Context and sources: John Lennard-Jones in Göttingen

Lennard-Jones from [Bristol] came to Göttingen with his family to study crystal theory with me. He continued and improved some investigations of my group concerning the forces which keep the atoms in ionic crystals together.

At the University, Herzberg learned that Professor Born had suffered a nervous breakdown from the long hours and months of strenuous effort in supervising and keeping up with his group of brilliant young theorists. … Born was forced to interrupt teaching and research and relax for much of the year that Herzberg spent in Göttingen.

Mayer: [W]hen I knew him as a student he was quite sick. … Just what was wrong I don’t know.

Kuhn: This went on really for a considerable period of time. He speaks of having had a small breakdown at the end of the summer of ‘25, I think, he places it…

Mayer: Then I am talking about a later time when he left for a semester, and since I was taking his courses you see, I know very well. And he went away—I don’t know where—to recuperate for a semester, and Heitler gave his lectures. And just what was really wrong I don’t know.

Kuhn: But you had seen signs of this before.

Mayer: Oh yes. He was nervous you see, and occasionally—. I know once we intended to go skiing—his wife and I and some others. We were already on the train. Born said he couldn’t go, left the train and went back. I don’t know why he said it, there wasn’t any disagreement in talk or anything. There was nothing. He suddenly said he didn’t feel like it—he couldn’t.

At the same time, however, it became clear that our familiar concepts such as position and velocity, wave and particle, could not simply be applied to the world of atoms. Born made a significant contribution to clarifying the meaning of matter waves. All of this crashed down on the uninitiated student like a waterfall in 1928. … We were somewhat overwhelmed. Unfortunately, Born couldn’t help much at that time, as he became ill and could only give a few lectures. We learned quantum mechanics from the lectures of G. Herzberg and W. Heitler. Both were young lecturers at that time. Herzberg’s lectures were then published as a book that is still one of the best introductions to atomic physics.

The poor condition of my nerves, frequently mentioned in these letters, was due not only to overwork but also to other worries, mainly political ones. At the beginning of the year 1929, I think, I was sent to a sanatorium at Constance on Lake Constance; there I was kept in bed at first, but was later allowed to sit in the lounge and talk to people. But the conversation of the patients, who were manufacturers, doctors, lawyers, or at any rate all people from the upper middle classes, was almost wholly about Hitler and the high hopes they had of him, interspersed with virulent attacks on the Jews. This drove me back to my room again. I was only able to recover completely when I escaped from the sanatorium and went to Köningsfeld in the Black Forest.

At this period quantum mechanics was being developed and my father received an invitation in 1929 from the Rockefeller Foundation to visit laboratories in Germany to study these advances. As a family we moved to Göttingen of which my only memory is that a monkey at the zoo reached out and took a lock of my hair to the consternation of my parents. While there my father learned to speak German—said in later years to be fluent—but with a Bavarian accent.

“[T]he atmosphere in Göttingen was delightful; it was simply delightful with Born and Franck at the head and a number of other very nice people as well. [...] There was a very friendly atmosphere, and everything was discussed. The atmosphere was quite favorable for my interests in chemical bonds and molecules too, because Franck at that time was working on molecules—Franck and Sponer and Herzberg too. At that time I studied all that I had missed before—the papers by Heisenberg, Born and Jordan on matrix mechanics, especially papers by Dirac which I read through in one night, all of them.”

[T]he wonder of chemical binding forces, as produced by the formerly unknown exchange integrals, was on the way to being understood, thanks to the application of wave mechanics to the hydrogen molecule by the world-renowned firm of Heitler and London. The former was a Göttingen man acting as Born’s assistant, and a not-too-sophisticated person, who was both able and willing to share his knowledge with less experienced people. …

In those days an institute for theoretical physics was not supposed to be in need of any room for its own purposes. It existed as a formal entity in virtue of the presence of a professor or leader, mostly residing at his home. Nevertheless, Born had—apart from his own office—succeeded in acquiring a room for his institute in which I had the opportunity to work when needed. … In this room was installed a 10 x 10 automatic electric desk computer, an excellent Mercedes [Euklid].

“[I]n Göttingen, there was a visit for six months by Lennard-Jones, who was a theoretician and was very much interested in the kind of work I was doing. I had already started writing an article on an extension, if you like, of what Hund and Mulliken had written. It later served as my thesis for the Habilitation in Darmstadt. When I came to Göttingen I talked to Heitler (of Heitler and London, the famous paper on the hydrogen molecule). He was in Göttingen as a “Privatdozent” and he was quite interested in the experimental results that I quoted in this, what you might call semi-theoretical paper. …

[I]t was actually due to Lennard-Jones who was visiting Göttingen for six months, and with whom I had a fair amount of contact because he was quite interested in my ideas, in fact my Habilitationsschrift was about molecular orbital theory. He was writing a paper on molecular orbital theory and found that I was on similar lines to what he had to say, so he suggested that I should come on another postdoctoral fellowship, to Bristol, where he was the theoretician, and I accepted that offer.

Almost the first person that I met in Göttingen was a man only a few years older than I was. Walter Heitler was the initiator, with Fritz London, of the wave-mechanical treatment of the problem of chemical valence, in particular, the understanding of the formation of the H₂ molecule. I had found some experimental results while still in Darmstadt about certain molecules like CN and N²⁺ and I discussed them with Heitler on the basis of his theory and we thought we had an interesting development. It turned out to be wrong, or, rather, not very significant, if you like. But it gave me a start to talk to people and of course the people I really wanted to work with—James Franck, who was an experimentalist, and Max Born, who was a theoretician. I don’t know whether I ever thought about becoming a theoretician, I don’t think I did, but I spent officially, at any rate, the first six months in Max Born’s institute [to which Heitler belonged], and the second six months in James Franck’s institute. …

Lennard-Jones was another one of those visitors that came along at the time of my stay in Göttingen. He was a theoretician and interested in molecular orbital theory. I was just then in the process of writing a lengthy paper on molecular orbital theory from a more experimental point of view. We had lots and lots of discussions at the time and indeed Lennard-Jones was preparing a summary paper on the subject for this very meeting on molecular structure that I was attending during my first few days in Bristol [Faraday Society Meeting “Molecular Spectra and Molecular Structure ”, September 24-26, 1929]. If you compare our two papers there’s quite a similarity in their points of view. Certainly Lennard-Jones had some good ideas. He was a very clear writer. I enjoyed the contacts with him[.]

Dr. G. Herzberg informed me about his application and asked me to write a few words on his personality. I fulfill his desire with great pleasure because he is one of the most able young scientists in the field of molecular physics whom I met. … Herzberg is a specially able experimental and theoretical spectroscopist. He published a great deal of very interesting papers on molecular spectra, and moreover a very important theoretical contribution to this field. I know him also personally because he worked after his degree for a year in Göttingen in my former institute. In this time I found, Dr. Herzberg is a very kind personality[,] a very good teacher[,] and especially able and industrious. I really believe we have not many physicists of his age who are to compare with him[.]

I asked Heitler whether he didn’t know of a quick topic for a PhD thesis. He suggested that since he and Fritz London had just made a quantum mechanical theory of the hydrogen molecule, which explained reasonably satisfactorily the strong bonding of the two hydrogen atoms in terms of what was called an exchange integral, it might be interesting to look into the lithium molecule. … That turned out to be a nightmare, because this is wave mechanics and perturbation theory; it involves calculating integrals over the space of the two electrons involved – that means six dimensional integrals with wave functions around two different centers. … [And] no computers. … Well, by hook or by crook I finally put a thesis together [in 1929]. … It was accepted as a thesis and on the strength of this I was recommended by my professor. The official professor was Max Born, but Heitler was the one who directed or helped me a little – but I don’t know how much he helped me. Anyhow, Max Born recommended me for a job in Bristol University in England, and that was because the professor of theoretical physics from there [Lennard-Jones] had come to Göttingen also to learn quantum mechanics. [H]e was there only for three months and didn’t know any German, so he decided he needed some more [tutoring]; so I was recommended to teach him some more quantum mechanics.

Born had an agreement with the Lennard-Jones laboratory in Bristol to send one of his assistants there on a rotating basis for one year at a time. In 1932-33, this was Martin Stobbe. … Born was able to negotiate an early exchange of Heitler with Bristol for Stobbe, who, as an “Aryan,” was not at risk.

[Delbrück was] a very brilliant fellow, and he wrote a very good thesis—this was later, it must be ’28. or ’29. But when he came to the orals [Professor Robert Wichard] Pohl objected to his answers on experimental questions and insisted on his having failed. I wasn’t powerful enough like Sommerfeld to bring him through, and so he did fail. And this fellow was so depressed that I feared he would commit suicide. So I took him home because I didn’t want to leave him alone in town. And my wife then told him how silly it was, and she set him right. And we told him that it doesn’t depend on such official things—he should be quite content that his Professor was content with him. And a half year later he got his degree. And now he is one of the leading men in America in genetics—he left physics.