42 PHOSPHORESCENCE 
These striking experiments were made some 
few years ago by Professor Quet, and have ex- 
cited general admiration wherever they have been 
seen. Now it has occurred to M. Hd. Becquerel, 
to enclose certain phosphorescent substances, such 
as sulphide of barium, etc., in glass tubes, in 
which a vacuum has been produced by the air- 
pump, and to submit them in these circumstances 
to the action of M. Ruhmkorff’s apparatus. 
We have already seen that sulphide of barium, 
of strontium, of calcium, diamonds, chalk, etc., 
acquire phosphorescence when submitted to an 
electric discharge in the air; as soon as the dis- 
charge has passed, they glow with phosphoric 
light of short duration, just as if they had been 
exposed to the sun, or as if they had been heated ; 
for these substances are phosphorescent by light, 
by heat, and by electricity. But when they are 
submitted to the rapid series of discharges of the 
induction apparatus in highly-rarefied air, that 1s, 
in the void produced by the air-pump, the effect 
is very striking. The substances named glow 
continuously with a vivid phosphoric lght, so 
long as the discharges continue to pass.* 
In these experiments it has been observed, that 
the glass of the tubes becomes slightly phospho- 
rescent at the same time as the sulphides. 
Quet made known in 1853 a very curious pro- 
* See Ed. Becquerel, Ann. de Chim. lv. p. 92 e¢ seq. 
