the Royal Opera House in Berlin and collaborator with Emanuel on Bach's obituary (the Nekrolog, 1754), and more significantly Johann Philipp Kirnberger. Kirnberger became Kapellmeister to the court in 1758 and music teacher of Frederick's niece, Anna Amalia. Not only did Kirnberger build up a large collection of Bach's manuscripts in the Amalien-Bibliothek, but with Friedrich Wilhelm Marpurg he promoted Bach's compositions through theoretical texts, concentrating in particular on counterpoint with a detailed analysis of Bach's methods. The first of the two volumes of Marpurg's Treatise on fugue (, 1753–1754) cites the opening segment of the six-part fugal chorale prelude Aus tiefer Noth BWV 686 as one of its examples. Kirnberger produced his own extensive tract on composition Die Kunst des reinen Satzes in der Musik (The true principles for the practice of harmony), twenty years later, between 1771 and 1779. In his treatise Marpurg had adopted some of the musical theories on the fundamental bass of Jean-Philippe Rameau from his Treatise on Harmony (1722) in explaining Bach's fugal compositions, an approach which Kirnberger rejected in his tract: This led to an acrimonious dispute in which both claimed to speak with Bach's authority. When Marpurg made the tactical error of suggesting that, "His famous son in Hamburg ought to know something about this, too," Kirnberger responded in the introduction to the second volume of his tract: Through Bach's pupils and family, copies of his keyboard works were disseminated and studied throughout Germany; the diplomat Baron van Swieten, Austrian envoy to the Prussian court from 1770 to 1777 and afterwards patron of Mozart, Haydn and Beethoven, was responsible for relaying copies from Berlin to Vienna. The reception of the works was mixed, partly because of their technical difficulty: composers like Mozart, Beethoven and Rust embraced these compositions, particularly The Well-Tempered Clavier; but, as Johann Adam Hiller reported in 1768, many amateur musicians found them too hard (""). Twenty-one prints of the original 1739 edition of Clavier-Übung III survive today. Because of its high price, this edition did not sell well: even 25 years later in 1764, C.P.E. Bach was still trying to dispose of copies. Because of changes in popular tastes after Bach's death, the publisher Johann Gottlob Immanuel Breitkopf, son of Bernhard Christoph Breitkopf, did not consider it economically viable to prepare new printed editions of Bach's works; instead he retained a master copy of Clavier-Übung III in his large