Adriaan Fokker
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{{Infobox_Scientist
| name = Adriaan Fokker
| image = AdriaanFokker.jpg
| caption = Adriaan Daniël Fokker
| birth_date = {{birth date|1887|8|17|mf=y}}
| birth_place = Buitenzorg, [[Dutch East Indies]]
| death_date = {{death date and age|1972|9|24|1887|8|17|mf=y}}
| death_place = [[Beekbergen]], [[Netherlands]]
| residence = [[Image:Flag of the Netherlands.svg|20px|]] [[Netherlands]]
| nationality = [[Image:Flag of the Netherlands.svg|20px|]] [[Netherlands|Dutch]]
| field = [[Physicist]]
| work_institution = [[Leiden University|University of Leiden]]</br>[[Teylers Museum]]
| alma_mater = [[Delft University of Technology]]</br>[[Leiden University|University of Leiden]]
| doctoral_advisor = [[Hendrik Lorentz]]
| doctoral_students = <!--please insert-->
| known_for = [[Fokker-Planck equation]]</br> [[Fokker periodicity block]]
| prizes =
| religion =
| footnotes =
}}
'''Adriaan Daniël Fokker''' ([[August 17]], [[1887]] – [[September 24]], [[1972]]), was a [[Netherlands|Dutch]] [[physicist]] and [[musician]].
Fokker was born in Buitenzorg, [[Dutch East Indies]] (now [[Bogor]], [[Indonesia]]); he was a cousin of the [[Aeronautics|aeronautical]] [[engineer]] [[Anthony Fokker]]. He studied [[mining engineering]] at the [[Delft University of Technology]] and [[physics]] at the [[Leiden University|University of Leiden]] with [[Hendrik Lorentz]], where he earned his [[doctorate]] in 1913. He continued his studies with [[Albert Einstein]], [[Ernest Rutherford]] and [[William Henry Bragg|William Bragg]]. In his [[1913]] thesis, he derived the [[Fokker-Planck equation]] along with [[Max Planck]]. After his [[Military service#Netherlands|military service]] during [[World War I]] he returned to [[Leiden]] as Lorentz' and [[Paul Ehrenfest|Ehrenfest]]'s assistant.
In 1928 Fokker succeeded [[Hendrik Lorentz]] as director of research at [[Teylers Museum]] in [[Haarlem]].
Fokker began to study [[music theory]] during the [[World War II|Second World War]], when the University of Leiden was closed; partly this was due to a desire to convince the [[Nazism|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 series (music)|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]].
He died at [[Beekbergen]] (near [[Apeldoorn]]).
==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==
* [[Fokker-Planck equation]]
* [[Fokker periodicity blocks]]
* [[Euler-Fokker genus]]
==External links==
*[http://www.xs4all.nl/~huygensf/english/fokker.html Short biography from the Huygens-Fokker Foundation]
*[http://www.teylersmuseum.nl/museum/collectionitems.jsp?view=%2Fxsl%2Fhtml&pageName=museum_collection_areas_item&lang=nl&id=3337 Fokker's Euler organ at the Teylers Museum]
{{BD|1887|1972|Fokker, Adriaan}}
[[Category:Dutch physicists]]
[[Category:Microtonal musicians]]
[[Category:Dutch music theorists]]
[[Category:Delft University of Technology alumni]]
[[Category:People from Bogor, West Java]]
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