OPTICAL PHENOMENA. 54:5 



this experiment, which I found was owing to my breathing. I therefore held rny face 

 from the flame, and also held a piece of cloth as a screen ; on doing which I was able to 

 singe paper, which became brown-coloured, and covered with a viscous moisture. I next 

 used a narrow slip of paper, and enjoyed the pleasure of seeing it take fire. The gas 

 was evidently inflammable, and not a phosphorescent luminous one, as some have main 

 tained. But how do these lights originate ? After some reflection, I resolved to make 

 the experiment of extinguishing them. I followed the flame ; I brought it so far from 

 the marsh that probably the thread of connection, if I may so express myself, was broken, 

 and it was extinguished. But scarcely a few minutes had elapsed when it was again 

 renewed at its source (over the air-bubbles), without my being able to observe any transi 

 tion from the neighbouring flames, many of which were burning in the valley. I repeated 

 the experiment frequently, and always with success. The dawn approached, and the 

 flames, which to me appeared to approach nearer to the earth, gradually disappeared. 

 On the following evening I went to the spot and kindled a fire on the side of the valley, 

 in order to have an opportunity of trying to inflame the gas. As on the evening before, 

 I first extinguished the flame, and then hastened with a torch to the spot from which the 

 gas bubbled up, when instantaneously a kind of explosion was heard, and a red light was 

 seen over eight or nine square feet of the marsh, which diminished to a small blue flame, 

 from two and a half to three feet in height, that continued to burn with an unsteady 

 motion. It was therefore no longer doubtful that this ignis fatuus was caused by the 

 evolution of inflammable gas from the marsh." 



The ignis fatuus of the churchyard and the battle-field we may conclude to arise from 

 the phosphuretted hydrogen emitted by animal matter in a state of putrefaction, which 

 always spontaneously inflames upon contact with the oxygen of the atmosphere ; and the 

 flickering meteor of the marsh may be referred to the carburetted hydrogen, formed by 

 the decomposition of vegetable matter in stagnant water, ignited by a discharge of the 

 electric fluid, or by contact with some substance in a state of combustion. This wandering 

 light has often been a source of terror to the ignorant, and has frequently seduced the 

 benighted traveller into dangerous bogs and quagmires, under the impression that it 

 proceeded from some human habitation. 



" Drear is the state of the benighted wretch, 

 Who then, bewilder'd, wanders through the dark, 

 Full of pale fancies, and chimeras huge ; 

 Nor visited by one directive ray, 

 From cottage streaming, or from airy hall. 

 Perhaps impatient as he stumbles on, 

 Struck from the root of slimy rushes, blue, 

 The wild-fire scatters round, or gather'd trails, 

 A length of flame deceitful o'er the moss : 

 Whither decoy'd by the fantastic blaze, 

 Now lost and now renew'd, he sinks absorb'd, 

 Rider and horse, amid the miry gulf: 

 While still, from day to day, his pining wife 

 And plaintive children his return await, 

 In wild conjecture lost." 



The production of inflammable gases is one of the processes in constant action in the 

 great laboratory of nature, and extraordinary disengagements of combustible elements 

 occur, though we are quite ignorant of the cause. In the middle of the last century 

 the snow on the summit of the Apennines appeared enveloped in sheets of flame ; and 

 in the winter of 1693 hay -ricks in Wales were set on fire by burning gaseous exhala 

 tions. 



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