INTERVAL, in music, is the distance or difference of pitch, arithmetically expressed, between any two tones of a given scale. Occi dental nations, including America, employ the diatonic scale (see Scat-EL an octave compris ing five tones and seven semitones, named after the first seven letters of the alphabet. The affix of a flat or sharp before a note denotes its quality but does not affect its name, and the eighth note being in unison commences a new octave. Taking the scale in the key of C major, the various intervals are: minor second= E-F or B-C; grave major C-D, F-G, A-B; grave minor third D-F; minor third= E-G, A-C, B-D; major C-E, F-A or G-B; perfect fourth= C-F, D-G, E-A, or B-E' ; acute fourth = A-D'; acute augmented fnurth=13-F; grave diminished fifth.= B-F'; grave fifth D-A; perfect fifth = C-G, E-B, F-C', G-D', A-E; minor sixth = E-C, B-G'; major sixth= C-A, D-B, G-E'; acute major sixth F-D'"; grave minor seventh.= D-C', B-A'; minor seventh E--D', R-4G ,• . seventhgC--B, ; octsve'rC-C. Di-.10; etc.' By taking various notes of the dia tonic scale as starting points and measuring known intervals from these; we arrive at inter mediate notes of the scale, of which the follow ing are examples: C# minor third below E; D# ;minor second below E; Eb miner third above C; Ab minor sixth above C; Bb minor seventh above C; B # 3 major third above C.
The difference of pitch between C and Cl or between D and D# is called a semitone, and an interval increased or diminished by a semitone is said to be .augmented or diminished. This applies especially to the interval of a fourth or a fifth, which with the octave are said to be perfect, because any augmentation or diminu tion mars their consonance. The major sixth or third may, however, be diminishrd to a %lime' sixth or third without destroying the consonance; and the term is also ap plied to the diminished second or seventh. In tervals confined within the octave are simple, when they exceed it compound; the octave be ginning a new series, the ninth is the octave of the second, and so forth.