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 1'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 insolation. 



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 

 light ceases, that is, when the substance is placed 

 in obscurity, the body gives back light 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 received; 

 but a quantity equivalent to the electric, chemical, 

 or magnetic vibration induced in it by the direct 

 influence of the solar light. 



