THE DISCRIMINATION OF HUE IN THE SPECTRUM 31 



I 



Eb 



H 



Fig. 4. Curves of discrimination sensibility for hues of the spectrum of gas light. A. A, A, 

 for normal trichromat ; B, B, B, for a deuteranope. Abscissae, wave-lengths. 

 (Konig.) 



Uhthoff used the method of least perceptible differences (v. p. 19), 

 and obtained the following results. 



X 050 040 030 020 



5\ 4-70 2-97 1-08 1'24 



X 490 480 470 400 



8\ 0-72 0-95 1-57 1'95 



010 000 590 

 1-08 1-02 0-91 



450 

 2-15 



580 570 550 530 510 

 0-88 1-10 1-00 1-88 1-29 



His maxima are therefore II at 490 pfj,, and III at 580 



v. Kries 1 points out that Konig's and UhthofFs methods are not 

 strictly comparable, since the former measures the general discrimina- 

 tion sensibility rather than the true specific or hue discrimination 

 sensibility, which is measured by the latter. 



Steindler used the interference spectrum of the arc-light, and 

 examined twelve persons with normal colour vision. She obtained four 

 maxima for her own right eye (Fig. 5) : I at 435 ^/M, ; II at 497 ^ ; 

 III at 585/x/x ; IV at 636 /Z/A. The corresponding minima were between 

 I and II at 454 ^ ; II and III, 535 pp ; III and IV, 624 /^t. 



Comparing different individuals, II or III may show the greater 

 discrimination sensibility. Thus her own III was greater than II 

 whereas we have seen that Konig's and Dieterici's II was greater than 

 III. The exact positions vary for I, 15 20/x/x; for II, 30/x/x; for 

 III, 15/x/z; for IV, 15- 20/z/x. The average positions were II, 492^; 



Nagel's Hundb. d. Phijaiol. d. Mcnschen, m. p. 252. 



