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Oral History Transcript — Dr. James Franck and Hertha Sponer-Franck

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Interview with Dr. James Franck and Hertha Sponer-Franck
By Thomas S. Kuhn and Maria Goeppert Mayer
At Franck’s summer home, Falmouth, Massachusetts
July 12, 1962

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James Franck and Hertha Sponer-Franck; July 12, 1962

ABSTRACT: Discusses his childhood and family life and his developing interest in physics. Describes the intellectual and educational environment at Berlin and its personalities, especially Planck, Einstein, Warburg, Lindemann, Meitner, and Drude. Details his research during first World War on mean free paths and his focus on kinetics; discusses the influence and his awareness of Bohr’s work during this time. Discusses the importance of Stark and Lenard’s work as well as their Nazi sympathies. Describes Stem and Gerlach’s experimental work and Pohl’s prejudice against theory; highlights the contributions of founding figures of quantum theory: Planck, Nernst, Bohr, Dirac, and Sommerfeld. Discusses reactions against Einstein and the sometimes precarious position of Jews in physics. Details the Ramsauer effect research; describes his time at Copenhagen and what he learned there. Hertha Sponer describes her research under Debye and the reasons for transferring to Gottingen to learn from Franck. Details the development of Gottingen’s program and lab, including obtaining funding; gives his impressions of luminaries of physics: Ehrenfest, Fermi, and Born. Describes the development of the Franck-Condon principle; Hertha Sponer’s discusses her entry into physics and her research at Berkeley with Birge on the benzine spectrum.

Transcript

Session I | Session II | Session III | Session IV | Session V | Session VI

Franck:

About Wood I want to say that he became an excellent physicist in spite of the fact that any test given to him at an early age to find out how good he was in mathematics, would bring the people to say, “study what you want, but don’t go into physics.” And it shows how uncertain that is. One has not to forget that mathematics is an appropriated language. And there are some people who can write but don’t learn stenography. And so it is with Wood. He could think quite clearly. And I sometimes thought of an example of the other type, of Fermi, who was really so excellent in mathematics. I told him, “Fermi, tell me: if you calculate things mathematically, are you convinced that this is right, by the very fact that you calculated?” He said, “No, by no means, as long as I have not at the same time thought it through entirely I would distrust the mathematical result. Now these things together show something. People in sociology believe that if you use nice mathematical formulas, then everything is scientific. It isn’t. What one doesn’t put into the equation will not finally be given by the mathematics. Of course there are times.

Think of Born's attempts to see what one should change in Coulomb’s law to avoid the mass of the electron...It didn’t work in that ease, but it is justified to try that out mathematically. Planck has also first just made a formula to fit on both sides, and then saw what it means. But the formula alone is nothing. And the great difficulty which we always have now is that nowadays the young people learn quantum mechanics as we learned Maxwellian theory. First you take the equation and then you deduce. My wife has sometimes also some undergraduates who say, “give me a formula. If I have the formula, I can work with it.“ And the formula is given by the law, and there is nothing more of interest. And this again brings us to Bohr. Namely, the fact that Bohr distrusted formulas very much and always wanted to use for instance the correspondence principle to get in touch with normal physics. That is lost with this method. And I regret that very much. But I don’t know, it might be inevitable to do it differently. But the correspondence principle was always an exceedingly great help to me, and nobody talks any more about the correspondence principle.

Mayer:

Oh yes, when we teach quantum mechanics we always mention it...I am talking about people like Teller and Fermi.

Franck:

It might be inevitable. But it is a pity. And in one or another way, I think: your whole enterprise should bring out this fact, that it was a help, but it also is a bridge to classical physics. And people don’t learn enough of classical physics nowadays. And of course I know, they can’t, because they can’t study that long. So it is something to think about. I want to mention your colleague there, Elsasser, who really developed into an excellent man as far as I am able to judge.

Mayer:

Excellent but a little crazy.

Franck:

I have the impression when I saw him, that I had, no contact with him. And I regretted that because our contact in earlier years was quite good.

Mayer:

Have you seen his biology papers?

Franck:

I didn’t like it.

Mayer:

No, nor I either.

Franck:

Anyway, I want to say a word about it in connection with the early history, namely with the experiments of Davisson and Germer--no, Davisson and somebody else. Now, the story of that is quite an interesting one as far as Gottingen and our group was concerned. Elsasser came one morning. Re wanted to start experimental work. And I was somewhat doubtful about it because he was more theoretically minded. And right in the beginning, when the topic he should take was not quite clear, he said that he just read something I don’t know which paper. I think the paper of Einstein, in which Einstein spoke of the wave theory of De Brogue. And he said, “Yes, it would be nice if one could show that an electron really has wave character.” And I had just read the day before that paper of Davisson and what do you say his name is? Kunsman. And when he said that to me, I said, “Yes, it would be. But how about if I tell you that it has been done. Only the authors don’t know it. Namely, in that paper of Davisson and Kunsman they have treated their metal surface in such a way that it became crystalline. And therefore I am sure that what they have done for us is to have studied just the wave character of electrons without knowing what it is.” Then Sommerfeld paid us a visit. Whether that was before or not I don’t know. Also Sommerfeld said, “Look at that paper and see whether you can make some sense of it.” Or this was that Sommerfeld came later and we told him. I don’t know that more.

Kuhn:

When you say this paper, you mean the Davisson and Kunsman?

Franck:

Yes. Anyway, that paper interested also Sommerfeld very much. Whether it interested me independently I don’t know. But I looked at the things, and when I looked at the things I thought it looks really like something like waves. And then when Elsasser came, it clicked in my mind that it would be that. And I said, “Now Elsasser, the best thing to do is make some experiments, and you make these experiments. Take a thin metal film through which electrons can penetrate a Lenard window and we will study that polycrystalline pattern -- what G. P. Thomson did. Well, we started those experiments, but it turned out after four weeks that it was hopeless for him to make such experiments. He was not gifted to do experiments. So I told him, “Now let’s see. You came with this idea of electrons and waves, and I showed you this paper of these men. Now you write a little note to the Naturwissenschaften and explain the situation and what they did.” And. Davisson and Germer, acknowledged this paper of Elsasser, this short note in the Naturwissenschaften. And Laue was always so pleased about it. And he sometimes could say exaggerated things. When he paid us a visit, I said, “At the moment we don’t come along so nicely.” He said, “This paper of Elsasser there. If nothing else would come out of this laboratory than just this short note, it would be enough for a laboratory. Anyway, I was pleased to think about it and tell a little bit about it. But I may again say, I would not have thought about these things had he not said electrons should be waves. And therefore it was quite correct to have him publish that. But at that time a better experimenter would be better in this case.

Kuhn:

Do you remember at what point the connection between the Davisson-Kunsman experiments and the Ramsauer effect was made?

Franck:

Oh yes. The Ramsauer effect would have been absolutely understandable to us at that time in which Hertz and I measured mean free paths. I don’t know what we would have said. We considered and measured the mean free paths especially since we knew by some English workers that the breakdown potential of the rare gases was exceedingly low. And I had in my own observations found that too, because just moving a mercury pump gives this red light of neon or of helium. And there were only two possibilities; that the mean free path would be extremely long in the rare gases, or elastic collisions. Now we concluded it was elastic collisions. If we would have found in argon that the mean free path is abnormally long, we would have become quite doubtful. So in some sense it was quite good that we had not studied argon in this respect. And I must say that I never understood later -- when was it clear; who cleared it up? -- that it was a phenomenon of diffraction.

Kuhn:

Elsasser says so in the same paper in which he discusses the Davisson-Kunsman. He says that these are both

Franck:

Oh! Oh! Even that I had forgotten. This was now much later than our work. This must be absolutely Elsasser’s idea because I would recollect it if it would be my idea. It must be entirely Elsasser’s idea.

Kuhn:

But the tie between those two effects had been made before Elsasser’s paper. There is a paper by Hertha Sponer and Rudolph Minkowski that treats the two effects together, not wave-like effects but as effects that are related to the same aspect.

Franck:

You want to ask Hertha, when she comes back, about it -- that she has to say about it? I didn’t remember that either. I know that Minkowski and. Sponer worked together. You see Minkowski sometimes, do you?

Mayer:

No.

Kuhn:

I have seen him. He is now in Berkeley and no longer in the south.

Franck:

Oh, he is in Berkeley. He is excellent, really excellent. He became such a good astronomer, astrophysicist, and all these things he makes about stellar long wave emissions. He has made very great contributions.

Kuhn:

In l921 there is a paper, “Uber den Durchgang von Electronen durch Atone” by Minkowski and Sponer.

Franck:

Very good. You tell her about it because this would be quite interesting too.

Kuhn:

So, the whole question of the Ramsauer effect as a difficulty, which a lot of people worked on. Hund did his thesis on the Ramsauer effect. And at Gottingen, at least, there must have been a great deal of concern with it. Do you remember any of the discussions of it, or anything about how people felt about it?

Franck:

I don’t know. I really don’t know. I know only that I had one man working with argon in Haber’s Institute. It was the time between 1918 and ‘20. He worked on molecules but also on argon. And with argon I never could understand his results. Therefore we went from atoms to molecules, but I kept that in mind that there was something. Probably that was still before Ramsauer’s paper came out.

Kuhn:

I think so. The Ramsauer paper is 1921.

Franck:

If we would have been not so blind, we would have found it. But you see, that bias always plays a role. We found no abnormal things in helium and. neon, so why should argon be abnormal? And. so we postponed that and said let us think a little bit more about it. That is the only connection I know…

Kuhn:

Was there talk about De Brogue at Gottingen? I may say, a number of people tell me that they really were not aware of the existence of that work until after Schrodinger.

Franck:

We were, we were. And I am sure that Einstein’s paper made it especially known to us. We were aware of it. But cannot remember whether it was primary information or via Einstein. I believe it came via Einstein Elsasser.

Kuhn:

That seems very likely. Do you remember anything about how that idea of Elsasser’s was received? Now it seems natural, but at the time it may have seemed very crazy.

Franck:

I can only say that in the paper which came very soon later, Davisson and Germer accepted it.

Kuhn:

It wasn’t so very quickly. I think there are a couple more years.

Franck:

Yes, yes. But you must consider that in our group I and Hund were all very much impressed by Laue’s results. And so, if there is a wave at all, that there should be the analogy to Laue and then to the work of Debye and Scherrer was obvious in our mind. Therefore I said, “All right, take a single beam, let it go through a crystalline metal there are always little crystals in it and one will get the Debye-Scherrer diagram.” And at that time it is a pity that we have not done it because it took longer until G. P. Thomson did it. This was that I had to tell Elsasser, “Go to Max Born. You are a theorist. You cannot make experiments. And we used quite a lot of time how much I don’t know; a quarter or half of a year. I think it auld have been published maybe three weeks after the first paper appeared because nothing came of it experimentally. But we used quite a time and. much glass before I told Elsasser, “You’d better go to Born.” And (theory) is his gift. And I may say, I don’t know enough about the magnetism of the earth and so, but I think everyone takes him very seriously, don’t they?

Mayer:

Yes.

Franck:

And he is an independent thinker. But he is a little bit difficult, I suppose or became...I was so pleased when I saw him in Chicago, but he was not pleased to see me, apparently.

Mayer:

He wasn’t? I am surprised, because he speaks of you occasionally with great warmth.

Franck:

I didn’t know whether I had in one or another way been not kind enough to him, or whatever it was. I felt a little bit that there was something between us, and I don’t know what. And it is a shame because I always came along quite nicely with former coworkers and pupils and so on…

Kuhn:

Do you recall any other particular pieces of research like the one you told us about on slow electrons in argon, where you felt great surprise at the results?

Franck:

I can only say that when we had this experiment, we immediately thought about the line 2537 because B. W. Woods’ results with the resonance radiation impressed us. We said that must be a particular one. We had no idea that it is the first absorption line at all…But we were not so astonished that it was this line. And there was also a paper of Stark who said that what we did is nonsense. Since this line is so easy to excite and has such a particular strength, it will be the only line which people find. But that doesn’t mean that others are not weaker and also there.

Kuhn:

I know that paper of Stark’s in which he says that at these pressures, this would be the overwhelmingly strongest line. Is that experimental right?

Franck:

It is in fact not right, but if you take a mercury line it is right, because the much stronger line, the 1849, does usually not go through normal quartz. It must be particularly pure quartz to transmit that line. And therefore it is really the strongest line of the mercury spectrum, as it should be, in spite of the fact that the transition probability is by no means as great as an ultra-violet line should have if it were a singlet-singlet transition...[Break. Conversation starts before recorder turned on.] The point is, they showed me that film. They sent me that film and asked whether I had any remark to make. And I said, “Yes, a historical one.” At that time we did not know of Bohr’s theory. And at that time we could not be at all certain what mercury line would come out first. But since we measured the inelastic impact, we knew that if any inelastic impact was before, it should be a very rare one -- e.g. meta-stable state of mercury.

Then we found the one line, which we calculated back from the 4.9 volt. And the funny thing was that I said to Hertz, “You are quicker with the slide rule; calculate it.” And he got the wrong result. And I think we got at least for half a day the wrong result. It was astonishing. Then we calculated both together and it fitted very well. But anyway, we were not astonished about it, but we had not any connection with the first absorption line and series and so on. We would therefore be not too astonished if, let us say, the red line would come first. Perhaps it would be so that all lines would come at the same time. Namely, when the ionization on was reached. All that we did not know. We only came to the conclusion, there must be a connection to the ionization potential, but bow it is we did not know. And you see in the previous papers that there we had a more clear picture of it. ..

Kuhn:

Is it your recollection sir, that the calculation you speak of, in which you said, “Hertz, you use the slide rule, you’re quicker with it, that that came after the experiment with the mercury line?

Franck:

After, not before.

Kuhn:

That cannot be quite right, because in the first of your papers, at the end of the paper you discuss the fact that before you got the spectrograph –

Franck:

Oh, oh. That was before we got the spectrograph.

Kuhn:

--that you should look for this particular line.

Franck:

That’s it. I mean the point is only, when we started the experiments with mercury, we did not know where the inelastic impact would be. I didn’t say that we--

Kuhn:

Here, let me show you. I’m sorry, but I do this only to see whether this will bring back other things. This paper is submitted on the 24th of April, this on the 21st of May. Now at the end of the paper of April 24 in which you do find as the ionization potential 4.9 volts -- you calculate what the corresponding line would be. But you don’t then do the experiment until the later paper. So the computation must have been done before the experiment.

Franck:

Before that experiment, but not before that one.

Kuhn:

Ah, right, right.

Franck:

We did not know what inelastic impact we would have. And. we did not expect that it just should be at 4.9 volts.

Kuhn:

Ah, then I misunderstood you, and this I think is very important, and so I would like to be sure that I understand you now. In practice, before you did the first paper, you utilized the Wood measurement to see where the first excitation potential should be.

Franck:

No. Before we made the first measurements we did not know where it would be, but we were not surprised that we found it at 4.9 volt, and calculated then that it would be the line 2537. That did not surprise us so much because Woods’ results on resonance radiation were known to us. But when we started the experiments, we wanted to find, the first inelastic, impact, wherever it was. And we did not know where it would be.

Mayer:

And you mean you did not find it exciting, that these two things agreed?

Franck:

No, no. We were not surprised because--

Mayer:

But wasn't it pleasing, wasn’t it very pleasant to find it?

Franck:

It was very pleasant, and actually we knew that it was a good paper. It might interest you to tell you only how the experiments have been made. The experiments have been made in my room down there, where Hertz and I worked. But when we wanted to make the experiments with the spectrograph, we went in a little room much smaller than this one behind the big lecture hall. This was a spare room. It was a little dark room, but not in use at all. And there we built up these very small things on a little table now twice as big as this one, and the spectrograph not greater than that. It was all so simple to do. And. then really the line came out. We were quite elated. That I remember. Anyway, what I meant to say, if we would have read Bohr, we would have known what to expect. And furthermore we both were at that time not very much in spectroscopy.

We did not really study very well Rydberg series and so on. This was a particular brand of science which did not look fruitful to us at that time. I remember Runge, who was in the early work on spectra very well. And after (retirement) I asked Runge whether he would not come to the laboratory and do further research. And he did it with Mannkopff. And I remember when he was sitting there and showed me a triplet, a triplet in whatever that particular system of atoms was. But he looked at it and. said, “Is it not a beautiful triplet? Is that not a beautiful triplet?” One could see the pleasure in him. A little bit like Paschen and like Hertha also is, in seeing in three such lines a real beauty. If one is so full of the things as Runge was Runge is quite a character, really a man. Shall I tell you an anecdote about Runge? Runge came here to the United States. Because he worked on spectra, he was often invited by astronomers. And Hale, when he had his new solar institute in Pasadena had long discussions with Runge. And then they were interrupted because a senator came to visit there.

Hale stood for quite a time together with the senator. And that made Runge a little bit unhappy. And he said when he came back, “Hale, I have so little time, so precious little time. We have so much to discuss. And now you have used more than two hours with this senator. Is that necessary? And then Hale said, “Yes, it is. And by the way, I had an exceedingly nice result in telling him a little bit about all the wonderful things which one can study by astronomical measures. I told him about the distances and so on. He said, “Professor, I must say, hearing what you have to tell me, I am not so certain whether it is of very great importance whether the Republicans or the Democrats will win in the next race.” This was really always quite nice, and Runge liked, to tell it. And you can imagine it too. It appeals to them. Really, I would not know a better method than to train our senators and congressmen than to send them for two days to the big telescopes and let them make observations, add see what people do. The stars have a great influence on them, and they would get a little bit of the spirit like that man got by his.

Kuhn:

Runge has always struck me as particularly unusual because of his combination of mathematics with this deep interest in experimental spectroscopy.

Franck:

You know he is father-in-law of Courant, and he was a more or less applied mathematician.

Mayer:

He was really in the mathematics department.

Franck:

He was in the mathematics department. And was a good mathematician. And even Hilbert, who did not like very much application, had much praise for Runge, because Runge knew mathematics. Runge was half English. His mother was English. And so he spoke English just as well as German. He did all of his work with several people together. I think with Paschen too -- Runge and Paschen -- when they were in Hanover. And, be had a great influence on Paschen too.

Kuhn:

Were there other people that you think of who had this real nthertica1 ability on the one hand, and real enthusiasm for experimental work, that is represented in saying, “What a beautiful triplet”?

Franck:

Yes. I don’t know the man well. Hertha knows him better. He was professor in Gottingen before Voigt. Voigt could do a lot of theory and was very much interested in spectroscopy and had a lot of papers on it. And I think that my generation my friends when I was a young student or assistant in Berlin; the other assistants and I had not such a high regard for Voigt’s papers. When one heard him talk it was somewhat tedious. And the way he worked on crystals with all these parameters he put in, we said if one puts enough constants in something one can always explain everything. But it turned out that all what he has done was really excellent. And that he was a kind of a lone wolf because there were not many other people in the country who were interested. I believe I mentioned one example, that he was quite clear about the possibility and no possibility of the Stark effect and such things...And he must have been a man who was interested very much in both theory and experiment. Generally that was in earlier times more so; there was not such a strict separation as it is to my regret today and you say in your field it is not.

Mayer:

No, it is not. On the other band the mathematicians by now are utterly uninterested in what is going on in physics. It is absolutely different from the way one--

Franck:

They are a lot like Landau...Because there is also some connection with physics. They decided that nowadays no mathematicians understand mathematics, that the last people who really could understand mathematics as a rule were Hubert and Poincare. And they think if it is really so, that the field is o broad now and that nobody nowadays is able to work into many fields, as for instance Hilbert has done, then it is necessary to have a survey of the whole of mathematics by the cooperation of many people...And apparently it also now starts to influence the people in physics. Namely, there a few months ago appeared one paper on nuclear physics--in this Physical Review letters. One paper--The same subject was treated in two papers one with 20 names, and the other said, ‘The high energy group of that and that place.’ They found it also now too stupid to put all the names on one thing and published under the name “The High energy group.” And I think that is probably influenced by the Bourbaki group....

Kuhn:

Let me take you back if I may, sir. Earlier you spoke of a terribly important thing in your life, the Berlin colloquium. You also said that later, and I suppose you meant particularly after the war, either it had become too large or something.

Franck:

After the war I was only for two years still in the colloquium. Then I went to Gottingen. No, mostly the time when I was a student, mostly the time from 1902 or ‘03 on. It was really wonderful because the colloquium was something which was informal. There were not only results given, but one heard also something about the struggles. One learned really how hard the work is, and bow much one has to battle really with the problem. Always the student talks in his dissertation the longest about that part where he was first in error and which one had to overcome with much difficulty. That one should not do. One should not give a diary. One should really bring it together. If one know that it was more difficult for the particular man, that doesn’t mean that it is of greater importance. But, on the other hand, if one really gets only the polished paper and reads that, one gets the wrong impression. All these things are not just bright ideas. As Hilbert used to say, who exaggerated always, “Now people speak of genius. There is nothing like genius. There is only industry.”

Kuhn:

When you spoke before of how great the colloquium was, you also said that later it ceased to have the same role...

Franck:

In Berlin later more and more people came in, so that from the library room, where one was sitting along a table as long as this room here is, or a little bit longer, it went to a classroom. Then it went to a bigger classroom. Then it went to the greatest classroom. Laue did what he possibly could to keep the colloquium going in the old spirit. And a lot of these things happened and remained. But it could not help the intimacy. This speaking or interrupting the speaker with a small remark between was impossible in such a big room.

Kuhn:

Did that expansion start immediately after the war? Did the expansion that you speak of, did that expansion begin immediately after the first war?

Franck:

No, it happened slowly. First the colloquium was just as nice. Some of the things I mentioned were after the war...One became narrow; one became a specialist. And I still remember -- I forgot his name, do you remember the name of the man who worked at the Kaiser Wilhelm Institute the man who worked very much on X-rays of (threads) and so on? He is dead a long time. He came always to the Berliner Kolloquium, to the physics colloquium. And I knew that he could not understand physics, and I asked him sometimes, “Why do you come?” And he said, “Because it is an aesthetic pleasure to see the physicists act. These are gifted persons here, and even if I don’t understand it, it is a greater joy to me to go there than in the theatre.” I think in Gottingen it was at least not so bad. We had quite a good colloquium in Gottingen too, but not as good as it used to be.

Mayer:

No, it was large, it was very large.

Franck:

No, it was in the beginning not very large, but it was probably before your time.

Mayer:

When I wasn’t there. There was Pohl, which meant it was very hard for theoreticians.

Franck:

Now, let us say, there was always when Pohl talked that was always very good to hear. And otherwise he did not disturb the colloquium at all.

Mayer:

He would light into theoreticians with no kind band. And I have seen him.

Franck:

But that was his specialty, yes. But I mean nobody took it seriously. Do you remember the daughter of (Admiral Fuchs)? She is now married to Bauer, and I met her again in Heidelberg. She is an exceedingly nice woman. She wanted to study physics. And in our way, in which we were quite informal, she was absolutely unable to understand the situation. Her father spoke once with me and said, “She wanted to study physics but we became doubtful because she found out that the professors also don’t know it.” And she went to the colloquium and saw that, let us say, Born said something. Then I said, “No, you can’t be right,” or Pohl, or what not. And she said, “Why shall I go in a field where people really do not know what is true or what is not true?” She was a real beauty, and I told him, “Now you will not long have to worry what she will do because she will give up anyhow. Early or later she will very soon marry. But anyway, she shouldn’t study physics because this is the essence of it, that we don’t know.” So it was at least in that respect not too bad. But we tried to do it a little bit in the way it was done, but of course it was already big. It was in the Kleiner Horsaal--maybe 60 or 70 people.

Kuhn:

You said yesterday that on your way to Gottingen, you went first to Copenhagen for three months?

Franck:

1920, yes. Bohr’s laboratory....

Kuhn:

In the fall or in the spring?

Franck:

I know it was not winter.

Kuhn:

Did you get to Gottingen already in 1920 or was it ‘21?

Franck:

I think it was 1920 I got a call to Gottingen. And I said yes, I win accept it, but I would like to take on the job only after three months time to go to Copenhagen. And that I did. And that was a wonderful time...It must be probably spring time in Copenhagen, and I went, then, a little bit later to Gottingen.

Kuhn:

Had you always wanted to go back to a university from the Kaiser-Wilhelm-Institute?

Franck:

Yes. I must say, the urge was not too great because they had a very nice method. For instance I was associate professor at the University, and at the same time at the Institute. Haber was full professor at the University and at the same time the Director of the Kaiser-Wilhelm-Institute. Hahn was also associate professor. Lise Meitner was she Privatdozent, I forgot?...These institutes always worked nice when they were connected with a university; loose contact, but connected. When they were entirely alone, like the (Kohler-Forschungs-Institute) of Franz Fischer, and so on, they did fine work, but it was not in the same spirit. It was more applied in one and. another way. I had at least always five or six co-workers which were students at the University, and they did their dissertations. So in this case, since my whole teaching was more in the laboratory than by lectures and by seminars, I felt quite happy. But on the other hand I had in this can an opportunity to get my own laboratory. I remember very well when I told Haber about it. I had before some calls; one to Sweden and one to Prague and so on, which I did not accept. But the call to Gottingen was too much; and furthermore I liked a small town. I bad small children, and I wanted that they grow up in. a small town and so on. There were a lot of things which -- and the reputation of Gottingen. Everything was very nice and very agreeable to go there.

Mayer:

Born was there before you, wasn’t he?

Franck:

Born came at the same time. And actually Born insisted that I should come. Born wanted to have me there with him. And actually he told them they should look into that because Voigt went away and Debye went away. Pohl was there; he had Riecke’s position. There was one position still open, and Born insisted that I should come there too. And we really had quite a nice cooperation between us. I think it was to both our advantage. To mine it was certainly.

Kuhn:

Before we actually let you get there, can you tell us something about the time in Copenhagen?

Franck:

At that time there were two, three, four people really in Bohr’s laboratory. One was Hevesy. I had a kind, of friendship with him, but it was never that we were really too much in the same field. Then there was Klein and Rosseland. Rosseland is an astronomer now in Norway, and Klein is a theoretical physicist in Stockholm. And they had studied this impact of the second type. They introduced that.

Kuhn:

They had started that even before you arrived there, had they?

Franck:

I am sure. Or it was just in the making. But anyway, I know that this influenced me very much, to see this idea that in equilibrium every process should go in both directions equally often. That one would have an excited mercury atom colliding with a slow electron and would give energy to it. And then Bohr’s attempt to say that all these things that started with Wood and so on were also another example of impacts of the second kind. Actually one should say they were a reversal of (chemiluminescence). All that became slowly clear. The whole atmosphere with these people, especially Klein and Rosseland. Then there was this excellent man, the Dutchman two Dutchmen. The one was the man who worked with Bohr on the first letter to Nature on periodic systems--Coster. I remember when I came in. (Bohr) had seen us before, I don’t know where. Yes, he invited me a long time that I should come. And that was the time when the Institute was quite new. And this man Coster was in the room because Bohr was just ready with writing down this periodic system to Nature.

He gave it to me to read. And I was highly impressed and. said so. And then Bohr said, “And how is the style?” And I said, “I must confess Bohr, since you ask me, these sentences are a little bit long.” It was typewritten, and sometimes one started the sentence on one page, and the next page was the end. And when I said that, Coster became red in the face, and he told me, “This paper is now written seven times. And every time an attempt was made to make the sentences shorter. But the result was just the opposite. It should be published, but now you must come and tell Bohr that he has too long sentences. Now it will be again four weeks that he works on it. And then, believe me, the sentences will be still (longer). I may tell you in all friendship, if after it comes back, you don’t tell him it is excellent, I’ll wring your neck.” So it happened. But this was only a small item. It shows why Bohr’s word style is so difficult. And why his language is so difficult. His language is because he is a Dane and he doesn’t pronounce consonants at all. But one cannot say that be is good in these things. And. why is it so? And the answer is because he is so afraid to make a statement which is not absolutely correct. Therefore, if he writes a statement, whatever it is in the sentence, something should be in it. Then he qualifies that. Then he qualifies the qualification. And all in one sentence. And he does the same thing which he did with the first theory he was not content with it. And in his talks at least, he qualified and qualified and qualified. And so came the correspondence principle, and so came also the complementarily out of it... Bohr was so superior that some people had difficulties with him, which I never understood. Never is not right.Which I understood only after Hitler came to power, and I was one and a half years in the laboratory. Bohr did not allow me to think through whatever I did to the end. I made some experiments. And when I told. Bohr about it, then he said immediately that might be wrong, what might be right. And, it was so quick that after a time I felt that I am unable to think at all. And this difficulty must have been felt by now, what is his name?...A Dutchman.

He had to leave Bohr on his own. He had to go away because he felt that be bad to think for himself, and Bohr was too quick for him. And even did not know really that he was too quick in this case. So I may say that I can understand that some people would feel: ‘Yes, to come to Bohr, to see him, to speak with him, and. to learn from him is wonderful, But if you stay too long, it is a question whether you will reach really your own ego because it is too quick.’ I will give you an example. I was for the last time in Copenhagen for one and a half years before coming permanently to the States. There was at that time Bohr’ s idea of the droplet model. Now I knew from work on spectroscopy and from thermodynamics and so on a little bit that if one has a complex molecule, one has a fluctuation of the energy from one degree of freedom to the other. So the total amount of energy present in a complex molecule in the form of oscillatory motion is much greater than the dissociation energy of the atom. And all that was known to me. And there I was sitting and worked on some problem I forgot now what it was of radioactive iodine. I wanted to learn a little bit about it. Hevesy was at that time again there. We worked there together on it. But there Bohr discussed these matters, and immediately saw this, without knowing all these things which I knew of the analogy to complex molecules. I have not seen such things, which I should because I was familiar with it. Bohr’s genius was so superior. And one cannot help that one would get so strong inferiority complexes in the presence of such a genius that one becomes sterile. You see? Therefore, I would like to say no one fitted really in that circle the whole time. But to be there for a time and to learn and to see this man and to understand the greatness of him and the goodness. He is really something. Yes, a man for whom one can feel only a hero worship. Now you asked me actually about Bohr, was it not?

Kuhn:

Well, I asked you about Bohr and about this time in Copenhagen. And you have certainly been responding wonderfully.

Franck:

I mean this was a mixture of the three months, which were full joy and pleasure. I did some little bit of experimental work with one man together, and this was just plain wonderful. The other time [I was at Copenhagen] I must say I felt so discontent with myself. That was not the reason why I went [away from Copenhagen). I went because in Denmark was no place for ray children and grandchildren. And furthermore Herzfeld was there [in America) and wanted to have me there. He was a good friend, and I thought I would go there anyhow. I remember another man who influenced me in an entirely other way. That was Fritz Haber. Fritz Haber was the first of the Geheimrate I knew with whom one could discuss for hours back and forth ideas without feeling there is a dignified man and you are a young man.

We could work together and discuss things. And then he asked me later whether I would take this position in his laboratory. And since I had a very ill-paid position at the University, he expected that I would immediately accept that. But I said, “Pardon me, but I believe that I don’t; I cannot accept it.” And he said why? “Oh, to tell you the truth, you are full of ideas, and they may be better than mine, but I want to do my own. I fear I will be only the man who will carry out one or the other of your ideas. And even if your ideas might be a hundred times better than mine, I would like to do mine.” And be said, “I understand you entirely, and I will make a contract with you. We talk together about our mutual work as much as we want to, but everyone makes a solemn oath to let the other alone to do what he wants to. Will you now accept the position?” I said, “Yes, with greatest pleasure.” And I may say, Haber was not always a simple man. I mean I cannot compare him with Bohr. I mean they were so absolutely different, but he was very decent. I did not find him on any occasion to be a boss. Never was. But I know that other people found sometimes that he could be. He was impatient. He was very impatient. And then he could become outspoken when he was impatient. But between us, he had shown to me only great friendship. Nernst and Haber did not like each other very much, which I understand very veil. Another physical chemist; that was too much for Nernst. And on the other hand, Haber was not a man who would bow to somebody else you see.

Kuhn:

I wonder whether this might be a good time to ask Mrs. Franck whether she would join us? I think she’s come back. [Enter Hertha Sponer] Professor Franck talked earlier about Elsasser’s work, and also he had forgotten that in that work it is not only the Davisson-Kunsman curves that are discussed but also the Ramsauer effect.

Sponer:

Yes.

Kuhn:

And I had also known that Fredrick Hund did his thesis on the Ramsauer effect.

Sponer:

Is that right?

Kuhn:

I believe so. But clearly that problem was a big problem for people in: Gottingen the problem of the Ramsauer effect was it not?

Sponer:

Yes, yes, we talked about it.

Franck:

Do you remember what you wrote about it?

Sponer:

No, not anymore.

Kuhn:

What was written about it I can read, I’d really be more interested in knowing whether there began to be considerable sense that there were a whole group of problems that were not going to come out right with the existing techniques. Now was the Ramsauer effect one of those?

Sponer:

Yes. First actually one did not believe in it so immediately. There was some doubt about the whole thing. That I do remember.

Franck:

You may remember the time in Berlin. She studied in Gottingen and came to Berlin and came back to Gottingen.

Sponer:

I took my degree with Debye...My thesis was in 1920.

Kuhn:

And it was after the thesis that you were then in Berlin?

Sponer:

After the thesis I was in Berlin...It was a little bit Debye’s fault that the thesis was not published. Debye left, and I did not know how much goes in a paper and so on, and. he didn’t care too much. And at the same time, at exactly the same time, same year, Kratzer did the same thesis with Sommerfeld. Same year. You know that of course.

Kuhn:

Yes. In fact a number of people did that problem at about that time.

Sponer:

Ja, about the same time.

Kuhn:

Reiche also did a paper.

Sponer:

Ja, I saw Reiche when I came to Berlin, and we talked about it. And when he heard of it and so on and saw what I had done, he said, “Well, this is a very nice piece of work.” But you see I had still not the courage to send it in all by myself, you see, without any blessing from someone. After all, it was the first time you see. And Debye didn’t care; did not care too much. He left, you see. He left Gottingen. Whether he went from Gottingen to--

Franck:

To Zurich.

Sponer:

No, he was in Leipzig.

Kuhn:

No, Leipzig was much later....

Sponer:

Now (Huckel’s) famous benzene paper, you know, was published a little bit before he went to Leipzig, isn’t that right...I mean it settles a little the time. I know the following conversation between Huckel and Debye. Huckel said to Debye, “That paper becomes awfully long.” You know it was a terrifically long paper, about thirty pages I think. And be told Debye about it, and Debye said, “Huckel, if you cannot say anything in a fairly short fashion, and, need so many pages, it cannot be right.”

Franck:

There Debye was wrong.

Kuhn:

Where did the idea come from that the Davisson-Kunsman curves and the Ramsauer effect might be the same thing? Tying those two together as you did in your 1924 paper with Minkowski?

Sponer:

If I could only now remember...Did we mention it in our paper?

Kuhn:

The paper treats the two things jointly.

Sponer:

We have the two things?...Yes, yes, I remember. But now the details.

Kuhn:

Do you have any recollection of how that paper got started?

Franck:

You repeated Ramsauer’s work with Minkowski?

Sponer:

No, it was not exactly a repetition. In our work we came close to these same things; but now how was that? If I only had a reprint here, I would remember pretty quickly.

Franck:

Can you leave these few notes you have about it?

Kuhn:

Surely I can leave them...

Franck:

Minkowski might remember.

Sponer:

He might. It is all such a long time. But we talked about it a lot. That much I know. And we also knew that there was a connection. I know that...

Kuhn:

I believe late in this paper you say that in conclusion or in summary that it may be said that the collisions of electrons with atoms, despite the validity of the energy and momentum laws, take place completely unmechanisch...Now this is a strange unmechanisch - mechanisch altogether.

Sponer:

Ja, a mix-up.

Kuhn:

And because it fits in so closely with what comes next in the wave picture...

Sponer:

Ja, but this was before De Broglie. Ours, as far as I remember. A little bit before...We did not know of it.

Kuhn:

Do you remember when you heard of the De Broglie work? You see, many people didn’t know of it until after they knew of Schrodinger.

Sponer:

No, we knew about De Brogue. We knew about De Broglie.

Franck:

...In your mind and my mind, this Ramsauer effect was something which needed especially explanation. That came already from the Berliner time where you worked also on electron impulses.

Sponer:

Ja, but I had nothing to do in Berlin with this Ramsauer -- ... I do know that Minkowski and I talked a lot about it. And you see it here in these words which you just read to me. -- I mean, in order to explain the experiments, we had a lot of discussions together. And we knew something was not quite fitting. Somewhere was something not quite fitting. Then we looked at the Ramsauer paper and thought that there was an explanation which we could not give directly. This is why we struggled with these sentences, but we were convinced that this had to be explained on a, let us say, non classical basis. And we talked a lot about it; in fact, days. We wrote it and rewrote it and so on. But we had not any help from the theoretical people. You see, it was not known at that time. And therefore this was all very doubtful... And when we were told this is nonsense Ramsauer and so on; you see all these things. We did not believe it that it was nonsense. It was something, but we could not give a real explanation of it...

Kuhn:

Did you talk with Fredrick Hund about this?

Sponer:

No...We did not talk much with Hund, as far as I know...

Franck:

I am sure that this whole thing s discussed in our colloquium--

Mayer:

I think Hund was certainly still around in ‘24 because that’s when I started studying...

Sponer:

But our paper was ‘20.... You see, it was much earlier. No, our paper was ‘23.

Franck:

In this paper is Hund--

Sponer:

No, no.

Kuhn:

It’s cited; it’s referred to...You certainly knew of it.

Sponer:

Oh yes, we knew about it, but we had not, that I remember, had many discussions with Hund about it.

Franck:

There is another point, Hertha, since you are here. We spoke before about Runge, and Runge and Paschen. And you have studied with Paschen. And Paschen came several times in our discussion.

Kuhn:

I’d love to know something about Paschen.

Sponer:

Personally, or what?

Kuhn:

Personally. His attitude toward what was happening in quantum mechanics.

Sponer:

I must tell you, I had left before the arrival of quantum mechanics...I came to Tubingen in 1917. And in 1917 there was a war; the first war. I did not see anyone who gave a real theoretical course. There was none. Paschen gave his big lecture. He gave a good lecture, and we had a Prakticum, which was good. And in this Prakticum he had some people. Wendt was a man who was completely unimportant, he never became important...I think he went to Braunschweig later, but he was assistant to Paschen in the Prakticum. This Prakticum was for a young student a very interesting affair. This was my first Prakticum, after all, I had at a University. And Paschen and the assistants (watched) the different experiments set up and so on. Paschen always came each time. He went from one to the next and. so on, asked the students “What have you done,” etc., and even asked, “Show me your book. Where did you write it down?” and so on. Even this he did.

He really made a big impression on us. He was so very, very large you see. He was a tall man. And he was far-sighted, which meant he looked like this, you see, down upon you. And then you were little. This was really a very impressive affair. And to tell you how his attitude toward the student was, in general, he did not consider the students...very much worthwhile or something. Only a very few would be. But he did come through the Prakticum and ask. And one day he came -- and this will tell you how his attitude was. He came to me and said, “What have you been doing today? Well, I had done something extremely tedious, I thought. I measured the expansion coefficient of something. And he said, “What did you get?” “Oh,” I said, “I get such a good result. It just fits beautifully.” I was so impressed you see, by myself. And then he said to me, “Do you know why that is?” Well, I thought that was because I measured well, you see, but I didn’t say so. “This you owe solely to the perfection…of the experimental apparatus that you have.” I was terribly disappointed. But I didn’t’ say anything. The same man Paschen, however, I heard his lecture you see. And we always were in fear of him because he was so sharp. And one day he gave a lecture on the development of pumps. And he gave a beautiful historical lecture on it. I was fascinated. So, I was so fascinated that I took all my courage -- at that time I was really very timid I took all my courage and went to the great man and said would he please allow me to go to the library of which he had a key. It was locked all the time. That was Paschen locked all the time.

Over in the same building where he lived also on the third floor. Well anyhow, he had the key. And I said, “I would like very much to read a little bit on this pump affair, pump development, and so, because I thought it was interesting. He said, “You are really interested?” “Interessieren Sie sich wirklich dafur?” And I said, “Yes, I do.” And then he looked again, thought it over, and said, “All right, come tomorrow,” I don’t know whether it was 2 or 3 or what -- “and the library will be open for you.” Out I went. And. then I came the next day. What the man had done. And. this I really like to tell because it gives you a little bit of the personality. He was very much feared, Paschen was. But there he had on the table several books, with some piece of paper in it, about pumps. Handbooks, etc., there were several for me to look in...And I think this is remarkable. And it gave a better insight than many other things because he was feared, you see. And he did treat his assistants not very well.

Kuhn:

Were you there then just for that one year? Two semesters.

Sponer:

Ja, two semesters. And I had to go. Why? Something again not known. We had to go because his last mechanic, his head mechanic, was drafted. And he bad to close the workshop. That was not known…He closed everything. And allowed only his rather advanced -- I don’t know his name anymore -- student who was working for his doctor’s degree and was in the finishing stage. And he kept him. He had admitted another student and said, “Out you go, because I cannot have any students now working. My head mechanic goes to war.” And be closed the workshop. Therefore, several of us who were in his Prakticum and wanted to stay, had to look for another university and left. And now was the choice, where do we go? There were a few students who always were together. And among them were three girls, I was one of them. And now where to go? And the two others I still remember them they said they are going to Greifswald, to Seeliger, because this is an easy affair. You can get your dissertation at Greifswald in a short time, and it is always the same problem I think Leitfahigkeit--no, gas discharges. Now, a friend of mine went also to Gottingen. And the one from Greifswald and I still have it wrote a postcard after a few months and said, ‘We, in Greifswald are in retirement, while you in Gottingen lead the hard life.’... In Gottingen I met Ode Clausius, the granddaughter of Clausius a brilliant girl. And she was offered, and actually not only offered but encouraged to take her degree with the famous mathematician (Hecke) in function theory. And she refused. And why? She had to go as fast as possible into a profession where she could finish so she could make money to help her mother get her younger brother through...She worked with Springer later, and she edited that one collection that came out a few years ago from Springer. A very brilliant girl.

Franck:

By the way, Hertha, do you remember a name which slipped nr mind, and I cannot come to it? The man who worked in Bohr’s laboratory and. vent to Holland and. became a very famous--

Mayer:

Kramer’s?

Sponer:

No, not Kramer’s.

Franck:

Kramer’s. You talk about Woldemar Voigt. I think you should say your opinion about Woldemar Voigt.

Sponer:

Oh yes. Well, Woldemar Voigt--yes, I had quite a bit of impression. First of all, I came to him with a certain recommendation, namely, front that (Reinstein) you know? From some private lessons I had before I went to the University. He got his doctor’s degree with Voigt in Gottingen. And Voigt gave mechanics. My first course was a mechanics course. His lecturing was in what we call today matrices. He put the whole thing up like that, as if it were a matrix. And that was very interesting, but we didn’t know it at that time, you see. He used the coefficients you see and. put them down and so on and then another one, etc. It was all really in a no, wait a minute it was as determinants from which you could go over to that.

Kuhn:

What sorts of problems did he put into this formulation?

Sponer:

I do not know. He had his whole book in this way. His whole book…You develop everything in a series, and broke off your series with a certain and put those coefficients in it, you see. And it was the same way as if you write it in a determinant way. And later, when all this came with matrices, etc., I took the old book out, compared, and saw to my astonishment where more or less it is the same thing; mathematically, purely, mathematical… Debye was entirely different when he put something up, you see. Entirely different. But Voigt was tedious for a student I assure you to go through all that. Then I had a course with him on crystal optics, for which I was too green in reality. It was more or less a seminar. That was the second or third year. But that was again very difficult. However, it has helped me a great deal later, going back to that course. You see, when I looked into modern theories of the Raman effect, for example, and such things, you really could use it. And also about the moments of inertia, you see, and all this here, this old crystal theory is very helpful. And actually I think, someone today who is a theoretical person and also a mathematician could take some of these old books of Woldemar Voigt on crystal optics and make a beautiful piece of work out of it, by just supporting it, and looking at these things from a modern point of view. And, this is what we need today. When I retire, maybe I might go into crystal optics because I am very much fascinated by this....

Franck:

I think since we have you here on the chair, could you not speak a little bit about your contribution to what is now called (Franek-Condon) principle and these things. The heat of dissociation and the thing with Birge and your lectures you gave in Leipzig and the excursions you made when you said, “How to tell my chemist.”

Sponer:

Yes, I was known in Germany as ‘How to tell my chemist’.

Kuhn:

You’ll have to explain that.

Sponer:

Well.

Franck:

Can I say in introduction a few words? The chemists - Nernst, for instance -- in the beginning did not like at all the idea that the molecule could take up much more energy than is necessary for dissociation and so on. And how that happened, how predissociation occurred, how were these things, that was her specialty. And she gave some excellent talks about it. And so we said often in Gottingen, “She has to trouble now again, how to tell my chemist.”

Sponer:

You know, when I was invited to the Bunsen Gesellschaft in Munchen, I gave a talk there.

Franck:

She gave a talk there, but also in Leipzig.

Sponer:

Oh yes, in Leipzig. There I felt really flattered. Debye invited me. He had always conferences in Leipzig when he was in Leipzig. And he invited me to give a talk there...And I’ve forgotten now how this talk was called. It was “Dissociation -- and something.” I’ve forgotten. But I can send you a reprint.

Kuhn:

You must have gotten to Gottingen in 1918.

Sponer:

Yes.

Kuhn:

And you took your degree in 1920.

Sponer:

Yes.

Kuhn:

That’s a very short time.

Sponer:

I know, and I am very much ashamed that it was so short, I wanted to wake it one semester longer. Now why was it so short? I finished of course the thesis, that is clear. Otherwise one couldn’t do it. I had not heard enough lectures, really, but Debye left...I said to Debye, I really wanted - although I finished to take some more Vorlesungen because I needed them. And up to now even I feel it. Mark this, up to now even. I missed a course in electromagnetic theory in this fashion. And Debye said, ‘Well, I tell you, in your case I would finish and have the examination now, before I go. Or do you want that Pohl takes over afterwards.’ Now I didn’t want that. And so he said, ‘Well, you just go in and do it. I’ll recommend it and you can do it.’ You see I was during this last semester before I left an assistant to Hilbert. He wanted an assistant who did nothing but the following: read for him article and tell him afterwards what was in the articles and talk about it. And you could ask questions. So I read for him. I read articles in theoretical physics. And he said which ones. He wanted to know this and this and so on. You read it and you tell me what is all about it. I was scared to death each time because of course he knew so much more. Particularly in mathematics and so. I prepared of course, these lectures, these meetings or so. I was there half a year - one semester so Hilbert knew me very well, so that was another point why I could take the examination. ‘Well they know you, they know you,’ Debye said. ‘You can finish.’

Franck:

After five terms you got the doctor’s degree. And at the end of four terms she read theoretical papers for Hilbert. I must say--

Sponer:

Ja, but I was good. I am not good any more.

Franck:

She has the appetite of a puppy.

Sponer:

I could just digest almost anything in no time, at this time, you see. But it is not anymore so. You lose this. Today I struggle. It is not nice to become old.

Franck:

Anyway, it is certainly true. A little bit longer studies would have helped you-–

Sponer:

Well, it would have helped me a lot, but Debye was the one. You see he left, and he said, “I would like that you finish. What can you do?” So I missed some things where I knew where I was weak.

Franck:

And Debye did another nice work. He sent her to me.

Sponer:

Oh ja. He said, “Well, where do you want to go now?” Well, I wasn’t so sure. I said, “Well I really would like to learn some more theory.” “No,” he said, ‘No, not this. What do you want? I send you to Sommerfeld? Sommerfeld has a very good school and you go to Sommerfeld, and since you want to learn some more theory and so on, that would be the place to go.” And I said, “Well, that would be very nice. But I would like first to go one semester at least to some one where I can really brush up my experimental physics, because I haven’t done anything since I took a Prakticum.” Oh, here I have to tell you I never finished the Prakticum. You see I had only one year with Paschen. When I came to Gottingen I needed Prakticum, of course. So I went into the Prakticum that Debye had. It was in scandalous condition. Very poor. He had Holtzmark, who at this time was with him. You see, Debye didn’t see me, so I just went to this Praktical. And Holtzmark was the assistant. The Praktical was in poor condition. And I had just been with Paschen, where everything had to work really, and well. There it was entirely different evidently. And so Holtzmark gave me something, and I have forgotten what it was. But I was not satisfied, not at all. And I said to Holtzmark, “Holtzmark, you know I didn't like this experiment, and it isn’t working well, and so on.” I was not nice really. I said this is wrong and this is wrong. And so next time he gave me something else. And that was still worse. It was a beginner’s experiment. And I said, “Well now look. I have already done these things. And they are just beginner experiments and I don’t want it. I want something else.” And he became mad. And he became mad and he said, “Well, go to Professor Debye and tell him that you are not satisfied with the Prakticum and see what he can do. I go down to him now and will announce you.” My heart jumped, but then I said well, I must do it.

So actually, Holtzmark ran down. He came back and said, “Professor Debye expects you.” I went down, slowly, slowly, and came to the door. Knocked. “Come in.” I went in. Debye said, and he had an amused expression on his face, he said, “Sit down.” I sat opposite him. “Would you please tell me what you do not like about my Prakticum?” And I just collected all my courage and I said well this and this and so. The experiments are not in order, and they need repair. And there are not no interesting experiments, etc., etc. “So,” he said, “You are the one who does not like my Prakticum. Well, if you do not like it at all, why don’t you do some theoretical work.” Well I said, “I do not know whether I could do that.” And he said, “I’ll tell you what you do. You go and read the paper by Schwarzschild.” You know, that paper by Schwarzschild? “You read the paper by Schwarzschild and then there: is an interesting paper by Stern on the Stark effect. You read these papers. Take first the Schwarzschild paper.” You know,…1916 it came out. “You read them. And then you come and see me, and we will talk about them.” That is how I became his student, That’s the whole story.

Kuhn:

What was it like, reading those papers?

Sponer:

Wonderful.

Kuhn:

This was in your first year?

Sponer:

That was in my second year. I was one year in Tubingen. And this was now in 1918. First year in Gottingen, second year at all.

Kuhn:

Where had you had enough mathematics to read the Schwarzschild paper? Or enough mechanics for that matter?

Sponer:

I had several courses in Tubingen mathematics. Quite a few. No, I got through. I got through with the mathematics. That I remember. I worked hard, but I could get through. This is how it started…Theoretical physics I took with Voigt, Woldemar Voigt, in mechanics. And then he gave these other courses. But Woldemar Voigt’s courses were tedious the way he presented them. But I had, no course with Debye at this time. I had started in Tubingen with chemistry because I said if I want to work on atoms and molecules I have to know chemistry. So I continued my chemistry in Gottingen. And there was Windaus.

Franck:

How have the times changed. I was sent a dissertation out of Gottingen. This was by a younger friend of mine. He went to Gottingen. And he sent me his dissertation with the remark, the integral which is usually found in a Gottingen dissertation will be on page so and so. How have the times changed.

Kuhn:

You were both in Gottingen in 1922 when Bohr came and lectured.

Franck:

Yes.

Sponer:

You...Well I had not seen you in 1922.

Franck:

Die Bohr Festspiele?

Sponer:

Oh, die Bohr Festspiele. Debye had it.

Franck:

Oh, oh. Debye had none of that.

Sponer:

Debye had a big meeting once and Planck came and everybody came.

Franck:

That was something else. That was something else. There I was too. But Bohr not then. There was Sommerfeld, there was Planck, there was Voigt. It was an excellent meeting. And especially it was Planck, the center of it. I came from Berlin over for that.

Sponer:

That must have been ‘20, was it?

Franck:

That was ‘20.

Sponer:

When Debye was still there.

Franck:

There was no meeting with Bohr, no meeting. 1922 was the first visit of Bohr in Gottingen at all. He had never been there before.

Kuhn:

Do you have recollections of that 1922 one when Bohr came?

Franck:

...In 1922 in one another way we went to (Karlshaven) and stayed there several days together and had nice talks. So I bad not only the meeting but also three days with him in (Karlshaven).... I know how we were sitting on the ruins -- (???) talking about what I mentioned to you. There he said things which I understood years later. That one could not be content with his theory, and it had to be changed. And it had to become entirely different, and that was only a beginning.

Kuhn:

Did those come as a surprise to you then? Because you had seen him earlier. Now had he said the same sort of thing earlier, or was this something he was now saying.

Franck:

I don’t know whether he had said it earlier. I can’t tell you that in certainty. But I remember that very vividly, that it was 1922 when he was very outspoken and. considered, it from all angles. I practically never went to these meetings. Twice maybe. To the meetings where theoreticists of the world came to Copenhagen and then discussed back and forth. I usually couldn’t follow, therefore I did not so often go. But he was really the man who gave here and there, then the people went away, all over the world and did things. How much it was already what they brought with them and Bohr added something. He directed, so to speak, the development of theory in all countries. That was also when Pauli and Ehrenfest met, and Ehrenfest said to Pauli, “I like your book on relativity much more than I like you.” Because Pauli was at that time so often outspoken. I knew that Bohr would tolerate him, but I feared that he would be impudent to Bohr. I told Pauli “If you go to Bohr, please behave yourself.” And then Pauli wrote me a letter. He didn’t know what I really meant because Bohr is no Bonze.

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