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appearances : for, it was sometimes globular, or else pointed like 
the flame of a candle ; afterwards it would spread itself, and involve 
our whole company in its pale and inoffensive light ; then at once 
contract, and suddenly disappear. But in less than a minute, it 
would begin again to exert itself as at other times ; running along 
from one place to another, with great swiftness, like a train of gun- 
powder, set on fire ; or else it would spread and expand itself over 
more than two or three acres of the adjacent mountains ; discover- 
ing every shrub and tree that grew upon them. The atmosphere, 
from the beginning of the evening, had been remarkably thick and 
hazy ; and the dew, as we felt it upon our bridles, was unusually 
clammy and unctuous*. 
The late discoveries in chemistry give us reason to hope, that an 
explication of this extraordinary appearance may, before long, be 
obtained. It is generally attributed to some inexplicable agency of 
the electric fluid on the inflammable air of marshes ; but it seems 
rather to depend on some hitherto unknown combination of phos- 
phorus, with carbon or sulphur, in hydrogen gas, separated from the 
wetted vegetable mould. 
It is true, that on phosphuretted hydrogen gas coming in contact 
with the atmosphere, actual inflammation takes place ; whereas in 
ignes fatui the illumination appears to be that of phosphorescent 
light only ; but that the subsequent industry of chemists will enable 
them to imitate this phenomenon still more closely, seems very 
probable. Indeed, there seems to be reason for expectation, that 
such a result may be the reward of a careful series of experiments, 
in which the phosphorus is combined, in different doses, with other 
gases, containing various proportions of the several simple com- 
bustible bodies — ^perhaps the gaseous oxide of carbon might be 
found well calculated to repress the combustion, whilst it permitted 
* Travels, or Observations relating to several parts of Barbary and the Levant, by Thomas 
Shaw, D. D. F. R. S. 2d edition, 1756, p. 334. 
