Will-O'the-Wisp

The Will-O'the-Wisp was once considered to be the work of fairies. But it is most correctly classified as something called ignis fatuus, which comes from latin meaning "foolish fire." It is a phosphorescent light seen hovering over marshy ground. At one time it was a common phenomenon, but seems to be reported only rarely in modern times. Supposedly, when the ignis fatuus was approached, it appeared to recede and finally to vanish. Sometimes it was noticed to reappear in another direction. This led to the notion that it was the work of a mischievous sprite, intentionally leading travellers astray. Hence the term has come to represent any deluding principle or aim.

As early as 1563, W. Fulke Meteors described it as "this impression seene on the land, is called in Latine, Ignis fatuus, foolish fire, that hurteth not, but only feareth fooles." And in 1663, Butler Hud decribed it as that which "... bewitches and leads men into pools and ditches." However, early in the 1900s, the Will-O'the-Wisp was finally discounted as an old wives tale and some scientists suggested that these phenomenon were actually composed of a phosphorus compounds formed by bacterial action. Other scientists refuted this possibility, saying that the Will-O'the-Wisp has always been incorrectly identified, and that it is simply ball lightning (also called St. Elmo's Fire).

More recent research has shown that reduced compounds do exist in decaying, phosphorus-rich organic matter. But many scientists today consider them simply to be a spontaneous ignition of these inflammable marsh gases (phosphuretted hydrogen) that results from decaying organic matter, and as such not particularly interesting. Some research in England, though, has established characteristics of spontaneous ignition, called cold blue flame, and no significant odor which seems at odds to the common marsh gas explanation (Mills, A.A., "Will-O'the-Wisp," Chemistry in Britain 16:69, February 1980).

One modern manifestation of this phenomenon occurs in a small area along the Mekong River, which forms the border between Laos and Thailand. Here, these ignis fatuus are a famous and ancient myth, one to which the local people attach religious significance. Naturally occurring lights can be seen coming not only from the river, but also from adjacent rice paddies. They seem to appear only during a full moon in October for only a day or two, and last for about 30 minutes. Every few minutes, beach-ball size lights appear under the water, rising from the bottom and float to the surface, then fly into the sky and out of sight. They can vary in intensity and some years are barely visible, though they were particularly dramatic in 1996. The local name for this modern Will-O'the-Wisp is Nekha Lights, named for a local fish seen in abundance at certain times of the year, called nekha.

As yet, there is no scientifically accepted explanation for the Mekong phenomenon. Gases forming in the muddy river bed would not come into contact with sufficient oxygen to combust, but it is possible that under low concentrations of oxygen, phosphorus vapour may be luminescent and may form through decomposition. The phenomenon may also be caused by phosphorescent bacteria, some of which are thought to live in the soil.

Mekong Mystery, New Scientist, 6 September 1997