Copson was awarded a D.Sc. by Edinburgh in 1928 and remained on the staff there until 1930, when he was appointed Lecturer in Mathematics at the University of St Andrews under Turnbull. He married the elder of Edmund Whittaker's two daughters, Beatrice Mary Whittaker, in 1931. Copson spent 1934 at the Royal Naval College in Greenwich, then returned to the University of St Andrews but this time to the chair of mathematics at Queen's College, Dundee (Queen's College was at that time part of the University of St Andrews and only became the University of Dundee in the 1960s). A lecturer in the department at the time wrote later (see for example ):-
The department at that time had a family atmosphere, decisions were taken during morning coffee, there were few official meetings, no teaching aids, no secretarial assistance, classes were small but teachers knew their students personally. Every member of the small staff might be called upon to lecture in any branch of mathematics, and Copson with his wide interests in mathematics was admirably suited to such an environment. Copson was generous in the help and advice he gave to new members of staff yet they were free to develop their interests both in teaching and research. Under Copson's leadership it was a most happy and successful department.In 1950 he was appointed to fill Turnbull's Regius Chair of Mathematics in St Andrews. He was Dean of Science in 1950-53 and was the first Master of the United College in 1954-57. It was a difficult period to hold such posts for the university was deciding on the site for building a new science complex which led to very heated debates. The final decision to build on the North Haugh, rather than in the town centre, has certainly proved correct.
A new Mathematical Institute was built on the North Haugh as part of the new science complex while Copson held the Regius Chair. The building work began on 8 September 1965 and on this occasion Copson cut the first sod with a spade which was subsequently presented to him. It carries the inscription (which is now almost illegible):-
E. T. COPSON M.A. D.Sc. F.R.S.E. F.I.M.A.
REGIUS PROFESSOR OF MATHEMATICS
ON THE OCCASION OF THE CUTTING OF THE FIRST SOD
TO INAUGURATE THE NEW MATHEMATICS BUILDING
NORTH HAUGH ST ANDREWS
8th SEPTEMBER 1965
The layout of the new building, and the name "Mathematical Institute", were due to Copson.
Copson studied classical analysis, asymptotic expansions, differential and integral equations, and applications to problems in theoretical physics. His first book was his most famous, namely The theory of functions of a complex variable (1935). It sold so well in the United States that he called an extension on his house in Buchanan Gardens, St Andrews, "The American Wing" since it was built with the profits. I [EFR] was first invited to this house while I was an undergraduate, and I played my first game of croquet on the lawn in his beautiful garden.
In total Copson wrote six books, all of which demonstrate his great skill as an expositor. The second book was The Mathematical Theory of Huygens' Principle published in 1939 and written in collaboration with Bevan Baker. Bateman, reviewing the book, wrote:-
Huygens' geometrical construction... is first justified ... by Poisson's analytical solution of the equation of wave-motions. A discussion is then given of the ideas of Fresnel and of the formula of Helmholtz which expresses these ideas in analytical form and gives the principle of Huygens for periodic processes. The diffraction formulae of Fresnel and Stokes are then obtained. Kirchhoff's famous formula is first derived from the formula of Helmholtz and then proved directly. ...The analogue of Kirchhoff's formula, due to Volterra, is derived and an interesting account is given of a method, devised by Marcel Riesz and based on the theory of fractional integration, which provides a powerful method of solving initial value problems for equations like the wave equation. The rest of the book is devoted chiefly to the problem of diffraction. ... Chapter IV contains a good account of Sommerfeld's theory of diffraction.Asymptotic expansions (1965) was written because Copson was pressed to write a more major work on that subject to expand on a shorter work written in 1943 at the request of the Admiralty. In 1968 he published Metric spaces which was based on lecture courses given at St Andrews, one of these courses I [EFR] was fortunate enough to attend. Copson writes in the Preface:-
There are many books on functional analysis; and some of them seem to go over the preliminaries to the subject far too quickly. The aim here is to provide a more leisurely approach to the theory of the topology of metric spaces, a subject which is not only the basis of functional analysis but also unifies many branches of classical analysis. The applications of the theory ... to problems in classical algebra and analysis show how much can be done without ever defining a normed vector space, a Banach space or a Hilbert space.In 1975 he published Partial differential equations which covers most of the classical techniques for first and second order linear partial differential equations, giving many examples and applications to physical problems.
In  the flavour of his papers is nicely summed up:-
His published papers span more than half a century. His last (1978), entitled "Electrostatics in a gravitational field" was relevant to the highly fashionable subject of Black Holes. It was typical of his work, very much on the borderline between mathematics and physical science, and exhibiting technical skill in classical analysis that is rare nowadays.Copson was honoured by election to the Royal Society of Edinburgh in 1924 and was awarded the Keith Prize of the Society in 1941 for an outstanding series of papers published in the Proceedings. He was Secretary of the Society from 1945 to 1950 and Vice-President from 1950 to 1953. He also served the Edinburgh Mathematical Society being Secretary (1924-30), editor of the Proceedings, and President on two occasions, 1930 and 1954-55.
As a lecturer he was outstanding, he gave lectures of remarkable clarity :-
Copson was a good teacher, whether behind the rostrum with his general class or in tutorials or seminars with his honours or research students. His influence in and beyond St Andrews can be measured by the number of members of university departments, not all in mathematics, who were his pupils.Tom Blyth, one of his students and then a colleague, wrote (see for example ):-
He firmly believed in the old Scottish tradition of the Professor lecturing on a sizeable part of the first-year syllabus: he did so entirely without notes, relying solely on his pocket diary to mark how far he had gone each day.His students, always aware that their teacher was a master of his subject, nevertheless sometimes played practical jokes. By the 1960s Copson was hard of hearing and wore a hearing aid. However he always turned it off when he lectured and alarm clocks were sometimes brought into the lecture room and would ring loudly at various times.
After he retired in 1969, Copson continued living in St Andrews. He still did some teaching, which he loved, and continued to write books and undertake research.
Article by: J J O'Connor and E F Robertson