DISTRIBUTION OF ENERGY IN FLUORESCENCE SPECTRA. 



177 



equality had been reached. In the meantime a third observer followed the 

 changes of temperature with the potentiometer and recorded the E.M.F. of 

 the thermo-junction for each setting of the spectrophotometer. Readings 

 were begun when a temperature of 1410 (absolute) was reached. Sub- 

 sequently the current was slightly reduced and further sets of readings were 

 made throughout the spectrum. 



t> 



HE 



E 



^ 



FUme 



Fig. 172. 



From these data the distribution of energy in the spectrum of the 

 comparison flame was computed. 

 Wien's equation 



I\=C\l 5 e~ 



AT 



Table 23. 



was taken as giving the energy in the region of the spectrum at which 

 measurements were made. The accepted value, for an ideal black body, 

 of the constant C 2 (i. e.,Ci = 14,500) was assumed to be applicable to the 

 present case, and the quantity C%/\T was calculated from the readings of 

 wave-length and temperature. 

 Since relative values only were 

 desired, the constant Ci was given 

 a value convenient for purposes 

 of computation. 



The two slits of the spectro- 

 photometer were maintained at a 

 constant width throughout, and 

 the distance (d) of the comparison 

 flame was varied until the inten- 

 sities of the spectra were equal. 



The energy of any given region of wave-length X was therefore propor- 

 tional to the ratio h/(i/d 2 ) where h was the energy of the corresponding 

 region of spectrum of the light from the black body, computed as above. 



Observations were made for twelve regions lying between 0.477 n and 

 0.656 m, and in the course of the determination the spectrum was traversed 



