1. A phosphorescent light that appears, in the night, over marshy ground, supposed to be occasioned by the decomposition of animal or vegetable substances, or by some inflammable gas;
you and your hearers will be misled by a Will-i'the-wisp, from one error into another, till you are plunged into religious frenzy; and then, perhaps, you will hang yourself in despair' 'Which the Lord of his infinite mercy forbid!
Tobias Smollett. The Expedition of Humphry Clinker (1771)
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“I only wish that you could come with me, Watson, but I fear that it won’t do. I may be on the trail in this matter, or I may be following a will-o’-the-wisp, but I shall soon know which it is. I hope that I may be back in a few hours.”
Arthur Conan Doyle. Sherlock Holmes: The Adventure of the Beryl Coronet
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“He is small and elusive.” Ignatius’ voice was cunning. “He is given to many disguises. He is a veritable will-o’-the-wisp, scurrying here and there in his never-ending search for marauders. [...]"
John Kennedy Toole. A Confederacy of Dunces (1980)