58 Mr. J. S. Dow on the Physiological 



Similarly for Vi(x), %i(x), and W X (V), e. g. 



e 2r >' x 3 



— - , where i/= -= + 0—7^- 



2x v2 b v2x 



27 



128 s/2x z 128a 4 



etc. 





cc. 



-a.M. 



-W^). 



1 



10 _1 x3-736 



10 _1 x2428 



2 



10" 2 x4-005 



10 _2 X3073 



3 



10" 3 X6-145 



10" 3 x5-072 



4 



10" 3 xll91 



10" 4 x 9343 



5 



10" 4 x2-070 



10" 4 X 1-829 



Y. Some further Notes on the Physiological Principles under- 

 lying the Flicker Photometer. By J. S. Dow, B.Sc* 



IN a paper read before the Physical Society of London in 

 1906 (see Phil. Mag. August 1906 ; Proc. Phys. Soc. 

 vol. xx.), the author discussed some of the phenomena of 

 colour-vision which affect heterochromatic photometry, and 

 referred to the theory, due to von Kries, of the action of 

 the minute light-percipient organs on the retina known as 

 the " rods " and " cones," by the aid of which some workers 

 in photometry have endeavoured to explain the "yellow spot " 

 and Purkinje effects. 



It was pointed out that, when the comparison of two 

 sources of light differing in colour was attempted, the reading 

 of a photometer of the " equality of brightness " pattern 

 would be found to depend upon : — 



(a) The obliquity at which rays from the illuminated 



surfaces strike the eye. 



(b) The distance away of the eye from the surfaces. 



(c) The size of the surfaces. 



It was, however, also found that, for some reason, the 

 effect was much less readily perceptible in the case of a 

 flicker photometer; and this suggested that the physiological 

 basis of such instruments might be found to differ from that 



* Communicated by the Physical Society : read November 12, 1909. 



