346 DR GEORGE WILSON ON THE 
external objects. It may startle us at first to be told that we see in part by light 
issuing from our eyes, but it must be so; and those traditions of learned men who 
could read by the light of their own eyes in what was darkness to others, are only 
exaggerations of a power more or less exercised by every human organ of vision.* 
To one result of this choroido-retinal reflection in the human eye I would, in 
conclusion, refer. The light which is thus reflected, is always coloured, being, as 
we have already seen, red, yellowish-red, or brownish-red, and differing neces- 
sarily in its tint, according to the abundance of pigment in different eyes. Each 
of us thus adds to every object on which he looks so much colour, but no two 
pairs of eyes the same amount, and hence one great reason why no two persons, 
almost, will be found to agree as to the matching of one colour with another 
where the coloured substances compared consist of different materials; and why 
very marked differences present themselves in the judgments of persons equally 
practised in observing and copying colours. 
Two artists, for example, paint from nature the same flower. The pigments 
which they employ for this purpose, will, of course, be as much affected by the 
colour communicated from the eye, as the flower is, so that, could the latter be 
imitated in its own materials, the copies might be identical. But as these must 
be made with substances whose lustre, transparency, and particular tint, differ 
from those of the body copied, the added colour from the eye tells unequally on 
the original and the copy, as compared together, and as seen by different eyes. 
Each, accordingly, objects to the other’s colouring, but neither can induce his 
neighbour to adopt his tints, and both appeal confidently to third parties (who 
perhaps differ from both), assured that the adjudication will be in favour of the 
appellant. Here each may have been equally skilful and equally faithful: and 
neither has any means of testing to what extent he sees everything as if through 
coloured spectacles, which give all objects a tint for him inseparable from their 
natural colour. A ‘ chromatic equation,” thus originated, belongs, I believe, to 
every eye. 
* Esser on the Luminousness observed in the Eyes of Human Beings, Edin. Phil. Journal, 
1827, p. 164. 
