means adopted have been devised with reference only to the management of the air, under the ordinary circumstances of its motion. The consequence is, that weak stoppings, or even doors, are employed to separate and guide the most important currents, such as the main ingoing and outcoming columns of air, the absolute division and permanent security of which involves the lives of all who are in the mine.

The greatest modern improvement in ventilation consists in the division of the works into districts; not only in order to afford purer air in each section, by a larger aggregate volume and a shorter run in the air currents, but for the purpose of isolation, in case of accident. To attain the latter object, the barriers separating these districts, and their system of air ways, must be of a nature not liable to derangement, which may, without difficulty, be effected.

The loss of life from after-damp is generally found to occur, to the largest extent, in the roads which the men have to traverse on their way to the shafts by which the mine is entered. This fact points out the necessity of making these roads the main intake air courses, and of securing these intake columns of air, both from the contact of fire-damp, and also from their being disturbed by the shock of an explosion, until they reach those points in the mine where they enter the workings in which the men åre engaged. It is only in case of the permanence of the arrangements made to establish this division, and to conduct columns of pure air to the extreme districts at all times, that the men can escape after an explosion, or that help can be speedily conveyed to the survivors, who may be suffering from it, but unable to effect their own escape. The system of using the main roads for return air ways, in which the currents, after they have received all the explosive gases yielded in the mine, are brought or kept in contact with lights (and thus both propagating an explosion and cutting off every avenue of escape, since these roads are sure, under such circumstances, to be swept by the fire or speedily filled with after-damp), ought not to be adopted except in small collieries, in which inflammable gas is never seen.

The foregoing considerations also point out the strong necessity for two independent shafts in all coal mines; and of providing for the accessibility of the downcast shaft to all the men engaged. Subsequently to an explosion, it is generally impossible

to descend or ascend in an upcast shaft, until after the lapse of some time, on account of its being filled with the after-damp.

If there be only a single shaft, and the division of the downcast and upcast currents be of a slight nature, such as by a brattice partition or pipes fixed in the shaft, the damage which is produced by an explosion generally prevents either escape or the rendering of assistance to the survivors. The number of bratticed shafts is fortunately diminishing. Where they are still continued to be used, it ought not to be permitted that any other light than the Davy lamp should be taken below the surface. The employment of a furnace for ventilation is objectionable in such cases.

OTHER INJURIES AND ACCIDENTS TO WHICH MINERS ARE LIABLE

There is another class of injuries resulting from defective ventilation to which miners are exposed. The circumstances producing these injuries are slow in operation, and from their effects being disease, and not immediate and sudden death, their existtence has been little considered. A careful examination of the state of mines leads to the conclusion, that the ultimate loss of life is greater from this cause than even from explosions.

VITIATED AND FOUL AIR.

These effects are the result of an inadequate supply of air, which thus becomes vitiated and unfit for breathing, on account of its having lost its due proportion of oxygen, which is replaced by the formation of carbonic acid. This gas has its sources from respiration, the lights of the mine, the decomposition of small coal in the goaves, and of timber in the workings. Air in this state is also usually found to be loaded with carburetted hydrogen, yielded from the whole coal or in the goaves. Sulphuretted hydrogen, arising from the decomposition of pyrites, is sometimes found to be present, especially in coal seams liable to spontaneous ignition. The gases formed by blasting are also allowed to load the air of mines to a very injurious extent.

This state in the atmosphere of mines arises from the want of the necessary air ways, and other arrangements to discharge such portions of the air in circulation, as may have acquired this con

dition, and to afford a fresh and pure supply, at any part of the workings.

The air in the leading drifts, and in the extreme workings of mines, is often found to be in an injurious and dangerous state, from the carburetted hydrogen and carbonic acid yielded or formed at those points, not being diluted and removed by a proper circulation. This may be caused by defective ventilation generally, or only locally. The latter case is of frequent occurrence, and arises from the main air currents returning to the shafts by leakage, without reaching the distant parts of the mine, or from a want of the requisite means to carry the circulation fully up to the face of the drifts and works.

Those districts and seams of coal least affected by inflammable gas, are generally those in which the ventilation is allowed to be in this imperfect and injurious state, on account of attention not having been called so imperiously to the subject, as it is by the violent catastrophes resulting from explosions.

Asthmatic diseases, at an unusually early period of life, are the unfailing results of ventilation which is deficient in quantity.

In reviewing the cases of explosions in mines, of which the attendant circumstances can be ascertained, it must be admitted that the greater part have been the result of a clearly defective system of working and ventilation.

The larger part of these cases show defects, arising either from a want of a proper system in the management of the ventilation, or that of the necessary volume in the quantity of air supplied.

ON THE LIGHTING OF MINES.

In the working of mines, where we do not find any fire-damp, we may use throughout the whole of the excavations any species of illuminating power we please: the most usual being the tallow candle or oil lamp.

In copper mines the candle is chiefly used, except near the shafts where more light is requisite, and where in consequence oil lamps or gas lights are substituted.

The pit candle is commonly of small size, weighing from 30 to 50 to the pound; it ought to be made of clean ox tallow, with the wick small and of fine cotton.

In the Anthracite collieries, small oil lamps are used, which are carried about by being stuck in the front of the miners' caps.

When gas is used, it may either be manufactured underground, or conveyed down the shaft from a gasometer at the surface. When made underground, the heat from the fires beneath the retorts may be economically applied to aid the ventilation of the mine.

The repeated accidents caused by the explosion of fire-damp in fiery mines, rendered desirable some method of lighting them by an agency, incapable of communicating combustion to the surrounding atmosphere.

Sir Humphrey Davy, in 1815, after having tried without success Kunckel's, Canton's, and Baldwin's Phosphorus, and likewise the electrical light, proceeds in his Treatise on the Safety Lamp to give the details of the various processes and reasonings by which he eventually arrived at the construction of "the Davy," a lamp which, for simplicity and safety under proper management, is still unequalled, and which affords a fine illustration of

the great advantage to be derived by practice from the aid of science.

"My first safety lamps gave light in explosive mixtures containing a great excess of air, but became extinguished in explosive mixtures in which the fire-damp was in sufficient quantity to absorb the whole of the oxygen of the air, so that such mixtures never burnt continuously at the air feeders, which in lamps of this construction was important, as the increase of heat where there was only a small cooling surface would have altered the conditions of security. I made several attempts to construct safety lamps which should give light in all explosive mixtures of fire-damp, and, after complicated combinations, I at length arrived at one evidently the most simple, that of surrounding the light entirely by wire gauze, and making the same tissue feed the flame with air, and emit light.

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"In plunging a light surrounded by a cylinder of fine wire gauze into an explosive mixture, I saw the whole cylinder become quietly and gradually filled with flame: the upper part of it soon appeared red hot, yet no explosion was produced. It was easy at once to see that by increasing the cooling surface in the top, or in any other part of the lamp, the heat acquired by it might be diminished to any extent; and I immediately made a number of experiments to perfect this invention, which was evidently the one to be adopted, as it excluded the necessity of using glass, or any fusible or brittle substance, in the lamp, and not only deprived the fire-damp of its explosive powers, but rendered it a useful light.

"I found that iron wire gauze, composed of 1-40th to 1-60th of an inch in diameter, and containing 28 wires or 784 apertures, to the inch, was safe under all circumstances in atmospheres of this kind; and I consequently adopted this material in guarding lamps for the coal mines, where, in January, 1816, they were immediately adopted, and have long been in general use."

Every Davy, to be safe, should of course be in a perfect state: it should always be securely locked when in use, and furnished with a shield, which, in order to combine the necessary protection from currents of gas, by which the lamp is liable to be assailed in every direction, with the requisite transmission of light, should be made of glass or other transparent substance, and extend from