Beethoven writes a note to Archduke Rudolph, who apparently is impatient for a composition lesson. Beethoven is apologetic, saying he was ill yesterday and the day before. Feeling better last night, he went into the City from Unterdöbling to have copyist Wenzel Schlemmer correct the sonata [almost certainly piano sonata #30, op.109]. But Schlemmer was not at home, so Beethoven left word asking Schlemmer to come to him. Beethoven says he will have Schlemmer deliver the copy of the corrected sonata directly to the Archduke. The composer promises that he will be at the palace to wait on the Archduke no later than 4 p.m. today. [The fact he asked Schlemmer to come to him, combined with the expectation that the note will reach the Archduke by the afternoon of the same day, strongly suggests Beethoven stayed at his apartment in the City the night before, rather than going back to his summer home at Unterdöbling in between.]
The dating of this letter is approximate. Beethoven was working on the corrections to the proofs of the piano sonata op.109 in the first part of June, 1821, and also had Schlemmer and Wenzel Rampl preparing a copy of the corrected sonata for Archduke Rudolph, so late June seems like a likely candidate. But it may be written at nearly any point between now and July 6, 1821. That seems like the latest possible date, since Beethoven then sends the corrected proofs of the sonata back to Schlesinger. Schlemmer and Rampl would no doubt have needed those proofs in preparing the Archduke’s copy of the sonata.
According to Sieghard Brandenburg, this proposed dating is consistent with the watermark of the paper (an uncrowned posthorn with shield, with a bell and ribbon, watermark type SG 83), which was used by Beethoven for four dated letters written between July and December 1821.
Brandenburg Letter 1432. Not in Anderson. The original is held by the Gesellschaft der Musikfreunde in Vienna, catalogued as A 84/128.
The Archduke’s copy of the sonata, while mostly written by Rampl, indeed bears corrections by Schlemmer as Beethoven describes. This copy from the Archduke’s music collection is also held by the Gesellschaft der Musikfreunde, and is catalogued as VII 17379 Q 11967.