368 CARNEGIE INSTITUTION OF WASHINGTON. 



These variations consist chiefly in the number, spacing, precise loca- 

 tion, relative brightness, and sharpness of the narrow bands in the 

 groups into which the bands are resolved on cooling; in slight differ- 

 ences in frequency intervals of the fluorescence series and absorption 

 series; in slight shifts in location of the groups as a whole, and of shifts 

 and minor rearrangements which appear to be dependent in some way 

 upon molecular weight, water of crystallization, and particularly upon 

 crystal form. 



Minor Investigations Completed, in Progress, or in Prospect. 



The work on the luminescence of the rare earths, of which a brief 

 preliminary account has already appeared,^ is being continued. Spectra 

 of the kathodo-luminescence and absorption of various preparations 

 of the oxides of neodymium, praseodymium, cerium, and erbium are 

 in process of observation and mapping. 



Drs. Wick and Wilber have in hand a study of the phosphorescence 

 of these compounds, and Dr. Howes is preparing for the investigation 

 of their luminescence at high temperatures. 



Miss Wick is also planning to investigate the photo-luminescence, 

 kathodo-luminescence, and the remarkable tribo-luminescence of the 

 double silicate known as hexagonite. 



The results of the study of the selective emission from erbium oxide, 

 made by the late Dr. Mallory, have been published in the Physical 

 Review.^ 



Papers have also appeared on the fluorescence and absorption of 

 the uranyl acetates^ and sulphates.^ 



^ Physical Review (2), 



* Mallory (with a note by E. L. Nichols): Physical Review (2), vol. 14, p. 54 (1919). 

 » Nichols, Howes, and Wick: Physical Review (2), vol. 14, p. 201 (1919). 



* Nichols and Howes: Physical Review (2), vol. 14, p. 293 (1919). 



