Over one hundred organ chorals by Bach are still extant and a large proportion of them are in his own handwriting. A fine collection of forty-five shorter pieces is presented by his "Orgelbüchlein" (Little Organ Book). The compilation of this was made in Cöthen, but the greater part of its contents belongs to the Weimar period. The pieces are almost wholly in Pachelbel's manner, but are more characteristic, richer and of greater depth. The melody always moves on uninterruptedly and, with few exceptions, in the simple style adapted to congregational singing. The other parts are artistically interwoven and reflect the particular sensations which the significance of the choral melody in the church liturgy and the import of the poem to which it belongs awaken in the mind. The musical thought from which the accompanying parts are developed is usually brief; it takes its character from the poem, into the meaning of which Bach penetrates very deeply. The effect is especially beautiful when he reproduces in his music the idea of certain visions, which have been called up by the poem. An example of this is furnished by the choral: "Vom Himmel kam der Engel Schaar" ("From Heaven came the Angel Host"), in which two of the accompanying parts with their ascending and descending strains seem to personify the Christmas angels coming down to the shepherds and again soaring upward. A favorite plan of Bach for increasing in an artistic manner the importance of the choral melody, is that of managing it after the fashion of a canon; that is to say, it is heard not merely in a single part, but recurs in another, after a certain interval, an arrangement from which surprisingly expressive harmonies result.