E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
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.)
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.