Pho*nau"to*graph (?), n. [Phono- + Gr. 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.
© Webster 1913.