Incidence

[Sarah]

The direction in which a body, or a ray of light or heat, fallson any surface.In equal incidences there is a considerable inequality ofrefractions. Sir I. Newton.Angle of incidence, the angle which a ray of light, or the line ofincidence of a body, falling on any surface, makes with aperpendicular to that surface; also formerly, the complement of thisangle.-- Line of incidence, the line in the direction of which a surfaceis struck by a body, ray of light, and the like.