n. [ Cf. F. incidence. ] [ 1913 Webster ]
1. A falling on or upon; an incident; an event; an occurrence. [ Obs. ] Bp. Hall. [ 1913 Webster ]
2. (Physics) The direction in which a body, or a ray of light or heat, falls on any surface. [ 1913 Webster ]
In equal incidences there is a considerable inequality of refractions. Sir I. Newton. [ 1913 Webster ]
3. The rate or ratio at which something occurs; as, the incidence of murder in Los Angeles; the incidence of cancer in men over 50. [ PJC ]
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. [ 1913 Webster ]