60 Dr. W. Pole on Colour-Blindness. 



question by immediately going on, page 458, to a further 

 investigation, entitled " Comparison with Dichromic Eyes." 



He begins with the remark that the fundamental colours 

 he has found do not coincide with those which Konig and 

 Dieterici had deduced from the comparison of colour-blind 

 eyes with normal ones, and which he had himself quoted in 

 former parts of this work. They had arrived at pretty nearly 

 the same hues of red and blue, but their third fundamental, 

 green, differed materially, and the intensities were very 

 different in all. 



Helmholtz takes some pains to explain and comment on 

 this, showing that the discrepancy is due to the attempt made 

 by Konig and Dieterici to apply the a old" assumption that 

 dichromic vision was simply caused by the absence of one 

 of the fundamental excitements of the trichromic eye. He 

 mentions that this assumption originated with Young, and 

 was, at an earlier period, accepted by most of the adapters of 

 the theory, including himself and Hering, as well as Konig 

 and Dieterici, and he thereby gives a good defence for their 

 zealous endeavours, but at the same time he leaves no doubt 

 that this assumption has vitiated their results. 



As a further proof of this he cites (p. 461) the determina- 

 tion by Konig and Dieterici of the colours wanting to the 

 red and green blind respectively, according to the funda- 

 mental colours chosen by them ; and he shows that when the 

 newly found fundamentals are substituted, such a determina- 

 tion leads to irrational results, giving negative values : whereas 

 (p. 460) Young's hypothesis only allows positive values of 

 the physiologically possible colours. 



Considering therefore, apparently, the old assumption as 

 now proved intractable, he goes on to explain that a more 

 general hypothesis respecting the existence of dichromatism 

 may be found, in which the necessity ceases that the missing- 

 colour should be one of the fundamentals *. 



* The folio wino- are the original words : — " Die hier gefundenen Grund- 

 farben stimnien nicht mit denen iiberein, welche die Hrn. A. Konig und 

 C. Dieterici aus der Vergleichung farbenblinder Augen mit normal- 

 sichtigen hergeleitet haben. Nnr die besondere, yon Th. Young ausge- 

 gangene und yon den nieisten Bjarbeitern der Theorie, auch von mir 

 selbst, yon E. Hering, A. Konig, und C. Dieterici friiher angenornniene 

 Erklarungsweise, dass bei den Dichromaten einfach eine der Grund- 

 erregungen des trichroniatischen Auges nicht zu Stande koinme, tritt in 

 Widerspruck mit dem bezeichneten Ergebniss. 



" Aber es ist eine allgemeinere Hypotkese iiber das Wesen der Dichro- 

 masie moglich, bei welcher die Nothwendigkeit aufhort, dass die fehlende 

 Farbe eine der Grundfarben sei, und dock die Kegel festgehalten wird 

 dass alle Farbenpaare, welche fur das normale trichromatische Auge 

 gleich aussehen, auch fur das dichromatische gleick aussehend bleiben.° 



