174 STUDIES IN LUMINESCENCE. 



The observations contained in Table 22 indicate a positive fluorescence 

 absorption of 15 per cent. But if we apply the additional zero correction 

 called for by the calibration curve of Fig. 164 the difference between F-\-T 

 and C is reduced to 0.9 division or 4.3 per cent. In other cases an equally 

 large negative result was obtained. 



The results of all of these experiments, which have been repeated many 

 times, and performed with more precautions to avoid false results than can 

 be indicated in this brief account, has been to convince us that the previous 

 results of both ourselves and of Miss Wick are due to some systematic 

 error, and that the supposed increase in absorption due to fluorescence 

 either does not in reality exist or is too small to be detected by these methods. 

 We have not been able to determine the exact nature of the error which 

 led to our preceding results. The peculiar relation between slit opening 

 and intensity brought out in Fig. 164 will explain some of the results but 

 not all. Another source of error which might have been an important one 

 is that resulting from the neglect of the slit- width correction, to the impor- 

 tance of which attention is directed in Chapter XII of this memoir. 



