CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL LABORATORY, 



HARVARD UNIVERSITY. 



STUDIES ON FLUORITE. 



IV. THE KATHODO-LUMINESCENCE OF FLUORITE. 

 By Hakby W. Mokse. 



Presented by John Trowbridge. Received March 20, 1907. 



I, In previous papers which have been presented to the American 

 Academy by the author, data on the light emitted by crystals of fluor- 

 ite from various localities, excited by light ^ and by heat,^ have been 

 discussed. The present research contains data on the spectra of the 

 light emitted by various fluorites under excitation by kathode rays. 



It was found in the first research that many fluorites, if not all, give 

 discontinuous spectra when excited by the light from certain sparks. 

 The metals which have strong ultra-violet lines in their spark spectra, 

 used as terminals for the passage of a strong spark, excite lines of 

 fluorescence in these fluorites ; and while these lines are in most cases 

 somewhat diff"use and broad in appearance, they are in other cases 

 apparently as sharp as the metallic lines which excite them. 



In the later paper, data has been given on the light emitted, in two 

 typical cases, by fluorites under excitation by heat alone. Here again 

 the spectra are discontinuous, and contain, beside broad-banded por- 

 tions, lines which are quite sharp. 



The spectroscopic side of the luminescence of fluorite is not ex- 

 hausted by a study of the fluorescence and thermo-luminescence 

 spectra. This mineral is most remarkable in the great variety of 

 ways by which its luminescence can be excited, and it is known to 

 emit light under the influence of kathode rays, X-rays, and radium 

 radiation, as well as by simply rubbing or breaking a crystal. 



Parallel with the spectroscopic investigation of the light emitted by 

 the crystals under various excitations, a careful series of investigations 



^ The Fluorescence Spectrum of Fluorite, Astrophysical Journal, 21, 83 

 (Mar. 1905) ; Studies on Fluorite, I. These Proceedings, 41, 587 (Mar. 1906). 

 2 Studies on Fluorite, II. These Proceedings, 41, 593 (Mar. 1906). 



