D4 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 1s 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, owmg 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 hght, 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 
