Source : Webster's Revised Unabridged Dictionary (1913)

Tonophant \Ton"o*phant\ (t[=o]n"[oasl]*fant), n. [Gr. to`nos a
   tone + fai`nein to show.] (Physics.)
   A modification of the kaleidophon, for showing composition of
   acoustic vibrations. It consists of two thin slips of steel
   welded together, their length being adjystable by a screw
   socket.