XIII. ACTION SPECTRA AND ABSORPTION SPECTRA 



445 



S. = A^' IsTeX d\ 



(23) 



Values of Sz cnn be ol)tained graphically from curves such as those 

 sho\\Ti in Figure 7. This is a useful method where experiments have 

 to be done out of doors with sunlight as the source, for example, when 



450 



500 

 WAVELENGTH, m/i 



550 



Fig. 7. Absorption {E) of radiation from a tungsten filament lamp of known 

 spectral characteristics, by a solution of eosin (/seX). Numbered curves are the 

 same through filters of known transmission {I JTeh) (see equations 22 and 23) 

 {12h). 



photosensitization of domestic animals by plant pigments is in ques- 

 tion {2, Ch. 12-15, 19; 27). In this case data for the solar spectrum 

 compiled by Moon {21) are useful. 



4. General Remarks 



The interpretation of an action spectrum may depend in consider- 

 able part upon biological information that does not enter into the 

 measurements themselves. There are certain effects that may be 

 grouped together, and there is a limited number of photoehemically 

 active substances to be found in biological systems ; both facts must 

 be taken into consideration when interpreting the experimental find- 



