The Science of Human Nature by William Henry Pyle (best ereader under 100 TXT) 📕

When all the vibration frequencies affect the eyes at the same time, we see no color at all but only brightness. This is due to the fact that certain vibration frequencies neutralize each other in their effect on the retina, so far as producing color is concerned. Red neutralizes green, blue neutralizes yellow, violet neutralizes yellowish green, orange neutralizes bluish green.

All variations in vision as far as color and brightness are concerned are due to variations in the stimulus. Changes in vibration frequency give the different colors. Changes in intensity give the different brightnesses: black, gray, and white. All explanations of the many interesting phenomena of vision are to be sought in the physiological action of the eye.

Besides the facts of color and light and shade, already mentioned, some further interesting visual phenomena may be mentioned here.

Visual Contrast. Every color makes objects near it take on the antagonistic or complementary color. Red makes objects near appear green, green makes them appear red. Blue makes near objects appear yellow, while yellow makes them appear blue. Orange induces greenish blue, and greenish blue induces orange. Violet induces yellowish green, and yellowish green induces violet. These color-pairs are known as antagonistic or complementary colors. Each one of a pair enhances the effect of its complementary when the two colors are brought close together. In a similar way, light and dark tints act as complementaries. Light objects make dark objects near appear darker, and dark objects make light objects near seem lighter.

These universal principles of contrast are of much practical significance. They must be taken account of in all arrangements of colors and tints, for example, in dress, in the arrangement of flowers and shrubs, in painting.

Color-Mixture. If, on a rotating motor, disks of different colors—say red and yellow—are placed and rotated, one sees on looking at them not red or yellow but orange. This phenomenon is known as color-mixture. The result is due to the simultaneous stimulation of the retina by two kinds of ether vibration. If the colors used are a certain red and a certain green, they neutralize each other and produce only gray. All the pairs of complementary colors mentioned above act in the same way, producing, if mixed in the right proportion, no color, but gray. If colored disks not complementary are mixed by rotation on a motor, they produce an intermediate color. Red and yellow give orange. Blue and green give bluish green. Yellow and green give yellowish green. Red and blue give violet or purple, depending on the proportion. Mixing pigments gives, in general, the same results as mixing by means of rotating the disks. The ordinary blue and yellow pigments give green when mixed, because each of the two pigments contains green. The blue and yellow neutralize each other, leaving green.

Visual After-Images. The stimulation of the retina has interesting after effects. We shall mention here only the one known as negative after-images. If one will place on the table a sheet of white paper, and on this white paper lay a small piece of colored paper, and if he will then gaze steadily at the colored paper for a half-minute, it will be found that if the colored paper is removed one sees its complementary color. If the head is not moved, this complementary color has the same size and shape as the original colored piece of paper. The negative after-image can be projected on a background at different distances, its size depending on the distance of the background. The after-image will be found to mix with an objective color in accordance with the principles of color-mixture mentioned above.

After-image phenomena have some practical consequences. If one has been looking at a certain color for some time, a half-minute or more, then looks at some other color, the after-image of the first color mixes with the second color.

Adaptation. The fact last mentioned leads us to the subject of adaptation. If the eyes are stimulated by the same kind of light for some time, the eyes become adapted to that light. If the light is yellow, at first objects seem yellow, but after a time they look as if they were illuminated with white light, losing the yellow aspect. But if one then goes out into white light, everything looks bluish. The negative after-image of the yellow being cast upon everything makes the surroundings look blue, for the after-image of yellow is blue. All the other colors act in a similar way, as do also black and white. If one has been for some time in a dark room and then goes out to a lighter place, it seems unusually light. And if one goes from the light to a dark room, it seems unusually dark.

Hearing or Audition. Just as the eye is an organ sensitive to certain frequencies of ether vibration, so the ear is an organ sensitive to certain air vibrations. The reader should familiarize himself with the physiology of the ear by reference to physiologies. The drum-skin, the three little bones of the middle ear, and the cochlea of the inner ear are all merely mechanical means of making possible the stimulation of the specialized endings of the auditory nerve by vibrations of air.

As the different colors are due to different vibration frequencies of the ether, so different pitches of sound are due to differences in the rates of the air vibrations. The low bass notes are produced by the low vibration frequencies. The high notes are produced by the high vibration frequencies. The lowest notes that we can hear are produced by about twenty vibrations a second, and the highest by about forty thousand vibrations a second.

Other Sense Organs. We need not give a detailed statement of the facts concerning the other senses. In each case the sense organ is some special adaptation of the nerve-endings with appropriate apparatus in connection to enable it to be affected by some special thing or force in the environment.

In the case of taste, we find in the mouth, chiefly on the back and edges of the tongue, organs sensitive to sweet, sour, salt, and bitter. In the nose we have an organ that is sensitive to the tiny particles of substances that float in the air which we breathe in through the nose.

In the skin we find several kinds of sense organs that give us the sensations of cold and warmth, of pressure and pain. These are all special and definite sensations produced by different kinds of organs. The sense of warmth is produced by different organs from those which produce the sense of cold. These organs can be detected and localized on the skin. So, also, pain and touch or pressure have each its particular organ.

Within the body itself we have sense organs also, particularly in the joints and tendons and in the muscles. These give us the sensations which are the basis of our perception of motion, and of the position of the body and its members. In the semicircular canals of the inner ear are organs that give us the sense of dizziness, and enable us to maintain our equilibrium and to know up from down.

The general nature of the sense organs and of sensation should now be apparent. The nervous system reaches out its myriad fingers to every portion of the surface of the body, and within the body as well. These nerve-endings are specially adapted to receive each its particular form of stimulation. This stimulation of our sense organs is the basis or cause of our sensations. And our sensations are the elementary stuff of all our experience. Whatever thoughts we have, whatever ideas or images we have, they come originally from our sensations. They are built up out of our sensations or from these sensations as they exist in memory.

Defects of Sense Organs. The organs of sight and hearing are now by far the most important of our sense organs. They enable us to sense things that are at a distance. We shall therefore discuss defects of these two organs only. Since sensations are the primary stuff out of which mind is made, and since sight and hearing are the most important sense organs, it is evident that our lives are very much dependent on these organs. If they cannot do their work well, then we are handicapped. And this is often the case.

The making of the human eye is one of the most remarkable achievements of nature. But the making of a perfect eye is too big a task for nature. She never makes a perfect eye. There is always some defect, large or small. To take plastic material and make lenses and shutters and curtains is a great task. The curvature of the front of the eye and of the front and back of the crystalline lens is never quite perfect, but in the majority of cases it is nearly enough perfect to give us good vision. However, in about one third of school children the defect is great enough to need to be corrected by glasses.

The principle of the correction of sight by means of glasses is merely this:[1] When the focusing apparatus of the eye is not perfect, it can be made so by putting in front of the eye the proper kind of lens. There is nothing strange or mysterious about it. In some cases, the eye focuses the light before it reaches the retina. Such cases are known as nearsightedness and are corrected by having placed in front of the eyes concave lenses of the proper strength. These lenses diverge the rays and make them focus on the retina. In other cases, the eye is not able to focus the rays by the time they reach the retina. In these cases, the eyes need the help of convex lenses of the proper strength to make the focus fall exactly on the retina.