Paul Émile Appell
Paul Émile Appell (27 September 1855, in Strasbourg – 24 October 1930, in Paris) was a French mathematician and Rector of the University of Paris. Appell polynomials and Appell's equations of motion are named after him, as is rue Paul Appell in the 14th arrondissement of Paris and the minor planet 988 Appella. Life. Paul Appell entered the École Normale Supérieure in 1873. He was elected to the French Academy of Sciences in 1892. In 1895, he became a Professor at the École Centrale Paris. Between 1903 and 1920 he was Dean of the Faculty of Science  of the University of Paris, then Rector of the University of Paris from 1920 to 1925. Appell was the President of the Société astronomique de France (SAF), the French astronomical society, from 1919 to 1921. His daughter Marguerite Appell (1883–1969), who married the mathematician Émile Borel, is known as a novelist under her pen-name Camille Marbo. Appell was an atheist. He was awarded Order of the White Eagle. Work. He worked first on projective geometry in the line of Chasles, then on algebraic functions, differential equations, and complex analysis. Appell was the editor of the collected works of Henri  Poincaré. Jules Drach was co-editor of the first volume. Appell series. He introduced a set of four hypergeometric series "F", "F", "F", "F" of two variables, now called Appell series, that generalize Gauss's hypergeometric series. He established the set of partial differential equations of which these functions are solutions, and found formulas and expressions of these series in terms of hypergeometric series of one variable. In 1926, with Professor Joseph-Marie Kampé de Fériet, he authored a treatise on generalized hypergeometric series. Mechanics. In mechanics, he proposed an alternative formulation of analytical mechanics known as Appell's equation  of motion. He discovered a physical interpretation of the imaginary period of the doubly periodic function whose restriction to real arguments describes the motion of an ideal pendulum.