it is calculated that almost seventy thousand persons are employed by these mines in various ways; and the capital by which the works are carried on amounts to more than three millions. sterling.

In one part of the mine, an accident had happened, called a crash. The pillars left to support the roof, being too slender, had failed; or else the floor of the mine was too soft, and had suffered the pillars to sink in; so that the roof fell in, with the whole mass of earth above it. This sort of accident seldom happens without giving notice, by previous cracks, and the falling of detached pieces from the roof. In this case, the miners sometimes build up stone piers, to support the roof, if a fall in that spot would greatly hinder the work; otherwise, they clear away more of the coal pillars, and let it sink in gently.

Many dreadful accidents arise from foul air, of

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FOUL AIR IN MINES.

which there are two sorts: one, the black damp, is of a suffocating nature; the other is inflammable, and, taking fire, explodes with great violence, ⚫ or perhaps sets on fire the whole body of coal, so as to destroy the mine. On this account it is very important to ventilate collieries thoroughly,

Mode of ventilating a coal mine by stoppages in the main passages. The arrows show the direction in which the air is forced by the stoppages, marked || and x.

though it is very difficult to do so; as, when a current of fresh air is introduced, it very frequently

VENTILATION OF MINES.

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only sweeps along the principal passages, without entering the chambers on either side, which, consequently, remain full of stagnant air. The only mode of ventilating a colliery is then to devise some method of forcing the fresh air into all the side chambers; and this is done by stopping up the main passages at regular intervals, with partitions of wood, or walls of brick or stone, so that the air cannot pass.

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THE SAFETY LAMP.

A few years ago, a dreadful explosion occurred at the Felling colliery, near Newcastle; and as these accidents are too sudden to allow of escape, more than one hundred persons, who were at work in the mine, perished in an instant, and their widows and children, amounting to

nearly five hundred persons, were, in consequence, plunged into distress and destitution.

Philosophy has, in modern times, endeavoured, with some success, to guard against this calamity, so terrible and so irresistible. Sir H. Davy has invented what is called a safety lamp, for the use of men working in the mines. It consists of a common lamp, covered with a skreen of very fine wires, woven very closely together. The

light enters between the bars in a sufficient degree to assist the workmen ; but the foul air is so dense, and, one might almost say, so ropy, that it cannot pass between the wires to get at the flame; and nothing short of actual contact with the blaze will set it on fire.

"What a valuable commodity coal is," said James. "It appears to me to be as precious as gold or silver."

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Precious, Britons may well call it," said his father; "for the abundance of it in our island has tended to raise England to its present importance as a manufacturing nation.

"It has been calculated, indeed, that as a mere commodity for sale, more value has been raised from our coal-mines, than from the silver-mines of Potosi, or the gold-mines of Mexico. This value becomes enhanced to the nation, in an almost incalculable degree, by the uses to which