in never could drive out, now became speedily so clear that the day-light and even objects at its mouth were distinctly seen from its furthest end. After blowing up the rock, the miners could instantly return to the place where they were employed, unimpeded by the smoke, of which no appearance would remain under-ground in a very few minutes, while it might be seen to be discharged in gusts, from the valve at the top of the shaft. The constant current into the pipe at the same time effectually prevented the accumulation of air unfit for respiration. The influx of air, from the level into the mouth of the pipe, rushes with such force as instantly to extinguish the flame of a large candle; and any substance applied, so as to stop the orifice, is held tight by the outward pressure.

"It is now more than two years since the machine was erected, and it has been uninterruptedly at work ever since, and without repair. The length of the tunnel has been nearly doubled, and the pipes, of course, in the same proportion, and no want of ventilation is yet perceptible.

'Two similar engines have been since constructed for other parts of the same tunnel, and have in every respect answered the purpose for which they were designed.

"The original one is worked by the small stream of water before-mentioned, by means of a light overshot-wheel twelve feet in diameter, and about six inches in breast. The two others are attached to the great overshot-wheel which pumps the water from the shafts which are sink ing upon the line; and, as their friction is comparatively nothing, this may be done in any case, with so little waste of power for this purpose as not to be an object of consideration, even if the power be derived from more expensive means.

'The size of the exhauster may always be proportioned to the demand for air; and, by a due consideration of this circumstance, this engine may be effectually adapted not only to mines and collieries, but also to manufactories, workhouses, hospitals, prisons, ships, and so on.

Thus, if it were required to ventilate a shaft of a mine, or a single level, which is most frequently the case, where three men are at work at one time, and we allow that those three men vitiate each twenty-seven cubic inches and a half of air per minute (as determined by the experiments of Messrs. Allen and Pepys), and allowing further that their candles vitiate as much as the. men, there will be six times twenty-seven and a half cubic inches of air to be drawn out in a minute, equal to 165.

'Now a cylinder five inches in diameter, working with a stroke at nine inches, will effect this by one stroke in a minute; though it would certainly be advisable to make it larger.

'Not being practically acquainted with collieries, or mines that suffer from peculiar gases that are produced in them, I cannot state, from actual experiment, what effect this machine might have in relieving them; but it must appear evident, to every person at all acquainted with the first principles of pneumatics, that it must do all that can be wished, as it is obvious that such a machine must in a given time pump out the whole

volume of air contained in a given space, and thus change an impure atmosphere for a better one. And in constructing the machine it is only necessary to estimate the volume of gas produced in a certain time, or the capacity of the whole space to be ventilated. It is easy to judge how much more this must do for such cases as these, than such schemes as have lately been proposed of exciting jets of water, or slaking lime, both of which projects, likewise, must fail when applied; as one of them has when applied to the case of hydrogen gas. But with such a machine as this, if the dreadful effects of explosions of this air are to be counteracted, it may be done by one of sufficient size to draw off the air as fast as it is generated; and by carrying the pipes into the elevated parts of the mine, where from its lightness it would collect. If, on the other hand, it is desired to free any subterraneous work from the carbonic acid gas, it may as certainly be done by suffering the pipe to terminate in the lower parts, where this air would be directed by its gravity.

In workhouses, hospitals, manufactories, &c., it is always easy to calculate the quantity of air contained in any room, or number of rooms, and easy to estimate how often it is desirable to change this in a certain number of hours, and to adjust the size and velocity of the engine accordingly. Where this change of foul air for pure is to take place in the night, means for working the machine may be provided by pumping up a quantity of water into a reservoir of sufficient height to admit of its flowing out during the night in a small stream, with sufficient fall, so as to give motion to the engine; or by winding up a weight of sufficient size, or by many other means which are easily devised.

'If, for instance, a room in which fifty persons slept was eighty feet long, twenty wide, and ten high, it would contain 16,000 cubic feet of air, and, if this was to be removed twice in eight hours, it would require a cylinder of thirty inches diameter, working with a four-feet stroke four times in a minute, to do it; or nearly that. Such a cylinder could be worked by the descent of ten gallons of water ten feet in a minute; or, for the whole time, by eighty hogsheads falling the same height.

'But this is a vast deal more than could be required, as the fifty people would in eight hours vitiate only 3000 gallons of air, which could be removed by 150 strokes of a cylinder, twelve inches diameter, with a four feet stroke, which would not require an expenditure of more than 1500 gallons of water properly applied, or about twenty-eight hogsheads.'

Mr. Price, in his Treatise on the Cornish mines, observes, that the comparative smallness of the largest fissures to the bulk of the whole earth is really wonderful. In the finest pottery we can make, by a microscopic view, we may discover numerous cracks and fissures, so small as to be impenetrable by any fluid, and impervious to the naked eye;' as, by the laws of nature originally imposed by the Creator, it happens that matter cannot contract itself into solid large masses, without leaving fissures between them, and yet the very fissures are as necessary and

useful as the strata through which they pass. They are the drains that carry off the redundant moisture from the earth; which, but for them, would be too full of fens and bogs for animals to live, or plants to thrive on. In these fissures, the several ingredients which form lodes, by the continual passing of waters, and the menstrua of metals, are brought out of the adjacent strata, collected and conveniently lodged in a narrow channel, much to the advantage of those who search for them; for if metals and minerals were more dispersed, and scattered thinly in the body of the strata, the trouble of finding and getting at them would be endless, and the expense of procuring them exceed the value of the acquisition. The insides of the fissures are commonly coated over with a hard, crystalline, earthy substance or rind, which very often, in the breaking of hard ore, comes off along with it, and is commonly called the capels or walls of the lode: but Mr. Price is of opinion that the proper walls of the lode are the sides of the fissure itself, and not the coat, which is the natural plaster upon those walls, furnished perhaps by the contents of the fissures, or from oozings of the surrounding strata. The breadth of a lode is known by the distance betwixt the two incrusted sides of the stones of ore; and, if a lode yields any kind of ore, it is a better sign that the walls be regular and smooth, or at least that one of them be so, than otherwise; but few of these fissures have regular walls until they have been sunk down some fathoms. Thus the inner part of the figure, in which the ore lies, is all the way bounded by two walls of stone, which are generally parallel to one another, and include the breadth of the vein or lode. Whatever angle of inclination some fissures make in the solid strata, at their beginning, they generally continue to do the same all along. Some are small at their upper part, and wide underneath, and vice versa. Their breadth, as well as depth, varies much; for, though a fissure may be many fathoms wide in one place, yet a little further east or west it may not be one inch wide. This excessive variation happens generally in very compact strata, when the vein is squeezed, as it were, through hard rocks which seem to straiten it. A true vein, however, is never entirely obliterated, but always shows a string of metallic ore, or of a veiny substance; which often serves as a leader for the miners, until it sometimes leads them to a richly impregnated part. Their length is in a great measure unlimited. The richest state for copper, according to Mr. Price, is from forty to eighty fathoms deep: for tin from twenty to sixty; and, though a great quantity of either may be raised at eighty or 100 fathoms, yet the quality is often too much decayed and dry for metal.' He says that the fissures or veins of the Cornish mines extend from east to west; or, more properly, one end of the fissure points west and by south, or west and by north; while the other tends east and by south, or east and by north. Thus they frequently pass through a considerable tract of country with few variations in their direction, unless interrupted by some intervening cause. But, besides this east and west direction, there is what the miners call the underlying

or hade of the vein or lode, viz. the deflection or deviation of the fissure from its perpendicular line, as it is followed in depth like the slope of the roof of a house, or the descent of the steep side of a hill. This slope is generally to the north or south; but varies much in different veins, or sometimes even in the same vein; for it will often slope or underlie a small space in different ways, as it may be forced by hard strata on either side. Some of the fissures do not vary much from a perpendicular, while some deviate more than a fathom; that is, for every fathom they descend in perpendicular height, they deviate likewise as much to the south or north. Others differ so much from the perpendicular that they assume a position almost horizontal; whence they are also called horizontal or flat lodes, and sometimes lode plots. Another kind has an irregular position with regard to the rest; widening horizontally for a little way, and then descending perpendicularly almost like stairs, with only a small string or leader to follow after; and thus they alternately vary and yield ore in several flat horizontal fissures. This, by the Cornish tinners, is called (but in Mr. Price's opinion erroneously) a floor or squat; which, properly speaking, is a hole or chasm impreg nated with metal, making no continued line of direction or regular walls. Neither does a floor of ore descend to any considerable depth; for underneath it there appears no sign of a vein, either leading directly down or any other way. This kind of vein is very rare in Britain. The fissures most common in Britain are the perpendicular and inclined, to whatever point their direction be. The perpendicular and horizontal fissures (Mr. Price says) remain little altered from their first position, when they were formed at the induration of the strata immediately after the waters left the land. The perpendicular fissures are more commonly situated in level ground, at a distance from hills, and from the sea shore; but with regard to the latter, the upper and under masses of strata differ in their solidity and properties. Hence (says Mr. Price) it is plain, that inclined fissures owe their deflection to some secondary cause, violence, or subsidence of the earth; for, though perpendicular fissures are seldom to be seen, yet such as are inclined at very considerable depths become more and more perpendicular, as the more central strata, by reason of the vast superincumbent weight, do not seem so likely to be driven out of their position as those which lie nearer the surface.' The fissures are often met with fractured as well as inclined; the reason of which, Mr. Price thinks, has been a subsidence of the earth, from some extraordinary cause. The original position, says he, must have been horizontal, or parallel to the surface of the earth: but we often find these strata very sensibly declined from the first position; nay, sometimes quite reversed, and changed into perpendicular. When we see a wall lean, we immediately conclude that the foundation has given way, according to the angles which the wall makes with the horizon; and, when we find the like declination in strata, we may conclude, by parity of reason, that there has been a like failure of what supported them,

in proportion to that declination; or that whatever made the strata to fall so much awry, must also cause every thing included in those strata to fall proportionably. Wherever the greatest subsidence is to the north the top of the lode or fissure will point to the north, and of consequence underlie to the south, and vice versâ: the slide or heave of the lode manifests the greater subsidence of the strata; but the same lode is frequently fractured and heaved in several places: all of which, by due observation, will show us they were occasioned by so many several shocks or subsidences, and that the strata were not unfooted, shaken, or brought to fall once only or twice, but several times."

Mr. Price observes that, though the metallic veins generally run from east to west, they are frequently intersected by veins or lodes of other matters, which run from north to south. Some of these cross veins contain lead or antimony, but never tin or copper. Sometimes one of these unmetallic veins intersects the true one at right angles, sometimes obliquely; and sometimes the mixture of both is so intimate that the most expert miners are at a loss to discover the separated part of the true vein. When this last is intercepted at right angles it is moved, either north or south, a very little way, perhaps not above a fathom; in which case, having worked to a small distance in one of these directions, if they find themselves disappointed, they turn to the other hand, and seldom fail of meeting with what they expected. Sometimes they are directed in their search by the pointing of a rib or string of the true vein; but, when the interruption happens in an oblique direction, the difficulty of finding the vein again is much greater. When two metallic veins near each other run in an oblique direction, and meet together, they commonly produce a body of ore at the place where they intersect; and, if both are rich, the quantity will be considerable; but if one be poor and the other rich, then both are either enriched or impoverished by the meeting. After some time they separate again, and each will continue its former direction near to the other; but sometimes, though rarely, they continue united. It is a sign of a poor vein when it separates or diverges into strings; but, when several of them are found running into one, it is accounted a promising sign. Sometimes there are branches without the walls of the vein in the adjacent strata, which often come either obliquely or transversely into it. If these branches are impregnated with ore, or if they underlie faster than the true vein, that is, if they dip deeper into the ground, then they are said to overtake or come into the lode, and to enrich it; or, if they do not, then they are said to go off from it, and to impoverish it. But neither these nor any other marks, either of the richness or poverty of a mine, are to be entirely depended upon; for many mines, which have a very bad appearance at first, turn out extremely well afterwards; while others, which in the beginning seemed very rich, turned gradually worse; but in general, where a vein has a very bad appearance at first, it will be imprudent to be at much expense with it. Veins of metal are often so compressed

betwixt hard strata that they are not an inch wide; nevertheless, if they have a string of good ore, it will generally be worth while to pursue them; and they often turn out well at last. It is an encouragement to go on, if the leaders of ore enlarge either in width or depth as they are worked; but it is a bad sign if they continue horizontal without inclining downwards; though it is not proper always to discontinue the working of a vein which has an unfavorable aspect at first. Veins of tin are worth working when only three inches wide, provided the ore be good and copper ores, when six inches wide, will pay very well for the working. Some of the great mines, however, have very large veins, with a number of other small ones very near each other. There are also veins crossing one another sometimes met with, which are called contras, vulgarly caunters. Sometimes two veins run down into the ground in such a manner that they meet in the direction of their depths; in which case the same observations apply to them which are applicable to those that meet in a horizontal direction. Sometimes a vein suddenly disappears, by becoming narrower, or of worse quality; which by the miners is called a start or leap, and is common in the mines of Cornwall. In one day they may thus be disappointed in the working of a rich vein of tin, and have no further sign of any thing to work upon: at the fractured extremity of their vein they perceive a body of clay or other matter; and the method of recovering their vein is to drive on their work in the direction of the former part, so that their new work shall make the same angle with the clay that the other part of the vein does. Sometimes they sink a shaft down from the surface; but it is generally a matter of difficulty to recover a vein when thus lost.

The method of discovering mines is a matter of so much difficulty that it seems surprising how those who were totally unacquainted with the nature of metals first thought of digging them out of the earth. Lucretius says, the discovery was made by the conflagration of woods, which melted the veins of metal in the earth beneath them; and Aristotle tells us that, some shepherds in Spain having set fire to the woods, the earth was thus heated to such a degree that the silver near the surface of it melted and flowed into a mass; and that in a short time the metallic mass was discovered by the rending of the earth in the time of an earthquake. The same story is told by Strabo, who ascribes the discovery of the mines of Andalusia to this accident. The discovery of gold has been ascribed to Mercury, Cadmus, Thoas of Thrace, Piseus king of Italy, Cæacus, and other fabulous heroes; but Eschylus attributes the discovery of all the metals to Prometheus. The copper mines in Cyprus were first discovered by Cinyras, the son of Agriopas; and Hesiod ascribes the discovery of the iron mines of Crete to the Cretan Dactyli Idæi. The extraction of lead or tin from its ore, in the island of Cassiteris, according to several ancient authors, was discovered by Midacritus. Moses, however, ascribes the invention of brass and iron, or at least of the methods of working them,