16 PBOCEEDINi I III-: A MM lilt AN ACADEMY. 



lowing certain definite bands in these spectra. Leooq 17 about as Long 

 Baur ami his students thought thai they had Bettled the matter finally. 18 

 I'rliaiii 10 has done wonderful work in separating the elements of the 

 ran- earths, and his opinion is undoubtedly of more importance than 

 that of any one else. An explanation along these lines must include 

 not only the case of a single chlorophane, hut it must cover also the 

 cases where the fluorescence, bhermo-luminescence, and kathodo-lumi 

 aesoence of the Bame crystal of fiuorite arc all different, even in their 

 minute details. 



While the author cannot expect to test the question by synthesis, 

 further study of the rare elements which are present in fluorites is 

 already under way, and examination of the light emitted by these same 

 fluorites under excitation by other mean- will also be taken up as > | 



a- possible. 



The author's thanks are due to the American Academy for a gener- 

 ous appropriation from the Rumford Fund, which has been of the 

 utmost assistance in this work. 



Tin: .ii.i i us'iv Physical Laboratory, 



Harvard Univbrsity. March 20, L907. 



17 Papers by Lecoq de Boisbaudran on this Bubject, to the Dumber "f thirty or 

 more, are n> be found in the Comptea rendu*, beginning with volume 100, and 

 continuing for many yean. 



« Her. d. d. Chem. Ges., 33. 1748, and 34. 2460. 



19 A \ i>ry complete bibliography of all the literature <>n the yttrium and cerium 

 earths is thai "i" Meyer, Bibliographie dei seltenen ESrden. (Leopold Voss, 

 Leipzig, 1906.) 



