‖ ignis fatuus
(ˈɪgnɪs ˈfætjuːəs)
[med. or mod.L., = foolish fire.]
A phosphorescent light seen hovering or flitting over marshy ground, and supposed to be due to the spontaneous combustion of an inflammable gas (phosphuretted hydrogen) derived from decaying organic matter; popularly called Will-o'-the-wisp, Jack-a-lantern, etc.
It seems to have been formerly a common phenomenon; but is now exceedingly rare.
When approached, the ignis fatuus appeared to recede, and finally to vanish, sometimes reappearing in another direction. This led to the notion that it was the work of a mischievous sprite, intentionally leading benighted travellers astray. Hence the term is commonly used allusively or fig. for any delusive guiding principle, hope, aim, etc.
| 1563 W. Fulke Meteors (1640) 11 b, This impression seene on the land, is called in Latine, Ignis fatuus, foolish fire, that hurteth not, but only feareth fooles. 1658 Phillips, Ignis fatuus, a kind of slight exhalation set on fire in the night time, which ofttimes causeth men to wander out of their way. 1663 Butler Hud. i. i. 509 An Ignis Fatuus that bewitches And leads Men into Pools and Ditches. 1688 J. Clayton in Phil. Trans. XVII. 789 Ignes fatui, tho there be many boggy Swamps and Marshes, are seldom, if any are seen there. 1774 Goldsm. Nat. Hist. (1862) I. xxi. 134 Floating bodies of fire..the ignis fatuus, or wandering fire. 1813 Sir H. Davy Agric. Chem. i. (1814) 26 To avoid being led astray by the ignis fatuus the most secure method is to carry a lamp. |
| fig. 1599 Broughton's Lett. xii. 40 To fetch light from their Heathenish Ignis fatuus. 1631 Star Chamb. Cases (Camden) 31 For S{supr} Arthur Savage, he is the primum mobile, the ignis fatuus that misleades all the rest. 1777 J. Adams in Fam. Lett. (1876) 264 What an ignis fatuus this ambition is? 1824 Byron Juan xv. liv, Following the ‘ignes fatui’ of mankind. 1896 Duke of Argyll Philos. Belief Pref. 7 That ignis fatuus of the time—uniformity of worship throughout the three kingdoms. |
| attrib. 1808 Byron To youthful friend xvii, An ignis⁓fatuus gleam of love. |