The first edition of the Encyclopedia Brittanica, printed in 1771, has an interesting entry:
DRACO VOLANS, in meteorology, a fiery exhalation, frequent in marshy and cold countries. It is most common in the summer, and though principally seen playing near the banks of rivers, or in boggy places, yet sometimes mounts up to a considerable height in the air, to the no small terror of the amazed beholders; its appearance being that of an oblong, sometimes roundish, fiery body, with a long tail. It is entirely harmless, frequently sticking to the hands and cloaths of people without injuring them in the least.
This is now called “swamp gas” and is actually methane mixed in with a few other components. It is the natural product of anaerobic decomposition of organic materials (plants) below the surface of the ground, usually in marshy areas. Here are a few photographs I found:
