Beethoven only wrote about a minute and a half of music for the glass armonica in the incidental music for Leonore Prohaska, WoO.96 (1815).
In 1815 Beethoven was commissioned to write the incidental music (Op.202/WoO 96—click here for the score) for a tragic play written by Friedrich Duncker (the King of Prussia's secretary) called Leonore Prohaska. The play "tells the story of a maiden who, disguised as a soldier, fought through the war of liberation." Among the movements for your usual Beethoven orchestra and chorus is a short little "Melodrama" for armonica and narrator—at the point in the play when the heroine Leonore is speaking to her true love from beyond the grave. The narration (written by Duncker) is as follows:
I entwined for you, Two flowers: one for love, and one for constancy. Alas! All I have for you now are death's flowers! And yet, from the earth on my tomb The lily and the rose bloom anew.
Melodram / Funeral Flowers (from Leonore Prohaska):
You can see Alan Alda learn how to play the glass armonica here:
Glassharmonica / Alan Alda's first lesson with Thomas Bloch
And here's a fine blog post which first alerted me to the existence of B.'s foray into "music of the spheres": http://impossiblekisses.blogspot.com/2011/03/beethoven-and-three-plates-in-my.html