In classical mechanics, anharmonicity is the deviation of a system from being a harmonic oscillator.
 An oscillator that is not oscillating in simple harmonic motion is known as an anharmonic oscillator where the system can be approximated to a harmonic oscillator and the anharmonicity can be calculated using perturbation theory.
 If the anharmonicity is large, then other numerical techniques have to be used.
In mathematics, especially potential theory, harmonic measure is a concept related to the theory of harmonic functions that arises from the solution of the classical Dirichlet problem.
 In probability theory, the harmonic measure of a subset of the boundary of a bounded domain in Euclidean space formula_1, formula_2 is the probability that a Brownian motion started inside a domain hits that subset of the boundary.
 More generally, harmonic measure of an Itō diffusion "X" describes the distribution of "X" as it hits the boundary of "D".
 In the complex plane, harmonic measure can be used to estimate the modulus of an analytic function inside a domain "D" given bounds on the modulus on the boundary of the domain; a special case of this principle is Hadamard's three-circle theorem.
 On simply connected planar domains, there is a close connection between harmonic measure and the theory of conformal maps.
Franz Schubert's Piano Sonata in C major D. 840, nicknamed Reliquie upon its first publication in 1861 in the mistaken belief that it had been Schubert's last work, was written in April 1825, whilst the composer was also working on the A minor sonata, D. 845 in tandem.
 Schubert abandoned the C major sonata, and only the first two movements were fully completed, with the trio section of the third movement also written in full.
 The minuet section of the third movement is incomplete and contains unusual harmonic changes, which suggests it was there Schubert had become disillusioned and abandoned the movement and later the sonata.
 The final fourth movement is also incomplete, ending abruptly after 272 bars.
George Harrison, {'1': ", '2': ", '3': ", '4': "} (25 February 1943 – 29 November 2001) was an English guitarist, singer-songwriter, and producer who achieved international fame as the lead guitarist of the Beatles.
 Often referred to as "the quiet Beatle", Harrison embraced Hinduism and helped broaden the horizons of his fellow bandmates as well as their American audience by incorporating Indian instrumentation in their music.
 Although most of the Beatles' songs were written by John Lennon and Paul McCartney, most Beatles albums from 1965 onwards contained at least two Harrison compositions.
 His songs for the group included "Taxman", "Within You Without You", "While My Guitar Gently Weeps", "Here Comes the Sun" and "Something", the last of which became the Beatles' second-most covered song.
"Yes It Is" is a song by the Beatles, released in 1965.
 Written by John Lennon (credited to Lennon–McCartney) it was first released as the B-side to "Ticket to Ride".
 It features some of the Beatles' most complex and dissonant three-part vocal harmonies and showcases George Harrison's early use of volume pedal guitar.
 Ian MacDonald describes the song as having "rich and unusual harmonic motion."
McDonald and Giles is an album of music released by British musicians Ian McDonald and Michael Giles in 1971.
 The album was first issued on Island Records (ILPS 9126) in the UK and in the US as Cotillion Records (SD 9042), a division of Atlantic Records.
 The album was recorded at Island Studios between May and July 1970.
 Although "McDonald and Giles" remains popular among King Crimson fans, its commercial success was limited.
 The duo did not record a second album.
Desolation Road is a 1988 science fiction novel written by Ian McDonald.
 It was McDonald's first published novel.
 The plot takes place on a far future Mars in a town that develops around an oasis in the terraformed Martian desert.
 McDonald published a sequel, "Ares Express", in 2001.
In aviation, relaxed stability is the tendency of an aircraft to change its attitude and angle of bank of its own accord.
 An aircraft with relaxed stability will oscillate in simple harmonic motion around a particular attitude at an increasing amplitude.
In physics, complex harmonic motion is a complicated realm based on the simple harmonic motion.
 The word "complex" refers to different situations.
 Unlike simple harmonic motion, which is regardless of air resistance, friction, etc., complex harmonic motion often has additional forces to dissipate the initial energy and lessen the speed and amplitude of an oscillation until the energy of the system is totally drained and the system comes to rest at its equilibrium point.
In mechanics and physics, simple harmonic motion is a type of periodic motion or oscillation motion where the restoring force is directly proportional to the displacement and acts in the direction opposite to that of displacement .

Question: What was the contribution of the "quiet Beatle" to a song Ian McDonald described as having "rich and unusual harmonic motion"?
Answer: use of volume pedal guitar