Page:Landscape Painting by Birge Harrison.djvu/40

 throughout the scale until with the ultra-violet it reaches 61,000 to the inch. Here we step out once more into the unknown.

Yet color has no actual existence. It is only by courtesy that we can use the word. Nature is a monochrome save when there are living eyes to see it. The trees are not really green, nor are the flowers red and yellow and blue. Each object simply reflects rays of light which vibrate at a given rate of speed; and these rays, smiting upon the sensitive retina of the eye, produce the impressions which we know as color. Were it not for the retina there would be no color; and when the sensory nerves of the retina are partially paralyzed or deficient, as in the case of the color-blind, nature appears to the eye in her true monochromatic garb.

The human eye resembles closely the