half are negative and produce chemical action; and that in the centre those opposite influences neutralise each other. The varying phenomena of Colour, then, are not owing to a mere difference in the vibratory speed of the rays of the spectrum, but also to the electric difference of these rays, which, positive at the red end, and negative at the blue, flash up into yellow or white light in the centre where they meet.

In considering, then, the impression made on our eye by the colours of the spectrum, there are two points to be considered. In regard to illuminating power, the strongest point of the spectrum is the yellow,-in point of vibratory power, it is the red; and the colour which makes the strongest impression on our visual sense is the red-orange or scarlet, which, lying between the red and yellow, combines in fullest force the illuminating and vibratory powers. Hence it would appear that Colour is a vibratory phenomenon of the ethereal rays,— intermediate between Heat on the one hand and Actinism on the other, and attended by an overlapping of the electropositive and electro-negative rays, of which Heat and Actinism are the representatives. But whether heat and actinism are not themselves the necessary products of a certain rate of vibration in the ether, and so the whole phenomenon of Colour be practically reducible to one of ratio of vibration, I do not profess to say. Men will get at the root of all those things by-and-by. Meanwhile, it is instructive to observe, from a paper upon Radiant Heat read before the British Association by Professor Powell, that heat-rays, or rays emanating from a hot body, when refracted, present identically the same phenomenon as those of light :-namely, that the rays of the heat-spectrum which vibrate most slowly have a heating but not an illuminating power; those of greater velocity, a luminiferous property also; and those of the greatest velocity, little heating or luminiferous, but higher chemical power.

There are some very curious phenomena connected with Colour, which invite attention from their interesting character,

and challenge inquiry from their importance. The primary colours of the spectrum, like the notes of the fundamental chord in music, blend beautifully, and are pleasing alike when seen mixed, side by side, or in succession. But when we come to mixtures of the secondary and tertiary colours, it cannot fail to be perceived that brilliance of hue is vanishing more and more; and there are some colours whose union produces nothing but a muddiness. This is the result of discord, which tends to extinguish light and colours, as it tends to destroy sounds, and ever produces a disagreeable effect upon the senses. A coloured grey or dull dingy brown is the most general result of the mixture of discordant colours; and this is precisely the colour of mud-which by universal consent is pronounced disagreeable, although, according to Lord Jeffrey's theory, people should like that colour as much as any other. Human nature, however, prefers the pure bright colours of the spectrum; and artists should remember in these days of loaded palettes and infinitesimal tints that brilliant and beautiful, or what Ruskin calls "holy" colouring, can only be produced by the use of the primaries, either side by side or in mixture. It must be remembered, also, that earthy pigments, however pure, are but poor representatives of the ethereal dyes, and that many things can be done with the latter which, owing to their imperfection, cannot be accomplished with the other. For instance, by means of a lens, we can reassemble the scattered rays of the solar spectrum and once more produce white light; but all the care in the world will not make a mixture of red, blue, and yellow paint, in the proper proportions, produce anything better than a neutral grey. The artist's palette contains only the dry bones of colour, which he can never vivify with the light of heaven.

Another phenomenon, curious in itself, and important as illustrating the action of colour upon our senses, is that displayed in what have been called the accidental colours. These show themselves in various ways. If the eyes are fixed upon

a red wafer upon a white ground, the wafer will appear bordered with a faint green-if the wafer be yellow, the border will be blue-if green, purplish white-if blue, reddish white -if black, by a vivid white. And if the eye be wholly removed from one of these wafers, and fixed on the white ground, it will there perceive a phantom wafer of the colour of the border which surrounded the real one. In these cases, as may be seen, the phantom colours are always the complementaries (or opposite) of the actual ones. A more complex form of this phenomenon is, that if, after looking for some time fixedly at red, so as to excite in your eye an aptitude to see in succession green, you turn your gaze upon a yellow, you will receive an impression resulting from a mixture of green and yellow,-the latter colour being modified by the phantom-supplementary of the red. A very interesting illustration of this law is furnished by the experiments of Mr T. Z. Laurence, which also satisfactorily demonstrate (what every one who has pressed his fingers upon his eyes must know) that sensations of colour may be excited altogether independently of any external colour-stimulus. "If, closing one eye (say the right), any highly luminous white ground, such as some portions of the sky on a sunny day, is viewed with the left through a dark tube, so as to exclude all extraneous light, after a little the eye will begin to feel fatigued, and a librating circular smoky spectrum will be perceived at the end of the tube. When the tube is laid aside and both eyes are directed to the sky, a similar spectrum will be observed, projected, as it were, on the surface of the heavens, but much darker. But if after a time each eye is alternately opened and closed, a rose-coloured spectrum is seen with the left eye, a pale-green one with the right. These appearances are seen still better if, instead of the sky, a white screen is used as the plane of projection in the second part of the experiment. At first an almost black circular disc is seen; this becomes lighter and lighter, till it is finally succeeded in the left eye by

a bright rose-colour disc, surrounded by a violet border; in the right eye by an equally bright green, with a rose border. These spectra sometimes appear as if upon the surface of the screen; sometimes, on the contrary, as if originating within. the eyeball itself, and indeed may be even seen with both eyes closed. To see the above phenomena in all their intensity, a slightly different plan must be adopted. As the field of projection, a sheet of dead black paper in a dark room is to be used; the spectra then seen with either eye are the same, and their colours most splendid, both as regards brightness and tint. At first an emerald-green disc appears, surrounded by a narrow carmine, or, perhaps, more accurately, magenta border; the magenta tint is then seen to encroach more and more upon the green, till the whole disc is of the former colour, surrounded by a bluish-violet border; this last, in its turn, invades the magenta, till the final spectrum is of one uniform indigo-violet colour."

These curious phenomena explain many facts remarked by dealers in coloured stuffs, and often greatly inconvenience artists who, wishing to imitate exactly the colours of their models, work at them so long at a time as to become partially insensible to the true tones. The experience of dealers in coloured stuffs shows, that when a purchaser has for some time looked at a yellow fabric, and is then shown orange or scarlet stuffs, he takes them to be amaranth-red or crimson; for his eye, excited by the yellow, has acquired an aptitude to see violet, and in consequence all the yellow of the scarlet or orange stuff disappears, and he sees red, or a red tinged with violet. A second fact connected with the phenomenon of "accidental colour" is, that if there be presented to a buyer, one after another, a dozen pieces of red stuff, he will consider the last five or six less beautiful than those first seen, although the pieces be identically the same. "What is the cause of this error of judgment? It is that the eyes, having seen six or seven red pieces in succession, are in the same condition as if

they had been looking fixedly for the same period at a single piece of red stuff; so that they have a tendency to see the complementary of Red-that is to say, Green. This tendency necessarily enfeebles the brilliancy of the red of the later-seen pieces [by dashing it with green]. And in order that the merchant may not suffer by the fatigue of his customer's eyes, he must take care, after having shown the latter six or seven pieces of red, to present to him some green pieces, in order to restore the eyes to their normal state. If the sight of the green be sufficiently prolonged to exceed the normal state, the eyes will acquire a tendency to see red-in which case the last six pieces will appear more beautiful than the others." *

The leading fact involved in those singular phenomena is, that whenever the visual sense has been long acted upon by a certain colour, nature at once relieves and gratifies itself by calling up a spectral colour which is the harmonious opposite of the one beheld. And this either simultaneously (as a fringe round the object, if it be small, or by blending with and modifying its hue, if large or in succession, after the coloured object is removed. These spectral hues, to use the common phrase, have no existence in the outer world; they exist only upon the retina of the eye, and are the result of the physical constitution acting in accordance with the wants of the animating Spirit within. I have no doubt, however-as the laws of Matter and of Mind are identical, and as the former always tends to produce what the latter naturally desires-that a similar phenomenon actually exists in the outer world, although too feebly to be discernible; and that the efflux of a certain kind of rays (say red) always tends to produce complementary vibrations (say green) in the surrounding ether. This is known to be the case with regard to Sound; for whenever any note is produced, the surrounding particles of metal or air always produce a series of complementary notes called the harmonics. Maupertuis long ago maintained that, after having listened to any * CHEVREUL, On Colours.

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