July 1724, it also belongs to both the chorale cantata cycle and the second year cycle. Its fourth movement is the model for BWV 647. BWV 137 is a cantata for the twelfth Sunday after Trinity: first performed on 19 August 1725 it is a later addition to the chorale cantata cycle. Its second movement is the model for BWV 650. BWV 140 is a cantata for the 27th Sunday after Trinity (or: the last Sunday before Advent): first performed on 25 November 1731 it is a later addition to the chorale cantata cycle. Its fourth movement is the model for BWV 645. For BWV 646 there is no extant model from which the chorale prelude may have transcribed. Apart from some original manuscripts of the preceding cantata models there are no extant manuscripts of the Schübler Chorales older than their 1747–1748 printed version: Bach's only extant autograph regarding the organ versions consists of the corrections and improvements he wrote, before August 1748, in his copy of the first edition. All six Schübler Chorales are in the chorale fantasia format: this means that one of the melody lines in the setting is the relatively unadorned chorale tune, which is called cantus firmus. The two central preludes of the set (BWV 647 and 648) are four-part settings, while the others are three-part settings (trios). Wachet auf, ruft uns die Stimme, BWV 645 Wachet auf, ruft uns die Stimme, BWV 645. Chorale melody The hymn tune of this chorale prelude is "Wachet auf, ruft uns die Stimme" ("Wake, Awake for Night is Passing"), Zahn No. 8405. Model The chorale prelude is a transcription of "Zion hört die Wächter singen" ("Zion hears the watchmen sing"), the 4th movement of the cantata Wachet auf, ruft uns die Stimme, BWV 140, which is a chorale for tenor voice accompanied by unison strings and continuo. This tune was also part of the introductory theme song for the Comedy Central TV game show Win Ben Stein's Money. Wo soll ich fliehen hin (or) Auf meinen lieben Gott, BWV 646 Wo soll ich fliehen hin (or) Auf meinen lieben Gott, BWV 646. Chorale melody Hymn tune: "Wo soll ich fliehen hin" ("Whither shall I flee?"), or, "Auf meinen lieben Gott", Zahn No. 2164. Model Since no model has been found for BWV 646, most scholars assume that the source cantata is one of the 100 or so believed