Theory of Colours — trans. Charles Lock Eastlake (1840)

If light impinges on a colourless body, is reflected from it or passes through it, colour immediately appears; but it is necessary here to remember what has been so often urged by us, namely, that the leading conditions of refraction, reflection, &c., are not of themselves sufficient to produce the appearance. Sometimes, it is true, light acts with these merely as light, but oftener as a defined, circumscribed appearance, as a luminous image. The semi-opacity of the medium is often a necessary condition; while half, and double shadows, are required for many coloured appearances. In all cases, however, colour appears instantaneously. We find, again, that by means of pressure, breathing heat (432, 471), by various kinds of motion and alteration on smooth clean surfaces (461), as well as on colourless fluids (470), colour is immediately produced.

692.

The slightest change has only to take place in the component parts of bodies, whether by immixture with other particles or other such effects, and colour either makes its appearance or becomes changed.

THE FORCE OF COLOUR.

693.

The physical colours, and especially those of the prism, were formerly called "_colores emphatici_," on account of their extraordinary beauty and force. Strictly speaking, however, a high degree of effect may be ascribed to all appearances of colour, assuming that they are exhibited under the purest and most perfect conditions.

694.

The dark nature of colour, its full rich quality, is what produces the grave, and at the same time fascinating impression we sometimes experience, and as colour is to be considered a condition of light, so it cannot dispense with light as the co-operating cause of its appearance, as its basis or ground; as a power thus displaying and manifesting colour.

THE DEFINITE NATURE OF COLOUR.

695.

The existence and the relatively definite character of colour are one and the same thing. Light displays itself and the face of nature, as it were, with a general indifference, informing us as to surrounding objects perhaps devoid of interest or importance; but colour is at all times specific, characteristic, significant.

696.

Considered in a general point of view, colour is determined towards one of two sides. It thus presents a contrast which we call a polarity, and which we may fitly designate by the expressions _plus_ and _minus_.

_Plus. Minus_.

Yellow. Blue.
Action. Negation.[1]
Light. Shadow.
Brightness. Darkness.
Force. Weakness.
Warmth. Coldness.
Proximity. Distance.
Repulsion Attraction.
Affinity with acids. Affinity with alkalis.

COMBINATION OF THE TWO PRINCIPLES.

697.

If these specific, contrasted principles are combined, the respective qualities do not therefore destroy each other: for if in this intermixture the ingredients are so perfectly balanced that neither is to be distinctly recognised, the union again acquires a specific character; it appears as a quality by itself in which we no longer think of combination. This union we call green.

698.

Thus, if two opposite phenomena springing from the same source do not destroy each other when combined, but in their union present a third appreciable and pleasing appearance, this result at once indicates their harmonious relation. The more perfect result yet remains to be adverted to.

AUGMENTATION TO RED.

699.

Blue and yellow do not admit of increased intensity without presently exhibiting a new appearance in addition to their own. Each colour, in its lightest state, is a dark; if condensed it must become darker, but this effect no sooner takes place than the hue assumes an appearance which we designate by the word reddish.

700.

This appearance still increases, so that when the highest degree of intensity is attained it predominates over the original hue. A powerful impression of light leaves the sensation of red on the retina. In the prismatic yellow-red which springs directly from the yellow, we hardly recognise the yellow.

701.

This deepening takes place again by means of colourless semi-transparent mediums, and here we see the effect in its utmost purity and extent. Transparent fluids, coloured with any given hues, in a series of glass-vessels, exhibit it very strikingly. The augmentation is unremittingly rapid and constant; it is universal, and obtains in physiological as well as in physical and chemical colours.

JUNCTION OF THE TWO AUGMENTED EXTREMES.

702.

As the extremes of the simple contrast produce a beautiful and agreeable appearance by their union, so the deepened extremes on being united, will present a still more fascinating colour; indeed, it might naturally be expected that we should here find the acme of the whole phenomenon.

COMPLETENESS THE RESULT OF VARIETY.

703.

And such is the fact, for pure red appears; a colour to which, from its excellence, we have appropriated the term "purpur."[2]

704.

There are various modes in which pure red may appear. By bringing together the violet edge and yellow-red border in prismatic experiments, by continued augmentation in chemical operations, and by the organic contrast in physiological effects.

705.