4. _Rhythm_ is the organization, in a musical scheme, of sounds in
respect of time.
5. _Melody_ is the organization, in a musical scheme, of rhythmic
notes in respect of pitch.
6. _Harmony_ is the organization, in a musical scheme, of simultaneous
combinations of notes on principles whereby their acoustic properties
interact with laws of rhythm and melody.
7. The _harmonic series_ is an infinite series of notes produced by
the subdivision of a vibrating body or column of air into aliquot
parts, such notes being generally inaudible except in the form of the
timbre which their presence in various proportions imparts to the
fundamental note produced by the whole vibrating body or air-column.
8. A _concord_ is a combination which, both by its acoustic smoothness
and by its logical origin and purpose in a musical scheme, can form a
point of repose.
9. A _discord_ is a combination in which both its logical origin in a
musical scheme and its acoustic roughness show that it cannot form a
point of repose.
10. The _perfect concords_ and _perfect intervals_ are those comprised
within the first four members of the harmonic series, namely, the
octave, as between numbers 1 and 2 of the series (see Ex. 1 above);
the 5th, as between Nos. 2 and 3; and the 4th, as between Nos. 3 and
4.
11. All notes exactly one or more octaves apart are regarded as
harmonically identical.
12. The _root_ of a chord is that note from which the whole or the
most important parts of the chord appear (if distributed in the right
octaves) as members of the harmonic series.