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XXXVI. The Theory of the Flicker Photometer.— II. Un- 

 symmetrical Conditions. By Hekbert E. Ives and E. F. 

 Kingsbury *. 



Synopsis. 



1. Introduction. 



2. The Sensibility of the Flicker Photometer. 



3. Critical Frequency-Illumination Relations with Superposed 



Steady and Flickering Illuminations. 

 •4. Critical Frequency-Illumination Relations with Unequal Light 

 and Dark Intervals. 



(a) Theoretical. 



(b) Experimental. 



(c) Discussion. 



5. The Flicker Photometer with Unequal Exposures of the 



Compared Colours. 



6. Some Effects of Accidental Dissymmetry on the Critical 



Frequency and Flicker Photometer Phenomena. 



7. Summary. 



1. Introduction. 



IN a previous paper | we have developed a theory of the 

 action of the flicker photometer. The essential part 

 of that theory consists in the treatment of the visual appa- 

 ratus as a conducting layer of matter receiving and trans- 

 mitting intermittent radiation according to the general 

 physical laws or! conduction. The principal assumptions 

 are as follows : — 



1. That the stimulus is transmitted by a medium having a 

 certain " diffusivity," by reason of which the amplitude of 

 a fluctuating stimulus is reduced. 



2. That the disappearance of flicker occurs when the ratio 

 oi maximum to minimum of the transmitted impression has 

 a certain value. 



By the application of the Fourier conduction equation, 

 on the basis o£ these assumptions, it was shown that the 

 behaviour of the flicker photometer toward different colours 

 and at different intensities may be derived from the beha- 

 viour of the colours separately with respect to the critical 

 speed of disappearance of flicker. 



The previous paper dealt only with what may be termed 

 symmetrical conditions. Critical frequency relations were 

 studied only for equal dark and light exposures, the flicker 

 photometer was considered only for that case where the two 



* Communicated by the Authors. 



t "The Theory of "the Flicker Photometer," Ives & Kingsbury, Phil. 

 Mag. Nov. 1914, p. 708. 



