288 MR J. CLERK MAXWELL ON COLOUR 



In one experiment, after looking at a bright light, with a red glass over one 

 eye and a green over the other, the two tints in experiment (4) appeared to him 

 altered, so that the outer circle was lighter according to one eye, and the inner 

 according to the other. As far as I could ascertain, it appeared as if the eye 

 which had used the red glass saw the red circle brightest. This result, which 

 seems at variance with what might be expected, I have had no opportunity of 

 verifying. 



This paper is already longer than was originally intended. For further infor- 

 mation I would refer the reader to Newton's Opticks, Book I. Part II., to Youxgs 

 Lectures on Natural Philosophy, page 345, to Mr D. R. Hay's works on Colours, 

 and to Professor Forbes on the Classification of Colours (Phil. Mag., March 1849). 

 The most remarkable paper on the subject is that of M. Helmholtz, in the 

 Philosophical Magazine for 1852, in which he discusses the different theories of 

 primary colours, and describes his method of mixing the colours of the spectrum. 

 An examination of the results of M. Helmholtz with reference to the theory 

 of three elements of colour, by Professor Grassmann, is translated in the Phil. 

 Mag., April 1854. 



References to authors on colour-blindness are given in Dr G. Wilson "s papers 

 on that subject. A valuable Letter of Sir J. F. W. Herschel to Dalton on his 

 peculiarity of vision, is to be found in the Life of Dalton by Dr Henry. 



I had intended to describe some experiments on the propriety of the method 

 of mixing colours by rotation, which might serve as an extension of Mr Swan's 

 experiments on instantaneous impressions on the eye. These, together with the 

 explanation of some phenomena which seem to be at variance with the theory of 

 vision here adopted, must be deferred for the present. On some future occasion, 

 I hope to be able to connect these simple experiments on the colours of pigments 

 with others in which the pure hues of the spectrum are used. I have already 

 constructed a model of apparatus for this purpose, and the results obtained are 

 sufficiently remarkable to encourage perseverance. 



Note I. 

 On different Methods of Exhibiting the Mixtures of Colours. 



(1.) Mechanical Mixture of Coloured Powders. 



By grinding coloured powders together, the differently-coloured particles may 

 be so intermingled that the eye cannot distinguish the colours of the separate 

 powders, but receives the impression of a uniform tint, depending on the nature 

 and proportions of the pigments used. In this way, Newton mixed the powders 

 of orpiment, purple, bise, and viride ceris, so as to form a gray, which, in sunlight, 

 resembled white paper in the shade. (Newton's Opticks, Book I. Part II. Exp. 



