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Oral History Transcript — Dr. Otto Laporte

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Interview with Dr. Otto Laporte
By Thomas S. Kuhn
At Ann Arbor, Michigan
January 31, 1964

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Otto Laporte; January 31, 1964

ABSTRACT: 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 ca. 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: Joseph Sweetman Ames, Ernst Back, Niels Henrik David Bohr, Max Born, Gregory Breit, Louis de Broglie, Constantin Carathéodory, Eugene Charles Catalan, Peter Josef William Debye, Paul Adrien Maurice Dirac, Paul Ehrenfest, Albert Einstein, Walter M. Elsasser, Walter Grotrian, Werner Heisenberg, A. S. King, Rudolf Walther Ladenburg, Alfred Landé, Max Theodor Felix von Laue, L. S. Ornstein, Friedrich Paschen, Wolfgang Pauli, Arthur Pringsheim, A. Schoenflies, Erwin Schrödinger, L. A. Sommer, Arnold Sommerfeld, Otto Stern, Merle Antony Tuve, Gregor Wentzel, Wilhelm Wien, Robert Williams Wood; Universität Frankfurt, Universität Göttingen, Rijksuniversiteit te Leiden, Mount Wilson Observatory, Universität Munchen, and Universität Munster.

Transcript

Session I | Session II

Kuhn:

Let me suggest that we step back a little bit, just back to the beginning of the Munich period, and let me ask you this time to tell me a little bit more about how you lived there, whom you saw, when you did physics, how much time you spent in the library, and that sort of thing. Did you live at home, for example?

Laporte:

Yes, we lived at home. My sister was taking courses in literature and I was taking courses in physics and in mathematics. I took a great deal of mathematics.

Kuhn:

Did you take mostly physicists' mathematics or did you take a good deal of abstract mathematics?

Laporte:

No, I told you I took abstract mathematics from Pringsheim, the elder Pringsheim, while at the same time having to endure Sommerfeld's criticism for doing that. Since I was always under the influence of Sommerfeld quite considerably, I must say that the abstract mathematics which I had has not really had any great influence on me. What I knew I have forgotten, too.

As it is now , I'm quite at home on a Riemann surface, but I don't know what the (Heine-Borel) theorem is, for instance. I know (Heine's) book on spherical harmonics; that's meaty stuff you see, but (Heine-Borel)—. I have yet to see where the Lebesque integral is to be used in physics. I understand it can be used a little bit in the formulation of the ergodic theorem where measure comes in, but I haven't had a chance to use that. Now, let me see—mathematics; yes, I took lots of mathematics courses, but the mathematics which I really learned I got from physicists. Sommerfeld was immensely fond of doing things in classes which were really mathematics. Once in statistical mechanics he needed to have the expression for the total surface of a three-dimensional sphere imbedded in four-dimensional space, so he immediately did it in n-dimensional space in a remarkably ingenious manner, and was smiling, terribly pleased. He did it all on the blackboard. Things of this nature—he was very fond of that kind of stuff.

Kuhn:

Was that something he did in the regular lecture course or in an advanced lecture?

Laporte:

He did that in the advanced lecture course where it was needed, you see. He would just take time. In heat conduction, you see, one is always led to these infinite series which are actually theta functions; so then he showed how, depending on whether you want to know the temperatures for large or for small times, when you put a hot body and a cold body together, that you have to use a (Jacobi) theta transformation. He said, "Rather than using a mathematical way of deriving then, we simply resolve the same heat conduction problem with two different methods and since the thing is unique, then we equate the two and we have the theta transformation function." Such things, you see. That's quite typical of Sommerfeld.

Kuhn:

Did he continue all the way through to give problems, even in the advanced course?

Laporte:

No, not in the advanced course.

Kuhn:

Were there things the students naturally did in the vanced course in order to become at home with this material?

Laporte:

It was finally so that there was an inner core of maybe 12 or so students and every one of those had a problem. This frequently was not meant to lead up to a degree, you see; it was just a problem.

Kuhn:

That related to what he was doing in the advanced course.

Laporte:

Yes, exactly.

Kuhn:

Was that about the total enrollment in the advanced course, about twelve?

Laporte:

Oh, no. There were perhaps twice as many, twenty. Twenty was the enrollment in the advanced course, yes.

Kuhn:

You each had a problem sort of extending throughout the semester that you worked on. Did you hand it to him at the end for criticism?

Laporte:

Well, we would go to him all the time when we got stuck, you see; we had frequent conferences and at times he would also say, "Now show this to Gregor Wentzel,"somebody like that. Wentzel was his assistant at that time.

Kuhn:

Was it that sort of problem, a problem in conjunction with the advanced course, that led to your own paper on transmission of electromagnetic waves around a sphere?

Laporte:

Yes. Sommerfeld talked to me about that problem and sort of gave it to me.

Kuhn:

At a time when he was doing advanced electromagnetic theory in the advanced course?

Laporte:

Yes. He had always had a great interest in that type of electromagnetism; in 1908 he published a paper which was quite fundamental

Kuhn:

Yes, I know of that.

Laporte:

You see, in this paper of mine for the first time I discovered what is now known as creeping waves and Regge poles. "The way I did it is well known row, a posteriori; we all know (where) We get the inner connection." You write down the standard solutions with the usual eigenfunctions, infinite series—it converges very poorly; you change it to an integral; you transform the path of the complex integral; you suddenly see that there is a row of poles, and if you take the residues around those poles it becomes another series; and in that series each term means the wave has crept another time around the earth, around the obstacle. Now the applied mathematicians have caught up with that.

Kuhn:

Do you remember what other subjects Sommerfeld's advanced course dealt with while you were there?

Laporte:

As I said last time, there was a great deal of stuff about the continuous x-ray spectrum. Another time he gave a course on relativity and it was two-thirds special relativity, very beautifully done. He did all his old papers; he once showed that one could derive the radiation from an arbitrarily moving charge, also in the complex plane, in a terribly elegant way by taking a few residues—very much better than it's done in the books. Then he was always interested in four-dimensional vector notation, four-dimensional curls and so on. But when it got to general relativity theory somehow it didn't please him so much. Why he presented it to us—. He had not worked at it himself; his heart wasn't in it. There were some subjects where Sommerfeld's heart was not, you see, and we all knew it, one of them being thermodynamics. We always used to say, "Sometimes you have to learn for yourself or you'll never learn it."

Kuhn:

When you say "thermodynamics", are you thinking of the phenomenological approach or the statistical approach or really both together?

Laporte:

Almost both together. And really, advanced statistical mechanics we never got; you know, the canonical ensemble and things like that. I found that out later on—I mean, how incredibly more detailed the education of Uhlenbeck had been in that respect, because he came from the Ehrenfest school, and Ehrenfest worked in statistical theory while Sommerfeld worked in spectra and so on—just the counterpart.

Kuhn:

What else would you point to as things which were not particularly strongly taught in the Sommerfeld school?

Laporte:

That's just about all, but that's a considerable slice. Thermodynamics and statistics was not particularly well taught. The situation was improved upon and I suppose Sommerfeld knew it. He had another assistant, a Privatdozent, and that was Karl Herzfeld; of course Herzfeld was a specialist in that field so what thermodynamics I knew I really got from Herzfeld.

Kuhn:

How much time in the typical week do you suppose you would spend actually listening to lectures?

Laporte:

Maybe eight to ten hours, and then there might have been two more hours of seminar. Sometime later it became less.

Kuhn:

In addition to the regular Sommerfeld seminar there would be a colloquium. Were there two colloquia? Was there a separate Sommerfeld and Wien colloquium?

Laporte:

No, no. The colloquium went back and forth. When we had it in our institute, Wien would come over and Zenneck would come from the Technische Hochschule so it sort of travelled about. Then after the big colloquium in which the professors were always referred to as 'die Bonzen', the Bonzen, we, the more advanced and eager students, would all travel to a very cheap restaurant and have dinner together.

Kuhn:

would that include both Sommerfeld and Wien?

Laporte:

Yes. They would sit at the head of a long table and then gradually, through all the ranks,you'd go down and we would sit at the other end.

Kuhn:

A group of a couple of dozen?

Laporte:

Yes, maybe 25, and in the summer sometimes one would go into the Englischer Garten, sit in the open and have a beer, you see.

Kuhn:

how much did you see of Sommerfeld himself?

Laporte:

Oh, quite a bit.

Kuhn:

Did you see him week to week, individually, for consultation on problems?

Laporte:

Almost, yes.

Kuhn:

I gather that, perhaps, as compared to any of the other senior figures, he spent more time individually with students.

Laporte:

Yes. And frequently he would say, "Walk home with me and we can talk about it." He spent a great deal of time with us and frequently what we would come in the evening to discuss something special.

Kuhn:

Come to his home?

Laporte:

Come to his house, and then after a little while Mrs. Sommerfeld would appear and serve two glasses of wine or something like that. Even Sunday mornings sometimes I've come. Then about twice a year he would have an evening when he would invite students and there was always a great deal of music. Sommerfeld was a very determined amateur player; they played two pianos or one piano and one organ or things like that. You know Heisenberg is a good pianist, or used to be—I don't know how he is now—and so they would play together or Heisenberg would play along and Sommerfeld would say, "Ah! Ah! Play fast!"

Kuhn:

You said something to me about journals. Did you do a lot of your work in the library at the Institute?

Laporte:

Yes, the Institute was really an extremely Spartan place and still is; it just consisted of a series of rooms, one next to the other. Demonstrates on board Here is the outside corridor, here there were windows which looked out onto the court. Here was the Lesezimmer, one big table, where we read, and there was one bookcase as much as these two together, and that was full of textbooks and so on. Then here was a room for one of the assistants, I think Gregor Wentzel. Then here was Sommerfeld's room and it was distinguished from the others merely by having a parquet floor while these all had linoleum floors. Here was Sommerfeld's desk and near there there was the Annalen der Physik and Die Zeitschrift für Physik. When you wanted to get the Annalen der Physik you had to go through here and knock, then go through here on tiptoe where Sommerfeld would frequently be talking to other people, and you would just go and get it out.

Kuhn:

Were all of the journals there so that it was his office that had all of the journals?

Laporte:

Oh, I forgot to say. Here somewhere on the wall there was a pigeonhole shelf and there were the new numbers.

Kuhn:

yes, so that was in Wentzel's office?

Laporte:

There was the Annalen, Physikallsche Zeitschrift, Zeitschrift Für Physik, the Journal de Physique, the Physical Review, and the Proceedings of the Royal Society.

Kuhn:

And Philosophical Magazine?

Laporte:

Phil. Mag., right, which was much better then than it is now and was important. And the Astrophysical Journal.

Kuhn:

How about the Proceedings of the Cambridge Philosophical Society?

Laporte:

I don't think so.

Kuhn:

I ask about that one particularly because Dirac publishes a good deal in that.

Laporte:

But Dirac would only publish things in it which were of an occasional nature. A paper Dirac regards as important goes in the Proceedings [of the Royal Society].

Kuhn:

Not in the beginning always.

Laporte:

Not in the beginning?

Kuhn:

I think now of course that's true.

Laporte:

I have a feeling that maybe—yes, some journals we didn't have; Wien had them. Oh yes, the Proceedings of the National Academy. of Science in Washington.

Kuhn:

How about Naturwissenschaften?

Laporte:

Naturwissenschaften we had, and Nature we had; but for the Proc. of the National Academy we had to go to Wien's place.

Kuhn:

How many of these journals would you look at every time they came in? Did Sommerfeld push "keeping up with the literature", really following it systematically?

Laporte:

No, he did not. There were certain papers which we were highly interested in; things were brought up in the seminar and in the colloquium and we would discuss them then, but keeping up—no. There were so many papers in there, for instance, on gaseous discharge, gaseous electronics, and that was never—no attempt was made to keep up.

Kuhn:

I didn't really mean to what extent did one read everything in them. I meant more nearly that when a new issue of the Zeitschrift Für Physik or the Proceedings of the Royal Society arrived, would one automatically make a point of going to see what was in it every time?

Laporte:

Yes, we did that even without Sommerfeld while they were still in the pigeonhole place.

Kuhn:

Well now, on any given day would you be likely to find a large number of the graduate students simply gathered around the table in the Lesezimmer?

Laporte:

Yes.

Kuhn:

You drew four rooms up here; what was this one?

Laporte:

That was the room where Herzfeld had a desk and there was, another desk here and then there was a staircase, a little private staircase which led downstairs, and down below were the rooms where the x-ray interferences had been discovered and so on. There was the mechanic, too, who would type an occasional letter which Sommerfeld didn't write in longhand, and things like that. You know, typing was something which was really regarded as quite unnecessary because any journal would accept papers written in longhand.

Kuhn:

And I gathered from what you said the other day that really these copies in the library were the only copies of the journal around, that nobody, Sommerfeld or anybody else, would have his own subscription.

Laporte:

I don't think so, I mean, it could conceivably be possible. Wentzel might have known that Sommerfeld had his own copy of the Annalen at home; that could possibly be. I'm not sure, but I don't think so.

Kuhn:

And none of the students would take it.

Laporte:

None of the students. No, it would be regarded probably as showing off.

Kuhn:

The students themselves, then, in the course of the day saw a good deal of each other in this set-up and there would be a good deal of talking back and forth about problems?

Laporte:

Yes.

Kuhn:

Whom did you particularly see yourself?

Laporte:

It was Wentzel and Pauli.

Kuhn:

Pauli was not there for very long while you were there, was he?

Laporte:

No, he left after about two years, although he was still there; he was finishing off the article on relativity.

Kuhn:

He must have been finishing that off when you arrived.

Laporte:

Yes. I mean, he was then reading the proofs.

Kuhn:

I'm not sure; I would have to check it, but I believe he went to Hamburg in the fall of '22.

Laporte:

Yes, well, you see, I got there in the fall of '20. I was in Frankfurt from March or April '20 until July—one semester.

Kuhn:

Ah! I'm sorry. You were at Frankfurt only for the first semester.

Laporte:

Yes. The French took our apartment away.

Kuhn:

I remember your saying that, but I had not realized that they had done this at the end of the semester.

Laporte:

You see, my father had been an officer in the army; he was a colonel. Shortly after the breakdown of a country the victorious army is apt to regard the higher eschelon officers almost like war criminals, so there was a special thing [Order] that all officers' apartments would have to be given over to the officers of the French army; so we were in particularly bad shape.

Kuhn:

Tell me about your contacts with Pauli in this period. He was still working on relativity problems when you arrived?

Laporte:

No, I don't think so. It is actually a mystery to me how Pauli was able to read that tremendous amount of literature he could, or at least get an idea of it. It is really a mystery to me. Pauli published one paper on the effect which space quantization was having on the Langevin formula while I was there. Then he was working quite hard on the hydrogen molecule ion which, as you know, was his Ph.D. thesis.

Kuhn:

There's a puzzle—in fact there are a couple of puzzles—I might tell you about which you may be able to illuminate. The one which is really in your time is in connection with the hydrogen molecule ion...

Laporte:

I cannot help you there, but I can give you another counter example. We talked and discussed a great deal about the hydrogen atom and how, by the simultaneous manipulation of an electric and a magnetic field, a crossed magnetic and electric field, you could cause the electron to fall into the nucleus adiabatically. You're familiar with that.... 4 And I remember that when I saw the first treatment with wave or matrix mechanics I immediately looked for that and it was there so I said, "I know it's right."

Kuhn:

Did that problem bother Sommerfeld very much also?

Laporte:

Yes, yes.

Kuhn:

Because he fudges that one quite badly, or at least a very closely related problem, in the third edition... Some of the same things come up in this question of the exclusion of zero for certain of the quantum numbers; those are very shaky arguments in some cases.

Laporte:

Quite ad hoc arguments, of course.

Kuhn:

And that bothered you.

Laporte:

Yes, oh yes, that bothered us.

Kuhn:

To the extent that you would have said this is a counter example?

Laporte:

No, no. To the extent that we wanted to solve the problem of the crossed electric and magnetic field as accurately as possible. We knew it couldn't be separated and it was then that the first calculus of perturbation appeared in the literature, which was a big paper by Born and somebody—I think it could have been Born and Jordan.

Kuhn:

No, it's Born and Pauli.

Laporte:

Was it Born and Pauli? With Fourier series, all with Fourier series, contact transformations, and so on.

Kuhn:

There is an early Born and Pauli paper around 1920.

Laporte:

There are two papers on calculus of perturbations.

Kuhn:

Well, there were earlier ones; Epstein and Schwarzschild had both done some earlier perturbation theory.

Laporte:

Yes, the Epstein method we never thought was so good, you see. That was built upon the French mathematician Delaunay. The other one, the Born method, I don't know (the date), was actually to be found in Poincaré's "Méthode nouvelle de la méchanique célèste." That occupied a great deal of my time as a student: to learn Hamiltonian mechanics and to learn it terribly well; to learn what Hamiltonian mechanics becomes when you introduce action and angle variables, and endless examples of contact transformations from these.

Kuhn:

We've been talking about this sort of puzzle and the extent to which it was discussed; what about the puzzle of the Stern-Gerlach experiment?

Laporte:

Yes, you're quite right. We talked a great deal about that.

Kuhn:

The Einstein-Ehrenfest paradox did bother you?

Laporte:

Oh yes, yes.

Kuhn:

What did you think?

Laporte:

Well, at certain moments, you see, there was a certain feeling that you do—well, the logic tells it to you one way and then you make a certain break and then you know that you have to omit certain states or certain orientations—call it "quantum mechanical translation" or something we carried out. I mean like in the Landé formula to translate the j2 to j(j+1).

Kuhn:

There's another puzzle, as I said, and the origins of this puzzle are before your time... It's a Stern-Gerlach puzzle. Gerlach told me the following story and he's got some documentation to back it up so I think it's right. When he and Stern first got the apparatus running, they got a single spot and he has a letter which he was writing to Edgar Meyer. Most of the letter was written the afternoon before they turned on the apparatus, then they turned on the apparatus and there's a postscript written the next morning. "One spot: Somnerfeld is right." Then they work on the 354 apparatus. In fact Stern goes off to Rostock and Gerlach and a graduate student get it running. "Two spots," says the graduate student. Now this he reproduces from memory, but with the other—. Gerlach tells the student: "Go send Stern a wire; Bohr is right."

Laporte:

I don't know that.

Kuhn:

There were disagreements between Bohr and Sommerfeld, big ones, on the subject of space quantization.

Laporte:

Did you say Bohr or Born.

Kuhn:

Bohr. Now I would have expected them probably to agree about this, or they didn't, I would think it would be just the other way around. I wonder whether anything you know about Sommerfeld's attitude toward space quantization illuminates that story.

Laporte:

I remember talking to Stern, although I forget exactly when Stern actually talked to me. I was, of course, terribly green. I think it was at the Physikertagung in Jena. I was extremely young and green but nevertheless I went to Jena; I wanted to breathe in the atmosphere, you see. That was one of the few times I heard Planck talk and so on. I was talking to Stern in a coffee houseand Stern said, ,"Now supposing we take sodium; that's an S-term. And now we apply some infinitely weak field and they all get aligned. Then I pass light through it. It's now an anisotropic medium. You should get double refraction. I know I won't get it; I know, of course; it's impossible that we get it." He said, "What is this difficulty?" Those were the things we used to talk about.

Kuhn:

He was terribly bothered about that problem right from the beginning.

Laporte:

Oh, yes.

Kuhn:

That was the reason he did not expect to get space quantization; that was what bothered him about the whole problem. Did you yourself see a great deal of Pauli?

Laporte:

Yes. Pauli, Heisenberg and I used to take bicycle trips together and things like that.

Kuhn:

At what point in your knowledge of Pauli did he begin to get deeply interested in spectroscopic problems, because his early interests are quite different from this, at least so far as publications show.

Laporte:

Yes. He always knew the essentials, of course. That was the wonderful thing about Pauli; he always knew where the nuclear point was or something or other. He was then still a fairly friendly man, a young man, although always with a somewhat satiric streak; it didn't get to be until later that he really became extremely nasty and embittered, as you know. He must have had some fight with Born I never knew about.

Kuhn:

Do you think that probably there was a real fight there rather than his simply disliking the way physics was done in Göttingen in the Born school?

Laporte:

Well, that too. I remember that after Heisenberg's first paper on the matrices that weren't matrices, Pauli was extremely abusive of the Göttingen school and said, "Here are those Göttingen guys; they have once more succeeded in dirtying up that beautiful paper of Heisenberg there and putting it into the mathematical mire," or something like that.

Kuhn:

He said this to you.

Laporte:

He said this to me and to others. There's a man in New York you might want to talk to sometime, since you get there often, named Ludlow [Johann F. Ludloff]. It's a very good Anglo-Saxon name but he himself—I don't know how he gets his name—but he's an aeronautical engineer. He studied physics with us and he was quite in that crowd. He knew all the people I knew. He was a student of Sommerfeld's. He went into aeronautical engineering quite early and has done quite good work. He's at NYU .

Kuhn:

Let me ask you another question in connection with this statement of Pauli's I know Pauli had some funny feelings about this transformation of the Heisenberg paper by Born. Do you think that there was also in it some element of the feeling that Born really had no business taking that over and that he should have let Heisenberg work it out for himself, that it was to some extent taking over someone else's work?

Laporte:

I cannot say that. After all Born and Heisenberg published together a lot, you see.

Kuhn:

What about Heisenberg in this period? What was he like?

Laporte:

Well, I have to confess here that at this moment I have forgotten whether Heisenberg was still in Munich when he published that first paper of the matrices 'that were not'.

Kuhn:

No.

Laporte:

He was already with Born?

Kuhn:

He was already in Göttingen.

Laporte:

That's what I mean.

Kuhn:

But he was there more of the time you were than Pauli was. Pauli presumably left in the fall of '22.

Laporte:

But he was working very hard on hydrodynamics, on the one hand; on the other hand he was always producing these rather wild and frenetic blasts of research. He did a great deal of this half quantum number stuff, you see, which was really cramp-like (attempts) to burst the bounds of what we knew. And while we all said that here was an i ensely talented man, it was not sure that it would ever lead anywhere. It was getting more and more mystical, sort of like the (eight fold wave) nowadays.

Kuhn:

How did Sommerfeld feel about it?

Laporte:

Sommerfeld, I think, was always sure that with Heisenberg's great talent, something great would come out of it. Let me see, I forgot to say that Heisenberg worked for a long time on a semi-classical, semi-quantummechanical theory of the anomalous Zeeman effect. There was a paper by Sommerfeld which gave the anomalous Zeeman effect completely classical, or sort of inspirational, and Heisenberg was given the job of justifying that from the point of view of quantum mechanics, and he did that. I remember that So, erfeld once presented that in an almost semi-popular lecture and he said, "The difficulty about the Paschen-Back effect has been cleared up by a krasser Fuchs." Krasser Fuchs is the German student name for "freshman".

Kuhn:

Ah, that I didn't know.

Laporte:

Yes, it's a term taken from the lingo of the German student fraternities; you know; the ones where they wear colored caps, you see. And Sommerfeld was sufficiently of the old regime—because we ourselves all laughed at people who would be wearing caps—we were much too serious although half of the students certainly did belong to such student organizations and did the fencing also, you see. We, of course, deeply disdained them; when we had extra money we used to go to the opera or to a string quartet—real highbrow stuff. But in Sommerfeld's day, I suppose, there was less of a stigma attached, even in physics circles.

Sommerfeld had a terrific scar on his forehead which it was said he got in a duel; I don't know about that. I never asked him, but you sec pictures of him with that great scar. Nowadays you'd say it was from an automobile accident, but Sommerfeld certainly wasn't in an automobile accident. Something else occurred to me—yes, Heisenberg worked on the anomalous Zeeman effect and he worked on these so-called, I might say, "wild" papers, and he worked on hydrodynamics. He worked very hard on that. I think he wrote two papers in hydrodynamics while in Munich.

Kuhn:

There was one early one and then he did his dissertation.

Laporte:

Yes, the earlier one I think had to do with the initiation of the von Kármán vortex scheme. ['Die absoluten Dimensionen der Kármánschen Wirbelbewegunel]

Kuhn:

Yes, that was the very first paper he ever published.

Laporte:

I see. You can see that fluid dynamics was not a subject yet "of research about which" a physicist had to be embarrassed, as it is nowadays.

Kuhn:

Though it was perhaps only in Sommerfeld's group in Munich that that was true; you wouldn't find the physicists at Gottingen doing that.

Laporte:

That could be so.

Kuhn:

Let's come back—we've scarcely talked about it—to your own work and your recollections of that. We've talked about the first paper, or what I take to have been the first paper, "Electromagnetic Radiation Around a Sphere." Now, how do we get from that? How do you begin to pick up the spectroscopic problems which you mainly then from there on deal with?

Laporte:

I told you that we always did spectroscopy and that Sommerfeld always had these innumerable talks and papers where he would say, "Now here we have a d term and here we have a p term and then I give this quantum numbers zero, one, two, and this quantum numbers one, two, three and then he drew these arrows always. That was just a great thing in those days.

Kuhn:

You say he always did this, but it wasn't always appropriate to do that. He gave one course on this while you were there.

Laporte:

He gave one course and he published a big paper in the Annalen on the inner quantum number and of course that paper was in preparation for half a year.

Kuhn:

That paper was probably out by the time you got there, or came out very shortly after you got there.

Laporte:

It came out very shortly after. He had a paper with Heisenberg in which he tried to derive the fact that when the level one made a transition to

Laporte:

(cont.) two, one and zero, he could get the intensity from the cosine. Then, you see, he went to America and when he came back he was just completely enamoured of spectroscopy because he had seen great spectroscopic installations at Mount Wilson and he was just very much in favor of that sort of thing. He turned that entire material over to me.

Kuhn:

Had it been a surprise to him to discover that there was such good spectroscopy in America?

Laporte:

I don't think so, because he was always aware—he was never a Teutonically centered man; I mean, where spectroscopy was concerned there was Paschen, and then there was Fowler, too. He knew about the English. I wonder whether that post-World War I trip—the one he made mostly to be the Carl Schurz professor at Wisconsin—was his first trip to America ever.

Kuhn:

So far as I know it was; I'm not perfectly sure, though.

Laporte:

Well, it could be. Before World War I one travelled even less. I think (Boltzmann) was the only one who ever came over.

Kuhn:

And that was fairly late in life.,

Laporte:

I wonder whether Max Planck ever came to America; I don't think so.

Kuhn:

I don't know that he did. So Sommerfeld came back with a lot of data?

Laporte:

He came back with a lot of data and with great enthusiasm.

Kuhn:

What form was this in, mostly pictures?

Laporte:

No. These were some Zeeman effect tables from Mt. Wilson, and then a great many references to papers which he hadn't known about; most important of those were the papers by the older King of Mt. Wilson, A.S. King, an astrophysical spectroscopist who was the first to do the spectra of metals in a carbon furnace. By gradually raising the temperature of that furnace he was able to show which lines appeared first, and that was the resonance lines. Oh, yes, of course one thing we've never talked about is that this whole time the Franck-Hertz experiment was going on. There was Franck-Hertz and Franck and Cario and collisions of the second kind came in, "Stösse zweiter Art." That was discussed a great deal in our colloquia.

Kuhn:

Yes. That interests me because I think of that as not having all been done; of course, it wasn't, but it has a very important role, doesn't it?

Laporte:

Yes.

Kuhn:

Certain key points enabling one to tell what the ground states are.

Laporte:

Yes. The idea of the resonance potential is that you put in that much energy and suddenly the line appears. So he came with the references to these papers by King.

Kuhn:

Now where did those appear, do you remember?

Laporte:

In the Astrophysical Journal.

Kuhn:

You say the Astrophysical Journal was one of the things in his office; how had he missed these? They were too long ago?

Laporte:

...I'm happy to tell you this. You see, the Catalan paper had just come out and for the first time one could see that there was something in spectra other than the alkalis and the alkaline earths. I mean, you know how it is; when the research is being done, one often just feels, "All right; I'm working on this and that and that. Maybe future generations will explain what goes on in these confoundedly difficult things where there are so many electrons. Why, it would be just like a problem in astronomy. We'll never be able to do much in those complicated things." Now, what was it, what did King observe? King observed the spectra of the following elements: scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel; and then he probably also did the ones of the next period: molybdenum and so on, ruthenium, rhodium, palladium. He did them at three different temperature

...Now all those spectra have a great many lines, let me say anywhere from a thousand to three thousand lines; therefore his paper consists of—that is, the very first paper—a description of the apparatus and from then on it's all wave length tables with intensities behind. The wave lengths themselves were known; there was the Kayser Handbuch, there were these tables by Exner and Hascheck, those Viennese spectroscopists.

Now you look through the Astrophysical Journal because you are interested perhaps in cosmology or in radiation pressure or something; suddenly you have pages of nothing but tables and you say: "What is he doing? Why, he's observing the spectrum of titanium under different conditions, so what?" That's all. But when Sommerfeld came back he realized suddenly that this was a way to obtain the simple lines. I don't know (how he worked with them) but anyway I found myself working with these tables and it was comparatively easy. Whenever there was a group of lines which appeared at lower temperatures, King had given that classification Roman I; the ones that came at medium temperature were Roman II; and the ones that came at high temperatures were Roman III, so I took all the class I lines and after a few weeks when I got the hang of it I was able to get my first multiplets like Catalan.

Now then—yes, there's an amusing anecdote that I can tell you. Before working on iron where I got my Ph.D., I worked on the spectrum of vanadium. I did the first work in vanadium. I don't know why I chose vanadium; perhaps we had the data for that. So I got multiplets and I put them together and so on. Sommerfeld said, "Now we have another Physikertagung, this time at Bonn." So I said I would present a paper. That was fine with Sommerfeld, so I was on the program there; my paper came and then I described these multiplets and so on and who should be sitting at the first table, on the first bench, but Landé, whom I had had as a professor, as you know, in Frankfurt. He knew me, too; we shook hands and so on. Then at the end of my talk there wasn't any discussion since it was new stuff, people didn't know so much about multiplets and probably hadn't read the Catalan paper, but Landé got up and said, "May I ask the speaker what is now the normal state of vanadium?" So I said, "Well, the normal state of vanadium, strange as it may seem, is an F term, quartet F. So Lande had just a ghost of a smile on his face, said "Thank you" and sat down. Then two weeks later I got a postcard from Landé saying that he had just received the following little galley proof sheet of our discussion which was going to be printed. lie said, "In view of the fact that your work is obviously incomplete because the normal—the lower—state of vanadium could never be an F state, I think it is better that we omit that discussion." Then he wrote "You don't need to answer this postcard," at the bottom, so I didn't answer it and it was omitted. [laughter] The point of course, it was an f term, you see.

Kuhn:

Were you darn sure that it was an F term in spite of this?

Laporte:

Yes, because of the King stuff, you see; it was the bottom state of all those lines.

Kuhn:

I mean, there was no uncertainty; you just didn't want to argue about it.

Laporte:

Well, I was overpowered you see; you don't argue with a man like Landé Of course the amazing thing was, you see, what had Catalan worked on? Catalan had worked in chromium and manganese, both of which have S terms as lowest states, accidentally because it's the middle of the period. Manganese has sextet S and chromium has septet S and then vanadium comes right afterwards and has a quartet F.

Kuhn:

When you get at this sort of problem, and as you work on it, clearly one of the things that you've got that you had to have to do it was the Catalan paper, the King paper, the King data.

Laporte:

And I used the Exner-Hascheck tables a great deal—very dreary tedious tables, but most complete. What I used to do is play King versus Exner-Haschek.

Kuhn:

Two sorts of questions: To what extent do any considerations of models, structures, quantum mechanics, play any role in this sort of diagnosis?

Laporte:

Well, we did always have the feeling always, of course, that we had here penetrating orbits—you know, that was quite the thing in those days; orbits are penetrated into the core. I forgot to say that; this is an important point. We ought to have spoken about that. You asked me how much Sommerfeld's interest in spectroscopy, and also Pauli's, were talked about. Well, even before Catalan and so on you heard a great deal of talking always on what takes the place of the Balmer formula in other spectra, this R/(n+^)2. There's a long paper by Sommerfeld and Wentzel; I think it's a Handbuch article for either the Handbuch der Experimentalphysik Wien-Harms or for the Müller-Pouillet or one of those many volume things, in which they assume a core here [diagramming], a K-shell, and then carefully fit ellipses together and calculate the phase integral for the whole thing; and in this way, of course, they get fractional quantum numbers. So there was a great deal of work on that then.

Kuhn:

What sort of a change in that work did the Schrödinger work on penetration make? Schrödinger also computes, by a somewhat different method, some penetrating orbits.

Laporte:

With wave mechanics?

Kuhn:

No, before wave mechanics. I think in '22. I'm not sure if I've got the date right.

Laporte:

I've forgotten.

Kuhn:

He suggests changing the running term in the series, shifting 1 so that there are some arguments about that.

Laporte:

Of course while I was in Munich there was this—. I told you about the great impression which the Bohr letter to Nature made and how the occupation numbers were changed from four plus four into two plus Well, you see, at the same time that suddenly indicated, which we had never done before, and which I am sure is due to Sommerfeld, that the principal series, S minus P series in, for instance, sodium, should be called 3S minus 3P but we always had said 1S minus 2P. We had taken the number nearest to the hydrogenic value. That was important, to link that up with penetration; that was something one was interested in.

Kuhn:

I think the Schrödinger paper is another step in this direction, but I don't think it convinces people. I take it then, and this is important and very interesting, that it's really the Bohr paper which makes that point for people.

Laporte:

Now to get back—what was your last question?

Kuhn:

I asked you how much a role in general models played here.

Laporte:

Well, we always thought there was this penetration and there were the certain quantum numbers which were angular momenta; and then of course the thing came about with these large numbers of terms. In iron and other spectra multiplets were all very wall, but you got too many multiplets, and I made a mistake in my paper on iron. [writing on blackboard I had the lowest state which may have been quintet D, and I had something else which may have been quintet P. And another quintet P and another quintet P. So I said, "Ah! the series numbers"—I fitted this into a series—I would have the limit here, and this was the ionization potential. That's in my paper on iron and I was promptly taken to task about that by the astrophysicist Grotrian. You have heard of Grotrian.

Kuhn:

Yes, oh yes.

Laporte:

He died. Men my age [would] know him, but he died quite a long time ago.

Kuhn:

He was a contemporary of yours?

Laporte:

Well, he may have been a little bit older, but what the hell—suppose he's 70 years old. He died 10 years ago; that must have been one of those unfortunate deaths of cancer or something like that. He said that iron would never in a million years have an ionization potential that small; because he knew; astrophysics could give him, in conjunction with the Saha equation, at least an estimate of the order of magnitude. So this was frankly wrong. But then the puzzle still remained, 'Why the devil were there so .ny terms?' And this is where the thing you mentioned the other day comes in—I hadn't thought of it—the gestrichene Terme.

Kuhn:

With which Grotrian himself was much involved.

Laporte:

Yes.

Kuhn:

So at the time you did the vanadium work—would this also be true at the time you did the iron work, because I can't remember what the date of the Grotrian paper is now. It's around '23. The recognition that there's a whole extra series which you can get from the first series by simply adding a constant wave number difference. You can divide your terms into two sets, one of which is related to the other by a constant wave number difference so it's a difference in the setting of the limits. I see, I see, You're now speaking of ionizing an atom in two different ways and you have then two limits. Yes, I think there was an important paper by Wentzel written about that, a short note.

Kuhn:

I haven't read the Grotrian paper but I have read the Wentzel paper. I think the Wentzel paper is after a paper of Grotrian's and what's new about the Wentzel paper is that whereas Grotrian has done this only for calcium, Wentzel now points out that it works very well for a whole other group of elements also. And I think Grotrian for calcium has also spotted what's going on in the sense that he'd seen that it depends which electron 620 you're working on. Wentzel, so far as I know, then talks about two electron transitions; maybe Grotrian does this also. But you yourself were much involved with this because you apparently do a good deal of the work on the selection rules that are applicable in two electron transitions.

Laporte:

Yes. Well of course at that moment I got very much involved in the parity business because I found out that there were many states here, but then these many states combined with terms down here—there was a whole group of terms down here and they combined backwards, you see—and then by the time they got far enough away from each other, I calculated what this would be, and I searched for it. I searched for it in every wave length list and I never found a trace of it; you would calculate something like 25 lines down to a hundredth of an angstrom unit and then when you don't find any, that shows a great deal. It was then that I came out with the parity business, the even and odd terms. That was done simultaneously, as you know, by Russell, Henry Norris Russell and me, as an empirical rule. That was the selection rule which in spectroscopy was never violated.

Kuhn:

And of course at that point you didn't think of it as a parity selection rule at all; what did you think of it as? As late as 1925 when I was already in Washington I used to talk about it to Gregory Breit and people like that, and we really couldn't think of a good explanation. The fact that it was almost never violated—. Do you see what I mean? If a rule is never violated it is so inapproachable as to make it—. Other rules were sometimes violated, you see—. High current density would overthrow it; or something like that. You've talked to Gregory Breit, haven't you?

Kuhn:

I haven't yet; I have tried to and I will see him a little later in the spring... He can tell you a great deal about things. He was then completely wrapped up in the phenomena of resonance radiation and he can tell you a good deal about that.. In a way, of course, it's unfortunate that you're only interested in the history of quantum mechanics and not just straight physics but I can tell you this, as far as the history of physics is concerned: Gregory Breit together with Merle Tuve, are the discoverers at the same moment of the Heaviside layer, the first positive proof of the existence of the Heaviside layer, and secondly, for the first time they had done radar

Kuhn:

That I hadn't known about Breit at all.

Laporte:

Breit was always very much interested in radio and Tuve did his Ph.D. work under Breit at the Department of Terrestrial Magnetism. They, for the first time, bounced a radio signal off the Heaviside layer, and from the time delay they clearly got the distance.

Kuhn:

Now as you worked on these problems, because clearly it is just in this area that things are suddenly opening up in about '23 to '25, did this look as though it was going to go all the way?

Laporte:

Well, I tell you now, so many rules had to be supplied and I claimed to be the one who first made the statement that the maximum multiplicity occurring in a spectrum is always equal to the column number of the periodic table plus one. I stated that first, in Naturwissenschaften, so that we would have triplets for the alkalis, quartets for the earths, quintets for titanium and so on. So that was either way, as far as I see it now, the first time that spectroscopy and the periodic table of elements were connected. Previously it could have been possible, you see, that the thing just became more complicated as you penetrated more into the jungle of the periodic table, the way the valences—you know the chemical valences of the atoms don't follow any particularly regular pattern. Or ferromagnetism, you see, What's ferromagnetic; I mean, on the surface of it it certainly doesn't constitute a consistent phenomenon. But there spectroscopy for the first time produced a phenomenon which clearly was connected with the periodic table. Then the next law, which is also very important, the next in importance and perhaps more important, was what used to be called the "displacement law of Sommerfeld and Kossel". I wonder if you know the name.

Kuhn:

Yes.

Laporte:

Very simple, even trivial; that is to say, you ionize by one or two steps and you get a spectrum qualitatively similar to the one [preceeding it in the periodic system by one or two places].

Kuhn:

Yes, yes.

Laporte:

And with that, you see, we started to have a general feeling for the systematics of spectra.. But as for the numbers of terms, that did not get cleared up until Hund's paper—Pauli and then Hund.

Kuhn:

In this same thing here you talk about the displacement law; this works fine, but there is also the other thing that isn't working, namely the quantum numbers of the ground state, of one element, should be related to the quantum numbers of the Rumpf one over to the right in the periodic table. This is the Aufbauprinzip.

Laporte:

Yes, you're working on the Aufbauprinzip of Bohr.

Kuhn:

And the problem of the Aufbauprinzip begins to get its first solution, if anybody thinks it's a solution, in the Verzweigungssatz of Landé and Heisenberg. This sort of thing concerned with multiplets must have—.

Laporte:

I have forgotten the Verzweigungssatz; what's the Verzweigungssatz?

Kuhn:

...Now to what extent did your work on the multiplets involve you with these questions—with the Aufbauprinzip, with the Vorzweigungssatz?

Laporte:

It was clear; we knew that it would alternate, that the first, third and fifth columns would give me doublets, etc., and half quantum numbers. The half quantum numbers were quite well established at that time.

Kuhn:

But did you make any use of this thinking in terms of a Rumpf and what happens when you add an electron to a Rumpf?

Laporte:

Well, yes, but wasn't that already fairly well cleared up at the time of 690 Bohr's paper? One of the important things about Bohr's paper which I hope you will emphasize was his remark about the Aufbauprinzip: "the Aufbauprinzip just goes along smoothly until you come to the famous 19th electron." Have you ever heard of the 19th electron?

Kuhn:

Not in this form, no.

Laporte:

The 19th electron: Now I haven't got Atombau and Spektrallinien here; that's in my other office.... The nineteenth electron is the last electron of potassium, that's the point. And Bohr said that if you take a potassium nucleus and you add 1, 2, 3..., 19 electrons, it goes into an S term; we now know doublet S. And then you do it with calcium, which can take 20 electrons. And what happens when we send the 19th electron there? It still goes into an S term because the normal state of Ca+ is an S term. That's as far as one knew spectroscopy in those days when Bohr's paper appeared. And there really—there was vision. He says, "However, supposing now I take a nucleus which can normally take 21 electrons and I fire in one electron after the other; everything goes according to program, the eighteenth electron closes my rare gas shell, the Argon-like shell, and now comes the 19th electron. It will go into doublet D and this is the beginning of the inner Aufbau of the d shell, and it starts with the 19th electron which is the electron of the alkalis." And the way he proved that was by saying, "Let us now put down here potassium—the lowest state is doublet S and here is doublet D." [Demonstrating on board] Then he showed here—I don't know what vertical scale we should use—and he said "Here is doublet S, the normal state, and doublet d is down here." Then he said, "It is in fact extrapolated and will go below." And that was all the experimental fact he had, together with intuition. That was the great case of the 19th electron.

Kuhn:

And this made a great deal of difference to you, and in your own work also.

Laporte:

Oh yes, yes. We knew what we were working on then, you see. I remember then in those days too I used to do some abstracting of papers for the review journal, physikalische Berichte, and there was a paper on oxygen, spectrum of oxygen. I knew right away that there we were in the p shell; I mean, we knew which electrons we were working with. That had come out of Bohr's paper. There was no thought of equivalent electrons yet, but I knew it was p and I knew that was the way the thing had to work. That was all right. A remarkable thing about Bohr was his using relatively few facts and then fitting this whole thing together, and, as you know, out of that paper of Bohr's there came the very quick discovery of hafnium. You know, they had been looking for hafnium among the rare earths and actually it had to be looked for in tungsten.

Kuhn:

You particularly were doing this; Wentzel I guess got involved with it a little bit on certain more theoretical questions, and where he was doing spectroscopy, it was mostly x-ray spectroscoy.

Laporte:

Yes, he was interested in questions of the passage of particle rays through foils and he published a rather clumsy paper on that and the whole thing finally led to an integral differential equation; and that integral differential equation was sort of the forerunner of shower equations.

Kuhn:

I didn't recognize it as that.

Laporte:

You know, those equations they have for showers now on which everybody worked; Heider, and so on. It was without pair formation and so on, but I mean it was for the passage through—. He was interested in that.

Kuhn:

Who else was—

Laporte:

interested in spectroscopy? Well, a great deal of what I'm telling you is not history but anecdote. There's one historical character of whom you may have heard who is not famous but notorious and that's a man named Sommer. Have you ever heard of him?

Kuhn:

I've heard of him but I can't think now in what connection.

Laporte:

He was the crook of the 1920's.

Kuhn:

Well there was another wasn't there?

Laporte:

Yes, there was another.

Kuhn:

His name I can't think of, but it begins with a P or an R. [Rupp].

Laporte:

Yes, the one who claimed to have found the polarization of electrons, is that the one?

Kuhn:

I think so, and he also had a lot of very odd electron diffraction results.

Laporte:

Yes, that's what I mean, electron diffraction. He claimed to have found, after two scatterings—

Kuhn:

What was his name?

Laporte:

I can't think of it.

Kuhn:

Well, it doesn't matter. Tell me about Sommer.

Laporte:

Oh, that's a very famous tale. Sommer is a very famous case; you ask Wentzel about Sommer and Wentzel will just squeal with pleasure. Sommer was a discovery of Sommerfeld's; he came from Bonn.

Kuhn:

He was at Munich, though, when this went on?

Laporte:

Yes, and Sommerfeld offered him an assistantship because he thought that there was a wide-awake fellow, L.A. Sommer, S-o-m-m-e-r. So he came to Munich

Laporte:

(cont.) and ten minutes after he had been in the Institute Wentzel and Herzfeld and Ott and I knew that he was going to disrupt the peaceful relations of that Institute. He was disagreeable, tried to set one against the other, always thought he was being discriminated against and not told things, and so on and so forth.

Fortunately I was fairly well along in my doctor's work and I left. He didn't really come into his own until after I left. After I left he became extremely famous for the following reasons; there are three things. He went to America to McLennan's laboratory in Toronto where a great deal of spectroscopy was being done. You know about that, don't you? They were measuring some g values there—I think it was g values—and Sommer asked what the g value was, or something like that, and they had some suspicion.

Of course it wasn't very hard to realize that this fellow was not a nice guy. They told him the wrong value, and he published it as his own. That's number one. Then he got into various difficulties with the law, both in this country and in Europe. He was mixed up in the divorce suit of Paschen's daughter. Paschen's daughter had married a spectroscopist whose name I cannot recall [H.Schüler] an experimental spectroscopist. They got a divorce and Sommer did something like—they needed witnesses or something like that, and Sommer had coached a maid to give false testimony; the maid broke down under the quizzing of the attorneys in question and confessed all, whereupon Sommer got in terrible difficulties with the law.

Finally it got so bad that von Laue wrote to everybody and said, "Please, we have to impeach this man, good and for all; tell me all you know." He went around and presumably got many answers, and Sommer heard about that. One day Sommer ambushed poor old von Laue as von Laue was getting on his motorcycle Sommer by that time was quite out of his mind, jumped on Laue and beat him up. That is the last I know, but it's such an interesting story; I mean, he actually would be a character for a novel. I think he had some trouble with the law here, too, but I've forgotten now. Have you met Dean [R.A.] Sawyer here? The Dean of the Graduate School?

Kuhn:

No.

Laporte:

He did work with Paschen once.

Kuhn:

I might write him....

Laporte:

You know whom you can ask about Sommer is Goudsmit, I think. Goudsmit knows because Goudsmit was on rather friendly terms with Back.

Kuhn:

I know I've heard of Sommer before and it may very well have been from Sam Goudsmit.

Laporte:

The polarization man I've forgotten. Was it Rummel, or—?

Kuhn:

It's almost like that, but that's not quite right. I've got it somewhere else... To what extent did you also in doing these diagnoses use g values?

Laporte:

Oh, a great deal, a very large amount. You see, I had Zeeman effect observations which were not in the least as good as Paschen's and Back's in Tubingen. In those days Paschen and Back did nothing else; they were just done with extreme love and care. The ones which I had were done in a much more slipshod manner at Mt. Wilson by a man named [H.D.] Babcock.

They were mostly unresolved; however they gave me enough indication and helped me a great deal. Oh, there is one development which you should be aware of too; Landé published some very great papers in those days, the g and the interval rule. And the interval rule for multiplets of course was quite tremendous, and for many multiplets it very well follows that: 1 to 3 to 4 to 5 to 6.

Then, at that same physics meeting in Donn, Ornstein, the Dutch physicist of the University of Utrecht, gave a major talk on work which he had done with another Dutch physicist named Dorgelo. They had measured intensities very carefully. These intensities of course followed the law that where the quantum numbers are bigger, the lines are stronger. And Sommerfeld said to me, as we were taking one of those tours—the Physical Society arranged tours and we were going along the Rhine in a little motor boat; all the physicists were in the motor boat—"I have cleared this question up. I now know how to calculate intensities in multiplets, but I'm not telling it to anyone because Ornstein and his crowd 'nave done the experiments. It is so simple they'll find the rules themselves. They must find it." And then a few days later they did have it. He told them, "There's a simple rule; go and find it." and you know what it was—the intensities are proportional to the quantum weights and if you do it both ways, both for this state and for that state, then up to triplets, up to triplet F, triplet D, triplet F combinations, you get a sufficient number of equations that you can determine every intensity. Afterwards it's not sufficient, and I think that's important. You see, in this way we had both g formulae as well as intensity formulae and intervals.

Kuhn:

Was your intensity data generally good enough to be able to use the intensity rules in order to work back for identification?

Laporte:

No, no. Just once. Also still before quantum mechanics there was a paper by, I think, either Sommerfeld and Hönl or Sommerfeld and— who is the astrophysicist at Kiel now, a terribly well-known man?—Unsöld. It was either Sommerfeld and Unsöld or Sommerfeld and Hönl, published in the Proceedings of the Berlin Academy [Sitzungsberichte 9, 1925, pp. 141-61. With H. Hönl]. They had proceeded very cleverly—I forget exactly what the historical background is—but by combining those formulae by Sommerfeld and Heisenberg with the cosines, intensity formulae, and cleverly replacing all squares by quantum number times quantum number plus one, they had been able to find real intensity formulae that would hold for any multiplet. That was sort of an empirical tour de force comparable to Landé, you see, They found quantum mechanical formulae which, as you know, were integrals over three spherical harmonics, and anything but trivial. They found them by intuition.

Kuhn:

All of the early quantum mechanical papers keep deriving those formulas with great triumph.

Laporte:

Yes, and you see—I'll give you an amusing thing. You asked, was I ever helped by formulae like this? Well, there is one case where I published in my doctor's thesis a sextet d minus sextet d', a 'gestrichene multiplett', 1, 2, 3, 4, 5 and so on. I got that out all right except this line wasn't there; 'I had to calculate it. Otherwise the differences check in both directions. Well, I said, "O.K., it just happens to be a weak line or it was somehow obscure." That would frequently happen.' In that paper of Sommerfeld and Hönl they found with great rejoicing that the mathematical expression for the intensity had an accidental root there; it vanished!

Kuhn:

But you had in fact already gotten that.

Laporte:

I'd gotten the thing but I didn't know why; the formula didn't exist, you see.

Kuhn:

And in general when the formulas did exist, the intensity measurements were not accurate enough.

Laporte:

No, they were never measurements; they were always estimates. We're doing intensity measurements now in the other building for spectra obtained under very high temperatures in a shock tube, and I know that intensity measurements are no joke, that they are a great deal of work. So the only intensities that were measured were those that were done by the Dutch people.

Kuhn:

I think I should now ask you, unless you think there is something I'm leaving out, about the transition to America and a little bit about your impression of America; that is, how you came—I know you told me a little bit about this at lunch but we should have it here—some of your impressions of science in America. You were already in America by the time spin, the Heisenberg paper, the Schrödinger papers, the whole question of interpretation, and all of these things came out.

Laporte:

The Hund papers.

Kuhn:

Yes, that's true.... I'd also like you to tell me just a little bit about what you said the other day—that Condon and Shortley had sort of closed off the field. I'd like you to elaborate that a little bit. When this whole sort of spectroscopic problem ceased really, in the form that it had up to this point, to be of first rate interest to people. So there are a whole lot of things. Why don't we start by getting into America?

Laporte:

Yes, you want to know how I came, under what circumstances. Well, that still had to do with Sommerfeld's trip to America. When he was here, he met the Reverend Raymond [Harry Emerson] Fosdick, I think his name was, who was a close friend of the very old Rockefeller, John D. Rockefeller, Jr., who died about ten years ago. Not the one who handed out dimes but his son, the real philanthropist. He was given sort of a glimpse, he was told ahead of time, that John D. Rockefeller was going to give a great deal of money 831 for the establishment of a foundation which would make it possible for younger scientists, post-doctoral scientists, to study anywhere. They would not have to come to America; a Hungarian could go to Germany, which, for instance, happened in the case of von Neumann.

Well, I got just about the first one of these and I elected to go to Washington to the Bureau of Standards. I went to Washington to the Bureau of Standards because there was a scientist there by the name of Meggers who was a great experimental spectroscopist, and Meggers was just very, very anxious indeed to get in on this new stuff but he had no contact with any kind of person acquainted with this kind of thing and he was anxious to get me there so as to get in on this. That's where I stayed for two years, being paid by this foundation, the National Education Board. This later on became the same as the National Research Council Fellowships.

Kuhn:

What was your feeling about science in and around Washington or in the United States when you got here? Did you find it a backwater after your Munich stay?

Laporte:

In some respects, yes, but in other respects, no; you know how it is. I wonder how I would have found it if I'd merely gone to London; I might have found things similar. Then, of course, my education was one-sided; I had never been properly made aware of the power of the experiment, I believe. I may have been told, but it never penetrated. Then I talked with Breit and with Arthur Ruark, who is now with AEC in charge of Project Sherwood, I believe; they did experimentation. From that point of view I did not find a backwater; they were doing good experiments.

Kuhn:

And they both had some theoretical orientation also, Breit particularly.

Laporte:

Oh, yes. Breit, you know, had been a student of Ehrenfest's. He had been in Holland for a year or so. And another thing I should mention which is amusing too, is that after having been in Washington for about a year I was preemptorily ordered to appear in the office of Professor [J.S] Ames of Johns Hopkins. Professor Ames was wearing a light grey cut-away, looking for all the world like a German professor. He said to me that something had to be done about the education of the younger men at the Bureau of Standards because so many were taking their degree at Johns Hopkins, with no chances to have the right kind of education. He said, "You of course had these things from Sommerfeld; I want you to give a course in Maxwell theory and physical optics to these young people. You can do it every day or four times a week starting at five o'clock when work is finished." So I thought it over and I said yes. I essentially used my notes from the Sommerfeld lectures and gave them what I thought was a very honest course on optics.

Ames was very highly regarded in those days and indeed he seems to have had a greater influence on the course of science in this country than his colleague, R.W. Wood. You know, they did not get along with each other; Ames was the theoretician and Wood the experimentalist. Ames was not productive and was just an organizer; Wood was terribly imaginative and productive. They did not get along together. If they had it might have had wonderful results in Baltimore, but they didn't. As it is, you see, we owe to Ames the NACA. It's he who started the National Advisory Committee for Aeronautics, NACA, and in his honor they have named that simply enormous aeronautics research laboratory at Langley Field. Isn't that called Ames Research Center?

Kuhn:

Something like that. You were in this country, I guess it was really during your second year in this country, when the new quantum theory broke. How did you feel about it and what sort of reception did you find it having here? People here I think were in general less prepared for it. They were less clear that the other was wrong; that is they had been most clear that the other was right, had become gradually convinced that it was right, and thus were less prepared to see that it was wrong.

Laporte:

Yes, and of course it did appear very abstract to them. This matrix stuff was very, very abstract; there isn't any doubt about that. People kept asking me all the time, "All right, all right, what's a matrix then?"

Kuhn:

Did you know?

Laporte:

Yes, I knew; I explained it as a tensor.

Kuhn:

You'd had tensors in the relativistic formulations?

Laporte:

Yes, and in elastics and so on. Oh, we had extra meetings, that's right. It fell to me to present, at the Bureau of Standards in the seminar, the three first Schrödinger papers in the Annalen der Physik.

Kuhn:

Did you pick these out to do?

Laporte:

I think so, yes, yes. And I remember that I worked with them intensely; there wasn't anything finally which I didn't present with confidence, either approving or disapproving.

Kuhn:

Was this a single meeting on all three, or did you give one on each one of them as they came out?

Laporte:

I think I may have just continued the talk for two weeks or something like that—one and then a week later once more.

Kuhn:

Do you remember when that was? I mean, what time of the year?

Laporte:

No, all I know is that I was in Washington. But before that I remember once— ah, you'll be interested in this—I was staying in New York with friends and I ran into somebody, or we may have had some tiny Physical Society meeting, yes I think we did. And there I met two young fellows, one had the name Kronig, an instructor at Columbia, and with him he had a student named Rabi. We said that all this new stuff had come out and I had some new manuscripts which were(also to be)talked over. Kronig, Rabi and I and a few other instructors or graduates from Columbia, whom I didn't know or don't remember, met in some classroom—I think it could have been in Hunter College or sauLeplace like that—and for the first time, I think that was for the first time, that I even saw this. [writing on blackboard]

Kuhn:

pq - qp, yes.

Laporte:

So that must have been a good half year before the time when I said I presented those papers.

Kuhn:

Yes, just about. Do you remember what that relationship did to people?

Laporte:

Oh, we knew of course it was matrices and therefore not trivial, and it was all like magnificent magic.

Kuhn:

This presumably was the Born-Jordan formulation and not the Dirac formulation.

Laporte:

No, no, not the Dirac.

Kuhn:

Because Dirac comes out with this relation almost at the same time, but then they're quantum numbers, not matrices.

Laporte:

Yes. His c number or q number was used, yes. Have you talked to Rabi?

Kuhn:

Yes.

Laporte:

Was he good to talk to?

Kuhn:

Quite good. He comes in later than you and gets very quickly to nuclear physics so that he's not as much involved as you with problems that are directly within my scope, but he was quite helpful. He did speak of there being regular meetings of this group that I assume you were in on.

Laporte:

I went to one meeting. Stationed in Washington I only got in to that one thing.

Kuhn:

Now tell me about these papers that you delivered at the Bureau of Standards on Schrödinger.

Laporte:

Well, those were the Annalen der Physik papers.

Kuhn:

How many people do you suppose came and listened to that?

Laporte:

Oh, there might have been 15. We had a rather good colloquium and twenty-five years later we had a reunion like a regular class; we felt both sheepish as well as reminiscent, and we gave another colloquium. We used to meet either at the Bureau of Standards or at the Department of Terrestrial Magnetism and we met regularly between 1924 and 1926. There had not been a colloquium before and we sort of started it. There were Breit, Tuve, and P.D. Foote and his associate Mohler, and Ruark; then there—who is the deuterium man?

Kuhn:

Urey?

Laporte:

Yes, Urey, who was in Johns Hopkins; (Hafstad), vice president for research but he may not have come all the time; then the geophysicist, the scientific director of the international geophysical year, Joe Kaplan—Kaplan bands, you know, and nitrogen after-glow; and Meggers would come occasionally, and several more. It was quite a good group.

Kuhn:

How did they respond to the Schrödinger stuff?

Laporte:

Oh, it was taken, it was accepted. There was one thing; you know I told you about the denominator (n+1); you knew right away it was right. You knew right away. Also the fact that aperiodic phenomena could be dealt with, you see. Well, one knew right away that this was going to be permanent.

Kuhn:

How about the interpretation that went with it?

Laporte:

Yes. In that of course you're quite right.

Kuhn:

Was there a sense of relief that it was classical again in the sense of the waves being the real thing according to Schrödinger, or did you all know that that couldn't be?

Laporte:

Well, I told you about Wien; didn't I mention that?

Kuhn:

Yes.

Laporte:

Wien's expressing that sense of relief that now everything was good and definite again.

Kuhn:

How about this group?

Laporte:

When did the uncertainty principle come out?

Kuhn:

'27. About the summer of '27, the summer or early fall.

Laporte:

You see by that time I was already here in Ann Arbor.

Kuhn:

But the argument had started very early; I mean, Sommerfeld had a big fight with Heisenberg at a colloquium in the spring of '26. No. Excuse me. Heisenberg had criticized Schrödinger when he delivered a paper and Wien apparently jumped all over Heisenberg saying, "Go learn physics before you talk to Professor Schrödinger." Then Schrödinger went to Copenhagen in the summer of '26 and Bohr worked out—and then also the Born paper came out.

Laporte:

Yes, the Born paper, because that finished the argument.

Kuhn:

Not for many people.

Laporte:

The probability idea.

Kuhn:

Yes. Now I wondered how that worked out with your group, with these people. I wonder for whom the Schrödinger equation appealed in part because it looked classical.

Laporte:

Obviously it appealed to me because it looked classical. I mean I cannot deny that; I would be lying "to say that this beautiful mathematics didn't appeal". It's not for nothing that I'm a Sommerfeld product, you see. I had a thought there yet—you know how things go through the mind and then they come out again. Of course, when the Heisenberg uncertainty principle did appear then a vast number of justifications would occur to one right away. I mean like the fact that a wide slit gives a narrow diffraction pattern and a narrow slit gives a wide diffraction pattern and so on. In this connection I did tell you, did I not, that once, travelling to Europe on a steamer with Otto Stern—I haven't told you that?

Kuhn:

I don't think so.

Laporte:

Stern and I met by complete accident on the Ile de France , I think it was; we had a lovely time over-eating and over-drinking and he would talk to me at length about the thoughts of various people. He told me that Einstein never had given up the hope that one day this indeterminacy would be removed and the notion of probability would be thrown out. He could not recognize them at that time. Where is Stern now?

Kuhn:

He's in Berkeley.

Laporte:

And you've talked with him?

Kuhn:

I've talked with him just a little bit; he is the one really important person who has not been willing to participate in this really.

Laporte:

He's quite outgoing, though. Or is he very frail?

Kuhn:

I don't dunk he's so terribly frail. He was persuaded in Zurich several years ago to make a couple of tapes and then he listened to them and he didn't like them at all; for one thing I think he'd let himself go and his tongue had been very sharp. I don't altogether know what this is about I've tried, Minkowsky has tried, Segrè has tried, but we've really not been able to get him. He saw me once and decided he wouldn't go on. At what point does your own field, the whole set of problems of atomic spectra really get to be much less interesting to physicists at large, change their whole relation to the field of physics? How would you date that and what is the process by which it occurs?

Laporte:

For awhile everybody became highly interested in doing more with the foundations of quantum mechanics; that is, such questions as 'how can you have an atom with two electrons relativistically?' Such questions are still not cleared up.

Kuhn:

Did you worry about those yourself?

Laporte:

No, not I myself, but this was, the kind of thing. I worried to a considerable extent about the question of spin, how to put spin invariantly into relativity. I wrote some papers on spinors also. Once you've written a paper about spinors you're certainly out of spectroscopy; and while I did retain a friendly interest in spectroscopy, I haven't done any work in it except, amusingly enough, in the last five or ten years.

Kuhn:

Really!

Laporte:

You see, because—you know about this—since the war work one can observe in extremely short times; a micro-second and a nano-second...are things of daily occurrence and we can now produce gases of a temperature between 5 and 50 thousand degrees for the duration of about one hundred micro-seconds. So there's a fairly well controlled condition where we can say, 'What are the spectra which are emitted?' and therefore we can now for the first time observe absolute transition probabilities. This is at least a hope. So I have some students working on that. Well, in Washington the work has gone on. Meggers and his group, (Charlotte Moore)—they are all doing nice work on it.

Kuhn:

What did you mean the other day when you said that somehow or other Condon and Shortley had just brought and end to it?

Laporte:

I mean they had really written the definitive work; you could see then at that time that to continue would only be equivalent to adding another decimal point, although I mean it isn't quite so, but it is roughly so. It's one of the nicest books, and as I say, why have they never enlarged the book and brought it up to date? Very peculiar.

Kuhn:

How much would it change if you did a new edition?

Laporte:

Oh, there are many things in which it could be brought up to date, you see, even in comparison with the experiment. More cases have been calculated; there has been this Israeli man, a very fine scientist, who's done a lot of work on it, Racah. Then you could, with perfect right, put in a chapter on the shell model if you wanted to because that's the same kind of thing. [Pause] No, it isn't so.

Kuhn:

I hadn't realized that you'd gotten involved with spinors; that suggests that I really ought to ask you one other question. You talked about a couple of things that you knew were right just as soon as you saw them. What about the Dirac equation?

Laporte:

Ycs. I knew right away that it was right too and for the simple reason that the Sommerfeld fine structure formula came out in complete detail. This is what we used to say; we used to always say, "If ever relativity and spin are formulated properly, the Sommerfeld fine structure formula will have to be derived." And then we used to say, "For God's sakes, how can such a complicated formula ever come out in a second way?" you see. It is, of course.

Kuhn:

When you say, "This is what we used to say," what group is this?

Laporte:

Oh, it was Goudsmit and Uhlenbeck and I or something like that. It is really just short of a miracle that this formula, the Sommerfeld fine structure formula which contains denominators and square roots and square roots in square roots, that that came—.

Kuhn:

...You say that it was perfectly clear that this had to be right. Was this in spite of the negative energy solutions?

Laporte:

Well, what offended me more than the negative energy solutions was the fact that it was not overtly, was not manifestly, Lorentz invariant, but that you had to go to all kinds of trouble to prove it.

Kuhn:

You didn't like that.

Laporte:

There's a certain partisanship involved. I always wanted to see it written in the gamma formulation rather than in the alpha-beta formulation, SQ I thought that one would have to do considerable things to Dirac. It wasn't until later that under Pauli's influence I realized that one has to do both, that the alpha-beta formulation of Dirac is not sufficient and the gamma formulation alone is not sufficient either. You've got to have both. When the Zitterbewegung appeared that again was of course a difficult thing to contemplate.

Kuhn:

How did you feel about the hole theory as Dirac first formulated it?

Laporte:

As I say, I think one knew it had to be right; it had this great kinship in a way with Maxwell's equations, a first order theory.

Kuhn:

You know, Bohr reacted by saying that it obviously had to be wrong because if you had this infinite sea of charge around, he wanted to put this in as the rho in Maxwell's equations and then everything blew up. He wasn't going to compute rho by subtracting off the infinites; he intended to just start out with it.

Laporte:

Yes. So that's what Bohr told you.

Kuhn:

Bohr didn't, but I've heard this from several other people. As a matter of fact, I think it shows in some of the correspondence with Dirac. Did you get yourself much involved with field theory in the early days?

Laporte:

No. You mean second quantization and so on?

Kuhn:

Yes.

Laporte:

No.

Kuhn:

Unappealing?

Laporte:

Somewhat, yes, somewhat brittle theory. And in those days one got those confounded infinities right and left, you see. The question still isn't quite settled. Did you read Dirac's very thoughtful article in the Scientific American? It's a nice article, sort of written ('pro domo'), only for the 'cognoscente'; only they would know what he was talking about. He uses no mathematics, you see, and he describes the most subtle problems of physics. He calls them all by name without saying what the difficulty really is; you just have to know them by their names. I enjoyed that.

Kuhn:

It's also so totally unlike anything else he's ever written; he uses pictures, mathematics, talks somewhat personally. It's the antithesis of Dirac as he is known.

Laporte:

Perhaps he's mellowing! Well now, are we talked out? I think we are.

Kuhn:

Probably we are. I have a feeling that if there were time to take this American period more slowly—. Let me ask you just one thing we touched on and see whether episodes in connection with it occur to you. I asked you about the initial appeal of the Schrödinger equation in terms of the classical formulation. How much attention really was paid to the problers of interpretation? Even before the Heisenberg paper is the transformation theory of Jordan and Dirac; then comes the Heisenberg paper. But on top of that appeared complementarity and duality from Bohr, which aren't quite the same thing as the uncertainty principle, although they're often taken as though they all came immediately and together. What sort of interest in measurement problems did you see people having?

Laporte:

I often had the feeling that in this country there was not the interest in these matters of principle; there were very few places where people were interested in it. You asked me a little while ago what my general feeling about Washington was; was it a 'backwater'. I'll give you, however, a general feeling about American science then and also now, and I may be wrong in calling it 'American science' because the same transformation may have taken place in Europe: I have the feeling one has a greater interest in results than in understading. The principle of the matter, the interpretation of the natter, is pushed aside. It's regarded as necessary but we'll do it another time"; as long as we can get something which can be measured or has been measured then we explain it. You might almost say it's sort of an engineering point of view. Do I make myself clear?

Kuhn:

Yes, yes.

Laporte:

Now that is perhaps understandable because of the great upswing in experimental physics, the money involved therein, and so on. It is necessary to interpret the phenomena and it is necessary to pose new problems for these expensive gadgets so we all have become engineers of natural phenomena.

Kuhn:

But if that has happened in Europe to some extent, it has happened there as a transformation; here it has happened more nearly as a continuation of a tradition which has actually been a good deal encroached upon. I put this to you now to have you contradict me if I should be,and I suspect I probably should. Certainly it needs qualification, so I'll put it badly. The three major European centers for quantum mechanics, Copenhagen, Göttingen, and Munich—

Laporte:

Don't you mention the Dutch under Ehrenfest?

Kuhn:

All right, include the Dutch; that would make this even stronger then. The Sommerfeld school, in Munich, would rate as the one which had coma nearest, not to American science because it was much more mathematical, but to being not terribly concerned with these problems of interpretation. They wanted to solve problems. They were mathematical, not experimental; but the matters of underlying first principle were also somewhat shoved aside there. Is that fair?

Laporte:

I think it's fair, I think it's fair. After that comes Göttingen, and after that, closely together, go the Copenhagen and the Dutch schools.

Kuhn:

Right. The Leiden school.

Laporte:

In Leiden they worried more about that than in Göttingen.

Kuhn:

Yes, I think that's also quite true. A number of people were at Munich but talked about going somewhere else and then suddenly discovering all the things they had missed. Now I may say that that happens not so often as the people who say to me, "I should have been trained at Munich; then I'd really be able to solve these problems," so the thing has both sides. I wonder if you had a similar experience—getting away from Munich at some point and then seeing people whose approach was really quite different.

Laporte:

Oh, yes, I felt that in Washington. As I said, the power of intelligent experimentation I had not been aware of.

Kuhn:

Did you get another sort of feeling, but of the same thing, when you started working with Goudsmit and Uhlenbeck, the things that Leiden training had done, differences between that attitude and the one you had acquired?

Laporte:

Yes. Well, there was more 'many-sidedness', you see; for instance, such questions as that statistical mechanics could still be a learned subject. Statistical mechanics, as you know, was always a step-child in Munich. Did you ever speak to Linus Pauling?

Kuhn:

I haven't yet but I hope to this spring.

Laporte:

I think he had a quite fruitful time in Munich. Have you talked to Elsasser ?

Kuhn:

Yes. Actually it was not I who talked with him but the person who's been working most with me on the project, my main assistant.

Laporte:

There's one more name I can't recall, a man who also worked in Munich and found it quite profitable.

Kuhn:

Condon?

Laporte:

Condon yes, but this is a European who then refugeed and has been in this country since and has become quite a well-known nuclear physicist.

Kuhn:

My question was not meant to suggest reservations about the fruitfulness of Munich; in some ways it seems to me to have been the best place of all to be, but it did have this sort of limitation I feel. I've been much impressed by the difference between the centers.

Session I | Session II