Fifty years since, many of the best pits were so full of the inflammable gas given forth by the coal, that they could not be worked without the greatest danger; and for this reason some were altogether abandoned, The rudest possible methods were adopted of producing light sufficient to enable the pitmen to work by. The phosphorescence of decayed fish-skins was tried; but this, though safe, was very inefficient. The most common method employed was what was called a steel mill, the notched wheel of which, being made to revolve against a flint, struck a succession of sparks, which scarcely served to do more than make the darkness visible. A boy carried the apparatus after the miner, working the wheel, and by the imperfect light thus given forth he plied his dangerous trade. Candles were only used in those parts of the pit where gas was not abundant. Under this rude system not more than one-third of the coal could be worked; and two-thirds were left. What the workmen, not less than the coal-owners, eagerly desired was, a lamp that should give forth sufficient light, without communicating flame to the inflammable gas which accumulated in certain parts of the pit. Something had already been attempted towards the invention of such a lamp by Dr. Clanny, of Sunderland, who, in 1813, contrived an apparatus to which he gave air from the mine through water, by means of bellows. This lamp went out of itself in inflammable gas. It was found, however, too unwieldy to be used by the miners for the purposes of their work, and did not come into general use. A committee of gentlemen was formed to investigate the causes of the explosions, and to devise, if possible, some means of preventing them. At the invitation of that Committee, Sir Humphry Davy, then in the full zenith of his reputation, was requested to turn his attention to the subject. He accordingly visited the collieries near Newcastle on the 24th of August, 1815; and on the 9th of November following, he read before the Royal Society of London his celebrated paper “On the Fire-Damp of Coal Mines, and on Methods of lighting the Mine so as to prevent its explosion.” But a humbler though not less diligent and original thinker had been at work before him, and had already practically solved the problem of the Safety-Lamp. Stephenson was of course well aware of the anxiety which prevailed in the colliery districts as to the invention of a lamp which should give light enough for the miners to work by without exploding the fire-damp. The painful incidents above described only served to quicken his eagerness to master the difficulty.