220 COLOUR VISION 



of controversy and the whole theory is thrown into disrepute, the 

 cardinal fact being overlooked that they are in no integral sense germane 

 to the theory. 



It may, however, be interesting to record some of the suggestions 

 which have been made. 



As regards the three fundamental component sensations Konig's 

 experiments led him to regard them as a red just outside the spectrum 

 and rather more purple than the spectral colour, and a blue at 470 fifji 

 slightly more saturated than the spectral blue. v. Helmholtz, on 

 the basis of Konig and Brodhun's observations on the sensitiveness for 

 discrimination of hues in the spectrum {v. p. 30), chose a carmine-red, 

 bluer than spectral red, a yellowish-green between 540 /x/a and 560 /x/x, 

 and an ultramarine blue, all much more saturated than the spectral 

 colours. 



As regards the retinal bases for the theory, Konig as already 

 mentioned regarded the visual purple as the basis of colourless scotopic 

 vision. With greater stimulus intensities the visual purple is trans- 

 formed into visual yellow, which forms the basis of the fundamental 

 blue sensation. He placed the substrata of the red and green sensations 

 in the pigment epithelium. If this were true, foveal vision should be 

 monochromatic in protanopes and deuteranopes. He regarded the cones 

 as a purely dioptric mechanism. 



CHAPTER II 



RESEARCHES BASED UPON THE THEORY 



I, Normal Colour Vision 



The first researches based on Young's theory were made by v. Helm- 

 holtz (1852-3)^. From them he elaborated the three-components or 

 Young-Helmholtz theory. He was followed by Clerk-Maxwell (1855-6)^. 



Clerk-Maxwell placed three slits in the spectrum of daylight at the 

 following places : (1) in the red {R) between the Fraunhofer lines C 

 and D, twice as far from the latter as from the former ; (2) in the 

 green (G) near E ; (3) in the blue (J5) between F and G, twice as far 

 from the latter as from the former. Lights from these slits were 

 mixed in the proportions to match a comparison white {W) derived 



^ References in v. Helmholtz, 3rd ed., ii. p. 137. 

 - Scientific Papers, Cambridge, 1890. 



