EXPERIMENTS ON COLOUR, AS PERCEIVED BY THE EYE. 127 



Mr D. R Hay. The experiments made in the present year were with the 

 improved top made by Mr J. M. Bryson, Edinburgh, and coloured papers pre- 

 pared by Mr T. Purdie, with the unmixed pigments used in the arts. A number 

 of Mr Bryson's tops, with Mr Purdie's coloured papers has been prepared, so as 

 to afford different observers the means of testing and comparing results inde- 

 pendently obtained. 



The colour used for Mr Purdie's papers were 



Vermilion . . V Ultramarine . . U Emerald Green . , EG 



Carmine ... Prussian Blue . . PB Brunswick Green . . BG 



Red Lead . . RL Verditer Blue . . VB Mixture of Ultramarine 



Orange Orpiment . OO and Chrome . . UO 



Orange Chrome . OC 

 Chrome Yellow . CY 

 Gamboge . . Gam 



Pale Chrome . . PC 



Ivory Black . . Bk 



Snow White . . SW 



White Paper (Pirie, Aberdeen). 



The colours in the first column are reds, oranges, and yellows ; those in 

 the second, blues ; and those in the third, greens. Vermilion, ultramarine, and 

 emerald green, seem the best colours to adopt in referring the rest to a uniform 

 standard. They are therefore put at the head of the h'st, as types of three 

 convenient divisions of colour, red, blue, and green. 



It may be asked, why some variety of yellow was not chosen in place of 

 green, which is commonly placed among the secondary colours, while yellow 

 ranks as a primary \ The reason for this deviation from the received system is, 

 that the colours on the discs do not represent primary colours at all, but are 

 simply specimens of different kinds of paint, and the choice of these was deter- 

 mined solely by the power of forming the requisite variety of combinations. Now, 

 if red, blue, and yellow, had been adopted, there would have been a difficulty 

 in forming green by any compound of blue and yellow, while the yellow formed 

 by vermilion and emerald green is tolerably distinct. This will be more clearly 

 perceived after the experiments have been discussed, by referring to the diagram. 



As an example of the method of experimenting, let us endeavour to form a 

 neutral gray by the combination of vermilion, ultramarine, and emerald green. 

 The most perfect results are obtained by two persons acting in concert, when 



