Color

in physics, a class of sensations made by light on the optic nerve. Light consists of transverse vibrations of so-called "ether." All the vibrations are inconceivably rapid and short, but they vary in rapidity and length. Sunlight consists of vibrations of all lengths. It creates the sensation known as white. Light falling on certain surfaces is wholly absorbed, none of it reaching the optic nerve. This sensation, or lack of sensation, is known as black. White and black are not regarded as colors. If white sunlight be caused to pass through a prism, the waves are sorted or grouped, or, better yet, arranged in order of shortness and frequency.

No doubt there are waves that are too short, and too frequent to create a sensation on the nerve of the human eye. For aught we know, the eye of beast or insect or bird may experience delicate sensations of color unknown to man. However that may be, the shortest and most rapid waves known to the human eye are called violet rays. We are virtually certain that there are light waves too long, too slow, to excite the optic nerve. It may be that certain animals see light that our more delicate optic nerve cannot detect, but, be that as it may, the longest and slowest waves that are noticeable to the human eye are known as red waves.

Between the extremes of violet and red there may be an imperceptible graduation. The eye recognizes an almost infinite number of colors, shades, and tints, but seven seemingly distinct colors attract particular attention. If a ray of white light be decomposed by a prism into a band of colored light known as the color spectrum, the eye recognizes seven unmistakable colors--violet, indigo, blue, green, yellow, orange, and red. The initials of these spectrum colors spell vibgyor.

The seven colors of the spectrum are called popularly the primary colors, but the term is used otherwise by scientists. It has been found, for instance, that yellow of the spectrum may be resolved into red and green, and that spectral red and green, combined, form yellow, Spectral red, green, and violet cannot be resolved into other colors. They are called, therefore, the primary spectral colors. In the case of pigments-coloring materials-it is found that blue is a primary color. As we deal with pigment colors, rather than spectral colors, red, green, and blue are considered the primary colors.

If the primary colors of the spectrum be painted on a disk, a sector to each color, and the disk be rotated rapidly, the colors blend into a white or gray. Colors that blend to form white or gray are called complementary; thus the primary colors are complementary. The term is applied more frequently, however, to a pair of colors that blend to produce white or gray. Such pairs of spectral colors are red and green-blue, orange and blue, yellow and indigo-blue, green-yellow and violet. In mixing dyes, however, it is found that blue and yellow are complementary. A color darker than standard is called a shade ; a color lighter than standard, a tint. Thus we have a standard blue, and a series of shades of blue, and a second series of tints of blue. At one time, it was held that an eye for color was distressed by placing any but complementary colors together. The modern milliner, however, claims that, by selecting the proper shades or tints, any colors may be combined without offending correct taste.

The analogy between harmony in color and harmony in music is close. The wave length of red is about double the wave length of violet. Color bears the relation to light that pitch bears to sound. Violet is an octave higher than red in the scale of colors. The visible colors comprise but an octave. The waves shorter than violet are known as ultra-violet; those longer than red are known as infra-red. The entire scale from the lowest infra-red to the highest ultra-violet is perhaps seven light octaves.

The following table gives the standard wave lengths. The unit is the micron, or 1/1000 of a millimeter.

As stated elsewhere, the list of colors is well nigh endless. Chapman's color chart for the identification of the plumage of birds contains thirty colors.

A red wall surface is a surface that absorbs all other rays and reflects red rays. A red pane of glass in a stained window is a pane that stops all other rays and allows the red rays to pass through. Green goggles stop all but green light, the color that is easiest on the eye. Wall papers should be chosen not only for harmony of color, but with reference to the demand for light. Yellow reflects three times as much light as dark brown. If a room be too light, vermilion and green and black will soften the glare; if a room or passage be deficient in light, yellows and white are to be preferred.

The power of various colors and surfaces to reflect light is shown in the following table, which gives the percentage of the total incident light that is reflected :

Students of nerve diseases have investigated the effect of color. The name of chromatography has been given to the new science based on the effect of color on the human body. It has been found that red is an excitant; that orange and yellow also excite, but in a less degree. Violet, indigo, and blue have a calming effect. Green excites a feeling of pleasure and then a sense of peace. According to the conclusions of the scientists, the various colors affect blonde people more than they do brunettes. Fleshy patients are more susceptible to the effects of colored lights than are spare patients. Nervous people should avoid living in rooms papered or draped with red. Violet, green, and blue are colors to be preferred.

See Smallpox; Cancer; Light; Finsen