"I know not if lessons of colouring have ever been given, notwithstanding it is a part so principal in painting that it has its rules founded on science and reason. Without such study it is impossible that youth can acquire a good taste in colouring, or understand harmony." - Mengs on the Academy at Madrid.

Having treated of the relations of colours, and exemplified them in a distinct essay,* we may speak more briefly on this important branch of our subject, upon which the expression of colours discussed in the preceding section rests, and their right application in practice depends.

Black and white are extreme colours, comprehending all other colours synthetically, and affording them all by analysis. The truth of this position is illustrated by the phenomena of the Lensic Prisms, whereby the fundamental fact upon which the true natural relations of colours rests is demonstrated; first, by the eduction of an aureola or iris of the three primary colours from a black spot upon a white ground, as in the following figure: -

On The Relations And Harmony Of Colours 3

* See "Chromatics; or, an Essay on the Analogy and Harmony of Colours," wherein the relations of each colour to every other colour, and to light and shade, are shewn by examples.

And secondly, by a like aureola from a white spot upon a black ground, as represented in the next figure, in which the order of the colours is inverted.

On The Relations And Harmony Of Colours 4

As these effects are produced by the Convex Lensic Prism, so by the Concave Lensic Prism they may be inverted, and these irides, or aureola?, reduced to a black or white spot at their centres.*

The Primary Colours are such as yield others by being compounded, but are not themselves capable of being produced by composition of other colours. They are three only, yellow, red, and blue; † and are sometimes, by way of distinction, called entire colours.

The Secondary Colours are such only as can be composed of, or resolved into, two primaries, and are also three only: namely, orange, composed of red and yellow; green, composed of yellow and blue; and purple, composed of blue and red.

The Tertiary Colours are such only as can be composed of, or resolved into, two secondary colours, or the three primaries; and these are also three: namely, citrine, composed of green and orange, or of a predominant yellow with blue and red; russet, composed of orange and purple, or of a predominant red with blue and yellow; and olive, composed of purple and green, or of a predominating blue with yellow and red. ‡

These three genera of colours comprehend in an orderly gradation all the colours which are positive or definite; and the three colours of each genus, united or compounded in such subordination that neither of them predominate to the eye, constitute the negative or Neutral Colours, of which black and while are the opposed extremes, and greys are their intermediates. Thus black and white are constituted of, and comprehend latently, the principles of all colours, and accompany them in their depth and brilliancy as shade and light; of which more hereafter.

"See Experiments on Light and Colours appended to the quarto edition of this work.

† See Note C. ‡ See Note D.

Colours thus generally defined are exemplified in the following scale of colours, in which their relations to each other, and to light and shade, are distinctly and in an orderly manner discriminated from white to black.

DEFINITIVE SCALE.

DEFINITIVE SCALE.

It is to be noted, however, that the above denominations of colours do not merely express the individual hues or tints by which they are exemplified in this diagram, but denote classes or genera of colours, each colour comprehending an indefinite series of shades between the extremes of light and dark, as each compound colour also does a similar series of hues between the extremes of the colours which compose it.

As each class or genus of colours, primary, secondary, and tertiary, has the property of combining in a neutral or achromatic state, when duly subordinated or compounded, it follows that each secondary colour, being compounded of two primaries, is neutralized and contrasted by the remaining primary, alternately; and that each tertiary colour, being a like binary compound of secondaries, is also neutralized or contrasted by the remaining secondary alternately.

These relations of colours will be readily understood by an attentive reference to the diagram or Scale of Chromatic Equivalents, Pl. I., in which each denomination of colours is opposed to its contrasting denomination reciprocally.

By the term equivalent we here denote such a relation of quantities in the combination of antagonist or opposite colours, as produces achromatic or neutral shades, in which the two constituent colours disappear.

Such antagonists or opposites of colours have received different denominations, according to circumstances: - thus, the spectral antagonist, called an ocular spectrum, which arises after long viewing a colour, has been variously denominated adventitious, accidental, etc. and is always its true opposite, but never its equivalent.- such colours simply opposed in juxtaposition are called contrasts, and may be either equivalent or unequal contrasts. All these correspondent colours have also been called complementary, although to be properly complementary they ought to be equivalent.

This Scale of Chromatic Equivalents is constituted of six circles, comprehending the primary blue, red, and yellow, and secondary colours, orange, green, and purple, alternately within a larger graduated circle, - the compound denominations appearing within the intersections or crossings of the circles: firstly, the binary, or secondary compounds, red-purple, red-orange, yellow-orange, etc. comprising the star formed by the alternate crossings of two circles; and secondly, the ternary, or tertiary compounds, russet, etc. comprehended in the smaller central star formed within the crossings of three of the circles alternately.* The graduated scale by which the whole is circumscribed, is divided round the inward edge by numerals diametrically opposed, denoting the proportions in which colours lying on any radius of the circle neutralize and contrast any colour, simple or compound, on the opposite radius; while the mediating colours, which subdue without neutralizing or contrasting, succeed each other side by side all round the scheme: e. g. red subdues and is subdued, or melodized, by the orange and purple contiguous to it, and so on.

* See Note E.