A musical instrument consisting of a number of glasses partially filled with water. The glasses are filled to different levels, hence the production of different notes when the player rubs their rims with a moistened finger. The sound thus produced has a haunting, otherwordly quality. It is most famously called for in the "Mad Scene" from the opera LUCIA DI LAMMERMOOR by Donizetti, although that part is now usually played by a transverse flute.
Opera fan A: What's your favourite recording of LUCIA?
Opera fan b: The one with Beverly Sills, because it uses the original scoring for glass harmonica.