PHYSICS. 413 



(3) Many, if not all, of the substances susceptible to flame-excitation 

 fluoresce at the same temperatures under kathode bombardment, and 

 when further heated the temperature at which they become inactive 

 is the same for the two types of excitation. 



(4) The luminescence spectrum under kathode excitation appears 

 in general to be the same as for flame excitation. 



(5) Many of the substances in question are excited by X-rays 

 throughout the range of active temperatures. 



Papers describing oiu- preliminary observations on flame excitation, 

 on the spectra of this high-temperature luminescence (by Professor 

 Howes), and on the type of decay of phosphorescence (by Mr. Wilber) 

 will be published shortly. 



Since the annual report of 1919, papers have appeared on the uranyl 

 acetates^ and on the uranyl sulphates.^ 



Dr. Murdock's paper on photo-active cells covering his investiga- 

 tions of several years past is ready for publication. 



The first of a series of papers by Dr. Howes on the kathodo-lumines- 

 cence of the rare earths is in the press. His measurements of the 

 fluorescence spectra show groups of very narrow bands arranged in 

 constant-frequency intervals. The constitution of the spectrum, at 

 least in the case of samarium, which forms the subject of this pre- 

 liminary paper, is independent of the amount of the element in solid 

 solution and of the heat treatment. 



The rare earths used in these experiments are of extraordinary purity, 

 being due to the kindness of Professor James, of New Hampshire Col- 

 lege, who isolated them. The solid solutions were prepared by Dr. 

 D. T. Wilber. 



^Fluorescence and absorption of the uranyl acetates, Nichols, Howes, and Wick, Physical 

 Review (2), xiv, 201. 

 ^Ibid., 293. 



