John Wheeler - Session III

GREGORY BREIT

I can't recall how it was I met Gregory Breit's sister. My memory is it was in Baltimore. It was certainly after he was dead, long dead. It might have been through Walter Elsasser, but he too is now gone, so I can't check with him whether it was through him that I met Gregory Breit's sister. But she told me how their father, a business man, had left them in the neighborhood of Odessa, in the south of Russia, on a business trip to America. And then he had, somehow, got the opportunity to make a new life in America, but it was going to be a tight push financially, so that the wife and the children could come over on the ship, but there wouldn't be much in the way of money for anything else. Well, the mother felt that she had to get some clothes for young Gregory, the little boy, and what did she get him? I guess he must have been about high school age at that time, perhaps primary school age. It was hot weather in the south of Russia, and she got him a sailor suit, short pants, and the neck like a sailor. So that's the suit in which he arrived in America.

They settled in Baltimore. He was just about the age to begin university, so he applied to Hopkins and he got in, but he was quite young for his place as a freshman, and here he was in this sailor suit among all these everyday students, he with his foreign background, and he just didn't fit in. I don't know all the troubles that he got into, but he was not exactly a hale fellow well met by the end of the year. I confess that I don't know with whom he worked or what his thesis topic was.

[Coming to a later time], Wigner had lost his position at Princeton, his original position, and Breit had a high regard for Wigner and got him a position at Wisconsin. So it was at Wisconsin that Breit and Wigner wrote together an important paper on the resonance features of an optical or a nuclear cross section. The formula they developed gave the cross section for a reaction or a scattering process and its dependence on energy, and let one predict the angular distribution. It was absolutely essential in the understanding of nuclear reactions.

From Wisconsin Breit moved to New York University. I don't know the how and why of that move. I do know he told me once about having been in an automobile accident and not having adequate insurance, so there was a big financial debt up against his name and he had to pay that off year by year so that he always felt that. Actually, Breit went from NYU to Wisconsin in 1934. Wigner moved to Wisconsin in 1936. The Breit-Wigner formula was published in 1936. (KWF) was strapped financially. What about his wife, Marjorie? My memory is that she was an American, but I don't recall what background.

FIRST POSTDOCTORAL YEAR - WORKING WITH BREIT

At the time I was finishing my graduate work at Johns Hopkins I had to decide what I would do next. Nuclear physics was a coming field, I think everybody felt at the time, and Breit had an interest both in the theoretical and the experimental side of the subject. I must have met him at some meeting and checked out that he would be agreeable to my applying for a National Research Council Fellowship to work with him for my first postdoctoral year on nuclear physics. I perhaps could even get hold of that application and see what words I used. At any rate, here I ended up at New York University in September of 1933, at the end of the summer after my Ph.D. at Johns Hopkins.

Why was Breit at the Bronx division of New York University rather than downtown? The uptown Bronx division of New York University has been abandoned nowadays, if I speak correctly, and I would have to check that to be absolutely sure. It was certainly an extra expense to New York University to have to operate two campuses. I think that the uptown campus always felt a little bit on the defensive, or worried about takeover by the downtown c pus. I can't recall any specific incident that showed the interaction between Breit uptown and our downtown colleagues, but there was a weekly seminar in which Rabi took a prominent part. It was Columbia, uptown, and downtown New York University. [We returned] often after the pow-wow to Rabi's apartment about 450 Riverside Drive in New York.

Breit had another National Research Council Fellow working with him, Norman Heydenburg, who was working on scattering of resonance radiation, a problem in optics which capitalized on some of the insights which were to prove later so important in nuclear physics. Breit also had going other collaborations, one with the people at the [Department of Terrestrial Magnetism at the Carnegie Institution]. He was very keen on getting an accelerator at work there to drive protons to produce nuclear reactions. In addition he had experimental work which I think was connected directly or indirectly with that Washington project, experimental work going at New York University itself.

I never saw the encounter, but I heard about it—Breit in a disagreement with another faculty member at the uptown physics department, and them getting into a wrestling match, ending up on the floor.

Through Breit I met some of the other people there. One of them was Crew. I' m sorry to say I'm not sure of his first name. Was it Henry Crew? At any rate, he was a son of one of the four or five founders of the American Physical Society, and through him I met the father. The father, old Mr. Crew, told me about being in a parade at Princeton, the annual parade at graduation time, marching down Prospect Street. The classes go by years, and his father there in the first contingent, the oldest living graduate of Princeton. I hope I have that right. He was certainly one of the oldest at that time.

There were other people around who collaborated with Breit in one way or another. One was Jenny Rosenthal. I should look up her papers at that time to find out what the subject was, but as I recall, it had to do again with this question of resonance and scattering and the connection between the two and domains of application of a relation like the Breit-Wigner relation.

Hugh Wolfe might have been connected with Columbia or New York University downtown. He had an interest in nuclear questions, reaction rates and so on. Fermi was, of course, working in Italy at this time with his group on reactions caused by neutrons and had marvelous experimental results which interested us all. Breit was interested not only in the physics side of things, but in the mathematics needed to describe the physics. I think especially of alpha particle radioactivity, penetration through a nuclear potential wall—tunneling, as one would say nowadays. The probability of tunneling was connected with the height of the barrier that had to be penetrated and the thickness of the barrier. He was immensely interested in semi-classical method of approximation to exact quantum-mechanical wave functions, and how much difference that would make in these predictions about radioactivity. It was about this time that Atkinson and Houtermans not only proposed that the sun's energy came from fusion reactions involving hydrogen and helium in the sun, but also did a first calculation of the rate of that process. Most people recall Eddington's statement to skeptics about this idea, Eddington saying, "If you don't think the center of the sun is hot enough, go d look for a hotter place."

K: John, on the subject of tunneling: It had been applied to alpha decay. Was this the first subsequent application—the application to thermonuclear reactions— where quantum mechanical tunneling had possible practical application?

I don't recall any other beside alpha decay of the heavy nuclei.

K: It must have been taken into account by Atkinson and Houtermans to get the calculated reaction rates.

Yes. How much was Chadwick guided by such calculations, and to what extent did he just simply plunge ahead and say, "We'll see what happens"? That I'd love to know. That surely is somewhere in the record.

It was not until a few years later that I learned from Heisenberg about the fate of Houtermans, how he had been communist, he'd had to leave Germany, he got a job at Kharkov in the Soviet Union. Then, about that time, Stalin had developed his suspicious streak and imprisoned people right and left. Houtermans was imprisoned in Kharkov, and gives in a book an account of the way in which the prisoners collaborated to produce self-consistent confessions, so that these confessions would link up with each other, and yet one of the requirements that the prisoners imposed on each other was no living person should be implicated. Heisenberg [Houtermans?] demonstrated the method of torture by which the prisoner had to stand close to a wall on his tiptoes tilted toward the wall, with his fingers held against the wall and had to keep that pose hour after hour. We were only then beginning to get acquainted with what the new world would bring both in the Soviet Union and in Germany.

Hugh Wolfe was another colleague in the New York area at that time. I can't recall with which institution he was formally associated, but I do recall going in his car with his driving through the sleet with the windshield just barely kept clear against the ice and snow, driving to a meeting. If I recall, it was in the Boston area, a meeting of the American Physical Society.

Breit had something of the German professor's sense of responsibility to his research students. Saturday afternoons he usually invited us to go for a long walk in the country. We'd take the train from Grand Central Station on to some New York suburb and walk for miles in the woods, and then take the train back. I was sharing a room with Norman Heydenburg in the Bronx at this time. Norman Heydenburg and I would very often have our suppers at the same place. I can recall that the waitress finally got impatient at me because I was always having apple for dessert. "Can't you take out another girl?" she said.

Lunches were at odd and end places near New York University. I recall one lunch where the results were discussed of a nuclear transformation that seemed to violate the rule of either parity symmetry or time reversal symmetry. The conclusion of the colleagues, who knew more than I did, was that this was surely an experimental error, that it couldn't violate such a well-determined principle. Later on it turned out that that was indeed first evidence of a great effect.

Through Breit I was learning about a type of reaction which might be called, I suppose, sub nuclear—the production of electron pairs out of a vacuum by gamma-ray absorption and the Dirac theory of the electron. So he taught me about the Dirac matrices, and we wrote more than one paper together capitalizing on that formalism—production of a pair by the collision of two photons in a vacuum, and the production of a pair by the collision of one photon with the field of force of an atomic nucleus.

The electron seemed like such a beautiful particle, and there were so many sophisticated ways to put electrons together, that I couldn't help feeling that somehow everything must be made out of positive and negative electrons and that the protons and neutrons themselves must be composite.

POSTDOCTORAL YEAR WITH BREIT (continued)

K: In case the previous tape didn't pick up that last sentence about thinking protons and neutrons as composites, you might back up to that.

What was the objection against thinking of electrons and protons as composite?

The connection between spin and the statistics was the vital factor, and there was no evident way one could get something like a neutron with a spin a half and its Fermi statistics out of positive and negative electrons, because there would have to be equal numbers of those particles to get charge neutrality and that would mean Bose statistics. But the book of Mott and Massey was a daily bible and in that I learned that the effective magnetic moment of a particle could be much diminished below its normal value if the particle were going around in a high-speed orbit. I used to dream of that being the story behind the neutron.

This idea of seeing what one can do with positive and negative electrons gave me always an urge to explore the idea of action at a distance between particles as a way to treat conditions where one normally would have thought there would be a lot of radiation. If one could have equal amounts of incoming and outcoming radiation, one could avoid that difficulty with a model of heavier particles made out of positive and negative electrons.

I cannot recall at this time a great deal of attention at Washington Heights, which is the place of uptown New York University—I can't recall any great amount of attention at this time to cosmic-ray work or to Rossi's impressive results on the penetrating power of energetic particles of the cosmic rays.

It was the depths of the Depression at the time that I was at New York University. I could see how many shops along the street had folded up, and the New Deal measures were at work to help people in businesses recover. There was the Works Progress Administration, WPA. That had taken on a lot of people who had lost their jobs and put them to work on projects that qualified. Physics research at New York University qualified and Breit was able to get somebody who was a computer, who had worked a lot with hand computers, who helped on calculating wave functions for particles penetrating a nuclear potential barrier so one could compare accurate results with semi-classical results. I was drawn into supervising that. I feel stupid. I can't right now remember this nice older man's name, nor do I know what eventually happened to him. But he worked away day after day conscientiously on this business. Irving Lowan was another younger colleague who came in from time to time to consult Breit about his work.

I always thought of Breit as being scrupulously fair and sticking to whatever he thought was right regardless of the consequences. It was not until later in life that I had a run-in with him on that account, because he wanted me to subscribe to the no-publish policy about papers in uranium physics. I said yes, if I know whom I'm subscribing to and know how I'll be someday released from this. Well, he was unwilling to concede anything on that score. But he was a leader, one of the several leaders, along with Szilard and Wigner, in getting the American nuclear physics community not to publish on anything that would help reveal important results about fission.

I think probably by now many people that have read the account by Flerov, about his wartime discovery that uranium undergoes spontaneous fission. He had published this, I believe, in Physical Review Letters. At any rate, he and his friends all felt that this was a great discovery and that he would get some great prize in consequence of it. So it was a great disappointment that it seemed to fall like a stone into a tank of oil—no response. And he tells how he was drafted into the military in the Soviet Union and how at one point he was stationed in that town where the journals had been moved for safety during the attack of Moscow, and he got a chance to look at the recent issues, journals from America and other countries. As he went through them, he was astonished to find nothing on nuclear fission. Then he suddenly realized that no information was very great information, and this stirred him up to get others behind the push to get the Soviet Union going in uranium fission work.

Breit's conscientiousness I recall showing up in his marking up of a manuscript for publication in the Physical Review, writing in the margin opposite a Greek letter, writing out and spelling the word and indicating again in colored pencil just how it should be made. But this very conscientiousness, this attention to detail, meant that he really was not the right person to take over any major administrative responsibility in the uranium project. Actually he did not, if I remember right, have any part at all in the Chicago project. At Los Alamos he was drawn into a study of an issue: Was there any danger if a bomb went off that it would somehow ignite the atmosphere and the whole atmosphere would blow up? He and a colleague whose name I can't at the moment remember wrote a definitive paper on that. It wouldn't start a conflagration.

I know that Breit had worked earlier with Ehrenfest, as also Oppenheimer had worked with Ehrenfest, and I had had the great pleasure of meeting Ehrenfest while I was still a graduate student when Ehrenfest came to Baltimore to visit Herzfeld.

I can't recall any day-to-day passion to get the latest bit of information about how things were going in Europe, any day-to-day passion on the part of Breit as I was to see later with others. Perhaps it was because this was the period of the so-called phony war when the Germans and the French confronted each other but neither side made an all-out attack.

K: John, what were the characteristics of Breit that made him antagonize other people, made him unpopular with many physicists?

Well, I was mentioning Tom Griffy. I wouldn't want to use his name here, but Tom Griffy told me hearing Breit at some Physical Society meeting, and Breit turning him off. He was very positive in his views and his statements. I should really talk more with Tom Griffy and get myself up to speed as to what was it that turned him off about Breit. He was very far from a hale fellow well met. He would, while considering a subject, go sniff, sniff. It might have been connected with problems he had because of his heavy cigarette smoking.

K: Was your year with Breit an exciting one? Is it one that you look back on with pleasure and feel was quite valuable?

I feel it was very valuable to me, all the acquaintance with some classical methods, with the most recent results in nuclear physics, with the Breit-Wigner formula [this came later-KWF], and then all this beautiful business about electron-positron physics, that was a joy. I did not at that time get into any of the things he had been involved in earlier—the Heaviside layer or behavior of radio signals in the atmosphere. Why had he been involved in those subjects? I can believe it might have been through his connection with the [Carnegie Institution's Department of Terrestrial Magnetism] in Washington. And why had he had any connection with that? I think because he had colleagues there who depended on him for advice, and because he saw that as a place to get important work done. But I do not know whether he got any financial support from that. There was a conference, more than one conference, at the Carnegie Institution for Terrestrial Magnetism on recent developments in nuclear physics, and Breit had an important part in arranging the program for that. I stupidly confess that I don't know whether he had been the originator of it. It seems to me the name Fleming comes in there. It may well be that somebody named Fleming was the director of the Carnegie Institution. He seemed like a benevolent helper of the nuclear enterprise and he would be present at the opening session of these meetings, but I don't think of him as an initiator.

NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards had people that Breit knew. To what extent was he able to call on them to help on clearing up issues that he was concerned about, that I don't know. I had worked with William F. Meggers at the Bureau of Standards; he had lively colleagues in spectroscopy. Humphries was one—and who was the other?—a hard bitten individual who was fun to kick things around with who had a favorite spider kept in the corner of the window. He would throw a fly and feed him now and again. He told me about his ability to see further in the infrared than most people. Evidently there's quite a bit of variation between one person and another, where his cut-off comes on the wavelength.

K: When did you work with Meggers? Was that while you were a graduate student?

While I was a graduate student, yes. I got $30 a month as a student assistant. That was a program the Bureau of Standards had. I can recall my father saying to me when I was telling him about the measurements of wavelengths and these spectral lines, "Well, don't you do any: g more? What about the brightness of these spectral lines?" Well, we didn't do anything with them.

ROWLAND'S LEGACY

I think it was from Meggers that I learned about this bookkeeper in Baltimore, Mr. Walters, who had brought to Henry Rowland, the great spectroscopist, his sheets where he had analyzed the spectrum of iron and played around with the numbers and found that by taking the reciprocals of the wavelength he could fit them into a pattern. So he had discovered the Ritz Combination Principle years before Ritz, but this didn't go to use because Rowland took it lightly from him and rolled it up and put the roll in his desk.

It wasn't until years later that I learned about mercury having got spilled, and why was mercury spilled there? Anyway, it created a bad atmosphere, but not in the area where I worked. It was a great inspiration, to think more about Henry Rowland, to work with people who every day were using his grating. I think I told the incident about Henry Rowland and the boat that he had built for himself in Baltimore. He insisted on having it painted before it was launched, and the workmen said, "That's never done. You wait and see where the water line is going to be." Rowland said, "Paint it here," and so it was launched and it didn't come out right. Then the workmen all laughed, and Rowland said, "Now put the masts in," and it came out okay.

But the ruling engine: What was the story about Rowland called in as an expert witness in some patent case, and the attorney saying, "What's your status in the world of physics, Professor Rowland?" "I understand I'm under oath. Then I have to confess that I'm the top man." [laughter]

CHOOSING BREIT

Why Breit? I suppose that Breit's having started at Hopkins meant that people at Johns Hopkins had a clearer view of what he had done and was doing than other people. At any rate, the Physical Review gave us all a chance to see who did what, and he counted importantly there in nuclear physics. What had he done, can I name any single thing? Well, the Breit-Wigner formula was so central to nuclear and optical physics that nobody could be unaware of it or its importance. [This is a slip of memory. It came later.] And Breit also had done things in pair theory, which indicated that he was not a one-track physicist. Oppenheimer had a similar record, both in pair theory and in nuclear physics, where he had worked on the so-called Oppenheimer-Phillips mechanism of a deuteron encountering a nucleus and the neutron working its way out of the deuteron into the nucleus to provoke a nuclear reaction.

Van Vleck was also highly regarded by all of us at that time, but his work was more in fields like magnetism and structure of solids, and did not seem so close to the great mysteries as the work of Breit and Oppenheimer. Of course, I had nothing like the acquaintance with either man, Breit or Oppenheimer, at Ns time that I was to get later, Breit by working with him and Oppenheimer through our connection with the wartime project. But I did know that both men had worked with Ehrenfest, and I recall Breit later telling me of a lunch he had with Ehrenfest. Ehrenfest is talking away and talking away and Breit had been responding but not piping up, and finally Ehrenfest saying to Breit, "Breit, behaupten Sie etwas!" ("Breit, stick up for something.") Behaupten Sie etwas.

So I had contacted people, I think by discussion at one or another physics meeting, about the idea of going to do a postdoc for a year, with one or the other. I suppose that what turned me off from Oppenheimer was a slight degree of what you might call know-it-all attitude, whereas Breit was more like me, somebody always puzzling.

K: Was Wigner somebody you considered, or basically only Oppenheimer and Breit?

Yes, I did consider Wigner at this time, but I hadn't really had an occasion to meet Wigner nor had I heard him, to the best of my memory, at any meeting. It was in the fall of my first year with Breit, my only year with Breit, that Wigner called Breit and told him about this Einstein talk that was going to come in Princeton, and it was being kept quiet but if he'd like to come and hear, why, he's welcome to. So that's how come I visited. I can recall at that time also meeting here at Princeton Phil Morse, whom I always enjoyed, and Ed Condon. Condon was in the first year of giving a course in quantum theory, and people told me later of what an inspiration it was to be there in that first year, to see him learning this subject as he taught it. [laughs] Condon at that time was deciding where he would go. Then he ended up, but I'm not sure which year, going to the Westinghouse Company as director of research in Pittsburgh.

CHOICE OF FIELD

At Johns Hopkins Dieke had come and represented molecular physics. It was always a treat to deal with molecular physics and have that case where you could treat the motion of the electrons essentially independent of the motion of the nuclear particles. I can recall that somebody in the chemistry department had put together a model of some complicated molecule, and had hooked it up to a motor with a rubber band, with a motor running at one speed or another, and determined the characteristic frequencies. A marvelous thing, a beautiful business. But I didn't see that there was any really deep mystery involved in the business of molecular physics or what today is called condensed matter physics.

It was about this time that Heisenberg, I guess, had brought in his theory of ferromagnetism, a beautiful business. Was anybody talking at this time in classes about the states of an electron going through a solid—the band gap and such issues? That was really coming on board. You had to follow that at seminars, or reading the literature.

It would be great to go back over the papers at that time and see what were the really great ones. This Fermi paper on beta decay was certainly one of them. I remember Breit having read that and studied it and talking about the impression it made on him. There were, of course, variants that one could consider, and the ones that came up in this country were different forms of coupling. I would like to look them up and see how many of them spoke of having consulted Breit about their ideas.

The neutrino: Certainly one, coming in at this time, got an impression of the reality of neutrinos. That meant that one would always feel keen on experiments, and I could recall in later years talking with Fred Reines, whom I've always called "Mr. Neutrino," about ideas for discovering neutrinos or proving their existence. And I certainly backed his experiment at the Hanford Reactor to prove neutrinos by direct absorption. And likewise at Savannah River, that reactor where he really did get the evidence for neutrinos.

MY WORK WITH BREIT

And what did I do at this time? Well, I can't think of anything to which I added the really vital initiating idea. Breit and I published at least one paper, maybe two or three, on Coulomb wave functions—wave functions for dealing with barrier penetration, and a paper on pair production by the collision of two photons. And then, at least one nuclear reaction—was it lithium?—that we dealt with in some detail. Well, we were always so busy analyzing things that we could easily visualize, questions that we could immediately state, that I can't recall getting off onto questions that I couldn't easily state, which would have been more fun. For example, the idea of everything made out of positive and negative electrons. There was a paper that I wrote [later] on so-called poly-electrons, objects made out of positive and negative elections, that was a reflection of that earlier interest. But these were objects which really had nothing to do with nuclear physics; they are more like fancy forms of molecular physics.

I published a paper on this super-light hydrogen in a Teller Festschrift a few years ago. One thinks of how gases are cooled by allowing them to expand through a nozzle and I think of the domain around some stars today where all our evidence makes us feel there are lots of positive and negative electrons around. If only one could dream up some set of circumstances there that would give the equivalent of the nozzle exhaust, which would cool off a lot of this stuff in order to condense. I'm sure that if one wanted to do something on a Manhattan Project scale, one could make the stuff liquid positronium [laughs]. But so what? What would you do with it? It would blow up.

PHYSICS AND PICTURES

K: John, a characteristic of your later research was the wonderful ability to make diagrams, make almost an art form of conveying the information. Did you have that characteristic already in your earliest work?

Well, I certainly feel today if I can't make a picture, I don't understand what I'm talking about. But making pictures: I had the great good fortune of having a course in engineering drawing as part of my required training in engineering. But that's scarcely the place to make pictures. And then I can recall being sent Saturday mornings to the art gallery in Youngstown, Ohio for a course in painting and drawing, and that was fun. I would have loved to go on in that. And then, in the year we spent, 1949, in Paris taking lessons with a French artist, that was not the business of expressing ideas in pictures; we were just drawing pictures. That's odd we should be talking about this, because last night I encountered Kay Kosmack at our retirement community. Kay Kosmack sets up the exhibits in the corridor—each week a different exhibit. I was saying to her how wonderful it would be if one could put together a collection of idea pictures in the Middle Ages or the Renaissance period. The great artists were trying to represent something greater than themselves, the Christian ideas, and now it's the idea of "I, my, me" that seems to be the central idea. Well, if you could get examples of artists who have done great things representing an idea . . . Michelangelo's symbol of the creation, the two fingers. As they say, "One day does not make a summer." Anyway, I've only got that one example, and if I don't think of another couple, I'll have to conclude it's not a great idea.

INTERACTIONS WITH OTHER PHYSICISTS

To see and hear Einstein at Princeton in October 1933 when he first settled in this country was interesting, but I can't say it was inspiring. I didn't get the feeling he had any great vision that one could subscribe to or develop or go on with. He seemed to be trying equations on the wholesale scale without any great physical idea to guide it.

But it was a pleasure to meet Condon, and was it at this time or later that Condon suggested to me the name resonating group structure for a view of nuclear physics that I was developing?

And Phil Morse, what was he doing at that time? It was fun to talk to him then, fun to talk to him in wartime days, and I feel it's a real loss not to have him around nowadays. There was the Condon-Morse potential, it seems to me, if I remember correctly the term, in molecular physics, where a simple analytical form had the right asymptotic behavior at large and small distance to describe the interaction of two atoms in a diatomic molecule. Let's see. Condon and Morse wrote a great book on atomic physics, and that was absorbing many people. It became a form of continuous crossword puzzle that could have fun analyzing spectra, trying to treat the spectra in more detail.

Our son-in-law Charlie Ufford's father was working on the spectrum of iron in his last days. And his aunt's husband, Lewis Green, at Haverford, also works nowadays on the spectrum of iron, if I'm not mistaken. But I think that my reaction to that is summarized in something that a German colleague from Munich, Hans Peter Dürr, once remarked to me. He was speaking about the regularities people seem to find in elementary particle physics, and to him they did not mean any more than what you would see if you looked at the spectrum of iron. You could find certain regularities there that you might think were great stuff, but they were just accidental because you had so many levels, it defined any pattern.

What else was there? Condon and Shortley was another book about this time. I must say my reaction to all these things was, wasn't there some simple way to boil it all down to a simple picture? It seemed so elaborate, so full of abracadabra, the analysis of atomic spectra, this theoretical prediction. And then there was the statistical analysis by Fermi, and then the model of the atom. Fermi's statistical model for the atom made a big impression on me. I was greatly struck by its simplicity. Maria Mayer, whom I had known at Hopkins, had worked with this model in analyzing atomic spectra and atomic energy levels, and that was beautiful business.

COURTSHIP

I'm trying to remember the name of the couple in New York who were kind enough to invite me to their place a couple of times. It might have been Holden; I'll have to find out. I can recall them, after supper, having some after-dinner drink—I don't know whether it was Benedictine or Drambuie— and I had not ever had any drink. They said, "You better learn." [laughs] So that began my fall from grace. [laughs] And through the Holdens—if that's the correct name —I learned that a Baltimore friend that I hadn't seen for some months was in the New York neighborhood. This was Janette Hegner. I had met her younger sister, now no longer living, Isabelle, at the young people's group at the Unitarian Church in Baltimore, and had been invited by Isabelle to a dance at the Hegner's house, and there I met her older sister. She quickly discovered I was so poor at dancing that she suggested we sit somewhere and simply talk. Well, I struck up quite a yen for her, and my best friend Bob Murray and I invited her to go for a walk in Druid Hill Park the afternoon of the day when I had just passed my Johns Hopkins final oral examination.

Not having seen her since that time, I got in touch with her. She was teaching at the Rye Country Day School. Let's see, that's about a half-hour train ride from Grand Central Station in New York. I invited her to, I think it was "Farewell to Arms," or one or another play. We were out three times together before we ended up engaged. That was the spring of 1934. I must have talked to her about this question of going abroad for a further year of postdoctoral work. At this time, Europe was still in the lead on physics, and it was natural to look to Europe as a place to go to. Janette had had a year herself of work after her graduation from college, a year of work in Rome on a fellowship to work on the history of the Resorgimento, the Italian unification movement, and she was very keen about Italy. She wanted me to make sure I got Italy in somehow. Well, if I had had any sense, I would have by hook or crook married her, but I had no money.

I was nevertheless paying by this time, by the spring of 1934, a young Dane, somebody in the Danish Consular Service in New York, paying him so much a week for lessons in Danish. So I had already decided to go to Denmak. He used to tell me, "You ought to marry that girl and take her to Denmark." "Where would I get the money?" "Well, borrow the money from her father."

[laughs] Well, he was right. It would have meant so much in terms of a closer tie with Mrs. Bohr. She was a wonderful person. But he [Bohr] himself had not been able to get married to her in his early days. He was in England and she in Denmark.

K: Did Janette want to get married that summer, or was she content to let you go off for your year in Denmark?

We didn't really have much choice about it. That summer of 1934, after things wound up in June, if I remember right, I had gone—it doesn't seem quite right—I'd gone to Vermont with the family. It would be my last chance to see my family, and she was going with her father to the west. He was involved in malaria studies. He was with the Johns Hopkins Department of Public Health. He had spent a lot of time in the tropics with tropical diseases, analyzing them, and he was going to be for the summer in La Jolla, California. She was going west with him. They were stopping on the way at Indian sites because her father was deeply interested in the Indian people. She told me about one Indian ceremonial they were planning to attend, and when they got almost there they were stopped by an Indian with a gun. In those days the Indian ceremonials were not meant for white visitors.

I recall by prearrangement telephoning to her in La Jolla. That was quite a thing, because in those days a long-distance telephone call cost money and was not something you did every day. So I drove in to the town 10 miles from where the family's camp was and phoned her from a local shop and reached her successfully.

TO COPENHAGEN WITH BOHR

I'm sure I must have described to Janette something about Bohr, about who he was. I have not checked up yet on whether it is true that I heard him at the Chicago World's Fair in 1932. I had not yet studied up all the things that he knew and had done, but the impression I had about him after talking with others was summarized in the statement I wrote in my application for the second year of National Research Council Fellowship, "I want to go and work with Neils Bohr because he sees further than any man alive."

I don't know whether I mentioned how he was really knocked out by the death of his oldest son, and so was not around the Institute in the beginning when I arrived. One day I came and there was this workman out tearing down vines that were disfiguring the front of the Institute building. I looked closer and it was Bohr himself. [laughs]

WORK WITH PLESSET

I had struck up an acquaintance there in Copenhagen with another American postdoctoral there on a National Research Council Fellowship, Milton Plesset. Plesset has taught for many years at Caltech. His wife has been dead now for

some years. Our work was inspired by the report at the International Conference on Physics that was held in Britain in the beginning of October of 1934, work by Gray and Tarrant, on the scattering of gamma rays by lead. Gray and Tarrant were not the first to do such experiments. Such experiments were already being done by Jacobsen, in Copenhagen, but they had been suggested in the beginning by Lise Meitner, the one who had suggested to Hahn and Strassmann to study uranium.

This scattering of gamma rays backward by lead was something that one really ought to understand. It was in the beginning called the Delbrück Effect, maybe because Delbrück had not had anything to do with it. [laughs] He had been brought into the enterprise, if I remember right, by Heisenberg because one had the idea that a photon comes in, produces a virtual pair in the field of a nucleus, and then that virtual pair annihilates, and the photon goes off in a new direction. So it was a question of pair theory. But even to calculate the production of pairs in the field of a nucleus was a second-order calculation, and this would be a fourth-order calculation. That was really quite an enterprise. Delbrück was struggling with this, with the advice of Heisenberg, as I always understood it, but not getting an answer.

I guess through my Ph.D. thesis I had acquired this great interest in the connection between scattering and absorption. If you knew the absorption as a function of frequency you could predict the scattering and conversely. So Plesset and I started on a paper to predict the absorption of lead for gamma rays so we'd be able to predict the scattering. Well, I can recall talking about this with Bohr, and he had Rosenfeld sitting with him. He always liked to have somebody around to talk over what was going on, whatever the issue was that was coming up. Because for him discussion was the way to get somewhere with anything. How could you think if you couldn't talk? So here was the office, and here was the blackboard, and me talking, and me a bit embarrassed, picking up the eraser to erase something and not making much progress because I was using the back of the eraser. Bohr got up and said, "It'd go better if you'd turn it like that." [laughs]

OTHER PHYSICISTS AT COPENHAGEN

K: Was Delbrück at Copenhagen?

It was only a bit later that Delbrück came to Copenhagen. If I make a horseback guess, I would say it would be around December. It was always a delight to talk to Delbrück, he was interested in so much. The talk that he gave once called "How Aristotle Discovered DNA" [laughs] was a real tour de force.

Other people were arriving also at about this time. Already I guess in September or October, Otto Robert Frisch had arrived as a refugee, and a little bit later James Franck, who was not in one sense a refugee because he had been told he was welcome to stay, but he didn't want to stay under the conditions in Germany. I can recall his telling me on a long walk we once had how it would be fifty years before Germany is recovered from this.

WORK WITH PLESSET (continued)

The work on the scattering of gamma rays: That paper we never published. Why was Bohr not very keen about it? I really don't know—maybe because we did not explain what had been seen and there was no exciting consequence. Plesset and I always talked about publishing it, and I don't know what the final status is. Somehow, the initiative for it, for anything that is done, lies in my hands. I'm afraid there are other things where the initiative also lies in my hands and I've got to get things done. [laughs]

BOHR

A profile of Bohr. That's a very interesting question. How does one go about that? He...

K: Since there are only a few minutes left on this tape, why don't we save your recollections of Bohr for next time, when there's more time. That's a big subject.

Yes. A great subject. A great subject.

JANETTE

K: Why don't you use the last few minutes to talk about your correspondence with Janette while you were there?

[laughs] Writing back and forth. Janette, by the time I got to Copenhagen, had come back from La Jolla, from California, with her father. She didn't want to be doing nothing. So she got a job with Johns Hopkins Hospital going to help people who had follow-up problems on medical issues. I can recall one of the stories she told of going to a family having trouble with a baby getting fed.

Well, they discovered that the mother didn't realize you had to pierce the nipple of the bottle if the baby is going to get any food.

The statistics of time taken: It could take anywhere from ten days to three weeks for a letter to cross the Atlantic. Those were not the days that people used transatlantic telephone. Telegrams sometimes, but not the telephone.

It was a miracle that our engagement survived. [laughs] I bought two vases at Liberty's in London and mailed them to Janette. What I didn't know is that she had to pay a big fat duty when she got them.

During my year in Copenhagen, we wrote to each other at least weekly.