middle movement. It is believed that it was written in 1719, to show off a new harpsichord by Michael Mietke which Bach had brought back from Berlin for the Köthen court. It is also thought that Bach wrote it for a competition at Dresden with the French composer and organist Louis Marchand; in the central movement, Bach uses one of Marchand's themes. Marchand fled before the competition could take place, apparently scared off in the face of Bach's great reputation for virtuosity and improvisation. The concerto is well suited throughout to showing off the qualities of a fine harpsichord and the virtuosity of its player, but especially in the lengthy solo cadenza to the first movement. It seems almost certain that Bach, considered a great organ and harpsichord virtuoso, was the harpsichord soloist at the premiere. Scholars have seen in this work the origins of the solo keyboard concerto as it is the first example of a concerto with a solo keyboard part. An earlier version, BWV 1050a, exists, and has many small differences from its later cousin, but no major difference in structure or instrumentation. It is dated ca. 1720–21. Concerto No. 6 in B-flat major, BWV 1051 Title on autograph score: Concerto 6to a due Viole da Braccio, due Viole da Gamba, Violoncello, Violone e Cembalo. Instrumentation: two viole da braccio, two viole da gamba, cello, violone, and harpsichord Duration: about 16 minutes The absence of violins is unusual. Viola da braccio means the normal viola, and is used here to distinguish it from the viola da gamba. When the work was written in 1721, the viola da gamba was already an old-fashioned instrument: the strong supposition that one viola da gamba part was taken by his employer, Prince Leopold, also points to a likely reason for the concerto's composition—Leopold wished to join his Kapellmeister playing music. This is supported by the knowledge that Bach wished to end his tenure under Prince Leopold. By upsetting the balance of the musical roles, he would be released from his servitude as Kapellmeister and allowed to seek employment elsewhere. The two violas start the first movement with a vigorous subject in close canon, and as the movement progresses, the other instruments are gradually drawn into the seemingly uninterrupted steady flow of melodic invention which shows the composer's mastery of polyphony. The two violas da gamba are silent in the second movement,