VISUAL SENSATIONS

The number of perceptions produced by the relatively few sense organs of the skin seems quite insignificant when compared to the many different colors occasioned by the activity of the retina of the eye, for the microscopic organs in the retina bring about all of our sensations of color and of light and shade. All of the rest of the rather elaborate apparatus of the eye has to do with spacial perceptions; with form and distance and movement and size.

The normal human retina is sensitive to only some four hundred wave lengths of light. The others, like the ultra violet rays, lie outside the visible spectrum. Yet so efficient is that one small layer of the eye that it can convert these four hundred ether vibrations into approximately twelve million hues and tints and chromas. This number seems astounding because it would probably be impossible for anyone to name as many as twelve hundred separate colors. In fact, although the persons responsible for the new shades in women’s stockings seem to have an unlimited color-vocabulary, most of us get along satisfactorily with an extremely limited one. Yet the fact that only a very few of these twelve million hues and shades have common names does not mean that they cannot all be detected under suitable conditions. Take the one color, black, for instance. How many vastly different shades do you group under that one word?

You can probably name immediately some ten, or maybe twenty objects which you would without hesitation describe as black. Black velvet, black satin, black cotton, black wood, coal, soot, ink, and so on. It is possible that it may never have occurred to you that these blacks are not identical. Yet a little critical attention to them will show you how very different they really are. The black paper looks decidedly grayish when placed beside the velvet. The velvet, itself, begins to pale when it is compared to the darkness of the inside of a black tube. The same variety holds for whiteness. White paper is different from white enamel and white paint. Indeed, it is somewhat difficult to find two kinds of paper whose whiteness is identical. And the white that is got from clear sky reflected in a mirror makes the white of any object look positively dirty.

Without examining any true colors at all we have already collected a variety of shades. And this variety grows when we remember all of the various grays which are darker than the whites but lighter than the blacks. Von Kries, the German physiologist, found that there were two hundred and four different shades of gray between the blackest of black paper and the whitest of white paper. And Kulper, the psychologist, estimated that the best visible black is a thousand times darker than the best visible white.

As soon as the true colors are added to the blacks and whites and grays, the possible visual sensations begin to multiply almost limitlessly. There are literally thousands of reds: dull reds, bright reds, yellowish reds, bluish reds. And there are bluish greens, greenish blues, yellowish greens and greenish yellows. But there is a limit to these color combinations. There are no reddish greens, no greenish reds, no yellowish blues and no bluish yellows.