The focus is the point to which converging rays are directed.
Diverging, starting from a point, and separating. Converging, drawing together towards a point.
464. What is the constitution of a ray of light?
A ray of white light, as we receive it from the sun, is composed of a number of elementary rays, which, with the aid of a triangular piece of glass, called a prism, may be separated, and will produce under refraction the following colours:—
1. An extreme red ray—a mixture of red and blue, the red predominating.
2. Red.
3. Orange—red passing into and combining with yellow.
4. Yellow—the most luminous of all the rays.
5. Green—yellow passing into and combining with the blue.