Ball lightning, the subject of yesterday's Weather Eye, is not the only gliding light to cause bemusement. There is another, whose ideal ambience is a mild, wet, autumn night; it is an elusive flame, which when seen wafting in the silent darkness between the gravestones of a lonely churchyard is thought of in ancient folklore as the souls of still-born children, flitting between the upper and the lower worlds - wandering spirits, vainly seeking out a peaceful resting place. It is the dancing light of the ignis fatuus, the foolish flame that "leadeth men up and downe in a circle of absurditie, so they never knowe where they be". It is the will-o'the-wisp.
It has a variety of other names as well. Liam an tSoip they called it here in Ireland; across the water it was sometimes known as "Jack o' Lantern", or by similar names that derive from its behaviour - like "Friar's Lanthorn", "Kit o' the candlestick, or ""Peg a' Lantern"; the origins of "Spunkie", "Gillian burnt-tail", "John in the Wad" and "Dick a' Tuesday" are all lost in local folklore, while "Elf-fire", "Robin Goodfellow" and "Hobgoblin" reflect the supposedly mischievous nature of the apparition.
Will-o'-the-wisps were observed more frequently in centuries gone by than they are now. Mostly seen in bogs and graveyards, they appear as tiny, often brightly-coloured flames a few inches high floating a short distance above the ground. They may seem to dance about, and indeed they are sometimes described as resembling a lantern being carried by a person moving in a zig-zag line. It is assumed in these cases, however, that what really happens is that one flame dies out and another materialises some distance away, giving merely the impression of a rapid movement.
It is believed to be caused by a flammable gas emerging from the ground, which bursts into flame spontaneously as soon as it is exposed to air. Such gases are sometimes a by-product of animal or vegetable decomposition, and the flame they produce on ignition is a kind of chemical luminescence peculiar for its relatively low temperature.
But no one has yet succeeded in capturing this elusive substance which ignites with such apparent ease. And such a coup de gas, to coin a phrase, is now unlikely, since nowadays a willo'-the-wisp is rarely seen. Some say this is because conditions for its appearance are less ideal; bogs are drained and cultivated, and the ubiquity of artificial light might make it hard to see. But others say it never really happened anyway - that it was indeed the ignis fatuus, the fire of fools.