1. IGNIS FATUUS, OR WILL-O’-THE-WISP
Will-o’-the-wisp is proverbially elusive. It has thus far escaped the fate of the rainbow, deplored by Keats. We do not know its woof and texture, and it is not given in the dull catalogue of common things.
A strong argument in favor of the reality of this phenomenon is found in the great number of names that have been applied to it. There are forty or fifty in the British dialects alone. A myth generally carries its nomenclature with it, as it spreads from one community to another, while a fact of nature may give rise to a variety of local names.
It is certain, however, that a great many different phenomena have been described as will-o’-the-wisp. Some of these are: (1) The phosphorescence of decaying wood (“fox fire”) and other vegetable matter. This is due to luminous fungi. According to H. Molisch there are some forty-five species of fungi, including twenty species of bacteria, that have the property of luminosity. Sometimes the ground under a forest is illuminated on all sides with a soft, white light from decaying leaves. (2) Fireflies, including glowworms (the wingless females of the firefly and the larvæ). (3) Luminous birds and animals. Their luminosity is supposed to be due to parasitic fungi. Certain species of skunk have been described as giving off in the darkness a continuous flame, the head being fiery red, which blends into a bright blue at the tail. (4) Ball lightning. (5) St. Elmo’s fire. (6) Moving lanterns, distant lights of houses, and other lights due to human agency. (7) Burning gas ascending from marshes, stagnant pools, and the like. Marsh gas and other inflammable gases commonly rise from such places, and are often ignited by man, or by lightning, etc. Such fires are sometimes seen by day as well as by night. (8) Burning naphtha springs.
Excluding the numerous reported cases of will-o’-the-wisp in which the phenomenon may be plausibly identified with one of those mentioned above, there remain several cases, some of them reported by very careful observers, which appear to belong to a different category. The reports in question differ somewhat in details, but yield the following composite description:
Small luminous bodies, “about as large as your fist,” or “the size of a candle flame,” are seen hovering a few feet above the ground; not only over marshes and pools, but also over dry land. Sometimes they are stationary; at other times they appear to drift with the wind, or even to move independently. They appear and disappear, after the manner of fireflies. They do not set fire to objects with which they come in contact, and are believed to be without sensible heat. Their color is most often described as bluish, but may be yellow, purple, green, etc.; rarely pure white. They are without odor and without smoke. Traditionally they are associated with graveyards, but in very few of the cases heretofore recorded were they actually seen in such places. The popular idea that they flee from the traveler who tries to approach them and follow him when he seeks to avoid them is also unsupported by the evidence thus far adduced.
One of the most circumstantial accounts of these objects is that published in the Belgian journal “Ciel et Terre” for July-August, 1920, by a retired army surgeon, Jules Rossignol, who observed them repeatedly in the autumn of 1908 in and about some marshy woods near Grupont. They were generally seen to rise from the ground, at first in the shape of little white clouds, which changed to luminous globes on attaining an altitude of a dozen yards, and returned by a circular path toward the ground. They lasted from one to several minutes before disappearing in the air.
It is astonishing that the phenomenon of ignis fatuus, though reported from so many parts of the world, has not yet been made the subject of direct scientific examination. Nobody has ever studied its light with the spectroscope, for example. Chemists have, indeed, attempted to reproduce the phenomenon, yet the chemical explanations of it that have appeared in reference books down to a recent date are quite untenable. It has sometimes been attributed to marsh gas (methane, CH4), and sometimes to phosphureted hydrogen (phosphine, PH3). But marsh gas, besides not being spontaneously combustible, diffuses too rapidly in the air to produce the effects described, while phosphureted hydrogen, though it takes fire spontaneously in the air, produces thick wreaths of smoke when burning and has a powerful odor—features never reported in connection with will-o’-the-wisp.
At least two more plausible explanations of ignis fatuus have been offered in the last few years. Mr. F. Sanford (“Scientific Monthly,” Oct., 1919) believes that it is due to “swarms of luminous bacteria which are carried up from the bottom of the marsh by rising bubbles of gas.” A Belgian chemist, M. Léon Dumas (“La Nature,” Dec. 11, 1909), claims to have produced little luminous clouds, corresponding to the traditional descriptions of will-o’-the-wisp, by combining the two gases sulphureted hydrogen and phosphine. Both these substances are produced in the decay of animal matter, especially of the brain and spinal cord. The body of an animal, buried in some wet place, would accumulate the two gases under pressure in the skull and spinal canal, and their escape, simultaneously, would fulfill the conditions of M. Dumas’ experiments.
(At the request of the present writer, these experiments were repeated at the Bureau of Standards, in Washington, with only partial success. Further trials with these and other gases due to putrefaction are desirable.)