The glass armonica was once so highly regarded that even Wolfgang Amadeus Mozart wrote for it. In 1791, the last year of his life, Mozart composed the 'Adagio and Rondo for Glass Armonica, Flute, Oboe, Viola, and Cello' (K. 617) for Marianne Kirchgessner, a blind virtuoso of the instrument. Mozart was fascinated by the instrument's unique, pure tones, which were unlike anything else available in the 18th century. However, despite Mozart's endorsement, the instrument's popularity was already beginning to fade. Its sound was too quiet to be heard in the increasingly large concert halls of the era, and the growing rumors of its 'madness-inducing' qualities (due to the lead content and high-frequency vibrations) scared away many potential players. Today, this Mozart piece is one of the most famous examples of classical repertoire for the armonica and is often performed using a modern celesta or synthesizer when a real armonica is unavailable.