**Joseph Ritt** was an American mathematician who worked on ordinary and partial differential equations.

- The Observatory measured the position of celestial objects for purposes of timekeeping and navigation and in 1904, six years before Ritt took a job there, the Observatory broadcast the world's first radio time signals.
- While he was in Washington D.C. Ritt did manage to continue his education as well as working at the Observatory.
- He studied at the George Washington University (it had university status from 1873 but had adopted its current name only six years before Ritt began to study there).
- He was awarded a B.A. in 1913 and, following the award, he took a summer graduate course at Columbia University (Columbia College had been renamed Columbia University in the year before Ritt took the course).
- Edward Kasner, who was on the faculty at Columbia University, recognised Ritt's remarkable talents and he was offered a fellowship to undertake research for his doctorate at Columbia.
- Ritt resigned his position at the Naval Observatory and began working for his doctorate which was awarded in 1917 for his thesis On a general class of linear homogeneous differential equations of infinite order with constant coefficients.
- In 1921 Ritt was appointed as an assistant professor at Columbia University and was promoted to associate professor in 1927.
- Ritt published two important papers in 1922, namely Prime and composite polynomials and On algebraic functions which can be expressed in terms of radicals.
- One year before the publication of this work, Ritt had published Theory of Functions which provides an introduction to the theory of functions in a series of short and to the point lecture notes giving the student an account of the fundamental definitions and theorems of the subject.
- Ritt had begun a new major research topic in the 1930s when he began to create a theory of ordinary and partial differential equations.
- The book considers the results obtained by Ritt and his students on topics such as differential polynomials, differential ideals, and differential manifolds.
- We left our description of Ritt's career at the point where he was associate professor at Columbia University.
- In the last three years of his life Ritt began a deep study of the applications of Lie theory to homogeneous differential equations.
- Ritt received many honours during his career.
- It is clear that Ritt took an unusual interest in reading the great mathematical works of his predecessors.
- Among his heroes were Niels Henrik Abel, Augustin Louis Cauchy, David Hilbert, Carl G J Jacobi, Joseph-Louis Lagrange, the marquis Pierre Simon de Laplace, Joseph Liouville and Jules Henri Poincaré.
- Their works set the standards Ritt tried to reach in his own mathematics, and were they to judge his work, he hoped it would be found worthy.

Born 23 August 1893, New York City, USA. Died 5 January 1951, New York City, USA.

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Origin Usa

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