The line of reflection is the line in which the rays of light are returned from the image formed in the glass to the eye of the observer.
Reflection—a turning back.
521. What is the angle of incidence?
The angle of incidence is the angle which rays of light, falling on a reflecting surface, make with a line perpendicular to that surface.
Fig. 14.—EXPLAINING THE LINES AND ANGLES OF INCIDENCE AND OF REFLECTION.
522. What is the angle of reflection?
The angle of reflection is the angle which is formed by the returning rays of light, and a line perpendicular to the reflecting surface. It is always equivalent to the angle of incidence.
Take a marble and roll it across the floor, so that it shall strike the wainscot obliquely. Let A in the diagram represent the point from which the marble is sent. The marble will not return to the hand, nor will it travel to the line B, but will bound off, or be reflected, to C. Now B is an imaginary line, perpendicular to the reflecting surface; and it will be found that the path described by the marble in rolling to the surface and rebounding from it, form, with the line B, two angles that are equal. These represent the angles of incidence and of reflection, and explain why the reflection of a person standing at A before a mirror, would be seen by another person standing at C. This simple law in optics explains a great many interesting phenomena, and therefore it should be clearly impressed upon the memory.