**Robert de Montessus** was a French mathematician, known for his work on continued fractions and Padé approximants.

- Robert de Montessus obtained his baccalaureate in 1886.
- Thus, he joined the French army but left in 1893 to take up a job at the Compagnie des Chemins de Fer de Paris à Lyon et à la Méditerranée.
- During the years 1895-1902, Robert de Montessus taught in different secondary schools (in Evreux, Yzeure, and Senlis).
- During the academic year 1898-1899, he followed the lectures of Paul Appell, Gaston Darboux and Émile Picard at the Sorbonne.
- Next, he worked for his doctorate in mathematics under Appell's supervision.
- The first contribution of Robert de Montessus in mathematics was to help Giuseppe Peano in editing the Introduction of the Formulaire Ⓣ(Formulary) in 1897.
- In 1902, his friend, the French mathematician Robert d'Adhémar, helped him to join the Catholic University of Lille.
- In the same year, Robert de Montessus published a paper entitled Sur les fractions continues algébriques Ⓣ(On algebraic continued fractions) in the Bulletin de la Société Mathématique de France.
- In 1903, Robert de Montessus became Maître de Conférences at the Lille Catholic University.
- Robert de Montessus defended his doctoral thesis Sur les fractions continues algébriques Ⓣ(On algebraic continued fractions) on 8 May 1905.
- In the first part of the thesis, Robert de Montessus dealt with different problems of convergence of algebraic continued fractions.
- The first part of his thesis was published in the Rendiconti del Circolo Mathematico di Palermo in 1905.
- In 1906, the subject proposed for the Grand Prix of the Paris Academy of 1906 was on the convergence of algebraic continued fractions.
- Moreover, Montessus de Ballore's theorem was soon cited by mathematicians such as Edward van Vleck, Niels Norlund, Oskar Perron and Edwin Wilson.
- In 1908, Robert de Montessus wrote a book on probability theory entitled Leçons élémentaires sur le Calcul des Probabilités Ⓣ(Basic rules of probability theory).
- De Montessus continued to publish works on continued fractions up to 1909.
- In 1917, Robert de Montessus joined the editorial team of the Journal de Mathématiques Pures et Appliquée headed by Camille Jordan.
- In the same year de Montessus was employed to work on ballistics by the French government.
- After 1919, Robert de Montessus devoted much attention to the theory of probability and applied statistics.
- He was in correspondence with several Belgian mathematicians such as Paul Mansion, Charles de La Vallée Poussin, Maurice Alliaume, but also with Maurice Fréchet and Charles Jordan.
- It is hard to conjecture the number of practical difficulties which de Montessus had to overcome in organizing this immense mass of data on the universities and learned societies of the world; the scientific qualities of which he had given evidence elsewhere came to his aid here.
- Between the two world wars, Robert de Montessus gave courses of lectures on various branches of mathematics in Warsaw, Kraków, Lwów (now Lviv in Ukraine), Budapest, Vienna and at other universities such as Lausanne and Geneva.
- En 1917, Camille Jordan avait introduit R de Montessus à la rédaction du Journal de Mathématiques.
- Ⓣ(In 1917,Camille Jordan had introduced R de Montessus as editor of the Journal of Mathematics.

Born 20 May 1870, Villeurbanne, Rhône, France. Died 26 January 1937, Arcachon, Gironde, France.

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