Gathered from the indications of J.G. Walther, the registration of another chorale appears to bear the marks of more positive authenticity. We refer to the Lutheran chorale, Ein' feste Burg ist unser Gott, mentioned in a previous chapter. Walther thus annotates it: "Für 3 clav."; for the left hand he directs "Fagotto"; for the right, "Sesquialtera." First of all must we notice this combination of a mutation stop with a reed; it is derived directly from the French organists. In Grigny,[162] for instance—we cite him especially because of Bach's study of his works—may be found in various instances a Bass Trumpet, or Cromorne en taille, accompanied by the Tierce or Cornet.[163] To a certain extent the Fagotto corresponds to the Cromorne, whose tone appeared somewhat veiled. This register, which Adlung tells us bore various names—Portunen, Dulcian, or Basson, among others—was sometimes added to the lower half of the great organ only, and was "of good effect in playing the basso continuo." Moreover, it was of small scale; even on the pedal it was not a noisy stop. As for the Sesquialtera, composed of the fifth and the tenth, it resembled more or less certain mutation stops of old French organs. It is noteworthy that the employment of a reed with a mixture is not mentioned by contemporary German writers; on the other hand, it would seem from the context[164] that this piece was played at the inauguration of the Mühlhausen organ, for whose restoration Bach had prepared the plans. He had demanded, among other improvements, that a Tierce be added to one of the manuals, in order that, by drawing it with a Quint, a good Sesquialtera might be produced; this in order to carry out all sorts of musical inventions of his own.
It is interesting to learn the details of this project, which, it is true, was not realized in its integrity; and it furnishes us with the most curious data upon the subject of Bach's ideas on registration and organ-building, and his own tastes.
Here it is in full:
Disposition of the new repairs upon the organ of St. Blasius.
1. Three new bellows, carefully installed, should insure a sufficiency of wind to feed the great organ, the choir, and the new swell.
2. The pressure should be increased in the four old bellows, to give speech to the new Subbass of thirty-two feet, and to the lower pipes of the other stops.
3. The old soundboards of all the bass pipes to be renewed, and the wind-supply so to be regulated that when playing with only a single stop drawn all the remaining registers may be brought on suddenly without producing unsteadiness, as has been the case up to the present time; this being of the greatest importance.
4. To be added is the Subbass of thirty-two feet, called the Untersatz, which will be made of wood, to serve as the best possible foundation for the weight of the ensemble. These pipes should have a special soundboard.
5. The Bombarde is to be furnished with new and larger resonators, and the mouths of the pipes shaped differently, in order to obtain more roundness in the emission of the tone.
6. As to the new features—the Glockenspiel on the pedal, composed of twenty-six bells of four-foot pitch, desired by the parishioners, who will have them made at their own expense; while the manufacturer must see that they are rendered playable.