Prof. J. D. Forbes oti the Classification of Colours. 175 



We therefore refer them at once to their places in Mayer's 

 triangle as intermediate between tlie secondaries and neutrality, 

 and dividing the interspace in the ratio of 3 to 1, as in the 

 former case; only here the compound is more neutral, because 

 the secondary colours are themselves one stage on the way to 

 neutrality. 



Thus we arrive at this conclusion, that all combinations of 

 three primary colours (as far as difference of quality is con- 

 cerned) may be represented by transitions from the primary and 

 secondary colours into gray ; and thence, though it may appear 

 at first sight paradoxical, though the quality of a primary or 

 secondary colour (such as red or green) is not changed by 

 diluting it with white, it ^5 changed by mixing it with gray, 

 or by first mixing it with white and then diminishing the in- 

 tensity of light in the mixture. 



Hence a classification of colours may be made, which, 

 although redundant in some parts, has the advantage of point- 

 ing out clearly the composition of each in this point, and also 

 of suggesting a convenient nomenclature, which I propose to 

 adopt in preference to Mr. Hay's (where they differ), as more 

 expressive of the composition of each. This diagram, like 

 Mayer's triangle, includes colours varying in quality, but of 

 standard ititensity and of the highest attainable purity. This 

 diagram was obligingly arranged for me by Mr. Hay out of 

 the coloured specimens in his work. 



The places marked by asterisks will supply a sufficient rela- 

 tive number of intermediate hues, as these evidently approach 

 the absolute uniforniity of neutral gray in the last column, 

 whilst the first contains the graduated colours of the spectrum. 



All these colours may be varied by mixing them with white 

 or black, forming what Mr. Hay judiciously calls tints or 

 shades of any colour. 



It is sometimes convenient to have these tints and shades 

 arranged in immediate apposition for the purpose of compa- 

 rison. This may be conveniently done for the principal co- 

 lours by having two diagrams. In one, the colours of the 

 spectrum form a circular ring, the colours passing through 

 tints into perfect white at the centre, and the shades continued 

 in outward radiating lines till they coalesce in a perfectly 

 black circumference. In the other, the principal intermediates 

 between the principal colours and gray may be exhibited with 

 like transitions. These intermediates may conveniently be 

 denominated by the following terms, sufficiently expressive 

 and in common use. 



