Phoneidoscope

Pho`nei´do`scope


n.1.(Physics) An instrument for studying the motions of sounding bodies by optical means. It consists of a tube across the end of which is stretched a film of soap solution thin enough to give colored bands, the form and position of which are affected by sonorous vibrations.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.