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Biographical Memoirs: Volume 56 (1987)

Chapter: John Hasbrouck Van Vleck

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Suggested Citation:"John Hasbrouck Van Vleck." National Academy of Sciences. 1987. Biographical Memoirs: Volume 56. Washington, DC: The National Academies Press. doi: 10.17226/897.
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Suggested Citation:"John Hasbrouck Van Vleck." National Academy of Sciences. 1987. Biographical Memoirs: Volume 56. Washington, DC: The National Academies Press. doi: 10.17226/897.
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Suggested Citation:"John Hasbrouck Van Vleck." National Academy of Sciences. 1987. Biographical Memoirs: Volume 56. Washington, DC: The National Academies Press. doi: 10.17226/897.
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Suggested Citation:"John Hasbrouck Van Vleck." National Academy of Sciences. 1987. Biographical Memoirs: Volume 56. Washington, DC: The National Academies Press. doi: 10.17226/897.
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Suggested Citation:"John Hasbrouck Van Vleck." National Academy of Sciences. 1987. Biographical Memoirs: Volume 56. Washington, DC: The National Academies Press. doi: 10.17226/897.
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Suggested Citation:"John Hasbrouck Van Vleck." National Academy of Sciences. 1987. Biographical Memoirs: Volume 56. Washington, DC: The National Academies Press. doi: 10.17226/897.
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Suggested Citation:"John Hasbrouck Van Vleck." National Academy of Sciences. 1987. Biographical Memoirs: Volume 56. Washington, DC: The National Academies Press. doi: 10.17226/897.
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Suggested Citation:"John Hasbrouck Van Vleck." National Academy of Sciences. 1987. Biographical Memoirs: Volume 56. Washington, DC: The National Academies Press. doi: 10.17226/897.
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Suggested Citation:"John Hasbrouck Van Vleck." National Academy of Sciences. 1987. Biographical Memoirs: Volume 56. Washington, DC: The National Academies Press. doi: 10.17226/897.
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JOHN HASBROUCK VAN VLECK March :13, 1899-October 27, 1980 BY P. W. ANDERSON JOHN HASBROUCK VAN VLECK was the most eminent American theoretical physicist between }. Willard Gibbs and the postwar generation. He has often been characterized as the "father of modern magnetism," but his influence was in fact much wider: He played a vital role in establishing the modern fields of solid-state physics, chemical physics, and quantum electronics. Many generations of students were in- fluence(1 by his unique teaching style, and he made important administrative contributions at a crucial time in the history of Harvard University. FAMILY AND EARLY YEARS The Van VIeck family is of the patrician Dutch stock that has given the nation three presidents, among other eminent citizens. "Van" (as he was always known) was prouc! of his ancestry, which had been tracer! by an aunts to prosperous burghers of Maestricht in the sixteenth century. One of the family, Tielman Van VIeck, was an eminent citizen of the Dutch colony of Nieuw Amsterdam and founded Jersey City. Van's immediate family was very distinguished academi ' More details will be found in The Royal Society memoir by B. Bleaney. 501

502 BIOGRAPHICAL MEMOIRS cally. His grandfather, John Monroe Van VIeck, was profes- sor of mathematics and astronomy at Wesleyan University in Micictletown, Connecticut, from IS53 to 1904, serving as act- ing president on two occasions. John Monroe's brother, Jo- seph Van VIeck, a successful New Jersey businessman, do- nated an observatory to Wesleyan in his honor. At the dedication ceremony in ~ 9 ~ 6, his son, E. B. Van VIeck, spoke anc! the young I. H. Van VIeck unveilecI the memorial plaque. All of John M. Van VIeck's four children were mathema- ticians, including Van's father Edward Burr Van VIeck (~863-19431. E. B. Van VIeck took a doctorate at Gottingen in IS93, taught for two years at Wisconsin, and then went to Wesleyan ~895-!905~. He marriec! Hester Raymond of MidcIletown in IS93, ant! here John Hasbrouck Van VIeck, his only chilcI, was born on March 13, TS99. From 1905 to 1929 Edward Burr Van VIeck was professor of mathematics at the University of Wisconsin in Madison, Wisconsin, where the mathematics building is named Van VIeck Hall in his honor. He was eminent in his field anct highly respected at Wisconsin. He was a member of NAS, president of the Amer- ican Mathematical Society, and recipient of four honorary degrees. His lectures were notecT for their formal clarity. The E. B. Van VIeck home was a cultivated anc! a pros- perous one, since he inherited a portion of his uncle's for- tune. He built up a notable art collection, especially of Japa- nese woodblock prints but also of other objects of beauty. It is said that a number of the prints were acquired from Frank Lloyd Wright. They were collected (luring the building of the Imperial Hotel and sold to repay debts. Edward Burr and his wife Hester react voraciously and traveler! widely, so that "the galleries, churches, and mountains of Europe were equally familiar." In this atmosphere Van absorbed his inter- est in travel and his deep cultivation very naturally. Except for a few periods spent cluring his father's sabbat

JOHN HASBROUCK VAN VLECK 503 icals in schools or kindergartens abroad, Van was eclucatect in the Madison public schools and went directly on to the University of Wisconsin. He did not recall any particular par- tiality toward science or mathematics as a boy, nor did his father make a special effort to interest him in advanced topics of mathematics, except for advising him to be sure to take mathematics through calculus in college. Reading his own remarks about this period of his life, one has the impression of a very normal boy with a rather matter-of-fact precocity. His interest in American football began early at Wisconsin, and he claimed that the Wisconsin song"On Wisconsin" was first sung at his first game in 1909 (information on this is containec! in an article of his on the history of football songs). He played in the Wisconsin marching band from 1916 until 1918 ~ his instrument is not recorclecI, but it was probably the flute, which he playocT later as a young assistant professor. His well-known interest in railroads began early: It was when he was about seven that he first spent a period of recupera- tion on one of his parents' European trips learning the rel- evant railroad schedules, and thereafter the family never again hart to consult a timetable. In college, an early interest in French was turner! off by his self-confessed "miserable" accent, anc! in geology by the obtuseness of a professor who "required all triangles to be solved graphically." In fact, until late in his college career, Van seems to have seen himself as a bit of a dilettante. His youthful preference tract been not to go into the academic life, and he recordecI in his reminiscences that "serious young men took engineer- ing rather than math or physics, where most of the students were girls." Just as he rebelled at solving triangles graphically, he evacled the physics senior thesis involving experimental work, including, worst of all possible fates, glassblowing by joining a debating team ant! arguing successfully against the government ownership of railroads. His states! reason (in

504 BIOGRAPHICAL MEMOIRS "Reminiscences of the First Decade of Quantum Mechanics," 1971) for taking physics was the otherwise light course load and the iclea that mathematics would involve him in his fa- ther's courses, which would not be "cricket." He click, however, make Phi Beta Kappa in his junior year, so one is permitted a great deal of skepticism about the rather frivolous motiva- tions he gives for his choice of careers. ~ note also the inclu- sion of an "unlisted reacting course in Moliere" in the accel- eratec! program he finally completed-surely not a common . ,% 1 (J ~ ~ ' interest tor a young scientist in the Middle West. EARLY CAREER IN PHYSICS Van's consciousness of physics seems to have been first raised by the experience of a course on kinetic theory taken from L. R. Ingersoll in his third year at Wisconsin. He was not well prepared because he had put oR the calculus to this same year, but he sat near Warren Weaver who was taking the course (though on the junior faculty, and was a very vocal critic of the textbook used. This stimulates! Van's interest enormously. In the next year he took a course from Professor March on dynamics that was his introduction to genuine theoretical physics and showed him very clearly the course of his future career. A fortunate accident took him to Harvard for the last semester of the 1919-20 college year: His father was spencl- ing a sabbatical there, anti urged him to finish up at Wiscon- sin in three-anct-a-half years and come take courses at Har- vard. He started out with three courses in math and physics and one in railroad administration. This latter convincer] him that he "would not get on very fast in the railroact business." The courses that influenced him positively were by Bridgman anct Kemble. He felt Bridgman's operational philosophy, while not explicitly stated, was very much implicit in the at- titucle to physics that he acquired, while Kemble was one of

JOHN HASBROUCK VAN VLECK 505 two or three teachers in the Unitecl States concerned about quantum theory. He was influenced negatively as well by a formal mathematical course in differential equations, a re- placement for his father's course, which he had been unwill- ing to take; this acIdecI to his lifelong distaste for empty for- malism. Thus, almost without conscious decision, he found him- self a full-fledged Ph.D. student at Harvard. He quickly com- pleted the requirements for an M.A. (1921) and finisher] a Ph.D. thesis uncler Kemble (19221. He stayer] on as instructor with Kemble for one more year, leaving for Minnesota in 1923. EARLY DAYS OF THE QUANTUM THEORY: HARVARD (1920 - 23) AND MINNESOTA (1923-28) His thesis topic attacked one of the truly knotty problems of the old quantum theory: the attempt to come up with a method of quantization that wouIcl give reasonable results for the helium atom. Once the hydrogen atom was more or less dealt with, anti simple harmonic motion unclerstoocI with De- oye's anti Planck's laws, the next stage was clearly more com- plex atoms. At about the same time, several European phys- icists were attempting the problem, anti Van's paper was essentially equivalent to results of Bohr, Kramers, and Kronig. In short orcler there followed a sequence of papers on various aspects of spectroscopy using the old quantum theory, and then a book, Quantum Principles and Line Spectra, finished in late 1925. During the Harvard years, Van was in constant touch with John Slater, who finished a mostly experimental thesis with Bridgman at about the same time, and then left for Copen- hagen to work for a year with Bohr. I think it is fair to say that this little American group kept in remarkably close touch with the enormous activity centered in Central Europe that

506 BIOGRAPHICAL MEMOIRS was to leac! to the new quantum mechanics, and it contrib- uted at least two papers of real significance, one of which was Van's paper of 1924 on the correspondence principle for ab- sorption. This paper comes tantalizingly close to the kind of considerations that led to Heisenberg's matrix mechanics; it was one of the few papers to attack the intensity question that was the key failure of oIc! quantum theory. Van maintained close contact with European physics, and was fortunate enough to accompany his parents to Europe in 1923; during the trip he made time to visit Bohr and hack extended dis- cussions with Kramers in Holland. The University of Minnesota invited both Van ant! Greg- ory Breit to come as assistant professors in 1923. This was a unique opportunity. Only graduate teaching was requirecl, and he would have someone to talk with, because Breit's in- terests were very close to Van's, so he left the annual instruc- torship available to him at Harvard with no apparent reluc- tance. (Slater got the only permanent faculty job!) He was at Minnesota for five years, rising to associate professor in 1926 and full professor in 1927. On Tune 10, 1927, he married Abigail Pearson of Minneapolis. Of his courtship he re- marked that they both loved dancing and that her ignorance of his work assured him that she would never interfere in it. He jokocl later that he made up his mine! when, at a dance, she introducer! him as the professor of chemistry. His first book was published as a Bulletin of the National Research Council. At that time NRC committees were occa- sionally former! with the express purpose of informing American scientists about important developments, and this book was a report of the Committee on Optical Spectra, with Paul Foote as chairman. It was well received, but by the time it was issued in early 1926 much of it had been supersecled by the enormous explosion of results from the new quantum mechanics. The exercise, however, was of considerable value

JOHN HASBROUCK VAN VLECK 507 to the author; his remarkably clear writing style had been formed, with the acknowledger! help of his father, and his very physical unclerstanding of classical dynamics and of the workings of the correspondence principle, which were to serve him well in his later career, hac! been developed. Van learned with great excitement of the new quantum mechanics through correspondence and the early published papers of Heisenberg on the matrix mechanics, which re- mainec! for a number of years his preferred form (in this, as in many other things, his style was unique). He sent in his first paper using it in early 1926, showing that the classical symmetry factor i/3 in the magnetic susceptibility is restored in the new theory. Nature asked him to shorten the piece, which slowed him down to what he called a "quadruple tie" in publication. He sailed for a visit to Copenhagen that sum- mer and completed another paper on the boat calculating mean values of inverse powers of r by matrix mechanics- only to learn that he had been beaten by practitioners of Schrodinger's wave mechanics. Nevertheless he wrote no less than four papers that year on the new mechanics, and for several years he continued to write papers discussing its na- ture and interpretation (such as tied. The little note in Nature fI0] was to set the theme for much of the rest of his career: the use of the new quantum mechanics to elucidate electromagnetic properties of matter. This had been an interest of his since an early seminar on the Weiss theory of ferromagnetism, and it was implicit in his correspondence principle paper; but from now on his inter- est led to a stream of fundamental papers, and it became clear that he hacI chosen this as his particular portion of the great work of verifying and using the new quantum theory. Bohr remarked, with characteristic insight, that while the spectroscopic successes of the quantum theory were more spectacular, the macroscopic ones such as Van worked on

508 BIOGRAPHICAL MEMOIRS were in some ways "more satisfying ant! more fundamental." The most funclamental immediate results were his demon stration of the general formula (which he always carefully called "Langevin-Debye") for the susceptibility (papers Ll0], ~ ~ i], ~ ~ 5] in the accompanying bibliography) and the detailed application to O2 and NO FI21. But at this time, he had al- ready begun the work on molecular ant! other spectra in the new mechanics that was a second major theme in his life with a paper with Hill on rotational distortion tI61. He was asked by the chemists to review the new quantum mechanics Ll7], and in general was an important teacher and proselytizer of the new knowledge in the American context. His worldwide reputation was assured by the series of remarkable experi- mental verifications of his results on O2 and NO in Leyclen, MIT, ant! Zurich. WISCONSIN ( 1928 - 34) AND PREWAR HARVARD: MAGNETISM, MOLECULES, CRYSTAL FIELDS, AND THE ORIGIN OF MAGNETIC RELAXATION Although Minnesota was, as he later said, very congenial, with Breit as a coworker, Tate and other experimentalists encouraging him, and a number of bright auditors interested in his lectures (fate himself, Bleakney, Brattain, and others), physics was more active at Wisconsin. Van accepted an over of a professorship at the University of Wisconsin in 192S, remaining there until 1934. This gave him the pleasure of overlapping for one year with his father and renewing several old associations. It was at Wisconsin that he conceived and finished his book, Theory of Electric and Magnetic Susceptibilities, although much of it was written on a European trip in the summer of 1930. His stay in Zurich was particularly produc- tive; arriving in vacation time, he worked until Pauli returned and, with characteristic rudeness, said: "_ don't republish my papers into a book!" In fact, the book, aside from being ar

JOHN HASBROUCK VAN VLECK 509 guably the first book in the modern field of solid-state phys- ics, contained-as Van defensively remarked much new material aside from the contents of the several papers on Langevin-Debye, "Van Vleck paramagnetism" (the second- order contribution of what he called "high-frequency matrix elements"), and the magnetism of the rare earth and iron group ions in salts (with Miss Frank (231), which had already appeared. There were new discussions of the averaging pro- cess for obtaining the fields ~ ~ ~ - ~ . 1 ~ fit in materials, of Heisenberg's tneory ot terromagnet~sm, ot aspects of ctielectric local fields and of dielectric theory in general, of Landau diamagnetism and its relationship to the classical theory, and the like. It is marked perhaps even slightly marred, as a modern text for physicists poorly trained in classical mechanics by careful discussion of the ways in which quantum mechanics, the old quantum theory, and classical physics differ. It just missed a number of very important developments, notably Van's own crystal field theory work and Neel and Landau's concept of antiferromagnetism, but in one sense it is not dated in the slightest: All results quoted in the book are, to my knowledge, correct to this day, needing no revision, only expansion. It was an enormously influential book and set a standard and a style for American solid-state physics that greatly influenced its development during decades to come for the better. We have, incidentally, R. H. Fowler's suggestion that Van write for the Oxford University Press to thank for the book's ex- istence. During the same Guggenheim fellowship trip that took Van to Zurich in 1930, he was invited to be the only American at the Solvay Congress. In Holland, he spent a number of days talking and walking with his friend Kramers, who pointed out to him Bethe's recent work on group theory. This led to a lifelong interest in group theory, which he still taught in inimitable style and from Wigner in the original Ger

510 BIOGRAPHICAL MEMOIRS man-when ~ was at Harvard in 1948. It also led to a series of applications that Van seemed to fee} were among his best work: to the spectroscopy and susceptibilities of magnetic ions in solids (papers t25], t36], t43l, t45l, t53], L54], t60], t611; and papers by his students M. H. Hebb, R. SchIapp, and W. Penney, later Baron Penney, on most of which his name, characteristically, (lid not appear). In these papers he intro- duced the "crystal fielct" concept in which a magnetic ion is envisaged as behaving more or less like a free ion perturbed by the anisotropic potential of the surrounding ions and at- oms. The orbital angular momentum in most iron group ions in solicls is "quenched" (a typical Van concept) by such fields, because of the weakness of spin-orbit coupling relative to the crystal field splittings, while rare earth ions retain free ion character but responc! to the local symmetry by the appro- priate splittings of the energy levels. This concept correlates enormous masses of spectroscopic, magnetic, and even chem- ical data on these compounds (the chemical energetics were clevelopec! by Penney anct by Orge} and BalIhausen, much later). It provides an absolutely essential starting point for the understanding of all the technically important insulating magnetic materials, such as ferrites, garnets, ruby, and the like. Van initiated both of the main branches of the theory of crystal fielcis, the naive electrostatic version anct the "ligand field" theory (now more generally accepted) in which the em- phasis is on semicovalent bonding to the neighboring "li- gand" ions or groups; ant] with his characteristic flexibility he demonstrated (paper t434) that both led to essentially the same experimental results. In the chemistry and spectros- copy of these ions, Van's (or SchIapp and Penney's) name for the field strength parameter, "Dq," is still used. Of the crystal field theory it has been said by Moffitt ant! BalIhausen (per- haps a bit extravagantly, but Van likoct to quote this state- ment): "It will be a long time before a method is developed to surpass fit] in simplicity, elegance and power."

JOHN HASBROUCK VAN VLECK 5 Other applications of group theory in paramagnetism first brought out by Van in the 1930s were the importance of Kramers' degeneracy (a consequence of time-reversal sym- metry) in leaving at least two degenerate levels for ocicI ions, anc! the application of the ~ahn-Teller theorem to deduce small distortions from perfect symmetry in certain cases, dis- tortions that couIc! leac! to complex mixed electronic-vibra- tional states (now called "vibronic") due to tunneling among symmetry-equivalent configurations ~ t54] ). Two experimental developments sparker! his continuing interest in paramagnetism: the adiabatic demagnetization method, especially as practiced at Oxforc! to reach tempera- tures below INK, and the paramagnetic relaxation work going on at Leyclen. The former stimulatect several of the papers aIreacly quoted, as well as t504; the latter led to Van's remark- able anc! prescient calculations of the paramagnetic relaxa- tion caused by lattice modulation of the crystal field param- eters ~ t59] ), as well as his invention of the "bottleneck" concept (~66], t671), which sparked many important experi- ments after the war. The sum total of his achievements in magnetism in the 1930s after his book appeared can best be appreciated by reading his 130-page Institut Henri Poincare lectures of May 1939. These were given in French (he re- marked that he hac! tract to go to the Riviera to recover, and he did not know what had been necessary for the auditors) and because of war conditions not published until 1947 (~7711. To summarize, he left in place, as a result of this body of work, the conceptual structure from which the science and technology of quantum electronics and much of the science of magnetism arose in the next two clecacles. To finish out his contributions to magnetism in this pe- r~ocI, we mention his paper on ferromagnetic anisotropy t49], a noteworthy first discussion of this difficult subject, further treater! in Harvey Brooks' thesis; ant! his important cIarifi- cation F63] of the Neel-Lanciau theory of antiferromagne .

512 BIOGRAPHICAL MEMOIRS tism, putting the subject in vector mode! form. This macle the theory much more suitable for experimental compari- sons than the qualitative form given by Nee! ant! Landau. As is often the case, the existence of a formal mode! stimulatecl theoretical interest, and the so-called "Heisenberg antifer- romagnet," which Van first introduced, has become a favorite subject of theoretical investigation, beginning with Kramers' and my own work on the antiferromagnetic ground state. Two other subjects, also relatecT to his interest in group theory, constitutes! much of the remainder of Van's work in this periocl. These were molecular spectroscopy and the theory of chemical binding. A number of papers (bell, t28], t29], f38], t40], t52i, F56], t571) showed his continue(1 interest in molecular spectra, which dates back to his early work on A-type doubling ant! was a lifelong theme of his work. There is also an important group of papers on CH4 anti on valence theory (~26], L27], t31], t32], F41], L421), which are the only prewar attempt, to my knowledge, to understancl directed valence bon(ling from a fundamental point of view, rather than to simply postulate it as Pauling (lid. Van particularly enjoyed trying to reconcile opposing schools of thought on the important questions. As I re- markect, he actually originated both schools in the case of crystal and ligand field theory. He triecI, in this sequence on chemical bonding, to show that Hun(l-Mulliken molecular orbital theory, and Heitler-Lonclon valence band theory as adapted by Pauling (ancl called the Slater-Pauling theory) couIct lead to the same results for clirectect covalent bonds such as in CH4. This work was unaccountably neglectecl, and it is not until very recently that a real attempt has begun to reach the level of fundamental conceptual understanding of the chemical bond that Van was seeking. Later, as we shall see, he trier! to build the same kind of "Van VIeck bridge" (as Purcell termed it) in the theory of ferromagnetism.

JOHN HASBROUCK VAN VLECK 513 Van picked up anc! contributed to whatever subject was at hancI. The local fielc! corrections in dielectric anc! magnetic meclia remained an interest (~35], L46], L47], L4X], and espe- cially t64l, which is a very important clarification of the local field problem which I, at least, found very useful later). He contributed to questions of the interpretation of quantum mechanics (id], t23], t651), to nuclear physics and the prob- lem of neutron diffraction (i 39], L58], L681), and to the theory of ferromagnetism (~44], F5111. As student or postcloc prob- lems he touche(1 on atomic energy level theory (~301), on band theory (~551), anct on intermolecular forces (~5611. In 1934 Van hacI accepted an offer to take up a full pro- fessorship at Harvard. Initially, his courses were listed jointly in the mathematics anti physics (departments, since his ap- pointment was in mathematical physics. He was asked by the then president of Harvard, }. B. Conant, to foster education on the less abstract and more applied sicle of mathematics. Conant believed that his mathematics department tract be- come too remote and that the courses at the graduate level were of little use then (as in my day as well) to physicists, chemists, ant! others who neeclecl acivancecI mathematical training. This is not a tendency that even Van couIcI stem (as experience in many other institutions attests), and twenty years later, when he took up his appointment as dean of Ap- plied Science, he resigned sadly from the Mathematics De- partment, and the Division is the present home of applied mathematics at Harvard. During this perioc! it is interesting to see Van's interests actually moving progressively away from the abstract or mathematical aspects the questions that hack concerned him initially having been solved by the new quantum theory- towarc! applications and his eventually most important role as an experimental consultant. Van regretted audibly the drift of the majority of his colleagues in theoretical physics

514 BIOGRAPHICAL MEMOIRS toward more abstract mathematics and toward! nuclear, and then particle, physics, although he had at least one student at Wisconsin, R. Serber, who later excelled in that domain, and he was to build up Harvarcl's strength in that area of physics while chairman of the department. From the first Van made a point of minimizing his role in his students' and associates' work. With some especially of the better known, such as Serber and Brooks, as well as with Hurwitz, JordahI, and myself there were no joint publica- tions at all. With others, such as Hebb, Schiapp, and Penney, the bulk of the work, though wholly inspired by Van's ideas, was not published under his name. This was even more true of postdoctoral associates; he brought John Bardeen and Nico Bloembergen to Harvard as junior fellows, as well as many visitors in other capacities, such as Broer, Van Kranen- donk, Gorter, Abragam, and others with whom his name is not usually closely linked. HARVARD: WAR AND IMMEDIATE POSTWAR YEARS VAN AS CONSULTANT, GREY EMINENCE, AND MIDWIFE TO THE BIRTH OF QUANTUM ELECTRONICS Although Van continued some teaching at least through 1943, he carried out several roles, especially that of head of the theory group (after 1942) at Harvard's Raclio Research Laboratory, a smaller, closely linked cousin of MIT's giant Radiation Laboratory (at which he spent some time in 1942- 431. The two laboratories played a very important role in the development of microwave radar, working closely with Bell Labs ant! other military and industrial laboratories. (Van had early contact as an adviser with the uranium project but was much more closely associated with radar work. Perhaps some future historian of science should trace the rather marker influence that the racier laboratories hack on Harvard and MIT physics, as contrasted to Chicago, Cal Tech, and Berke

JOHN HASBROUCK VAN VLECK 515 fey, which were heavily involved in Los Alamos and the bomb project and developec! in a very different way.) Several wartime projects strongly influenced by Van can be iclentifiect through later papers: one on the theory of WINDOW (clouds of metal foil strips used to food racier), an unlikely collaboration with Morton Hamermesh ant] Felix Bloch (~7311; a classic and technologically vital pair of reports on identifying pulses in the presence of noise, carried out with David Midclleton (~7214; an(l, particularly, his (1iscovery that the ill-fated "K-bancI" racier operating at A = 1.25 cm would be a fiasco because of atmosphere absorption by mo- lecular lines of O2 and, particularly, water. In order to work out this conclusion quantitatively it was necessary to revise accepted theories of collision broadening (since the relevant lines wouIct be severely broadenecl) in such a way as to include induced emission as well as absorption, and the appropriate revision was carried out with V. F. Weisskopf (~701~. This paper was of the utmost importance both experimentally and theoretically in the immediate postwar years. Its experimen- tal significance is evident and well known: It was a chief too! for interpretation of the mass of experimental data that were procluced in the great outburst of radio-frequency spectros- copy after the war in Bleaney's lab at Oxford, Wilson's and Purcell's at Harvard, Townes' at Bell and Columbia, and Gorcly's at Duke, among others. But it had an even deeper significance, in that it was the precursor of my own work (it- self stimulated by Van) on pressure-broaclening and line- breadths in magnetic resonance spectroscopy, and of other early versions of the calculation of physical results using fluc- tuation-clissipation methods, and hence sparked one of the earliest lines of inquiry into what became the many-body theory. In my opinion Van's status as a figure of major importance to the history of science rests most securely on his role in the

516 . BIOGRAPHICAL MEMOIRS Immediate postwar years at Harvard, rather than on his pre- war achievements, massive as these are. During this time, for instance, he was closely associated with no less than four No- be! prizes (those to Purcell, Townes, Bloembergen, and the joint prize in which we participated). I suppose that with his no-nonsense attitude to scientific credit and to who did what, and with his persistent belief-against all odds that all his associates were as quick an(1 perceptive as he was, Van himself would never have realizer! the important role that he playact as adviser and consultant, but all of those who worked near him at that time, especially the experimentalists, gave him much credit for the very rapid progress they macle. It is hard to take one's minct back to that time and rec ognize the mental leap that coherent spectroscopy required. Rabi's molecular beam methocls, of course, have often been cited as the original for raclio-frequency spectroscopy, but the peculiar environment anc! detection methods made that a rather esoteric specialty. It was really Van who noticed the early measurement of Cleeton and Williams on ammonia (its importance to him he mentioned in his charming little article, not in the bibliography, entitlecl "Molecular Spectroscopy in Ann Arbor and Outer Space," although I never heard him refer to Rabi's method as seminal) and, during the war, single-mincledly pushed on with identifying the levels of O2 and H2O that could lie in the centimeter wave region and hence interfere with the proposed "K-bancl" racier (~74], F75] were based on this work). At the same time he maintained close rapport with the Leyclen group, which was pushing re- laxation spectroscopy up in frequency from the radio- frequency end, culminating in Gorter's work cluring the war and shortly after, and which was the most technically close (because of its emphasis on line-width and relaxation, as well as its instrumentation) to the Purcell group's discovery of nu- clear magnetic resonance, and especially to electron para

JOHN HASBROUCK VAN VLECK 517 magnetic resonance. Most of those who later took part in the explosion of coherent spectroscopy after the war met at war- time conferences at which Van's work was discussed. (I was at one such where Bleaney, Van himself, and Townes, at least, were present.) In any case, he was a central figure perhaps the central figure in taking the first steps in establishing the field that eventually came to be known as quantum electronics. In es- sence, this fielcI can be clefinect as the physics of the interac- tion of coherent electromagnetic radiation with atomic, mo- lecular, or solid-state systems of quantized energy levels. The first step, of course, is the mental leap of recognizing that suitable systems of energy levels exist in reasonable profu- sion, and with energy level breadths that do not overwhelm the quantization of the levels and leave one with a featureless classical smear. Van brought together the knowle(lge of mo- lecular energy levels, the appropriate techniques (Waller's moment methoc! as appliecI by Broer in HolIancI cluring the war, and then by Van [79] and the Van VIeck-Weisskopf pressure-broadening theory) for estimating line breadths, and an encyclopedic knowle(lge of the physics of electric and magnetic interaction that were necessary to get a start in this field. One finds his help acknowledgect and his papers quoted in early papers in all the coherent spectroscopies: NMR, EPR, molecular microwave spectroscopy, and later ferromagnetic resonance spectroscopy as well. His name even appears on an experimental paper in molecular microwave spectroscopy, the discovery paper (by Dailey et al.) of hyperfine structure in this fielct, which also determiner! the quadrupole moment of Ni4 t701. Other papers directly on the various quantum electronic spectroscopies were Van VIeck ant! Weisskopf (al- ready mentioned, the discovery of exchange narrowing with Gorter L76], his beautiful overall summary of clipolar broacl- ening and exchange narrowing L79], a paper on ferromag

518 BIOGRAPHICAL MEMOIRS netic resonance L83], L87], and a pair on pressure broadening (~82], t9711. A number of other papers continue(1 his prewar interest in calculating molecular, ionic, ant! atomic energy levels: t78l, t80], L89l, t93], t94], anti t95], with some empha . ~ sits on t ne new spectroscopes. There were at least two other contributions of major im- portance during this immediate postwar period. Tom Kuhn, later to become very well known as a philosopher and histor- ian of science, collaborated with Van in inventing a new tech- nique, the quantum (defect method, for using spectroscopic data ctirectly to calculate bane] energies in the alkali metals t84], t96], t981. This was an important forerunner of modern pseudopotential methods, anc! is very close to the most recent "norm-conserving pseudopotential" method. It was refined extensively by Frank Ham, and the elegant mathematical ma- chinery has been a source of a number of developments. Van's student Hurwitz hac! written an unpublished thesis about the many-body theory of ferromagnetism in metals. What Van and he wanted to do was to strike a mictdle ground between the free-electron theory purists, especially Stoner, who were determiner! to apply the pure Bloch band theory of ferromagnetism and ignore the necessarily strong elec- tronic interactions otherwise; and the naive "Heisenberg moclel" theorists who proposes] that the magnetic electrons stay in purely atomic states with no itinerant character at all. Van's micldIe ground, expressed at a seminal meeting in 1952 and written up for Reviews of Modern Physics in 1953 (~91], t92], t} 104), had the essential components of the correct way to treat strongly magnetic itinerant electrons. Though little regarclec! in the heat of battle of the time, it formecT a basis for important work by Hubbard, Gutzwiller, Herring, myself, Moriya, ant! others that advancect this difficult problem greatly in the years to follow. This work, in which he was

JOHN HASBROUCK VAN VLECK 519 groping toward the same set of concepts being considered by Mott at the same time with regard to the Mott transition but not to magnetic phenomena, makes their joint Nobel prize seem a little less arbitrary. HARVARD: THE LATER YEARS SC IENTI ST-ADMINISTRATOR After the great burst of creative energy that I have just oescr~becr, van was never again to be at the forefront of sev- eral active scientific areas at once, as he had been throughout the quarter century from 1925 to 1950. One may speculate that this purely relative slowing down coincided with his assumption of two demanding administrative jobs, chairman of the Physics Department (1945-49) and dean of Engineer- ing and Applied Physics (1951-571. He had been, from th start, involved in the discussions that led to the combining of the Engineering School with the Department of Applied Sci- ences to make the School, and it was only natural to give the new entity a good start by making him its first dean; its sec- ond was his student Harvey Brooks. Also during 1952-53 he was president of the American Physical Society. He was closely associated with the work of the APS, and Bill Havens, the present secretary, remembers his help with much grati- tude, both at that time and later. As chairman of the Physics Department, Van presided over the admission-and recruit- ment of an extraordinary group of students in the first few years, brought back at irregular times and from the ends of the earth, mixing refugees, returning servicemen, and bright young products of the wartime accelerated courses. It sur- prised me to find how many of us felt that he personally intervened to get us to Harvard. At the same time he was recruiting junior and senior faculty: Bloembergen, Pound, Schwinger, Ramsey, and Purcell, among others, were his ap

520 BIOGRAPHICAL MEMOIRS pointments. Those years were a golden age of Harvard phys- ics, and few of us who Participated in them can have been unaware of that fact. Even more demanding was the creation of the Engineer- ing and Applied Physics School. The no-man's lanct between engineering and physics, or more accurately, bordering mathematics and chemistry as well, is a very sensitive region, with clelicate problems of defensiveness, snobbery, and intel- lectual fragmentation. To get the new entity going, to keep the lines of communication open, and in particular to make the resulting unit operate well with the Physics Department, was a remarkable achievement. Van has left Harvard, as his most enduring legacy, one of the worIcl's strongest groups in these areas, particularly in conclensecl-matter physics and materials science, the successor areas to his own interests. One of his stratagems in cloing this was the "Van VIeck Bridge," an actual physical connection between Cruft Labo- ratory, where many of the applied scientists were, and the Jefferson Physics Lab. After six years as dean, Van returned in 1957 to more or less private academic life, although first he server} as vice president of the IUPAP, 1958-60, anc! then he took up two visiting professorships: the Lorentz Professorship at Leyclen in 1960 ant! the Eastman Visiting Professorship in Oxford, 1961-62, where Abigail and he were the first to occupy the new residence providecI. Then he returned to Harvard until his retirement at the age of seventy in 1969. All during this period, of course, he was maintaining a Eve! of scientific publication that wouIct have seemed high for anyone else, especially if one includes the many review papers he was asked to give, anct the increasing stream of scientific reminiscence and commentary that began to flow. His strictly scientific output resumed its normal flow in 1957, and dealt mainly with aspects of magnetism, a fielcl that

JOHN HASBROUCK VAN VLECK 52 increasingly claimed his scientific attention. He was delightecI to find his old friends, NO ancl O2, captured in 1957 in a solicl-state "cIathrate" compound by H. Meyer, ancl to inter- pret the results of measurements on them (~102], ti20], and a similar measurement by Huang, FI5311. He wrote a stream of papers on various aspects of rare earth magnetism, in- cluding some basic papers on the now technically important garnet materials (used in bubble memories), the first of these in 1960 with Werner Wolf (~!13], F! 19], t123], ti27], t128i, tI30], tI31], [1321, ti34], Ll38], Ll39], tI40], Ll47], tI64], ti661; the last two in 1974 ancl 1975, well after his retire- ment). Other rare earth materials discussed includecl euro pium metal ~ ~ ~ 41; Sm intermetallic compounds ~ ~ ~ X]; EuO, where he helped interpret the surprising ferromagnetic be- havior discoverect by his old frienc! Richard Bozorth and Bernd Matthias ~ ~ 2 ~ ]; Eu2O3 ~ ~ 50], ~ ~ 521; ancl Ho-Er alloys Ll591. He retained an interest in the theory of magnetism in metals, and continued to the end to be properly skeptical of reports of progress. (} well recall being asked repeatecIly: "Do you really think the 'U-T' mocle} explains magnetism?"- his name for Hubbarcl's mocle! baser! on his own nomenclature of 1953 for the relevant parameters ancl on his private joke about the University Theater in Harvard Square.) His own work inclucled mostly review and discussion papers (~1031 in 1957; a set of Varenna lectures, t! 10], ti25], Ll41], all given at meetings, the last at a Sanibe! symposium in his honor in 19661. His interest in magnetic anisotropy and other weaker effects led to a few papers: a review article at the first "Bo- zorth" conference in 1956 t99], and tI 121; these in aciclition to several of those on the rare earth materials. Finally, he continuccl his interest in spectroscopy and re- laxation, ancl particularly in the new concepts being intro- ducect by Bloembergen ancl Abragam of spin temperature

522 BIOGRAPHICAL MEMOIRS and in his own oIct idea of the Van VIeck bottleneck at the phonons, which led to several reviews and some original pa- pers: another set of Varenna lectures of 1957 ti053;~103], tI08],~16],~17],~! 221 (a paper at a Quantum Electronics conference in 1961: the field now had a name); tI28], and 1354. Reviews proliferate in his later work; in addition to those we have aIreacly mentioned, there was one on spin waves, with Van Kranendonk (who also took an interest in his oIcI field of pressure broadening, tI063~; EPR and magnetism f901; exchange tI091; antiferromagnetism tS6], (where he kindly publicized my own early work); rare earth magnetism tI373; and line breadths (with David Huber, his last contri- bution of some ten or more to Reviews of Modern Physics, tI6734. One very small group of papers commemorates a rather bizarre incident in Van's life. These are the papers on "Hid- den momentum" tI4X] and FI511. (The first is a colIabora- tion, delightful to behold, between one of the clepartment's youngest and most famous particle theorists, Sidney Cole- man, and Van, about to retire in 1968.) Van had been asked to referee a paper by the now notorious Nobel prize winner, Bill Shockley, proposing a new point of view on energy and momentum transport by light in the presence of polarizable media. This esoteric question hac! some small experimental interest in view of the availability of high-power lasers and the capability of measuring their effect on media, but on the whole the subject clid not merit the extreme importance Shockley placed on it as an example of the success of his so- callect "Try-simplest-cases" way of carrying on scientific in- vestigation (I always wonclered what he thought the rest of us cloy, and of the short-sighteciness of the scientific estab- lishment. Shockley somehow seemed to identify the physical science establishment with that primarily biological one that

JOHN HASBROUCK VAN VLECK 523 opposed his views on heredity and race (a subject in the com- plication of which the application of "Try simplest cases" can be a disastrous blunder). In any case, ~ presume Van tract been an outspokenly opposed referee on Shockley's paper, anct after a rather bitter correspondence not marked on Shockley's side even by the normal perfunctory courtesies, Van felt moved to write a refutation. The bizarre event was that Shockley then threatened both Van anct the Physical Re- vaew with a lawsuit for libel, on the basis that this paper callect his scientific reputation into question, a reputation which was of immense value to him in the great work he felt he was cloing on behalf of "human quality." ~ believe this is the only public controversy in which I. H. Van VIeck has ever been involved, ant! the story does him honor. TEACHING AND OTHER PERSONALIA ~ clon't know if there exists anywhere a full list of Van's graduate students. It doesn't really matter, because some of those most influenced by him, such as John Bardeen, Walter Brattain, W. G. (Baron) Penney, anct Nico Bloembergen, were not formally his students. As ~ have already remarked, most of his students publishect their work independently, so it is rather hard to trace them; a fair list is given in Bleaney's memoir. Among those who were, formally, or consiclerec! themselves, his students, are at least two eminent aciministra- tors of science and technology, one a peer of the realm in England and one his successor as clean at Harvard; one of the country's premier historians of science; an eminent ant! widely respected particle theorist; an eminent plasma theo- rist; and a Nobel prizewinner. Just as Van wrote the first American thesis on the old quantum theory, his student E. L. Hill wrote the first one on the new quantum mechanics. Van was a master of that delicate judgment that allows the student just the amount of freedom he can manage, while at

524 BIOGRAPHICAL MEMOIRS the same time the student remains conscious that there is a "safety net" in case he cannot make it on his own. Van seems to have been remarkably successful at the process; there were very few failures. (I know of none, in fact, but merely suppose there must have been some.) The decision to work with him was one of the wiser choices of my life. Van's early lectures at Minnesota, Wisconsin, and at the famous Michigan summer schools of the early 1930s where, as he saicl, American physics came of age, had a great influ- ence historically. By the 1940s, however, his teaching style tract become unique, and is rememberer! with fondness by everyone I spoke to. Most of the material was written in his inimitable screw! on the board, and he spoke in a very per- sonal style, using such favorite phrases as "engineering ap- proximation" (often referring to a highly sophisticated math- ematical procedure quite beyond the capability of your average engineer), "hand that over to our mathematical slave," and the like. Especially in group theory, his intuitive feeling for the subject often bewilderec! us as he scribbled clown symmetry functions in an offhand shorthand to dem- onstrate what we thought were exceedingly abstruse points. He tract a schoolmarmish way of interrupting himself with a "what?" to the class, usually getting a murmur that he took to be the end of his sentence, and I suppose like most lectur- ing tricks it served to maintain a proper pace. But he (lic1 at least once come into class and start his lecture with "A clever trick is what?" In all of his classes, however, he used two basic techniques of the genuinely gooc! teacher. First, he presented a set of carefully chosen problems, which really contained the meat of the subject, often with "hints" that I usually found hope- less as helps but highly useful as explanations. Second, he supplied a "crib" for examination study, which we always thought was practically cheating, saying precisely what couIct

JOHN HASBROUCK VAN VLECK 525 be asked on the exam. It was only after the fact that you realized that it contained every significant idea of the course. He continuer! to lecture at summer schools until quite late in life, often in exotic places, in keeping with his love of travel. Several of his lecture note sets the Henri Poincare in 1939, and Varenna in 1957, for instance are important scientifi- cally. As time went on he was increasingly in demancl for semi-ceremonial speeches, anc! often these, with their gentle wit ant] unmistakable flavor, took the form of reminiscences or remarks on the state of his beloved! science, as his articles on walking with Dirac; on his "Swiss visits of 1906,1926 and 1930"; or his deploring of barriers between minds in his pres- idential address. Nonetheless, more often than not he chose to emphasize technical content, to the end of his life. His wit was ever gentle; he was never sarcastic or self-important, de- lighting in strange juxtapositions ("Molecules in Michigan and Outer Space"), coinciclences, anc! in ricting his own in- congruous hobby-horses to extreme lengths-as in using the official or football nickname for every university in the coun- try, as "Sooner" for a person associated with Oklahoma. He never told "jokes" in the usual sense of the word, especially avoiding off-color speech. He loved travel and knew the cities of the work] well- well enough to have a favorite hotel in Hong Kong, for in- stance. Abigail almost always traveled with him. They were inseparable, and her wit was an excellent foil to his, slightly more personal and acerbic, occasionally expressing the im- patience with people that Van never permitted himself. Bridge was a favorite avocation of theirs, and still is for her; they were excellent players. In his younger years Van was a dedicates] walker, both in the fields near Madison ant! in the wilct places of the world-Coloraclo, the White Mountains, the Alps, and many other places. Incidentally, he always managed his own investments, and

526 BIOGRAPHICAL MEMOIRS ~ believe very much increased the reasonably comfortable fortune his father left. The only detail ~ ever heart! revealecI was that he spotted the departure of a first-rate young crystal chemist from Bell Labs for the newly formed Texas Instru- ments Corporation at the right time, and invested in TI, a huncired-fold winner. In any case he had enough to give gen- erously to Wisconsin, inclucling the gift of his father's print collection, and to Harvard. LAST YEARS In 1969 Van retired, remaining in Cambridge except for the inevitable travels (we find papers in this period from Mel- bourne, Rumania, Cambridge, London, and Holland) and writing an occasional scientific paper, as we have seen. He kept in mind until very late the project of updating his book, but surely that was too massive a task. The only replacement at a comparable level is the six-volume Racl~o-Suh! series, so some very rigorous selection would have been requirecl. Hon- ors continued to flow to him, such as the coveter! Lorentz meclal, 1974; Chevalier of the Legion (l'Honneur, 1970; for- eign membership in The Royal Society; and finally the Nobel prize. Aside from an operation, he remained in good health until about 1975, when he began to have a heart weakness that required a pacemaker. At this time the \'an VIecks de- cided to give up their lovely old house on Fayerweather Street for an apartment at 989 Memorial Drive, in which Abigail still lives. I saw Van in London in 196S, at the time of his "signing the book" at The Royal Society, and his speech was as spar- klingly witty and as full of new ideas about magnetism as ever. We attended a play of which ~ remember only that it was a bit modern anct negative for the Vans' determinecIly old- fashioned point of view with regard to literature, or music, or styles in science, for that matter. The result was some sharp discussion from Abigail.

JOHN HASBROUCK VAN VLECK 527 Ten years later, in Stockholm, with his pacemaker, the wit was still there, but it seemed that there was a short "duty cycle"; he sparklecI for an hour at a time or so, anti then rested. His brief speech, as the eldest, on behalf of the physics laureates is a mode! of taste and grace, complimenting his hosts and his fellow laureates with a sure hancI. He continued to travel, but encountered medical prob- ~ems again on a trip to the West Coast to honor his old frienc! Julian Schwinger. Finally, on October 27, 1980, his heart gave out for good, ant! we lost the grandest representative of what he himself caller! the "Coming of Age of American Science." In speaking of his own father at the cledication of E. B. Van VIeck Hall at Madison, Van quoted his father's precepts: "Two qualities may be noticed as especially needed by the American Escientist]. The first is a broad, liberal culture. The pursuit of Escience] in itself is doubtless narrowing ... its abstract height tends to separate one from daily life. A wicle liberal culture therefore is eminently desirable." The second is "moral fiber and force, as exhibited in pa tience with students." self. No one can have better satisfied these goals than Van him FIRST AND FOREMOST, I have freely borrowed material from Bre- bis Bleaney's admirable memoir for The Royal Society. For the op- portunity to read this memoir, I am very grateful. Among other unpublished material I used for background were interviews by T. S. Kuhn from the AIP Center for the History of Physics. The speeches given in memorial services at Harvard and at Wisconsin were quite useful, as well as those at the dedication of E. B. Van Vleck Hall at Wisconsin, including Van's own. Finally, his fairly ex- tensive reminiscent articles were very helpful, as were some in- sights from conversations with Abigail Van Vleck, Nico Bloember- gen, and others.

528 BIOGRAPHICAL MEMOIRS BIBLIOGRAPHY 1922 L11 The normal helium atom and its relation to the quantum theory. Philos. Mag., 44: 842- 69. 1923 L3] F21 With E. C. Kemble. On the theory of the temperature vari ation of the specific heat of hydrogen. Phys. Rev., 21:653 61. Two notes on quantum conditions. Phys. Rev., 22:547-58. 1924 L41 A correspondence principle for absorption. l. Opt. Soc. Am., 9:27-30. The absorption of radiation by multiple periodic orbits, and its relation to the correspondence principle and the Ray leigh-}eans law. Phys. Rev., 24:330-65. 1925 On the quantum theory of the polarization of resonance ra- diation in magnetic fields. Proc. Natl. Acad. Sci. USA, 11:612-18. 1926 F71 F81 Note on the postulates of the matrix quantum dynamics. Proc. Natl. Acad. Sci. USA, 12:385-88. On the quantum theory of the specific heat of hydrogen, Part I. Phys. Rev., 28 :980-1029. t9] The dielectric constant and diamagnetism of hydrogen and helium in the new quantum mechanics. Proc. Natl. Acad. Sci. USA, 12 :662-70. 1927 F10] On dielectric constants and magnetic susceptibilities in the new quantum mechanics, Part I. Phys. Rev., 29:727-44; cf. Nature, 118~19261:226. F111 Dielectric constants and magnetic susceptibilities in the new quantum mechanics, Part II. Phys. Rev., 30:31-54. L121 The theory of the paramagnetism of oxygen and nitric ox- ide. Nature, 119:670.

JOHN HASBROUCK VAN VLECK 529 F131 Physical optics report of Progress Comm. for 1925-26. I. Opt. Soc. Am., 14:108-13; and 16~19281:301-6. 1928 . The correspondence principle in the statistical interpreta- tion of quantum mechanics. Proc. Natl. Acad. Sci. USA, 14: 178-88. On dielectric constants and magnetic susceptibilities in the new quantum mechanics, Part III. Phys. Rev., 31:587-613. With E. L. Hill. On the quantum mechanics of the rotational distortion of molecular spectral terms. Phys. Rev., 32:250- 72. F171 The new quantum mechanics. Chem. Rev., 5:467-506. 1929 181 The statistical interpretation of various formulations of quantum mechanics. l. Franklin Inst., 207:475-94. F191 On A-type doubling and electron spin in the spectra of dia- tomic molecules. Phys. Rev., 33:467-506. With A. Frank. The mean square angular momentum and diamagnetism of the normal hydrogen molecule. Proc. Natl. Acad. Sci. USA, 15:539-44. F211 On the vibrational selection principles in the Raman effect. Proc. Natl. Acad. Sci. USA, 15:754 - 64. With A. Frank. The effect of second order Zeeman terms on magnetic susceptibilities in the rare earth and iron groups. Phys. Rev., 34:1494-96. 1932 L231 Some mathematical aspects of the new physics. Am. Math. Mon., 39:90-96. F241 Theory of the magnetic quenching of iodine fluorescence and of A-doubling in 3IIo states. Phys. Rev., 40:544-68. t25] Theory of the variations in paramagnetic anisotropy among different salts of the iron group. Phys. Rev., 41:208-15. 1933 F261 On the theory of the structure of CH4 and related molecules, Part I. I. Chem. Phys., 1:177-82. L271 On the theory of the structure of CH4 and related molecules, Part II. i. Chem. Phys., 1:219-38.

530 BIOGRAPHICAL MEMOIRS With Paul Cross. Molecular vibrations of three particle sys- tems with special applications to the ethyl halides and ethyl alcohol. I. Chem. Phys., 1:350-56. With Paul Cross. A calculation of the vibration frequencies and other constants of the HERO molecule. i. Chem. Phys., 1 :357-61. L301 With N. Whitelaw. The quantum defect of nonpenetrating orbits, with special application to At II. Phys. Rev., 44:551- 69. 1934 L31 ~ On the theory of the structure of CH4 and related molecules, Part III. i. Chem. Phys., 2:20-30. F321 Note on the Sp3 configuration of carbon and correction to part III on CH4. }. Chem. Phys., 2:297-98. A new method of calculating the mean value of 1/rS for Ke- plerian systems in quantum mechanics. Proc. R. Soc., 143 :679-81. The Dirac vector model in complex spectra. Phys. Rev., 45:405-19. Concerning the tensor nature of the dielectric constant and magnetic permeability in anisotropic media. Phys. Rev., 45:115-16. With W. G. Penney. The theory of the paramagnetic rotation and susceptibility in manganous and ferric salts. Philos. Mag., 17:961-87. With M. H. Hebb. On the paramagnetic rotation of tysonite. Phys. Rev., 46: 17-32. Magnetic dipole radiation and the atmosphere absorption bends ofoxygen.Astrophys. J.,80:161-70. t33] L341 L35] L361 L371 t381 1935 L39] On the cross section of heavy nuclei for slow neutrons. Phys. Rev., 48:367-72. F401 The rotational energy of polyatomic molecules. Phys. Rev., 47:487-94. With A. Sherman. The quantum theory of valence. Rev. Mod. Phys., 7:167-228. L42] The group relation between the Mulliken and Slater-Pauling theories of valence. l. Chem. Phys., 3:803-6.

JOHN HASBROUCK VAN VLECK 531 L43] Valence strength and the magnetism of complex salts. }. Chem. Phys., 3:807-13. 1936 [44] Nonorthogonality and ferromagnetism. Phys. Rev., 49:232 40. 1937 L45] The puzzle of rare-earth spectra in solids. }. Phys. Chem., 41 :67-80. L461 With R. L. Joseph. The influence of dipole-dipole coupling on the specific heat and susceptibility of a paramagnetic salt. J. Chem. Phys., 5:320-37; errata 32~1960~:1573. t471 On the role of dipole-dipole coupling in dielectric media. J. Chem. Phys., 5:556-68. t481 Revised calculation of the translational fluctuation effect in gaseous dielectrics. l. Chem. Phys., 5:991. t49] On the anisotropy of cubic ferromagnetic crystals. Phys. Rev., 52: 1178-98. 1938 L52] L501 On the adiabatic demagnetization of cesium titanium alum. J. Chem. Phys., 6:81-86. L511 Note on the second or Gaussian approximation in the Hei- senberg theory of ferromagnetism when S > /. l. Chem. Phys., 6:105-6. On the isotope corrections in molecular spectra. }. Chem. Phys., 4:327-38. 1939 F531 On the magnetic behavior chrome alum. }. Chem. Phys., 7:61-71. Of vanadium, titanium and t541 The Jahn-Teller effect and crystalline stark splitting for clus- ters of the form XY6. }. Chem. Phys., 7:72-84. With T. Bardeen. Expressions for the current in the Bloch approximation of "tight binding" for metallic electrons. Proc. Natl. Acad. Sci. USA, 25:82-86. t561 With G. W. King. Dipole-dipole resonance forces. Phys. Rev., 55:1165-72. F57] With G. W. King. Relative intensities of singlet-singlet and singlet-triplet transitions. Phys. Rev., 56:464 - 65.

532 BIOGRAPHICAL MEMOIRS On the theory of the forward scattering of neutrons by par- amagnetic media. Phys. Rev., 55:924-30. 1940 F59] Paramagnetic relaxation times for titanium and chrome alum. Phys. Rev., 57:426-47, 1052. L60] Note on the Zeeman effect of chrome alum. i. Chem. Phys., 8:787-89. F61] With R. Finkelstein. On the energy levels of chrome alum. }. Chem. Phys., 8:790-97. F621 Electronic conduction and the equilibrium of lattice oscil- lators. Rev. Univ. Nac. Tucuman, Ser. A, 1:81-86. 1941 F631 On the theory of antiferromagnetism. J. Chem. Phys.,9:85- 90. L641 The influence of dipole-dipole coupling on the dielectric constants of liquids and solids. Ann. N.Y. Acad. Sci.,40:293- 313. L65] Note on Liouville's theorem and the Heisenberg uncertainty principle. Philos. Sci., 8:275-79. t661 Paramagnetic relaxation and the equilibrium of lattice oscil- lators. Phys. Rev., 59:724-29. F671 Calculation of energy exchange between lattice oscillators. Phys. Rev., 59:730-36. L681 Nuclear physics and inter-atomic arrangement. Univ. Pa. Bi- centennial Conf. :51- 68. 1945 L691 A survey of the theory of ferromagnetism. Rev. Mod. Phys., 17:27-47. L701 With V. F. Weisskopf. On the shape of collision-broadened lines. Rev. Mod. Phys., 17:227-36. 1946 t711 With B. P. Dailey, R. L. Kyhl, M. W. P. Strandberg, and E. B. Wilson, in The hyperfine structure of the microwave spec- trum of ammonia and the existence of a quadrupole mo- ment in N'4. Phys. Rev., 70:984.

JOHN HASBROUCK VAN VLECK 533 F721 With D. Middleton. A theoretical comparison of the visual, aural and meter reception of pulsed signals in the presence of noise. J. Appl. Phys., 17 :940-71. 1947 F73] With F. Bloch and M. Hamermesh. Theory of radar reflec- tion from wires or thin metallic strips. ]. Appl. Phys., 18:274-94. F74] The absorption of microwaves by oxygen. Phys. Rev., 71 :413-24. The absorption of microwaves by uncondensed water vapor. Phys. Rev., 71:425-33. L76] With C. T. Gorter. The role of exchange interaction in par- amagnetic absorption. Phys. Rev., 72: 1128-29. L77] Quelques aspects de la theorie du magnetisme. Ann. Inst. Henri Poincare, 10: 57-187. 1948 L781 With R. S. Henderson. Coupling of electron spins in rotating polyatomic molecules. Phys. Rev., 74: 106 -7. t79] The dipolar broadening of magnetic resonance lines in crys- tals. Phys. Rev., 74:1168-83. 1949 L801 With L. H. Aller and C. W. Ufford. Multiplet intensities for the nebular lines 4S-2D of O. Astrophys. I., 109:42-52. F81 ~ The present status of the theory of ferromagnetism. Physica, 15: 197-206. F82] With Henry Margenau. Collision theories of pressure broad- ening of spectral lines. Phys. Rev., 76: 1211-14. 1950 L831 Concerning the theory of ferromagnetic resonance absorp- tion. Phys. Rev., 78:266-74. L841 With T. S. Kuhn. A simplified method of computing the cohesive energies of monovalent metals. Phys. Rev.,79:382- 88. t851 Landmarks in the theory of magnetism. Am. i. Phys., 13:495 -509.

534 BIOGRAPHICAL MEMOIRS 1951 L861 Recent developments in the theory of antiferromagnetism. Phys, 12: 262-74. Ferromagnetic resonance. Physica, 17: 234-52. L871 L881 With I. Ollom. On the splitting of the ground state of Ni+ + in NiSiF~6H JO. Physica, 17:205 -8. F891 The coupling of angular momentum vectors in molecules. Rev. Mod. Phys., 23:213-27. 1952 L90] The significance of the results of microwave spectroscopy to the theory of magnetism. Ann. N.Y. Acad. Sci., 55:928-42. 1953 L91] Models of exchange coupling in ferromagnetic media. Rev. Mod. Phys., 25:220-27. L921 Two barrier phenomena. (Retiring address as president of the American Physical Society.) Phys. Today, 6:5-11. L93] With A. Abragam. Theory of the microwave Zeeman effect in atomic oxygen. Phys. Rev., 92:1448-55. 1954 L94] With G. R. Gunther-Mohr and C. H. Townes. Hyperfine structure in the spectrum of Ni4H3, II. Theoretical discus- sion. Phys. Rev., 94: 1191-1203. L951 With K. Kambe. Improved theory of the Zeeman effect of atomic oxygen. Phys. Rev., 96:66-71. L96] The cohesive energies of alkali metals. Proc. Int. Conf. Theor. Phys., Kyoto and Tokyo, pp. 640-49. 1955 L971 The role of Boltzmann factors in the impact model. Proc. Conf. Broadening of Spectral Lines. Pittsburgh: University of Pittsburgh. 1956 t981 Fundamental theory of ferro- and ferri-magnetism. Proc. IRE, 44:1248-58. t99] The theory of ferromagnetic anisotropy. AIEE Special Pub- lication T-91, Conference on Magnetism and Magnetic Ma- terials, October 16 -18.

JOHN HASBROUCK VAN VLECK 535 [100] Blurred borders of physics and engineering. J. Eng. Educ., 46:366-73. 1957 t1011 Dangerous gulfs: Some reflections on the social implications of computing machines. In: The Computing Laboratory in the University, ed. Preston C. Hammer, pp. 223-32. Madison: The University of Wisconsin Press. F1021 With H. Meyer and Mary C. AI. O'Brien. The magnetic sus- ceptibility of oxygen in a clathrate compound, II. Proc. R. Soc. London, Ser. A, 243:414-21. 1031 Magnetic properties of metals. Nuovo Cimento, Suppl., 6:857-86. 1041 Line-breadths and the theory of magnetism. Nuovo Ci- mento, Suppl., 6:993-1014. F1051 The concept of temperature in magnetism. Nuovo Cimento, Suppl., 6: 1081-1100. 1958 1061 With }. Van Kranendonk. Spin waves. Rev. Mod. Phys., 30: 1-23. L107] The physical meaning of adiabatic magnetic susceptibilities. Z. Phys. Chem., 16:358-67. t1081 The magnetic behaviour of regular and inverted crystalline energy levels. Faraday Discuss. Chem. Soc., 26:96-102. 1959 L1091 Some recent progress in the theory of magnetism for non- migratory models. i. Phys., 20:124-35. F1101 Fundamental questions in magnetism. In: Magnetic Properties of Metals and Alloys, pp. 1-17. Metals Park, Ohio: American Society for Metals. 1960 F1111 The puzzle of spin-lattice relaxation at low temperatures. In: Quantum Electronics, a Symposium, ed. C. H. Townes, pp. 392- 409. New York; Columbia University Press. ~112] With C. Kittel. Theory of the temperature dependence of the magnetoelastic constants of cubic crystals. Phys. Rev., 118:1231-32.

536 BIOGRAPHICAL MEMOIRS [113] With W. P. Wolf. Magnetism of europium garnet. Phys. Rev., 118: 1490-92. With R. M. Bozorth. Magnetic susceptibility of metallic eu- ropium. Phys. Rev., 118: 1493 -98. Frontiers of physical science in the Netherlands and the United States. Inaugural address as Lorentz Professor at the University of Leiden, March 4. Leiden: Leiden University Press. t1161 Note on the gyromagnetic ratio of Co++ and on the ~ahn- Teller effect in Fe+ +. Physica, 26:544-52. 1961 L1171 Relaxation mechanisms in nuclear magnetic resonance. Ned. Tijdschr. Natuurk., 27: 1-21. F1181 With I. A. White. Sign of Knight shift in samarium inter- metallic compounds. Phys. Rev. Lett., 6:412-13. L1191 Primitive theory of ferrimagnetic resonance frequencies in rare-earth iron garnets. Phys. Rev., 123:58-62. L120] Theory of the magnetic susceptibility of the nitric oxide clathrate. }. Phys. Chem. Solids, 20:241-54. L1211 With B. T. Matthias and R. M. Bozorth. Ferromagnetic in- teraction in EuO. Phys. Rev. Lett., 7:160-61. F122] Recent developments in spin-lattice relaxation. In: Advances in Quantum Electronics, ed. I. R. Singer, pp. 388 - 98. New York: Columbia University Press. 1962 F1231 Exchange fields in rare earth iron garnets. J. Phys. Soc. Tpn., Suppl. B-I, 17:352-57. (Also in: Proc. Int. Conf. Magn. Crys- tallogr. 1961, vol. I.) 1 24] The so-called age of science. In: Cherwell-Simon Memorial Lec- tures, 1961-62, pp. 25-50. Edinburgh: Oliver and Boyd. L125] Note on the interactions between the spins of magnetic ions or nuclei in metals. Rev. Mod. Phys., 34:681-86. F1261 Note on the use of the Dirac vector model in magnetic ma- terials. Rev. Univ. Nac. Tucuman, Ser. A, 14:189-96. F1271 The magnetism of some rare-earth compounds. In: Physical Sciences: Some Recent Advances in France and the United States, ed. H. P. Kallmann, S. A. Korff, and S. G. Roth, pp. 113- 28. New York: New York University Press.

JOHN HASBROUCK VAN VLECK 1963 537 L1281 With R. Orbach. Ferrimagnetic resonance of dilute rare- earth doped iron garnets. Phys. Rev. Lett., 11 :65-67. L129] The theory of paramagnetic relaxation. In: Magnetic and Electric Resonance and Relaxation, Proceedings of the 11th Colloque Ampere, Eindhoven 1962, ed. J. Smidt, pp. 1-13. Amsterdam: North-Holland Publishing Co. L130] With W. H. Brumage and C. C. Lin. Magnetic susceptibility and crystalline field levels of ytterbium gallium garnet. Phys. Rev., 132:608-10. L1311 With R. C. LeCraw, W. G. Nilsen, and i. P. Remeika. Ferrom- agnetic relaxation in europium iron garnet. Phys. Rev. Lett., 11 :490-93. 1964 F1321 Ferrimagnetic resonance of rare-earth-doped iron garnets. Ferromagnetic resonance and relaxation. i. Appl. Phys., 35:882-88. L133] American physics comes of age (Michelson Prize Address). Phys. Today ~ June) :21-26. F1341 Theory of the relaxation of rare-earth iron garnets. In: Pro- ceedings, Magnetism Conference, Nottingham, pp. 401-3. 1966 F1351 With D. L. Huber. The role of Boltzmann factors in line shape. Rev. Mod. Phys., 38:187-204. 1361 With David Middleton. The spectrum of clipped noise. Proc. IEEE, 54: 2 - 19. F1371 The magnetic history of the rare earths. In: Proceedings of the Fourth Rare Earth Conference, Phoenix, April 1964, pp. 3-17. New York: Gordon and Breach. F1381 With M. M. Schieber and C. C. Lin. The magnetic behavior of thulium garnets in a cubic field. }. Phys. Chem. Solids, 27: 1041-45. L1391 Note on the crystal field parameters of rare earth garnets. t. Phys. Chem. Solids, 27:1047-51. F140] The molecular field model of exchange coupling in rare earth materials. In: Progress in the Science and Technology of the Rare Earths, vol. 2, pp. 1-22. New York: Pergamon Press.

538 BIOGRAPHICAL MEMOIRS t1411 Some elementary thoughts on the Slater intra-atomic ex- change model for ferromagnetism. In: Quantum Theory of Atoms, Molecules, and the Solid State, pp. 475-84. New York: Academic Press. 1967 L1421 The evolution of crystal field parameters for rare earth salts. In: Interaction of Radiation with Solids, pp. 649-62, New York: Plenum Press. L1431 Thirty years of microwave spectroscopy (Fourth Annual A1- pheus W. Smith Lecture). Columbus: Ohio State University. 1441 Non-mathematical theoretical physics. Sci. Light (Tokyo), 16:43-49. 1968 [145] Magnetic case history of the Eu3 - ion. J. Appl. Phys., 39:365-72. do. ~ 1461 The widening world of magnetism. Phys. Bull., 19: 167-75. L1471 With N. L. Huang. Strong orbital anisotropy in the exchange interaction in Fe3+Eu:GaG. Solid State Commun., 6:557-59. 148] With Sidney Coleman. Origin of "hidden momentum forces" on magnets. Phys. Rev., 1 7 1 (51: 1 370-75. 1491 My Swiss visits of 1906, 1926, and 1930. Helv. Phys. Acta, 41:1234-35. 1969 F1501 With N. L. Huang. Isotropic coupling caused by anisotropic exchange in Eu=?O3. In: Polarization, Matiere et Rayonnement, volume jubliaire en lthonneur d'Alfred Kastler, pp. 507-21. Paris: Presses Universitaires de France. t1511 With N. L. Huang. Note on the Dirac electron and hidden momentum forces. Phys. Lett., 28A:768-69. L1521 With N. L. Huang. Effect of the anisotropic exchange and the crystalline field on the magnetic susceptibility of Eu~O~. J. Appl. Phys., 40: 1144 -46. L1531 With N. L. Huang. Magnetic susceptibility of nitric oxide molecules absorbed on silica gel. }. Chem. Phys., 50:2932- 35.

JOHN HASBROUCK VAN VLECK 539 1970 [154] A third of a century of paramagnetic relaxation and reso- nance. In: Magnetic Resonance (a symposium held in Mel- bourne, 1969), pp. 1-10. New York: Plenum Press. L155] Spin, the great indicator of valence behavior. Pure Appl. Chem., 24:235-55. L1561 Group theory for permutation degeneracy in four electrons, and the Pauli exclusion principle. Bull. Polytech. Inst. Jassy, Rumania, 16~20~:3-4. L1571 A lyrical account of magnetism, prelude to a new journal. Int. }. Magn., 1:1-9. 1971 F1581 Reminiscences of the first decade of quantum mechanics. Int. I. Quantum Chem., 5:3-20. 1972 L1591 With R. M. Bozorth and A. E. Clark. Magnetic crystal ani- sotropies of holmium-erbium alloys. Int. I. Magn., 2: 19-31. L1601 On the theory of the dielectric constant of dilute solutions of polar molecules in non-polar solvents. Mol. Phys.,24:341- 48. L1611 Travels with Dirac in the Rockies. In: Aspects of Quantum Theory, ed. A. Salam and E. P. Wigner, pp. 7-16. Cambridge: Cambridge University Press. 1973 F1621 Central fields in two vis-a-vis three dimensions: An historical divertissement. In: Wave Mechanics, pp. 26-37. London: Butterworths. F1631 X = C/(T + 1~), The most overworked formula in the history of paramagnetism. Physica, 69: 177-92. 1974 F1641 With M. E. Foglio. Theory of the magnetic anisotropy and nuclear magnetic resonance of europium iron garnet. Proc. R. Soc. London, Ser. A, 336:115-40. 1651 Koninklijke Nederlandse Akademie van Wetenschappen. Bijzondere Bijeenkomst der Afdeling Natuurkunde op za

540 BIOGRAPHICAL MEMOIRS terdag 28 September 1974, des namiddags te 3.30 our, voor de plechtige uitreiking van de Lorentz-medaille aan Prof. Dr. }. H. Van Vleck. Cambridge: Harvard University, 13 pp. 1975 L1661 With M. E. Foglio and R. F. Sekerka. Theory of the width of the ferromagnetic resonance line of europium iron garnet. Proc. R. Soc. London, Ser. A, 344:21-50. 1977 F1671 With D. L. Huber. Absorption, emission, and linebreadths: A semihistorical perspective. Rev. Mod. Phys., 49:939-49. 1978 L1681 Quantum mechanics: The key to understanding magnetism. Science, 201: 113-20. 1980 t169] Reminiscences of my scientific rapport with R. S. Mulliken. i. Phys. Chem., 84:2091-95. BOOKS 1926 Quantum Principles and Line Spectra. Washington, D.C. search Council Bull. 54. 316 pp. 1932 : National Re The Theory of Electric and Magnetic Susceptibilities. Oxford: Oxford University Press. 384 pp.

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Biographic Memoirs: Volume 56 contains the biographies of deceased members of the National Academy of Sciences and bibliographies of their published works. Each biographical essay was written by a member of the Academy familiar with the professional career of the deceased. For historical and bibliographical purposes, these volumes are worth returning to time and again.

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