Source : Webster's Revised Unabridged Dictionary (1913)

Phonoscope \Pho"no*scope\, n. [Phono- + -scope.] (Physics)
   (a) An instrument for observing or exhibiting the motions or
       properties of sounding bodies; especially, an apparatus
       invented by K["o]nig for testing the quality of musical
       strings.
   (b) An instrument for producing luminous figures by the
       vibrations of sounding bodies.