Of the Meteor Called the Ignis Fatuus, 1729

William Derham and Thomas Dereham (1729), Of the Meteor Called the Ignis Fatuus, from Observations Made in England, by the Reverend Mr. W. Derham, F. R. S. and Others in Italy, Communicated by Sir Tho. Dereham, Bart. F. R. S. Philosophical Transactions, Vol.36, pp.204-214. As reprinted in The Gallery of Nature by Edward Polehampton (1815), as Of the Ignis Fatuus, as observed in England, pp.498-501

It being the opinion of divers skilful naturalists, particularly Mr. Fr. Willoughby and Mr. Ray, that ignes fatui are only the shining of a great number of the male glow-worms in England, or of the pyraustæ in Italy, flying together, Mr. D. consulted his friend, Sir Thomas Dereham, about the phenomenon, being informed that those ignes fatui are common in all the Italian parts. But of the pyraustæ, or fire-flies, he says, he never observed any such effects, though there is an immense number of them in June and July. He also says, that these pyraustæ are called Lucciole, i.e. small lights, and that they are not the farfalls, as Mr. Ray thought, which are butterflies.

But Mr. D. has reason to think, that insects are not concerned in the ignes fatui, from the following observations; the first made by himself, and the others received from Italy, by the favour of Sir Thomas Dereham.

His own observation he made at a place in a valley between rocky hills, which he suspected might contain minerals, in some boggy ground near the bottom of those hills. Where, seeing one in a calm, dark night, with gentle approaches, he got up within two or three yards of it, and viewed it with all possible care. He found it frisking about a dead thistle growing in the field, till a small motion of the air made it skip to another place, and thence to another, and another.

It is about fifty-five years since he saw this phenomenon, but he had as fresh and perfect an idea of it, as if it was but a few days. And as he took it then, so he is of the same opinion now, that it was a fired vapour.

The male glow-worms Mr. D. knows emit their shining light, as they fly; by which means they discover and woo the females; but he never observed them to fly together in so great numbers, as to make a light equal to an ignis fatuus. And he was so near, that had it been the shining of glow-worms, he must have seen it in little distinct spots of light; but it was one continuous body of light.

As to the comunication from Italy, it is observed that these lights are pretty common in all the territory of Bologna. In the plains they are very frequently observed; the country people call them cularsi, perhaps from some fancied similitude to those birds; and because they consider them as birds, the belly and other parts of which are resplendent like our shining flies. They are most frequent in watery and morassy ground, and there are some such places, where one may be almost sure of seeing them every night, if it be dark; some of them giving as much light as a lighted torch, and some no larger than the flame of a common candle. All of them have the same property in resembling, both in colour and light, a flame strong enough to reflect a lustre on neighbouring objects all around. They are continually in motion, but this motion is various and uncertain. Sometimes they rise up, at others they sink. Sometimes they disappear of a sudden, and appear again in an instant in some other place. Commonly they keep hovering about six feet from the ground. As they differ in size, so also in figure, spreading sometimes pretty wide, and then again contracting themselves. Sometimes breaking to all appearance into two, soon after meeting again into one body; sometimes floating like waves, and letting drop some parts like sparks out of a fire. And in the very middle of the winter, when the weather is very cold, and the ground covered with snow, they are observed more frequently than in the hottest summer. Nor does either rain or snow in anywise prevent or hinter their appearance; on the contrary, they are more frequently observed, and cast a stronger light, in rainy and wet weather. But since they do not receive any damage from wet weather; and since, on the other hand, it has never been observed, that any thing was set on fire by them, though they must needs in their moving to and fro, meet with a good many combustible substances, it may from thence be inferred, that they have some resemblance to that sort of phosphorus that shines in the dark, without burning any thing. As to the appearance of this phenomenon in mountainous parts, they differ in nothing else but in size; these latter being never observed any larger than the flame of an ordinary candle. In general, these lights are great friends to brooks and rivers, being frequently observed along their banks; perhaps because the air carries them thither more easily than any where else. In all other particulars, as in their motion, the manner of their appearance, their disappearing sometimes very suddenly, their light, the height they rise to, and their not being affected either by rainy or cold weather, they are the very same with the cularsi above described, or the large Will with a Wisp, as observed in the plains.

A young gentleman, a very accurate and skilful observer of natural appearances, travelling sometimes in March last, between eight and nine in the evening, in a mountainous road, about ten miles south of Bologna, as he approached a certain river, called Rioverde, he perceived a light, which shone very strongly on some stones that lay on the banks. It seemed to be about two feet above the stones, and not far from the water of the river: in figure and size it had the appearance of a parallelopiped, somewhat above a Bolognese foot in length, and about half a foot high, its longest side lying parallel to the horizon: its light was very strong, insomuch that he could very plainly distinguish by it part of a neighbouring hedge, and the water in the river. The gentleman's curiosity tempted him to examine it a little nearer; in order to which, he advanced gently towards the place, but was surprised to find, that insensibly it changed from a bright red to a yellowish, and then to a pale colour, in proportion as he drew nearer; and that when he came to the place itself, it was quite vanished. On this he stepped back, and not only saw it again, but found that the farther he went from it, the stronger and brighter it grew; nor could he, on narrowly viewing the place where this fiery appearance was, perceive the least blackness, or smell, or any mark of an actual fire. The same observation was confirmed by another gentleman, who frequently travels that way, and who asserted, that he had seen the very same light five or six different times, in Spring and Autumn, and that he had always observed it in the very same shape and the same place; which seems very difficult to be accounted for. He said further, that once he took particular notice of its coming out of a neighbouring place, and then settling itself into the figure above described.

[Phil. Trans. Abr. 1729.

Sean B. Palmer