Q. How is it known, that a ray of light consists of several different colours?
A. Because, if a ray of light be cast upon a triangular piece of glass (called a prism), it will be distinctly divided into seven colours: 1.—Red; 2.—Orange; 3.—Yellow; 4.—Green; 5.—Blue; 6.—Indigo; and 7.—Violet.
Q. Why does a prism divide a ray of light into various colours?
A. Because all these colours have different refractive powers. Red is refracted least, and blue the most; therefore, the blue colour of the ray will be bent to the top of the prism, and the red will remain at the bottom.
Here the ray AB received on a prism, would have the blue part bent up to C; the yellow part to D; and the red part no further than E.
Q. What is meant by the refraction of a ray?
A. Bending it from its straight line.
Thus the ray AB of the last figure is refracted at B into three courses, C, D, and E.