154 EXPERIMENTS ON COLOUR, AS PERCEIVED BY THE EVI 



No. 2. represents the relations of Mr HAY'S red, blue, groen, white, and yellow papers, as deter- 

 mined by a large number of experiments at Cambridge. (See Note II.). The use of the 

 IK >int D, in calculating the results of colour-blindness, is explained in the Pa|T. 



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. G. 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. BBYSON, Optician, Edinburgh. 



