San-ichiro Mizushima and Pauling’s 1955 Visit to Japan

4Pauling’s itinerary and schedule during February 21 to March 11, 1955, appear similar to what was earlier planned in correspondence with San-ichiro Mizushima (1899–1983), Professor of Physical Chemistry at the Tokyo University and a leading researcher at the Riken (Institute of Physical and Chemical Research). Mizushima first attracted international attention with a 1926 paper, published in English, which provided experimental support for Peter Debye’s theory of the dipole moments of molecules. Invited by Debye to Leipzig, Mizushima learned quantum mechanics, with applications to chemistry, and, upon his return to Tokyo, investigated molecular structures using Raman and infrared spectroscopy, electron diffraction, and dipole moment measurements. He began corresponding with Pauling in February of 1936 about their common research interests, including Mizushima’s investigations, in collaboration with Yonezo Morino, of internal rotation around a C-C single bond in the dichloroethane molecule.4

5By the early 1950s Pauling and his Caltech collaborators Verner Schomaker and Robert B. Corey were following Mizushima’s publications on internal rotation and on proteins that were appearing in the Journal of Chemical Physics and the Journal of the American Chemical Society (JACS). Mizushima visited Pasadena in late September of 1950 following an invited talk at an American Chemical Society symposium in New York, and in 1951 he gave lectures at several American universities, including Cornell and Notre Dame, which resulted in the 1954 book Structure of Molecules and Internal Rotation. The physical organic chemist and historian of chemistry Stephen J. Weininger remembers the book as the first text by a Japanese author that Weininger ever consulted while in graduate school at the University of Pennsylvania in the early 1960s. Mizushima held a visiting professorship at the University of Notre Dame in the 1950s, where he may have felt especially at ease because he was Roman Catholic, and he continued to pay visits to Pasadena.5

6It is hardly surprising that Pauling worked with Mizushima in planning his and Ava Helen’s visit to Japan. The schedule that Pauling eventually followed was a busy one, punctuated by sightseeing, and so enjoyable that he extended the trip several days beyond his original itinerary, writing to his secretary Beatrice Wulf in Pasadena that “Bangkok was fun, but nothing compared with Japan.”6

7Pauling and Ava Helen had arrived in Tokyo from Bangkok.7 They stayed in Tokyo at the Imperial Hotel, and his first lecture (February 22) was on “The Chemical Bond” at Tokyo University, followed by a Chemical Society reception and dinner at the Gakushi Kaikan, a kind of university club established in 1928 for the seven imperial universities. There was sightseeing in Tokyo and then seminars and lectures in the next few days on “Proteins” and the “Hemoglobin Molecule in Health and Disease” at Tokyo University. Pauling also enjoyed an evening of Kabuki theatre and a dinner hosted by the Asahi Press.

8Pauling and Ava Helen were in Kyoto for his 54th birthday on February 28. Hideki Yukawa (1907–1981), Nobel Physics Laureate in 1949 for his theoretical work on nuclear forces and his prediction of the existence of the meson, was among those who watched Pauling cut a birthday cake. Pauling visited Kyoto University on March 1, gave a public lecture on hemoglobin in health and disease at Osaka University on March 2, spent time sightseeing in Osaka and Nara the next day before a morning seminar on proteins in Osaka, and then returned by train to Tokyo where Mizushina joined him for the last part of the trip in order to discuss arrangements for a speech to be made for Japan’s National Broadcasting Corporation. Most of the last part of Pauling’s time seems to have been spent sightseeing and visiting with friends, including stops in Kamakura and Hakone.

9Pauling’s biographer Thomas Hager reported that Pauling was “mobbed” in Tokyo and Kyoto, where his public lectures were so popular that hundreds of people had to be turned away. Pauling was known in Japan not only as a great scientist, but also as an activist scientist who had been speaking out against atomic weapons and in favor of world peace. His arrival in Japan occurred just a year after the United States had detonated the Bravo hydrogen bomb test at Bikini Atoll, dumping radioactive debris on US servicemen, Marshall Islanders, and the Japanese crew of the Lucky Dragon (Fukuryu Maru) fishing boat.8 In Pauling’s March 10 radio speech, he explicitly spoke of deaths from wartime and postwar radiation, and about health and long term genetic dangers of radioactive fallout, praising the Japanese government for its commitment to demilitarization and calling upon scientists to work toward world peace. His later trips to Japan focused on the issues of nuclear disarmament and world peace.9

Pauling’s Long Friendships with Yoshikatsu Sugiura and Yoshio Nishina

10In setting up his visit, Pauling had asked Mizushima to arrange a visit with the widow of Yoshio Nishina (1890–1951). Nishina had died in early 1951 and had been a good friend since Pauling’s visit to Niels Bohr’s Institute in Copenhagen in 1927 during Pauling’s first trip to Europe on a Guggenheim Fellowship. Pauling also asked Mizushima to see Yoshikatsu Sugiura (1895–1960) whom he likewise had first met in Copenhagen10. While Nishina’s name is closely associated with the development of quantum physics both in Europe and in Japan, it was Sugiura who introduced quantum chemistry into Japan when he returned in 1927 to Riken after three years on a Riken postdoctoral fellowship in Europe.11

11Sugiura had obtained his Ph.D. under Hantaro Nagaoka (1865–1950), with investigations of the hyperfine structure of spectral lines, and he developed his work in Copenhagen in discussions with Bohr, Werner Heisenberg, and occasionally Oskar Klein. Later, in Göttingen, Sugiura worked under Max Born and stayed in the same boarding house as Paul Dirac and Robert Oppenheimer, who became good friends.12 It was here that Sugiura completed his first internationally known work by calculating the exchange integral that was needed for the explanation of covalent bonding between two hydrogen atoms. He had begun his work before seeing a proof of what became the famous 1927 paper on hydrogen bonding by Walther Heitler and Fritz London, and he was able to complete the solution to the problem.13

12Pauling, who had met Sugirua in late April 1927, independently tried to evaluate molecular integrals for simple molecular systems. Once he learned of Sugiura’s evaluation, Pauling came to think that his efforts were wasted.14 How closely Pauling and Sugiura stayed in touch is not clear in Pauling’s papers. But Professor Sugiura of Rikkyo University was one of the honored guests at the Chemical Society reception and dinner for Pauling on February 22.15

13Yoshio Nishina (1890–1951) died a few years before Pauling’s first visit to Japan, but he was even closer to Pauling personally than was Sugiura. Like Sugiura, the young Nishina had worked under the direction of Nagaoka who sent him to Europe, where Nishina spent time in Cambridge, Göttingen, and Copenhagen. When Nishina’s Riken support came to an end, Bohr arranged fellowships for him so that he could remain in Europe where he worked in Copenhagen with George de Hevesy and Dirk Coster, among others. Nishina spent some time in Paris and in Hamburg, where he worked under Wolfgang Pauli’s guidance and published a paper with Isidor Rabi on the dispersion of x-rays. Returning to Copenhagen, Nishina collaborated with Oskar Klein in using Dirac’s new relativistic electron theory to calculate the cross section for Compton scattering of free electrons.16

14Nishina was in Copenhagen during April and May of 1927 at the time of Pauling’s stay there, and they got on well together. Nishina left Copenhagen to return home in late October 1928. The trip included a stop at Arthur Compton’s laboratory in Chicago and a visit to Pasadena and the Mount Wilson Observatory in late December before sailing from San Francisco to Kobe.17 Nishina saw the Paulings in Pasadena, and he wrote them postcards in April of 1929 with news of his difficulties in readjusting to life in a Japan that had been much changed by the earthquake of 1923 and by his marriage a few weeks previously.18

15Nishina received his doctoral degree in 1930 from Tokyo Imperial University and began giving lectures on quantum mechanics in Japan, including a series of lectures in 1931 at Kyoto University. He arranged visits to Japan of European leaders in quantum mechanics, including Heisenberg and Dirac in 1929, Hevesy in 1931, and Bohr in 1937. Nishina stood by and translated his European visitors’ lectures as they delivered them and then edited and published the lectures.19

16In July of 1931, Nishina became a chief researcher at Riken with his own research group, emulating the leadership styles that he had found in Cambridge and Copenhagen and eventually building a program in nuclear physics.20 His 26-inch and 60-inch cyclotrons, modeled on those at Ernest Lawrence’s laboratory in Berkeley, were destroyed after the war because of his laboratory’s wartime participation in the Japanese Army atomic bomb project. After obtaining Allied security clearance, however, Nishina became a principal scientific liaison with Allied authorities and one of the most important scientists in Japan.21 He visited Pasadena in the spring of 1950, by which time he had been President of Riken since 1946, where he was rebuilding the postwar research institution. He remained keen on applications of quantum mechanics in theoretical chemistry and corresponded with Pauling about translations into Japanese of Pauling’s books.22 Pauling must have greatly missed the presence of Nishina when he visited Japan in 1955.

Masao Kotani and the Uses of Atomic Orbital and Molecular Orbital Methods in Japanese Theoretical Chemistry

17Among those who were invited to the Chemical Society reception and dinner for Pauling was Masao Kotani (1906–1993), who was a molecular physicist and Professor of Physics at the University of Tokyo. Kotani and Pauling began corresponding in the late 1930s about Kotani’s work in calculating molecular integrals for diatomic molecules. Kotani sent Pauling his research group’s first “Tables of Integrals Useful for the Calculation of Molecular Energies”, published in 1938, and later sent progress reports of his group in the 1950s.23

18Kotani had first learned quantum mechanics in small reading groups of friends who studied the journal papers and books of Born, Heisenberg, Schrödinger, Dirac, and other European physicists.24 His physics education and early research took place entirely at Tokyo’s First High School and Tokyo Imperial University, where he moved up the ranks from Lecturer to Professor between 1929 and 1943. He traveled abroad for the first time only in 1950, after the war, with a trip to Paris followed by trips to Copenhagen and London.

19In September 1951 Kotani was in New York to attend overlapping meetings of the American Chemical Society, the International Congress of Chemistry, and a Shelter Island Conference on Long Island organized by Robert Mulliken, a pioneer of the molecular orbital (MO) approach in quantum chemistry, which was the rival to Pauling’s atomic orbital (AO) theory.25 The atomic orbital theory had its origins in the Heitler-London method of 1927 for calculating resonance wave functions of electrons or electron density between atomic nuclei. The AO theory is consistent with traditional chemical theories of a valence bond between two atoms. Pauling (at Caltech) and John C. Slater (at MIT) developed AO theory for larger molecules in the late 1920s and early 1930s. Independently, also in the late 1920s and early 1930s, Friedrich Hund in Leipzig, Erich Hückel in Stüttgart, and Mulliken in Chicago developed MO theory. This approach assumes that each electron in a molecule moves in a potential field that results from all the nuclei and other electrons present in a molecule. Pauling had no sympathy for MO on grounds of its intrinsic mathematical complexity and his view that MO is an abstract physical theory rather than a theory based in chemical intuition and representation.26

20One of the emphases at Mulliken’s 1951 Shelter Island conference was the need for tables of previously calculated molecular integrals, a task that had been inaugurated by Sugiura and continued by Kotani’s group in Tokyo.27 By this time, postwar electronic computers were becoming available to research teams, making feasible the previously impossibly time-consuming calculations required in the MO approach. Some physicists, such as Kotani, used both approaches in their work.28 In addition, the emphasis of MO theory on molecular spectroscopy was appealing to Japanese scientists interested in the electronic structures of molecules, such as Mizushima’s student Saburo Nagakura (1920–2020) and his group at the University of Tokyo.29

21Kotani helped in organising an international theoretical physics conference in Kyoto in September 1953, a major postwar scientific event in Japan, along with a two-day symposium that took place at the Nikko national park. Mulliken, Slater, and Per Löwdin gave lectures in Kyoto, and the seventeen foreign attendees included Charles Coulson and John Van Vleck.30 Kotani discussed with the foreign scientists recent research at the interface of physics and chemistry called Busseiron in Japan, and he explained the work in terms of statistical mechanics and solid-state physics for participants such as Slater, Frederick Seitz, and Lars Onsager.31

22Kotani and Pauling first met in Japan in the spring of 1955. Pauling had declined to attend Mulliken’s Shelter Island Conference in 1951, and he was not present in Kyoto in 1953.32 When Pauling came to Japan in 1955, he seems not to have been aware of the very recent work of Saburo Nagakura at the University of Tokyo and of Kenichi Fukui (1918–1998) at Kyoto University, both of whom were pioneering MO theory in Japan.33 In 1981 Fukui was to become the first Japanese Nobel laureate in chemistry and the third laureate in quantum chemistry (following earlier awards to Pauling in 1954 and to Mulliken in 1966). As detailed by Yasu Furukawa, Fukui was educated in chemistry at the Kyoto Imperial University Faculty of Engineering, where he taught himself quantum mechanics from mostly German literature. During wartime research on synthesis of gasoline additives, he formulated the idea of studying the quantum mechanics of chemical reactions of hydrocarbons, rather than focusing on the roles in chemical reactions of geometry and molecular structure.34

23Using Erich Hückel’s molecular orbital methods and a mechanical calculator, Fukui calculated the electron density of the naphthalene molecule and proposed that the molecule’s unexpected reactivity at unpredicted sites in electrophilic substitution was best explained by what he called frontier orbital theory, i.e., that the highest occupied molecular orbital of one reactant and the lowest unoccupied molecular orbital of the other play a dominant role in chemical reactions. His surprising new theory, published in a series of papers in the Journal of Chemical Physics beginning in 1952, was supported by Robert Mulliken’s 1952 charge (or electron) transfer theory for overlapping molecular orbitals and by the work more than a decade later on conservation of orbital symmetry by Robert Woodward and Roald Hoffmann.35

Characterizations and Recognition of Japanese Science around 1955

24There is no record of Japanese chemists or physicists discussing with Pauling the avant-garde work at Tokyo and Kyoto using molecular orbital theory. Indeed Pauling’s focus in the 1940s had gradually turned away from quantum mechanics to the structure of proteins and other very large organic and biological molecules, such as the proteins hemoglobin and keratin, and to nucleic acids and genetic materials such as DNA. By 1955, identification of the molecular basis for genetic diseases had become the dominating interest in Pauling’s scientific program. In this, he was influenced by his deep concern about genetic mutations that could be caused by radioactive fallout from the testing of nuclear weapons, the subject principally addressed in his March 10 speech on Japan’s public broadcasting system.36

25Neither during his visit to Japan nor later did Pauling seem to ruminate on ways in which Japanese and Western scientists might differ or converge in their approaches to understanding the world. It must be noted, however, that Pauling did not think of himself as a meditative or “philosophical” type. Some Japanese scientists, Yukawa among them, wrote popularly about effects of cultural differences on scientific practices, notably in Yukawa’s 1973 collection of essays entitled Creativity and Intuition: A Physicist Looks at East and West37. The historians Kenji Ito, Morris Low, and Dong-Won Kim are among those who have written on ways in which Nihonjinron (theories of distinctive Japanese character) may or may not apply in Japanese physics.38

26Reflections on that question appear in Mizushima’s article “A History of Physical Chemistry in Japan” published in the Annual Review of Physical Chemistry in 1972, a year before Yukawa’s book.39 In his essay, Mizushima discusses at some length the contrasts he sees between East and West, and how the contrasts have changed or not changed, especially in the sciences. Just after the Meiji Restoration in 1868, he writes, the phrase “Japanese spirit and Western technology” signified what became a traditional practice in Japan of introducing new culture not by substitution, but by placing ideas or customs side by side, preserving the old, while adopting the new.40

27When late nineteenth-century policies of the Japanese government for study abroad brought Western science and mathematics more centrally into Japanese education, Mizushima suggests, Japanese aesthetic sensibility remained one of simplicity and irregularity, exemplified in Japanese floral arrangements or in painting, in strong contrast to Western preference for complexity and symmetry.41 Mizushima does not suggest, however, that there are substantive differences between Japanese and Western methods and theories in contemporary physical and chemical sciences.42

28In his autobiography, the Göttingen physicist Max Born referred to Asians who came to study physics in Göttingen as his “exotics”, writing that: “Many foreign students came to work with me. To start with the exotics, there were some Indians and Japanese; of the latter, several became well-known physicists, such as Sugiura.”43

29Indeed, as already discussed, Sugiura and Nishina each completed calculations in quantum mechanics in the late 1920s that had eluded their Western colleagues, and each almost immediately acquired international recognition among international peers. In 1939, Yukawa, who had not studied at all in Europe, became the first Japanese physicist invited to a Solvay Physics Congress, although the Congress never took place because of the outbreak of war in Europe.44 His theoretical work of the 1930s predicted the existence of a nuclear particle heavier than an electron and lighter than a proton, a prediction partially fit by the discovery in 1937 of “mesons” in cosmic rays. The identification by Cecil Frank Powell and Guiseppe Occhialini in 1947 of the pi meson, or pion, which almost exactly fit Yukawa’s prediction, resulted in a cascade of nominations for the 1949 Nobel Prize.45 With the war concluded, the award to Yukawa marked a restoration and new beginning for East-West relations in the sciences.

30When Yukawa learned of the Nobel Prize, he was a visiting professor at Columbia University. In accepting the award in Stockholm, he explicitly spoke of the award’s meaning for the Japanese people in their “reconstruction of Japan as a peaceful and cultural country.” The President of the Swedish Academy of Sciences in turn praised Yukawa as “the first Japanese to receive a Nobel Prize.”

You have told us already what this means, not only to you personally, but also to scientific life in Japan, an enlivening stimulation in these days of great distress. . . And are you not the very best example of the importance of science in bringing nations and races together? Not many years ago Japan and the United States stood against each other, armed to the teeth, bent upon destruction. Today you work happily in the midst of American colleagues.46

31In August of 1983, Pauling received a telegram, while at his ranch in Big Sur, saying that his good friend Mizushima had passed away from lung cancer. There is a reprint in Pauling’s correspondence of a booklet titled “Aus meiner Eurapareise.” It contains poems written by Mizushima, in German and in French, set to music for soprano and tenor. The songs are nostalgic meditations on the Rhine River, Flanders, and Paris, reflecting Mizushima’s visits abroad, his European memories, and his international fluency and sophistication.47 The experiences of Pauling’s first visit to Japan in 1955 owed much to this remarkable Japanese scientist, as well as to the renewed emphasis on exchanges and cooperation between Japanese and American science, both of which had once been on the periphery to European science. Pauling’s visit was one of many events that marked a new era for Japanese science on an international stage, as Japan’s science moved from the global periphery to become one of the global centers.