced to its smallest integrant particles, it is then in its most favourable state for combination: it is therefore probable, that when these exhalations meet earths disposed to receive them, they combine more or less intimately with those earths, according to their nature. Perhaps this is the chief operation of the grand mystery of metallisation.”