II
The document just cited, which is preserved in the archives of Mühlhausen, is full of interest; we will now make a further study of two of its sections, which treat of the same subject.
I refer to the combination of organ with orchestra in the performance of the cantatas.
First, Bach speaks of the Fagotto, whose tone so easily assimilated with that of instruments; here he agrees with his contemporaries, who recommended the use of a sixteen-foot stop of more definite timbre than the bourdons, although not stronger,—it was also called Dulcian,—"dolce suono,"—in performing the basso continuo. The employment of the Stillgedackt, the softest stop in the organ, interests us in its use as a means of filling out this same figured bass. Such a register evidently lacked power, but was sought for that quality of indefiniteness, even of vacuity, which it possessed (still, in German, means quiet); this produced more the effect of diaphony, of a harmonic filling-in, like the sostenuto of certain of our wind-instruments, than of polyphony in real parts, which one could not distinguish.
These lines of J. Th. Mosewius[169] will give us, further, an idea of the rôle which the organ played in the orchestras of Bach and Händel: "It is a widely prevailing impression, and one confirmed by the new instrumentation which Mozart and Mosel made for the Händel oratorios, that by their use of the organ these two masters (Bach and Händel) supplied those features of our instrumentation which were then lacking. Such an opinion is correct, if nothing more is meant than that in concert rooms where no organ is available, it must be replaced by other instruments.[170] It must not be inferred that this new instrumentation maintains reciprocal relations with the original accompaniment. In the former it is the string-quartet which serves as the foundation of the harmony, and it is only the wind-instruments which affect the color. With Händel (and Bach) the organ, which fills out the figured bass, serves as a background for all the other instruments; the color is added by all the other voices of the orchestra, whether strings or wind."
Nothing could be more just than this statement of Mosewius; the organ serves to combine all the parts of the orchestra, unifying them without betraying its agency by any too assertive quality; a gray background, if you will, upon which some livelier colors are displayed, as in paintings of the school of Panselinos.
This testimony of Bach himself, specifying in his plans stops of a very soft and well-rounded quality for the accompanying organ, is corroborated by his contemporaries.
Scheibe, Adlung, and others permitted in the accompaniment of arias and recitatives but a single bourdon of eight feet, called, from its use for such purposes, Musikgedackt. A recitative, especially, was to be sustained lightly, for fear of covering the voice of the singer; a few prolonged notes to guide him, occasional soft chords, and, curiously enough, if one believe in the strict treatment of the organ, arpeggios, as upon a clavecin.
The staccato was generally employed in playing the bass; but this license stopped here, and for ordinary organ pieces Bach exacted from his pupils the strictest legato.
Even in playing in the choruses, and with full orchestra, the organ had to be content with the "half-tone" tint; neither reeds nor mixtures, said Schröter,[171] organist in Nordhausen; Petri[172] made a similar recommendation.
Moreover, the accompaniment, at least such of it as was contrapuntal in nature or consisted of successive chords, was played usually upon the positif (choir), whose pipes were less powerful than those of the great organ; the bass was executed upon the latter manual in the manner already indicated, sometimes also legato. The pedal itself might be added here; in certain passages it only marked the accents with stops of more emphatic quality, when it was desirable to emphasize the breadth of the rhythm, or to avoid confusion, when the movement was too rapid. This is confirmed by Saint-Lambert (Traité d'accompagnement, p. 58): "When the tempo is so rapid," says he, "that the accompanist cannot conveniently play all the notes, it will suffice if he play and accompany only the first notes of each measure, leaving to the basses the task of performing all the notes, which they will be able to accomplish much more easily, having no accompaniment to play in addition. Very rapid tempi are not suited to accompanying instruments; on this account, if particularly quick passages are encountered, even in a slow movement, the accompagneur (sic) may leave them to the other instruments; or, if he play them himself, he may so modify them as to play only the principal notes of such passages; that is to say, the notes which fall upon the principal beats of the measure."
Again, the organist was obliged to take into consideration the small number of orchestral players and of voices. Bach, in a memorandum of August 23, 1730, enumerates twelve singers and eighteen players, besides the organist; the Kapelle over which Gerlach held sway in the new Protestant church at Leipzig, was still smaller: four singers and ten players.
It is true that Bach, first of all an organist himself, did not always bequeath such an ungrateful task to the organ; besides the organ of accompaniment, he gives us examples of what he calls organo obligato. Numerous cantatas furnish such instances; we find one in the Passion according to St. Matthew, with the added interest of an indication of the registration. It is where the chorus, in unison, sings the chorales, O Lamm Gottes, unschuldig, and O Mensch, bewein' dein' Sünde gross.[173] The register which Bach prescribes here is the Sesquialtera, undoubtedly in combination with some foundation stops. The character of this register, thus particularly selected, seems to call for the tasto solo; without doubt Bach demanded it because of its decisive quality, for the purpose of bringing out the chorale sung by the ripieno against the other two choruses and the two orchestras, which he treated independently. The brightness of the Sesquialtera would seem to recommend it also for the sinfonie, or prelude, of the cantata composed for the election of the Council[174] (August, 1731). This idea is supported by the fact that a Sesquialtera was undoubtedly added to the positif of the organ in St. Thomas' Church in 1730 or 1731, by the organ-builder, J. Scheibe.
A register of quite opposite effect was used to support the whole orchestra in the Reformation Cantata[175] (1717). The Luther chorale-melody is here entrusted to the sixteen-foot Bombarde on the pedal, accompanied in the orchestra by the violoncello and the violone, a similar instrument.
In these particular instances we see that Bach departed from the general custom of omitting the reeds and mutation stops;[176] but here the organ derived from its own resources sonorities most individual in character, the accompaniment being furnished by a second instrument (the orchestra). Moreover, as W. Rust, the authorized editor of the Bach cantatas, says, "When the organ is obbligato it does not present itself in a polyphonic capacity, for then it would cover up all the other instruments; but it should be treated as a solo part, like a flute or an oboe."[177]
With regard to Bach's orchestra, we should remember that the cantata Die Himmel erzählen ("The heavens declare the glory of God") suggests the registration for the first movement of the sonata in E minor. True, it will be said that Bach wrote these trios for pedal-clavecin; but their performance upon the organ, too, should not be neglected. Certain adagios, by reason of their long-sustained notes, demand an instrument capable of prolonging the tone. This first movement, in fact, is but a transcription of the Sinfonie (adagio and vivace) which serves as an overture to the cantata just mentioned. The instrumentation: Oboe d'amore, Viola da gamba, and continuo. These are timbres to be found in all organs; we may add that the Viola da gamba of the organ was one of Bach's favorite stops. It is not unwarranted to consider that in many chorales the cantus, placed in the tenor, was played with this register upon a separate manual, just as Bach would have given it to the violoncellos in the orchestra.
For we must take into consideration this practice of Bach's of transferring to the organ resources of the orchestra, to the orchestra those of the organ. Thus, in the Pastorale (Hirtengesang) of the Christmas Oratorio, Bach produces the effect of an organ whose manuals respond to each other, the one with foundation stops contrasted with the chorus of oboes upon another.
This passing from one manual to another Bach seldom indicates in his organ compositions; one piece, however, furnishes us with directions which are authentic beyond question, and extremely interesting. It is the great prelude in E flat major, published in Part III of the Clavierübung. On comparing these indications with others, particularly with those in the D minor (Doric) Toccata, one may decide to play upon the great manual (Oberwerk)[178] all that is written with pedal; where the pedal is silent, one may change to the choir (Rückpositif). In carrying this deduction to its limits, one might even formulate the rule that when the parts are reduced to two, they should be played upon the swell (Brustwerk).