DISTRIBUTION OF ENERGY IN FLUORESCENCE SPECTRA. 



181 



was placed in front of slit b. In the figure, A is the comparison flame; si 

 and s 2 are screens to prevent stray light from entering slit a; f is the cell of 

 fluorescent liquid, and C. II. is the Cooper-Hewitt mercury arc lamp. 



The procedure was as follows: 



vSlits a and b were set at equal widths of 50 divisions =0.05 cm. The 

 comparison flame was then moved up to a point on the track just in front 

 of the aperture in screen s 2 - The observing telescope was set for that 

 region of the spectrum corresponding with the maximum of the fluorescence 

 band to be measured. The fluorescent solution in cell / was diluted until 

 its spectrum for that region was slightly stronger than the corresponding 

 region in the spectrum of the comparison flame. By slightly shifting the 



63y& 



Fig. 176. Eosin (to left) and resorufin. 

 The observed points are marked by circles. 



.S4 S6A 



Fig. 177. Fluorescein. 



The observed points are marked 

 by circles. 



observing telescope in either direction two places could now be found, lying 

 a short distance from the crest of the fluorescence band, at which the two 

 spectra were of equal brightness. The circle readings of these positions 

 were noted, and the position of the comparison flame was read upon the 

 scale of the photometer track. The flame was then moved to a slightly 

 greater distance from slit a, and two new positions were found for the observ- 

 ing telescope, corresponding to points of equal brightness of the band 

 farther from the crest. In this way the entire band was explored several 

 times, and from these sets of readings the intensity of the band at various 

 wave-lengths was computed in terms of the corresponding intensities of the 

 spectrum of the acetylene flame. 



