On the Vision of Colours. 43 
so. Accordingly we find, that bodies of all colours, 
when placed in homogeneal light of any colour, ap- 
pear of that particular colour. Hence a body that 
is red may appear of any other colour to an eye that 
does not transmit red, according as those other co- 
lours are more copiously reflected from the body, 
or transmitted through the humours of the eye. 
It appears therefore almost beyond a doubt, that 
one of the humours of my eye, and of the eyes of my 
fellows, is a coloured medium, probably some modi- 
fication of blue. I suppose it must be the vitreous 
humour; otherwise I apprehend it might be disco- 
vered by inspection, which has not been done. It 
is the province of physiologists to explain in what 
manner the humours of the eye may be coloured, 
and to them I shall leave it; and proceed to shew 
that the hypothesis will explain the facts stated in the 
conclusion of the second part. 
1. This needs no further illustration. 
2. Pink is known to bea mixture of red and 
blue; that is, these two colours are reflected in ex- 
cess. Our eyes only transmit the blue excess, which 
causes it to appear blue; a few red rays pervading 
the eye may serve to give the colour that faded ap- 
pearance. In candle-light, red and orange, or some 
other of the higher colours, are known to abound 
more proportionably than in day-light. The orange 
light reflected may therefore exceed the blue, and 
the compound colour consist of red and orange, 
