LIGHT-PRODUCING ORGANISMS 15 



can be seen to glow like beads of fire wben it is flying 

 about a flame. Both, of these cases, are, however, purely 

 reflection phenomena and due to reflection out of the eye 

 again of light which has entered from some external 

 source. The correct explanation was given by Prevost in 

 1810. The eye of any animal is quite invisible in absolute 

 darkness. The same explanation applies to the moss, 

 Schistostega, which lives in dimly illuminated places and 

 whose cells are almost spherical, constructed like a lens, 

 so as to refract the light and condense it on the chloro- 

 plasts at the bottom of the cells. Some of this light is 

 reflected out of the cells again and gives the appearance 

 of self -luminosity. The alga, Chromophyton rosanofjii, is 

 another example of apparent luminosity, due to reflection 

 from almost spherical cells. 



There are several light phenomena known which have 

 nothing to do with living organisms. Commonest of these 

 is St. Elmo's fire ("corposants" of English sailors), a 

 glow accompainying a slow brush discharge of electricity, 

 which appears as a tip of light on masts of ships, spires 

 of churches or even the fingers of the hand. It is best seen 

 in winter during and after snowstorms and is a purely 

 electrical phenomenon. 



Less well known is th Ignis fatuus (Will-o'-the-Wisp, 

 Jack-o '-Lantern, spunkie), a fire seen over marshes and 

 stagnant pools, appearing as a pale bluish flame which 

 may be fixed or move, steady or intermittent. So uncom- 

 mon is this phenomenon that its nature is not well under- 

 stood, but it is believed to be the result of burning phos- 

 phine (PHg -f- P2H4), a self -inflammable gas, generated 

 in some way from the decomposition of organic matter 

 in the swamp. The difficulty witb this explanation is that 



