Probably after giving the Archduke his lesson for the day, Beethoven stops by Diabelli’s music shop. Diabelli is working on the engraving of a Gradual, Offertory and a Tantum ergo. Beethoven in his discussions with Karl has been interested in the text of the Tantum ergo, and he is thinking about setting this hymn from the Pange Lingua for Diabelli, possibly in connection with the Missa Solemnis.
Beethoven sends a short note to Schindler, probably today, saying that he has discussed the conflict of publication of the Missa Solemnis with the subscriptions with Diabelli, and that Schindler needs to meet him at the coffee house to talk. [Beethoven has in mind a delay of a year before the publication of the Mass would be appropriate, to protect the subscribers.] He also says that Barbara Holzmann (the “old woman”) has made a delicious soup that Schindler really needs to taste. [Based on a note written a day or two after, Schindler tried it, but did not much like today’s soup.]
Brandenburg Letter 1615, Anderson Letter 1156. The original of the letter is in the Berlin Staatsbibliothek, aut. 36, 24.