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

But as the sun at last was about to set, and its rays, greatly mitigated by the thicker vapours, began to diffuse a most beautiful red colour over the whole scene around me, the shadow colour changed to a green, in lightness to be compared to a sea-green, in beauty to the green of the emerald. The appearance became more and more vivid: one might have imagined oneself in a fairy world, for every object had clothed itself in the two vivid and so beautifully harmonising colours, till at last, as the sun went down, the magnificent spectacle was lost in a grey twilight, and by degrees in a clear moon-and-starlight night.

76.

One of the most beautiful instances of coloured shadows may be observed during the full moon. The candle-light and moon-light may be contrived to be exactly equal in force; both shadows may be exhibited with equal strength and clearness, so that both colours balance each other perfectly. A white surface being placed opposite the full moon, and the candle being placed a little on one side at a due distance, an opaque body is held before the white plane, A double shadow will then be seen: that cast by the moon and illumined by the candle-light will be a powerful red-yellow; and contrariwise, that cast by the candle and illumined by the moon will appear of the most beautiful blue. The shadow, composed of the union of the two shadows, where they cross each other, is black. The yellow shadow (74) cannot perhaps be exhibited in a more striking manner. The immediate vicinity of the blue and the interposing black shadow make the appearance the more agreeable. It will even be found, if the eye dwells long on these colours, that they mutually evoke and enhance each other, the increasing red in the one still producing its contrast, viz. a kind of sea-green.

77.

We are here led to remark that in this, and in all cases, a moment or two may perhaps be necessary to produce the complemental colour. The retina must be first thoroughly impressed with the demanding hue before the responding one can be distinctly observable.

78.

When divers are under water, and the sunlight shines into the diving-bell, everything is seen in a red light (the cause of which will be explained hereafter), while the shadows appear green. The very same phenomenon which I observed on a high mountain (75) is presented to others in the depths of the sea, and thus Nature throughout is in harmony with herself.

79.

Some observations and experiments which equally illustrate what has been stated with regard to coloured objects and coloured shadows may be here added. Let a white paper blind be fastened inside the window on a winter evening; in this blind let there be an opening, through which the snow of some neighbouring roof can be seen. Towards dusk let a candle be brought into the room; the snow seen through the opening will then appear perfectly blue, because the paper is tinged with warm yellow by the candle-light. The snow seen through the aperture is here equivalent to a shadow illumined by a contrary light (76), and may also represent a grey disk on a coloured surface (56).

80.

Another very interesting experiment may conclude these examples. If we take a piece of green glass of some thickness, and hold it so that the window bars be reflected in it, they will appear double owing to the thickness of the glass. The image which is reflected from the under surface of the glass will be green; the image which is reflected from the upper surface, and which should be colourless, will appear red.

The experiment may be very satisfactorily made by pouring water into a vessel, the inner surface of which can act as a mirror; for both reflections may first be seen colourless while the water is pure, and then by tinging it, they will exhibit two opposite hues.

[1] Reservoirs in which water is collected from various small streams, to work the mines.--T.

VII.

FAINT LIGHTS.

81.

Light, in its full force, appears purely white, and it gives this impression also in its highest degree of dazzling splendour. Light, which is not so powerful, can also, under various conditions, remain colourless. Several naturalists and mathematicians have endeavoured to measure its degrees--Lambert, Bouguer, Rumford.

82.

Yet an appearance of colour presently manifests itself in fainter lights, for in their relation to absolute light they resemble the coloured spectra of dazzling objects (39).

83.

A light of any kind becomes weaker, either when its own force, from whatever cause, is diminished, or when the eye is so circumstanced or placed, that it cannot be sufficiently impressed by the action of the light. Those appearances which may be called objective, come under the head of physical colours. We will only advert here to the transition from white to red heat in glowing iron. We may also observe that the flames of lights at night appear redder in proportion to their distance from the eye.--Note F.

84.

Candle-light at night acts as yellow when seen near; we can perceive this by the effect it produces on other colours. At night a pale yellow is hardly to be distinguished from white; blue approaches to green, and rose-colour to orange.

85.