Dr. W. Pole on Colour -Blindness. 



59 



the percentages of the " Urfarben," x } y, and z, contained in 

 some of the chief hues of the spectrum. 



Red ...... 



Orange ... 

 Yellow ... 

 Green .v. 



Blue 



Violet ... 

 White ... 



Wave- 

 lengths 



end. 

 600 

 580 

 520 



480 

 end . 



X. 



y- 



z. 



61 



20 



I 9 



- 47 



30 



23 



36 



39 



25 



15 



51 



34 



31 



29 



40 



35 



25 



40 



33 



1 



33 



33 



If we apply to these quantities the principle that a mixture 

 of equal proportions of the three fundamental colours will 

 make white, we may form an idea of the enormous grade of 

 saturation of the ideal fundamental colours, compared with 

 that of the spectral hues. For example, spectral red will 

 contain 42 parts of x,\ part of y, and 57 of white; spectral 

 yellow will contain 11 parts of x, 14 of y, and 75 of white; 

 spectral blue will contain 2 parts of x, 11 parts of z, and 87 

 parts of white. This is a somewhat astounding idea ; but 

 a glance at the diagram on page 457 will show it is what the 

 author intends. 



The author points out that all simple colours excite the 

 three nerve-elements simultaneously, and with only moderate 

 distinctions of intensity ; facts for which there are analogous 

 phenomena in the known photochemical effects of photo- 

 graphy. 



This brief account gives a very vague idea of the skill 

 and labour that has been embodied in the work referred to ; 

 and, considering the entire novelty and difficulty of the 

 attempt, the acuteness of the logical reasoning required, and 

 the complicated nature of the relations involved, 1 should 

 venture to say it may be pointed to as one of the most striking- 

 examples of the application of high mathematics to physio- 



u research. 



But it may be asked, What immediate connexion has this 

 with Colour-blindness ? The author has himself answered the 



