ON RADIANT MATTER. 



17 



Radiant Matter exerts Powerful Phosphorogenic Action v)here it 

 strikes. — I have mentioned that the radiant matter within the dark 

 space excites luminosity where its velocity is arrested by residual gas 

 ■outside the dark space. But if no residual gas is left, the molecules 

 will have their velocity arrested by the sides of the glass ; and here we 

 come to the first and one of the most noteworthy properties of radiant 

 matter discharged from the negative pole — its power of exciting phos- 

 phorescence when it strikes against solid matter. The number of 

 bodies which respond luminously to this molecular bombardment is 

 very great, and the resulting colors are of every variety. Glass, for 

 instance, is highly phosphorescent when exposed to a stream of radiant 

 matter. Here (Fig. 2) are three bulbs composed of different glass : 

 one is uranium glass («), which phosphoresces of a dark-green color ; 

 another is English glass {b), which phosphoresces of a blue color ; and 

 the third (c) is soft German glass — of which most of the apparatus 

 before you is made — which phosphoresces of a bright apple-green. 



My earlier experiments were almost entirely carried on by the aid 

 of the phosphorescence which glass takes up when it is under the influ- 

 ence of the radiant discharge ; but many other substances possess this 



phosphorescent power in a still higher degree than glass. For in- 

 stance, here is some of the luminous sulphide of calcium prepared ac- 

 cording to M. Ed. Becquerel's description. When the sulphide is ex- 

 posed to light — even candle-light — it phosphoresces for hours with a 

 bluish-white color. It is, however, much more strongly phospho- 

 rescent to the molecular discharge in a good vacuum, as you will see 

 when I pass the discharge through this tube. 



VOL. XVI. — 2 



