What to Observe, 1841

Julian Jackson (1841), What to Observe; or, The Traveller's Remembrancer, p.99.

IGNEOUS METEORS.—The Ignis-fatuus, St. Elmo's Fire, &c.—The former of these is a meteor so well known as hardly to require being noticed here, but in order that our article on Igneous Meteors may be complete, we shall say a word on those curious appearances so long, and still unfortunately, the terror of the ignorant. This meteor is by some explained to depend on two principle causes, 1st. a disengagement of carbureted hydrogen gas, and 2nd. its inflammation by electricity; but this idea seems erroneous.

The decomposition of organic bodies, animal and vegetable, it is true, disengages a quantity of inflammable gas, and this is the reason why this meteor is found most frequently hovering over burial places, swamps, &c.; and, as heat facilitates putrefaction, the ignes fatui are more frequently seen in summer than in winter: but as the phenomenon is often observed when the atmosphere is by no means overcharged with electricity, it seems probable that the disengaged gas is phosphuretted hydrogen, which is known to inflame spontaneously on coming in contact with the air. The ignis fatuus deserves no particular notice, unless in any spot it be remarkably frequent, or present any thing very extraordinary. Some very remarkable ignes fatui have been described by different writers and travellers.

Note: the "phosphuretted hydrogen" theory dates back to at least 1806, in Jane Haldimand Mercet (1806), Conversations on Chemistry, vol.1, p.99; the electrical spark theory, on the other hand, does not seem to be prevalent in the early 19th century. This is an interesting quote also for the fact that the ignis fatuus is regarded as quite common, whereas other commentators of the time, e.g. E.G.R. (1855), note that it's becoming increasingly rare due to drainage.