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and it is their confusion under one name that has caused the 

 considerable degree of mystery that has become attached to it. 

 The luminous owl is quite a simple phenomenon in itself, and apart 

 from its moving luminescence has none of the features character- 

 istic of the Ignis Fatuus. The dancing swarm of midges that have 

 become luminous owing to pathological causes is a nearer approach 

 to our ideal, though its motions are very different from those of the 

 popular conception. 



We also see that the popular explanation of the mystery, viz ;— 

 the spontaneous ignition of marsh gas evolved from decaying 

 organic matter, though supported by definite scientific observations 

 relates not to the Will-o'-the-Wisp, but to a very different 

 phenomenon that should be designated by a difi'erent name, such as 

 ' Marsh Lights' or 'Marsh Fires.' If we asi< how it is that this 

 explanation is now so widely received at the expense of the older 

 and once very popular theory of the insect origin of the light, I can 

 only suggest that it is because of its scientific foundation in 

 contrast with the unsatisfactory and unconvincing nature of the 

 evidence for the latter, and consequently, since it was the only 

 explanation in the field that was in any way satisfactory, the fact 

 that phenomena of very different character were involved has 

 continued to be overlooked. 



That the Ghost Swift Moth is the true source of the popular 

 legend of the Will-o'-the-WiU is in my opinion practically certain, 

 smce it is the onbj simple and natural solution of the luminous 

 insect theory. It is of course possible that the mystery of the 

 luminous insect may not be so simple as I contend, that it mm/ 

 .depend on some rare instance of an insect becoming luminous owing 

 to pathological causes, but the probabihties ^ against such a 

 supposition are immense. At the same time that the simplicity of 

 the Ghost Swift theory is a very strong point in its favour, in some 

 ways this very simplicity militates against it, for if that be the 

 true explanation of the Will-o'-the-Wisp how is it that it has not 

 been proved to be so beyond question long ago ? Probably because 

 the testimony of a few sturdy countrymen, who had convinced 

 themselves that it was nothing but a fly, a " Moggy-long-legs," was 

 insufficient to outweigh the very circumstantial evidence^ of the 

 marsh gas explanation that appealed so much more forcefully to the 

 theoretical scientist ; and because with the spread of the study of 

 entomology the Ghost Moth has become more generally known for 



