Figure 2-12. Beam of light reflecting back.

TM 9-258

c. These simple experiments illustrate one of the

reflected is termed the reflected ray. An imaginary line at

right angles to the surface is called the normal or

dependable forms of action of light. Light can be

perpendicular. The angle between the incident ray and

reflected precisely to the point where it is required

the normal is the angle of incidence, while the angle

because any kind of light, on being reflected by a

between the reflected ray and the normal is the angle of

smooth, polished surface, acts in the same manner.

This action of light is put to use in many types of fire-

control instruments.

d. The ray of light which strikes the surface is

called the incident ray (fig 2-13). The ray which is

Figure 2-13. Terms used with reference to reflected light.

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