192 



STUDIES IN LUMINESCENCE. 



Having computed in this way the intensity of the rays which actually 

 reach the region in the solution under observation, and which are therefore 

 available for producing excitation, it was only necessary to find the amount 

 of energy absorbed in each case by multiplying I e~ ,82a by a. Finally 

 the absorbed fluorescence, divided by the absorbed energy which produced 

 it, gave the quantity sought, that is, the intensity of fluorescence excited by 

 unit quantity of absorbed energy of the particular wave-length in question. 



In the case of eosin the observed data, as well as the derived quantities 



corresponding to several 



steps in the computation, 

 are given in Table 27. In 

 the case of resorufin the 

 same thing is shown graphi- 

 cally (Fig. 184). The ob- 

 served points in each case 

 are connected by full lines, 

 while in the case of com- 

 puted values the points are 

 connected by broken lines. 

 In curve / we have the in- 

 tensity of the exciting light 

 after reflection from mag- 

 nesium carbonate. Curve 

 77 gives the intensity of the 

 light actually reaching that 

 flie ordinates of curve 77/ are 



Curve III 



62// 



Fig. 184. 



Resorufin. 



part of the solution opposite the slit S' . 



obtained by multiplying each of the ordinates of curve 77 by a. 

 therefore gives the energy actually observed from the exciting light for each 

 wave-length. When the ordinates of curve IV, which shows the observed 

 fluorescence, are divided by the ordinates of curve 77/ we have the quan- 

 tity desired, namely, the fluorescence excited per unit of observed energy 

 (curve V). 



Table 27. Eosin. 



