7. _Stillgedackt_ (a species of Bourdon) of eight feet, which will blend perfectly with the "music."[167] As it will be made of good wood, it will be much more resonant than if of metal. [Footnote 167: [The filling-out of the figured bass by the organ, made necessary in music with orchestra by the paucity of the instrumental numbers, was referred to as the "music."--TR.]] 11. Between the swell[168] and the great organ a coupler shall be constructed. Finally, the whole instrument shall be revoiced, and the tremulant made to vibrate regularly. [Footnote 168: [The word _swell_ I have used in the foregoing merely to designate the third manual; and it by no means implies that the pipes belonging to that keyboard were enclosed in a swell-box. Although this invention was applied to an English organ for the first time in 1712 (St. Magnus Church, London Bridge), its adoption in Germany has become general only within comparatively recent years, and then only in newly-built instruments.--TR.]] 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.