Color.

The Living Age 2594, 24.3.1894

From Longman's Magazine.

Much of the charm of life depends on the blending of the varied colors which adorn nature and beautify art. It is the want of color that intensifies the disheartening chill of winter, for a colorless landscape is stripped of its main element of beauty and fascination. The very insects are decoyed by the bright hues of flowers to follow out nature's presentative work of crossfertilization. The countenance would be expressionless in emotion without the lightning flashes from the angry eye or the roseate light of love on the cheek of maidenhood. The glory of the heavens in sunrise, the triumphal rainbow - arch, the sweet, unstained foliage of June, or the brilliant afterglow of autumn would be to the sensitive eye no more than the dead monotony of photographic effects of mere light and darkness - meaningless and lifeless.

But what is color? It is a common delusion that color is inherent in a body which retains it under all circumstances and conditions. Now, has the gorgeously colored tulip any charm during the night? Has a dark-red rose any beauty when an eye is not looking on it? It is not from a Berkeleyan point of view that this question is asked; for there is by the aggregate evidence of the senses a certainty of the material existence of what is outside of us. But when dosium is burned in a flame, the varied hues in conservatory or a drawing-room are reduced to a curious monotony of yellow. Is color, then, an inherent property of the detailed material phenomena? Very little is said about the nature of color by the ancients, though many of their poets poured forth brilliant effusions when spellbound by nature's enchantment. It is not easy to understand their ideas. They seem to have held color as a property of a body, just as its density or hardness or smell is a property. And they were of opinion that a body could communicate its color to light. Then, is not the occult cause of color in the external object?

Of course the eye has much to do with color. In the color-blind the apparent colors of objects differ widely from their colors as perceived by normal eyes. As the conception of size varies in men according to the formation of the crystalline lens in the eye - some having telescopic, others microscopic formations - so the sensation of color differs in men according to the means of impressing the optic nerves. The apparent color of any light which falls on the normal retina depends mainly on the relative intensities of the excitement produced by the light on certain organs of sense. In color-blindness one or more of these organs of sense is wanting or imperfect. The most common form (called Daltonism, from the famous discoverer of the automatic weights of the elements) depends on the absence of the red sense. From the experiments of Holmgren on two persons, each of whom was found to have one color-blind eye, the other being nearly normal, it was found that these persons could describe the various colors with one eye, but that there was a dead uniformity of color when looking with the other eye. Thus theory was verified by actual observation. A jaundiced vision blanches all nature. A large dose of the medicine santonine affects the color-sense consideraby, and, besudes distorting other colors, makes all persons incapable of perceiving violet and purple. A distinguished scientiest assures us that a purple object appears perceptibly bluer to one eye and redder to the other. Then, is not the main producer of color in the bodily organism?

There is something in the object t ooccasion the sensation of color, which is only recognized by a normal organism. These two necessary components will be again referred to in other connections.

The color of any object depends on its power of retaining or rejecting certain of the constituent colors of white light. All colored bodies possess the property of stopping some of the rays that fall on them, and reflecting others. For example, a violet body absorbs all the rays that fall upon it except the violet, which it reflects. It has been calculated, by the aid of very fine instruments, that the different color-sensations are produced by the vibration of the ether of space through which the waves of light from the object pass. Thus the waves which produce red sensations vibrate at the rate of about four hundred and ninely million million times in a second, whereas the waves which produce violent sensations vibrate at the rate of about seven hundred and forty million million times in a second. Yet it takes a definite time for the sensation to be recognized by the mind, and when the sensation is impressed, it persists for about one-seventh of a second.

The gorgeous display of the rainbow, at the sight of which the hearts of all pure-souled people leap with rapture, suggested to Sir Isaac Newton the necessity for having seven primary colors corresponding to those seen here. But Young and Helmholtz have now conclusively proved that there are only three primaries, viz., red, green, and violet. Moreover, a one-colored rainbow is occasionally observed. On Christmas day, five years ago, Mr. Aitken of Falkirk, one of the most reliable of observers, saw the rare and curious phenomenon on the Ochil Hills. It consisted simply of a red arch, and even the red had a sameness about it. Stranger still, there was also part of a secondary bow, which, too, was of a red hue - not rosy, but deep furnacy. The hills were covered with snow, the setting sun was glowing with a rich hectic light, and the depth of color on all around was indescribable in beauty. The monochromatic rainbow explained all, for the rainbow is simply nature's spectrum of the sun's light. On that occasion tehe sun's light was shorn of all the rays of short-wave length on its passage through the atmosphere, and only the red rays reached the surface of the earth. The depth of the red on the hills was, however, intensified by the overganging of a dense curtain of clouds, which screened off the light of the sky and admitted only the direct softer light. The seven colors of the spectrum are, therefore, not necessary the primary. Sir Isaac's superstition got the better of his calmer scientific judgment.

The three primary color-sensations are considered to be red, green, and violet. Certain mixtures of violet and green produce a blue; red and green also give a yellow. But it is important to observe that these are primary color-sensations, and not primary colors, though the expression "lights of primary colors" is admissible. For it is commonly imagined that the blue and yellow mixed in certain propotions produce various kinds of green. If yellow and blue pigments be mixed together with water, the green color produced is not a mixture of blue and yellow colors. It is the one color which is not freely absorbed either by the yellow or by the blue pigment. The yellow pigment removes the greater part of blue, indigo, and violet rays; the blue pigment removes the greater part of the red, orange, and yellow. Thus the light that finally escapes is mainly green. It is curious to notice, too, that the sunlight passing through glass of one color is not only of that color. What is called the ordinary solar spectrum is produced by allowing a ray of sunlight to enter a narrow slit and pass through one or more prisms. If a bit of red glass be held over the slit the whole length of the spectrum is not reddened; there is no color in the spectrum of the glass whan that color does not exist in the ordinary (rainbow) spectrum. If the red glass be pretty pure, only red and a little orange are visible in the spectrum; all the rest is cut away. Wonderful is it also that the colors seen in natural objects are chiefly residuals left after internal absorption. A tulip with green leaves can only be seen in pure light or in the corresponding colors of the spectrum. If it is placed in the red band of teh spectrum the flower shines brilliantly red, while the leaves shine dull red, not green. If moved to any other band of the spectrum the red petals become black and the green alters much.

Is there any substance known to man which has no color? It is a natural and excusable delusion to consider that pure water is colorless. Looking through a crystal vessel filled with water, one would be astonished to be told that water has an inherent hue. Waterfalls in the Scottish Highlands, where there is no contamination, present to the eye the purest whiteness, without any symptom of leadenness or tinness. Skilled observers, like the late Sir Robert Christison, consider that water is more or less colored by some suspended matter. It is now, however, known that water is a blue transparent medium absorbing the rays of the red end of the spectrum and transmitting the rays of the blue end. If a very long blackened tube, which has a clear glass plate fixed to the bottom, be filled with pure water, and through this a white surface be examined, the light transmitted will be found to be blue. Even distilled water has the same property. To thoroughly verify this, take three different sets of apparatus for the distillation and examination - one of glass, the second of brass, and the thirds with a platinum condenser.  If the color of the distilled water is due to impurities, as the impurities in these three cases must be different, the colors will also be different. But put samples of the water distilled by the three sets of apparatus into three darkened tubes (with glass plates at the ends), and through the tubes look at a bright white surface; the effect is the same in all three cases - the color is blue, almost exactly of the same hue as a solution of Prussian blue. This is corroborated by the fact that the purer water is in nature the bluer is the tint. The writer of the work entitled "Across Patagonia" describes a lake seen on the Cordilleras as one "whose crystal waters were of the most extraordinary blue he ever beheld."

Various instruments have been constructed to determine and illustrate the mixing of color-lights, but the best of these is the result of the ingenious inventiveness of Mr. John Aitken of Falkirk. A simplified form of his chromomictor, sufficient for plain experiments, can be here described. Procure a common eye-piece from any optician, and fix it to the end of a brass tube. To the other end of the tube fix a circular piece of wood, a concentric circle having been cut out of it. Into this circle fit equal sector pieces of red, green, and violet-colored glass (the three primaries). Inside of this arrange a circular blackened disc of metal, with a round opening cut out eccentrically in it, so as in one porisiton of its movement to be exactly opposite the circle with the colored glasses, and in the diametrically opposite position of its movement to uncover only a portion of one of the glasses. As the instrument is moved round by the hand this blackened plate allows the sunlight to pass through differently proportioned parts of the three colored sectors. The eye, looking through the eye-piece, receives the combination of different proportions of the three primary color-lights. By this kaleidoscopic arrangement an endless variety of tints and shades of color can be produced.

Curious effects are simply produced in this way. in the top of a box have a circular window, glazed with three sections of red, green and violet glass, so proportioned that the resultant light produced from the three is white. Place a flat, opaque ring a short distance above the white bottom of the box, and the eye will be dazzled with the gorgeous display of prismatic-like colors on the bottom. This will be covered with most varied and brilliant hues, caused by the penumbra of the opaque body being lighted with different colors on the different sides. When the red and the green circles of light overlap, a brilliant yellow is produced; where the green and the violet overlap are the blues; and the red and the violet give the purples; while in the centre, when all the three circles overlap, white is produced. This is the best practical and simple way of testing the theory of the three primary color-lights. These experimetns explain why there is so little appearance of colored light in some cathedrals, though the windows are heavily stained; though the sun blazes through brilliantly colored glass, yet there is only visible the characteristic "dim religious light."

And two colored lights which when mixed produce white light are termed "complementary." All are familiar with the changing color of printed names with the eyes open and shut, or when fixed steadily on the name and transferred suddenly to a white surface. On has too often to amuse himself in this way at a railway junction, waiting for a train. He looks on the yellow letters with an indigo-blue enamel surrounding which tell of some remarkable soap or cocoa; he lifts his eyes to the grey sky, and then he sees blue letters on a yellow enamel. If the blind on a bedroom window be white, and the light not very bright, and if the observer looks steadily at a black object on the table, on closing his eyes again he will see the exact form of the object wuite white - not a bad way of accounting for ghosts.

Colors formed though thin films of through mica-schist by polarized light are extremely beautiful. What a variety of brilliant hues in concentric circles are presented on the window of a closed carriage when the clear moon whines through on an intensely frosty night! The glorious tints on soap-bubbles entrance a Newton as well as amuse a child.

The secret of the production of color is not yet revealed. The unrivalled hues of the tulip and the rose are formed from the black soil. But how? None can say. Yet one is no less startled by the endless variety of color now produced from coal-tar. From that apparently useless substance, perfumes, medicines, and sweeteners have been formed which have startled men. But color appeals t othe eye. Only thirty-six years ago Perkin "gathered up the fragments" in coal.tar, and produced the beautiful mauve dye. Now, from the greasy material which was considered useless, is produced madder, which makes coal-tar worth a hundred pounds a ton. This coloring matter alone now employs an industry of two millions sterling per annum. One ton of good cannel coal, when distilled in gas retorts, leaves twelve gallons of coal-tar, from which are produced a pound of benzine, a pound of toluene, a pound and a half of phenol, six pounds of naphthalene, a small quantity of xylene, and half a pound of anthracene for dyeing purposes. According to Roscoe, there are sixteen distinct yellow colors, twelve orange, thirty red, fifteen blue, seven green, and nine violet, besides the number of browns, and an infinite number of blendings of all shades. What a marvellous color-producer is coal-tar!

Why is it that the colors of a soap-bubble change as the film gradually alters the thickness? Another cause of color is here involved - that of interference. If a stone be thrown into a smooth pond a circular wave is produced, gradually widening towards the edge of the pond; if a second stone be thrown into the pond, a second wave will be produced, which will influence the first. If the stones be dropped in simultaneouslyat tge same spot, the wave will just be doubled in height; and if the second stone be thrown in exactly a wave-length behind the first, the same effect would be observed. Of, however, the second stone be thrown into the water exactly half a wave-length begind the first, the motion of the water will be destroyed. Similarly with light; when light impinges on the soap-bubble, part of it is reflected from the exterior surface, and part enters the film, and is reflected from the interior surface. This latter portion traverses the water medium between the two surfaces twice, and is therefore kept behind the first reflected ray. The two sets of waves interfere with each other, and produce a colored light instead of a white light. Other waves, again, may destroy each other, and extinguish the light. Some of the constituent colors of the impinging white light - formed by their passage through the film - interfere so as to destroy each other, while others remain unaffected. As the film diminishes in thickness, the colors must necessarily vary. In this way is accounted for the marvellous variety of beauty of colors in the soap-bubble, the iridescence of oil upon water, the changing color of steel when being tempered, and the gaudiness of some insects' wings.

The beauty of dress depends much upon the harmony of colors. This is affected by a combination of the three primaries, either pure, or in combination with each other. Colors are modified in tone by the proximity of other different colors. By ordinary gas-light blue becomes darker, red brighter, and yellow lighter. By this artificial light a pure yellow appears lighter than white itself when viewed in contrast with certain other colors. In this way highly polished brass is often mistaken for silver. At twilight blue appears much lighter than it is, red much darker, and yellow slightly darker. Colors, too, have the power of influencing the beholder in various ways. We speak of warm colors - like the "rosy red flushing in the northern night;" red is then a warm, cheerful, and exciting color. We speak, too, of cold colors - like the leaden grey of threatening clouds.

The shades of blue have been lately employed to detect the grades of impurity of the air. This sanitary detective is Mr. Aitken's last marvellous discovery. The principle on which the construction of the koniscope is based has been explained before in our article on dust. A dust-particle, at a certain temperature and degree of moisture in the air, becomes a free surface to attract the moisture so as to form a fog-particle. When a jet of steam is made to pass through a tube containing dusty air, beautiful colors are observed in the steam. With ordinary condensation the color varies from a fine green to lovely blue of different depths. The pale blues equal any sky blue, while the deeper blues are finer than the dark blues seen in the sky, having a peculiar softness and fulness of color. Instead of using steam, he produced a fog by rarifying the air in a closed tube containing air, and all around wet with water. By a stroke of the air pump attached, the air became rarified, the dust-particles seized the moisture in the air and from the sides, and formed fog-particles. The same colors were seen: slight blue with ordinary air, impregnated with dust-particles. The tube of the koniscope is graduated by noticing the depth of the blue produced, and counting the number of imperfect color-sense in the compulsory class for officers' certificates, and one in sixteen in the voluntary class. Some described black as green, others red as green, pink as green, drab as green. The color test should be made compulsory for  all public servants on sea and land who have so many thousands of lives at the mercy of their eyes in discriminating the colors of signals at night.

Why is it that in the zenith we have in fine, clear weather a deep, rich blue? Because there is always above us a haze, however fine. The particles in the haze of the heavens correspond with those of the tube in the oniscope, and the blue color is caused by the light through depth of fine haze. If there was no dust haze above us, the sky would be black, that is, we would be looking into the blackness of limitless space. But through the dust haze the blue light pierces for a considerable distance, and becomes of a deep shade. Sky and sea and earth are all colored. Gladsome are all animated beings who can appreciate the fine tints and the endless variety of hues. The birds are vain in their gorgeous plumage, and ladies show their taste by their choice of harmonious colors to suit their complexion. No flash, but harmony of color, manifests the educated taste and the refined mind. "Be true to nature and nature  will be true to you," is and order which mus tbe obeyed without dispute, in color as in all else; who breaks that order will suffer sometime.

J. G. McPherson.