Scientific American 20, 11.11.1865

There are three simple colors — red, yellow and blue — and, by a mixture of these, alt others are made. The way those are mingled to form the seven colors of the rainbow, is best seen by observing their position in the solar spectrum. When light passes from one medium to another of different density, it is always bent or refracted from its straight course, some of the rays being retracted wore than others. Of the primitive colors, the red ray is refracted the least, yellow next, and blue the most. By passing the light through a triangular prism, it is twice refracted in the same direction, and as the more refrangible rays are, of course, bent the most at each refraction, the colors are to this way as widely separated as they can be by any process, though they are not completely separated even by this plan, for the different colors lap over each other on their borders. It is by this lapping over and consequent intermingling, that the other four colors of the spectrum are formed. The position the spectrum of the three primitive colors Is illustrated in the annexed diagram, and a glance at this will show which of them mingle at their bound. arid, and what, consequently, should be the position of the secondary colors of the spectrum resulting from the mixture.

Orange is a mixture of red and yellow, and the position of orange in the spectrum is between the red and yellow. Green Is a mixture of yellow and blue, and the position of green is between the yellow and blue. Indigo and violet are mixtures of blue and red, and the position of these is beyond the blue. This is the most curious and mysterious thing in the spectrum; while the red are the least refrangible rays of light in the sunbeam, a portion of them are found beyond the blue; indigo and violet are formed as they would be it the spectrum were bent in a circle, and blue were thus made to touch red at the opposite end of the spectrum. Most observers now recognize a third color resulting from the mixture of red and blue, which they call lavender; the position of this is beyond the violet.

Beside the seven or eight colors of the spectrum, a great many others are found in nature and art, and all these are seen on examination to be mixtures in various proportions of red, yellow and blue; scarlet is a mixture of red and yellow, with a larger pro-portion of red than in orange; by widing hlue to red in increasing proportions we have, first, pink, then crimson, then purple, then indigo, while violet and lavender seem to be fainter shades of the mixture. By looking at the trees of a forest, we see that there arc not merely several shades of green, but innumerable colors of green, resulting from the different proportions in which blue and yellow are mingled.

The endless variety ot colors with fancy names, invented by traders who sell dry goods, or women who purchase them, will be seen on examination to result from mingling in different proportions of red, yellow and blue. Finally, white results them blending the three primitive colors in the exact proportions In which they occur in the sunbeam, while pure black is simply the absence of any light whatever.

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