Margrethe Bohr - Session II

Margrethe Bohr:

When the Germans came, all of Harald Bohr’s letters were burned. Also some of the Pauli correspondence was burned by mistake. You see, one was afraid because they had these committees helping the Jewish immigrants from Germany, and there were lots of papers about those committees. All that, I think we burned out there, but no other letters. But by mistake, at the Institute, Miss Schultz burned some of Pauli’s letters…

Kuhn:

Did you say that you had found some letters of Harald Bohr’s here?

Margrethe Bohr:

Oh, yes, there are some written to my husband, yes. And those I will find out more about. There are also a few in there from earlier. There are a few that I can give you, and there are also one or two from my husband to Harald. Harald came over to see him in Cambridge there in 1911 at Christmas time when my husband was not terribly happy with the work . . . . Now I have been reading those letters, and how wonderfully my husband takes everything. He always keeps his optimism, always keeps his courage. He must have been very down-hearted at that time in Cambridge, I think. But still he says, “I haven’t got anything out of it but one thing, and that is that I have seen a really great man.” That is Thomson; it is so nice the way he puts it. That he expresses often: “I’ve seen a great man!” Thomson was always very nice — he was very charming and a very spiritual man, but he just was not quite so great as my husband because he didn’t like criticism. Then Niels says also so nicely that he has given Thomson the paper, and Thomson expressed interest in hearing about it. Then my husband optimistically thinks Thomson will go back and read it. And then after some time Niels — he also had to give an answer here to the Academy about printing — says in a letter to me, “No, I’m afraid he hasn’t seen it because I passed Thomson’s desk today, and I saw the same papers were lying on the top of my book.” So he hadn’t read it. But Niels had courage all the same. He suddenly decided that if he was depressed, then he would go to the laboratory; he came to the decision to take the matter up with Thomson.

But when he came to the laboratory it was Saturday, and no one was there. Then he went home a little disappointed, and then he suddenly got the idea: “I’ll call on Thomson.” Then he paid a call on Thomson in the afternoon, and there he had a talk with him. So you see, Niels could always keep going. Thomson and my husband now and then had conversations, but I don’t think Thomson ever really read it. He didn’t go into those things he didn’t agree about. Then later in the spring when he came to Manchester, Niels got this message from the Cambridge Philosophical Society, that they could only print the article if it were half as long. They wouldn’t even promise to print it; they said, “If it were half as long, then perhaps we could print it.”… Then in the so Philosophical Magazine he printed the little note about an article on radiation. Then he apparently has a correspondence with Reinganum. He writes a long letter to him about some points where he also disagreed with him; it’s a long, long, letter — 9 pages, I think. That is also from Cambridge, I think. I picked out some of the things and wrote them down here. Yes, that’s in ‘11.

Kuhn:

Did he speak of knowing other people at Cambridge?

Margrethe Bohr:

Yes, he knew (A. W. Hiller), but he was of course in another subject. He was very helpful to him. And he knew some of the older people who were very delightful to him; Professor (Barcroft), who was then proctor at the University, and Professor (Solly), who knew Professor Hoffing here. But the only one in the laboratory who really spoke to him, I think, was E. A. Owen, the one I have mentioned before. Niels helped him with some calculations for some papers and he helped Niels with translations, with the language. They were friends.

Kuhn:

Does he speak in the letters of the problems he is having with English?

Margrethe Bohr:

Yes, but not much. I think he spoke English very well when he came. I think his grandmother being English had helped him. There were always English-speaking people in the family. I remember he also told me, and it also comes back, that when he was settled in Cambridge he read David Copperfield. He read it very, very carefully and he looked up every word he wasn’t sure of, and when he finished that he had the feeling that he knew English.

Kuhn:

Was it David Copperfield or was it The Pickwick Papers?

Margrethe Bohr:

No, it was David Copperfield. He mentions it several times in his letters, and I also remember that.

Rosenfeld:

He also read The Pickwick Papers before because he knew The Pickwick Papers by heart.

Margrethe Bohr:

Oh, he had read them in Danish.

Rosenfeld:

But he must have read them in English too because he quoted it in English.

Margrethe Bohr:

Yes, then he read it in Cambridge; he took up reading with a dictionary. And I remember he told me, “I looked up every word, and that gave me a foundation of English,” he said, “So I felt I knew it.” He knew the words; the pronunciation was not always so good, but his vocabulary was good. But even to the last he could not always pronounce it so well. There were certain mistakes he always made even though they often told him. For instance he always said “Exaggeration” incorrectly. And the English don’t always understand; if you say something slightly wrong, they don’t know what you mean.

Rosenfeld:

I have still a vivid memory of the time when I traveled together with you — it must have been in ‘31. We arrived in London, and we went out of the station and got into a taxi cab. We had the address, but the driver could, not understand what Bohr said. A crowd gathered around us with everyone making his own guess about what it could be. I was quite reminded of The Pickwick Papers. That was my first visit to England.

Margrethe Bohr:

A point which Niels also makes in such a beautiful way is that: “Of course, what does it mean that it’s not going so well for me — who says it should go well. Perhaps it’s very good for me to have a disappointment and that it be different here from what I expected.” Of course he had expected something very different from Cambridge. He was so enthusiastic when he came there, and he loved always these old buildings; he loved the whole atmosphere so. But then he found the atmosphere in Manchester.

Kuhn:

When he spoke of being disappointed, what sorts of things did he point to?

Margrethe Bohr:

That was only with regard to the atmosphere in the Cavendish. He got the experimental work from Thomson, and Niels said, “It isn’t anything; it can’t bring anything out.” And Thomson also realized that at last. And then Niels wasn’t used to the way things were there. There was no one to help him, and you had to do everything yourself — you had to blow glass and you had to do all such things. And the glass broke for him. That was only true in the beginning, but that of course he overcame. He got a man from the Institute to give him some lessons in glass blowing, so he got quite expert in that. But he was eager to do something, to start something, and this he thought was such a waste of time for him. It was a waste of time there in Cambridge, except that he got this experience. But it’s so nice the way he always speaks of Thomson: “In any case, although I haven’t gotten anything out of it, I’ve seen a great man.” Also, Sir John Larmor was very nice to him. He went to Larmor’s lectures. He also writes, “Tonight I am going to dine with Sir John Larmor in St. John’s College.” They were nice to him always. They felt he had something on his mind. Larmor was very nice to him in later years, but I think he apparently took him in from the very beginning. Thomson also invited him to dinner in Trinity, and so on, but he, did not take up really the discussion about the paper on the points where he disagreed with Thomson.

Kuhn:

Did he talk about the thesis with Larmor, do you know?

Margrethe Bohr:

I don’t know what he talked about with Larmor, but he probably did also. He probably would have told him.

Rosenfeld:

Larmor would be interested.

Margrethe Bohr:

Surely, yes, but Thomson was the man in Cambridge. If he didn’t want to look into his own things, there was nothing for the others to do really without offending him. I think he found much sympathy in Jeans also. Then Jeans was one of those who first recognized his calculations there about the atoms which he began later. From reading the letters, that seems to have developed very fast. He began these things when he came to Manchester. He did some experiment there, but then he stopped the experiment about July.

Kuhn:

Here I would say that if by any chance the letters enable us to actually pick out dates for the sort of week to week and month to month schedule, it really becomes of great interest to try to put this together.

Margrethe Bohr:

From the 9th of May he writes, “I’ve received a letter from the secretary of the Cambridge Philosophical Society telling me that the council of the Society has come to the decision that this paper was too long, but that they perhaps would take it if it were half as long.” That’s on the 9th of May.

Kuhn:

That’s the thesis.

Margrethe Bohr:

Yes. And then on the 15th of May he has the proof for this little note to the Philosophical Magazine, and on the 4th of July it appears. Then on the 6th he tells in the letters about a new idea on which he is working day and night . . . . This is the 6th of June, 1912, of course. This was the 10th of June that he tells me of this new idea. Then he writes on the 12th; he says, “We are working on a little theory on the absorption of alpha rays.” Then he writes on the 17th that his work is continuing. He writes about these new ideas and that he thinks perhaps he has gotten in on something important. I also remember that he was home here by Easter time, and he told something of the new ideas. That can’t have been the alpha rays, I think . . . Were the papers on the alpha rays and on the constitution of atoms closely connected?

Rosenfeld:

Well, in the sense that in the alpha ray paper he already used these conceptions about the structure of the atoms which are based on Rutherford’s model.

Margrethe Bohr:

Then on the 26th he continues eagerly — he is very taken up with those theories. Then a few days later he thinks there is something wrong. It doesn’t work. He had a difficulty in it. Two days later it goes better again.

Kuhn:

He says nothing that hints of what the nature of the difficulty would be?

Margrethe Bohr:

Well, I can try to look it up. I think the letter is upstairs. Then it goes up and down in these days, and on the 5th of July he writes, “Perhaps it’s not so hopeless with all the little atoms, even if the result of the collisions goes up and down.” Then on the 11th he has finished his experimental work with Rutherford, and has now completely time to concentrate on these calculations and to finish them before he leaves. Then on the 22nd he gives Rutherford the first half of the paper. Then he writes when he is over for a visit to Rutherford in September, 1913, — more than a year later — he writes to me in Lund that Rutherford has sent the third part in for him. It’s just before the conference in Birmingham. So it went very fast with these three parts.

Rosenfeld:

Oh, yes, yes, surely.

Kuhn:

There is a terribly big jump from July, 1912, to September, 1913.

Margrethe Bohr:

Yes, but you see there are no letters.

Kuhn:

Right. But can we ask you about that time?

Margrethe Bohr:

Yes, but I only remember we were working. I couldn’t tell you much about it. We were eagerly waiting after the papers went off to Rutherford — oh, how we were waiting for the answer. I remember how exciting it was. And Rutherford was delighted with the first paper he sent over; with the second one he was not so pleased as with the first one. And Niels was a little disappointed. And that was surely the one about which he went over to see Rutherford; Rutherford wanted to shorten it.

Rosenfeld:

That was really the first.

Margrethe Bohr:

Not the first — no, not the first.

Kuhn:

I think perhaps when you say the first paper, you may mean the alpha particle paper — the one that you actually gave him when you went over to England after the wedding.

Margrethe Bohr:

No, because were there not three papers about the atoms? No, it was a new idea. There must be a letter from Rutherford.

Rosenfeld:

Yes, you see, he had this idea about the consequences of Rutherford’s model. He must have written a whole paper at that time about it.

Margrethe Bohr:

Yes, he must have done that.

Rosenfeld:

Then when he came to Copenhagen, he heard about Rydberg’s work on the hydrogen atom and looked into that. Then he decided to rewrite the paper he already had.

Margrethe Bohr:

Oh, I see, yes. That I don’t remember.

Kuhn:

But again we’re jumping too much; it may be that we will have to. You first, yourself, met Rutherford in the period right after the wedding?

Margrethe Bohr:

Yes, just after the wedding when we went there in August.

Kuhn:

When did you actually get back to Copenhagen?

Margrethe Bohr:

Around the first of September.

Kuhn:

Now, already in that fall did you begin to work with Professor Bohr?

Margrethe Bohr:

Oh, yes. We worked all that time there. He was dictating and writing and so on. I didn’t work with him; I only worked as his typist — writing for him.

Kuhn:

But actually writing on a paper?

Margrethe Bohr:

Yes, yes.

Kuhn:

Almost from the time you first got back?

Margrethe Bohr:

Yes; almost right away. And sometimes we went into the country to be completely quiet. He was writing continuously all these first years. But it went quicker for me — faster than I had thought … He went over again to England in ‘14, I think, in January. That may also have been with a paper. But then we moved over there ourselves by the autumn.

Kuhn:

In those early years when he dictated, how did a working day go? Did this start in the morning?

Margrethe Bohr:

Yes; it started in the morning, and then we went for a walk, and so. It went on so. I suppose we had some pauses I don’t remember; I had the feeling we were writing very much. And sometimes we went into the country to a pension and stayed there. We worked all day, except that we did go for walks. And we wrote these papers. It must also have been very concentrated when I see he could get the three out so fast.

Kuhn:

It seems clear that it was not until after the middle of February of 1913 that Professor Bohr first learned of the Balmer series which plays such a crucial role in the first paper. On the other hand, it seems very likely that there was another paper all prepared during the fall, and that this enabled him, as you say, to prepare the whole thing so very quickly when the time came.

Margrethe Bohr:

Yes. I was surprised when I read that the third part was delivered in September, only one year after. I remember also that all the Rydberg discussions stretched for a long time, didn’t they? Was it only through ‘13 and ‘l4 then, do you think?

Rosenfeld:

It was during ‘13 — February, ‘13 — according to what we can find...

Margrethe Bohr:

I remember Rutherford’s letter. I remember that certain things made an impression, and I remember the impression his letters made on us. With the first letter on the first paper we were delighted; with those on the second paper we were disappointed. I remember he was taking a slightly more doubtful attitude. But, of course, Rutherford was slower in seeing it than some others.

Kuhn:

And when you speak of Rutherford’s being more delighted with the first paper than with the second, I wonder whether the first paper may not be the one you gave him in August, the alpha scattering paper?

Margrethe Bohr:

No; it was one that he sent over, and the reply came to our apartment there in St. Jakobsgade; I remember it so well, because we were waiting so eagerly. And it made this absolute impression on me; I remember the difference. With the alpha paper we stopped two weeks in Cambridge to work and then gave it to Rutherford.

Rosenfeld:

But you do not remember that he said something about now having heard about the Rydberg series?

Margrethe Bohr:

No, but I remember the Rydberg coming in, and talking about it, and going to Sweden — Rydberg lived in Lund. There are also some letters from him, but he doesn’t write anything about Rydberg. You see, there were letters written from Lund. It must have been in ‘13. But I had a brother over there as a professor of mathematics there in Lund. So I am not sure why Niels went to Lund, but there were visits. But then he also went to see Oseen. He had already before written a long letter to Oseen about things from England. So we both went to see Oseen, I remember. I think he went several times, and there was a long correspondence with Oseen . . . Oseen was a very good friend. Again, he understood Niels so well; from the very beginning he had connection with him. He was also the one who sent in a recommendation when Niels applied for a post at the University here after the end of the English stay, in 1916. In 1915 Oseen did that; he wrote a very nice recommendation to the University here. I have it here.

Kuhn:

What is the date on that?

Margrethe Bohr:

I suppose we can see on the other papers here. Here is one from Rutherford, March 16, 1914…

Kuhn:

I take it these letters then were actually written before you went to Manchester, perhaps in hope of getting a job here in Copenhagen instead.

Margrethe Bohr:

March 16, 1914; yes, that was before. But I think in ‘15, when I was in London, and he in Manchester, Rutherford wrote a recommendation that would enable us to stay another year in Manchester, for which we were very happy.

Kuhn:

How did the Manchester job come into being in the first place?

Margrethe Bohr:

Rutherford wrote to him and asked if he would take over after Darwin. Rutherford wrote and asked him if he would take it… So we decided to go and were very happy to go over again. But he was also pleased to go back in ’16. Then I think that he felt that he had gotten what he could in Manchester; things were upset with the war; also many people were away. Rutherford wanted him to stay on as a professor in Manchester. But then Niels felt that, first of all, it was a little difficult being a foreigner and not joining in the war. They did not have conscription, and that meant simply asking people to join the army. All those young men who have a band, they have joined, and all those who haven’t a band are looked at a little askance. So that was one little difficulty. But also he felt that, taking the University as a whole, he preferred the Copenhagen atmosphere to that at Manchester — apart from Rutherford. He thought he could then just as well work without Rutherford.

Kuhn:

How much was Rutherford there during the time you were there?

Margrethe Bohr:

He was there the whole time. He wasn’t there when we came; that was when he was in New Zealand, but that was only a month or so; then he came back. Then he was always there. We saw a great deal of him and his family.

Kuhn:

What sort of work did Professor Bohr do there? Did he do much lecturing, for example?

Margrethe Bohr:

He gave some lectures, yes. Then he wrote his papers; he had no experiment, but he went into the lab and he worked there. He had his room there, and he was working there. Then he was also working when he came home. But there must be many manuscripts over there at the Secretariat.

Rosenfeld:

Yes. There are even manuscripts of his lectures there.

Margrethe Bohr:

He was happy there; he was certainly happy there. But after all, Manchester is not a town that we liked. Of course, the atmosphere in Manchester is not like the atmosphere in Cambridge at the University. There are more eminent men to talk to in Cambridge. When they offered Niels a Royal Society professorship later in ‘20 or ‘21, he was, in a way, tempted to take it. That was a professorship which was to be completely free — there were no duties; he could decide himself whether he would live in Cambridge, whether he would live in London, wherever he wished. That was something quite new that was offered.

Rosenfeld:

Yes. I don’t think that exists?

Margrethe Bohr:

Yes, it came into being. Niels didn’t take it, but then somebody else did . . . Niels writes that he feels he can’t give up his professorship here at Copenhagen. He writes to Jeans, “I have given very much thought to the possibility of accepting your most honorable offer of the Royal Society professorship. The University vacation still lasts in Copenhagen, and I have not yet had the opportunity of communicating with the Danish authorities. I should be very thankful before doing so, to hear your view about a point which may be decisive for the possibility of my acceptance of the professorship. Following your kind invitation I shall try quite frankly to explain my position.” Then he writes that they have started an institute here and all this, and therefore he says that perhaps he could be in Copenhagen part of the year to remain as leader of the institute. That was, of course, not possible…

Kuhn:

Were there other people at Manchester to whom he was close?

Margrethe Bohr:

No, not so much you see. Now, during the war, people went away and so on. No, there was no one really. They were all nice, and there were many people he liked to talk with, but there was no one to whom he was particularly close. The one I remember he most enjoyed was Professor Alexander; he was an old man in philosophy. There was no one very brilliant; everyone had gone to the war.

Kuhn:

Where did you live?

Margrethe Bohr:

First we lived (out from Dittsbury), Victoria Avenue. We had to take furnished houses. Later we took over Professor (Haas’s) house; it was near the White Lion there. Then we went away, I think, to Derbyshire during the summer; we had a little house there in nice surroundings. I enjoyed it, and we had a happy life. What I think was nice about the atmosphere was that people saw each other from the University. I remember when I came home I felt terribly lonesome because I didn’t know anyone at the University, at least in comparison with what I had seen in Manchester. Here people lived more by themselves; there were no gatherings at the University where you met people. At Manchester there was always, once or twice a year, a large gathering for everybody from the University. Of course, universities were smaller then than they are now.

Rosenfeld:

Yes, but it is still like that in Manchester now.

Margrethe Bohr:

And there was altogether more of that sort of thing. Then all the University people lived out there in (Fallowfield, Worthington, Dittsbury), so one met the others. It was the custom then in England that one had to call on people. This stopped completely with the war, I think. . . . But then you were always supposed to pay calls on different people now and then. Each lady had printed on her visitor’s card what day she was at home; then she had to sit at home on the first Friday or the third Friday of the month and wait to see if anybody came. Then she also had to run around. I remember later when we were talking about this professorship. I was up in the Lake District together with the Rutherfords - - Niels had come back to Cambridge. Then Lady Rutherford said to me, “If you come over you will have to pay 400 calls here in Cambridge.” So it amounted to something. She said always very nicely when we talked, “Oh, we don’t call you a foreigner.”

Kuhn:

You spoke of Professor Bohr’s waiting for the reply from Rutherford and, of course, in his pleasure at Jeans’ reaction in 1913. Are there other reactions of people you remember?

Margrethe Bohr:

I don’t remember anything so clearly as these. Of course, life was simple. We were two alone, and so I was in it all. Later when the children were born, I couldn’t follow so closely, and, then other assistants came in. But there was nothing like the reaction from Rutherford. That was, of course, the one who was sending them in. It was difficult to get things printed; that I remember often. It was difficult to get things out. Niels writes one place about a little note he sent in to the Philosophical Society. The answer came back from the Philosophical Society saying that they couldn’t publish it right away, for they first had to publish a paper by O. W. Richardson, or something like that. But then Niels wrote back, and he explained to them that it had to be published. But I remember that that was always a problem — “When will they bring it out.” We often went to Fleet Street; Francis was the man’s name; the printing press was there. He was very nice always, but it didn’t come out right away. Their problems and worries I remember, but otherwise I don’t remember if there was anything from Germany or so. Then he went down to Germany; that was later, of course.

Kuhn:

In 1914 he gave at least two lectures in Germany, one at Gottingen and one at Munich.

Margrethe Bohr:

Oh, yes; I think I have that also because he took a trip afterwards with Harald. And my brother-in-law was with him. But didn’t he give a lecture earlier — in 1911 — in Germany? I think he did. A very nice letter from the time when he was writing his Gold Medal paper for the University . . . shows the way he had to have someone to help him. Harald and my mother-in-law were sitting and helping him write. And he says, “My father is sitting upstairs trying to write down the calculation, bringing a little of it down at a time.” The work was done, but all his life be couldn’t write it unless there was somebody at his hand to help him.

Kuhn:

So his father was doing calculations?

Margrethe Bohr:

I think the calculations were done, but he was putting them in, or bringing them down; I don’t know what he said. He writes so nicely about it. He also wrote a letter to Harald thanking him. Harald had helped him when he was sending in his paper to the Academy here. “How we were sitting and writing and making the calculations, and how the last evening there was so much to be done that you and my father and mother helped me. We three were up in my room while father was sitting down in his own room going through the tables and now and then he brought them.” This was a letter written to Harald. He is just reminding him; it’s later. He says, “They have just told me about how it was here.” My brother-in-law came over to him there in Cambridge, and then they had two weeks together. They were discussing whether he should do something else; then he wrote to Rutherford. But he stayed another term in Cambridge. I think Thomson was sorry. Thomson felt it was a little disappointing that he left; he was not used to having people leave. When Niels came up to Manchester he said, “I don’t know what they all are thinking of me; I think they think I’m a little crazy since I’m leaving Cambridge.”

Kuhn:

Was he excited at Manchester from the very beginning?

Margrethe Bohr:

Yes, he was. He was prepared for it and already after a day or so he felt at home at the laboratory. There was a friendly atmosphere, and he knew people, and it was quite a different atmosphere at the Institute. English people were queer then; I mean they didn’t talk to a foreigner then. It was always different in Yorkshire and those places; they were more human there. I don’t think anybody talked to him at the Cavendish, except Owen. He talked with the older people because he had something on his mind, and he had introductions to them, and so on. So there apparently wasn’t any general comradeship there. He has never mentioned one thing about it. He knew a Danish lady, Miss Lehmann; she was studying at Cambridge. He also knew Hardy and Littlewood through my brother-in-law. He once had a little party and he wrote to me about how complicated it was when a lady should come to tea to a college. She should first of all have a chaperon, but one wasn’t old enough so he had to find another one. That was very difficult. I think that it was Mrs. (Hill) and perhaps Mrs. (Barcroft) who ended up being the chaperons to escort Miss Lehmann. She is still alive, but she is old; she is very old. She is quite an able lady.

Rosenfeld:

Does she live here?

Margrethe Bohr:

She lives, I think, in Holte, but she was just in America. I think she is quite acknowledged. I know Niels, a year or so ago, had a letter — I forget from whom it was; it was from America or England — asking if one couldn’t give some kind of recognition from the Academy to Miss Lehmann, because she deserved it. So I don’t know whether she got a medal or something; Niels also thought she should have it. She has worked at the Institute under my brother. Inge Lehmann her name is; she is a daughter of the Professor Alfred Lehmann, the psychologist.

Kuhn:

When you got back to Copenhagen then in 1916, were there many duties at the University?

Margrethe Bohr:

Well, the term was beginning in September, and there were not many students. There were always few for that subject. I don’t remember any Danes at all coming to our house. The first physics student I remember was Kramers; he was here in September. He came up from Holland for a kind of students’ meeting. Then he came to see both Harald and Niels; then he began right away working with my husband. We came back in July, I think, and had a vacation in the country, and so on. Kramers came for the students’ meeting at the end of August or September; he came up to see my husband. He was quite young — 21 — but he had finished his University career. Then he remained here; he just simply remained, and they began working. I don’t remember any Danes. The first Danish student I at all remember is Julius Jacobsen in 1920, and he was an experimentalist. I don’t remember any others.

Kuhn:

How was it arranged for Kramers to stay?

Margrethe Bohr:

I suppose he got a stipend from here, from Carlsberg Foundation, or something like that, or Niels got that for him for a time. Then later when the Institute came, he got an appointment at the Institute. I think he must have gotten a Carlsberg Foundation stipend. Maybe it was a Rask-Orsted; I don’t know if that had begun then. When did America get the West Indian Islands — what you call the Virgin Islands? When they were sold to the United States, they made a Rask-Orsted Foundation with some of the money, and that gave stipends. But in any case, Kramers must have received a Danish stipend.

Kuhn:

Your impression is that it really was not arranged: until he had gotten here that he was to stay?

Margrethe Bohr:

Oh, no; we never heard about him. No. And he was not coming to see Niels; he was here for a students’ meeting. He just thought he would call on the two brothers; then they got so interested in talking that he stayed.

Kuhn:

Was Professor Bohr delighted with him from the very beginning?

Margrethe Bohr:

Yes; that was a very happy cooperation, yes. And he stayed for 10 years. But then the next one who came must have been Klein. I remember him in any case from our apartment there in Hellerup. But then things begin to run together in my memory. Then our eldest child was born there in November ‘16. So then I had more to do and wasn’t always writing quite so much as in the earlier years.

Kuhn:

From the beginning did Kramers work as you had, taking dictation?

Margrethe Bohr:

Yes; I think so, yes. They were working together. Kramers was a very good help in putting phrases together, I mean, in giving them a good form, and so on. And he also had brilliant ideas himself and wrote papers by himself.

Kuhn:

Would they be together the whole day?

Margrethe Bohr:

Yes; they were together most of the day I think then. Kramers had his music in the evening. I don’t remember if they also worked in the evening. But Kramers, in any case, got an enormous amount of influence in Copenhagen. He was so many-sided. First of all he spoke Danish right away almost; then he had his music and played beautiful cello. So he got to know many people in a short time in Copenhagen. Then later he got engaged to a Danish gir1; I don’t remember when that was. It seemed so long then, and it now seems shorter.

Kuhn:

Did you yourself, get the impression that having a technically trained collaborator, as Kramers was, made a great deal of difference in the way Professor Bohr was able to work?

Margrethe Bohr:

I suppose it must have gone better with Kramers. What papers were written then, and what work was done, I don’t remember. Then there was so much connection with Sweden, with Siegbahn, who came over sometimes I remember. . . . You see, when he was young, and when he was dictating first to his mother and later to me, he had so much in his head that I don’t think he ever missed it that one couldn’t help him by responding to what he said. In the younger years he had so much in his head that just had to be put down, and he could concentrate while he dictated. And to a large extent, I think it continued. But then, of course, it must have been a great thing to be able, to discuss the problems as they came up later. . . But in the first years, when he was so young, and he had all these ideas, I think he had in his head what he really wanted to say.

Kuhn:

When he dictated would he dictate notes, or did he dictate whole papers?

Margrethe Bohr:

He dictated whole papers, not notes. I think he had it fairly well prepared in his head.

Kuhn:

Would he have notes that he had worked out first himself in this early period?

Margrethe Bohr:

I don’t think so. But that the papers over at the Secretariat perhaps can show.

Kuhn:

With the exception of one folder, there is very little still there that is before a full draft.

Margrethe Bohr:

No. I think I also mostly remember that he simply dictated the paper. . . . Oh, he must sometimes have written little notes. I have forgotten that in the later years he could write more easily. For many years he never wrote at all, but he has written down a good deal by himself even at that time — more than I remembered. Oh, but there were so many things. If I had only read all those letters while Niels was still alive, there could have been so many things I could have taken up and asked him about. But you don’t think of it when you have him. I did begin to look up some of these letters from Manchester we took one or two and were so delighted to see them. If there had only been time, but I thought there was time, you see. I had decided that I would take them up. I thought we had the, winter and could do it in the evenings, and so on. It would have been so interesting to discuss so many of the problems we took up in the letters, about religion, and so on. He always said so little about a thing because he always had so much to do. He was always, as you say, behind. But then he would write, “All this I will tell more about, all this I will really tell about when I come home.” And then there wasn’t always time to do it, you see. . . The life was so full. There was something the whole time. And I couldn’t always manage to keep order in the papers.

In the beginning, I could manage it, but they grew to so many. Then Fru Schultz helped, and when we moved out here in 1931, it grew out of my hands. There were so many papers, and there were so many people coming and the five children were here, and in a large house you waste so much time. Then Miss Hellmann came, and we should have done it together, really, but, so to say, she frightened me a little. She is so good, and I could do it with her now, but then I was younger. My husband said, “You must go up there and talk with her.” I hadn’t always the courage to go up because she was so expert, and she did it all, and so on. She didn’t mean to frighten, she’s really extremely helpful. But I was scared when Niels said, “You must go out and help her.” I said, “No, I cannot.” Miss Hellmann must also have had too much to do because, it wasn’t always so well arranged. In any case, they couldn’t always find the papers when they were sitting and working and wanted this and this paper. I hadn’t had any training as a secretary; I didn’t know the systems to really keep order in things. So I put it, as you say, in envelopes and wrote outside what was there. It was a very primitive way, and not the efficient way, the good way.

Kuhn:

Professor Bohr spoke of his sense, in the early days, of isolation — that other people were not working on these problems. Then, gradually, more people were working and it was a school and a tradition, and then ultimately he becomes not only a person doing research, but a public figure. I wonder what is your own sense of the times and of the ways in which each of these two different transitions occurred.

Margrethe Bohr:

I also think sometimes of how it took place. You see, before the war, while we lived here in the 30’s, there were, of course, a tremendous number of people coming here. However, while we lived at the laboratory, there were so many students that we hardly had any private life. Niels had so much to discuss with them, so it was a little difficult. They came in and out of our villa across from the Institute. This was so nice; we asked them ourselves to do it — but when there were so many —. Then we came out here; then, of course, this was a little too far. Niels always said, “If it had only been on the other side of Faeelledparken, it would have been so wonderful.” Then there would have been a little distance between our home and the Institute. But this was, of course, peaceful, and gave him really so so much. But then, also, came the problem that when they came out here, he no longer had the possibility to say, “Now you should come over for two hours and then go home.” You couldn’t just send them home; so they had some difficulties here. Except when he worked with you, Professor Rosenfeld, Niels said it was such a rest: “It doesn’t matter when I stop, Rosenfeld has always something to do right away.” You simply took a book or something else, so that was so nice. That was a rest for him. But if he had to consider, “Well, what, shall they do now when I am tired and I stop?”, then it was a little problem. Then, oh, the 30’s were such terrible years. There we nearly collapsed because of the immigration.

That created daily problems, and was really very strenuous. Then there was the gloomy outlook: “What shall it be?” They were taken up from ‘34 — all the 30s — with the committees; what could they do and how could they help them. The people came, and I remember when we went to America in ‘33 we had such a long list of people for whom we should try to find places. And the year afterward, we went to Russia together. And then came ‘35 and ‘36 and so that was taken up. Of course, there was then the Bologna Conference, and there was Rutherford’s death which was a terrible shock. It came completely unexpected; I mean, he had been ill two or three days, but nobody knew it. Then he went to America in ‘39; there were also these problems with Meitner and Frisch, for which I have a long correspondence here. He and Eric went over. Then came the war; then came the Germans in ‘40. Who worked here then, and who was here; I don’t remember; it was in a way a peaceful time to work because there was nothing going on. One never knew what happened. Still there were problems the whole time. They were pressing to go away — should he go or should he not go. It was what was heavy on one’s mind the whole time. It was on mine terribly also: “What will happen?” Those were very gloomy years. Then we finally went off, and we came back. Of course, he had got into these problems about which he writes in The Open Letter. He so gradually had grown among the population; they made him a public figure. It shows everywhere since those days how loved he has been by the common man in the street, and not only in Denmark. That was also, of course, always his way with them; when he had something to do with workmen or whatever, they got to know him. The Institute was always building. As soon as they had finished one thing they were starting another. Oh, I hoped I should never see an architect again. Niels was so modest; he never would ask for more than was necessary, but when this was finished they always needed a new extension. Then he would apply for more money and then begin with architects again. But he liked it; he liked architects, and he liked hand work to occupy himself with, and he liked to see it. He certainly took part in every little detail; it amused him. . . . It must have taken a good deal of his time, some of his time. But it was a relaxation for him. He never rested in the way that others do, or relaxed completely. He always did something else; that was so characteristic for him. Even if he went for a walk, to the last there was something the whole time which occupied him. Either the street should be built so, or he was concerned with the town planning; the whole time he was observing something and was occupying his mind with something. That was the way; be never just simply sat and didn’t do anything.

Kuhn:

When did he read detective stories?

Margrethe Bohr:

Yes, that he did sometimes during the night. When he traveled by train, or so, he did that; yes, he began reading those. Yes, that was a relaxation, and also he solved cross-word puzzles.

Kuhn:

Could you tell what a typical day would be like for him. What time would he get up? When would he have breakfast? Would he have done anything before breakfast?

Margrethe Bohr:

He usually had breakfast at 8:30 or something like that; later it got to 9:00. Then he started working right away. He would get up about half an hour before breakfast. He didn’t do anything before breakfast. I often wanted him to go for a walk before, but he didn’t do it. Then he worked and had lunch, and worked again.

Kuhn:

Would he work at home then in the morning?

Margrethe Bohr:

Yes, he worked at home. That was when we were out here at the Aeresbolig.

Kuhn:

Before that he would work at the Institute?

Margrethe Bohr:

Yes, we also had our home there, you see. . . .Even after we moved out here sometimes he went into the Institute in the mornings — that was several times a week. Maybe for a time he did it each morning; I don’t remember. Perhaps he did go in for a time on bicycle each morning.

Rosenfeld:

Yes, I don’t know whether it was regularly each morning, but it was very often, in any case.

Kuhn:

If he worked at home, would whoever his current assistant was come to the house?

Margrethe Bohr:

Somebody always came to the house if he worked at home. There was always somebody at the house; he never worked alone.

Kuhn:

Then this would be the morning and what time would lunch be?

Margrethe Bohr:

12:30, or something about that time. And then after lunch he went on and worked again.

Kuhn:

He went straight back to work after lunch; he took no walk or anything?

Margrethe Bohr:

He went straight back to work, yes. They almost worked during the lunch also.

Rosenfeld:

One worked continuously except perhaps when something went wrong, or when one could not go on. Then one took a stroll in the garden here. During those walks in the garden the conversation was about something quite different. It would be about anything. Sometimes when nothing occurred to him, he said, “Well, tell me something.”

Margrethe Bohr:

But he was not like Pauli, whom I knew a little. Always when he came home to his wife, it was to be entertained and to hear something nice. She must tell him something witty and amusing, and she always broke her head to find something to tell him. Then one day she couldn’t find anything; she didn’t know what to do, and said, “I have nothing to tell you today.” And then he said in his way, he was always sitting and knocking on the table — “Oh, ja, ich kann mich auch langweilen!”

Kuhn:

Well, this work then would generally go on until dinner? Would he then work again in the evening?

Margrethe Bohr:

Yes, most evenings until a few years ago. I think it’s only the last two years perhaps that no one came in the evening. There was always work going on.

Kuhn:

Until how late?

Rosenfeld:

Oh, it was very different; it could be until very late. It could be until midnight.

Margrethe Bohr:

He has worked tremendously. Of course, when Kramers was here, he played sometimes. That was an interruption sometimes; he was very musical. Then he could go in and play a little on the piano. No, he has worked very, very much when one thinks of it. And also in the summer.

Kuhn:

Did the children see him?

Margrethe Bohr:

Yes, he did play with the children when they were smaller, certainly. I have so many remembrances of him playing ball, and so on. Then the visitors also played. I remember Heisenberg playing, and we played in the evening with the young people when they stayed with us there. When Kramers was here we had games together with the children; it must have been in the 20’s. We did it also later when Heisenberg was here; I remember Heisenberg especially playing hide and seek out there. I don’t remember how it was in the 30’s up in Tisvilde. But it was always work because from each year to the other he said, “Next year I’ll have a real vacation.” Next year there was also something that absolutely had to be done. I remember one year Hevesy had the house next to us; he rented the house for the summer. It was just when his little daughter was born; oh, it must have been in ‘26 or ‘27, or something like that. There was very little time for Niels, so Hevesy came over and played with the children, but Niels was mostly working.

He was practically always working. For instance, I also remember Bjerrum coming once. He was just passing by with some of his relations and wanted to show them the garden. He just came unexpectedly and wanted to show it to them. They came up here, and I went in to fetch Niels. He was sitting and working with somebody; it was in the evening. But when he had been sitting with the guests for five minutes he made, an excuse; he had to go in again, somebody was waiting for him. He really has worked. If it would have been better if he had had pauses, that I don’t know. He went occasionally for a trip to the mountains. And then sometimes, for instance, I remember Kramers and he went away to a pension in Jutland, and were sitting there and working, so they had peace and could finish things. But there it generally happened that Kramers came home completely overworked. Niels had an extraordinary constitution; that he has had. No one could keep up with him. The young people were tired before he was tired.

Kuhn:

Yes, I have heard that over and over again. Were those trips to the mountains or the working trips to Jutland planned in advance?

Margrethe Bohr:

No, they came suddenly. Oh, no nothing was ever planned in advance; no, he didn’t like planning it at all. If it was planned, it would be changed. And I can see this when he writes his letters from Manchester. My mother liked a wedding and she liked to do it in the proper way and so on, and therefore she wanted to know the date and how long he would be home and so on. “Oh, is it really necessary to know all this,” he said. And what was it he said about the wedding dinner — “We should think about what train we should take and get away from it all.” He wanted to see if we couldn’t make the dinner earlier in the day, and my mother didn’t like to have so many people early in the day. My mother calculated three hours for the dinner. And then he said, “How is it really possible to use three hours for a dinner? Can’t we take the ferry at 7:00?” But that was also different fifty years ago; I mean, people did these things more formally and wanted them just so.

Kuhn:

With people like Kramers and other assistants with whom he worked closely, was that a really close personal relationship as well as a close professional relationship?

Margrethe Bohr:

With Kramers that was a personal relationship; they were very good friends, yes. Oh, that was a very warm friendship; always, until he died. And it was also with Pauli.

Kuhn:

What about Klein and Heisenberg?

Margrethe Bohr:

Oh, it was also with Klein, yes. Niels had that kind of a relationship with most. Well, with Heisenberg it was not so much —. Heisenberg had some difficulties which came up occasionally. But then in between he was a pleasant man. And as Darwin, who was here once together with Heisenberg, said, he was what you call well-bred. I mean, he had nice manners and was pleasant in that way. But, there were difficulties with Heisenberg.

Kuhn:

That was true before the war?

Margrethe Bohr:

Before the war; oh, yes, long before the war. He was not the open man as the others had been, so that you could talk openly. He was not quite that open kind.

Kuhn:

You may not want to talk further about it, but if you would, I would like terribly to know because of Heisenberg’s own role in these whole developments.

Margrethe Bohr:

Oh, he could be a little unfair. I always remember once when he was here, there was a lecture and Niels had been away —. It’s difficult to talk about it, but he could do things that were not quite right, and so on. I think it was taken up with him then because there were so many here who objected to his taking advantage. But then at other times he could be so nice; then one forgot about it. And probably it is the same thing that happened with this book of Jungk, where he gives a description of his visit here which is quite a different way around from our impression of it. He never said those things; Jungk reports; it must have been wishful thinking. We remember how it was, and also how it gradually came up so often. I mean, he was a good friend. In 1938, when he was newly married, they both came up and stayed with us. There they were completely taken up by Hitler and the fact that now Hitler was a reality. And I remember Chievitz was so angry. Once when Elizabeth Heisenberg and I were out walking in the forest completely alone — there was nothing to be afraid of — then we talked a little bit about the things in Germany. I said, “Wouldn’t it be nice for you to get rid of this terrible government and get some decent people.” She was a German lady, her father was a professor in history, and so on — a nice person. Then she said to me, “Ach, aber was sollen wir doch ohne einen Führer?” That was the attitude of nice young Germans, so I gave up.

Rosenfeld:

That was Mrs. Heisenberg?

Margrethe Bohr:

That was on their wedding trip, yes. Then they went back, and then came this terrible first day with the persecution of the Jews where they have smashed the synagogues and all their sacred things. Then she wrote me back a little note, and I remember she said, “Jetzt muss ich Dir veelleicht in manchem Recht geben.” That had also shocked her. Oh, there were very few Germans who had a clear attitude, I mean, apart from Planck and Laue. There were not many. To give an example of the way they thought, Heisenberg told me once they had a young girl in the house, “A nice young girl,” he said. It was in 194l when the Germans invaded Russia and he said, “She came rushing into my room and said, ‘Ach, Herr Professor, jetzt sturzen auch die Russen uber unsere Grenzen hinein!’” And Heisenberg was surprised, but he said, “Ja”, and he did not tell her that she was wrong. I asked him, “Didn’t you tell her?”, and he said, “No.” It’s so strange; you have to be educated in Germany to understand it, I think. He left her in that belief. That was the way in Germany, never to do anything against the authority. But, I mean, then he was, of course, not pro-Nazi; I don’t think he was ever pro-Nazi.

Rosenfeld:

I think he was fundamentally a German nationalist. He was sorry that Hitler was such a bandit — but he was happy to see that Hitler could lead Germany to what he thought was greatness.

Margrethe Bohr:

That I also think; that was the way it was. It was the same thing with Weizsacker.

Kuhn:

Among that group of assistants, starting with Kramers, who were the ones whom you think of as having been the closest and most important to Professor Bohr?

Margrethe Bohr:

There were Kramers and Klein and Pauli and Landau.

Kuhn:

Pauli was not here nearly so long as the others.

Margrethe Bohr:

Yes, he was here several times. Pauli was a very good friend.

Rosenfeld:

Yes, Pauli did not work in that way for very long, but Pauli kept always very closely in touch with Bohr’s work. Bohr had always the greatest regard for Pauli’s advice and encouragement and so on. So in that way he played a very important part. He was very beneficial because he was very critical. Also, I must say that Pauli is the only one, I think, who clearly understood Bohr’s thinking fully and also his intentions, you see. He understood not only the statements, but also the intentions, that is the general aims and ideas. He was most in harmony with Bohr’s thinking.

Margrethe Bohr:

But I suppose Kramers understood it also.

Rosenfeld:

Also Kramers, yes, so long as he was here, but in the later years he was not so close.

Margrethe Bohr:

No, when he went away then he wasn’t so strong. There were so many nice people; I don’t remember any who were not nice really. Who else was there in that regard? He was very fond of Landau, also.

Rosenfeld:

Yes, but Landau was more a stimulus to contradiction. . . . But surely there was Klein . . . And of those, scientifically, would say also Heisenberg.

Margrethe Bohr:

Yes, yes; surely, absolutely. And Franck was also a close friend. I’m thinking of who there was from America. First of all the Lauritsens, but he was also very fond of Bacher. There was Oppenheimer, of course, but he got to know him later.

Kuhn:

Wheeler?

Margrethe Bohr:

Yes, Wheeler; certainly yes. Pegram he was very fond of also. He only saw him occasionally, but he esteemed him highly as a very fine man. Veblen also was a good friend of my husband. And, of course, later in the years, there was Rabi.

Rosenfeld:

Yes, Rabi, also, yes.

Margrethe Bohr:

He had many good friends in America whom he was happy to see when he came over. And he had many in England. Of course, there was Darwin, and he was very fond of Chadwick. That, of course got especially close during the war.

Kuhn:

What about Dirac?

Margrethe Bohr:

And Dirac, yes, I had completely forgotten him; oh, yes, surely.

Kuhn:

Dirac’s cast of mind was, of course, very different from Professor Bohr’s. Did Professor Bohr ever express feelings about the rather different way in which Dirac approached physics?

Margrethe Bohr:

Well, he often did that, but, I mean, he was —

Rosenfeld:

Yes, he was rather amused, of course, to see Dirac’s unexpected reactions, not only in physics, but also in other respects.

Margrethe Bohr:

He was very fond of Dirac, yes. But, of course, in that time the relation was more like that between father and son; there was this difference in age. Dirac also felt towards my husband as toward a father. Niels was very amused when many years later Dirac said that what he loved most was his first stay in Denmark, and then Dirac continued, “but perhaps one always likes the first place best.” Niels was so amused. Nevertheless, Dirac loved my husband truly; I don’t think he ever came to anyone he loved more than my husband. . .

Kuhn:

I think this is the place where we should stop for today.