Notes proper to a key.
diatonic chord is one having no note chromatically altered.
diatonic harmony is formed by the tones of a single minor or major scale;
diatonic interval is formed by two tones of the major or minor scale. A diatonic interval is one formed of two notes of a diatonic scale unaltered by accidentals.
diatonic melody is one not including notes belonging to more than one scale.
diatonic modulation is one by which a key is changed to another closely related to it.
Diatonic Ninths - "On the diatonic ninths, atomic vibration reaches 900,000,000. On the Dominant Etheric Sixths, 8,100,000,000. On the Interetheric ninths, 24,300,000,000 all of which can be demonstrated by sound colors." [Keely and His Discoveries]
1) One of the three genera of music among the Greeks, the other two being the chromatic and enharmonic.
2) The modern major and minor scales.
3) Chords, intervals, and melodic progressions, etc., belonging to one key-scale. A diatonic chord is one having no note chromatically altered. A diatonic interval is one formed by two notes of a diatonic scale unaltered by accidentals.
4) The scale of eight tones, the 8th being the octave of the first. Other scales are major scale and minor scale, which are also classed as diatonic.
DOMINANT, DIATONIC THIRDS: "The fundamental mode of vibration changes as we reach the fifth subdivision, to the dominant, the diatonic third of the mass chord, which controls the vibratory states of both etheron and interetheron." [Keely and His Discoveries]
The triplet B, D, F, has been called the imperfect triad, because in it the two diatonic semitones, B-C and E-F, and the two minor thirds which they constitute, come together in this so-called imperfect fifth. But instead of deserving any name indicating imperfection, this most interesting triad is the Diatonic germ of the chromatic chord, and of the chromatic system of chords. Place this triad to precede the tonic chord of the key of C major, and there are two semitonic progressions. Place it to precede the tonic chord of the key of F# major, and there are three semitonic progressions. Again, if we place it to precede the tonic chord of the key of A minor, there are two semitonic progressions; but make it precede the tonic chord of E♭ minor, and there are three semitonic progressions. This shows that the chromatic chord has its germ in, and its outgrowth from the so-called "natural notes," that is notes without flats or sharps, notes with white keys; and that these natural notes furnish, with only the addition of either A♭ from the major scale or G# from the minor, a full chromatic chord for one major and one minor chord, and a secondary chromatic chord for one more in each mode. [Scientific Basis and Build of Music, page 52]
But, as the subdominant sixth and dominant seventh suggest that the chromatic chord should be a 4-note chord, we must find out how Nature completes this diatonic chromatic triad and makes it a 4-note chord, and that according to its own intrinsic character as of minor thirds. Nature has always a rationale in her operations which it is ever delightful to discover. Wedged in between the minor dominant and the major subdominant, this triad, B D F, has already B, the top of the dominant minor, for its root; and F, the root of the subdominant major, for its top; and its middle is the mysterious D which, in its two positions as root of the minor subdominant and top of the major dominant, stands at the two extremes of the whole twofold diatonic key, bounding and embracing all; and which in its two degrees as D26 2/3 and D27 claims kindred with both minor and major modes of the twofold key system. Surely this Janus-faced D, looking this way toward the minor and that way to the major, seems to say, "the complement of this chord, of which I am the heart, is not far to seek nor hard to find on either side." It has already B in common with the minor dominant; the very next step is to the middle of this chord, G. Roots and tops of chords may not be altered, but middles may with impunity be flattened or sharpened as occasion may require. No two of them in succession in the chord-scale have the same structure; the chromatic triad, in claiming this middle, claims it sharpened, for it must have [Scientific Basis and Build of Music, page 54]
The chord-scales may be either major or minor, or may be found in a sweetly mingled condition; a piece may be wholly major or wholly minor, but not wholly chromatic. Chromatic chords do not usually succeed each other, but come into diatonic compositions for the purpose of producing certain effects peculiar to them, or by solving difficulties which may arise in composition. They are used as musical condiments to spice or sweeten a passage; but nobody makes pudding all of spice or sugar. The structure, character, and progression of the various chord-scales will be found so amply set forth in several parts of this work that it is not necessary to enlarge further in this place. [Scientific Basis and Build of Music, page 69]
The intervening chord between the Diatonic and Chromatic systems, B, D, F. - This chord, which has suffered expatriation from the society of perfect chords, is nevertheless as perfect in its own place and way as any. From its peculiar relation to both major and minor, and to both diatonic and chromatic things, it is a specially interesting triad. F, which is the genetic root of all, and distinctively the root of major subdominant, has here come to the top by the prime 2. D, here in the middle, is diatonically the top of the major dominant, and the root of the minor subdominant; and on account of its self-duality, the most interesting note of all; begotten in the great genesis by the prime 3. B, the last-begotten in the diatonic genesis, top of the diatonic minor, middle of the dominant major, and begotten by the prime 5, is here the quasi root of this triad, which in view of all this is a remarkable summation of things. This B, D, F is the mors janua vitae in music, for it is in a manner the death of diatonic chords, being neither a perfect major nor a perfect minor chord; yet it is the birth and life of the chromatic phase of music. In attracting and assimilating to itself the elements by which it becomes a full chromatic chord, it gives the minor dominant the G# which we so often see in use, and never see explained; and it gives the major subdominant a corresponding A♭, less frequently used. It is quite clear that this chromatic chord in either its major phase as B, D, F, A♭, or its minor phase as G#, B, D, F, is as natural and legitimate in music as anything else; and like the diatonic chords, major and minor, it is one of three, exactly like itself, into which the octave of semitones is perfectly divided. [Scientific Basis and Build of Music, page 101]