In the 17th century epic poem Paradise Lost, John Milton compares Satan to a will of the wisp. He hovers over bogs, marshes, and swamps and "blazing with delusive light, misleads the amazed night-wanderer from his way."
Tolkien uses the term will of the wisp in The Lord of the Rings when Gollum warns Frodo Baggins and Samwise Gamgee about the ghost lights scattered across the Dead Marshes of Mordor. The will of the wisp is a symbol of sin, and following it leads to destruction.
The will of the wisp is believed to be a chemical luminescence caused by the spontaneous ignition of naturally occurring methane gas, phosphine, and diphosphine compounds produced in decaying organic material in bogs and marshes. It was formerly believed to be the spirits of fairies, elementals, and other spirits that roamed the earth, but is now generally believed to be a natural phenomenon.
It was originally named ignis fatuus, which means 'foolish fire'. Eventually the word was extended to describe any impractical or unattainable goal.
Historically, the will of the wisp was seen as a dangerous symbol for sin because it was thought to lead travellers to the wrong places. In particular, it was believed that the will of the wisp could be used to reveal where a thief had hidden his treasure.
Nevertheless, the will of the wisp is a fascinating natural phenomenon that has captivated explorers and ghost hunters alike for centuries. In recent years, however, it has become a rare sighting in many regions and is now considered merely a mythological figure.