16 PHOSPHORESCENCE 



Dessaignes and the elder Becquerel have re- 

 marked that those bodies which are good conductors 

 of electricity are not phosphorescent after insola- 

 tion. We shall have occasion to refer again to this 

 important fact. Biot and Becquerel have both 

 proved that electricity acts upon the solar phos- 

 phori in the same manner as insolation. An elec- 

 tric discharge renders them luminous in the dark 

 for some time after the discharge has passed (a 

 discovery originally made by Grothuss, and with 

 which both Canton and Dessaignes were familiar) , 

 and they have also shown that differently-coloured 

 rays of light modify this action in the same man- 

 ner as the differently- coloured rays of the solar 

 spectrum. Moreover, phosphori that have lost 

 their phosphorescence, or that have ceased to shine 

 in the dark after a first insolation, recover their 

 luminous property when acted upon by the electric 

 light an observation we owe to Grothuss and 

 Becquerel and when this light is passed through 

 certain transparent screens, such as plates of glass, 

 of quartz, or different salts, it is observed that these 

 screens become obstacles and sometimes com- 

 pletely prevent any phosphorescent radiations. 



Electric discharges proceeding from a battery 

 communicate a recognizable phosphorescence of a 

 longer or shorter duration, to a great number of 

 bodies which are bad conductors or non-conductors 

 of electricity. This phenomenon may be observed, 



