] 86 Dr. Houstoun and Miss Dunlop on a Statistical 



so that we have 



y=?,f r {n)z- s «l n e<" v \ 



yi =^(n)r'^f; 



where s>i = £a + — ^ — . 



Linear combinations of ?/, yi,...y n _ v therefore exist which 

 behave, when \z\ is large, like z ~ Sn/n e nzl/7 \ or like 



2~ s J n e n cos 



/ i/u . 2tt£ . 27T^ n \ 



( nz sm 1 



\ n n J 



XV. A Statistical Survey of the Colour Vision of 1000 

 Students. By R. A. Houstoun, D.Sc, Lecturer on 

 Physical Optics, and Margabet A. Dunlop, Thomson 

 Experimental Scholar in the University of Glasgow*. 



TTNDER the title of "A Statistical Survey of Colour- 

 KJ Vision," there appeared a paper by Dr. R. A. Houstoun 

 in the Roy. Soc. Proc. A, vol. xciv. p. 576 (1918). This 

 paper described the results of a test made on the colour 

 vision of 79 observers by means of an apparatus similar to 

 the Edridge-Green colour perception spectrometer. Each 

 observer determined the number of monochromatic patches 

 he saw in a continuous spectrum ; this number varied from 



Fig. 1. 



O O x X O v X 

 X OOXOOOX 

 X QQOOOQO 



O 



10 15 20 25 



five in the case of the colour-blind to twenty-six in the case 

 of an observer with exceptionally good colour vision. The 

 results were exhibited in the diagram (fig. 1) where the 



* Communicated by the Authors. 



