In 1979 I was given the best academic advice I ever received, which was to write to Jerry Ericksen, include a paper of mine, and ask if he would be amenable to the idea that I should visit him for a few months. I followed the advice, affably given by Matt McCarthy (Galway), and the following year I arrived in the Department of Mechanics, Johns Hopkins, to be greeted by Jerry in his office, smoking a pipe beneath a poster of Newton measuring the world. (This poster depicts a famously ambiguous work of William Blake which encourages the scientist to see his work in a wider perspective, it seems.) At any rate, I was soon to realise that Jerry’s scientific perspective encompassed many and various disciplines, and that this breadth of knowledge allowed him to work on far-sighted, influential projects, to great effect. The members of that department and its previous incarnation (the Natural Philosophy group of the Department of Mechanics and Materials Science), with Clifford Truesdell as chair of rational mechanics, had long provided a driving force in the resurgence of continuum mechanics, of course, and many mechanicians of today and the past few decades owe much to time that they spent there.
Working during that visit on a project to do with crystal mechanics, I asked Jerry for suggestions as to what to read: ‘read the masters’ was the non-specific answer, ‘decide for yourself’ my interpretation of his reply. Jerry liked to hear different opinions, to appreciate different mathematical methods and consider their possible application to mechanics, and to understand why people thought in the way that they did. So there was an open atmosphere in discussions, and no academic prejudice, which inspired.
Jerry would always be scrupulously careful to differentiate between what others wrote, his own interpretation of what they wrote, and his own ideas and opinions, and this care is particularly apparent in some papers of his which appear to be written in an almost conversational manner. It seems to me that this allows those papers to ‘cut through’ to different areas. The ideas are distilled in these papers, in them he kept the ‘book-keeping’ to a minimum and by so doing wielded Occam’s razor (as he was fond of saying), the effect being to get the central ideas across and to encourage others to use them.
Jerry moved to the Department of Aerospace Engineering and Mechanics, University of Minnesota, a few years after my first visit to see him, and I spent a few months there as well in the mid 1980s, during an IMA programme. One of Jerry’s papers on the ‘Equilibrium of bars’ led to a paper by John Maddocks (EPFL) and myself, and I presented a version of that joint paper as part of the programme. I met with Jerry afterwards - he was highly amused that the talk had provoked a lot of discussion, and recall particularly his remark that it had ‘set the cat amongst the pigeons’, which was perhaps an early indication that his cunning plan, to write the original paper in an informal style, was having the desired cut through effect.
After these two visits I met Jerry only occasionally, at conferences, but we did write letters to each other. I was grateful for support that he sometimes provided - at a meeting in SISSA, Trieste, I spoke about work relating to crystal symmetry in elasticity. At that talk, Ronald Rivlin repeatedly questioned why some details I provided were necessary, and suggested an apparently simpler option. My responses were not enough to satisfy his questions or refute his suggestion, so I was delighted when Jerry entered the discussion and announced (when the option was raised once more) that ‘it just doesn’t work that way’. This understated announcement was enough validation for Professor Rivlin, who sat down quietly, presumably content. I was relieved, and thankful for the intervention.
Much of my work in the last couple of decades has concerned the theory of defects in mechanics. The origins of the work lie in another ‘cut through’ paper of Jerry’s - ‘Thermoelastic considerations for continuously dislocated crystals’. Many things are apparent in this exploratory, but nevertheless deeply considered, paper: first, the need to secure the thermodynamical foundations of general continuum mechanics is of paramount importance, second, he considered J. Willard Gibbs a master of the art of thermodynamics - a fact which provided a delayed, explicit (if sadly incomplete), response to my request for reading recommendations, third, the careful conversational style is completely honest, and last, the paper is full of ideas, unresolved problems and unexplored avenues, generously laid out, available to all. Cesare Davini (Udine) and myself exploited some of the ideas introduced in the paper, and that work has evolved over the years by realizing connections with the theory of Lie groups and moving frames. (I continue to marvel at these connections.) Professor Truesdell’s preface to a volume dedicated to Jerry Ericksen, on the occasion of his sixtieth birthday, includes a perfect appreciation of his papers, in my estimation: ‘Some are decisive, some are prophetic and all are forthright’. This particular paper on defects is prophetic and forthright, no doubt - so many open problems are introduced and discussed that it is not decisive, but that feature is a gift to those who study the work, and come to recognize its prescience.
After my visit to Johns Hopkins I decided for myself that Jerry Ericksen was a master of the art of continuum mechanics. I am very grateful to him and I shall never forget him.
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Parry, G. Recollections of Jerry Ericksen. J Elast (2022). https://doi.org/10.1007/s10659-022-09930-3