Incidence
the manner of falling on, or the direction in which a body, or a ray of light, heat, etc., falls upon any formed by two straight lines, one the line of incidence of a ray of light or heat, or plane, and the other a perpendicular to that plane. The angle formed by the perpendicular and the line of departure that plane. The angle formed by the angle of reflection, and is always equal perpendicular and the line of departure taken by the elastic body is called the the straight line taken by a ray of light or heat, or an elastic body moving to strike a plane at an acute or right 1 angle.