methods of working which ascend without outlets; to work, if possible, by descending, rather than by ascending, and to redouble the usual precautions on entering into excavations after an interruption of the work. A great number of accidents have taken place, for example, on Monday mornings, when the miners descend after having quitted the mine on Saturday.

M. Bischof reports that having visited a gallery which had been abandoned for several days, he found the gases liquated to such an extent that they were inflammable in every part of the area; detonating in the middle portion, while the almost pure atmospheric air filled the lower part.

It is very dangerous to allow these liquations to be produced; it is necessary that the current of air should be sufficiently active to produce immediately the diffusion of the gas in the air and its withdrawal out of the mine before the mixture has become explosive. But, notwithstanding the precautions of ventilation-aérage-many mines would be completely unworkable if there had not been found the special means of guarding them from the fire damp-grisou. The coal beds, most dangerous, are those which are the most valuable for their good qualities; science and industry have therefore been called on to seek the means of combatting the effects of the grisou, and we proceed to expose those which have been successively employed.

MEANS TO DESTROY OR CHECK THE FIRE-DAMP OR GRISOU, IN SUBTERRANEAN WORKS.

The first idea which presented itself to the explorers was to disembarrass themselves of the gas by allowing the liquation to establish itself and by setting it on fire, so as to burn it, in the absence of the miners. For this purpose, a workman, clothed in vestments of moistened leather, his visage protected by a mask with spectacles of glass, advanced, crawling on his belly, in the galleries where the fire damp was known to exist, and holding forward a long pole, at the end of which was a lighted torch; he sounded thus the irregularities of the roof, the front of the excavations, and set fire to the grisous. This method, which has been employed, within twenty years, in the basin of the Loire, and even occasionally at the present day, in some of the English fiery collieries, has numerous inconveniences. The workmen, whom they called pénitents, were exposed to dangers to such an extent, that a great number perished. When the gas, instead of being simply inflammable, was detonating, the solidity of the mine was constantly compromised by the explosions; the fire attacked the coal and the timbers; the gases, which resulted from the combustion, became stationary in the works, and menaced the workmen with asphyxia; at length it became necessary, in certain mines, to repeat, even three or four times a day, this perilous operation, and yet it in no respect obviated the rapid disengagements which caused these numerous accidents. This method was equally

in use in the English collieries; only the penitent or fireman, instead of carrying the fire himself, caused it to be moved by means of a slider placed over a line of poles connected together, and directed by a system of pullies and cords. The danger was thus diminished for the fireman, who retired into a niche formed in a neighbouring gallery; but in the meanwhile many were still overtaken, and, besides, all the other inconveniences remained.

The method called the eternal lamps was evidently better. It consisted in placing towards the top of the excavation, and in all the points where the fire-damp collected, lamps constantly lighted, which burned the grisou as fast as it was produced; the danger was diminished in a considerable degree, because there could not be formed such large accumulations of inflammable or detonating gas. This mode of proceeding was, however, renounced in a great number of mines, on account of the production of carbonic acid and of azote; a production the more sensitive, since, to facilitate the liquation of the gases, the air ought not to be very strongly agitated.

At length it was devised to profit by the property possessed by platina in sponge to facilitate the combustion of the hydrogen with which it was brought in contact, and pellets, composed of one part of platina, and two parts of clay, were made, and were placed near the points at which the grisou or fire-damp concentrated. But all these efforts, based upon the incited combustion of the inflammable gas, proved to be only dangerous and incomplete palliatives, which substituted for a great peril a series of other dangers, less imminent, doubtless, but equally distressing.

From that time all the well disposed continued to search for processes based upon another principle. Two only could conduct to a good result: 1. The withdrawal of the gases out of the mine; 2. A mode of lighting different from that which was in use, and which would suffice for the purposes of the miner without compromising his safety.

The principle of withdrawing-entrainement—of the gases by a rapid ventilation is, without contradiction, that which was the most natural to conceive; because it was already applied to all the other deleterious gases. Dr. Véhrle proposed at first to effect the decanting of the gases by making the excavations (stalls?) communicate by ascending passages with a gallery embracing all the works, and uniting with an ascending shaft. But this project, otherwise impracticable, offered a remedy for only a part of these accidents; the execution alone of the necessary works could not have been made without the greatest danger, if these works had been undertaken in the coal; while, in the rocks of the roof, the expenses would have rendered them impracticable. But a good ventilation alone could not suffice to place the miners in security; it was an excellent auxiliary means, but it always left unsolved this important problem: the prevention of the inflammation of the gases which disengage themselves from the surfaces of the stalls.

The lighting alone could conduct to the solution of this problem,

and numerous attempts had been made, under this head, when Davy discovered the safety-lamp. Before him, they had operated with a small number of lights, placed in the lowest positions, and at a distance from the stalls; the workmen kept these lamps in view, and when the blue nimbus, the indication of hydrogen, began to show itself, they extinguished them or withdrew, covering them with their hats. They made use of, also, in the most infected mines, various phosphorescent matters, and particularly a mixture of flour and lime formed from oyster shells, called Canton phosphorus, although the uncertain and ephemeral light which these materials produced, was but a very feeble resource. At length it was observed that the proto-carbonated hydrogen was somewhat difficult of ignition, and that the red heat was insufficient to accomplish it; thus it was practicable to carry a red coal, or a red hot iron into the fire-damp without inflaming it, the white heat alone having the necessary temperature. They profited by this discovery by lighting the stalls by means of a wheel of steel, which was made to turn against a fragment of flint: a workman was detailed to this service, and the sparks, which were thus produced in a continuous manner, sufficed to light the miners. It happened, occasionally, that these sparks set fire to the grisou; but this discovery, imperfect as it was, was not the less a real benefit.

Such was the state of the question, when Davy commenced the series of experiments which conducted him to the object in view. Many mines had been abandoned notwithstanding the palliatives in use, and a number of those which were maintained in activity, only produced coal at the price of the lives of a great number of men. Davy discovered that the gas, contained in a vase, which only communicated with the exterior by long and straight tubes could not be set on fire; that the flame was difficult of transmission in proportion as the tubes were reduced, and that, consequently, the more their diameters were reduced, the more their lengths might be shortened. He thus arrived at the proof that a plate of thin metal, pierced with holes of about one hundred in an inch, did not communicate fire to the exterior gas, although the interior was charged with lighted gas; the cooling produced by the gas in this small passage sufficed to reduce the temperature of the white heat of the interior down to the red heat of the exterior, and the inflammation could not be communicated. Such was the series of ideas which conducted Davy to surround the flame of the lamps with an envelope of metallic gauze, and thus to construct the safety-lamp.*

LOCAL VENTILATION.

In the sinking of a shaft the work would soon be stopped by the want of air, were it not for the plan of dividing its total section into two unequal parts, by means of a partition of planks, the joints of which are hermetically closed with moss, &c. The smallest compartment is reserved for the ladders; and a current of air is established

* Burat Géologie appliquée, 1846, p. 472.

between these two compartments in the manner of an excavation having two orifices. This movement is sometimes facilitated by carrying up the level of the orifice of the small compartment, by means of planks, built up as a chimney.

The excavation of a long gallery or tunnel would become impossible, through the want of air, if a spontaneous ventilation were not produced by similar means. Thus, there are directed from the surface of the ground, towards the gallery, troughs which are arranged similarly to the works which have two orifices of different levels and unequal sections. At other times they establish upon the gangways a floor for carriages [roulage]; reserving the lower part of the gallery beneath for draining and for a current of air, which enters by the lower part and returns by the principal or upper section.

If this precaution do not suffice, the current may be rendered more active by means of a small shaft disposed in such a way as to accelerate the circulation during all the working time. For this purpose, two doors are placed at the entrance of the gallery, so that one of the two shall always remain closed during the work, and the air is forced to leave by the shafts. This disposition is equivalent to the case of an excavation having two orifices of different levels.

We have translated freely from the excellent work of M. Burat, already frequently quoted, most of the matter which is comprised in the preceding pages in relation to the deleterious gases which are constantly generated in coal mines, and on the means resorted to for ventilating them. Our work would be incomplete, without adverting to a subject so immediately connected with the mining of coal, and with the safety of the operators, whose lives are hourly perilled, who are exposed to accidents inseparable from its extraction, and ресиliarly attendant on this branch of mining economy..

VENTILATION OF FIERY COLLIERIES.

There have been numerous suggestions on the ventilation of those coal mines which are subject to explosions; among others we may mention the published views of Mr. Dunn, of Newcastle. We hope to be pardoned here for remarking that it is disadvantageous to an important practical science, and especially embarrassing to inquirers into these subjects, that the valuable information conveyed by the most capable English authorities, is so compounded of absolute technicalities, for the most part also entirely local and unscientific, as to. be almost untranslateable. This is, perhaps, the main cause why the English mining processes, from Cornwall to Scotland, varying in their progress through every district, continue to be so little comprehended elsewhere.

Mr. Dunn, at page 341 of Volume X., of the London Mining Journal, furnishes a sketch of the general principles of ventilating the collieries in Northumberland, which are moderately troubled with inflammable air. At page 405 of the same volume, he follows up the first communication by a description of the more elaborate process,

as practised in Northumberland, of ventilating fiery collieries. We can do little more here than refer the reader to those articles, and to the instructive diagrams which accompany them. Our description would be unintelligible without the elaborate drafts which are necessary to elucidate the whole process.

The object aimed at by this system is by one series of channels to ramify, through every part of a mine, currents of respirable air, while by another series to withdraw from it and to discharge at the surface the impure air and inflammable or deleterious gases.

Mr. Dunn observes, that until late years the said current of impure air was kept as much as possible together or united; and it was no uncommon circumstance to have it travel twenty or thirty miles before reaching the upcast pit, and then loaded with gases, which steamed from the candle, and even the furnace fire, in thick vapours and flakes of blue flame, alarmingly visible to the naked eye. But, in modern practice, these currents of air are divided and subdivided in countless branches, so as to prevent the air which becomes adulterated in one quarter, from spreading the contagion among the workmen of another. They are conducted through passages either adopted for the purpose, or provided by anticipation in the laying out of the works. To guard against the dangerous influx of gas during the working of pillars, and in order to obviate the danger at the furnace, a "dumb drift" is provided, sloping up into the shaft some fathoms above the furnace, at which point the inflammable air effects a junction with the general air of the pit, and is carried upwards in safety, so that the furnace may be blazing below with good and secure air, and a perfectly inflammable portion may be coming in from above. (See the diagram, page 98.)

The fall of the barometer is a sure presage of increasing discharge of inflammable gas; for when the barometer stands steadily,—say at 29°-and the pressure is uniform, nothing exudes but the ordinary "makings" of the mine:-but when a sudden fall of the barometer portends a lightening of atmosphere, and consequently a change in the counterpoising pressure upon the orifices whence the gas escapes, or upon the main body accumulated in the wastes, then it is that extraordinary eruptions take place,―enough to overpower and adulterate even the main current of air, and consequently to subject the mine to explosion.

"Blowers" are sometimes met with in the coal, but more generally in the stone, and contiguous to the fissures of dykes. They originate in the chinks or crevices and other receptacles, which, being filled with inflammable air under high compression, are discharged momentarily, and without previous warning. They are often known to endure for many years; although, generally, they decline as the supply of pent-up gas is exhausted. Many very calamitous events have arisen from the miners unexpectedly coming in contact with these blowers; for the discharge is so sudden that the general air-course, although previously safe and satisfactory, becomes, in the course of