190 PHOSPHORESCENCE. 
transformation depends upon the nature of the 
body and the intensity of the action. 
The phosphorescence of minerals, or mineral 
substances artificially produced, is an example of 
one of the vibrations of matter already alluded to, 
and which may be owed, in the first place, to heat, 
electricity, solar l'ght, chemical action, etc. In 
a great many cases, as Dessaignes and Becquerel 
have shown, electricity is the immediate vibration 
to which the light produced may be referred ; and 
that is the reason why bad conductors are more 
readily phosphorescent than other bodies, and, 
probably, why the most refrangible rays of the 
solar-spectrum are the only ones which will induce 
phosphorescence after isolation. 
My own idea of phosphorescence after insolation 
is as follows:—The light of the sun, acting upon a 
mineral substance, occasions a certain vibration 
(electric, chemical, or magnetic) ; but this vibra- 
tion not being able to continue when the action of 
hight ceases, that is, when the substance is placed 
in obscurity, the body gives back lhght whilst 
losing the vibration (electric, chemical, or mag- 
netic) occasioned in it by the rays of the sun. 
The body in question does not, in this case, give 
back the entire quantity of light it has recewed ; 
but a quantity equivalent to the electric, chemical, 
or magnetic vibration induced in it by the direct 
influence of the solar light. 
