72 



COLOUR VISION 



The dissimilarity of the peripheral and achromatic scotopic luminosity 

 curves shows that Hess's experiments do not prove all that he attributed 

 to them, for he chose colours of equivalent " white value " and stated 

 that they remained good matches both in peripheral photopic and in 

 scotopic vision. The matches are valid only for peripheral photopic 

 or scotopic vision. 



On comparison of the peripheral photopic luminosity curve with 

 Konig's and Abney's luminosity curves, making allowance for the fact 

 that the two former are with gas light, the latter with arc light, we see 

 that they agree, so that the statement on p. 71 is correct. Polimanti 1 

 has confirmed the statement on the same individuals using the same 

 apparatus and source of light with the flicker method (Fig. 26). 



Afe-2-5 /Va-2Ai-1-5/Va-1 A'i-0-5 Na 



Fig. 26. Photopic periphery luminosity curve (flicker method). 



Photopic central luminosity curve (flicker method). Photopic 



periphery luminosity curve (equality of brightness method). Abscissae, arbitrary 

 scale of wave-lengths of prismatic spectrum of gas light, measured from the 

 D line (Na), with certain absolute wave-lengths indicated ; ordinates, arbitrary scale. 

 (Polimanti.) 



Siebeck 2 , using minimal fields, has adduced further confirmation. 

 He found that with spectral lights of moderate intensity it was impossible 

 with accurate foveal fixation to abolish the sensation of colour without 

 that of light by reduction of the field, but that this was readily effected 

 1'5 from the centre. He compared the luminosities of the lights under 



1 Ztsch.j. Psychol. u. Phyx'iol. d. Sinnesorg. xix. 272, 1899. 



2 Ibid. XLI. 89. 1907. 



