IGNIS Fatuus

, a common met<*>or, chiefly seen in dark nights about meadows, marshes, and other moist places, as also in burying grounds, and near dung-hills. It is known among the people by the appellations, Will with a Wisp, and Jack with a Lantern.

Dr. Shaw describes a remarkable Ignis Fatuus, which he saw in the Holy Land, that was sometimes globular, or in the form of the flame of a candle; and presently afterward it spread itself so much as to involve the whole company in a pale harmless light, and then contract itself again, and suddenly disappear. But in less than a minute it would become visible as before; or, running along from one place to another, with a swift progressive motion, would expand itself at certain intervals over more than 2 or 3 acres of the adjacent mountains. The atmosphere had been thick and hazy, and the dew on the horses' bridles was uncommonly clammy and unctuous. In the same weather he observed those luminous appearances, which skip about the masts and yards of ships at sea, and which the sailors call corpusanse, by a corruption of the Spanish cuerposanto. Shaw's Travels, p. 363.

Newton calls it a vapour shining without heat; and supposed it to be of the same nature with the light issuing from putrescent substances. Willughby and Ray were of opinion that it is occasioned by shining insects: but all the appearances of it observed by Derham, Beccaria, and others, sufficiently evince that it must be an ignited vapour. Inflammable air has been found to be the most common of all the factitious airs in nature; and that it is the usual product of the putrefaction and decomposition of vege<*> able substances in water. Signor Volta writes to Dr. Priestley, that he fires inflammable air by the electric spark, even when the electricity is very moderate: and he supposes that this experiment explains the inflammation of the Ignes Fatui, provided they consist of inflammable air, issuing from marshy ground by help of the electricity of fogs, and by falling stars, which have probably an electrical origin. See Priestley's Obs. on Air, vol. 3, p. 382; the Philos. Trans. Abr. vol. 7, p. 147 &c.