uo8 



VISION. 



and he regards this reduction as an experimental procedure which does not 

 necessarily carry with it any physiological significance. By fundamental 

 sensations, on the other hand, he means the colours which correspond to simple 

 physiological peripheral processes. In order to arrive at the elementary sensa- 

 tions, he constructs elementary sensory curves in the following way. He assumes 

 the division of the spectrum into five regions : two end regions (red end to 

 655 A. and 430 A to violet end), in each of which only one elementary sensation is 

 present ; two intermediate regions (655 A to 630 A and 475 A to 430 A), in each 

 of which two of the elements are present ; and a middle region (630 A to 475 A), 

 in which all three elementary sensations are present together. The inter- 

 mediate regions are characterised by the fact that every colour-tone in each of 

 them can be matched by mixing the light at the point where it joins the 

 middle region with light from the corresponding end region. In dichromatic 

 vision there will be only three regions, namely, the two end regions, and a 

 middle region in which the two elementary sensations of the dichromatic eye 

 occur together. 



Starting from these assumptions, Konig has calculated from a series of 

 equations the curves of excitability of the three elementary sensations of the 

 normal eye (Fig. -396), and the two of the dichromatic eye (Fig. 397). The short 



A,A,B f 



TiedL \ *z\Blue 



Fig. 398. — The curve represents the colours of the spectrura, while points at the 

 three angles represent the fundamental colours. 



wave or cold curve of the latter was the same in all cases, and corresponded 

 with the blue or violet curve of the normal eye. The warm curve of the 

 colour-blind differed in the two groups, and the two curves corresponded fairly 

 closely with the red and green curves of the normal eye. On the basis 

 of these results, Konig deduced the three fundamental colours by means 

 of the colour triangle, and concluded that they were a red lying outside 

 the spectrum, being rather more purple than the red of the end region, a 

 green at 505 A, and a blue at 470 A. The green is much more saturated than 

 spectral green, as is seen by the figure of Kb'nig's colour triangle (Fig. 398). 



Helmholtz 1 calculated the fundamentals mathematically by another 

 method, from the degree of sensibility for differences of colour-tone in each 

 part of the spectrum. He has taken as his data the observations of Konig and 

 Brodhun, 2 on the degree of sensitiveness of the eye for changes of colour- 

 tone, and has arrived at the conclusion that the three elementary colours are a 



1 " Handbuch d. physiol. Optik," 2te Aufl., S. 449. 



2 Ztschr. f. Psychol, u. Physiol, d. Sinnesorg., Hamburg u. Leipzig, 1892, Bd. iii. S. 97. 



