In music, major fourth and minor fifth are intervals from the quarter tone scale, named by Ivan Wyschnegradsky to describe the tones surrounding the tritone (F?/G?) found in the more familiar twelve tone scale.
A major fourth is the interval between the perfect fourth (500 cents) and the augmented fourth (600 cents) and thus 550 cents (Fhalf sharp). It inverts to a minor fifth. Wyschnegradsky considered it a good approximation of the eleventh harmonic (11:8 or 551.28 cents). A narrower undecimal major fourth is found at 537 cents (the ratio 15:11). 31 equal temperament has an interval of 542 cents, which lies in between the two types of undecimal major fourth.
The term may also be applied to the "comma-deficient major fourth" (or "chromatic major fourth") is the ratio 25:18, or 568.72 cents (F?). Wikipedia, Major fourth
Ramsay
contrast. In the fifth, the ratio being 2:3, the excess of 3 above 2 is 1; this 1 bears a simple relation to both the notes which awaken it. The grave harmonic in this case gives the octave below the lower of the two sounds; 1 is an octave below 2. This is the simplest relation "a third sound" can have to the two which awaken it, and that is why the fifth has the smallest possible degree of contrast. The octave, the fifth, and the fourth may be reckoned as simple ratios; the major and minor thirds and their inversions as moderately complex; the second, which has the ratio of 9:10, and the major fourth F to B and its inversion, are very complex. [Scientific Basis and Build of Music, page 61]
See Also
Fourth
Fourth Phase Of Water
INTERATOMIC FOURTH SUBDIVISION
major
Major Ninth
Major Scale
Major Second
Major Seventh
Major Sixth
Major Third
Perfect Fourth
7.13 - Fourth