by J. W. S. Cassels, rev.
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Mordell, Louis Joel (1888-1972), mathematician, was born on 28 January 1888 in Philadelphia, Pennsylvania, the third in the family of eight children (four sons and four daughters) of the Hebrew scholar Phineas Mordell (1861-1934) and his wife, Annie, née Feller (1865-1938), who were both recent immigrants from Lithuania. When at the age of fourteen he entered the Central High School of Philadelphia he was already fascinated by mathematics and had read widely. In 1906 he scraped together the single fare to Cambridge to compete in the scholarship examination. Top of the list, he was awarded a scholarship at St John's College. In 1909 he sat part one of the mathematical tripos and was third wrangler. The following year he was put in the middle of the three divisions of the first class in part two.
Mordell's reading had already attracted him to the theory of numbers, which in its various aspects was to become his life's work. There was little interest in the subject at that time in England, and he regarded himself as self-taught, but his investigations won him a Smith's prize.
In 1913 Mordell left Cambridge for a lectureship at Birkbeck College, London, where he remained, apart from two years as a statistician at the Ministry of Munitions, until 1920. On 24 May 1916 Mordell married Mabel Elizabeth (1895/6-1971), the only daughter of Rosa and Joseph Cambridge, a small farmer in the town of the same name. They had a son and a daughter. His years at Birkbeck were productive, his main interest being in modular functions and their application to number theory.
From 1920 to 1922 Mordell was lecturer at the Manchester College of Technology. This period saw his most important single discovery, his 'finite basis theorem'. This states that the rational points on a non-singular plane cubic can all be obtained from a finite number of them by a definite process, confirming the earlier conjecture of Poincaré. It seems likely that Mordell failed to realize the full significance of his work: in any case he had no part in later developments. In 1922 he moved to the University of Manchester where, after a year as reader, he was appointed to the Fielden chair of pure mathematics, which he occupied until 1945. He was now a leading figure in the mathematical world and was elected FRS in 1924. He took British nationality on 10 December 1929.
Mordell was an enlightened head of department and very concerned with the quality of the teaching. He built up an extremely strong school of mathematics, particularly in the 1930s when almost every young mathematician of note seems to have passed through the department. He was very active in assisting refugee mathematicians from Germany or Italy. A topic which occupied him at this time was the estimation of the number of points on algebraic varieties over finite fields; in the early 1940s he became interested in the geometry of numbers and initiated a period of great advance by himself and others.
In 1945 Mordell succeeded G. H. Hardy in the Sadleirian chair in Cambridge and was elected to a fellowship of St John's. He rapidly built up a powerful research school. After his retirement in 1953 he retained his fellowship and his house in Cambridge, though he travelled extensively. His enthusiasm for the theory of numbers never left him: he was working and publishing right to the end. He was a problem solver of great ingenuity and it gave him particular pleasure to obtain or extend by elementary means results that had first been found by sophisticated ones. He had the gift of imparting his enthusiasm and was in great demand as a lecturer. He enjoyed travelling. He was awarded the Sylvester medal of the Royal Society in 1949. He was president of the London Mathematical Society (1943-5) and received both its De Morgan medal (1941) and its senior Berwick prize (1946). He was a foreign member of the academies of Norway, Uppsala, and Bologna and an honorary doctor of the universities of Glasgow (1956), Mount Allison (1959), and Waterloo (1970).
Mordell, who had enjoyed robust health throughout his life, died from a brain haemorrhage at Addenbrooke's Hospital, Cambridge, on 12 March 1972.
J. W. S. CASSELS, rev.
J. W. S Cassels, Memoirs FRS, 19 (1973), 493-520
L. J. Mordell, 'Reminiscences of an octogenarian mathematician', American Mathematical Monthly, 78 (1971), 952-61
L. J. Mordell, Reflections of a mathematician (Montreal, 1959)
J. W. S. Cassels, Bulletin of the London Mathematical Society, 6 (1974), 69-96
H. Davenport, 'L. J. Mordell', Acta Arithmetica, 9 (1964), 3-12
'Phineas Mordell', Universal Jewish encyclopedia (1971)
ILN (19 June 1909)
personal knowledge (1986)
St John Cam., papers
Trinity Cam., corresp. with Harold Davenport
photograph, repro. in Cassels, Bulletin
portrait, repro. in Strand Magazine (Jan 1950)
Wealth at death
£143,881: probate, 26 May 1972, CGPLA Eng. & Wales
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