178 



STUDIES IN LUMINESCENCE. 



four times. Good agreement existed between the various readings in each 

 region with the exception of the observations immediately following changes 

 made in the resistance of the primary circuit. These were rejected and all 

 other readings were used in the computations and averaged for each wave- 

 length separately. The results are given in Table 23 and are shown graphi- 

 cally in Fig. 173. 



.48 .50 .52 .54 .56 .58 60 .be -64 66^ 



Fig. 173- 

 Distribution of energy in the spectrum of the acetylene flame. The points marked S correspond to Stewart's 

 direct measurements with the radiometer. The points marked .4 are derived from Angstrom's measure- 

 ments of the Hefner lamp. The dotted line is computed from Wien's equation. 



Table 24. 



Spectrophotometric comparison of the acetylene comparison flame, viewed through 

 the circular diaphragm and ground glass, with flame of a Hefner standard lamp. 



Wien's equation has been employed, although in quite a different way, 

 by Knut Angstrom 1 for the determination of the distribution of energy in 

 the spectrum of the flame of the Hefner lamp, and it is of considerable 

 interest to compare his determination, which involved neither the direct 

 measurement of temperatures nor observations upon a black body, with 

 the results of the experiment just described. 



o 



Angstrom, Nova Acta Upsaliensis, in, vol. xxn, 1904. 



