1921-22.] New Method of investigating Colour Blindness. 
75 
VII. — A New Method of investigating Colour Blindness, with a 
Description of Twenty-three Cases. By Dr R, A, Houstonn, 
Lecturer on Physical Optics in the University of Glasgow. 
% (MS. received December 5, 1921. Read January 9, 1922.) 
During the past four years I have been conducting surveys of the colour 
vision of students in the University of Glasgow. The first survey * was 
made by a colour-perception spectrometer very similar to Dr Edridge-Green’s 
instrument, and embraced 7 9 observers. The second survey f was made by Dr 
Edridge-Green’s bead test, and embraced 100 observers. The third survey, I 
carried out in collaboration with Miss Margaret A. Dunlop, was made by an 
original method, called here for short the microscope test, and embraced 
1000 observers. At present there are two other surveys under progress. 
The object of these surveys is to find a numerical method of specifying 
goodness of colour vision ; to see, by the application of statistical methods, 
whether the colour blind fall naturally into groups or are merely outliers 
of a homogeneous population; to find whether colour blindness is a Mendelian 
characteristic for men and merely an extreme case of normal variation for 
women ; and to throw light on the subject of colour vision generally. 
Consequently, the normal have been investigated with as much care as 
the colour blind. But in the course of the four years I have made the 
acquaintance of many trained observers with abnormal colour vision, and 
have been possessed with an ever-growing desire to know exactly, 
irrespective of all theory, what was the matter with their colour vision. 
In spite of the vast literature on the subject, the tests generally have 
been of a very superficial nature, and unsatisfactory to the man with 
mathematical instincts. As these abnormal cases were beginning to leave 
the University, I addressed myself last spring to the problem of finding 
a method of testing which would describe their condition independent of 
theory, and, indeed, independent of words. This paper describes how the 
problem was solved, and gives data for twenty-three cases of colour 
blindness, four of normal colour vision, and one case of exceptionally 
good colour vision. 
* Roy. Soc. Froc., A, 94, p. 576, 1918. 
t Proc. Phil. Soc. of Glasgow, 1920. 
t Phil. Mag., 41, p. 186, 1921. 
