1 86 



STUDIES IN LUMINESCENCE. 



In the cell used in these determinations .v 2 was 36.5 mm. and .\\ was 

 2.5 mm. 



The coefficient a was determined by measuring the transmission of a cell 

 containing a sufficient thickness of the fluorescent liquid to reduce the 

 intensity of light of the wave-length of the middle of the absorption band 

 to about 40 per cent. The correction for the losses of light in the glass and 

 the solvent was determined by measuring transmission through the same 

 cell when filled with absolute alcohol (or in case of fluorescein with water) . 



The correction for absorption, like that for slit-width, is of importance 

 only in certain regions. The form of the fluorescence curves after the 

 application of both corrections is shown in Figs. 176 and 177. 



.50 



.55 



Fig. 180. 



.60 M 



THE ENERGY CURVES OF FLUORESCENCE. 



From the data corrected in the manner indicated in the two preceding 

 sections curves for the distribution of energy in the fluorescence spectrum of 

 the three substances under investigation were derived by multiplying each 

 ordinate of the corrected curves of Figs. 1 76 and 1 77 by the ordinate of same 

 wave-length in the energy curve of the acetylene standard (Fig. 173). 



The resulting curves are given in Fig. 180. They suggest by their form 

 a close resemblance between black-body radiation and fluorescence, except- 

 ing that the range of wave-lengths in the latter case is much smaller. 

 Attempts to find some simply modified form of Wien's equation which will 

 represent the results have thus far been unsuccessful. 



