[ CLXV]
Angles of Reflection
In Fig. 291 we take a side view of the reflected object in order to show that at whatever angle the visual ray strikes the reflecting surface it is reflected from it at the same angle.
Fig. 291.
We have seen that the reflected line must be equal to the original line, therefore mB must equal Ma. They are also at right angles to MN, the plane of reflection. We will now draw the visual ray passing from E, the eye, to B, which is the reflection of A; and just underneath it passes through MN at O, which is the point where the visual ray strikes the reflecting surface. Draw OA. This line represents the ray reflected from it. We have now two triangles, OAm and OmB, which are right-angled triangles and equal, therefore angle a equals angle b. But angle b equals angle c. Therefore angle EcM equals angle Aam, and the angle at which the ray strikes the reflecting plane is equal to the angle at which it is reflected from it.