1835.] Accidental and Complementary Colours. 287 



state of bodily health. In the one case, by practice, and 

 from a knowledge of an invariable result, I find that I can 

 get a distinct and complete view of the accidental tint almost 

 immediately after regarding the fundamental colour, whereas 

 I have employed unpractised persons, whom I shall arrange 

 into four classes, to look for accidental tints, and the results 

 of my observations I may be allowed to state thus : — 



1. Persons with acute perception of colour. 



2. Those with an indifferent, that is, not acute perception 



of colour. 



3. Those with a positively bad perception of colour. 



4. Where the perception of colour is absent. 



The persons in the first class are two artists in oil colours, 

 (one eminent in his profession, but whose name I do not 

 feel myself at liberty to mention), and amateur artists con- 

 sisting of several ladies and gentlemen who have obligingly 

 made observations for me. In all these instances the per- 

 ception of the accidental tint was more or less ready, though 

 not so ready as that obtained by the eye employed in the 

 almost daily observance of these phenomena. 



The second class includes persons not engaged in the 

 practical observance of colour, and hence I term their per- 

 ception indifferent. They have generally required a longer 

 time than persons in the first class to obtain a sight of the 

 accidental tint. 



In the third class the observers have obtained the 

 accidental tint with great difficulty, and sometimes not 

 at all. 



In the fourth class I have been able to make but one 

 observation. It is the case of a gentleman in a scientific 

 institution in London, with whom I passed a few pleasant 

 hours last July. On beginning to converse with him on 

 the subjects of sound and colour, he desired me to omit the 

 latter ; and from him I ascertained, for the first time, his 

 utter incapability to distinguish any colour except deep 

 black, and blue, and he often mistook the one for the other, 

 and bright white. On offering him a disk of green glass 

 he said it seemed to him to resemble grass ; but the disk 

 was by no means of that shade ; and on holding up light 

 blues and reds, &c., he declared his inability to name any 



