260 



Calcium Sulphide. 



Tlu> calcium suliiliide is the luminous sulphide as prepared by E. H. 

 8arg( nt tfc Company. Chemists, of Chicago. The sulphide was spread on 

 a cardlioaid witli nuu-ila.uc and excitisl by sunlight. A tin can was 

 placed around the iron pipe and aluminum window placed in the tin 

 can. ^^'ith this arrangement some of the external heating effects were 

 eliminated. 



,C I fl/A P. 



60 SaC . 



PLRTE .U , 



riiotographs III and IV were taken with tlie sulpliide screen parallel 

 to tiic aluminum windoA\ so that the rays must fall on the back side of 

 the screen while their effect was photographed from the front side. 

 Photograph III was taken with the sensitive plate about 4 cm. from 

 the screen while IV Avas less than 1 cm. and in no case was the sulphide 

 screen more tlian 2." cm. from the source. In III the exposures were 

 alternated .<o that 2. 4. (J and S were exposed to all radiations that 

 might come from a Welsbach l)urner and ])ass tlirough an aluminum 

 window, while 1, W, ."> and 7 were taken when a lead screen was placed 



