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LXXIV. The Theory of the Flicker Photometer. 

 By Herbert E. Ives and Edwin F. Kingsbury*. 



Synopsis. 



1. Introductory Review of Experimental Facts about the Flicker 



Photometer. 



2. Geueral Outline of Theory , 



3. Mathematical Development. 



4. Comparison of Experimental and Calculated Values. - 



5. Discussion of some Consequences of Theory. 



6. Colour Flicker and Brightness Flicker. 



7. Summary and Conclusions. 



1. Introductory Review of Experimented Facts about 

 the Flicker Photometer 



TWO papers by one of the present writers t, which 

 appeared in the Philosophical Magazine for July and 

 September, 1912, dealt with a number of newly discovered 

 phenomena of the flicker photometer and with the relation- 

 ship between brightness and the critical speed of flicker. 

 Certain similarities were found to exist between the results 

 from the two methods of photometry, which suggested that 

 a theory of the flicker photometer should be capable of de- 

 rivation from the critical frequency-illumination behaviour 

 of the individual colours which in the flicker photometer are 

 alternated with each other. The most striking similarity 

 was that each method exhibited a reversed Purkinje effect. 

 A difference was that the critical frequency-illumination 

 relationship was found to conform to a very simple law, 

 while the relative values of different colours at different 

 illuminations as given by the flicker photometer appeared to 

 follow no simple system. 



In the present paper it is shown how, by considering the 

 visual apparatus to possess the practically universal charac- 

 teristics of physical recording instruments — namely, a co- 

 efficient of conductivity and a coefficient of capacity (such as 

 thermal), as represented by the constant (diffusivity) in the 

 Fourier conduction equation — the complicated behaviour of 

 the flicker photometer is completely explained from the 

 critical frequency phenomena. 



In order for the present paper to be understood, the 

 salient points of the earlier articles must be reviewed. This 



* Communicated by the Authors. 



t " Studies in the Photometry of Lights of Different Colours." 

 H. E. Ives. 



