PART II 



THE CHIEF FACTS OF COLOUR BLINDNESS 



CHAPTER I 



INTRODUCTION : COLOUR NAMES 



It has long been known that certain persons show peciiKarities of 

 colour vision distinguishing them from the normal^. The colour blind- 

 ness of the chemist, John Dalton^, first led the attention of scientists 

 to the analysis of the sensations of the colour-blind. In 1807 that 

 remarkable genius (" bewundernswiirdiger Forscher," v. Helmholtz), 

 Thomas Young, discussed Dalton's case in his Lectures on Natural 

 Philosophy. So great was the stir produced by Dalton's defect that 

 colour blindness was long known as Daltonism. In 1810, the great 

 poet Goethe referred to these abnormalities of colour vision in his book 

 on the Theory of Colours^. An enormous literature on the subject 

 sprang up during the nineteenth century*. 



During this period two types of colour blindness were fairly clearly 

 distinguished. They had this in common' that in them the whole gamut 

 of colour sensations could be referred to a function of two variables. 

 Since normal colour vision is a function of three variables and these 

 types of colour blindness display colour systems which are functions 

 of two variables the normal are conveniently classed as trichromats, these 

 types of the abnormal as dichromats. 



As already mentioned the dichromats can be divided into two groups, 

 and to these a rare third group has since been added. The names given 

 to the groups varied according to the theoretical predilections of the 

 writer. Thus, v. Helmholtz called them red-blind, green-blind, and 



1 Turberville, Phil. Trans. Roy. Soc. Lond. 1684 ; Huddart, op. cit. Lxvn. 1, 14, 1777 ; 

 Whisson, op. cit. LX^^^. 2, 611, 1778 ; and others. 



2 Lit. and Phil. Soc. of Manchester, 1794; Edin. J. of Sc. ix. 97, 1798 — reprinted in 

 Edin. J. ofSc. v. 188, 1831. 



' Zur Farbenlrhre ; translated by Eastlake, London (Murray), 1840. 



■* V. Helmholtz, 2nd ed. BibliograiAy, pp. 1176-1198, complete to the end of 1894. 



