212 



SECTIONAL ADDRESSES 



to give up all classifications by types, arrange colour defectives in distribu- 

 tion tables and give a colour graph or profile for each subject, showing 

 his efficiency or deficiency for each colour in terms of a per cent, of the 

 normal or average attainment.' Troland ^* states that the original 

 restriction of colour blinds to protanopes, deuteranopes and tritanopes 

 is not adequate any longer, and allowances must now be made for more 

 types of variation. Edridge-Green ^^ recognises seven diff"erent types of 

 colour vision, and Schjelderup ^s states that there are at least eighteen 

 significant species of colour blindness. Collins ^^ reaches the conclusion 

 that it is quite unprofitable to try to classify the colour systems of the 

 colour blind because there exist so many individual variations. 



40 



35 



30 



25 



20 



15 



10 



1-5 



_L 



1-0 



Mi 



TTT-l 



JIL 



1-5 s: 05 



Black blocks denote colour blinds. 



1-0 



One group in which the colour defect is not extreme has been definitely 

 recognised. Seebeck, in 1837, found certain cases which he was reluctant 

 to classify as colour blinds, who yet showed signs of colour abnormality. 

 It was not until 1881, however, that these cases were understood. In 

 that year, Rayleigh found that a number of individuals with otherwise 

 normal colour vision were unequally sensitive to red and green. In 

 equating red (lithium line 670-8 y.[x) and green (thallium line 535 (x[z) to 

 match a yellow (sodium line 589 ix[i), since known as the Rayleigh equation, 

 some were found to require far more red than the normal, others required 



^* Bull. Nat. Res. Counc, 1922, Part 2, No. 27. 

 2° Physiology of Vision. 

 26 ■ - ~- 



' Zur Theorie der Farbenempfindungen,' Zsch. f. Sinnesphysiol., 51, 49-45. 

 ^' Ibid. 



