When I first went to King’s as a research student, I joined and mixed with a small group of pure maths students. I might never have come to work with Felix, a Professor of Rational Mechanics, but for a twist of fortune. When I applied for a grant, it turned out that the Science Research Council, as it then was, had a residency requirement for its PhD grant holders that I did not meet. (Not only I, but my parents also should have lived in the UK for a number of years.) So I found myself in need of financial support, and the Department stepped in with a “tutorial studentship”, which meant that I had to teach up to six hours a week. Felix happened to be in charge of tutorial organization and so I came into frequent contact with him. In a rather stuffy institution, he was a remarkably unaffected professor. Everything about him seemed different: he was somehow both relaxed, as evidenced by his easy relationships with students, and intense, or intensely rigorous, as one could discover by entering into an argument about politics — by which I mean not British party politics, but the more esoteric reaches of, say, a Marxist approach to the analysis of science and progress through science. For an aspiring mathematician who had never given these matters much thought, this was exhilarating.

It was not long before I discovered that he taught a course of interest to me, although in principle it was classified as “applied mathematics”, and I began to attend. He was a highly engaging teacher — not “lecturer” — who consequently demanded a degree of participation from his students. I recall two incidents: once he was leading up to an observation by asking a series of questions, until a frustrated undergraduate said “look, you are the professor, we are the students, just TELL us!” Needless to say, Felix took the trouble to explain why he was teaching the way he was. Another time, he wanted to use the physical space of the classroom to make a point, so he began moving around and chalking arrows — vectors — on the walls. I remember thinking, a student wouldn’t get away with this!! As I got to know him better, I also came to admire Felix’s extraordinary love and evidently unconditional commitment to his children, as each appeared to be carving out a life so different from his: if I learned something from this and been half as good a parent, I should be very proud.

Although never officially a member of his research group, I began spending more time in their seminars. He invited me to attend a workshop at the International Centre for Theoretical Physics in Trieste. Much of the scientific content went way over my head, but it was wonderful to feel part of a scientific community. We had a running joke about encountering each other in rarefied places such as this, an expression of surprise at seeing the other and exclaiming YOU?! — so much as to say, or challenge, what on earth could possibly have brought you here? It was so easy to forget that this was a man who had played a significant part in the development of General Relativity! I briefly tried to work with him and Michael Crampin on what became their highly successful book, Applicable Differential Geometry, but there was no way I could keep up. Nevertheless, the experience brought us even closer and after I left King’s we continued to see each other regularly. I especially enjoyed a close friendship with him and Marta over the few years of their life together and shared his deep feeling of loss at her untimely death.

Felix’s retirement from King’s signalled also his retirement from mathematics. I was amazed, first at the determination with which he shed this former life, not least in his giving away his library of mathematical books, and second, at the enthusiasm and energy with which he picked up his new activities, especially mosaics. He took me to see his workshops, a succession of them, as he searched for the right environment in which to work, and he proudly showed me his public mosaics on the South Bank.

When I last saw Felix, I sensed a frailness that I had not seen, or perhaps not noticed, before. I wondered even then if this would be my last visit. His life has been long, eventful and highly productive. I am sad at his passing, but, much more than that, grateful for his friendship and wisdom over the years. May he long be remembered for what he was, a sharp intellect, a great teacher, a loving friend.