n. [ Phono- + Gr. a'yto`s self + -graph. ] (Physics) An instrument by means of which a sound can be made to produce a visible trace or record of itself. It consists essentially of a resonant vessel, usually of paraboloidal form, closed at one end by a flexible membrane. A stylus attached to some point of the membrane records the movements of the latter, as it vibrates, upon a moving cylinder or plate. [ 1913 Webster ]