or lower edge, which shaft is 180 yards in depth. E is another shaft, distant 1200 yards from A, which is also sunk to the coal on its higher, or north-western, side. If the coal be supposed to rise from B to D at the rate of one yard in twelve, then D must be 100 yards higher than B; consequently the depth of the shaft, E, from the surface will be 80 yards.

It has already been observed that it is possible to sink pits to these or to greater depths, without danger to the lives of the workmen. It is now to be added that it is also possible to open a communication below ground, between pits situated at considerable distances from each other; and that when two or more pits are sunk for one mine, the first operation is to open such a communication.

Let it be supposed, then, that a communication between the shafts A and E has been opened in the usual way, by digging a passage through the coal from B to D. The whole passage, A, B, C, D, E, will then resemble a tube, of which the two divisions, A, B, and E, D, are perpendicular to the horizon, and of which the middle part, B, C, D, has a considerable angle of declination from it.

It would seem to be evident, à priori, that a current of air, if it should move at all, without mechanical impulse, would proceed, in a tube of this form, and in this position, from A to E, and not from E to A; but this may easily be subjected to experiment.

1. Let a tube be constructed of any material which conducts heat slowly, as glass, for instance. Let it be made exactly of the form represented in Fig. 1, and placed precisely in the same position with respect to the horizon. Let heat be applied to any part of the middle division, B, C, D, by the flame of a lamp, or otherwise, and a circulation of air will commence, and proceed from A to E, which may be made evident by placing a little down of feathers over each opening of the tube: the ascending air will carry it upward from E, while the descending current will press it downward into A. 2. Let the tube be filled with carbureted hydrogen gas, or fire-damp. The same effects will follow, without the application of heat, or of any mechanical impulse whatever. Apply heat, as before, and it will increase the rapidity of the current. 3. Fill the tube with any proportions, equal or unequal, of fire-damp and common air: the current will still take the same direction, and will still be quickened by the application of heat.

These are all the cases that can possibly occur, involving the chances of danger from inflammation, or explosion, in the passage A, B, C, D, E, considered as the first openings of a coal-mine; for this passage must either be filled with common air, with fire-damp, or with certain proportions of each with the other. But with whichever of these kinds or mixtures of air it may be filled, it must circulate; because, first, the temperature is known to be in general higher below ground than at the surface, which would begin the circulation; and, secondly, because B, being 100 yards deeper than D, would continue it in the direction C, D, E,

So long, then, as there is only the passage B, C, D, between the two shafts, the ventilation of this passage is an operation of great simplicity; but this passage is only the base line, as it may be called, from which numerous excavations are to proceed in different directions, as far as the right of working extends, or as far as it may be possible to carry them with safety. Hence it is obvious that, as the space thus hollowed out below ground enlarges, the atmospheric current ought to flow through every part of the workings, to enable the workmen to breathe, to supply air for the necessary quantity of light, and to prevent the fire-damp from stagnating in dangerous quantities.

To give your readers an idea of the mode in which this may be effected, Fig. 2 represents a ground plan of the coal-field, of which Fig. 1 is a perpendicular section. In this figure, B is the downcast, or lower shaft; D, the upcast, or higher shaft; and C, the passage connecting them, as already shown in Fig. 1. The shaded rhomboidal figures are the pillars or masses of solid coal, left standing to support the roof; and the parallel and oblique openings between the pillars are the workings, or excavations, left empty by removing the coal; and through which an adequate supply of atmospheric air must be constantly directed, to ensure the safety of the mine.

It is a fact well known, and particularly by miners, that the current of atmospheric air in a mine will, when unobstructed, always. take the most direct passages it can find, from its entrance to its outlet. Hence the direction of this current when introduced at B, the downcast shaft, would be along the passage C, to the upcast, shaft at D. This, however, would not answer the purpose of ventilating the other parts of the mine; but if we stop the passage C at or near to the shaft B, we shall turn the current into the two next passages, e, e, on each side of B. If we want to carry it further, it is only necessary to stop the passages, e, e, and then will it proceed to the next pessages, f, f, and so on, by similar means, to the extremities of the workings, g, g. To distribute this current equally the shaft B may be divided by a partition across it; but in practice it will be found to divide itself accurately, in proportion to the demand opened for it.

It is not, however, to be understood, that the whole of the cir culating current is to be introduced into any one passage, unless on some very particular occasions. In the ordinary circumstances of the mine, it must be carefully distributed through all the passages by a judicious application of stoppings; and these must be so constructed as to admit the necessary supply of air to the passages in which they may be placed.

Nothing can answer so well for a stopping as a door, hung on hinges from the roof, so as to swing freely in either direction, and so placed, that, when at rest in its perpendicular position, it may accurately shut up the passage. It is obvious, that by opening such a door more or less, the current of air through the passage in which it stands may be regulated at pleasure; and that it may be fixed at

the point which has been found to admit the requisite supply.* These doors, or stoppings, may be made of light materials, as they are not intended to withstand the application of any considerable force. In placing them there is only one rule to be observed, which is, that they must always be fixed in the lower opening of the passage, with regard to the general dip of the mine, and not in any higher part of it. Stoppings for instance, must not be put into the upper ends of the passages h, h, but into the lower extremities, as in the similar passages, i, i. While these precautions are attended to, the stoppings can never, by any accident, become the means of accumulating the fire-damp.

Recollecting then the rise of the mine, and the levity of the. fire-damp, an attentive examination of the figure will show, that if the stoppings be judiciously placed, the passages clear, and the shafts open, no atmospheric air, much less inflammable air, can possibly stagnate, or accumulate, in any part of the workings. It will be observed, that the air, in this mode of ventilation is never. turned down the slope, after having once ascended it; but that it invariably proceeds upward from the moment it begins to ascend, until it is discharged by the upcast shaft at D. It will also be evident, that the circulating current is perfectly under our command; and that the whole, or any part of it, may be excluded from, or admitted into, any part of the workings at pleasure.

It does not seem necessary to say any thing more in illustration of the general principles; but it is proper to notice certain circumstances which may occur to interrupt or derange their operation.

The passages of a mine are frequently obstructed, and sometimes entirely stopped up, by falls of stones, and other matters, from the roof; when this happens, an accumulation of fire-damp, more or less extensive, must unavoidably take place; but, in the mode of working and ventilating, which it is the object of this paper to explain, the limits of such accumulations are accurately fixed. Let it be supposed for instance, that a fall of the roof has occurred at K, so as to shut up the two passages 1, 1, below it. It is obvious, that the fire-damp will gradually collect, until these two passages are filled with it down the slope, as far as to the next openings below: but whenever they are filled so far, the accumulation must stop; because, as fast as new supplies of fire-damp arrive, they will proceed up the passages, m, m. It may be added, that the fire-damp, having so many other passages to escape by, would, in ordinary circumstances, collect very slowly below the fall at K, and thus afford a greater chance of its being discovered by the per

It is to be observed in fastening these doors at this point, that they are to open down the slope; and that the fastenings must be slight; merely sufficient to keep the door in its proper position, and to give way so as to allow the door to shut on the application of a slight degree of force. Their being accidentally shut cannot produce any bad effects, as no fire damp can accumulate either above or below them. The only inconvenience will be a temporary derangement of the atmospheric current.