coal could not be extracted unless some safety-lamp be provided which shall afford a light, and yet not kindle this highlyinflammable gas. The safety-lamp of Sir Humphry Davy answers to this necessity. It consists of a common oil-lamp surmounted with a covered cylinder of very fine wire gauze, the apertures in which should be very minute. Since the fire-damp is not inflamed by heated wire, the thickness of the wire is not of importance. The cylinder, or cage of wire, is made of double joinings, the gauze being folded over in such a manner as to leave no apertures. It is fastened to the lamp by a screw, and fitted to the screw by a tight ring. A second top is always fixed one-half or three-quarters of an inch above the first, and to this a hand-ring is attached, by which the lamp is carried. The simple, but long undiscovered, principle of safety in the lamp is this:-The flame of the oil-lamp, though greatly enlarged by the fire-damp that passes through the fine wire-gauze, will not spread beyond the gauze, or pass through its apertures when they are sufficiently minute-that is, one hundred in a square inch at least (they may be 400 to 900 in the square inch). In such case, the flame being supplied with only a limited quantity of air, produces such a quantity of azote and carbonic acid gas as to prevent explosions of the fire-damp. The most explosive condition of the air of a mine is when it contains one part of fire-damp to seven or eight of common air. When such a mixture is formed, the cylinder of the lamp will be filled with flame, but the flame of the wick will appear within the flame of the firedamp. When the fire damp increases to a proportion of onethird part to the whole air, the flame of the lamp will disappear, and the flame in the cylinder of wire-gauze become paler. This ought to be a signal to leave the place, as the air is no longer fit for respiration.

Discussions of the most animated character have been held respecting this lamp as to its real inventor, whether Stephenson, Clanny, or Davy; as to its absolute safety in critical circumstances; and as to its modifications and improvements. Evidence of witnesses to Parliamentary Committees, opinions of miners, and opinions of scientific men, have been conflicting and confusing. After all, the practical men of the North mostly adhere to the simple Davy lamp, or to some simple modification of it; and, after frequent and lengthened conversations with them, we agree with them. Had we space we would describe some curious experiences in traversing the mines with a Davy lamp. It has been an inestimable boon to coal-miners.

As this lamp has but a feeble illuminating power, it is dispensed with by the men as much as possible. They prefer a

naked candle, giving them greater light at vastly greater risk. The indisposition to adopt, or enforce the adoption of, Davy lamps in fiery mines, is one chief cause of explosions; while we must admit that a too confident reliance on this lamp is an evil in the opposite direction. It is, however, now abundantly proved, that if a thorough ventilation, and a judicious and general use of the lamp were enforced, explosions would be few and rare. Wherever firedamp abounds in a mine, constant vigilance is necessary to prevent a surprise from that secret foe. When once the air and the gas are combined in the dangerous proportion (1 of gas to 7 or 8 of air), a single candle may kindle the whole mine and kill half the miners in an instant. Great and sudden falls in the barometer are thought to indicate a critical time for the pit, as the atmosphere will not then press so heavily or the gas be so firmly imprisoned. A presumed very frequent cause of explosions is the sudden issue of a 'bag' or 'blower' of the pent-up gas from the loosened coal. We ourselves have listened to the gas hissing, with a low hiss, out of every pore of the coal in a deep recess, and in one pit we applied a candle, by permission, to the roof, and immediately the whole passage glowed with a beautiful lambent, bluish flame, playing most sportively along the upper parts. This was near the shaft, and therefore not dangerous; in any recess it would have been fatal.

Other causes of explosions are, either insufficient air to sweep away the gas as it exudes from the coal, or enough only to dilute it to the dangerous proportion (and thus bad ventilation is often worse than none at all), or the kindling of the contaminated air as it passes out of the pit after ventilating it. To avoid this last cause a 'dumb furnace,' or separate brick channel, is carried over the open flaming furnace, and through this dumb furnace the whole vitiated return air' is carried out. Once more, a derangement of the course of the air-current will produce a complete confusion and an explosion. This may be occasioned by the careless leaving open of a trap-door (and many explosions are traceable to this cause) on the part of the little boys, or by some culpable neglect in the customary precautions. Carelessness is not now common in the great Northern collieries, for the system of discipline is too rigid to permit it; but in other coal districts (as Staffordshire, &c.) the carelessness of working miners and of superintendents is often gross and fearful.

The chemical effects of an explosion in a coal mine are much more complex than those of the mere combustion of light carburetted hydrogen gas. The amount of firedamp at first ignited may be trivial, and yet may produce the most destructive

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effects. As it accumulates, from its lightness, at the upper parts, and diffuses itself with considerable difficulty, it often acts as a train, and communicates the flame to the distant parts, and to the pent-up reservoirs of gas in the waste and abandoned districts (goaves) of the pit. Therefore, in almost all accounts we find that two explosions have been mentioned. The first was, we believe, local, at the spot where the cause occasioned it; the second, general, aided by accumulations of foul gas in the other parts. Where more than one explosion takes place they are not simultaneous, but nearly always successive. Sometimes they are two or three in number, succeeding each other at intervals of some seconds, with, perhaps, a momentary interval of repose between. In one mine (Jarrow) which exploded in 1846, the attending heat was so great that it thoroughly coked the coal lining part of the walls to the depth of nearly half an inch. The amount of surface so acted upon was considerable; and this effect must have required the playing of the flame upon the coal for some time with the intensity of a blow-pipe.

Another effect of an explosion is at once to blow up and ignite an immense quantity of coal-dust lying about the pit, and thus to produce an evolution of fire damp and the production of much carbonic acid-a gas well known to be most fatal to animal life. This is, moreover, produced during an explosion by the union of the oxygen (necessary for the respiration of the men) with the carbon of the firedamp; and the carbonic acid mixed with the residual nitrogen of the atmosphere, and with that which is present in the explosive gas itself, forms the fatal and dreaded afterdamp, which consists of 8 volumes of nitrogen, 2 of aqueous vapour, and 1 of carbonic acid gas. Being of much greater specific gravity (0·9614) than the fire damp, which is about half the weight of common air, it hangs lower down than the firedamp, which ascends to the roof. Then the poor pitman has two enemies, and the men spared by the blazing of the firedamp may be, and often are, suffocated by the afterdamp. The best chance of escape is to fall flat on the ground till the afterdamp passes away. At the calamity at Aberdare (Wales), two men were saved by strongly pressing a wet cloth to their mouths in passing through the afterdamp, whilst seven of their companions were killed who did not adopt this precaution. In any manner avoid inhaling it. The men suffocated by it present a peculiarly calm and sleep-like appearance after death.

The visible and generally destructive effects of such a catastrophe are those which are commonly observed and understood. Nothing, perhaps, affects the mind with deeper sadness than to stand, as we have done, at the mouth of a pit recently exploded.

But a day or hour before, it was the scene of busy activity and manifest prosperity. All around were the signs of both. Coal-baskets were coming up continually, and were hurried off in clattering wagons, after having been dashed against the sounding wires of the large screens. Loud were the calls of the men, the songs and laughter of the lads; and the great, ponderous steam-engine went on pumping or drawing with the sighs, groans, and motions of a giant. Now all is still-sad-awful! One or two grave and saddened men are at the pit's mouth awaiting the manager; the great steam-engine is noiseless; the pulleys over the pit, that were wont to run round so continually and conspicuously, revolve no longer; wagons lie up, useless and lumbering; lads and boys, for a wonder, are seen to weep; and the doors of the pitmen's cottages are closed as if on a Sunday.

Let us descend with the manager. How unlike to itself is the whole pit! At the bottom of the shaft, where pitmen were wont to stand in a group, smoking and joking, all is silent; and we get out of the descending cage or basket without proffered help. A little way inwards we come upon various signs of disaster. All things are idle. The once busy passages of the mine are vacant and voiceless; the full train of coal-wagons stands unmoving on the pit railway; no ponies and no putters' (or pushers of the train) appear. If the scene of the explosion has been a confined recess, we see, as we approach it, one glimmering Davy-lamp here, and another there, they are held by men who are searching for the dead bodies of their companions. Here we must climb over a mass of shattered stones and coals, which have been blown down by the force of the explosion. There, the sides of the passage bear the marks of the scorching blast of fatal fire. And now we join the searchers. They sadly greet us. In this spot should be some two or three of their lifeless companions; so we trace the course of the firedamp. It is here that huge blocks of the roof have been dislodged, for here the gas met with resistance. They have been digging and clearing away the rubbish for some two or three hours; the light is but that of three or four very feeble glimmering lamps. These we lift up, ever and anon, and peer anxiously into the turned up rubbish. In half an hour's time we make a discovery of the most thrilling kind to those who are unaccustomed to such scenes; we see a dark, dull mass of apparent coal; but this is pronounced to be a dead body! A minute inspection does indeed clearly prove that it was once a living man;-we say no more, than that this mass is decently wrapped about and sent up the shaft. For ourselves the scene is too sickening; nor is the place without peril, for the shattering effects of the catastrophe

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have loosened the roof, displaced the props and supports, and the sudden crashing noise we heard a minute or two ago was the fall of a quantity of coal strata-in the passage we had not long previously passed through! In our cautious, scrambling return to the shaft we visit the stables of the pit. Most of the horses were out in the galleries of the pit at the time of the accident, and were killed with their drivers; but, singularly enough, one little pony was stalled in these stables, and, being away from the danger, had been spared, and was heard by the first descending miner after the calamity to neigh most shrilly, thus indicating his loneliness and his fears. Such are our recollections of a visit to a pit after an explosion.

If the pit be a contracted one, and if the number of workings be small, then the rapid expansion of the gas, after its ignition, will produce much more violent effects than if the workings be more extended. In one case of this kind, of the effects of which we were eye-witnesses, everything was swept before the violence of the blast. Strong Memel timbers were broken and driven like chips or straws. Many of the coal-tubs, made of strong planks bound with iron, were shattered to pieces, and the explosion was distinctly felt at the surface by a sudden rush of wind and dust upwards against the current of air; the cage, then at the mouth of the pit, being lifted several feet high. The timbering in the shaft and in the mine was covered with coal dust, and many of the props supporting the roof were charred.

A considerable number of the disasters and deaths in coalmines are attributable to other causes than explosions. These are, falls of stone from the roof, falls of blocks of coal while hewing, falls down the shafts in descending or ascending, entanglements in the pit machinery, breakages of the ropes, and accidents connected with the passages of the train of coal-wagons. Such causes are productive of numerous fractures of limbs and deaths. One collier told us that from one or other of these dangers a man was pretty sure of being 'mashed up' at the age of forty or forty-five. In examining some hundreds of young persons employed underground, we discovered that very few of them had. escaped some kind of 'laming' or injury. Young lads based their whole chronology on the intervals between their first or second or third lamings.' A South Staffordshire authority assures us, that in those districts 'mining accidents are so nume

* The explosion at Willington Colliery, near Newcastle, in April, 1841, by which thirty-two persons were killed. A detailed account, with illustrative map, is to be found in the Report on the Newcastle Collieries, by J. R. Leifchild, Esq., printed in Appendix to Reports to Government, by the Children's Employment Com missioners. 1841-2.