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In footnotes or endnotes please cite AIP interviews like this:
Interview of Samuel A. Goudsmit by Thomas S. Kuhn on 1963 December 5, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/4640-1
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This interview was conducted as part of the Archives for the History of Quantum Physics project, which includes tapes and transcripts of oral history interviews conducted with circa 100 atomic and quantum physicists. Subjects discuss their family backgrounds, how they became interested in physics, their educations, people who influenced them, their careers including social influences on the conditions of research, and the state of atomic, nuclear, and quantum physics during the period in which they worked. Discussions of scientific matters relate to work that was done between approximately 1900 and 1930, with an emphasis on the discovery and interpretations of quantum mechanics in the 1920s. Also prominently mentioned are: Gladys Anslow, Robert Fox Bacher, Ernst Back, P. A. Boeser, Niels Henrik David Bohr, Hendrik Brugt Gerhard Casimir, Walter Colby, Dirk Coster, G. H. Dieke, Paul Ehrenfest, Albert Einstein, Enrico Fermi, George Hartwig de Hass, Werner Heisenberg, David Inglis, Edwin Crawford Kemble, Ivan Robert King, Oskar Benjamin Klein, Ralph de Laer Kronig, Alfred Landé, Otto Laporte, T. van Lohuizen, Hendrik Antoon Lorentz, Fraulein Mensing, Edgar Meyer, Robert Andrews Millikan, J. Robert Oppenheimer, Friedrich Paschen, Wolfgang Pauli, Linus Pauling, Isidor Isaac Rabi, Harrison McAllister Randall, Adolf Smekal, Arnold Sommerfeld, Thomas, Uhlenbeck (George's father), George Eugène Uhlenbeck, Albrecht Unsöld, W. van der Woude, Vry, John Wulff, Pieter Zeeman; Universiteit van Amsterdam, Rijksuniversiteit te Leiden, University of Michigan, Teyler's Museum, Universität Tübingen, and Universität Zurich.
Tell me about your home. Pretend for the moment that we were doing a total biography.
From cradle to the present. The relevant thing is still that I want you to know something about the educational habits in Europe.
But that’s too late to start.
That’s not late; that is very important, because of my family background. It is the wrong idea in America that in Europe very few people go to high school and to the university, that only the rich ones go. That is wrong. It’s quite true that only few people go, but it has nothing to do with wealth: it has to do with family habits and tradition. An underpaid schoolteacher will send his children to high school and to the university, whereas in my family where there were rich merchants, I was the only one of all my uncles, aunts, cousins, in a large, large tribe, who finished high school. And I was considered a failure, because I wanted to study. My parents were not rich, but that had nothing to do with it. My cousins were much richer, and they thought it was a grave mistake.
In fact, my mother, as my sister told me only recently, wanted to take me out of high school. And my sister was taken out of high school, did not finish, and had to become an apprentice in a business somewhere. She refused, and she got a clerical job then. But in my family it was customary to get a much more expensive education than studying, namely, to be sent to some foreign country to learn the business. One cousin went to America, several went to France, some of them stayed in the Netherlands. One of my closest friends never went to high school, but went to England, and is a rich businessman in England now.
What was the business?
In my mother’s branch of the family, they were all in ladies’ hats, in millinery. That was the way these families ran: it had. nothing to do with financial circumstances. I am sure that George Uhlenbeck’s family — I visited his home — I don’t want to judge it, but it can be on the tape — probably was not half so wealthy as some of my uncles. But I’m sure that his family didn’t think of not sending all the children to high school, to the Gymnasium, or whatever it might have been.
What was the difference in the two cases?
The difference was simply that his family had always been an educated university family. His uncle, I should know, his favorite uncle, was a famous linguist, and my favorite uncle was a wholesaler in ladies’ hats and things like that. That was the difference. And they really thought that I was going to be a failure, that I’d always be a poor high school teacher instead of a successful businessman. So therefore that is important. Especially on my mother’s side that attitude was very strong. My Fathers family was poorer than my mother’s. My father was a little bit more interested in education. He had gone to trade school for a couple of years where he learned physics and algebra and geometry. Then be became a carpenter; that was his first job. Inter he worked in a wholesale business of hand-made furniture, which he later took over himself.
There was an evolution there, and be became what is called here a ‘jobber’, an agent for factories to the wholesalers for bathroom fixtures and primarily toilet seats. But it started out as hand-made, mahogany toilet seats which were made in his shop, and things like that: a most uninteresting business. My mother’s business was far more interesting because you needed psycbolo, and I was always in the shop. My father and mother went twice a year to Paris to buy the new models; not what they liked, but they had to guess what the tcb women would buy. When the new models came in, I was in the shop, looked at them, made remarks as a child, and said, “Take that feather off or change it, because she won’t ever sell it here,” and the personnel was always upset because my mother listened to me. I used to draw sketches when I saw interesting hats in a cafe — that was when I was 10, 11 or 12 years old — and gave them to my mother and said, “This looks like a nice hat.”
This was a manufacturing and sales business? My mother’s was purely retail sales. She had a shop, and so had all my aunts and uncles, but some of them were in the wholesale business. Their agents were Parisian houses for the ribbons and the feathers — I don’t know what you call the details. How, they had another effect, namely,that I didn’t even belong in university surroundings.
The schools in Holland don’t educate, they teach the education you get at home. These fellows who come over here, especially the refugees, were always considered so much better educated than the American equivalents. People thought it was the schools. That is not so. The education was in the borne. In a home like Uhlenbeck’s, there were always books around. In my home, there was very little of that. My parents had subscribed to a kind of a book club for a number of years. Being a traveling salesman for his business, my father read a lot on the train, and I was the other one in the family who did the reading, and nobody else did.
What sort of things did you read?
Oh, I don’t know. I remember having read in translation nerson, Poe, - mostly essays, I didn’t read fiction in those days except the Jules Verne type of fiction, that I liked very much, and detective stories. So I was totally uneducated compared to the other people.
When you say they taught in school, and educated in the home —
They trained in school.
Techniques, ja. But the real education of these people whom you know, like Uhlenbeck, really came from the home. His father, when he retired from the Dutch East Indies, where he was a high official, worked for a great publisher, Nijhoff. That is quite different from toilet seats. It was not much education. It was a good business, until, as n Lang said to me, the bottom fell out. [Laughter] So you see, this is important. I was an exception. I was sent to the university mainly because my father always wanted to study a little more; he offered his support, over the objections of my mother, who went to high school to ask whether it really wasn’t a mistake, and I heard from my sister that the high school principal said, “No, that boy should study.
It will be good for him; it would be a shame if he didn’t continue.” My father taught me a little algebra, a little geometry, by rote, already when I was very small. There were certain formulas he had memorized, and when Sunday morning as a small child I played in his bedroom in bed with my parents, he would teach me things like ?r2, and. the formula for the triangle, the square root of s times s-a, times s-b, times s-c. I learned that before I knew what the symbols meant. As a result, already in elementary school I was ahead in arithmetic. I did all the problems a little different from the rest of the class. That was my father’s influence.
I’m particularly curious about what you say now about the family background, because my impression is that in many Jewish communities, one would have a direction to learning.
No. Not in Holland, because there was no discrimination. Don’t forget. In the other countries where there was discrimination, the Jews had to become doctors or lawyers, because those were the only free professions; they couldn’t get jobs. In Holland, the percentage of Jews in physics, in medecine, or in law was a little larger than the average, maybe a factor of two, but that was mainly because they lived in cities, it was more a difference between urban and rural —. That was the main difference. And so that’s why it was not so. And I never was aware that most of the fellows with whom I talked were Jewish, on the contrary.
Were they mostly Jewish in fact?
No, no. About the percentage as the Jewish population in Holland 10%. Most of the fellows I worked with were not. And of course, in family relations, intermarriages were not very common in Holland. In social relations, you stuck to Jews a little more than otherwise.
But only a little.
But only a little.
Was your family religious?
My parents were not. My grandparents were, of course. They stuck to the old rules, and I had one uncle who was a rabbi, and one uncle who was an official of the Jewish community on my father’s side; on my mother’s side, none of them were religious. But on my father’s side, a few were. My father himself was extremely liberal. But I was Bar Mitzvah, but only in a small way. So religion did not play an important role; and being Jewish also very little, So I went to the university with this handicap, being the only one and considered a failure. And it was indeed true that in Holland, what was the outlook? I would become a high school teacher.
There was just nothing else.
Nothing else. All high school teachers were Ph.D.’s. And it so happened that the two teachers I learned physics from were both pupils of Zeeman. The first one was van Lohuizen, and- the other one, (Hallo), was the principal of the second high school I went to; be also was a Zeeman pupil; purely accidental, I suppose. This had really nothing to do with interest in that at first, except that when you have good high school teachers they encourage you. What happened to me is really this: first of all my father’s influence; then, my sister, who is older than I am she went to high school first.
Was there just the one sister?
Ja. She lives in the Bronx now.
So there were really just two of you.
Just two of us. But lots of cousins and family relations. Most of my mother’s family lived in Amsterdam, my father’s family in The Hague. We lived in The Hague. The thing which first struck me as physics and I always remember it I think I remember it, you know bow that is, when the hypnotist comes, you probably will find out it isn’t so is my sister’s high school book which I read. And there I right away picked out a part of physics which fascinated me; and it was spectra; that you could tell, by means of spectra, what the stars were made of. That I found so fascinating; it was incredible.
I also read the other parts of the book, the mechanics part, and I thought it was the dullest there was and I couldn’t understand it. I tried in vain to understand how an airplane stayed up in the air. I still don’t quite understand it. But it was in that book. It was a book by (Boumann) one of the old physics books. A Dutch book. I still remember going to the airfields the first demonstrations must have been around 1912 or something like that in the Netherlands — knowing the names and telling my mother this is called the stabilizers, and that’s called so-and-so. She was greatly in— pressed. I got it out of that physics book. But I did not understand these vectors. But spectra, that fascinated me. So I got out of the public library, lending libraries, other books on physics and astronomy at the time, trying to read. I don’t remember anymore what I learned.
There was only one thing which also shook me: that was the passage of Venus before the sun; that that had happened twice, and that it would not happen again until 2002. And it suddenly dawned upon me, there was something I would never see. That made a deep impression on me. It really made me feel sad. I still remember reading that, “I’ll never see that.” So that was the background, bow I got interested in physics. Then, when I went to high school, I read a little more
You went actually to two different high schools.
Ja. The reason is again I don’t think it exists anymore — that it was possible in Holland to go to a kind, of junior high school where the whole curriculum was covered in three years. In the second year you had to decide whether you really wanted to finish or to take a complete high school. It was just one of these safeguards. If I had been a failure, my mother would say, “O.K., now you come into business, you have your diploma.”
You already not have gone even to this junior high school?
I might not have gone to the junior high school at all. I might just have taken some evening lessons in French or so, because, for my mother’s business, you had to know French, things like that, and bookkeeping. They learned a few things, but just what was needed for the business in my family. And all the acquaintances and all the friends I knew were that way.
So it was really reading, writing, arithmetic, and beginning languages.
And beginning — or whatever was needed for the business, bookkeeping and so on. No education whatsoever. There was some, let me see. My mother used to know opera singers, and so we bad musical evenings at borne quite often. People played the piano, or brought a violin and a cello, and had a little trio. For several years we had it every Friday night. It was not very highbrow; a little Beethoven, Brahms, and so on. But I was exposed to it.
Did you play yourself?
I did not play myself. My sister learned to play the piano, and I was so upset by all the tortures she went through, and I am not musical. I learned to play myself, with two fingers, tunes, but never was musical. Then my sister at one time had a book reading club when she was in high school. I’m sure that the main reason was to get some boys over. I was exposed to that a little bit, I used to listen in, and they read a few highbrow books in Dutch here and there. She liked the boys and I liked some of the girls who used to come there very much, but I was still too small then.
How much younger than she were you?
Three years and a half. So that was my education: the book reading club of my sister when she was still in high school before my mother took her out and the musicales which we had every Friday night for several years, which was very nice, singing and so forth, but on a fairly low-power level. But at least it wasn’t all one negative —. They were not anti-intellectual, but business came first. Then in high school, that I was interested in physics helped, because that is true, if you have good teachers, they encourage you. When I showed a little more interest than the average, then a man like van Lohuizen helped me. He gave me books, told me what books to read out of the library.
Was this then in the second high school?
It was in the first high school. Then, fortunately, the second high school I went to, after I decided that I will go on, van Lohuizen taught there too. You see, I chose that second high school because he was there also the physics teacher, as well as the other man; there were two physics teachers there. He helped me, and was interested. We became friends, I went to his home. But my interest in spectroscopy was really, earlier than that, before I went to high school.
But he did encourage that.
Ja, he then encouraged it very much. But he didn’t know at the beginning that I was interested in that, because I tried to understand relativity. I wrote a little essay on relativity which worry that the Nazis got it completely wrong in my high school days — trying to understand what it was about it was special relativity still in those days, 1916,1917 or so. I went to art school also, because I began to draw these hats. They thought I might have a little bit of talent, and ray father always did a little drawing. He learned that too, mechanical drawing as well as hand drawing, for his business. He said, “Well, we’ll send you to art school.”
So I went for a couple of years, two afternoons a week, to art school. I enjoyed it very much, but it turned out, as I bad suspected, I have no talent. I learned some tricks, and so in school I used to make the best drawing, but it was the tricks again which I learned. I knew exactly with pencil and paper to draw the same thing, and one is glass and the other is wood, and I know the tricks to make the one look like glass and the other like wood. When we had free drawings in school, you had to draw something at home. And always I did something like a little silver vase and a glass one. That I used as my sketch, and I impressed the teacher that you could tell the difference; and mine were always exhibited. They never looked like the object, but it made no difference, you see. I was very good at fooling teachers that way, impressing them with a little outside knowledge which really was irrelevant.
But where did you learn these tricks?
Mainly from my father; but also in the art school. You see, that was the thing which ‘took’ with me. I did some fairly nice sketching at times in pastel, still lifes and pastel, and I used to enjoy it, but I haven’t done it since, except when I was sick. Then I was on Cape Cod, and I sketched a little bit; in fact, my daughter Esther was so surprised, she never knew I could do it. But that was the only time. This was the educational background. Then at the university
I’d like to know a little bit more in educational terms, really sort of formally, what you actually knew, had learned, in the sciences, but not just in the sciences, by the time you got to the university.
There is still one other important fact. From high school, you could not go to the university. It wasn’t even sure that I could go. The only thing which was open in those years was engineering, the engineering school. But just when I was in high school they changed the law. George Uhlenbeck was older than I was, and he missed out on that, and lost one or two years on that account, and went to the engineering school first, as you know, and then after the law was passed, was able to transfer to Leiden.
What would you have needed to have? Was it a different school?
A different school, because they required in addition to the three foreign langages, also Latin and Greek. And that was only done in the Gymnasium, which was one year longer than —.
So high school was Realschule?
Ja. So that was changed, it was possible to enter the university.
What determined which of those two you selected? I’m interested —- in your case it may be fairly clear; in George’s case, with a background of learning in the family, one would rather have expected that he’d have gone to Gymnasium.
Ja, I really don’t know, you’d better ask him. I’m surprised about that. Sometimes it was too expensive maybe, but I doubt it very much that that had anything to do with it, because tuition is low. Maybe he didn’t like languages, thought that he might not get along with Latin and Greek, and things like that. That was my trouble. One of the things, of course, which did stand out when I went to high school was that there were very few things that I could do well. Don’t forget that the schools, especially in Holland, are quite different from the schools here. You learn several subjects, there are no electives, and they are tough. All “A” students don’t exist.
So you never get the impression that you are good at everything. And in my case, and that’s the case with many students, you drop out of more and more subjects — you just get a passing mark -_ languages, history, and all the humanities were in that class. I had great trouble with them. In fact, I had to take special lessons in English because I almost failed and, in fact, my final exam I just passed. Whereas the sciences came out all right; but with the years, when they got more and more difficult, even that reduced: biology dropped out; then chemistry dropped out. That means I did not get an NA”, I got something like a “B-”. So there was really nothing left over but physics and mathematics. Then when I came to the university, mathematics was my failure, and physics was left over. And if it hadn’t been for Ehrenfest, I might not have succeeded in that.
So, you see, it was fairly easy to decide what you wanted to do. For the American students it’s much harder, because they get all “A’s” and they really believe that they are good in it, which is, of course, not true. And so that made it very much simpler. But then I had another piece of good luck. I had a friend I think it was a friend of my sister’s, I’m pretty sure of that whose father was a teacher, and whose brother was a musician, who was slated to go on to the university and high school, and he was two years older than I was. He influenced me quite a bit. He was a mathematician.
What was his name?
(Van Rees.) But there was one thing which disappointed me in him: he did not have research ambition. George Uhlenbeck knows him, and be was known at Leiden among the students as one of the best mathematicians, but his aim was to be a high school teacher. And indeed, when be finished, be became a high school teacher, as is customary, first in a small village in the Netherlands. When he turned out to be a good teacher, then several years later be got & job as high school teacher in Rotterdam. When that job was open, that was the job I think for which there were some overtures made, that was the job I’d get as soon as I finished, the one in the little village. That was really the horizon: I didn’t know any better. But be influenced me quite a lot. He was a little bit ahead of me, he was a student a year ahead, be told me about Leiden and the people, and the studying and the pleasure of it. He had a great influence on me. I saw him very, very often.
Even when he was at Leiden and you were still at The Hague?
And I was still in high school. Because he was engaged to a girl who was a friend of the girl I was engaged to at the same time, so we often went out together, the four of us.
You were engaged already in high school?
Oh, gosh, I was really — I don’t know what you call engaged, maybe even earlier than that. Against my parents’ wishes and so — that’s another story, it has nothing to do with physics. It has something to do with it, but not too much. But with all these stories and hindsight you can tell them so much more rationally than they really happened. But anyway, we were very close together, and he had a great influence on me. By the way, he was offered professorships later on, and didn’t take them. Even after the war be was asked to teach at a new university in Eindhoven. He still is a high school teacher in Rotterdam. He’s probably very, very happy.
Does he do any research? Does he publish papers?
No, no more, But he could. He had been in those earlier years an excellent teacher. But even as a teacher he did not want to join that new university. So in that we differed radically. But he had a very great influence in the early days. I came often to his home, and he came often to my home, we went out together every day.
You found the idea of teaching fairly repulsive?
No, no, not at all. My ideal was my high school teacher, I thought it was a nice life, I admired him very much. I still like teaching.
That’s what I was going to ask, because you do it well, and you do it with apparent pleasure.
Well, then, why do you say this was just the opposite from you?
Oh no, at that time it probably was not. You are quite right. Because as I said, my aim was to follow in his footsteps. When he left the little village, I get that job in the little village as high school teacher. Then of course things changed, and I became more ambitious and wanted to stay in research. But he had a great influence on me in the early years, and also during the early years of my studies.
Now let’s see if we can straighten this out a little bit more, because when you talked about the only thing one could see to do was teach high school, and indicated that your parents thought this was failure, did you to some extent also feel that?
No, I thought it was great. I thought it was a very respectable, well-paid job. I admired my- teachers.
Did you have any interest in going into the business?
I had more interest in my mother’s business than in my father’s business; but my mother gave up the business before I finished high school, so that opportunity wasn’t there any-more. My mother’s business was more romantic.
There was a time when you think you wanted to go into it, or thought you would go into it, saw this as a —?
The remarkable thing is that I never really thought. I always found that circumstances pushed me in one direction or another. I never made any decisions myself. At least that was the feeling I had in those days. The things I wanted to do, I knew, but I didn’t know whether they were going to be hobbies, in my high school days. I wanted to solve mysteries, and there were three professions where one could solve mysteries: the police, archaeolo, or science. I was aware of all three of them. What they have in common is just solving mysteries, nothing else.
Where did that interest in solving mysteries start?
That I don’t know. That must be — I don’t know where that is.
Do you read a lot of detective stories?
Ho, no more. I never read many- of them, just a few selected ones. But that was really a driving force: anything which was mysterious, which I couldn’t see, I didn’t like, I wanted to solve it. Also travel I always hoped to do a lot: to see China, and see this and that. Of course, that never materialized. But it was part of it that nothing should remain a mystery for me. That was a very important driving force as a young man. That I chose physics was simply that I failed in the other. I kept the other things as a hobby, at least two of them: detective work –
What do you mean when you say you failed in detective work?
There were aspects of it which I didn’t like: that you could not specialize only in documents, you bad to see murderers and things like that which didn’t appeal to me; a lot of drudgery. And there was no formal way of doing it, you had to start at the bottom, you had to join the police force or something like that. But I took a course in Amsterdam in scientific crime detection, and even helped the man in his laboratory a couple of times, setting up spectroscopic apparatus.
What about archaeology?
It is Egyptology, of course, that it became. I read about it. You know the well-known story of how I studied it by mistake.
I don’t think I know that.
When I was a student at Leiden, we had that club, Huygens, where you had to give lectures. I always talked about spectra lines, because it was all I knew about, and they began to make fun of me. So when it was my turn again, I had to select another subject. But I didn’t dare to talk about anything else, because I was the dumbest in the group; all the other fellows knew everything. So I announced a lecture on mathematics of the ancient Egyptians in the hope that nobody would knew anything about it, and that I could read up on it. I had read about it. When the time came I got scared, because there was Nijhoff, the son of the publisher, I’m sure he knew it all.
So I went to an Egyptian museum, and. asked the old professor whether be couldn’t help me with that subject, and he said sure, and he gave me some books. He said, if you are interested, why don’t you come to my lecture sometime, and I promised to do that. You know, you have no registration in Europe, lectures are free and open . . . . I gave that lecture by the way, it was probably one of the lousiest lectures I ever gave, on mathematics of the ancient Egyptians. But during the summer I got a postcard from the man saying, “My lectures start October so—and—so.”
So I think, “I’ll be polite, I’ll return the books, and sit in his lecture.” So I go to the museum and ask the doorman where this professor Boeser lectured. He said, over there. And I open the door; it’s his office, I am the only student. And so for about two years I had every week a private lesson in ancient Egyptian hieroglyphics. He always started with a Latin proverb; he always translated it for me because he knew I came from high school and therefore didn’t know any Latin. Three make a lecture, God, the teacher, and the student. So that I couldn’t walk out, you see. And after a while it became fun, but I always remained an amateur. He finally let me go when I told him I wanted to buy some of those things and collect: that was below his dignity. But I still found a postcard from him wishing me good luck in America.
That’s fascinating. By the time you finished high school, how far had you gotten in the various sciences and in mathematics?
In mathematics, just algebra, trigonometry, -—
No calculus at all?
No calculus at all. A little probability.
That’s pretty much the American curriculum. Is it usual not to have had any calculus by the time you get through high school?’
Ja, ja. Not at all. It’s probably a little stiffer. We knew trigonometry, we really knew how to solve all those problems. The only thing Ihave to say in favor of the Dutch system is the units. We get probably the same number of hours, but we get it fewer tlines per week, and spread out over several years. The result is you cannot afford to forget it. Here the students learn French, and they get two semesters of French all condensed in one year, and they never bear the language again, and, of course, they don’t know it.
Whereas we get it one or maybe two hours a week, and spread that out over so many years that you do not have a chance to forget it. We have every week about 16 to 18 different subjects, whereas here you have every day. Here the unit is the day, you get five subjects, every day is exactly the same; in the Dutch schools, every week is exactly the same. I have at home some of these curricula for the schools, which are interesting to study. But the trouble with that system is then you cannot have electives.
It must be rather rigid, otherwise you can’t do that. But I think it could be done here too, with at least part of the curriculum, and that’s enough to give an improvement in the retention. It makes a lot of difference whether you get French one hour a week over seven years instead of seven hours a week over one year, a lot of difference So that’s what I knew, and it wasn’t very much.
Well, now physics.
In physics — just elementary physics; no calculus involved. But you learned it well, problems you had to solve in high school. And so it was rather fragmentary.
Chemistry, a little astronomy, a little mechanics, several hours of mechanics. Mechanics was a separate subject in our school, so-called theoretical mechanics or whatever it was called. But a little stiffer, a little better, it was not superficial. It was rather dull, let me say it that way. It didn’t try to make it nice by bringing in locomotives and airplanes. Even the airplane book was vectors’. Nothing else like that. It wasn’t very appetizing, but it came natural to me, and I was lazy. So I got good grades for those subjects which came naturally. I remember that I had been sick, I had the flu or something; I was out of school for a while. When I came back we had a physics exam on subjects which I had not studied with the class; nevertheless I got an “A” or the equivalent, because these things had come naturally to me.
Meanwhile, what were you doing with your spectroscopy?
Reading about it, but not understanding it.
What were you reading?
I was reading the popular books on astrophysics. In those days it was Flammarion who wrote popular books on astronomy and astrophysics, the creation of the universe and creation of the solar system. It was very superficial, and I have no recollection of what I really learned outside.
Were you doing anything with van lohuizen about it?
No, no, he did nothing else but encourage it. The main thing he probably did for me is take me to Ehrenfest at one time, but that was after high school. You see, he still did some research, and when I was a student at Leiden he tried to tell me a little about what the kind of research he was doing which I did not understand at the time. But I remember that he was showing off with his proofs of a paper to the academy which turned out to be an important paper where be I think it was Bohr, on a visit to Leiden colloquium, which he attended from time to time, who had asked him to see whether the Zeeman effect couldn’t be resolved to see that the levels were split.
And I think that was his main contribution at the time. His dissertation was rather unimportant, and probably even wrong, I think. It was spectral series, trying a better form with more constants to fit the series spectrum of lithium better or whatever it was. But this work was really a contribution. Can you resolve the levels? It was much later that I understood what he had done. The moment when he showed it to me, I didn’t know what it was all about. So I went to Leiden, and like so many of these young students - -.
excuse me, when do you suppose he gave you Dunz?
Later, later, when I started to write my first paper. So I was already a student then, a second year student or so. He gave me a copy of his dissertation and some other things at the time. He gave me also a copy of Fowler’s book on spectral lines, which is a successor to this, which I still have, also with his name in. I’ll bring it in some day, but that’s not a rare book. I think everybody has Fowler’s book, Fowler’s spectral lines, but this may be a rare book, but that was later. So where are we now. Out of high school, I’m going to the university. Let’s see, were there any troubles there? No, I went to Leiden simply because it was nearest. I commuted from my home in The Hague to Leiden, on the train every day as many students did.
How long a trip was that then?
I had to go on my bicycle, or the streetcar, for about fifteen minutes to the station, leave my bicycle there, take a train which took about 20-2 minutes in the early days; lately it was speeded up now that they’ re all electric, and then had to walk for about fifteen minutes to the university every day. That was good. It was frowned upon — the people who didn’t live in Leiden, couldn’t afford to have a room there. That was wrong, because we were a group. We always met the same people, and there was a lot of discussion going on during that half hour or twenty-minute train ride and the walk to the university. So you mingled with chemists and astronomers and other people, and just because I commuted I got to know a lot of people whom I might not have gotten to know otherwise.
How did it happen that you all went at the same time if you were going to different schools?
There were not so many trains! It was like the Long Island railroad. You all got on that 8:30 train or whatever it was in the morning. And we used to complain every so often, because it was crowded, and once the complaint was so violent that they had a special car for us hooked on in The Hague and taken off at Leiden again during one season.
What did you study there?
At Leiden? Well, the more or less compulsory things, I took a course in elementary physics —.
Was this largely a practicum?
It was a practicum plus a good demonstration course, a more advanced demonstration course by very good teachers. I took mathematics, which was analytical geometry and calculus, rather stiff, and I did not do well in that. I had to take chemistry, including some practical work in chemistry, I had to study crystallography.
That was a required course?
That was required. I was very lucky again that just by the time I had to come up for ray exams they didn’t require it anymore. So I never passed the second exam in crystallography.
You didn’t like that subject?
No; because I had to learn all these —. You see, I have no three-dimensional vision, I have no three dimensional brain, and so I could not remember these classes of crystals and so on — very stupid. In fact, this may help you understand things, if I now can jump suddenly 40 years later for one moment. It came to me very clearly in Copenhagen at that meeting that I had made a very grave mistake in my life, again pushed by circumstances. The grave mistake is that I should have known, from the very beginning, and that Ehrenfest knew it, but I didn’t realize it clearly enough, that I am not, and never was, a theoretical physicist. That I should have stuck to experimental work, or close to experimental work. And so many of the things now become clear to me because of that. But it was never as clear to me as after this Copenhagen shindig.
I don’t know why that revealed it to m but it has had a very serious effect on the things I have been doing and am doing and so on. I have been always a misfit as a result, it’s very sad. Ehrenfest should have explained it to me more explicitly, and be didn’t. He did it only in an underhanded way by sending me away from Leiden, and making me an assistant to Zeeman three days a week. But he didn’t quite say why. He should have told me, “You are not a real theorist, you’d better stick to the interpretation of experiments, you will be better there.” But then, because of the spin, people always classed me as a theorist, but I never, never was, because I never could do the mathematics sufficiently well for a theorist, and I’m totally lost, of course, in modern theory, because that’s all mathematics. And George knows that I don’t know any mathematics.
There are even anecdotes about it in Leiden that when they asked me a question on my exam about Maxwell equations and so on, then I’d say, “Oh, that’s the part George always does.” That story is almost true, the real story is as follows. When I went for my final exam, we were walking towards the academy building there, Einstein, Ehrenfest, and myself —
Einstein was there.
Einstein was often visiting in Leiden. He was there again for a number of months, arid we were walking, and he (Ehrenfest) said, “The trouble with you is I don’t know what I can ask you, all you know is spectral lines. Can I ask you Maxwell equations and things about that? I said, “No, please don’t.” So it’s almost true, you see. But the anecdote is a little better, “That’s the part George always does.” Essentially the anecdotes are always better than the true story, but that’s how it happened. So at Leiden, as I was beginning to say, in the early years I was very obnoxious. I was sure I knew everything, or could know everything. It was in those years that I thought my parents were dumb, and if they just gave me a couple of years, I’ll know everything.
Does everything mean everything in the sciences, or —?
Well, maybe everything in the world, I can’t specify it. You know I recently heard a story of a well known physicist here who, not long ago, when he was drunk, really said, “If I were ten times as smart as I am now, I’d know everything.” I won’t mention his name on the tape. A very nice fellow by the way, very clever, but not that clever; the factor ten is not the right factor. And there was one incident — you know there are these incidents which often you can’t forget. That was the meeting with George Uhlenbeck. George Uhlenbeck I had vaguely known, because he had gone to the same high school, the second high school, that I went to. Also I was a member of the debating club, and when he was a student be used to come back and visit the debating club occasionally.
So I had seen him; he hadn’t seen me, but I had seen him. When he came to Leiden, I had already been at Leiden a while when he entered there; we had lunch together there quite often. One had lunches also in a special way in those days. He once put me in my place, which I can never forget, but which he has completely forgotten. He was reading a highbrow book, by a Dutch writer, which I only halfway understood, but similar books had been read in my sister’s book reading club, so I knew what it was about. I made the remark to him at lunch, “How can you read such stuff, it’ all such nonsense, what this fellow writes makes no sense; I believe that only physics makes sense.”
He got mad, and said, “Here, take it. I bet you can’t even read it.” He turned the book around and made me read it out loud and I, of course, failed completely. That made a deep impression on me, the fact that he was right, that I couldn’t read it. I didn’t know how to read this good Dutch. But he has completely forgotten that. I can never forget that incident, I still see it as if it happened yesterday — in the lunch room, in front of all the other students.
When you say it was different, how one had lunch, that there was something special about it—?
Well, we were poor. You brought your own sandwich or whatever it was, you bought coffee in that place where you went, except the law students were always rich, and they used to buy their lunch, and buy pastries. We were always jealous of them, we used to tease them. I remember we had a battle once, where they threw the pastries in our face from the balcony. There was a balcony in the lunch room. There was one other incident —.
Why were they rich? They were just richer?
They were richer than the physics students, because they came usually from the families who were already in business and then wanted to get a law degree, not always to become lawyers. It was somewhat like here; many students go into the law school in order to go into business later on. So they were usually a richer type of student than the poor physics students who came from somewhat poorer families — not too poor. I could have bought a sandwich, I’m sure. But it wasn’t done.
While I was mentioning that to Irene the other day, suddenly I remembered a funny incident that has nothing to do with physics. One of these rich students had ordered his lunch, and had a couple of fried eggs, and they fell in his lap. One of the physics students, it was a student he didn’t like at all, instead of helping him, says, “Wait a minute, you forget the pepper and salt,” and he speckled pepper and salt in his lap. [Laughter] That struck me as so funny, that’s also one of those incidents I can’t forget.
It was very mean, but that gives you a little of the atmosphere. There was also a little bit of an atmosphere of rivalry between the students who had come from high school and those who had the complete education. I did not feel that, because I always stuck with the people who had had a high school education. Most of the physics students came from the high school in that day. With that conceit came the following. There were in those days these socalled prize competitions, a hold-over from the old French academy. Ther were posted.
Were they French Academy competitions or university competitians?
They were in those days of the Teyler’s Museum. They were posted, but nobody ever paid any attention to them, or saw them. There were a few cases. Casimir is a famous case; his famous work that became his dissertation was the answer to one of those prize competitions. But I remember when I was in my first or second year there was one about spectroscopy. It was to find a better foundation and an extension of a rule of Sommerfeld that in the periodic table the alternate elements had either doublets or triplets in the spectra. I was sure I could solve that.
You were asked to find an explanation?
Not an explanation, but a better foundation and extension, because Sommerfeld had postulated that only on the basis of two columns in the periodic table — the alkalis, and the alkaline earths. There was some rule about it, and so they had as a prize competition to extend it, and to give it a better foundation, showing whether it’s really true throughout the periodic table. I thought I could solve that. The way I thought I could solve it is by finding empirical rules for these doublets, and then may be able to find bow it goes with the periodic table. I hadn’t the faintest idea really what was involved.
You mean, you could find the empirical rules for something like doublet separation that would enable you to pick them out?
Yes. To pick them out, and extrapolate, things like that. And of course, I did not solve the competition; but trying out these empirical rules, I found an empirical rule. I was all enthusiastic about it, I told my family about it - - of course they didn’t know what it was all about and I told Lohuizen about it. He said, “Oh, that may be nice, I’ll take you to Ehrenfest.”
This was in your second year.
It was in either my first or second year. I don’t know exactly. You have the chronology. My first paper was the result of that, it was published December ‘21.
That would be your second year.
Probably my second year. Well, I worked on it that summer I remember, towards the end of my first year, I got interested in that. So I got introduced to Ehrenfest. He was always interested in people who wanted to do something on their own. He looked it over, he bad me write it down. Then, instead of telling me it was wrong, he said, “Look, there is a paper in PHILOSPHICAL MAGAZINE which does something similar, why don’t you study that?” And of course it was exactly the same. Then I got even more ambitious. I said, “Gee whiz, maybe it’s wrong, maybe I can prove the man is wrong.” By that time, I believe, Sommerfeld’s book had appeared. That was heralded as the Bible, so I began to study that. On the basis of Sommerfeld’s book I discovered, or thought I discovered the z law for the doublets or the triplets. With that I went to Ehrenfest myself. It was still wrong; but Ehrenfest at least couldn’t say it wasn’t new. So he let me publish it, a short note in Naturwissenschaften. But because it was wrong, the main paper was published in that obscure journal, the Archives Neerlandaises.
But when you say because it was wrong, you mean what?
Well, I asked him to publish it, it could be published in the Academy. And I have the letter where he says “the Academy is filled” and I should publish somewhere else. I am so sure that that was an excuse, that he didn’t think it was good enough. That’s the first letter I have in these letters, a letter from Ehrenfest, “Sorry, but I can’ t publish this in the Academy, but publish it somewhere else.” He insisted that I write it up and get it published in that French journal.
Do you remember what your original rule was, We one that was also in the Phil ..?
Ja; a rule with z^2 , a purely empirical rule. But then I got that power rule out, and tried to compare it -. You couldn’t prove that was a fourth power rule, but I could prove that if you applied the fourth power rule that you got screening constants, just like for the X-ray doublets, which also were not understood, so-called relativistic doublets. And I called that the relativistic interpretation of the alkali doublets. At that time it was wrong because there was no interpretation for it. There was no reason why it should be like that. That was my first paper, and that gave me then an entree into the colloquium.
Before we get you into the colloquium, how much spectroscopy had you done at that stage of the game, and where did you begin to look at tables of spectral lines?
At that time, when I began to study these doublets, I probably got the numbers out of these tables, and out of Kayser from the library.
Were you already looking at Konen then?
And I was looking at Konen’s book, but I didn’t understand it.
How did you do with Sommerfeld?
Sommerfeld. You see I was very good at picking out what I needed; I never read a book from beginning to end; I started in the middle, where there was something I knew, and then, when necessary, went further or went back and learned a little more. But there were enormous gaps in my education as a result, because I picked out just the things which would be useful to the funny little idea I had, and nothing else. I was able to avoid all the other things which were not of immediate application to those ideas, and —
How were you doing meanwhile in the lecture course?
Lousy. Because as a result I neglected it. That also meant that I took a year and a half longer to pass my first exam than nomal. As you know I had gained a year in high school. I skipped the last year of high school, but that was not because I was good; that was because there was a flu epidemic and the high schools were closed. I did not have the flu. Then a student I knew in art school arid another student who is now a diannd merchant here in town said, “Can’t we work together and try to do the final exam, because the three of us did not have the flu? Let’s work on our own, and see whether we can’t pass the final exam this year.” Because they had also eased the final exams.
You didn’t have to know this part of history, you didn’t have to know that thing and so on. So we worked together privately in my father’s shop; my father was the timekeeper, he saw to it that we really worked. We even had a little chemistry lab, up there, in his workshop because you had to know a little practical chemistry. The three of us entered the final exams of the high school, which is equivalent to university entrance, trying it out. If we had failed, we would have gone back to high school for the last year, that was all there was to it. We passed!
Actually the flu epidemic was in what nonr1ly would have been your next to last year?
You took the time studying, and —
We took the time studying, and took the final exam. So, you see, it didn’t mean that we were any better, it was just lucky that we didn’t have the flu, so that was about 1918 or 1917, in Holland, about that time; I don’t know exactly when it was. I can look it up, I have my diplon somewhere still. But then I lost that year again at the university.
I take it you started in the university the fall of 1919?
Probably, I did the final exam in the summer of ‘19.
You went to Leiden in the fall, and then took your exams after what, 3-1/2 years instead of after two?
Ja, the first exams.
What were you examined in for the first exam?
Well, that was mathematics and physics, and — I don’t know what it was. But I didn’t have to do chemistry because I was so late, chemistry and the crystallography were dropped.
Already at the first exam?
Already at the first exam. These were requirements that were dropped, but I had a little more physics than normal. I don’t know exactly what they examined me in, but you know how it is in Leiden, the exam is a formality usually, but you have to go to each of the teachers privately, and they give you an oral privately, not at the end of the course, but when you feel you are ready for it. And I studied like bell for some of that; I remember very well that Ehrenfest had denied me access to the colloquium until I finally passed that first exam, because I was one of the few in the colloquium who hadn’t even passed the first exam. Usually you weren’t allowed in the colloquium until after your so-called (Kandidats) exam.
He denied me access to the colloquium just to force me to work for my exam. And I remember I really had to cram, especially for some of the mathematics which I didn’t know. I learned it quite well. I was all alone at home, my parents were away visiting my sister in Paris at the time for several months. At that time I taught myself to play a couple of pieces on the piano — a Beethoven sonata, and a little Mozart thing, just by rote. I went from my book to the piano, from piano to the books, and so on. That was all I ever knew at that time. And I remember that I went to visit my sister and she almost fell off her chair when I sat down at the piano and began to play.
I could read the notes a little bit, and I just learned it by heart. Again to convince myself that I had no talent, and why did I do it? First of all, as a psychological reflex, I think, from my cramming, and because of my mathematics friend who came( of course, from a musical family, and had taught himself the piano. I said, “Gee, if he can do it, why can’t I try it?” This was again the impetus, you see. I learned pretty soon that I couldn’t, But these two pieces I honestly learned by heart at that time. So, back to physics, Ehrenfest refused me access to the colloquium until I passed my exams. Then I finally did, but not too well. Then I had time again for physics. I have to look at my publications, I don’t know whether I published something already before that exam, or whether there was a gap.
My feeling is that you’d have taken the exam in ‘23. You had published the two papers on doublets.
Some of these are duplicates, as was customary in those days.
Two sorts of things before we get you back into your second round of physics. I’m terribly interested in this first paper, because it’s not unlikely that it’s got a good deal to do with what happened afterwards. How did you feel about the whole subject of the application of Sommerfeld’s relativistic theory to optical doublets?
I was convinced that it was right, but not for theoretical reasons. I was a man who liked empirical relations and empirical formulas, and I was sure that it was no accident at that time, but I did not understand relativity, I did not understand the detailed mathematics of Sommerfeld’s derivations. But there was that formula: why shouldn’t it apply to these doublets also? I was very proud of it, proud of having a publication, and as I’ve often told—.
But there were enough data?
No. If you now submitted the same thing to the PHYSICAL REVIEW I’d reject it. If you present it as an abstract at a meeting I’d say it s not well founded. I was very proud of the fact that it did get published, especially in the Naturwissenschaften. I even got a letter from a real physicist telling me that he was interested and wanted to get the detailed papers — Smekal — he wrote me a letter that he was very much interested in my interpretation. That made me very proud, to get as a young fellow a letter from a real physicist who had already published quite a lot.
What about this business of jiggling with the quantum numbers, which you point out has got to be done?
People jiggled with quantum numbers all the time. In those days there was nothing strange about it, it was normal. Don’t forget that I didn’t understand what I was doing.
Now you’re being unfair to yourself; you’re quite clear-cut about what’s obviously true in this case, for example, that the doublets cannot belong to the same— that you’ve got to reverse the function of the inner quantum number and what had been the running number for the terms.
Ja. I thought, well, that’s what it tells, but not knowing what the interpretation of those numbers was. Don’t forget one didn’t know what these inner quantum numbers were. The only quantum numbers one understood were the n and k of Bohr, and one didn’t understand the doublets and triplets at all. But the analogy with the X-rays, that was clear to me was no accident, but why, I didn’t know. And then I forgot it, then I had to work for my exams.
Did you hear from anybody besides Smekal about it?
No, not a word.
Nothing from Lande, nothing from Sommerfeld? In your first exposure to the colloquium, because you started going —.
Ja. In a typical European way, I understood only part of what was going on. But being exposed to it you absorbed quite a lot. Another thing happened, I had met Paschen; one should not forget that. It must have been 1921, I think. I accompanied my father to Germany in either ‘20 or ‘21, I think ‘21 because Ehrenfest was mad that I interrupted the lectures in the middle of the year and had to go to Germany.
Were you getting lectures from Ehrenfest as early as that?
I may have been sitting in, ja.
Because I think he would not have been giving one of the courses that was required for the comprehensive exam.
No, I think I sat in on some of that. I must look up in my notebook — you see, that is a thing where memory is very dangerous.
You have a notebook on this sort of thing?
I have a notebook, ja. I haven’t got it with me, I forgot to bring those because I didn’t think of it at the moment.
These would be notes on the lectures?
Yes, and they have some dates in them.
If you’ve got notes on Ehrenfest’s lectures at this time, this is something which —
They are lousy because I was such a lousy student, I didn’t understand the mathematics. There are hundreds of students who listened to Ehrenfest’s lectures, and there are some of them whose notes must be perfect.
Yes, but most of them don’t keep their notes.
That may be. Anyway [my notes] will tell you what subjects he discussed at that time, and more or less how he did it. From that point of view it may be of significance. Anyway, I think he was a little mad, and asked me where I went, and I said I went to southern Germany, so be said, “Well, you are near to Tuebingen, go and visit Paschen.” I don’t know whether it was during the lectures, that I was already in his lecture, or because I was in the colloquium, something like that; so I visited Paschen.
That was also a marvelous experience which I could never forget. Paschen didn’t treat me as a freshman but as a physicist. He showed me the 4686 line, the famous helium line with the fine structure, which he had set up with an interferometer in his laboratory. I did not understand it. I didn’t know what it was all about until I came back to Leiden. Two years later I went a whole summer to Paschen. There I learned the technique of spectroscopy. He made me build a spectrometer, told me how to measure spectra lines, what to look for — it was really marvelous. I spent the summer there.
You’d had no previous experience with actually getting data yourself?
No, no, never, I didn’t know how to measure anything. And I liked it very much. Anyway, I worked for exam, and I don’t know exactly which summer it was now because I worked at home it may have been even later that year. Anyway, these things were important to me. Then I remember that Coster lectured at Leiden about papers by Lands and by Lande and by Millikan where they had done exactly the same with the relativistic doublets as I had done, but they had more data. Millikan had really taken the ultra-violet spectra and now they had lithium, beryllium, etc. and the whole sequence. So he had data, and bad come to the identical conclusion. T: This must have been appreciably later, though?
About 2-1/2 years later, I think, or maybe 3 years later than I did it. And Lande, also on the basis of other people’s data, had come to exactly the same conclusions.
This would have been late enough so that already now it’s after the Rurnpf model?
No, — I don’t know.
Yes; the Heisenberg-Rumpf model, I think, wasn’t published until ‘23.
When did Millikan publish his stuff, I can tell — I may have —.
I may have that. [They hunt for the dates.]
I wrote a letter about it to someone once. I found it just the other day again at home. I have here a letter from (Breit) which may —.
That’s something also we can figure out, but my impression is that Lande’s involvement with the question of relativistic versus magnetic doublets really comes after the magnetic explanation.
That may be. I don’t know that anymore. I can look it up, but from memory I do not know the sequence.
I really think he’s got most of the g factor first and then comes back to the —-
That may be. I also do not know whether I knew Lend already or whether I got to know him later. But even that can be figured out from all those postcards, do you remember, which I have — the Lande postcards, that whole set. But anyway, Coster said, I put up my hand and said, “I talked about exactly the same thing 3 years ago” And suddenly Coster remembered, “Oh, this poor man,” he said, “he talked about the same thing 3 years ago.” And I thought it was hilarious, and I was rather put out, of course, at the time. But that was at a time when I was also in the middle of exams, and it didn’t make much impression on me. But then, when my exam—.
In the middle of the first exams?
On the first exams, ja.
But then it can’t have been 3 years, can it?
Sure. Because my first paper was ‘21.
But that was already your second year?
Ja. When was the Millikan paper?
Well, that I’m just not sure of.
Anyway I think I was still under the weather. I don’t think I had done anything. Because I see here, my next paper was then finally on some multiplets which I had found in iron and manganese and so on. When I had time again, I began to work on multiplets, trying to find multiplets in all the spectra. Now when did I go to Amsterdam, do you know that? When did Ehrenfest finally decide that I should be an assistant of Zeemann?
Well, I’ll tell you what I’ve got on it, — these things are never altogether reliable — ‘23. Now that would be after your exam?
I’m not even sure that it was right after or about the same time.
Probably - - you started in ‘19, then probably it was the summer of ‘21 already that you worked — or do you think it was as late as the summer of ‘22 that you spent really cramming for the exam?
Summer of ‘22.
Then the following summer would be the one in which this would come, this would be all right, this would put you at Tuebingen in 1923.
Ja. Where were we, I’m lost now?
Well, we haven’t been quite sure either where we were. In these early things in the colloquia, what were the topics of particular interest, what were people really worrying about?
I do not know; I have no precise recollection. I always remember the bad things. This happened to me, which gave Ehrenfest an excuse to kick me out of the colloquium for a while. I had gone to the colloquium, and they were probably the most interesting things, but they had nothing to do with spectral lines. Van Lohuizen as a high school teacher couldn’t always go, and he had asked me what was in the colloquia in the last few weeks, I said, “Oh, nothing of importance.” Van Lohuizen, being a little naive, when he came again — I wasn’t there — Ehrenfest asked, “Why didn’t you come?” and then he said, “Oh, Goudsmit had said there was nothing of importance.”
So then Ehrenfest stormed into the room, and said, “What did you say? You told Lohuizen that what was discussed in the colloquium was of no importance” He was furious. He said, “You’d better stay away for awhile and study a little while.” So that’s what I remember. But I do not know what these subjects were then: I was so narrow that if it wasn’t directly connected with atomic structure and spectra lines, then it didn’t stick with me.
Now there were some interesting things going on in spectroscopy itself right at this time. One of the particularly interesting things surely is Lande’s reinterpretation of the significance of the inner quantum numbers.
Well, I took these things for granted, you see. I never had the feeling of difficulties, never. I always had the feeling that these were empirical rules which some people understood and could interpret, if not now, then later on? My interest was really in the mechanics of the empirical rules. By empirical rules, I mean also quantum numbers. Even in the years when the Pauli principle came up, to me that was no more than an additional empirical rule like selection rules, like assigning quantum numbers. It was just an additional rule which explained a lot more and put order in this mess.
But the whole Modellmaessige side of this was of no concern to you.
No concern to me. But that reflects upon me, you see.
But you were also a contributor; there are different models certainly more important to Lande, but not exclusively important.
I knew the model but just did not understand it. I wrote you about that time when Lande came just the 5th of December, St. Nicholas, and that we gave him the “R” and. the “K” and the “J” in chocolate letters, which to us was marvelous, we had them on a cartoon. To him it probably merely meant that he got some good chocolate to eat.
No, he remembers it; and be doesn’t remember very much.
No. But that he remembers! And I took him around Amsterdam and The Hague and so forth. I was very narrow. After that, my work consited mainly of trying to find multiplets and analyzing spectra, which I thought was simple.
Now how did you do that? Did you do it from tables, did you do it from pictures?
No, because I did it sometimes from tables, sometimes from pictures. I had learned from Paschen that you couldn’t do it from tables. Paschen had told me, he had said, “Look at these lines, you can tell the ones which belong together by the way they look. You can never do it from tables, it’s not numerology. See, this line is a little more diffused, this in the discharge comes out a little longer on the spectrogram. You can tell, look at them.” And so, wherever I could, I did not go by the numbers but by the characteristics, but you could also do that from tables.
For instance, I remember once on a bet, opening Kayser’s book to some complicated spectra — I don’t know what it was, germanium or something — and picking out a multiplet, not by looking at the numbers and taking all the differences, but by looking at intensities. The Kayser Handbuch has numbers, and then also has next to each spectra line a little bit whether it was diffused or strong, you know, and there were some lines which just fell in a group which looked like a multiplet. That’s how I found them. Then I took the reciprocals in order to see whether the wave numbers fitted, and, damn it, it was a multiplet. I didn’t even publish it, it was so trivial I thought, it wasn’t worth while. But I did, I began with manganese, I think, and there was iron,’ and so. It was after Catalan had found the existence of multiplets.
Was that itself a big source of excitement?
To me that was, of course.
Where did you first know of the Catalan paper?
I think right when it appeared. We had good contact with England and so on. I think I still have some correspondence with Fowler about that in these letters. That was exciting because I’d always been interested in these empirical rules and now it gave Sommerfe1d’s rule, which I tried to learn about, more sense; relativistic doublets and triplets and so on, I got that extension. From then on, it became for me a kind of numerology, but I want to say it was not numerology, because the people who tried to analyze spectra by means of numerology never got anywhere. Even at M.I.T., where they built a big machine, they never got any spectra analyzed that way.
You have to look at them. You have to look at the lines, and if you can’t look at the lines themselves, then look at characteristics of the lines rather than anything else. There was a fellow in California, King, an astrophysicist. Be looked at all spectra in an oven, and classified them when they appeared, and whether they looked diffased and whether they were reversed or not. Those were the most marvelous sources of information because you couldn’ t look at the lines themselves, you could tell by his classification which belonged together. So his spectra were more valuable than the very precise measurements which were published. So that’s the way it was done. It was a skill.
What books, what journals where did you get pictures when you used pictures?
The pictures in Amsterdam. I looked at the spectra which were measured in Amsterdam, especially Zeeman. Then the Zeeman effect of course helped. In Zeeman’s lab, I told them what spectra they might look at — scandium was one of them. There were also many Zeeman effects published in obscure journals which I got hold of through Zeeman. There was a Hungarian publication which published excellent Zeeman effects; I couldn’t read the Hungarian, but the tables were there. That gave the spectrum of lanthanum, and one got things like that by just looking around in the literature. I was always excited, it was like solving puzzles, nothing else. It was not difficult. Then there were these little fights with Sommerfeld. Sommerfeld tried to monopolize the information on the iron spectrum, and he lectured in Amsterdam, and I had published something on the iron spectrum.
Where had be gotten the information, from Paschen?
Ja, from Paschen and other people. But he wanted to do it all, and I had published “Multiplets of the Iron Spectrum” based on some measurements made at the Bureau of Standards here. A fellow had found preliminary multiplets and I had properly assigned them and. so on. I remember Sommerfeld being quite upset because I ‘scooped’ some of his fellows. The one I scooped was Otto Laporte. But it didn’t matter, because what I had done was again the minimum one can do, out of laziness. When Otto Laporte published his paper, it was the complete iron spectrum, nothing left undone. So I never deserved, never got any credit for being the first.
Neither did the poor man at the Bureau of Standards who did it even earlier but not so well. Maybe there’s a footnote somewhere in Laporte, but I’m not even sure. Laporte is the man who really did the iron spectrum, because he did it from A to Z, everything. And it looked like quite a feat, because the iron spectrum was in the old days proverbially the most complicated spectrum. Of course from a multiplet point of view, it was the easiest, just for that reason. There are some spectra which they haven’t analyzed yet because they are really complicated, like tungsten, and uranium, and so on. But iron was the simplest. So that’s how it went. You see, I was a contributor only in this narrow field of interpretation of spectra, and that I knew quite well. I knew the spectra by heart, I knew all these rules by heart, but I was not a theoretical physicist, I did not know what they meant, I never felt that there were difficulties, I took the Bohr atom as something obvious.
How about the more complex versions of the Bohr atom? Were you concerned with things like Ellipsenverein, these models, before?
I looked at them, but I felt that I could not contribute anything there. Therefore I say I didn’t understand it.
Did you think they could contribute anything to you?
That’s why I read them. And I must honestly admit that I remember in the old days trying to play with models like that, but never succeeding - trying to improve it, trying to see whether one could get better results. But I never succeeded because you needed a lot of mathematics. You needed to compute orbits and things like that. I couldn’t do that. I always hoped that a very sin1e model would give the right results, and it never did. I did speculate.
Did you worry about helium at that time at all?
Ja, ja, but with no results. Only trying out, let’s say, two circles and whether I couldn’t get the radius of the one circle so that it gave the helium lines. Of course it never did, never did — pure speculations.
Did you read Lande’s early papers on helium, in which he tried crossed orbits?
Ja, but I didn’t understand. The only paper of Lande I understood were the ones where it was numerology, the Zeeman effect, “g-factor”; by ‘understood’ I meant that they stuck. I knew that by heart, inside out, I could do that on a desert island, derive the formula and so on, without knowing what the things meant.
What about the Rumpf?
That I did not understand. I never understood the difficulty and never was aware of the famous Pauli paper. For me, it was purely empirical rules and nothing else.
You say you were never aware of the famous Pauli paper —
In which he proves that it couldn’t be the Rumpf, remember, because if it were, then it could only be the innermost electrons, and then there would be a large relativistic effect. It was probably very important, it didn’t hit me at all.
It’s important too for me that you didn’t know that particular paper.
I can’t say I didn’t look at it, but it didn’t register with me, because it was not on my level at all. Had absolutely nothing to do. Let me see what else I did in those days?
I do want to get you to talk more about being in Zeeman’s lab in ‘23. This is early still, we’ve skipped past it, but let’s not go further.
In Zeeman’s lab in ‘23, psychologically it was important, because the atmosphere in Amsterdam was quite different from the atmosphere in Leiden.
Tell me more about that difference.
The difference was that Leiden was a rather high-brow university, and Amsterdam was a little low-brow university. I found more people of my kind in Amsterdam, I mean, the uneducated type, than I found at Leiden. It was a little easier for me to make friends there. It was also a very remarkable reaction I had: on Wednesday I traveled on the train from Amsterdam to Leiden to go to the colloquium, and I always had the feeling I had to turn a switch, already then, because now I know I cannot use certain expressions, I cannot tell certain jokes. It was very significant. As far as the physics was concerned, I learned experimental techniques of spectroscopy.
I tried to set up a couple of experiments myself. I did not quite succeed in doing that. It was Dieke who wanted me to get better data on the hydrogen spectrum, so with the help of the technicians I designed a discharge tube and a special cathode which we had read in the literature would give a very nice hydrogen spectrum and tried to take pictures of that, but it didn’t come out. I tried to do it, and I probably would have gone on with it further, but then I suddenly got interested in other things, the Zeeman effect, the scandium spectrum. But I measured lines, and I helped the other people with the interpretation and advised them on what to do and bow to do it.
What things? You told them to do scandium, because of its particular position in the periodic table?
Because it looked as if the multiplets were easy and that it would be nice to compare it, and because of its position in the periodic table it was one of the spectra of second — of hoeherer Stufe, with different limits and so on. I always looked for the easier things which were easy to do; and the hydrogen molecular spectrum was not an easy thing to do.
The thing Dieke wanted was a more accurate molecular spectra.
Ja, That has been his interest from the very beginning.
Were you tempted, did you consider going into experimental work?
[Pause] Ja. Let me say it this way. I would never have been an experimenter as such, but I would have been much better being near to experiments and help with the interpretation of experiments and directing experiments than as a theorist. The few things I did which were worthwhile were always of that kind, even later on. By telling people what would be worthwhile doing, and then giving them some advice on how to do it, and hope that they had the skill, (poor guys), so they could get it done. When they were in difficulties the only thing I could do was to encourage them, but not always give them advice.
Even when I came to Michigan, the first work was experimental; but I never got my hands dirty. I was much better at that. Even recently at Brookhaven I got really mad at the lousy way of interpreting some experiments. I insisted that they listen to me, and write it up the way I think it would be most convincing. And I think (Rothpool) listened to me and did it that way.
As you worked on the Zeeman effect, by that time you had the g factor. What was that like for you? Did suddenly lots and lots of things then open?
Ja, ja. It suddenly fitted, you see. At that time I began to understand what Lohuizen had tried to do, but didn’t quite succeed. So my opinion of him was a little, “Stupid, he should have done that several years earlier, but he didn’t.” I don’t know — probably there weren’t enough data.
And there were some ideas that had come along in the interim also.
Ja. But you ask here whether I knew the background of that paper of Van Lohuizen. I remember very well that be told me that it was the visit of Bohr at Leiden which either Bohr himself or Ehrenfest had told him, “Look for this.” But he succeeded only part way. See, what else did I do? You see, this is all spectral analysis. Then I began to get interested in intensities a little bit. I bad studied the intensities papers by Ornstein, Dorgelo, and so on, and tried to see whether they couldn’t be simplified so that I could understand them. I tried to understand Kramers’ thesis, but didn’t, and still don’t. I now know what’s in it. I may probably understand it now, a little too late. I had discussed with Coster intensities in X-ray spectra at the time. Coster was also very encouraging to me. I liked him. He was a difficult man, but I got along with him marvelously. He tried to help my parents in the war.
In that paper with Coster on intensities, you’re also worrying, I think, about the parallels?
Ja, ja. See, I had no inkling of that, I had completely forgotten, I just had the library make a reprint for me just now, because I hadn’t seen that paper maybe in 20 years.
But that brings you back in some part to your earlier concern again?
Ja. But I wasn’t even aware of that step in between.
Can you remember anymore now that you’ve seen it again? Can you remember more about how that —?
Ja, I remember that it was more Coster than I, because I was not sufficiently familiar with some of the intricacies of the X-ray spectra. Sommerfeld had presented it very simply in his book, and that’s as much as I knew. Of course it was Coster’s main field, and he knew many more of the intricacies about the intensities and so on. He discussed it with me for several evenings. He was in Haarlem then, and I used to go up there. Those were very nice discussions. That’s all I remember about it.
I always had the feeling that he was the dominant factor in that, and that he had adopted my ideas and adapted it to his field. So that paper was Coster. I must honestly say that the reason why I have forgotten so much about it is not that I haven’t seen it in such a long time, but because it was primarily his contribution. He understood my ideas better than I did. He had accepted some of my ideas and said this ought to be applicable to the X-ray spectra. And again these quantum numbers show up. You see how you have to change quantum numbers around.
It’s exactly this aspect of it that for the obvious reason particularly concerns me. By this time, one’s got now, at least for the optical series, the definitely competing theories. When does this paper go in? — just before the Pauli papers — but this whole issue of optical versus electromagnetic, versus relativistic thing is now wide open. How did you feel? Were you still pretty sure they were relativistic?
Ja. But only on the basis of the empirical relations, because, don’t forget, I did not understand relativity; I did not really know what it meant. I was aware that there were difficulties there, but —.
What did you know about the magnetic interaction theories?
Nothing. Except the interaction with the external field.
These internal Rumpf magnetic interactions —
I did not understand, did not understand at all. And the interval rule I did not understand how that came about. I only understood interaction with an external magnetic field. I understood the Paschen-Back effect and things like that.
Did you try to work an those things?
How about the Pauli papers in which he traces across from the Zeeman effect to the Paschen-Back effect?
Those I knew, those I understood. Those I knew very well, the sum rules. I think I wrote some similar papers or something later on, which I could only have written if - it shows that I really understood them already at the time.
Yes, There is one paper like that.
The strong field, and weak field, and how they were related, how you had a one- to-one correspondence, not the transition from one to the other. That I didn’t understand. For instance I also didn’t understand a much older paper which I should have understood. That was on phenomenological theory by Voigt for the Paschen-Back effect and the transition from weak to strong field which is perfectly correct. It really gives The formulas are there. It really gives the whole Paschen-Back effect from weak to strong field, but I don’t know what the assumptions are anymore.
That thing of course goes on right through the literature. Heisenberg was very nice about this, points out that they get that same formula three times. Voigt gets it by assuming some very odd ad hoc couplets between two electrons in a classical theory. Sommerfeld applies it to terms, and then he and Jordan get it out again.
Ja, ja. And I should have known, I should have understood it. I knew of its existence, but never understood what it was all about, because I was not a mathematical physicist.
How hard did you wrestle with these things? Did you try to do the Rumpf model — did you work - -?
No, I did not.
Did you work very hard on the Kramers thesis?
No. Ja, on the Kramers thesis a little harder, but I had to give up. I did not learn any good mathematics for a long time. Not until I had to teach courses in advanced mechanics at Michigan. That’s when I began to learn a little bit, when I had to struggle with it for some of the papers I wrote later. And it was a mistake from the very beginning to do it. I should have stuck to experiments and empirical rules. What else do you want to know, my relations with Kronig at the time?
I’d like to know about those papers and about how you got together on that whole subject with Kronig, and there’s the very interesting — there you’re right in an area where there’s real trouble, where the correspondence principle is saying something somewhat different from the Ornstein-Dorgelo theory.
The trick again was that I probably was good at guessing formulas. Kronig came to Leiden. I think he had a Rockefeller fellowship or a National Education Board Fellowship, and we bit it off very well. We saw each other quite a lot. He was very frank with me, he told me about the poetry he had written and things like that, so I felt very much attached to him in those days. We began to discuss these intensity things, and he knew all the physics behind it, I only knew the rules.
There were some rough rules for the Zeeman effect intensities based on the correspondence principle, and the question was, couldn’t we pin that down, couldn’t we by just guessing at least I thought of guessing, be thought of a model — find precise formulas for them. And we succeeded. But mainly, I think, I was the one who gave the clue to the formulas. I still have a letter where he says “Your remark has acted as oil on a machine,” because then he left and went to Copenhagen, so we never quite finished it together. The paper was written when he had already left Leiden.
Did he write it?
I think I wrote most of it that time, and sent it to him for his comments and so on, and he wrote part of it. But I think of that paper, because it was published in the Dutch Academy, I wrote most of it originally, but I cannot prove that at the moment. You have to make a word study with a computor, and that kind of nonsense. My contribution was again that suddenly I knew the formula, I knew how you had to replace L by L*1 and I just said “Now we know how these intensities” — don’t forget we knew the sum rules. That we believed in, that the sum of the intensities bad to add up to a certain thing. And it was such a conlicated thin
you had five levels here, and seven levels here, and all these lines and selection rules. Is it possible to invent a formula which would just obey the sum rules and looks plausible and gives the right result? It was honestly guesswork, and b knowing that kind of formula very well, without understanding bow they came about, I was able to guess it all right. But Kronig was the one who knew the correspondence reasons for it, who knew the sum rules, you see; I was the one who was good at putting in j times j+l and showing that it just would give the right result. Things of that nature, that was my contribution.
So, you see, it was also typical for me that a1nst always I needed to work with somebody; very seldom could I do a thing alone, usually with somebody. I worked very closely with Kronig in those days. Kronig went further, of course, and also did the multiplet intensities much better. But our work was the Zeeman effect, and then, of course, other people independently had done it too, and I don’t know, these formulas were rediscovered by at least 3 or 4 different people independently.
We’ve talked in at least some detail about the part of your period at Leiden, education up to the time you took the Kandidats exams. Then what did you do?
After that I sat in on the lectures of course at Leiden, still went to Amsterdam, as you know, regularly, —
You were there what, 3 days a week?
Three days, Monday, Tuesday and Wednesday I was in Amsterdam. Wednesday night I came to the colloquium and then stayed Thursday and Friday in Leiden. I have forgotten whether one went Saturday or not; probably did in the morning, I don’t know. My trouble was, I did not take many regular courses, and there are big gaps in my education as a result. I am not an all-round physicist.
What did you have to do, for instance, with an eye to future exams?
I almost failed. And there’s another anecdote about it, in my final exam, you had to have a major and two minors. The story in Leiden is that when Sam did his exam, his major was spectra lines, his first minor was spectra lines, and his second minor was spectra lines. And it’s true. First of all I had not taken all the courses which were required. For instance do you know well, I shouldn’t get it on the tape because it is so shameful, that I really never took a course, and still do not know maxwell theory! Honest! It’s a shame, but it just happened that Ehrenfest wasn’t there, the course wasn’t given, I never taught it, and I never studied it for myself. So it was quite true, when Ehrenfest walked with Einstein and myself, “Don’t ask me that, I never took that course.”
What about Hamilton-Jacobi theory?
I learned that much later, I learned that a little bit. I took a good course in mechanics, but Ehrenfest had a fight with the professor, and I had been sick — I don’t know what it was, I think it was again that flu year, or another flu year then — and stayed away, and had been stupid enough to tell the professor that I’d make up. I never did, because I got interested in research and spin and things like that, you see. But I knew it very well, I studied it. Mechanics I understood, the simple mathematics. You needed no more, at least the mechanics I know you didn’t need too much highbrow mathematics.
But this didn’t get you into things like contract transformations?
A little bit. I knew what they were. And also I taught it at Michigan later on and had no difficulty with doing it, at least the main points I can teach still very well, but not the detailed mathematics, not the existence theory and so on. So I knew it very well, but Ehrenfest and that professor Van Woude had had a quarrel. So Van der Woude refused to give me an exam, he said, “you didn’t come to my lectures.” So there I couldn’t finish for my doctoral. So what was to be done? Ehrenfest, of course, was a powerful man, he said, “We’ll find something.” So he went to the astronomers.
The astronomers were always very friendly. Ehrenfest said, “look here, this fellow, he must have his 3 subjects, and the mathematicians don’t want to give him an exam. Are you willing to take him on?” And the astronomers said, “Sure, we know him, and we have listened to his colloquium lectures, he’s all right, we’ll give him an assignment.” The assignment was the theory of Darwin and Fowler and Eddington of the star spectra. And I had to study that quite well, including the mathematics, and I learned it very well, I had to write a little essay about that.
The other subject then was experimental physics. I’d been with Zeeman, at his lab, and so de Haas was willing to consider that as requirement for experimental physics. Ehrenfest took of course, the spin work, and other things like that. So you see, it’s quite true: first major was spectra lines, first minor was spectra lines, second minor was spectra lines. That’s how I finally passed my exams before the thesis, the doctoral exam.
When did you actually pass those? Just before, or sometime before?
No, some time before. I don’t know exactly when it was, I’ll have to look that up. As you know, writing a thesis can be put off in the Netherlands for a long long time if you don’t want to do it. My main time was spent trying to learn more about spectra by working in Zeeman’s lab, trying to write papers on spectra lines, things like that, coupling schemes, giving lectures to the colloquium or to the Dutch Physical Society about spectra lines, and to the Huygens [Club] about spectra lines.
Who else was involved with this sort of work at Leiden?
Nobody. There were those experimenters who worked with Zeeman, but they did very little when it came to the theory of spectra. Zeeman himself was not active at all. He was just a gentleman who came to the laboratory one hour a day. He was very nice and friendly, would invite you to dinner - there are lots of stories about that. It was always very painful, we were poor, and it was the old Dutch habit that if you were invited to dinner at a gentleman’s house the maid had to get a tip; and the tip you had to give the maid was always much more than we would have spent for our supper. So we weren’t always very happy. Then we were placed among his daughters and family according to seniority. I was very lucky, I was youngest or the latest of the assistants, and I was with the youngest daughter, who was by far the most intelligent and nicest, the one I looked up this summer again.
That correspondence just can’t be gotten?
It can’t be gotten. But I’ll still try.
Is there a chance that George can do something about this when he’s there?
Only by asking Miss Zeeman again in Amsterdam and she is very helpful and very nice.
I think the best chance is for somebody who’s there for a while.
By the way, I am getting photographs of the wall. I just got a letter from (???) and I told him what I wanted again. Finally clicked you see, it took a long time.
If we go much further we’re going to get into spin, and I think we should save that for Saturday. Look, on page 3 of this outline, we’ve given a list of a lot of the things, and we ought to stay away from No. 9 and the things after that. Some of the others I’ve already asked you. I really just wonder whether looking at some of these great big developments of the time you were there will remind you of things.
I tried. They do not. And s imply because of w own narrowness. I did not take part in these great developments.
Now, what about the Bohr-Stoner theory, because that one you were interested in?
That I again took as a new rule. You see, the Stoner sub-groups, it was natural to me. I don’t know for sure, it was the kind of thing that when I read it, I might have said, why didn’t I think of it? It fell in line with what I had known, but again, like the Pauli principle, to me it was just another rule for understanding spectra.
Now the Bohr thing did not have the same sort of effect on you. You think it was Stoner’s paper rather than Bohr’s?
Stoner’s paper, ja, ja, definitely. Because Bohr I probably didn’t understand. But Stoner’s was such a natural thing. Then also the interpretation of some of the magnetic properties, and I didn’t quite get it right away.
How did you talk about spectroscopy with Ehrenfest? This was not on the whole his sort of work at all, was it?
No. He let me talk about it in the colloquium, and of course he had a lot of patience. Even if he wasn’t interested he didn’t show it, because he always tried to encourage me. Of course it was often talked about in a derogatory way.
By the other physicists. They called it “zoology,” “the cosine pest,” and things like that. It was not considered right, but I didn’t feel it, I thought what I did was nice contributions.
And it was.
But in terms of what was going on in those days it was really a minor side line. I say it was a nice contribution, but so was a nice contribution just measuring those spectra, that was just as important, because measuring them and getting them in the table, and Kayser’s Handbuch I think is also an important contribution. But is it really physics in the modern sense? I still think it is, I still think that physics is an experimental science, you must first get the data. But I was not in on the excitement, because it was outside the capacity of my brain. I met the people. I was friends with Fermi from the very beginning when he came to Leiden and so on, but the physics itself went past me.
There’s one thing I ought to know more about than I do. In the earlier part of the time you were in — the ortho- and para-helium series, one’s a singlet and one’s a doublet. Do you remember how the resolution to a triplet comes?
I don’t know whether I was the first one who proposed it or so.
I’m just not sure.
I’m not sure.
There’s an awful lot, and more, almost more in this whole spectroscopy — spectroscopy after ‘22 becomes incredibly complex.
I wish I could find that helium [paper], I think it is mentioned on that paper with Uhlenbeck. By the way there’s one interesting thing I like about the spin which I had completely forgotten about until a year ago, because the reprints — these are the reprints of the spin paper — but if you look at the original article, there’s a little appendix by Ehrenfest, which is again a typical Ehrenfest thing.
Yes. That is certainly worth knowing, that there’s a note by Ehrenfest.
That he had heard the same idea from de Haas, who is setting up an experiment. I don’t believe a word of it, to be honest.
Some of this at least, not in the form of an inner rotation in its original form does go back to the Einstein-de Haas —. That’s not presumably an inner rotation, but it is an anomalous gyromagnetic ratio and gets into some of these issues.