181 
CEAP THE, I: 
THEORY. 
Ir will be easily seen, by examples that have been 
brought forward in preceding chapters, how diffi- 
cult and how ineffectual have been the attempts 
to give a satisfactory explanation of phospho- 
rescence. T'heopinions on this subject published by 
Dessaignes and Becquerel certainly merit the most 
consideration. The theory to which they lead may 
be seen condensed in the following paragraph :— 
“Tt is perfectly demonstrated, at the present 
day, that an evolution of electricity takes place 
in bodies whenever the equilibrium of their mole- 
cules undergoes a change of any sort, either in 
their chemical constitution or in their physical ag- 
oregation. If these molecules are not separated 
thereby, we observe a recomposition, more or 
less rapid, of the two electricities that, for an 
instant, were put in hberty; and this may deter- 
mine, according to the nature of the body and 
the tension of the electricity, a production of 
