of them. Schemellis Gesangbuch was published in 1736, and contains some of Bach's probably least known compositions. Clavier-Übung III For organ, containing: Prelude in E-flat major, BWV 552/i German Kyrie and Gloria settings, BWV 669–677 Catechism chorales, BWV 678–689 Four duets, BWV 802–805 Fugue E-flat major, BWV 552/ii The Prelude and Fugue were published separately as a pair by C. F. Peters in 1845 in Volume III of the Organ Works of J. S. Bach, with the fugue listed in the contents as the "St Annen-Fuge". Clavier-Übung IV In 1741 or 1742 another Clavier-Übung volume was published, the Aria with diverse variations for double manual harpsichord, later known as the Goldberg Variations, BWV 988. Not thus numbered in the print it was the fourth Clavier-Übung publication. This publication does not carry a reference to Johann Gottlieb Goldberg: the music was published over half a century before the perhaps exaggerated anecdote involving Goldberg was printed in Forkel's biography of Bach. Publication The work was published by Balthasar Schmid in Nürnberg. Ms. 17669 is at the Bibliothèque nationale de France (BnF). It contains corrections by Bach as well as the autograph manuscript of the canons BWV 1087. Canon triplex a 6 The Canon triplex a 6, BWV 1076, which had appeared on Elias Gottlob Haussmann's portrait of Bach in 1746, was printed in 1747. Canonic Variations on "Vom Himmel hoch da komm' ich her" The Canonic Variations on "Vom Himmel hoch da komm' ich her", BWV 769, for organ, were published on the occasion of Bach's admission to Mizler's "Society of the Musical Sciences" in 1747. Musikalisches Opfer The Musical Offering, BWV 1079, was published in 1747, after Bach's visit to Frederick the Great in Potsdam. The work contains a trio sonata for flute, violin and continuo. Schübler Chorales The Schübler Chorales, BWV 645–650, is a set of chorale preludes for organ, published around 1748 as Sechs Chorale von verschiedener Art (Six Chorales of Various Kinds) by Johann Georg Schübler. Publication There is some doubt whether Bach commissioned the publication, which mainly, perhaps even exclusively, consists of arrangements of cantata movements which he had composed a few decades earlier. The work was published in Zella Melsi, and the engraver apparently prepared the print unsupervised by the composer. It is likely that Bach at least chose the six pieces, determined their sequence in the publication, and gave some instruction on the organ registration