Adriaan Daniël Fokker (Buitenzorg, Dutch East Indies (now Bogor, Indonesia), August 17, 1887–Beekbergen (near Apeldoorn), September 24, 1972) was a Dutch physicist and musician. Fokker, a cousin of the aeronautical engineer Anthony Fokker, 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 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.

Links

H.A.M. Snelders, Fokker, Adriaan Daniël (1887-1972), in Biografisch Woordenboek van Nederland.

Short biography from the Huygens-Fokker Foundation

Adriaan Fokker's Euler-organ at the Teylers Museum.