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CHAPTER VI. 



DURATION, INTENSITY, AND COLOUR OF PHOS- 

 PHORIC LIGHT IN MINERAL BODIES. 



THE duration, the intensity, and the colour of 

 phosphoric light produced by mineral substances, 

 depend upon the nature of the phosphorescent body. 

 I shall mention only a few examples of colour. 

 The most general tint of light is that seen in the 

 glow-worm and other phosphorescent animals, of 

 which we shall speak hereafter ; it is a greenish- 

 yellow light, at times approaching to whiteness. 

 Some bodies however appear, during their phos- 

 phorescence, to emit light which differs a little 

 from this as to its colour. Certain marbles and 

 amber (succinum) give a phosphorescent light of 

 a golden yellow ; some specimens of fluor-spar, 

 arseniate of lime, and chloride of calcium, emit a 

 greenish light; other varieties of fluor-spar pro- 

 duce a bluish-violet radiation, and that which is 

 called Chlorophane gives a green phosphorescence. 

 Oriental garnet shines with a reddish phosphores- 

 cence, whilst Harmotome (a sort of zeolite) gives 



