"The frequency of accidents, arising from the explosion of the fire-damp, or inflammable gas of the coal mines, mixed with atmospherical air, occasioned the formation of a committee at Sunderland, for the purpose of investigating the causes of these calamities, and of endeavouring to discover and apply a preventive. Sir Humphry received an invitation, in 1815, from Dr. Gray, one of the members of the committee; in consequence of which he went to the North of England, and visiting some of the principal collieries in the neighbourhood of Newcastle, soon convinced himself that no improvement could be made in the mode of ventilation, but that the desired preventive must be sought in a new method of lighting the mines, free from danger, and which, by indicating the state of the air in the part of the mine where inflammable air was disengaged, so as to render the atmosphere explosive, should oblige the miners to retire till the workings were properly cleared. The common means then employed for lighting the dangerous part of the mines consisted of a steel wheel revolving in contact with flint, and affording a succession of sparks: but this apparatus always required a person to work it, and was not entirely free from danger. The fire-damp was known to be light carburetted hydrogen gas; but its relations to combustion had not been examined. It is chiefly produced from what are called blowers or fissures in the broken strata, near dykes. Sir Humphry made various experiments on its combustibility and explosive nature; and discovered, that the fire-damp requires a very strong heat for its inflammation; that azote and carbonic acid, even in very small proportions, diminished the velocity of the inflammation; that mixtures of the gas would not explode in metallic canals or troughs, where their diameter was less than one-seventh of an inch, and their depth considerable in proportion to their diameter; and that explosions could not be made to pass through such canals, or through very fine wire sieves, or wire gauze. The consideration of these facts led Sir Humphry to adopt a lamp, in which the flame, by being supplied with only a limited quantity of air should produce such a quantity of azote and carbonic acid as to prevent the explosion of the fire-damp, and which, by the nature of its apertures for giving admittance and egress to the air, should be rendered incapable of communicating any explosion to the external air. These requisites were found to be afforded by air-tight lanterns, of various constructions, supplied with air from tubes or canals of small diameter, or from apertures covered with wire-gauze, placed below the flame, through which explosions cannot be communicated; and having a chimney at the upper part, for carrying off the foul air. Sir Humphry soon afterwards found that a constant flame might be kept up from the explosive mixture issuing from the apertures of a wire-gauze sieve.