2013 June 24
Will o' the wisp -- the eerie, errant light guiding travellers to ... who knows where?
From the Middle Ages to the 1800s, "foolish fire" was a common image in art and literature, an object too of both superstitious dread and (remarkably inconclusive) rational investigation. Today, with wilds and wetlands vanishing and travellers safely cocooned in GPS-equipped autos, the Irrlicht is rarely seen and rarely mentioned -- absorbed, perhaps, into the more glamourous UFO, which young J. Allen Hynek famously attempted to explain as "swamp gas". Harry Potter still contends with "hinkypunks" (a West Country expression saved from extinction by the magic of J. K. Rowling), but muggle science pays little attention to the ignis fatuus. It was not always thus ...
Chapter XX: The Ignis Fatuus, from The Aerial World: A Popular Account of the Phenomena and Life of the Atmosphere by George Hartwig [New York: Appleton, 1875]. Hartwig's words are in bold; my comments are in light italics. The pictures and all but one of the journal references are my additions.
ALONG with the shooting stars, the luminous phenomenon known under the name of ignis fatuus is reckoned among the fiery meteors, although its origin is very different, and the only property common to them both is that of shining in the dark. From unknown ethereal heights the shooting stars dart down upon the earth, but the ignes fatui are the low-born progeny of bogs and stagnant waters.
There is something spectral or ghost-like about their desultory wanderings in the midnight gloom of marshes and burying-grounds, and they thus furnish superstition with ample matter for many a dismal legend. Often have they been taken by the horror-struck wanderer who saw them moving among the tombs for departed spirits unable to find rest in the grave ; and in Scotland, where they are called Elf-candles, they are supposed to portend the death of some inmate of the house near which they make their fatal appearance.
According to another very common belief, they are goblins of a malignant nature, who, by the delusion of a hospitable light, mislead the benighted traveller into some deep morass, where he meets with a miserable end ; and it is to this superstitious notion, alluded to by Goldsmith, that the ignis fatuus of the naturalist owes its popular name of Will-with-a-wisp or Jack-with-a-lantern:
"Turn, gentle Hermit of the dale,
And guide my lonely way
To where yon taper cheers the vale
With hospitable ray."
"Forbear, my son," the Hermit cries,
"To tempt the dangerous gloom ;
For yonder faithless phantom flies
To lure thee to thy doom."
--- The Hermit, 1-4 and 12-16.
But though superstition has founded so many wondrous tales on the ignes fatui, they are a rather uncommon phenomenon, which but few philosophical observers ever had the good fortune to meet with. Dr. Derham happened one night to perceive one of them, and got so near that he could have a very good view of it. This is by no means easy to be obtained, for, among other singularities of the ignis fatuus, it is observed to avoid the approach of any person, and to fly from place to place as if it was animated, and possessed of an instinctive aversion to society. That which the Doctor observed was in some boggy ground betwixt two rocky hills, and the night was dark and calm, by which means probably he was enabled to advance within two or three yards of it. It appeared like a complete body of light without any division, so that he was sure it could not have been occasioned by insects, as some have supposed, the separate lights of which he could not have failed to distinguish, if they had been the cause. The light kept dancing about a dead thistle till a very slight motion of the air, occasioned, as he supposed, by his near approach to it, made it skip to another place, after which it kept flying before him as he advanced. [ Of the Meteor called the Ignis Fatuus by W. Derham, Phil. Trans. R.S.L. 36, 204 (1729)]
In a completely dark and wind-still night (December 2, 1807) the celebrated astronomer Bessel [ Annalen der Physik 120, 366 (1838)] saw on a moor in Hanover a great number of small flames of a bluish colour, similar to that of impure hydrogen. Their luminous power was inconsiderable. They often remained immovable, and often to all appearances made horizontal movements. On the spot where they appeared the colonists had dug a quantity of turf, which had rendered the ground uneven, and favoured the collection of water. The flames were not seen on the higher parts of the moor.
Professor Knorr, of Kiew, [ Annalen der Physik 165, 620 (1853)], once saw, while still a student, as he was wandering at night through a swampy country, a very curious ignis fatuus, which, without any of the usual mobility of the phenomenon, continued quietly to shine on the same spot. It glimmered through the leaves of some high reeds, with a bush of alders at its back, so that the light stood as in a green recess. The bush, the reeds, and the grass, were so prettily illuminated as to form a charming picture. The swamp prevented him from coming quite near, but with the assistance of a stick he was able to beat down the rushes, and thus to render the upper part of the little flame completely visible. It was about five inches long and an inch and a half broad. In its centre the light was faint and pale yellow, towards the borders it became more violet, and lost itself in the surrounding darkness without any sharp outlines. The air was quite calm and the light motionless, nor did it exhibit anything like the vivacity of an ordinary flame when the observer agitated the air. He held the point of his stick at least a quarter of an hour over the flame, without perceiving the least trace of heat.
Some very remarkable ignes fatui were observed in October 1859 by Herr List in the valley of the Fulda [Poggendorff's Annalen, Band cviii. p. 656 (1859)]. A heavy white fog covered the country, and damp mouldy vapours filled the air. The moon was shining through the mist when Herr List saw, scarce two paces before him, a small flame on the roadside. On his advancing towards it, it disappeared, but soon after he saw a new light, followed by several others. All these flames remained fixed on the same spot ; to keep them alive he was, however, obliged to approach very carefully, and to avoid causing a draught. They were about the size of a hen's egg, and gleamed, without changing their place, upon and between the blades of grass. They had mostly a greenish-white light. On touching them he found that they emitted no heat. Some of them made their appearance with a crackling noise, such as that which takes place when phosphuretted hydrogen gas explodes spontaneously in the air. The atmosphere was perfectly quiet. Each flame lasted seldom longer than a minute or a minute and a half.
Beccaria [letter quoted in Derham, op. cit., p. 206] relates that an intelligent gentleman travelling in the evening, between eight and nine, in a mountainous road about ten miles south of Bologna, perceived a light which shone very strangely upon some stones which lay on the banks of the river Rioverde. It seemed to be about two feet above the stones, and not far from the water. In size and form it had the appearance of a parallelopiped, somewhat more than a foot in length, and half a foot high, the longest side being parallel to the horizon. Its light was so strong that it plainly illuminated part of a neighbouring hedge and the water of the river. On wishing to examine it more closely, he was surprised to find that, as he approached, it changed gradually from a bright red, first to a yellowish and then to a pale colour, and when he came to the place itself, it quite vanished. Hereupon he stepped back, and not only saw it again, but found that the farther he receded the stronger and brighter it grew. No smell or any other sign of fire was perceptible.
Dr. Shaw relates in his Travels to the Holy Land  that while he was journeying in the valleys of Mount Ephraim an ignis fatuus made its appearance, and attended him and his company for more than an hour. Sometimes it would appear globular, or in the shape of the flame of a candle ; at others it would spread to such a degree as to involve the whole company in a pale, inoffensive light, then contract itself, and suddenly disappear, but in less than a minute would appear again ; sometimes running swiftly along, it would expand itself at certain intervals over more than two or three acres of the adjacent mountains. The atmosphere from the beginning of the evening had been remarkably thick and hazy.
As the various ignes fatui that have been observed differ so much in character, it is evident that they cannot all be referred to one and the same cause. In many cases they probably proceed from the self-igniting phosphuretted hydrogen gas, which is frequently developed by the putrefaction of organic matter in marshes, moist ground, burying-places, and dunghills, where the phenomenon most frequently appears.
"Phosphuretted hydrogen" is an old name for the spontaneously-combustible poisonous gas phosphine (more properly called "phosphane", PH3). Phosphorus -- the dangerous glow-in-the-dark element, with its three alchemically-coloured allotropes and its Promethean connexions to life and fire -- fascinated the reading public in the Eighteenth and Nineteenth Centuries much as radioactive elements would in the early Twentieth. The phosphane theory lives on today, although with less vigour than the related hypothesis linking marsh lights to natural methane. Both gases (and many others) are indeed produced biologically in wetlands -- a fact not only known in the 1800s but of some significance in the history of science:
Sometimes vegetable and perhaps also animal substances may in a certain state of decay emit a phosphoric gleam, and give rise to ignes fatui. Thus in 1781 Chladni [Über den Ursprung ... Eisenmassen IV, 27 (1794)] saw in a garden near Dresden, on a fine summer's evening, soon after a rain, many small luminous bodies hop about in the grass according to the direction of the wind. They were very difficult to catch, and proved on examination to be small gelatinous masses, similar to the spawn of frogs or boiled sago. They had no remarkable smell or taste, and seemed to be mouldering vegetable substances.
Sir Isaac Newton [ Opticks III, Qu. 10] calls the ignis fatuus a vapour shining without heat, and supposes that there is the same difference between this vapour and flame that there is between the shining of rotten wood and burning coals. So much is certain, that there are still many unsolved enigmas in the history of the ignes fatui, and that in this apparently insignificant phenomenon also the veil has not yet been entirely raised which hides from our view the secret laboratories of Nature.
Nor has that veil lifted yet in 2013. Some theories are more popular than others, but none seem wholly adequate. One of the best websites on the subject (with links to others) is Sean B. Palmer's page, Will-o'-the-Wisp.
Rev. Charles Dodgson, not surprisingly, had something to say about the phenomenon:
"Come, listen, my men, while I tell you again
The five unmistakable marks
By which you may know, wheresoever you go,
The warranted genuine Snarks.
"Let us take them in order. The first is the taste,
Which is meager and hollow, but crisp:
Like a coat that is rather too tight in the waist,
With a flavor of ... "