280 NICHOLS— PHOSPHORESCENCE. [April 22, 



fluorescent and phosphorescent substances made by Professor Mer- 

 ritt and the present writer, of which a few typical examples have 

 been given in this paper, lead to the following general conclusions. 



1. The emission spectra of fluorescent and phosphorescent bodies 

 even when they appear to consist of a single broad band are fre- 

 quently complex consisting of a group of overlapping bands. 



2. The various components of a broad band vary in intensity 

 (both relative and absolute) with the temperature. 



3. Sometimes neighboring components of a band are similarly 

 affected by a given change of temperature; sometimes they are op- 

 positely aflfected, one component increasing in brightness while 

 another diminishes. 



4. Change of temperature is frequently accompanied by a shift 

 of the bands of a fluorescence spectrum and this shift, which is 

 sometimes toward the red and sometimes towards the violet, appears 

 in many cases to be due to simultaneous and opposite changes in the 

 intensity of overlapping components. 



5. The rate of decay of phosphorescence depends upon the tem- 

 perature and the complexity of the changes observed when the, 

 phosphorescent light is studied as a whole may probably be ascribed 

 the independent variations, as to brightness, duration and position 

 of the various overlapping bands 3f which the spectrum is com- 

 posed. 



6. Many of the changes in the color of fluorescence and phos- 

 phorescence may be ascribed to these independent variations in the 

 intensity and differences in the duration of the overlapping com- 

 ponents. 



Physics Laboratory of Cornell University, 

 April, 1910. 



