Instructions for Making Phosphorescent Screens 

 adapted for the Observation of " N " Rays 



(i) If one proposes only to ascertain the 

 production of " N " rays in given circum- 

 stances, a phosphorescent screen, made as 

 follows, may be used with advantage : some 

 powdered calcium sulphide is mixed with col- 

 lodion, diluted with ether, so as to form a very 

 thin paste ; then, with a water-colour brush, 

 drops of this paste are painted on blackened 

 cardboard, so as to produce stains several milli- 

 metres in diameter, close to each other. The 

 screen then presents the aspect of a spotted 

 fabric. If, after being exposed to light, it is 

 examined in a dark room, and in perfect silence, 

 some of the spots will appear less luminous 

 than the others. Usually, some will not seem 

 to be sharply separated from their neighbours, 

 but will form a sort of confused nebula less 

 visible than the rest. Now, if one speaks aloud 



