172 



COLOUR VISION 



V. Kries found the observed value to be 137, and so on, as in the follow- 

 ing table. 



From this table we also see that the stimulus value of the yellow- 

 green (552 fMfju) is to that of the red (670-8 fiiA.) as 101 : 4-9 or about 5 : 1 

 for the protanope, whereas for the deuteranope it is only as 64 : 33 or 

 about 2:1. 



The luminosity of the spectrum. The luminosity curves of dichromats 

 were investigated by Hillebrand (1889)^, who found the protanopic 

 maximum at 560 — 658 /x/x, and by Konig and Ritter (1891)^. The 

 following table gives the values for two trichromats and three 

 dichromats at the intensity value H. 



Figs. 47 and 48 show the curves. 



Ritter's protanopic curve for the lowest intensity A is almost 

 identical with Konig's. Konig thus early demonstrated the identity 

 of the protanopic achromatic scotopic and the normal achromatic 



1 Sitz. d. Wiener Akad. xcviii. 3, 70, 1889. 



- Konig, p. 144. 



