**Thomas Cherry**'s mother, Edith Sarah Gladman, was a graduate in classics who had been born in England. Thomas Cherry's father, also named Thomas Cherry, was born in Gisborne, Victoria, Australia, although his father, Edward Cherry, had been born in England and had emigrated to Australia in 1855. Thomas Cherry Senior was a Bacteriologist and Agricultural scientist and employed giving a bacteriological service to doctors and hospitals in Melbourne at the time that his second Thomas, the subject of this biography, was born. Thomas (or Tom as he was known to his family and friends) had an older brother John Howard Cherry, and two younger brothers Henry Lister Cherry and Richard Ormond Cherry and a sister Margaret Lilias Cherry. Thomas was brought up in Glen Iris on the outskirts of Melbourne which at that time was almost in the country.

An indication of the rural nature of Glen Iris is that Thomas had to walk over 6 km each day to attend primary school. He then attended Scotch College where his talents for mathematics and science were quickly recognised. He was dux of the College in 1914 and entered Ormond College of the University of Melbourne. He graduated with a B.A. in 1918 having won the Dixson scholarship for pure and applied mathematics, the Professor Wilson prize for mathematics and natural philosophy, and the Wyselaskie scholarship in mathematics. After he graduated, with World War I still being fought, he enlisted in the Australian Imperial Force. He was assigned to the Australian Flying Corps where, by his own account, he (see [1] or [4]):-

... learnt telegraphy and solo whist.

His service with the Flying Corps was short (from 25 July 1918 to 24 December 1918), and he then began to study medicine at the University of Melbourne. However, his real love was mathematics and his godfather, Sir John MacFarland the Chancellor of the University of Melbourne, offered to lend him sufficient funds to study mathematics at the University of Cambridge in England. He jumped at the chance and entered Trinity College, Cambridge. The high quality of his work led to him receiving a Senior Scholarship and an Isaac Newton studentship. He graduated with a B.A. in 1922 and a doctorate in 1924. His Ph.D. thesis *Differential Equations Of Dynamics* was written under guidance from Henry Baker and Ralph Fowler. His first papers *On the form of the solution of the equations of dynamics, On Poincaré's theorem of 'the non-existence of uniform integrals of dynamical equations'*, and *Note on the employment of angular variables in celestial mechanics* were all published in 1924 and *Some examples of trajectories defined by differential equations of a generalised dynamical type* in the following year. Of these four papers, the third appeared in the *Monthly Notices of the Royal Astronomical Society* while the other three were published by the *Cambridge Philosophical Society*.

In 1924 Cherry won the Smith prize for applied mathematics and was elected a fellow of Trinity College. He undertook research on ordinary differential equations, particularly those arising from dynamics and celestial mechanics, for four years. Although based at Cambridge, he had two periods away. The first was the academic year 1924-25 which he spent at the University of Manchester teaching courses which had been taught by Chapman who had resigned as Professor of Applied Mathematics (Milne was appointed to fill the chair from 1925). Cherry also spent one term teaching at the University of Edinburgh in 1927 substituting for Charles Galton Darwin (son of George Howard Darwin).

During his time as a fellow of Trinity College, Cherry spent time with his two main hobbies, mountaineering and scouting. As well as climbing many mountains in Britain, he also climbed the Matterhorn in Switzerland and mountains in the French Pyrenees. As a scoutmaster in Cambridge he met Olive Ellen Wright who was a Girl Guide leader. Although Cherry returned to Australia in 1929, he came back to England to marry Olive on 24 January 1931 in Holy Trinity parish church, Cambridge; they had one daughter Jill. In fact Cherry had returned to Australia in March 1929 to take up a professorship at the University of Melbourne. His chair was titled 'Mathematics, Pure and Mixed' ('Pure and Mixed' would be 'Pure and Applied' in today's terminology). He held this chair until 1952 when the University of Melbourne decided to create separate chairs of 'Pure Mathematics' and 'Applied Mathematics'. He could have chosen either, and he certainly did not find it an easy decision to make, but eventually chose 'Applied Mathematics'. He held this chair until he retired in 1963. A note which he wrote explains the reason why a decision between the chairs of pure or applied mathematics was so difficult for him. He wrote (see for example [1]):-

While I am interested in the facts of Nature, I am much more interested in scientific theories, and particularly in fundamental questions, e.g. whether the classical principles of dynamics form a sufficient foundation for Statistical Mechanics. When such questions are formulated mathematically, they become problems in pure mathematics, and it is really to this subject that most of my work belongs. On the fundamental questions themselves I have perhaps arrived at understanding, but have found nothing sufficiently interesting to publish.

Cherry explains his attitude towards leading the Mathematics Department at the University of Melbourne, and in particular he describes his love of teaching (see for example [1]):-

For over20years I was responsible for the whole mathematical syllabus, pure and applied, and I have always regarded the associated teaching as my chief responsibility. For over a decade the stint was four courses of lectures per term. Since I am really attached to teaching this was no burden. At one time or another I have taught every subject in the curriculum, at all levels.

Let us look more closely at a few of Cherry's papers to give at least an indication of the topics on which he undertook research. In 1937 he published *Topological Properties of the Solutions of Ordinary Differential Equations* and in 1947 he published the first part of *Flow of a compressible fluid about a cylinder*. A Gelbart writes in a review:-

The author states that he has solved the problem of finding the exact solution of a two-dimensional uniform flow of a compressible perfect fluid about a cylinder. He assumes that the circulation is zero and the speed at large distances from the cylinder is subsonic, though this need not be so in the neighbourhood of the cylinder. The solution contains an infinite number of parameters which theoretically can be fixed to determine the shape of the cylinder .... Since the author uses the solutions of Chaplygin, in the form of an infinite series of hypergeometric functions, of the linear second order partial differential equation in the hodograph variables of the potential function, this series diverges for values of the velocity whose speeds exceed the speed at infinity. The essential part of the paper is to overcome this difficulty by successfully continuing "analytically" the solutions into the region of higher speeds.

In the second part of the paper, published two years later, Cherry extended his results to cover the case where circulation is not zero. Also in 1949 he published *Numerical solutions for transonic flow* which:-

... presents the flow patterns past a cylinder, produced by superposition of a cosine-term solution and a sine-term solution to that generated from an incompressible flow past a cylinder without circulation.

In *On expansions in eigenfunctions, particularly in Bessel functions* (1949) Cherry gives a form of the integral theorems of Fourier, Hankel and Heinrich Weber which is applicable to functions which are exponentially large at infinity.

In his own notes, Cherry gives us a good insight into his personality and approach to research (see for example [1]):-

By taste, or upbringing, I have preferred always the "do it yourself" method. This began when, at the age of seven, my attendance at school involved a walk of nearly four miles every day. With the help of prizes and scholarships, whose attainment involved little effort for me, I have been practically self-supporting since the age of17. I have "directed" the initial research efforts of a fair number of students, but by force of circumstances, reinforced by inclination, I have not tried to form a "research school".

He related these comments on his personality to his hobbies:-

My love of camping and mountaineering connects in one direction with 'do it yourself' and in another direction - via the shapes of hills - with geometry and mathematics.

In early 1965 Cherry suffered a heart attack after a particularly difficult incident during his climbing. He made a quick recovery and continued to work at his usual strenuous pace, spending the academic year 1965-66 at the University of Washington in Seattle. However he died following a second heart attack in November 1966.

Cherry received many distinctions for his contributions to mathematics. he was awarded the Lyle medal by the Australian National Research Council in 1951, he became a Foundation Fellow of the Australian Academy of Science in 1954, and was elected a fellow of the Royal Society of London in 1954. He received honorary degrees from the Australian National University and the University of Western Australia in 1963. He was made a Knight Bachelor in 1965. He served as president of the Mathematics Association of Victoria during 1929-34 and again during 1946-48, he was foundation president of the Australian Mathematical Society during 1956-58, and also foundation president of the Victorian Computer Society during 1961-63. During 1961-64 he was president of the Australian Academy of Science, being the third president of the Academy.

**Article by:** *J J O'Connor* and *E F Robertson*