Adriaan Daniël Fokker (1887-1972)

Adriaan Daniël Fokker was born on August 17, 1887, in Buitenzorg (Bogor), Java. He was the son of the director of the Nederlandsche Handelmaatschappij in Batavia (Jakarta) and a cousin of the aircraft manufacturer Anthony Fokker. In 1894 his family returned to the Netherlands. He studied mining at the Delft University of Technology and physics at the University of Leiden under Hendrik Lorentz, where he obtained his doctorate in 1913. A publication emerged from his dissertation in 1914 presenting a theory that would later be known as the Fokker-Planck equation, after it was independently described by Max Planck in 1917. In physics, Fokker’s name is therefore to this day primarily associated with the Fokker-Planck equation, a second order partial differential equation, which is related to the Brownian motion. Between 1913 and 1914, Fokker worked in Zürich as an assistant to Albert Einstein, and published an article on the theory of general relativity with Einstein as his co-author. He continued his studies with Ernest Rutherford and William Bragg. From 1914 to 1918 he was affiliated as a lecturer with the University of Leiden. Thereafter he was successively appointed as a physics teacher at the gymnasium in Delft and as extraordinary professor at the Delft University of Technology (1923-1927). From 1927 he was involved with the Teylers Foundation in Haarlem, and from 1928 to 1955 he was professor of physics at the University of Leiden and curator of the Physical Cabinet of the Teylers Museum. In the 1920s and 1930s he developed into a leading figure within the Dutch physics community, not least through his organisational and editorial activities. He also gained an international reputation as a physicist, specialising among other things in the theory of relativity. From 1921 to 1933 he was editor of Physica – Nederlandsch Tijdschrift voor Natuurkunde. A practical field of interest within acoustics was already early on the acoustics of halls. For numerous existing and new concert and theatre halls he acted as an advisor. Churches also regularly called upon him in this context. During the Second World War, when the University of Leiden was closed, he began studying music theory, inspired by the description of a 31-tone temperament by Christiaan Huygens (1629-1695), which had just been published in volume 20 of Huygens’ Oeuvres complètes. Fascinated by Huygens’ invention, he immersed himself in harmony, tuning systems and temperaments, and subsequently projected his own revolutionary ideas regarding just intonation onto the 31-tone system.

The year 1942 was a turning point in his life. From that moment on, he would devote most of his attention to music, although physics was not forgotten. In 1943 he designed a small organ to make playing in the Euler-Fokker tuning systems possible. His music-theoretical research found its expression in 1945 in the book Rekenkundige bespiegeling der muziek (Arithmetical Reflections on Music). But Fokker was not the kind of man to stop at theoretical considerations. His ideas had to be thoroughly tested. Thus, in 1950 he commissioned organ builder Bernard J.A. Pels to construct a pipe organ with 31 tones per octave. In doing so, Adriaan Fokker became the first to put Christiaan Huygens’ theories into practice. This 31-tone organ (Fokker organ) did not have a movable keyboard as in Huygens’ sketches, but two manuals with 31 keys per octave arranged above one another. The large number of white, black and blue keys are compactly arranged and form mysterious, diagonally ascending patterns. The organ is tuned in meantone temperament, but it has additional notes, allowing unlimited modulation to all keys—a feat that is, for example, impossible on a church organ tuned in meantone.

In 1951, the so-called Fokker organ was installed in the Teylers Museum in Haarlem. The unique instrument was placed in the central hall of the museum, where Fokker served as curator of the Physical Cabinet. From September 1951 onwards, demonstrations and concerts on the 31-tone organ were held here every first Sunday morning of the month, involving various musicians. Fokker became a passionate advocate of the 31-tone system and was constantly engaged in arousing the interest of composers and musicians. To him, it was a system that carried unprecedented new musical possibilities. He regarded the organ as an instrument that opened doors to the music of the future, free from the limitations of the twelve-tone system. Fokker gave lectures around the world and succeeded in engaging numerous singers, musicians, and composers, thus sparking a genuine 31-tone movement. Dutch composers such as Peter Schat, Henk Badings, Hans Kox, and Jan van Dijk, and abroad, among others, Alois Hába, Ivan Wyschnegradsky, and Alan Ridout, made significant contributions to the 31-tone repertoire.

In 1960, Professor Fokker founded ‘Stichting Nauwluisterendheid’ (the name was changed in 1966 to the Huygens-Fokker Foundation) in order to manage the organ and promote the music. In the 1950s and 1960s, Fokker gave numerous lectures both in the Netherlands and abroad about the 31-tone system. He also wrote articles on musical subjects and a musical autobiography: Neue Musik mit 31 Tönen. Under the pseudonym Arie de Klein, he composed short pieces in a large number of different tone genera, with notable titles such as Tenacitas (1948), The Harmonic Starfish (1952), Jacob’s Dream (1959), Sevenths in the Tatra Mountains (1964), Hotel Room 315 (1967), Rippled Diesis Waves (1971) and 6:7:8:9 (1972). In 1964, Adriaan Fokker received the ‘Zilveren Anjer’ from Prince Bernhard for his services to Dutch culture. At the end of his life he was still involved in the development of one final 31-tone instrument, namely the electronic ‘archiphone‘, which was built in 1970. He passed away on 24 September 1972 in his hometown of Beekbergen, after thirty years of intensive, uninterrupted musical activity and dedication to 31-tone music.

According to Professor Leigh Gerdine, Fokker achieved the following highly desirable objectives with regard to the 31-tone system:

1. he established the physical basis for the existence of the minor triad and minor tonality in the mirrored (reciprocal) versions of his interval relationships;
2. he made the seventh an acceptable harmonic interval – something Hindemith did not dare to pursue further because he was unsure of where it would lead;
3. he devised – and built – a keyboard that brilliantly solves the problems of 31-tone music, and eliminates some inadequacies of the current 12-tone keyboard;
4. he made the challenges of a new rational sound spectrum accessible, enabling both stronger consonance and stronger dissonance, as well as a more authentic performance of early music (pre-Bach) alongside expanded possibilities for the music of the future.

Read the article by Rudolf Rasch on Fokker’s musical activities: Adriaan Daniël Fokker: Musicus tricesimoprimalis (1988, in Dutch). Or the story about Einstein and Fokker (Sander Germanus, 2024). More information about Adriaan Daniël Fokker can be found on the website of the Huygens Institute.