164 



COLOUR VISION 



each part and correlating the results mathematically. The principle 

 is the same. 



The average of the results, which did not differ materially inter se, 

 is shown in Fig. 44, where the abscissae are wave-lengths of the matched 

 spectral colours and the ordinates are arbitrary units of intensity. 

 Wi is the deuteranopic red or " warm " curve, Tf 2 tlie protanopic red 

 curve, and K the blue or " cold " curve common to both. H is the 

 monochromatic curve of which more will be said later. 



18 

 16 

 14 

 12 

 10 

 8 

 6 



Fig 



.720 700 680 660 640 620 600 580 560 540 520 500 480 460 440 420 400 380 



a B C D E b F G H 



44. Equal-area gauging curves for dichromats and nionochromats {H). 



Ifj , deuteranopic " warm " curve ; W2, protanopic " warm " curve ; K, " cold ' 

 curve common to both types of dichromats. Abscissae, wave-lengths of the 

 interference spectrum of sunlight ; ordinates, arbitrary scale. (Konig.) 



It is to be noted that the curves are so drawn that the areas enclosed 

 between each curve and the axis of abscissae are all equal. They 

 therefore represent the relative magnitudes of the stimulus values of the 

 given elements — red or blue — in the unanalysed light from which the 

 spectrum is derived {v. Part III, Section III, Chap. 11). They do not 

 establish any quantitative relationship between the stimulus values for 

 different individuals, since these are qualitatively of a different order. 



V. Kries^ used as his gauging lights a red (589-2 /x^u, for protanopes, 

 645 /x/x. for deuteranopes) and a. blue (460-8 ^a^u.), and determined the 

 relative amount of each which must be mixed in order to match exactly 

 the spectral colours. 



1 V. Kries and Nagel, Ztsch.f. Psychol, u. Physiol, d. Sinnesorg. xii. 1, 1896 ; v. Kries 

 op. cit. xm. 241, 1897. 



