The Halloween Jack-o'-lantern, made from pumpkins in the US and originally turnips in the UK, began its existence as a wisp of glowing marsh gas or "spooklight." We begin our episode with a montage of modern American spooklights including that of Oklahoma's "Spooklight Road," North Carolina’s Brown Mountain, and the flying saucers sighted in Michigan in 1966, famously identified by investigator Allen Hynek  as "swamp gas."

"Jack-o'-lantern"  was just another name given to what's more widely known now as a Will-o'-the-wisp -- a wavering, bobbing light seen in marshy places, understood as mischievous spirit intent on leading travelers off course and into their doom in muck and mire.  Flaming methane produced by rotting vegetation in such environments, is said to the the cause of the phenomenon, though the mode of ignition is still largely a matter of debate. The Latin name for such lights, ignis fatuus  (ool's fire), was also applied to phenomena having nothing to do with swamps, as it's been used interchangeably with "St. Elmo's Fire" to describe electrical discharges seen on ships; masts and other rodlike protrusions when atmospheric conditions are right. We hear a dramatic first-person account from 1847, in which St. Elmo's Fire (identified by antiquarian Henry Duncan as ignis fatuus) appears on a coachman's whip during a storm.

A mirage in a marsh. Coloured wood engraving by C Whymper. Gas. Contributors: Charles H Whymper (1853–1941).

We then hear what scientists of the 16th and 17th century made of ignis fatuus, often relating it  unexpectedly to meteors or luminous insects, while mocking "the superstitions" who imagined it as wandering spirits alight with the flames of Purgatory.

Along with marsh spirits exlusively dedicated to misleading travelers, ignis fatuus could also be a temporary  form  taken by shapeshifting fairy folk like Puck or Robin Goodfellow.  We hear an example of this from  the 1628 pamphlet, Robin Goodfellow, his Mad Pranks and Merry Jests. We also see the term appearing in literature of the 16th and 17th century as a metaphor for treachery or deception, in works by John Milton and William Shakespeare.

We run through the variety of colorful regional names by which Will-o-the-Wisps were known: Bob-a-longs, Pinkets, Spunkies, Merry Dancers, Nimble men, Hinkypunks, and Flibberdigibbets, as well as some female variants including Peg-a-lantern and Kitty with the Candlestick. In Wales, these mysterious lights could be omens of death, also known as "corpse candles," or "death lights." Appearing around the home of the dying or at the deathbed, they were also called "fetch lights," as they would arrive when required to fetch the soul to the other side. In Cornwall, fool's fire is associated with the piskies, in particular Joan the Wad and her partner Jack-o'-the-Lantern, the former having acquired a mostly positive reputation in the 20th century as a luck-bringer. Mrs. Karswell also reads  some tales of ignis fatuus in the western counties, where the lights are called "hobby lanterns" (from hobgoblin) or  "lantern men."

We then shift gears to discuss the pumpkin form of Jack-o'-lantern, beginning with a well-circulated Irish origin story. A quick summary: the light carried in a hollowed vegetable (a pumpkin in the New World or turnip in the Old) represents the spirit of a notorious sinner, "Jack," or "Stingy Jack," who upon death finds he is too wicked for Heaven and too troublesome for Hell. Consquently, he is condemned to wander the earth till Judgement Day, given the peculiar lantern to light his way.

This, at least, is the most recent version of the tale, but when it first appeared in print, in a 1936 edition of the Dublin Penny Journal, there's no mention of any hollowed vegetable, much less of Halloween -- meaning this "ancient legend" actually...