Source : Webster's Revised Unabridged Dictionary (1913)

Phonautograph \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.