Oct. 24, 1878] 



NATURE 



677 



ambiguous and confused." And again — "We find that 

 his sense of colour was not only narrow, but also vague, 

 and wanting in discrimination." 



The article is an expansion of a chapter in the same 

 author's "Studies on Homer and the Homeric Age," 

 published in 1858 (vol. iii. page 457), from which the 

 proposition is quoted ; " That Homer's perception of the 

 prismatic colours, or colours of the rainbow, and d. fortiori 

 of their compounds, were, as a general rule, vague and 

 indeterminate," Mr. Gladstone gives many examples 

 illustrating these opinions, and by powerful and inge- 

 nious reasoning, he endeavours to establish from them 

 the general conclusion that "the organ of colour was 

 but partially developed among the Greeks of the heroic 

 age." 



I have no intention of disputing this conclusion, in 

 favour of which no doubt much may be said, but I think 

 it may be worth while, on scientific grounds, to point out 

 how remarkably the anomalies and imperfections in 

 question correspond with those that might be expected to 

 arise if the writer were assumed to be colour blind. 



Mr. Gladstone makes some allusion to the possibility 

 of a defect in the poet's organisation ; but it appears to 

 me that, probably from the facts connected with colour 

 blindness not being fully known to him, he hardly gives 

 this point the attention it deserves. In his earlier essay 

 he expresses the opinion that such a supposition "cannot 

 be resorted to, when we bear in mind Homer's intense 

 feeling for form, and when we observe his effective and 

 powerful handling of the ideas of light and dark." From 

 this remark it is clear that Mr, Gladstone was unaware of 

 the fact that colour blindness can, and usually does, co- 

 exist with a perfect feeling for form, and with as vivid 

 ideas of light and dark as are possessed by the normal- 

 eyed. In the later article he mentions the defect more 

 specifically, and refers to Prof. Wilson' s book on the sub- 

 ject (published in 1855), but he does not add anything to 

 the argument, and appears to leave the point still open to 

 discussion, when further data can be supplied. 



In 1856 I presented to the Royal Society a paper on 

 Colour Blindness, which was afterwards published in the 

 Philosophical Transactions, vol. 149, p. 323. Its object 

 was to state my own case (which happens to be one of 

 the most decided on record) and to show that the general 

 phenomena attending this defect of vision were more 

 simple, uniform, and consistent than was generally 

 supposed. 



Before I wrote that paper the general impression was 

 that, although there were certain broad particulars in 

 which the sensations of different colour-blind patients 

 agreed, yet there were many varieties of the defect, dif- 

 fering much in character as well as in severity, each being 

 denoted by its own peculiar symptoms, and each, there- 

 fore, requiring special classification. Prof. Elie Wart- 

 mann, of Lausanne, whose paper on the subject was 

 published in England in 1846, held the opinion that there 

 were as many varieties of the defect as of individuals 

 affected with it, so that no classification Avas possible, 

 Dr, Wilson did not go so far as this, but he considered the 

 cases as varying much in degree, and he inclined strongly 

 to the opinion that the most severe form of the defect 

 was very rare. 



To illustrate the great variety of mistakes made by the 

 colour blind, and to show the confusion resulting there- 

 from, I gave the" following list of "symptoms" which 

 had been observed in various patients, and which were 

 all combined in my own case : — 



Blue and yellow are always perfectly distinguished, even in 

 their lighter or darker tones, and are never confounded with 

 each other. 



Only these two colours are seen in the solai spectrum, the 

 blue corresponding to the more and the yellow to the less 

 refrangible rays. The red space is seen as yellow. 



Red, though frequently identified in certain cases, is often 

 confounded with black, white, or grey, with orange, with 

 yellow, with green, with brown, with blue, and with violet. 

 Crimson and pink have no relation to the red of vermilion. 



Green is a colour most perplexing to the patient, who cannot 

 be said generally to manifest any definite sensation about it at 

 all. It is confounded not only with red, but also with black, 

 white, or grey, with orange, with yellow, with blue, with violet,, 

 and with brown. 



Orange is confounded with "yellow ; violet is confounded with 

 black or grey, and with blue. 



No wonder that philosophers should have de^aired of 

 finding any reasonably simple diagnosis for such a hete- 

 rogeneous mass of symptoms ; it was, however, my object 

 to show this could be done. By a long and careful study 

 of my own sensations, aided by a masterly suggestion of 

 Sir John Herschel's that had been published shortly before, 

 I found, in the first place, that notwithstanding the ap- 

 parent variety of the symptoms in different persons, the 

 defect was uniform, or nearly so, in all; and in the 

 second place, that in spite of the apparent complexity of 

 the phenomena, this defect was of a very simple character. 

 I believe the explanations I gave have been generally 

 accepted, and subsequent experience has amply confirmed 

 them. 



As few people have"a clear understanding what Colour 

 Blindness really means, and as without such an under- 

 standing it would be impossible to make my remarks 

 intelligible, I must ask leave to describe the defect as 

 briefly as I can, referring to the Philosophical Transac- 

 tions for fuller details and demonstrations. 



In the first place we see white and black, and their 

 intermediate or compound grey (provided they are free 

 from alloy with other colours), precisely as others do. 



Secondly, there are two colours properly so called, 

 namely, yellow and blue, which also, if unalloyed, we 

 see, so far as can be ascertained, in the normal manner. 



But these two are the only colours of which we have 

 any sensation ; and hence the defect has been given by 

 Sir John Herschel the scientific name of dichromic vision. 



But now comes the difficulty of the explanation. It 

 may naturally be asked : Do we not see objects of other 

 colours, such as roses, grass, violets, oranges, and so on ? 

 And if we do see them, what do they look like ? The 

 answer is that we do see all such things, but that they do 

 not give us the colour sensations correctly belonging to 

 them ; their colours appear to us varieties of the other 

 colour sensations which we are able to receive. 



This will be best explained by examples. Take first 

 the colour red. A soldier's coat or a stick of red sealing- 

 wax conveys to me a very positive sensation of colour, by 

 which I am perfectly able to identify, in a great number 

 of instances, bodies of this hue. If, therefore, the investi- 

 gation of my experience ended here, there would be no 

 reason to consider me blind to red, or as having any 

 grave defect in my vision regarding it. But when I 

 examine more closely Avhat I really do see, I am obliged 

 to come to the conclusion that the sensation I perceive is 

 not one that I can identify separately, but is simply a 

 modification of one of my other sensations, namely, 

 yellow. It is, in fact, a yellow shaded with black or grey — 

 a darkened yellow, or what I may call yellow brown. I 

 find that all the most common hues of red correspond 

 with this description, and in proportion as they are more 

 scarlet or more tending towards orange, the yellow I see 

 is more vivid. The explanation, I suppose, is, that none 

 of such reds are pure, they are combinations of red with 

 yellow ; so that I see the yellow element of the com- 

 bination, while the true red element is invisible to me as 

 a colour, and acts only as a darkening shade. 



I obtain a further proof of this by the change of sensa- 

 tion when the hue of red is altered. I find that as the 

 colour approaches crimson the yellow element becomes 

 fainter and the darkening shade more powerful, until very 



