Opeidoscope

[Sarah]

An instrument, consisting of a tube having one end open and theother end covered with a thin flexible membrance to the center ofwhich is attached a small mirror. It is used for exhibiting upon ascreen, by means of rays reflected from the mirror, the vibratorymotions caused by sounds produced at the open end of the tube, as byspeaking or singing into it. A. E. Dolbear.