INCIDENCE n.
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…
INDEX n.
That which guides, points out, informs, or directs; a pointer or a hand that directs to anything, as the hand of a watch, a movable finger on a gauge, scale, or other graduated instrument. In printing, a sign [*] used to direct particular attention to a note or paragraph; -- called also fist.