[Footnote 177: We should add here, that the organs were not of the same pitch as the other instruments, for they were tuned to chorus-pitch, a whole tone lower than the normal diapason. The organ at Weimar, on the contrary, was a minor third higher.] 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_). [Footnote 178: _Oberwerk_ means literally the higher manual; in two-manual organs the stronger was, at that time, found above the other. The name _Rückpositif_ came from the custom of placing the pipes behind the back (_Rücken_) of the organist. Finally, the swell bore the name _Brustwerk_, the pipes being placed facing the breast (_Brust_) of the player. In a three-manual organ the great keyboard was situated between the swell, which was above, and the choir, which was below it.] III