128. Artists, and especially painters and dyers, admit that the mixture of three primary colours, in a certain proportion, gives black; hence, when these three colours are so mixed that two predominate, black will result, formed from the union of the whole of the colour, which is in small quantity, within suitable proportions of the two predominant colours. For example, if blue be mixed with red and yellow, a little black is produced, which reduces or _breaks_ the orange. 129. We must remember that the _primary colours_ of painters are not those of the prismatic spectrum, but substances employed by them, as red, yellow, and blue colours. SECTION II. _Of Diagrams designed to Represent and Define Colours and their Modifications._ 130. Various contrivances have been proposed under the titles of Tables, Scales, Colour-Circles, Chromatometers, &c., for representing either by numbers or a rational nomenclature, colours and their modifications. They are generally founded on these three propositions:—1. There are three primary colours. 2. Equal portions of these colours being mixed, produce pure secondary colours. 3. Equal portions of the three primary colours produce black. 131. But we know of no substance which exhibits pure colour; that is, which reflects only one kind of coloured rays, whether pure red, pure yellow, or pure blue. And since it is impossible to procure pure colouring matters, how can it be said that orange, green, and violet are composed of two simple colours mixed in equal proportions? Or that black consists of a mixture of equal parts of three simple colours? [Illustration: PLATE VII.] These chromatic tables, &c., point out mixtures which do not produce the results deducible from the principles on which they are said to be based. 132. But most of the blue, red, and yellow colours with which we are acquainted, give, by their binary compounds, violet, green, and orange inferior in brilliancy to the natural violet, green and orange colours of objects. This result would be explained by admitting that colours mixed two by two, reflect at least two kinds of coloured rays; and that where there is any mixture of colours which reflect separately red, yellow, and blue, there is produced a certain amount of black which reduces the brilliancy of the mixture. 133. Conformably with this view, the violet, green, and orange colours which result from a mixture of coloured matters, are most brilliant when the respective colours of these materials approach each other. For example, a mixture of blue and red inclines more to violet than a mixture of blue and yellow inclines to green, and that of red and yellow inclines still more to orange.