A form of instrumental music existed in the German Protestant Church which was peculiar to that institution, and which was exceedingly significant as forming a connecting link between organ solo playing and the congregational worship. We have seen that the choral, at the very establishment of the new order by Luther, became a characteristic feature of the office of devotion, entering into the very framework of the liturgy by virtue of the official appointment of particular hymns (Hauptlieder) on certain days. As soon as the art of organ playing set out upon its independent career early in the seventeenth century, the organists began to take up the choral melodies as subjects for extempore performance. These tunes were especially adapted to this purpose by reason of their stately movement and breadth of style, which gave opportunity for the display of that mastery of florid harmonization in which the essence of the organist’s art consisted. The organist never played the printed compositions of others, or even his own, for voluntaries. He would no more think of doing so than a clergyman would preach another man’s sermon, or even read one of his own from manuscript. To this day German unwritten law is rigorous on both these matters. The organist’s method was always to improvise in the strict style upon themes invented by himself or borrowed from other sources. Nothing was more natural than that he should use the choral tunes as his quarry, not only on account of their technical suitableness, but still more from the interest that would be aroused in the congregation, and the unity that would be established between the office of the organist and that of the people. The chorals that were appointed for the day would commonly furnish the player with his raw material, and the song of the people would appear again soaring above their heads, adorned by effective tonal combinations. This method could also be employed to a more moderate extent in accompanying the congregation as they sang the hymn in unison; interludes between the stanzas and even flourishes at the ends of the lines would give scope to the organist to exhibit his knowledge and fancy. The long-winded interlude at last became an abuse, and was reduced or suppressed; but the free organ prelude on the entire choral melody grew in favor, and before Bach’s day ability in this line was the chief test of a player’s competence. In Bach’s early days choral preludes by famous masters had found their way into print in large numbers, and were the objects of his assiduous study. His own productions in this class surpassed all his models, and as a free improviser on choral themes he excelled all his contemporaries. “I had supposed,” said the famous Reinken, who at the age of ninety-seven heard Bach extemporize on “An Wasserflüssen Babylon” at Hamburg,—“I had supposed that this art was dead, but I see that it still lives in you.” In this species of playing, the hymn melody is given out with one hand or upon the pedals, while around it is woven a network of freely moving parts. The prelude may be brief, included within the space limits of the original melody, or it may be indefinitely extended by increasing the length of the choral notes and working out interludes between the lines. The one hundred and thirty choral preludes which have come down to us from Bach’s pen are samples of the kind of thing that he was extemporizing Sunday after Sunday. In these pieces the accompaniment is sometimes fashioned on the basis of a definite melodic figure which is carried, with modulations and subtle modifications, all through the stanza, sometimes on figures whose pattern changes with every line; while beneath or within the sounding arabesques are heard the long sonorous notes of the choral, holding the hearer firmly to the ground idea which the player’s art is striving to impress and beautify. This form of music is something very different from the “theme and variations,” which has played so conspicuous a part in the modern instrumental school from Haydn down to the present. In the choral prelude there is no modification of the theme itself; the subject in single notes forms a _cantus firmus_, on the same principle that appears in the mediaeval vocal polyphony, around which the freely invented parts, moving laterally, are entwined. Although these compositions vary greatly in length, a single presentation of the decorated choral tune suffices with Bach except in rare instances, such as the prelude on “O Lamm Gottes unschuldig,” in which the melody is given out three times, with a different scheme of ornament at each repetition.