490 



this mysterious light, which burns without producing heat 

 sufficient to be recognised by our most delicate instruments, we 

 kuow but little. 



There are instruments so infinitely more sensitive than the 

 best thermometer, that they will record instantaneously an 

 increase of heat if a human being passes in front of them, 

 though at several yards' distance. Yet no effect is produced 

 on them by any of the Fire-flies or the Glow-worm. The 

 spectroscope itself gives little or no information, the spectrum 

 of the light being without bands or bars, and being what is 

 technically called a " continuous " spectrum. 



Last year I tried numbers of Glow-worms with the spectro- . 

 scope, and always with the same result. I never saw the Fire- 

 flies alive, but, no matter what may be the colour of the light, 

 the spectrum, whether of the Glow-worm or any of the Fire- 

 flies, seems to be always continuous, and so to give but little 

 information as to its source. 



There appears, however, to be little doubt that animal elec- 

 tricity is the real cause of this curious phenomenon, and that 

 the force which is expended in the torpedo and electric eel, in 

 giving shocks accompanied by slight electric sparks, may 

 develop itself in these insects by producing a continuous light. 

 And just as the electric fishes can emit or withhold the shock 

 as they please, so can the Fire-flies and Glow-worms give out 

 or retain the light by which they are so well known. 



Then we come to the multitudinous luminous inhabitants of 

 the sea, which, as many of my readers have probably seen, 

 convert the waves into rolling masses of living fire. 



Magnetism. 



Now we come to another condition of electrical force, called 

 Magnetism. 



One form of it is strongly developed in the Loadstone, an 

 ore of iron. This ore has the property of turning east and 

 west when suspended freely, it attracts any object made of iron, 

 and can communicate its powers to iron by merely stroking it. 

 There is in the Museum at Oxford a splendid specimen of the 

 Loadstone, which has imparted its virtues to thousands of iron 

 magnets, and has lost none of its virtues by so doing. 



All bodies are now known to be magnetic in some way or 



