PHYSICS. 319 



Miscellaneous . 



The fine white luminescence of cadmium phosphate, prepared as 

 prescribed by W. S. Andrews, has been examined with the disk phos- 

 phoroscope and spectrometer.* This substance is excited chiefly by 

 wave lengths too short to be transmitted through glass. The phosphor- 

 escence, though of measurable intensity only for a fraction of a second, 

 is of the persistent type, as shown by the form of the curve of decay. 



The changes of color during decay, as brought out by the phos- 

 phoroscopic method of observation, are remarkable and indicate that 

 the spectrum consists of a number of broad overlapping bands. The 

 approximate location of these has been determined. 



Data concerning the prevalence of series of constant frequency in 

 the fluorescence and absorption spectra of substances capable of 

 luminescence is being gathered by working up observations already 

 published and by new measurements. 



Thus recent photographs of the ultra-violet absorption spectrum of 

 anthracene by Mr. J. M. Hyatt show the presence of two or more 

 such series. The investigation in the case of most substances is 

 rendered difficult by the width of the bands, which often overlap; but 

 in all cases where it has been found possible to locate the bands series 

 of this description have been found, and we incline to the belief that 

 this spectral structure is characteristic of luminescence in general. 



The published report of the investigation of the kathodo fluores- 

 cence of willemite by Dr. T. B. Brown,t the progress of which has 

 been noted in previous numbers of the Year Book, contains the follow- 

 ing conclusions: 



(1) The fluorescence is directly proportional to the rate of impact 

 of the kathode particles as measured by the current through the tube. 



(2) The relation between the ratio of fluorescence to current and 

 the electronic kinetic energy as measured by the discharge potential 

 is non-linear, with indications of a maximum at higher potentials. 



(3) There is no indication of a minimum potential below which no 

 fluorescence would be produced. 



The studies of the fluorescence of the uranyl salts at room tempera- 

 ture by Miss Wick| and of new absorption bands in the spectra of 

 these compounds by Dr. Howes,§ referred to in the Year Book for 

 1917, have since been pubhshed. 



During the year duties connected with the war have taken much 

 of the time and attention of those engaged in the investigations 

 referred to in this report. They have, however, felt it no less a patriotic 

 duty to continue their work in pure science in such small ways as 

 might still be possible. 



* Nichols and Howes: Proc. Nat. Acad. Sci. (1918). 

 t Brown, T. B.: Physical Review (2), xi, 39 (1918). 

 % Wick, Frances G.: Physical Review (2), xi, 121 (1918). 

 § Howes, H. L.: Physical Review (2), xi, 66 (1918). 



