In"ci*dence (?), n. [Cf. F.
1. A falling on or upon; an incident; an
event. [Obs.] Bp. Hall.
2. (Physics) The direction in which a
body, or a ray of light or heat, falls on any surface.
In equal incidences there is a considerable
inequality of refractions. Sir I. Newton.
Angle of incidence, the angle which a ray of
light, or the line of incidence of a body, falling on any surface,
makes with a perpendicular to that surface; also formerly, the
complement of this angle. -- Line of
incidence, the line in the direction of which a surface
is struck by a body, ray of light, and the like.