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Biographical Memoirs: Volume 70 EGON OROWAN August 2, 1901-August 3, 1989 BY F. R. N. NABARRO AND A. S. ARGON EGON OROWAN DIED in the Mount Auburn Hospital in Cambridge, Massachusetts, on 3 August 1989, a day after his 87th birthday. He is buried in the Mount Auburn Cemetery. Together with G.I. Taylor and Michael Polanyi, he was responsible for the introduction of the crystal dislocation into physics as the essential mediator of plastic deformation. Though he occasionally spoke at meetings concerned with science and technology policy, and wrote letters to the press on a number of topics, he was an essentially private person and left no biographical notes. In compiling the present Memoir, FRNN has been principally responsible for the period 1902-1951, which Orowan spent mainly in Europe, and ASA for the period 1951-1989, when Orowan was affiliated with the Massachusetts Institute of Technology. 1. ANCESTRY AND EARLY LIFE Egon Orowan (Orován Egon in Hungarian) was born in Obuda, a part of Budapest1 His father, Berthold Prepared as a Biographical Memoir for the Royal Society of London and the U.S. National Academy of Sciences. 1   References preceded by the letter R refer to numbered papers deposited in the archives of The Royal Society.

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Biographical Memoirs: Volume 70 Orowan, was a mechanical engineer (R2) and "managed some kind of factory in what is now Rumania" (R3). Berthold's parents were Jakob Orowan and Maria Neubauer, and Jakob was the son of Heinrich Orowan. The origin of the name Orowan is not clear. It sounds Slavonic to Hungarians and Hungarian to Slavs, and, according to family tradition, Heinrich was the first to use it. Egon told one of the writers that Orowan meant "a range of hills", but this meaning does not seem to be familiar to speakers of Hungarian or Czech. Egon Orowan's mother was Josze (Josephine) Spitzer Ságvári. Her father, Mor Spitzer Ságvári, was originally named Spitzer (R3) but "became bankrupt in an agricultural crisis, went to Budapest and magyarized. Egon Orowan says his name was Mor, but Lorent [his nephew, Lorant Toth of Hungary (R4)] says it was Moris." One of Orowan's cousins, Endre Ságvári, "was an excellent Communist," and a park in Budapest was named for him. To compensate, the Orowans were also related to either Goering or Goebbels (R3). Orowan's wife, Jolan Schonfeld, was a pianist, who studied under Bela Bartok in the Budapest Academy of Music about the year 1919 or 1920. Here she met Egon Orowan, and they became friends, but were not at that time deeply attached. She stayed in Germany until about 1938, then left her work and all her possessions, and fled to her sister in Paris. After a year she found work as a domestic servant in England. She and Egon Orowan met again, and married on 20 January 1941. According to the biographical note in his Berlin Dr. Ing. thesis (R2), Orowan studied at the Staatsobergymnasium in the IX district of Budapest, taking his Reifeprüfung in June 1920. In the academic years 1920/21 and 1921/22 he studied physics, chemistry, mathematics and astronomy in the University of Vienna. He did practical work in the winter

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Biographical Memoirs: Volume 70 semester of 1922, and began his studies at the Technical University of Berlin in the summer semester of 1928. After initially studying mechanical engineering, then electrical engineering, he transferred to physics under the influence of Professor R. Becker. At the end of 1928 he became Becker's assistant, and underwent his Diplom-Hauptprüfung at the end of the winter semester 1928/29. He began his doctoral research in autumn 1931, and at the time he presented his thesis (1932) he was assistant to Professors M. Volmer and W. Westphal. One of his papers is dated 8 July 1933 and addressed from Berlin-Charlottenburg; another, received 30 August 1933, describes him as ''zur Zeit in Budapest". As Orowan explained in his talk at the Sorby Centennial Meeting (R4A): "For a time I could not find employment, and I lived with my mother, rethinking the results of my experiments of the last three years." (Orowan's father died in January 1933). A letter (R5) from Professor László Bartha, Director of the Research Institute for Technical Physics of the Hungarian Academy of Sciences, says that Orowan worked with the Tungsram Research Laboratory between 1936-1939, under the supervision of Dr. Imre Br6dy. According to this letter and to (R6), Br6dy invented the krypton-filled light bulb. With the help of Mihály (Michael) Polanyi, he developed a new process for extracting krypton from air. Bartha's letter says that "Orowan was the person, who helped him to verify the large-scale separation of krypton from air by fractioned distillation of liquid air. He played an important role at the installation of a pilot plant for krypton manufacturing in a small town—Ajka—about 80 miles from Budapest. I could not find any papers or notes of him from that period." By 1937, Orowan had moved to Birmingham (R2). The reasons for his move are not clear. According to his daughter (R3) "my understanding (which may not correspond to

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Biographical Memoirs: Volume 70 reality; sometimes things were hidden from me as a child and never rose to the surface) is that after a couple of years managing that tungsten process in the factory, he was offered a job in Birmingham sometime around 1937 and he went there, well before Hitler really started to misbehave." [Hitler had remilitarized the Rheinland in March 1936, occupied Austria in 1938, and Czechoslovakia in 1939]. EXPERIMENTAL WORK IN BERLIN Orowan's doctoral thesis was not on the topic of crystal plasticity on which he started to work under Richard Becker, although his first published paper (1)2 and his most outstanding contribution to physics (9) were on this topic. His thesis was on the cleavage of mica. His own account (R4A) is that: "The change of the subject was my fault, not Becker's. I received the problem when I was running across the main court of the Technische Hochschule one day; a fellow student ran along the other diagonal, we came within earshot near the center, and he shouted to me: 'What is the tensile strength of mica?' I shouted back 'I will tell you tomorrow.' This was the start of the doctoral thesis; I informed Becker about it when it was finished . . . in fact I could have done little if I had studied at an efficiently organized university which took care of all the students' time." In (R4A) Orowan claims that this work "represented the first confirmation of the Griffith theory in the case of a crystalline material." The measured ("technical") tensile strength of a crystal is usually orders of magnitude less than the theoretical tensile strength. Griffith showed that this could be explained by the concentration of the applied 2   References without the prefix R are to publications of Egon Orowan, numbered according to the bibliography at the end of this Memoir.

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Biographical Memoirs: Volume 70 stress which occurs at the tip of a pre-existing crack. The question arose whether these cracks (or other centres of weakness) were accidental surface defects or were defects necessarily and systematically present in the real crystal, the so-called "Lockerstellen". The technical strength does not seem to vary greatly from one sample to another, and this fact seems to point to the existence of a systematic array of defects. The precise lamellar cleavage of mica occurs not so much because the binding energy between sheets is small as because the sheets remain elastic even under large stresses in their plane, as is shown by their flexibility. Orowan had the simple idea of stretching a sheet of mica in its plane, using grips much narrower than the sheet, so that the edges of the sheet were free from stress and cracks in the edges would not lead to fracture. The simple idea was less simple in execution; he had to design complicated self-centering grips which ensured that both edges of the strip were simultaneously free from tensile stress. Nevertheless, the sheets were cleaved from blocks whose edges were cut very gently with a diamond saw. These sheets with unstretched edges had tensile strengths up to ten times those usually measured, showing conclusively that the usual tensile strength is controlled by defects in the edges of the sheets. Sheets with stretched edges had strengths which were of the usual order, but differed systematically between those cleaved from blocks cut with a diamond saw and those cut with shears, again demonstrating that the observed strength is determined by surface defects on the edges of the sheets. Orowan gave a detailed discussion of the fracture process in this exceedingly anisotropic material. The explanation is complicated, depending on the ability of a freshly-cleaved pair of surfaces to come together and heal perfectly. There is a footnote, which is interesting in connection with his later

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Biographical Memoirs: Volume 70 preoccupation with seismology and tectonics, in which he points out that the differing plastic properties of mica and of quartz play an important role in geology. The most important conclusion is that dangerous defects are extremely rare in mica; a sheet may be reduced to half of its original thickness over a region several millimeters long by the peeling-off of imperfect layers, and yet break in another region where the stress is only half as great. This could not happen if the thinned region contained many dangerous defects. In a paper submitted soon afterwards (5), Orowan struggled with a number of problems of brittle fracture, the effect of sample size, the effect of grain size and the Joffé-effect that a crystal of rock salt is stronger when it is being dissolved in a liquid. The principal new results are that the grain size is the effective upper limit of the size of a crack, so that, in rough agreement with experiments, the fracture stress is inversely proportional to the square root of the grain size, and that plastic flow increases the fracture stress when glide planes and fracture planes intersect, but decreases the fracture stress when these planes coincide, as for basal glide and fracture in zinc. A passing observation (6) was that a sheet of mica usually makes a sound like cardboard when it is struck; a similar sheet cut carefully with a diamond saw rings like steel. The damping in the former case arises entirely from the friction between cleaved layers at the cut edges. ON CRYSTAL PLASTICITY Orowan has given a full personal account (R4A) of the way in which he became involved in crystal plasticity: "My own introduction to dislocations happened on a hot Saturday afternoon in 1928. Until less than a year before that, I studied electrical engineering; I was more interested in phys-

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Biographical Memoirs: Volume 70 ics, but my father, a mechanical engineer, knew that one could not make a living from Physics (this was before the Age of Government Contracts). So we compromised on electrical engineering which provided, at Berlin-Charlottenburg, a thrilling course of lectures on electromagnetic theory by Ernst Orlich, and also the nerve-racking tasks of computing, designing, and drawing a transformer, a motor or generator, and (this was my choice) a reversing rolling mill. Once a week, to soothe nerves and collect energy for another six days, I spent a day in the advanced laboratory course in physics offered by Ferdinand Kurlbaum whom I saw once, across the courtyard during the semesters I worked in his laboratory. At the beginning and the end of the semester I had to acquire his signature for my roll card; this was given by the laboratory assistant who had the necessary rubber stamp. However, Kurlbaum died in 1927 and his temporary successor, the recently appointed professor of theoretical physics, Richard Becker, did not possess a signature stamp. I had to appear in his presence; he signed the card, asked why I, an electrical engineer, worked in the physical laboratory, and I explained. In the course of the following minute my life was changed by the circumstance that the professor's office was a tremendously large room (it was the room in which Gustav Hertz, Kurlbaum's eventual successor, developed the cyclic gas diffusion apparatus with which he separated the isotopes of neon and which was to play a prominent role in the manufacture of the bomb of Hiroshima). Becker was a shy and hesitating man; but by the time I approached the door of the huge room he struggled through with his decision making, called me back, and asked whether I would be interested in checking experimentally a "little theory of plasticity" he worked out three years before. Plasticity was a prosaic and even humiliating proposition in the age of De

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Biographical Memoirs: Volume 70 Broglie, Heisenberg, and Schrödinger, but it was better than computing my sixtieth transformer, and I accepted with pleasure. I informed my father that I had changed back to physics; he received the news with stoic resignation. . . . . .The assignment was to make single crystals of zinc, tin, etc., and to find out whether they had a trace of plasticity left at the temperature of liquid air: Becker's theory demanded complete brittleness at very low temperatures. Whatever Becker's theory might imply, Polanyi, Meissner and Schmid showed in 1930, before Orowan's equipment and crystals were ready, "that these metals were almost as ductile in liquid air as at room temperature." This was odd, "because the papers of Polanyi and Schmid contained the stereotyped remark that their metal crystals were drawn from the melt and then broken into pieces of suitable lengths in liquid air. When I asked Polanyi about this, he replied "Metal crystals broke in liquid air in those days: today they don't." Though Orowan was not able to complete his experiments before the work of Meissner, Polanyi and Schmid became known, they formed the basis of his Diplomarbeit in February 1929 and of his first publication. One Saturday afternoon he had only one zinc crystal available. He dropped it on the floor, found it bent, straightened it, left it to anneal for some time, and tried a practice run. To his surprise, it extended with sharp jerks instead of flowing smoothly. From this observation, often repeated, he drew a surprising amount of information and was "led, almost unavoidably, to the concept of dislocation." It must also have led to his interest in the problem of the strain aging of steel. His paper with Becker (1) poses two questions, which are fundamental: How does local gliding begin and what determines the number of glide processes which initiate every second?

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Biographical Memoirs: Volume 70 How does the local gliding grow into an elementary act of gliding, and what determines the development (rate of gliding and extent of the individual act) of the elementary glide act? One clear observation was that, in a stress relaxation experiment, the average size of the glide steps remained constant, while their frequency fell as the stress became less. It is interesting to notice that this purely experimental paper on an unfashionable branch of physics was addressed from the Institute for Theoretical Physics of the Technische Hochschule, Berlin - Charlottenburg. The real development of this work came only when Orowan returned to Budapest and stayed at home, unemployed and thinking. It led to the papers Zur Kristallplastizität I-V (7, 8, 9, 13, 14), and to several other papers (15, 16, 17, 19) in which the work is extended or applied to the observations of other workers. Paper I begins by considering Becker's formula that the rate of deformation u of a crystal gliding under a stress s is given by Here C is an undetermined constant related to question (2) above, S is a stress which should be of the order of the theoretical yield stress of the crystal, and therefore perhaps 1/30 of the shear modulus G. By analyzing this formula, Orowan arrived at the important conclusion that the phenomena of crystal plasticity cannot be explained by ther-

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Biographical Memoirs: Volume 70 mal fluctuations alone or by the presence of stress concentrations alone; both factors play an important role. Becker had shown that the ratio p = S/s could be determined by analyzing experimental results. The value of p turned out to be about 2.5. Yet it was well known that for pure single crystals the ratio of the theoretical shear strength S to the observed flow stress s was of order 102-104. The only solution seemed to be that glide was initiated in small regions where the local stress s was not the applied stress s, but was enhanced by a stress concentration factor q to the value s = qs. Orowan also pointed out that, although Becker's formula (1) led to a rate of deformation which would become unobservably slow if the applied stress was held constant, in practice one adjusts the applied stress to obtain a convenient rate of flow. The consequences of this are developed further in (17). Becker's formula, with or without Orowan's stress concentration factor q, then shows that the flow stress s at temperature T is related to flow stress s0 at zero temperature by the simple formula This formula fitted the observations for zinc and cadmium rather well. Later arguments have modified the formula, but the basic ideas underlying it remain valid. Paper II, which is concerned with the theory of creep, is densely argued. It sets out to show that the "static" theory of creep, in which steady-state creep results from a balance between the rate of work hardening and the rate of recovery by softening, must be replaced by a "dynamical" theory based on modifications of Becker's formula. Orowan began by showing that the static theory leads to what has become known as the Baiey-Orowan equation. If the flow stress is s,

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Biographical Memoirs: Volume 70 from statements made by scientists in these companies it is clear that he was a very effective industrial consultant. Throughout his life Orowan maintained a keen interest in all modern social and technological developments and often commented on major happenings through letters to editors. These include comments on the real causes of the disastrous Scott expedition to Antarctica; effect of possible valve malfunction due to a design inadequacy in the Three Mile Island nuclear power station accident in 1979; and a particularly detailed back and forth correspondence with the presidential commission investigating the ill-fated Challenger Shuttle disaster of 1986, on the possible ''real" cause of it which Orowan thought was due to a short-transverse brittleness in the main rocket casing, bringing in eventually into the debate a sizable group of NASA scientists and Senator Patrick Moynihan, the Senate overseer of the commission. During his years in the U.S.A. Orowan continued to receive honors and awards that were, however, more in recognition of his earlier work in Europe and less for his activities in the U.S.A. These included membership in the American Academy of Arts and Sciences (1951), the U.S. National Academy of Science (1969), corresponding membership in the Göttingen Academy of Sciences (1972), an honorary doctor of engineering degree from the Technical University of Berlin (his former alma mater) (1965), the Eugene Bingham medal of the American Society of Rheology (1959), the Gauss medal of the Braunschweiger Wissenschaftliche Gesellschaft (1968), the Paul Bergse Medal of the Danish Metallurgical Society (1973), the Acta Metallurgica gold medal (1985), and the Vincent Bendix gold medal of the American Society of Engineering Education (1971). In his professional activities (and his intellectual hobbies) Orowan went for the unusual and hidden explana-

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Biographical Memoirs: Volume 70 tions of things, often drawing support from forgotten historical facts, and clever anecdotal quotations or overlooked aspects of phenomena, partly for their shock value and partly to impress. His early education in engineering and his eventual practice as an applied physicist (or chemist, or metallurgist) was both a source of strength in his professional life and a cause of a split personality. He lectured to engineers on the merits of the scientist's approach and to the scientists that of the engineer. While he criticized some scientists of whom he did not approve as ". . . Oh well! he was only an engineer . . .", he took great pride in associating himself with prominent chief engineers. FAMILY LIFE AND PERSONAL CHARACTERISTICS His daughter Susan has written "My mother was probably his best friend, although I don't think they realized it until the last couple of years. He looked after her full-time at home from 1984 until she went to a nursing home in 1986. . . . When she died, in October 1986, I think he started to believe that he didn't want to live any more". He had many other friends. Susan remembers Peierls, Shoenberg, Dirac, Perutz, Bragg and Besicovich from England, and especially Laszlo Tisza and Leo Gross in America. Susan, after majoring in languages at Tufts, had a distinguished career in librarianship, and is presently University Librarian at Georgetown University. Her husband, Dr. David Martin, is Dean of the School of Education at Gallaudet University, D.C. Susan's memories of Egon's private life are very clear. . . . "He liked plants, flowers, trees. He and Laci (Tisza) used to go to Jamaica Plain to the botanical gardens as one of their favourite outings". David Tabor has noted similarly (R17): "One aspect of life in the U S A that he prized above many others was the size, scale and openness of the American

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Biographical Memoirs: Volume 70 National Parks". Susan continues: "Modern culture, though, and particularly 'American' things: popular music, foods, recent clothing fashions, and computers were among the things he looked down on". Many of the comments at the MIT Memorial Service are revealing. Ali Argon learned from Orowan: "Problems had to be solved completely. . . . Your first reaction should be extreme skepticism, including of course on your own work". This skepticism could sometimes be expressed almost too forcibly. Tabor recalls: "His powerful intellect was most evident at the seminars or lectures that he attended. If a particular point caught his interest he would continuously interrupt... Experienced lecturers could take these interruptions with good humour and sometimes with enjoyment, but junior speakers would often feel frustrated. . . . Orowan, who in private life, as David Shoenberg recounts, was a warm and friendly person, appeared only to understand the intellectual aspect of his interjections, and to be quite oblivious of their effect on the lecturer and the audience". In fact in private life he could be almost excessively gentle. Peierls recalls (R15): "He had strong views about most matters and about people, which he would express clearly, but always with a veneer of politeness. We [Peierls and his wife] used to tease him about this, and once introduced him to a woman who was not only unattractive to look at, but also with a very unpleasant manner, and rather boring conversation. We wondered how he would express his comments about her. When asked, he said 'She is very cerebral (durchgeistig)'." There was another "very dark spot" in Orowan's "plasticitycareer'', which throws an interesting light both on his thinking and on that of the Royal Society. He submitted a paper "Mechanics of continental drift" (and probably a companion paper) to the Royal Society. It did not meet with approval from the referees, but the Royal Society does not

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Biographical Memoirs: Volume 70 lightly reject the work of a senior and distinguished Fellow, and it went to further referees. Sir Charles Frank wrote (R18) "I was involved as third or fourth referee". Orowan's approach from first principles could lead him to neglect the work of others, and Frank found "extensive recitation of ideas . . . without due reference to past work . . . and a degree of ignorance of the 'plate-tectonics' revolution . . . I tried (unsuccessfully) to get him to salvage from it a shorter paper". Orowan ceased to pay his subscription to the Royal Society, which leads automatically to expulsion. Mr. Neville le Grand, who was Finance Officer of the Royal Society at the time, has explained (R19). "On the first occasion of Orowan's lapse, I wrote the usual reminder letters but we then realized the possible reason for this. So far as I can recall I spoke with [Sir] David [Martin] (and I believe Flect or Menter whoever was the Treasurer at the time) and we decided on a somewhat phony ground to make the transfer from one of the R.S.'s own funds to cover subsequent payments". There are many stories illustrating Egon Orowan's approach to life. Sir Alan Cottrell recalls (R20) one he told of his student days in Berlin:— Sometime, in the 1930's, the German education authorities changed the rules for matriculation, which required all candidates thereafter to pass an examination in the physical sciences. This set a problem for a nearby convent, where the nuns made a modest income by teaching. None of them knew any science, of course. And so, one of them was sent to Orowan to 'learn physics'. This caused difficulties both for Orowan and the unfortunate one so chosen, due to the vast chasm between the religious and scientific outlooks. After one long session, Orowan finally felt that he was breaking through, on the subject of atmospheric pressure. And so he pointed to a barometer on the wall and said 'tell me, why does the mercury, in that, stay up?' She thought for a moment and said, in a perfect demonstration of the dogmatic approach, 'Oh, because it is a barometer'.

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Biographical Memoirs: Volume 70 His daughter Susan has many memories (R3):—"He was a highly skilled amateur photographer. . . . He particularly liked clouds, and had a terrible fondness for obese people, which always embarrassed me". At the MIT ceremony she reminded the audience of some of Orowan's characteristic phrases: "It's very simple", and "I understood it a month ago, but now. . ." She also quoted one of his more intimate remarks: ''Let me close by telling you that in my early teens I was at one stage terrified by the thought of dying. I confided this in Daddy who immediately resolved the problem, the business about the essence of the simplicity. He said, 'Do you remember what it was like before you were born?', and I said, 'No' And he said, 'Well, that's what it'll be like after you die'." In the preparation of this memoir we have been helped by many people and organizations, particularly Professor Orowan's daughter, Dr. Susan Martin, The American Institute of Physics Niels Bohr Library, Professor Lázló Bartha, Sir Alan Cottrell FRS, Mr. J. Deakin, Dr. M. Doyle, Sir Charles Frank FRS, Mr. M. le Grand, Dr. P. Hoch, Dr. S. Keith, the MIT Archives, Sir Neville Mott FRS, Sir James Menter FRS, Professor J. F. Nye FRS, Sir Rudolf Peierls FRS, Professor D. Shoenberg FRS, Professor D. Tabor FRS and Dr. D. Tichy.

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Biographical Memoirs: Volume 70 BIBLIOGRAPHY (1) 1932 (With R. BECKER) Über sprungshafte Dehnung von Zinkkristallen. Zeits. f. Physik 79, 566-572. (2) Bemerkung zu den Arbeiten von F Zwicky über die Struktur der Realkristalle. Zeits. f. Physik 79, 573-582. (3) 1933 Die Zugfestigkeit von Glimmer und das Problem der technischen Festigkeit. Zeits. f Physik 82, 235-266: errata 83, 554. (4) 1934 Zur Struktur der Realkristalle. Helv. Phys. Acta 7, 285-293. (5) 1933 Die erhöhte Festigkeit dünner Fäden, der Joffé-Effekt und verwandte Erscheinungen von Standpunkt der Griffithschen Bruchthorie. Zeits. f. Physik 86, 195-213. (6) 1934 Die Dampfungsfähigkeit von Glimmer als empfindlische Eigenschaft. Zeits. f. Physik 87, 749-752. (7) 1934 Zur Kristallplastizität I: Tieftemperatur-plastizität und Beckersche Formel. Zeits. f. Physik 89, 605-613. (8) Zur Kristallplastizität II: Die dynamische Auffassung der Kristallplasticität. ibid, 614-633. (9) Zur Kristallplastizität III: Über die Mechanismus des Gleitvorganges. ibid, 634-659. (10) Bemerkungen zu einer polemischen Arbeit von F Zwicky, ibid, 774-778. (11) 1934 Mechanische Festigkeitseigenschaften und die Realstruktur der Kristalle. Zeits. f. Krist. 89, 327-343. (12) 1934 Rupture of Plastic Crystals, in Intl. Conf. Physics, London, II, 81-92. (13) 1935 Zur Kristallplastizität IV: Weitere Begrüdung des dynamischen Plastizitätsgesetzes. Zeits. f Physik 97, 573-595. (14) 1935 Zur Kristallplastizität V: Verfollsst ändigung der Gleitgeschwindigkeitsformel. Zeits. f. Physik 98, 382-387. (15) 1935 Kristallplastizität. Schweizer Archiv 7, 1-9. (16) 1936 Discussion to the Article: G. I. Taylor, A Theory of the Plasticity of Crystals. Zeits. f. Krist. (A) 93, 188-191. (17) 1936 Zur Temperaturabhängigkeit der Kristallplastizität. Zeits. f. Physik 102, 112-118.

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Biographical Memoirs: Volume 70 (18) 1936 Discussion to the Article: M.J. Buerger, On the Non-existence of a Regular Secondary Structure in Crystals. Zeits. f. Krist. 93, 169. (19) 1938 The rate of plastic flow as a function of temperature. Proc. Roy. Soc. Lond. A168, 307-310. (20) 1939 Theory of the fatigue of metals. Proc. Roy. Soc. Lond. A171, 79-106. (21) 1940 Problems of plastic gliding. Proc. Phys. Soc. 52, 8-22. (22) 1941 Strength and failure of materials. In Design of Piping Systems, New York, John Wiley, (Chapter One). (23) 1941 Origin and Spacing of Slip Bands. Nature 147, 452-454. (24) 1941 (with K.J. PASCOE), An X-ray Criterion for Distinguishing Lattice Curvature and Fragmentation, Nature, 148, 467-470. (25) 1942 A New Method in X-ray Crystallography. Nature, 149, 355-356. (26) A type of plastic deformation new in metals, ibid, 643-647. (27) 1945 The Calculation of Roll Pressure in Hot and Cold Flat Rolling. J. Inst. Mech. Eng. Feb. 1944; Proc. Ins. Mech. Eng. 150, 140-167 (1943); (Discussion: Journal Dec. 1945, Proc. 152, 314-324). (28) 1944 The fatigue of glass under stress. Nature 154, 341-343. (29) (With J.F. NYE & W.J. CAIRNS) Notch brittleness and ductile fracture in metals. Theoretical Research Report No. 16/45, Ministry of Supply, Armament Research Dept., England. (30) 1945 Fracture and Notch Brittleness in Ductile Materials, in Brittle Fracture in Mild Steel Plates, British Iron and Steel Research Association Part 5, 69-78. (31) 1945/46 Notch Brittleness and the Strength of Metals. Trans. Inst. Eng. Shipbuilders Scotland Paper No. 1063, 89, 165-215. (32) 1946 (with K.J. PASCOE) A Simple Method of Calculation Roll Pressure and Power Consumption in Hot Flat Rolling. In First Report of the Rolling-Mill Research Sub-Committee of the Iron and Steel Industrial Research Council, London, The Iron and Steel Institute, Special Report No. 34, Section V, 124-146.

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Biographical Memoirs: Volume 70 (33) 1945 (With J.F. NYE & W.J. A.R.D. CAIRNS), Theoretical Research Report. (34) 1946/47 The Creep of Metals, West of Scotland Iron and Steel Inst. 54, 45-96. (35) 1947 Classification and nomenclature of internal stresses. In Symp. Internal Stresses in Metals and Alloys, London, The Institute of Metals, 47-59. (36) 1948 Discussion on Internal Stresses. In Symp. Internal Stresses in Metals and Alloys, London, The Institute of Metals, 451-453. (37) 1948 Measurements of roll pressure distribution over the area of contact. British Iron and Steel Research Association, 1-7. (38) 1948 M.S. Paterson and E. Orowan, X-Ray Line Broadening in Cold-worked Metals, Nature 162, 991-992. (39) 1948/49 Fracture and Strength of Solids, Rep. Progr. Phys. 12, 185-232. (40) 1949 Joint Meeting of the British Glaciological Society, the British Rheologists' Club and the Institute of Metals, J. Glaciology 1, 231-240. (41) Improvements in or relating to stress indicators. British Patent. (42) 1949 Mechanical Testing of Solids. In Principles of Rheological Measurement, Edinburgh, Nelson, Part X, 156-180. (43) 1949 (with W. SYLWESTROWICZ, Experiments on the yield phenomenon in low carbon steels. The British Iron and Steel Research Association Report No. MW/B/48, 8. (44) 1949 The Size Effect in Notch Brittleness. The British Iron and Steel Research Association Report No. MN/B/31/ 49. 7. (45) 1950 Can Plastometer. The British Iron and Steel Research Association. (46) 1950 Photoelastic dynamometer. J. Sci. Instr. 27, 118-122. (47) 1952 Stress concentrations in steel under cyclic load. Welding J. Res. Suppl., 1-11. (48) 1955 (With D.K. FELBECK) Experiments on Brittle Fracture of Steel Plates. The Welding J. Res. Suppl., 34, 1-6.

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Biographical Memoirs: Volume 70 (49) 1955 Energy Criteria of Fracture. The Welding J. Res. Suppl., 34, 157-160. (50) 1955 Condition of High Velocity Ductile Fracture. J. Appl. Phys., 26, 900-902. (51) 1960 (With A.S. ARGON, & Y. HORI.) Indentation Strength of Glass. J. Amer. Cer. Soc., 43, 86-96 (52) 972 (With M.J. DOYLE, A. MARANCI, & S.T. STORK). The Fracture of Glassy Polymers, Proc. Roy. Soc., A329, 137-151. (53) 1970 The Physical Basis of Adhesion. J. Franklin Inst. 290, 493-512. (54) 1970 Surface Energy and Surface Tension in Solids and Liquids. Proc. Roy. Soc., A316, 473-491. (55) 1952 Creep in Metallic and Non-metallic Materials. Proc. First. U.S. Natl. Cong. Appl. Mech., (ASME: New York), 453-472. (56) 1954 Dislocations and Mechanical Properties. Dislocations in Metals, (ed. by M. Cohen)(AIME: New York), 359-377. (57) 1964 Continental Drift and the Origin of Mountains. Science, 146, 1003-1010. (58) 1965 Convection in a Non-Newtonian Mantle, Continental Drift, and Mountain Building. Phil. Trans. Roy. Soc., 258, 284-313. (59) 1966 Age of the Ocean Floor. Science, 154, 413-416. (60) 1966 Dilatancy and the Seismic Focal Mechanism. Reviews of Geophysics, 4, 395-404. (61) 1967 Incompatibility of Some Tectonic Theories with Fennoscandian Viscosity. Phys. Earth Planet. Interiors, 1, 1-7. (62) 1967 Island Arcs and Convection. Geophys. J. R. Astr. Soc., 14, 385-393. (63) 1967 Seismic Damping and Creep in the Mantle. Geophys. J. R. Astr. Soc., 14, 191-218. (64) 1969 The Origin of the Oceanic Ridges. Scientific American, 221, 102-119. (65) 1974 Origin of the Surface Features of the Moon. Proc. Roy. Soc., A336, 141-163.

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Biographical Memoirs: Volume 70 (66) 1959 Our Universities and Scientific Creativity. Bulletin of the Atomic Scientists, 15, 236-239. (67) 1963 Enterostomy Appliance, U.S. Patent Number 3, 100, 488. (68) 1967 Prostheses for Ileostomies. New England J. Medicine, 276, 571-574.

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