298 MR J. CLERK MAXWELL ON COLOUR, AS PERCEIVED BY THE EYE. 



Note IV. 



Description of the Figures. Plate VI. 



No. 1. is the colour-diagram already referred to, representing, on Newton's principle, the relations of 

 different coloured papers to the three standard colours — vermilion, emerald-green, and ultra- 

 marine. The initials denoting the colours are explained in the list at page 276, and the numbers 

 belonging to them are their coefficients of intensity, the use of which has been explained. The 

 initials H.R., H.B., and H.G., represent the red, blue and green papers of Mr Hay, and serve 

 to connect this diagram with No. (2), which takes these colours for its standards. 



No. 2. represents the relations of Mr Hay's red, blue, green, white, and yellow papers, as determined 

 by a large number of experiments at Cambridge. — (See Note II.). The use of the point D, in 

 calculating the results of colour-blindness, is explained in the Paper. 



Fig. 3. represents a disc of the larger size, with its slit. 



Fig. 4. shows the mode of combining two discs of the smaller size. 



Fig. 5. shows the combination of discs, as placed on the top, in the first experiment described in the 

 Paper. 



Fig. 6. represents the method of spinning the top, when speed is required. 



The last four figures are half the actual size. 



Colour-tops of the kind used in these experiments, with paper discs of the colours whose relations are 

 represented in No. 1, are to be had of Mr J. M. Bryson, Optician, Edinburgh. 





