Where the 1998 version of the Bach-Werke-Verzeichnis described BWV 855a as only a Prelude, based on its appearance in the Klavierbüchlein für Wilhelm Friedemann Bach, BWV 855a may also refer to both this Prelude and a Fughetta in E minor, found in a manuscript copy made between 1750 and the early 19th century, once owned by F. Konwitschny but later lost. The Prelude and Fughetta were published in Series V, Volume 6.1 of the Neue Bach-Ausgabe, based on various sources for the Prelude, and on the Konwitschny source for the Fughetta. BWV 855a is an early version of BWV 855, No. 10 in the 1722 first book of the Well-Tempered Clavier. \new PianoStaff << \new Staff \new Staff >>
Prelude and Fugue, BWV 855, No. 10 of ''The Well Tempered Clavier'', Book I
This piece was written by Bach in 1722, and it was written for harpsichord. \version "2.18.2" \header % Workaround pending https://gitlab.com/lilypond/lilypond/-/merge_requests/287 # \score
Prelude
There are 41 measures. The bass line is made up of running sixteenth notes throughout. The treble line is made up of running sixteenth notes throughout with mixed notes in between. \version "2.18.2" \header upper = \relative c'' lower = \relative c \score
Fugue
The fugue is in 2 voices and there are 42 measures. \version "2.18.2" \header Dux = ContreSujet = Comes = upper = \relative c' lower = \relative c \score
Siloti's arrangement of BWV 855a: Prelude in B minor
made an arrangement the Prelude BWV 855a for piano, transposing it to B minor: \new PianoStaff << \new Staff \new Dynamics \new Staff >>
This arrangement has been described as "perhaps Siloti's most tender and perfect" transcription. It transposes Bach's original down from the original E minor into B minor, with the steady sixteenth note figuration that was originally given by Bach to the left hand being instead assigned to the right hand. Siloti also adds a repeat of the entire work, in order to allow for a change of voicing where the melody in the left hand is emphasized. The chords in the left hand are arpeggiated; however according to Siloti's daughter Kyriena, he would omit the arpeggiation on the first pass and restore it on the repeat in order to heighten the effect of the left-hand melody. It has been performed by many pianists, most famously Emil Gilels. The date of the arrangement is uncertain: it was first published by A. Gutheil of Moscow, and was performed by Siloti in public for the "first time" in February 1912.
