Adriaan Daniël Fokker
17 August 1887|
Buitenzorg, Dutch East Indies
|Died||24 September 1972
|Institutions||University of Leiden
|Alma mater||Delft University of Technology
University of Leiden
|Doctoral advisor||Hendrik Lorentz|
|Known for||Fokker–Planck equation
Fokker periodicity block
Fokker was born in Buitenzorg, Dutch East Indies (now Bogor, Indonesia); he was a cousin of the aeronautical engineer Anthony Fokker. He studied mining engineering at the Delft University of Technology and physics at the University of Leiden with Hendrik Lorentz, where he earned his doctorate in 1913. He continued his studies with Albert Einstein, Ernest Rutherford and William Bragg. In his 1913 thesis, he derived the Fokker–Planck equation along with Max Planck. After his military service during World War I he returned to Leiden as Lorentz' and Ehrenfest's assistant. In 1928 Fokker succeeded Hendrik Lorentz as director of research at Teylers Museum in Haarlem.
Fokker made several contributions to special relativity, and some less well-known contributions to general relativity, particularly in the area of geodetic precession, the phenomena of precession of a freely falling gyroscope in a gravitational field.
Fokker began to study music theory during the Second World War, when the University of Leiden was closed; partly this was due to a desire to convince the Nazis he would be of no use to the war effort, and partly it was a response to reading the work of Christiaan Huygens on the 31 equal temperament. The year 1942 consequently marked a turning point in his life; after then he wrote many pieces in 31-equal, which are notable for using the 7th harmonic as a consonant interval (31-equal has a much better approximation of the 7th harmonic than the ubiquitous 12-equal). He also made notable contributions to music theory, such as the Fokker periodicity block.
Musical instruments 
Fokker designed and had built a number of keyboard instruments capable of playing microtonal scales via a generalized keyboard. The best-known of these is his 31-tone equal-tempered organ, which was installed in Teyler's Museum in Haarlem in 1951. It is commonly called the Fokker organ.
See also 
References and notes 
||This article needs additional citations for verification. (November 2008)|
- Short biography from the Huygens–Fokker Foundation
- Fokker's Euler organ at the Teylers Museum
- H.A.M. Snelders, "Fokker, Adriaan Daniël (1887–1972)", in Biografisch Woordenboek van Nederland. [13-03-2008]
- Oral History interview transcript with Adriaan Fokker, 1 April 1963, American Institute of Physics, Niels Bohr Library and Archives