His schooling took place in London after his family moved to Shepherd's Bush in 1899 when Leopold was three years old. In fact their house in Shepherd's Bush remained home to Albertus and Laura, together with their two children and Aleathea, until 1926 when they moved to a new home in Acton. This then became home to all five for the rest of their lives. Leopold was educated at Latymer Upper School in Hammersmith where, in addition to his academic work, he took part in sport, particularly in athletics. In December 1914 he won a Foundation Scholarship in Mathematics and Physics to study at Jesus College, Cambridge. He entered Jesus College to begin his studies in October 1915 but, after missing two terms through ill health, he waited until 1917 before he sat Part I of the Mathematical Tripos. Despite his ill health, Pars continued to take part in athletic events at University and won the Mile in the inter-University sports. Despite the ill health which affected him throughout his undergraduate days, he produced outstanding results.
Alan, as Pars became known when he was an undergraduate, then took a London University M.Sc. and, in 1921, he was the First Smith's Prizeman at Cambridge. His prize essay was entitled Vector and Tensor Fields and was in two parts. Part 1 was Geometrical Vector Theory and the Restricted Principle of Relativity and Part 2 was On the General Theory of Relativity. On the strength of this work he was awarded a Fellowship at Jesus College in 1921 which he held for 64 years :-
Pars never married, and the bachelor quarters he occupied in college were among the rooms most frequented by undergraduates. They could hardly fail to be charmed by his friendly interest in their activities, astounded by his wide knowledge range of exact quotation, and delighted by his knowledge of and enthusiasm for the theatre - though latterly few may have been aware of his earlier skill as a mountaineer.Appointed Praelector in 1923, he held this post, which made him responsible for presenting the undergraduates for their degrees, until 1946. He was appointed Director of Studies for mathematics at Jesus College in 1925, and a University Lecturer in 1927. He remained in the first of these roles until 1951, and in the second until 1961 when he retired. He became President of Jesus College in 1958 and was a founder member of the Department of Applied Mathematics when it was set up in 1959. His only extended time away from Cambridge during his career was when he took study leave for one year. He spent the academic year 1948-49 at the Institute for Advanced Study at Princeton and at the University of California at Berkeley.
Pars's first publications, influenced by Larmor and Eddington, were on relativity and were part of his prize essay. Thereafter he published little, although he did publish two valuable textbooks, Introduction to dynamics in 1953 and Calculus of variations in 1962, until he published a monumental 650 page work Treatise on analytical dynamics in 1965. This book, published 4 years after he retired, was his life work in a single book.
A colleague, writing after Pars's death, described the book in these terms:-
A Treatise on Analytic Dynamics is a massive, scholarly, systematic 650-page survey of the classical canon of mathematical dynamics. It is an exposition of enormous elegance, rigour and clarity, honed by decades of teaching undergraduate Tripos candidates and broadened by a perspective which encompassed all the major developments in dynamics from Galileo to the mid-twentieth century. Within its context it is a pedagogical masterpiece.Pars's aim in writing the book is described in  as:-
... to give a compact, consistent and reasonably complete account of the subject as it then stood. He based his treatment on the theorem of Lagrange that he called the fundamental equation, which he proceeded to translate into six different forms, each exploited in appropriate contexts.Pars devoted much of his life to teaching, which explains his relatively small research output, and so it will come as no surprise that someone so devoted to teaching undergraduates should be an expert :-
He was a teacher and lecturer of great skill and clarity whose range ... was beyond the reach of most of his younger colleagues in the faculty.After retirement from teaching he remained as President of Jesus College until 1964. On leaving this role he visited the Florida Atlantic University, the University of Sydney, and his travels took him to visit friends in Trinidad, New Zealand, Tasmania and Uganda. Although after retirement he lived at his home in Acton with his sister Dora, he continued to make visits to exotic places but retained his connection with Jesus College where he kept his College rooms. He dined there frequently and remained on the College Council until the end of his life :-
[He] was a familiar sight in Cambridge, taking his regular afternoon constitutional in his characteristic attitude with eyes downcast and walking stick raised behind.We have mention above some of Pars' interests outside mathematics such as mountaineering anf the theatre. Like his father he had a great love of music and, also like his father, he played the piano. As Taunt writes in :-
Though by no means an eccentric, he was a great Cambridge character, a survivor of an era which is passing from living memory.
Article by: J J O'Connor and E F Robertson