HERMANN VON HELMHOLTZ 



amount, a red-blind person sees what is to him white, 

 and when the red and violet are equal, a green-blind 

 person will have a sensation of what in turn is to him 

 white, although, to the normal eye, these parts are 

 bluish-green in the one case and green in the other, 

 as the green sensation is in each added to the sensa- 

 tions of red and blue. 



The subject is fully discussed in Helmholtz's great 

 work, Handbuch der physiologischen Optik, the first part 

 of which appeared in 1856 and the last in 1867. The 

 first part of a new edition appeared in 1885, and the 

 last in the year of the death of Helmholtz, 1894. In 

 the new edition he returns to the subject of colour 

 vision, and materially modifies the views in his earlier 

 writings as to what is now universally known as the 

 Young-Helmholtz theory of colour sensation. It is 

 fitting that the two great names should be linked 

 together. Helmholtz finally held that luminosity or 

 brightness plays a more important part in our per- 

 ceptions of colour than has been supposed. He also, 

 by analysing the colours of the spectrum with great 

 care, aided by his pupils, and more especially by 

 Arthur Konig, was able from these data to determine 

 three fundamental colour sensations, the first red (a), 

 which is a highly-saturated carmine-red ; the second 

 green (/>), like the green of vegetation ; and the third 

 blue (c), like ultra-marine. Each spectral colour he 

 supposed to be made up of certain proportions of these 

 fundamental colours, or of a combination of two of 

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