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discovery originally made by Grothuss, and with 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 m 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 msolation, 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, 
