PHOSPHORESCENCE. 69 



he went out of the room, but the natural pheno- 

 menon generally recedes as we approach it. 



It is a common practice, in chemical lectures, to 

 imitate the Will-o'-the-wisp by throwing fragments 

 of phosphuret of calcium into water, when flames 

 arise, owing to the spontaneous combustion of 

 phosphuretted hydrogen gas. But the imitation 

 is very bad indeed, and can hardly be said to 

 resemble the mysterious natural phenomenon, 

 much less explain it. For my own part, I think 

 the ignis fatuus to be sometimes the light from a 

 burning gas, which light is invisible in the day- 

 time, and at other times to be connected with 

 those curious cases of luminous mists mentioned 

 above, and in which electricity doubtless plays an 

 important part. 



The luminous appearances known in Scotland 

 as Elf-candles belong either to this category of 

 phenomena, or to that which will be treated of in 

 a future chapter of this Work. 



