MORSE. — THE KATHODO-LUMINESCENCE OF FLUORITE. 



11 



and these might be expected to be a property of the crystal, and to per- 

 sist under other forms of excitation. None of these lines appear in 

 either the thermo-luminescence or kathodo-luminescence of these crys- 

 tals. That the same substance can, however, give the same spectrum 

 under excitation by light and by heat has been shown by Becquerel, 12 

 and Urbain 13 has proven that the same spectrum, modified only slightly, 

 is shown by the same substance under excitation by kathode rays. 

 The necessary conclusion from the author's experiments is, however, 

 that this is by no means always the case. The purple Weardale fluorite 

 (No. 5) has been most carefully studied both in fluorescence and in 

 kathodo-luminescence, and there is no relation whatever between these 

 spectra as far as the wave-lengths of lines are concerned. The West- 

 moreland fluorite, and that from Amelia Court-House, have been inves- 

 tigated in both thermo-luminescence and kathodo-luminescence, and 

 no coincidences of importance are visible. 



Plate gives a very good idea of the relation between the kathodo- 

 luminescence spectra of the seven crystals examined. The two upper 

 spectra are very evidently similar. They are both "chlorophanes," 



12 Journal de physique, 68, 444, and 69, 109. 



13 Comptes rendiis, 143, 825 (1906). 



