236 REPORTS OF INVESTIGATIONS AND PROJECTS. 



XVIII, p. 355, 1904) dealt with those changes in the fluorescence and phos- 

 phorescence of nearly 200 substances under the action of ultraviolet light and 

 the X-rays, which could be directly noted by inspection when the substances 

 were cooled to the temperature of liquid air. Up to the present time, with 

 the exception of an important photographic investigation by Becquerel, noth- 

 ing further has appeared. 



Our present work consists in measurements with the spectro-photometer of 

 the fluorescence bands of several typical substances (willemite, anthracene, 

 resorufin, and fluorescein) at temperatures ranging from -f-20° C. to 

 -185° C. 



The data obtained make it possible to plot the energy curves of the fluores- 

 cence spectra of these substances for any temperature within these limits, to 

 indicate the effect of temperature upon the intensity of any wave-length of 

 the spectrum, and to describe the progressive changes as regards intensity, 

 width, and location of the various bands. 



The remarkable shifting and narrowing of the fluorescence bands, together 

 with successive increases and diminutions of intensity with lowering temper- 

 ature, indicate a complexity of phenomena that can be elucidated only by 

 further study, and measurements are now in progress upon the correspond- 

 ing variations in the absorption spectra of these substances when cooled to 

 the temperature of liquid air. 



Mr. R. C. Gibbs, under our direction, has made a very complete spectro- 

 photometric study of the effect of temperature upon the absorption and 

 fluorescence of uranium glass. The range of temperature in his experiments 

 is from 300° C. to —185° C. 



The experiments on short-time phosphorescence, the beginnings of which 

 were described in the Physical Review, vol. xxvii, page 209, have been con- 

 tinued throughout the year by Dr. C. W. Waggoner, who made use of the 

 new "wheel" phosphoroscope ; a form of instrument especially devised for 

 this investigation. He has also been engaged in the development of methods 

 of preparing phosphorescent compounds of known composition and definite 

 heat treatment in the electric furnace and has produced several series of such 

 compounds in which manganese, cadmium, etc., are the active components. 

 In this work he was assisted by Mr, B. H. De Long, a chemist paid from the 

 funds placed at our disposal by means of the grant from the Carnegie Insti- 

 tution of Washington. 



Mr. H. E. Howe has completed an experimental investigation, highly in- 

 structive although negative in result, concerning the electrical conductivity 

 of fluorescent vapor of anthracene. 



Dr. C. A. Pierce has continued his extended photographic studies of 

 thermo-luminescence, the earlier results of which were published in two 

 papers in the Physical Review (vol. xxvi, pp. 312 and 454). 



