[From the Proceedings of the Royal Institution of Great Britain, Vol. vi.] 



XL VII. On Colour Vision. 



ALL vision is colour vision, for it is only by observing differences of colour 

 that we distinguish the forms of objects. I include differences of brightness 

 or shade among differences of colour. 



It was in the Royal Institution, about the beginning of this century, that 

 Thomas Young made the first distinct announcement of that doctrine of the 

 vision of colours which I propose to illustrate. We may state it thus: We 

 are capable of feeling three different colour-sensations. Light of different kinds 

 excites these sensations in different proportions, and it is by the different 

 combinations of these three primary sensations that all the varieties of visible 

 colour are produced. In this statement there is one word on which we must 

 fix our attention. That word is, Sensation. It seems almost a truism to say 

 that colour is a sensation ; and yet Young, by honestly recognising this ele- 

 mentary truth, established the first consistent theory of colour. So far as I 

 know, Thomas Young was the first who, starting from the well-known fact that 

 there are three primary colours, sought for the explanation of this fact, not in 

 the nature of light, but in the constitution of man. Even of those who have 

 written on colour since the time of Young, some have supposed that they ought 

 to study the properties of pigments, and others that they ought to analyse 

 the rays of light. They have sought for a knowledge of colour by examining 

 something in external nature something out of themselves. 



Now, if the sensation which we call colour has any laws, it must be 

 something in our own nature which determines the form of these laws ; and I 

 need not tell you that the only evidence we can obtain respecting ourselves 

 is derived from consciousness. 



The science of colour must therefore be regarded as essentially a mental 



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