136 STUDIES IN LUMINESCENCE. 



DISCUSSION OF RESULTS. 



The accuracy of individual measurements with a non-direct method, such 

 as the photographic method described in this chapter, is not great. Con- 

 clusions must be drawn from the indications of many experiments, rather 

 than from the too exact interpretation of a single determination. A general 

 survey of the curves obtained, of which only few examples have been given, 

 shows that the minima, corresponding to the maxima of the usual curves of 

 distribution previously employed, occur within the limits X = 0.555 ^0.003. 

 These limits were seldom exceeded and the variations were not consistent 

 with each other. For some sets of curves the limits could be contracted to 

 0.002 n or possibly to 0.001^. Hence, if the maximum of the band 

 changed under any of the conditions, it must have been within the limit 

 == 0.003 M an d probably within even smaller limits. From certain considera- 

 tions, such as the bend in the decay curve of phosphorescence, and the 

 smooth, symmetrical shape of the whole band, one would expect, if the two- 

 band theory is correct, a considerable change in the band under the condi- 

 tions studied. No changes were found that were not explained by the 

 limitations of the method. 



Hence the following conclusions are drawn from the work above : 



1 . The fluorescence and phosphorescence bands of Sidot blende coincide 

 with each other. 



2. No change in the position of the band of phosphorescence occurs with 

 decay in the case of either Sidot-blende or Balmain's paint. 



3. No change in the position of the band of fluorescence occurs under the 

 action of infra-red rays. 



4. No change in the position of the band of fluorescence occurs with a 

 change, between +20 and +120 , in the temperature of the powder. 



5. No change in the shape of the band, discernible by this method, was 

 found under anv of the above conditions. 



