102 



p. LATIMER AND E. I. RABINOWITCH 



Some pigment fluorescence could be measured together with the 

 scattered hght. In spectral regions away from the fluorescence bands, 

 colored glass filters were used to prevent this contamination. Close 

 to and in the fluorescence bands, it was necessary to measure the sum 

 of the scattered light and fluorescence, and to correct for fluorescence. 

 This correction could be based either on the different spectral com- 

 positions of the two components or on their difi"erent degrees of polari- 



400 450 500 550 600 650 

 WAVE LENGTH m/i. 



700 



750 



Fig. 3. Scattering and absorption of the diatom Navicula minima. 



zation. The first method failed near the peak of the fluorescence band; 

 the second had no such limitation. 



To determine the fluorescence correction with colored filters, the 

 transmission factor of a filter for scattered light, Tg, was determined 

 at each wavelength with a white surface in the beam, and that for 

 fluorescence, Tf, by exciting the fluorescence wdth light which ap- 

 propriate filter combinations could prevent from entering the de- 

 tector. From the observed average transmission factor for com- 

 bined scattered light and fluorescence, Ts,f, the fraction of detector 

 response due to scattering, x, was found by means of the eciuation: 



TsX+ Tr{l~x) = Ts.f 



This method of determining the fhiorescence correction was used by 

 us with two tj^pes of colored filters — one which preferentially trans- 



