x PREFACE. 



cause of the varied phosphoric phenomena with 

 which observation has already furnished us, or to 

 explain these phenomena in a satisfactory manner. 

 A flame is always a flame, light is everywhere 

 light ; but it remains necessary to ascertain how 

 this light is produced in the different circum- 

 stances under which it is observed. I myself do 

 not pretend to have snatched from Nature the 

 entire secret of Phosphorescence, but I have 

 reasons to hope that the observations contained 

 in this work will prove, that, owing to the 

 rapid progress that natural science has made 

 during the present century, I have been able 

 to tread in a firmer path than many who have 

 preceded me, and that I have penetrated a little 

 way into the track which will conduct us finally 

 to the desired goal. 



My work is essentially divided into four parts. 

 The first treats concisely of mineral phospho- 

 rescence ; it includes also the history of certain 

 meteorological manifestations of light, some of 

 which are extremely remarkable. In the second, 

 I have said what I know of the emission of light, 

 by plants and vegetable substances ; and have pro- 

 ceeded in the third division to investigate the 



