Hughes
If the chords of the twelve keys and the thirteenth octave are struck, all agree in their method of development. We see here the order in which the chords are repeated, and the working of the double tones. As an example of the latter, we may trace the chords belonging to the key of D?, and compare them with those belonging to the key of F#, also the first chord in the key of A?. The fourth note in depth, sounded last of the seven of each harmony, has been seen as preparing for the chords; it prepares equally for the scale, and the scale for the chords, the octave chord of the scale, ascending, preparing for the latter to descend. Descending is ascending reversed. [Harmonies of Tones and Colours, Diagram V - The Chords of the Twelve Major Keys, page 27a]

See Also

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A flat
key of A
key of A flat
key of C
key of D flat
key of E
key of F
key of F sharp
key of G
progression of keys
root of the fifth higher keynote
root of the fifth keynote
The Major Keynote of C