In workings where powder and certain substitutes for blasting cannot be employed with safety or advantage, and where, therefore, mechanical appliances have to be used for the bringing down of coal and stone, the risk of accident from falls must obviously be reduced by the employment of drilling and wedging or cutting appliances, which increase the ratio of work done to the time spent by the men in close proximity to the working-face. Of the numerous coal-cutting or kirving machines which have been devised, but few seem to have established such claims to efficiency and economy as to give promise of their extensive adoption. Some progress has been made in recent years in the employment of hydraulic pressure in the forcing down of coal; thus it has been applied by Mr. Chubb to the working of a range of pistons placed inside the hole, and by Messrs. Bidder and Jones, and Grafton Jones, to the forcing of a long wedge into a hole in the coal.2

Compressed air has been applied with more success to the bringing down of stone; one of the most powerful and efficient machines for the purpose is that devised by Messrs. Dubois and François, called the bossoyeuse, which has been used for some years past on a considerable extent at coalmines near Liège and at Blanzy. Holes, grouped in a particular way, are first made by the compressed air-borer of those engineers; so-called plug-and-feather wedges are then driven into the holes by a ram acted on by compressed air. The rock is thus rapidly broken in from one hole to another, and the expedition with which the rock is removed by this mode of working is said to compare favorably with blasting. A machine of analogous description to that of English and Beaumont, which has been used in the drift of the proposed Channel Tunnel, has recently been applied at the Bridgwater Collieries, to the boring out of a drift in the stone 7 feet 2 inches in diameter. One serious defect of this system, if applied in localities where fire-damp may

(1) Minutes of Proceedings Inst. C. E. vol. xxviii. p. 118. (2) Ibid. p. 113.

occur, appears to be that, if the cutters come upon hard, gritty stone, sparks are abundantly given off. It is doubtful whether the risk of accident arising from this may be efficiently guarded against by keeping a jet of water playing upon the face of the stone.

In some of the Cleveland mines a rotary borer actuated by compressed air, which has been devised by Mr. W. Walker, is in use for preparing holes for powder-charges, and is said to effect great economy in time.

Considerable improvements have of late been made in hand-drilling machines, and their employment in combination with compound wedges of recent invention has greatly facilitated the getting of coal by hand. One of the most efficient is that of Messrs. Asquith and Ormsby, who by using an endless chain for working the drill are readily able to bore holes close to the roof; an efficient modification of the plug-and-feather system of wedging enables them to work with considerable expedition in coal and stone.

Although the efficient support of the roof and sides in mine-workings, and the increased facilities for the expeditious performance of mechanical work connected with coal-getting, must contribute to the diminution of the death-rate from falls, it is evident that the provision of good illumination in the mine-ways and working places would be invaluable as a protection against accidents of this class. Vigilance on the part of the miner must often be of little avail, if, as is still very frequently the case, he is dependent upon a source of light, whereby to observe the first signs of an impending fall, which is insufficient to enable him to see distinctly in his immediate vicinity. The utter inadequacy of the light furnished by the safety-lamps hitherto most generally employed, i.e., the Davy, the Stephenson, and the Clanny, has been the chief cause of the frequent yielding to the strong temptation to employ naked lights, even in regions where the possibility of an explosion from the presence of fire-damp is scarcely doubtful.

The importance of effecting improvement in the illuminating power of safety-lamps has been borne in mind by

many of those who have devoted skill and ingenuity to the attainment of greater security in the use of lamps in mines, where fire-damp is either prevalent, or where its sudden disengagement from coal or stone may occur at any time. One of the chief, and most laborious, branches of experimental investigation upon which the late Royal Commission entered was the determination, by trustworthy and searching methods of experiment, of the relative merits of the numerous varieties of safety-lamp which have been devised in recent years, and especially since the appointment of that Commission.

These and similar experiments and their results will be dealt with in Part II. of this Paper, it being desirable in the first instance to review the circumstances and conditions relating to the existence, in mines, of that great (in the eyes of the public, the chief) source of calamity, fire-damp, the gas which escapes, either gradually and almost continuously, or fitfully and in sudden outbursts, from coal, or from stone adjacent to coal-seams.

Fire-damp, as it comes off from so-called blowers and from freshly-cut coal, consists almost entirely of light carburetted hydrogen or marsh-gas, being mingled with only small proportions of nitrogen and of carbonic acid. The recent analytical investigations of Mr. J. W. Thomas, Dr. E. Von Meyer and others, have shown that, as would be inferred from the known laws governing the escape of gases on their passage through porous bodies, the portions which first pass from these into the air contain the highest proportion of marsh-gas, while those which are evolved at later periods contain comparatively high proportions of carbonic acid and nitrogen. The composition of fire-damp in one and the same mine may, therefore, differ materially, according as to whether the gas has escaped chiefly from blowers or from the freshly-cut coal faces; or whether it has been drawn out, or expelled to some considerable extent, from old workings by a diminution of atmospheric pressure, or by local disturbances, such as falls in the goaves or old workings.

It has long been well known that fire-damp exists, in a

more or less condensed condition, in coal, even some time after it has been brought to the surface; its gradual escape has constituted a fruitful source of disaster to coal-laden ships and to steam-vessels carrying large provisions of coal. But the conditions under which the gas supplies are confined in seams and in the contiguous strata, and the causes of certain frequently recurring phenomena connected with the escape of the gases from coal, are still but little understood. In many cases the gas finds vent gradually and quietly, though evidently under considerable pressure from the faces of the freshly-cut coal; in others its escape from new faces is made manifest by a singing or hissing sound, and, if the face of the coal be wet, as in the case of drifts under the sea, it may be covered with minute bubbles. Sudden and violent eruptions of gas occasionally even overpower for a time the most efficient ventilation, and are accompanied by the dislodgment and projection of large quantities of coal, much of it in a disintegrated state. The issue, in some localities, of powerful jets, or so-called "blowers," from the coal, many of which have furnished a continuous supply of gas for long periods, demonstrates that fire-damp must exist in the strata under very high pressures.

Experiments have been made at the instance of the late Royal Commission by Mr. Lindsay Wood,' with a view to obtain measurements of the gas pressures which may be developed in cavities bored into the coal at from 750 to 1268 feet below the surface, in the Hetton, Elemare, Appleton, Boldon, and Harton Collieries, county Durham. Holes, ranging from 14 inch to 3 inches in diameter, and in length from 7 to 47 feet, were bored into the coal either horizontally or at a small upward inclination. A pipe was inserted into the hole, the extreme end of which was left as a gas-chamber. To the projecting end of the pipe, which was made tight by means of a long india-rubber washer, was attached a Bourdon, or Schæffer and Budenberg

(1) North of England Institute of Mining and Mechanical Engineers. Transactions, vol. xxx. 1880-81, p. 163.

gauge. In several instances the pressure recorded by the gauge considerably exceeded 200 lbs. on the square inch, and occasionally exceeded 300 lbs.; in one instance (in Boldon Colliery) it reached 461 lbs. The gas, having in several of the experiments been allowed to escape freely from the hole for some time, was found not to be proportional to the maximum accumulation of pressure; when the pipe carrying the gauge was again fitted into it, the pressure once more accumulated gradually to about the former maximum. Among the observations made, one of the most curious was the great difference in the maximum pressures developed, respectively, in three holes bored to different lengths parallel to and within short distances of one another. Some experiments corresponding to the foregoing were carried out for the Commissioners in several collieries in South Wales, the results of which were, generally, in accordance with those obtained by Mr. Lindsay Wood; at the Celynan Colliery, Abercarn, where there have been many sudden outbursts of gas, the maximum accumulation of pressure, in a hole bored to a distance of 47 feet 10 inches into very hard and compact coal, at a depth of 1480 feet from the surface, was 430 lbs. on the square inch, the gas being given off from the open hole at the rate of only 0.3 cubic foot in twenty-three hours. A hole was bored to a depth of 20 feet into a different heading in the same seam, where the coal was very soft, and represented in this respect the character of those parts of the seam in which sudden outbursts generally took place in this colliery; the maximum pressure here recorded was 318 lbs. on the square inch, but the gas escaped at the rate of 34.5 cubic feet in twenty-three hours. These experiments show that the pressure of gas may vary considerably in one and the same seam, in consequence of variations in the character and consequent permeability of the coal, and probably also of the roof and floor, and of the adjacent strata.

When fire-damp becomes distributed through the air in sufficient amount, a mixture is formed which will ignite with a more or less violent explosion when flame or a whitehot body is approached, or immersed in it, the violence of