E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Ignis Fatuus
means strictly a fatuous fire it is also called. Jack o
Lantern, Spunkie, Walking Fire, Will o the Wisp, and Fair Maid of Ireland. Milton calls it Friars Lanthern, and Sir Walter Scott Friar Rush with a lantern. Morally speaking, a Utopian scheme, no more reducible to practice than the meteor so called can be turned to any useful end. (Plural, Ignes fati.) (See FRIARS LANTHORN.)
1
When thou rannest up Gadshill in the night to catch my horse, if I did not think thou hadst been an ignis fatuous or a ball of wildfire, theres no purchase in money.Shakespeare: 1 Henry IV., iii. 3.
According to a Russian superstition, these wandering fires are the spirits of still-born children which flit between heaven and the Inferno.