by F. E. Hackett, rev. Julia Tompson

© Oxford University Press 2004 All rights reserved

**Orr, William McFadden** (1866-1934), mathematician, was born at Ballystockart, Comber, co. Down, on 2 May 1866, the eldest son of Fletcher Blakeley Orr, a farmer who owned corn and flax mills, of Ballystockart, and his wife, Elizabeth, daughter of David Lowry, farmer, of Ballymachashan, Killinchy, co. Down. He received his early training in mathematics at the local national school. After spending two years at an intermediate school in Newtownards, he entered the Methodist college, Belfast, where he came under the mathematical direction of James Adams McNeill, afterwards headmaster of Campbell College, Belfast. He obtained a scholarship in mathematics at the Royal University of Ireland in 1883, and graduated in 1885 from Queen's College, Belfast, then a constituent college of the Royal University. He then moved to St John's College, Cambridge, in April 1885, was senior wrangler in 1888, and obtained the first place in part two of the mathematical tripos of 1889. In 1891 he was both elected to a fellowship at St John's and appointed professor of applied mathematics at the Royal College of Science for Ireland, Dublin. When in 1926 this institution was absorbed by University College, Dublin, he was offered and accepted an equivalent position in that college as professor of pure and applied mathematics, from which he retired in 1933. In 1909 he was elected FRS, and he received the honorary degree of DSc from Queen's University, Belfast, in 1919. In 1892, shortly after he obtained the post in the Royal College of Science, Orr married Elizabeth Campbell *(d.* 1926), daughter of Samuel Watson Campbell, of Melbourne, Australia, who originally came from co. Down. They had three daughters, the eldest of whom died in Orr's lifetime.

His contemporaries at the Royal College of Science record that Orr's teaching was characterized by accurate definition, logical rigour, and clear statements of underlying assumptions. The scrupulous style of his teaching is shown in his *Notes on Thermodynamics for Students* (1909), which is a model of precision in the formulation of principles. He always endeavoured to provide his students with the mathematical tools needed to deal with the physical, chemical, and engineering problems that they met in the laboratories, where he was frequently to be seen modestly deploring his own lack of experimental knowledge. Mathematics under his inspiring influence became, for staff and students alike, an integrating subject in the small college.

Orr's role model was McNeill, of whom he wrote an appreciation containing an unconscious self-portrait, in which he described the persistence with which his teacher would repeatedly attack a difficult mathematical problem and expressed the view that this trait was a moral one, an attempt to live 'the strenuous life' of which he approved. Combined with this stoical austerity, Orr exercised quick and effective generosity towards students and teachers in difficulties.

Orr's mathematical outlook was moulded in the Cambridge tradition of Lord Rayleigh, A. E. H. Love, and Sir Joseph Larmor, with whom he carried on an active correspondence. He was best known for his work on the stability of the steady motions of a liquid. He also worked on the problems arising from the whirling of shafts in his 'Note on Mr. Lees' paper on the whirling of an overhung shaft' *(Philosophical Magazine,* 45, 1923), which was supplemented by correspondence and discussion with his colleagues, and he wrote papers on several issues in mathematical physics. He felt very strongly that clear thinking in applied science rests upon a solid grasp of fundamental principles. He therefore aimed at the best possible exposition in all his work, and especially in textbooks. The climate of the quantum and relativity physics of the twentieth century was not congenial to him, but he never ceased to take an interest in these developments and to look forward to a reconciling synthesis with classical dynamics. Orr died at Nobles Hospital, Douglas, Isle of Man, on 14 August 1934.

F. E. HACKETT, *rev.* JULIA TOMPSON

**Sources **

A. W. Conway, *Obits. FRS,* 1 (1932-5), 559-62

*The Campbellian* (Nov 1907)

Venn, *Alum. Cant.*

*CGPLA Eng. & Wales* (1935)

**Archives **

Air Force Research Laboratories, Cambridge, Massachusetts, Strutt MSS

St John Cam., letters to Sir Joseph Larmor

**Likenesses **

photograph, repro. in Conway, *Obits. FRS,* 558-9

photograph, RS

**Wealth at death **

£5014 *3s. 6d.* in England: administration with will, 25 Feb 1935, *CGPLA Eng. & Wales*

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