Because this collection was made at Cöthen, it must not be supposed that the chorales which it comprises were composed only during the period of Bach's service to Prince Leopold of Anhalt; Bach rather made a practical arrangement of them, whereby they might serve as a useful work for his pupils. It comprises forty-five chorales, of which a goodly portion undoubtedly belong to the years in Weimar--perhaps to a still earlier period. These chorales are generally written after the models furnished by Pachelbel; but where Pachelbel is merely calmly devout, or placidly harmonious, Bach, with a more exalted piety and distinctly more poetic, lends to them whatever of mystic character he could derive from the text of the hymns; in addition, he imbues them with all the picturesqueness suggested by the sense of the words. And what variety in the choice of means to be employed! Sometimes there are progressions which fairly chill us, simply the result of a note purposely prolonged, or a succession of chords strikingly disjointed, which seem to clash with incompatible harmonies, as at the close of _Alle Menschen müssen sterben_; or a false relation seems fraught with fatality, as well as with complete desolation, as in _O Mensch, bewein' dein' Sünde gross_. At other times will be found motives whose symbolic character is not the result of chance; for example, all the irreparability of the primeval fall of man[131] is symbolized by diminished sevenths, pitching obliquely downwards, as if in a veritable vertigo; or the gliding of scales in opposite directions depicts the balancing of a flying object hovering in space--skimming over the earth, and already out of range, while, in the repetitions, the flapping of wings emphasizes the rhythm. [Footnote 131: _Durch Adam's Fall ist ganz verderbt._ Buxtehude employed fifths to symbolize this descent.] Certain rhythms also assist Bach in his task; to express the fulness of joy in the chorale _In Dir ist Freude_, Bach constructed his prelude upon a _chaconne_ movement, a _carillon_ theme, repeated unceasingly by the bass; the sole subject perceptible, of which the other parts are but an indistinct reflection; even the melody of the chorale is lost sight of in the vibrations of the bass, but, nevertheless, it presents itself in the voices, which repeat it in fragments, sometimes with elaboration, like the hum of a great people celebrating a festival, who emerge in vast throngs from the church whence the final reverberations of the organ still voice its rhythm,[132] and who betake themselves, thenceforth busy with their pleasures, to the sunny square now invaded by the sound of the bells ringing their full peals. [Footnote 132: Organists often played the _sortie_ (postlude) in the form of a _chaconne_, with full organ (see Mattheson: "_Der vollkommene Capellmeister_," and Becker, "_Rathgeber für Organisten_"). The prelude to the chorale "_Heut' triumphiret Gottes Sohn_" is conceived in the same manner.]