The Extinction of the Ignis Fatuus

Abstract

Ignis fatuus, a luminous phenomenon witnessed over the centuries by observers around the world, is no longer seen in modern times, suggesting that it is extinct. An explanation for this disappearance can be found in the description of ignis fatuus as a cool flame of methane. Unlike a conventional flame, which generates large amounts of heat, ignis fatuus is a flame that glows without heat through a chemiluminescence process. Its characteristic bluish color is due to the emission of excited formaldehyde, which is formed in the slow combustion of methane. It is generally accepted that the phenomenon is a spontaneous combustion of swamp gas in contact with the oxygen in air, but an analysis of the energies involved in the cool flame process indicates that the phenomenon is not spontaneous in nature. Experiments carried out in the 19th century show torches being used to ignite ignis fatuus. The abandonment of fire in favor of night lighting may hold the secret to this mystery of ignis fatuus’s extinction.