When Bach performed his Magnificat for the first time on Christmas Day 1723, the accompanying parts of the alto aria "Esurientes" were played on two treble (alto) recorders in F. Later, when Bach re-wrote the Magnificat, he transposed the whole work down a semitone (from E flat to D). The recorder parts of the alto aria, transposed from F to E, where now too low for these instruments and had to be given to the flutes, obviously more for practical than aesthetical reasons. The reprint of the firs...