c: 



PROCEEDINGS 



OF THE 



AMERICAN PHILOSOPHICAL SOCIETY 



HELD AT PHILADELPHIA 

 FOR PROMOTING USEFUL KNOWLEDGE 



Vol. XLIX August-September, 1910 No. 196 



THE EFFECTS OF TEMPERATURE ON PHOSPHORES- 

 CENCE AND FLUORESCENCE.! 



By EDWARD L. NICHOLS. 



(Read April 22, igio.) 



Fluorescence and phosphorescence are closely connected phe- 

 nomena, the precise relation of which is not completely settled. In 

 a general way we may say that the emission of light by a body 

 under any one of the numerous stimuli which produce luminescence 

 when observed during excitation is termed fluorescence; the after 

 glow is phosphorescence. According to the quite generally accepted 

 view, first expressed by Wiedemann and Schmidt- and since de- 

 veloped by ]\Ierritt^ and in somewhat different form by Lenard* and 

 others, luminescence is a phenomenon of dissociation in which nega- 

 tive ions or in the language of Lenard " electrons " are separated 

 from the molecules by the action of light, cathode rays, X-rays, the 

 radiation from radioactive materials, etc. These are supposed to 

 return later to the aggregation from which they have been torn 

 loose or to some other molecule and to produce by their collision 

 the vibrations which are the source of the emitted light. 



^ The apparatus used in the experiments described in this paper was pur- 

 chased in part under a grant from the Carnegie Institution. 



-Wiedemann and Schmidt, Annalcn dcr Physik, LVL, 1895, P- 1/7. 

 'Nichols and Merritt, Physical Review, XXVII., 1908, p. 368. 

 * Lenard, Annalen der Physik, XXXI., 1910, p. i. 



PROC. AMER. PHIL. SOC. XLI.X. I96 R, PRINTED SEPTEMBER 6, I9IO. 



