Phoneidoscope \Pho*nei"do*scope\, n. [Phono- + Gr. e'i^dos form
+ -scope.] (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.
[1913 Webster]