**Michel Plancherel**'s main research fields were analysis, mathematical physics and algebra. He is best known for Plancherel's theorem in harmonic analysis.

- Donat Plancherel was a teacher, first in Villaz-Saint-Pierre and later in Bussy.
- However two of Michel's siblings died in early life.
- Simultaneously, he was a professor at the Collège St-Michel (1896-1912) and at the École secondaire de jeunes filles.
- After moving to Fribourg, Michel was sent to school and attended the Collège St-Michel in the section which prepared for ETH Zürich (called Eidgenössisches Polytechnikum at that time).
- However, Michel chose to study at the faculty of science at the University of Fribourg.
- Under Lerch's supervision, Michel finished his excellent doctoral thesis Sur les congruences (mod 2m ) relatives au nombre des classes des formes quadratiques binaires aux coefficients entier et à discriminant négatif Ⓣ(On the congruence (mod 2m) on the number of classes of binary quadratic forms with integer coefficients and negative discriminant) in 1907.
- In 1910, Michel Plancherel became Privatdozent at the University of Geneva, and in 1911 extraordinary professor in Fribourg being the successor of Lerch who went to Brno in 1906.
- Plancherel occupied his chair for higher mathematics during the next 35 years, until he retired in 1955.
- The confidence his colleagues put in Plancherel bestowed him the dignity of rector at ETH between 1931 and 1935.
- At ETH Plancherel gave courses not only for mathematicians but also for students of electrical and mechanical engineering.
- In the Swiss army, Michel Plancherel reached the rank of colonel.
- After the flight of 550 Hungarian students in 1956 to Switzerland, the rectors of the Swiss universities commissioned Michel Plancherel to raise funds to help these students.
- Plancherel collected over 2 million Swiss Francs, an immense sum at that time.
- During the great depression in the 1930's Plancherel was the director of the service for voluntary work, and, after 1948, president of the Swiss Winterhilfe, an organization to help people during hard winters.
- It is reported that Plancherel was deeply enrooted in his Christianity: among other activities he presided the Mission Catholique Française in Zürich.
- Michel Plancherel died on March 4, 1967: In full possession of his physical faculties and of unbroken intellectual freshness.
- Michel Plancherel was buried on March 8, 1967, on the cemetery of Fluntern in Zürich.
- Michel Plancherel's main research fields were analysis, mathematical physics and algebra.
- In his work he achieved fundamental results, one of them is the famous Plancherel theorem in harmonic analysis and which is now known in many generalizations (Plancherel measures).
- Proof of the impossibility of ergodic systems: the 1913 papers of Rosenthal and Plancherel.
- The papers by Rosenthal and Plancherel marked a watershed in the development of the foundations of statistical mechanics, for they brought to a close the classical age of Maxwell, Boltzmann and Ehrenfest and stimulated the development of ergodic theory as a new branch of mathematics.
- In algebra Plancherel obtained results on quadratic forms and their applications, to the solvability of systems of equations with infinitely many variables and to the theory of commutative Hilbert algebras (theorem of Plancherel-Godement).
- The scientific estate of Plancherel is administered by the library of ETH Zürich (Wissenschaftshistorische Sammlungen der ETH-Bibliothek).

Born 16 January 1885, Bussy, Kanton Freiburg, Switzerland. Died 4 March 1967, Zürich, Switzerland.

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Origin Switzerland

**O’Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive