In Bullokar's "English Expositor" (1616), we have a quaint account of this phenomenon, "Fire-drake; a fire sometimes seen flying in the night like a dragon. Common people think it a spirit that keepeth some treasure hid, but philosophers affirme it to be a great unequal exhalation inflamed betweene two clouds, the one hot, the other cold, which is the reason that it also smoketh, the middle part whereof, according to the proportion of the hot cloud being greater than the rest, maketh it seem like a bellie, and both ends like unto a head and tail."posted by XMLicious at 1:54 AM on May 16, 2012
If I had my copy readily available I would quote the various explanations, as I believe it differs from species to species.
posted by These Birds of a Feather at 8:42 PM on May 15, 2012 [1 favorite]