Page:The fairy tales of science.djvu/120

92 a small hole in the window-shutter, be allowed to fall on a prism, its subtle constituents are mysteriously disturbed, and precipitate themselves at different distances on a white tablet, or screen, placed to receive them. What marvellous change is this! A moment since the beam formed a bright spot on the screen, but now in place of the spot we see a lengthened band of variegated colours! On one side of the prism a pencil of brilliant white sunlight falls upon the surface of the glass; on the other the pencil spreads out and paints upon the screen a ribbon whose beauteous hues infinitely surpass the colours that lie on the artist's palette! Examine these colours attentively. At the bottom of the band we find red, above it orange, then yellow, green, blue, indigo, and lastly violet. These colours pass by insensible gradations into each other, so that it is impossible to say where one colour ends and another begins.

We have thus decomposed the visible principle of the sunbeam into its elementary colours, for our readers must know that white is a compound of seven hues. The natural colours of bodies depend entirely upon the manner in which they decompose the sunbeams. A rose is red because its petals have the property of absorbing all the elementary colours of light except red, which it reflects. The pigments used by the artist are not, in themselves, colours; they are merely substances that absorb certain rays and reflect others. Our readers will now understand