Survey of the Colour Vision of 1000 Students. 191 



This does not make the average distance the same in each 

 case, but it reduces the inequality sufficiently to make it 

 negligible. Thus to return to the example already cited by 

 way of illustration, the observer's values for the black disks 

 13*6 and 15 were left as they were, his values for the red- 

 green were corrected to 15*3 and 17*06 and his values for 

 the blue-green to 14*6 and 13" 2. This gives a mean value 

 of 14*3 for the black, 16*18 for the red-green, and 13*9 for 

 the blue-green. These three numbers were assumed to 

 specify the observer's ability to distinguish black from white, 

 red from green, and blue from green respectively. Similar 



Table. 



Range. 



0& < 1 



1& < 2 



2& < 3 



3& < 4 



4& < 5 



5& < 6 

 6& < 7 



7& < 8 

 8& < 9 

 9& <10 



10& <11 



11 & <12 



12 & <13 



13 & < 14 



14 & <15 



15 & <16 



16 & <17 



17 & <18 



18 & <19 



19 & <20 



20 & <21 



21 & <22 



22 & <23 



23 & <24 



24 & <25 



25 & <2C> 



26 & <27 



27 & <28 



28 & <29 





Men. 



Black. 



Red- 





green. 





3 





o 





2 



1 



2 







1 







2 



2 



1 



7 



5 



8 



5 



16 



13 



68 



23 



139 



40 



202 



68 



177 



95 



104 



120 



51 



115 



30 



114 



J3 



71 



11 



61 



^ 



49 



1 



30 







6 







3 







1 



1 



2 



... 



1 



"Blue- ! 

 green, j 



1 



3 



4 



4 



13 



17 



46 



57 



75 



109 



132 



142 



90 



64 



37 



17 



10 



3 



3 



1 



5 

 







1 



Women. 



Black. 



Red- \ 





green. 





1 



























2 



1 



1 







1 



1 



5 



2 



21 



7 



25 



5 



46 



18 



35 



21 



14 



16 



6 



24 



6 



20 



2 



18 







16 







6 







4 







3 



1 



1 





1 



Blue- 

 green, 



2 



1 

 



3 



6 



10 



21 



20 



27 

 16 

 16 

 13 

 13 



10 

 



