a kind of light, supposed to be of an electric nature, appearing frequently in mines, marshy places, and near stagnating waters. It was formerly thought, and is still by the superstitious believed, to have something ominous in its nature, and to presage death and other misfortunes. There have been instances of people being decoyed by these lights into marshy places, where they have perished; whence the names of Ignis-fatuus, Will-with-a-wisp, and Jack-with-a-lantern, as if this appearance were an evil spirit which took delight in doing mischief of that kind. The general opinion is, that this light is owing to the decomposition of animal or vegetable matter. IGNITION properly signifies the setting fire to any substance; the sense is sometimes limited to that kind of burning which is not accompanied with flame, such as that of charcoal, cinders, metals, stones, and other solid substances. The effects of ignition, according to the old chemical doctrine, are first to dissipate what is called the phlogiston of the ignited substance, after which it is reduced to ashes. Vitrification next follows; and, lastly, the substance is totally dissipated in vapour. All these effects, however, depend on the presence of the air; for in vacuo the phlogiston of any substance cannot be dissipated. Neither can a body which is totally destitute of phlogiston be ignited in such a manner as those which are not deprived of it: for as long as the phlogiston remains, the heat is kept up in the body by the action of the external air upon it; but when the phlogiston is totally gone, the air always destroys, instead of augmenting, the heat. But for the explanation of the phenomena of ignition, according to the views of modern chemistry, see COMBUSTION, CHEMISTRY Index.