EXPLANATION OF PLATE 1. 



Fluorite crystal No. 5. Magnesium spark as exciting source. 



Same crystal and spark, with inductance in the secondary discharge 



Same crystal. Iron spark. 



Same as No. 3, with inductance in secondary circuit. 



Fluorite crystal No. 4. Iron spark. 



Fluorite crystal No. 5. Cadmium spark. 



Fluorite crystal No. 4. Cadmium spark. 



Fluorite crystal No. 5. Aluminium spark. 



Same, with inductance in secondary circuit. 

 Fig. 10. Fluorite crystal No. 4. Aluminium spark. 

 Fig. 11. Fluorite crystal No. 4. Zinc spark. 



Fig. 12. Fluorite crystal No. 6. Arc between carbon terminals as exciting 

 source. 



In each photograph the exciting spark forms the two outer spectra and the 

 fluorescence spectrum is in the middle. 



