James Franck and Hertha Sponer Franck - Session V

Sponer:

I did not stay in theory but went into experimental physics. And that was the following way. Debye, when he left, said “You go to Sommerfeld.” And I said “Yes, I would like, but not immediately. Later perhaps. Because I had never really done experimental research. And I think I should know something of that sort too. The Praktikum is not really scientific experimental research.” So he said “Well, let me think about it.” Yes he said, “I know someone. He is nice; he is not so old. He is a young man still. He is in Berlin at the Kaiser-Wilhelm Institute. Yes, and he does good work. You go to him.” Here he sits. This is how I came to Berlin. This is how I came to know him. And so I went to Berlin. Do you remember?

Franck:

I remember.

Sponer:

He said you can learn and so on, and this is how I came there. Now this was however a change. And it is really difficult to go again back.

Franck:

Let me just tell a joke about Debye. Debye said, “How, are you content with laboratory?” And I said, “Oh Debye, I’ll always defend you.” He said, “Why do you defend me?” Now, you see the laboratory was in such a disorder, that I said even if Debye had not done much for the laboratory, he could not have got it in such disorder in the few years he was there. So it must have been that way before. But that’s the way one could talk with Debye. And he had no objection to that.

Sponer:

No, he really took such things very nicely. I saw him at his 70th birthday…All his pupils who were in this country were invited to celebrate it. And so was I. And I went to it in Ithaca, Cornell. And this was really quite nice, because some people who had been in Gottingen before and some who knew about it had a play. And they played a scene, and showed him. One of them was impersonating Debye, and the others his students, and it was really most amusing what they produced. And many people were there who didn’t know about it, but Debye took it wonderfully. He just was so happy about that whole performance. And of course the one who was Debye had a long cigar, because he always had a cigar. He always smoked a cigar.

Franck:

I must say he was one of the men whom I never really understood entirely. A man of rare gift. He has done a lot of things. But still I believe he could have done 10 times more if he wanted to.

Sponer:

Ja, Pohl sagt “Sein Gebirn lauft auf Kugellagern.”

Franck:

Really, exceedingly nice things he has done. Pohl told me, by the way, something which I do not know whether it is true: That Debye had also the idea of the Mossbauer effect before. I have not heard about it, Pohl told it to me…

Sponer:

Oh, he is enormously gifted, and fast like anything. And he is a good speaker too.

Franck:

Excellent. He is too good a speaker.

Mayer:

Yes, I agree. When you come out of the room, you feel be must know everything. [three voices at once]

Franck:

I remember there was a meeting in Hamburg of the Naturforscher many years ago, and Debye gave a public lecture in the evening. And I said, “Debye, to my regret I cannot come.” He said, “Why do you regret?” Oh, I say, “I like so much to see how you deceive the people. Because they think they understand.” And he smiled and said, “You are quite right, that’s what I intend to do.”

Sponer:

He has an enormous gift to make you—When you left you were absolutely easy, wonderful. But then you begin to think about it.

Franck:

But his talks were always a pleasure, a great pleasure. [Break] Other things are entirely wrong. For instance, it was entirely wrong to say that the center of all these things was Gottingen. The center of all was Copenhagen. And the whole thing was done as a kind of an overestimation of Gottingen. There are so many nice things in it which one could read. But I was disgusted really, by that tendency in it.

Kuhn:

Let me ask you one thing that really goes back to an older conversation. You had started to tell me something that Lindemann had said immediately after the paper with the mercury line came out.

Franck:

You remember in the other paper we mentioned Lindemann and that he could explain something with this electric photo effect and what not. All these things are aberrations. Lindemann’s idea, our idea, all these things were just not right. But we tried always to find a relation to ionization…Lindemann said it can work without quantum theory. And I do not know how he did it without quantum theory. And he did it without quantum theory. We others did it with quantum—Stark and Hertz and I and everyone practically. Lindemann was an outsider. He took the frequency of this electric photo-effect, but how he did that without quanta I forgot entirely and I think he would not like to be reminded if he were around. And he wrote to me, this paper—or he mentions this paper “Why do you put in with this all the idea about quanta? Why, you can do it without.”

Kuhn:

And this paper now, was the paper in which you found the mercury emission line?

Franck:

That’s it. Even after we found that, he stuck to his guns and said one can do it without quantum theory. And therefore we should not make a good paper later appear bad because we put in quantum theory.

Kuhn:

That must have been very unusual, at least to have a man that young opposed to quantum theory in those years, was it not? Can you think of many other people as young as Lindemann who would have taken that attitude?

Franck:

No, no. I know that Seeliger, the son of the astronomer, the man working on gas discharge, wrote one and another nonsense about ionization, And I disliked that very much, by two reasons. First, he heard of our paper and we discussed it with him when he was in Berlin. We spoke a little bit about it and said that we would really not know whether there is a definite ionization potential or not, because we were in progress. So he made a theory in which he said there would be no sharp limit for ionization. And whatever that was, I don’t know. And he published it without mentioning us. Now Hertz and I thought, that serves him right. Because in the mean time we knew it was wrong. So that was the only man whom I know who did at all something like that. It was a little bit unusual at all to do something about ionization potential, with the exception of Lenard, who started this work; and Stark, who had an idea about it, in connection with quantum theory. Lenard probably would not have taken quantum theory, because Lenard’s attitude was always, ‘what he has not done is not good’. And there are such people.

Kuhn:

Did he resist the idea that the ionization energies were all different?

Franck:

Yes, he continued to call it the 11 volt limit. And I made a little bit a joke in that little book with Jordan in saying it would be time to give up this term 11 volt limit if the 11 volt limit for instance in Cesium lies at — I don’t know — 3½ volt, and in hydrogen at 13.6 and so on, why call it the 11 volt limit? But he didn’t give it up; he called it as long as he wrote something about it the 11 volt limit.

Kuhn:

Was he critical of your work?

Franck:

He ignored it. But he didn’t criticize, no. He was at that time more interested in phosphorescence and these things. I said something about Gilbert Lewis which was not right. Lenard did not read literature because he was convinced that everyone else would make nonsense that was Lenard’s attitude. Gilbert Lewis did not think that. But he said if I think about it I want to be independent, and then later I’ll see. But the trouble was that he thought only in playing Skat in the faculty club. And, having a few people in occasionally asked the question, “Do you know of any paper about this subject? Let me know.” So he did not bother...But Gilbert Lewis really was a very independent thinker, arid I did him injustice at the very end of his life, and I still regret it. Because I always said, I cannot understand this idea of the triplet state responsible for the phosphorescence in (???), I cannot understand that the factor between (the singlet—triplet and the singlet-singlet transitions) should be bigger than 10. And he had such a case, in which it is much bigger.

Kuhn:

Professor Mayer and I were talking last night, and one thing we would be particularly grateful if you would tell us about is the way in which Gottingen became after 1920 so very much the center. This, after all, must have been your doing and Professor Born’s.

Franck:

Yes, it might be because we both were interested in it, and furthermore, don’t forget that Sommerfeld did not want, and could not keep his extremely bright students always in Munich. And so the only place in Germany, with the exception of with him, to have a contact with other people, was to send them to Gottingen. And so, I may say, the school of Sommerfeld was a great contribution also to the flourishing of Gottingen. Would you not say that too?

Mayer:

Yes; I agree.

Franck:

And then of course there was the (radiation) of Niels Bohr’s influence, and, the way we managed to invite him and to, have contact with him. And it became just a kind of a center. And then, don’t forget also the influence of mathematics there. Gottingen was really the center of mathematics for such a long time. I would say that Born learned so much mathematics just because he studied in Gottingen...

Mayer:

Did you really get many young people from Munchen? I know Heisenberg came from Sommerfeld.

Franck:

And Pauli...My memory is a little bit hazy, but he was there at least two years I am certain. I remember this discussion with Pauli when he wanted to go to Bohr and I said he should behave. That was in Gottingen of course. And he was quite a time there. Then came this excellent school of Born, with Hund and with Jordan. Jordan learned also a good deal from me, in writing this book. This book is by no means a good source of exact literature citations, because actually it, was always this way. I dictated a great part to Jordan. And then Jordan went over it. I didn't look up the literature, so I ascribed a good deal of things to Mr. Miller which were done by Mr. Mayer, or what not. And Jordan thought that I would know, and I thought that he would look at it. So when this book came out we went to the meeting of Naturforschaund Arzte and many people said something about this book, and always with nice words and very important and what not, but you see, on page so and so you quote me wrong. You ascribe that to me and that, but I have done that. Then came the second and the third and the fourth. And then the fifth came and started first to say nice words, but (then I said immediately, “Where did I—.”) So in that respect, don’t use it as a source…

Kuhn:

You and Born both came together in 1920, or very nearly together, in 1920. Did you talk about what ought to be done, and make a deliberate effort to change things? Did you make changes in the teaching program?

Franck:

No. We didn’t. Of course, I mean, Pohl changed the whole aspect of lectures in experimental physics.

Kuhn:

Now that was done when? Before you came?

Franck:

Yes. We both were on the list there for Gottingen, and he got the position; I was at that time in the war, and said I would come when I had leave of absence. I didn’t know what it meant, that they invited me. And Pohl got that position first. But anyway that was nicer for me, because I got then the official chair, and Pohl had the dnofficia1 or whatever it is. But anyway Pohl has changed the expenenta1 physics, and was very strong in preparing teaching in experimental physics for beginners.

Mayer:

He was excellent.

Franck:

I had the laboratory course, as the main thing, with Praktikum. And we used a good deal of the instruments of Voigt to make an advanced laboratory course, where more complicated things were measured. Really it was by that time quite modern and better—equipped than I have seen before, because we took a great part of the old instruments for that purpose. And that was also where Heisenberg took part for a short time. You see Heisenberg passed his doctor’s examination, after already being known over the world. And he did not study at all experimental physics. And Willy Wien asked him about experimental physics, and he failed horribly in that part. And Sommerfeld had quite a time to convince Willy Wien that it would be a shame for the University if Heisenberg would fail with the doctor’s examination after being already a famous man. And so this story was then told by Willy Wien to the father of Heisenberg. And since Heisenberg wanted to go to Gottingen, he wrote a letter to me whether I could not see that his son would learn some experimental physics. So I told him in a letter I would see what I could do. Then Heisenberg came, and I told him this story with a smile, and said “Now Heisenberg, the only thing I can do for you is to ask you to come to our advanced laboratory course and see whether you like it.” And after a time I saw that he was sitting there forlorn and absolutely uninterested, and so I told him, “Do you mind if I throw you out?” Oh, he would be elated if I threw him out So I said “All right, I’ll throw you out.” And that was that. Because I couldn’t see for the world why it would be necessary for Heisenberg to make these experiments if he didn’t want to. He could always get the information reading about it or what not. And that was this point, and I couldn’t help his father more than I tried.

Kuhn:

Then he was actually enrolled in the course?

Franck:

Not enrolled. He attended. I mean he was not a student anymore, but anyway he attended, and came really quite nicely. But one could see how he suffered. And for instance, Wien was really upset that Heisenberg didn’t know how a storage battery worked, but why should he know it? If he wanted to know it, he could read it and understand it, in five minutes. In such things I half—heartedly took him, but I saw it has no sense. And he was so pleased. He could say with good conscience to his father that I had thrown him out! I must say, Born and I discussed many things together. We were quite independent, but anyway, our colloquium, and our cooperation in mutual appreciation of what the other side did was, I think, a great factor. And it was probably not in many other places. Maybe Berlin, but at that time in Berlin I don’t know why it did not work so well.

Kuhn:

Berlin at the beginning of the century, when you yourself were there, was, as you said, place to go. For physics after the war, it is not any more.

Franck:

Rubens was very good, but he had not a great school. In a classical way, he was excellent. But I may say that he was so absorbed in his work. He felt often the obligation to ask the assistants what they did. And it was also the custom that every time one sent in a paper one showed it to him. When I showed him those papers of Hertz and myself, he said “Oh yes, I know. It is about ionic mobility.” And I became so fed up with it that I always said “Yes.” “Now then, I don’t have to look at it.” And the first time he knew what was going on in our things, was when he read the paper, I think in 1916, and be wrote me a letter. I was in the meantime again in the war. Rubens said “I had no idea that there was such beautiful work going on.” And this was really one of the things. Then came Nernst. About his greatness we have spoken. But I can’t say that he contributed very much to physics at that time. He was absolutely not in these modern things. I remember a discussion with him in which I tried very much, arid where we always said (Hertha) should give a talk, to get an understanding of what an excited state means. He was not interested. He was interested in such things as high voltage, and he had some men working on high voltage. And he even did some nice work a genuine Nernst idea going into some relatively high mountains, and over a valley, having a wire, and getting the potential difference between the wire from these high spots to the valley.

Kuhn:

You spoke of this as a “Nernst experiment.”

Franck:

A ‘Nernst experiment” is a mixture of an idea with practical background. I remember another story where Nernst decided it would be a good idea to change the climate. And he wanted to change the climate by taking such coal mines which one could not use any more, which were difficult to reach, and burning down there the coal; all the carbon dioxide should go into the air. And since it was measured at that time by Rubens that the absorption of the carbon dioxide was not an entire absorption, that would mean the total amount present in the atmosphere was not sufficient to absorb ail the radiation in the neighborhood of 108 microns, or whatever that is. And he calculated that if one would make it better the temperature would go up, and that it would be a very good idea to get more plant growth. And he told me about it. He said the only thing to propagate such a project is to write a detective story about it. I mean, nowadays one would say science fiction. And he asked whether I would not write with him about it. And I said “Yes, I would, but I think the deduction is wrong.” And he understood why. He compared the absorption of CO2 in a little tube with the absorption of CO2 in the atmosphere with all other gases. But because of the impacts with the other gases broadening occurred, and by the broadening total absorption would occur… Nernst was also the man, the first man I think, of academic rank or what not, who got a car and drove around with the car. Arid was always sitting in one place or another and always something happened with the car, and he was not a good driver, and it was long stories about Nernst and his automobile.

Mayer:

Yes, the older inhabitants in Gottingen still told me about it.

Franck:

When he got his Nobel Prize, he told us about the trip. And he went to the station and ordered a ticket to Stockholm. It was during the Inflation, the greatest inflation. The man said, “But that is an expensive trip nowadays.” Nernst said, “Not for me, I am Walther Nernst.” And it was in the newspaper that he got the Nobel Prize at that time, and then he said, “By the way. I do not have to pay it. I use the trip also for consultations in Sweden.” And so they pay that.” He was an astonishing man in each respect. But I would like to say, it could not be different. Then also, Berlin became too big. That was another thing. Too many students and too much mass fabrication. All these things played a role.

Kuhn:

What about the roles of Planck and Einstein?

Franck:

Yes. That of course remained. But Einstein never had pupils. He had some co-workers, and that remained of course....But he was not a man to get a school and to get many co—workers. That was not his type. And Planck, now Planck really was not young any more, and later he became president of the Kaiser-Wilhelm-Gesellschaft and there he was entirely absorbed in that work. Haber was very busy, and this Institute of his, in Physical Chemistry, that was excellent. (Bodenstein) in physical chemistry was by no means a physicist. He was a very good man, but I remember I tried very much to discuss matters with him about the relation of photo—chemistry to light absorption, that excited molecules could be quenched and that there chemistry occurred. And then after making that clear, then came that Franck—Condon principle of the band conversions. I gave a talk there at the Faraday society, and (Bodenstein) was also there. And when I was through, I asked him what he thought about it. And he said “Well, he finds that I am actually somewhat an unreliable man, because I always told him that one needs //an impact to dissociate an excited molecule//. And now I say that it is not true. One goes into the continuous spectrum at the end of the band conversion. It dissociates in one act. Now after he learned the first thing, how could I now without blushing say it is all not true what I said before? And I said to him, “But this is a specialty. It is only a few cases where you get so much oscillation transferred with one electronic transition.” He had decidedly difficulties to understand, but when I told him that, then he understood and was quite happy again. Hanle was one of my students in the ‘20’s, and he worked very independently; not very able with his hands, but very independent and with good ideas. Now, he came to us, and I never knew why he came to us, but anyway, he was with Lenard. You heard, that Lenard, as (???) said, gave very interesting lectures, and so attracted many people.

Kuhn:

I had not realized. He was a great teacher then? A great lecturer?

Franck:

No, he was not a great teacher. He was a great lecturer. He could not stand any independence, and this is not a sign of a great teacher. But his lectures were excellent; only Pohl gave later better lectures. He was there; and be read something about principle of relativity, that was taboo. But in his independent way he went to Lenard and told him that he had read a paper about principle of relativity. He understood that he was against it, but he found it wonderful. Whether he would be not nice enough to explain to him why that was wrong and why it is not wonderful? Now this of course was identical with his being thrown out of the laboratory. But on the other hand, Lenard was decent enough to give him recommendation to some other place. He didn’t want to have him anymore. And also Hanle didn’t want to stay. And he said somebody else, I don’t know who, in Heidelberg, told him, “Hanle you better go, as quickly as possible, and you have the choice to go to Munich to Sommerfeld and Wien, or to go to Gottingen to Born and Franck.” So he went first to Munich, and spoke With Willy Wien, and found that Willy Wien seemed not to be very much interested in him. No. It is that Hanle was always a future professor; absent—minded. And when he came and wanted to speak with Willy Wien, he had left the letter of recommendation of Lenard forgotten at home, and had to tell Wien he had a letter of recommendation but he would give it to him later; he had forgotten it at home. Now whether that was the reason or what, Willy Wien smelled a rat or he didn’t like it or what not. He was very unkind. So he never went and got his letter and took the next train and came to Gottingen and then came to the laboratory.

Kuhn:

You told that story somewhat differently yesterday.

Franck:

Yes, what did I say?

Kuhn:

I don’t remember now what you said, but you told more about what Wien said, and it also involved his being a boss, and perhaps also something about the sort of physics he was interested in.

Mayer:

- No, what you said, among other things, yesterday, was that Hanle felt he had just gotten rid of one boss, he wasn’t going to be working under a boss again.

Franck:

Oh, Wien was somewhat bossy, yes. And Hanle didn’t like to have that. He had enough of that. And therefore he said no, he will not try.

Kuhn:

To come back now to building up the program at Gottingen. How much of a role did Hilbert play in that?

Franck:

A (catalytic) role. I remember that when I got a call there, Hilbert asked me to come to his colloquium and give a talk there. And as it is, if one comes to a new laboratory, one has not found the time to prepare anything if one does not leave the laboratory. So, on that very day on which I had to speak in the afternoon, I left the laboratory and went in the woods to prepare myself, where I was undisturbed. And then I found, ‘Now, I know what I want to do, and it is all right. But, the funny thing was—such thing can happen only in Gottingen—Of course I didn’t know the surroundings—that I found myself in the woods and I didn’t know where I was. The question was how could I come in time to this colloquium? And I found a road; on that road there came a big beer transport with big horses before it. And I asked where the man was going. He said he is heading to Gottingen. “All right, I get on with you.” And he brought me to the University. I ran down from there to Hilbert’s colloquium, to the amusement of the students. Anyway, this colloquium went quite well, and we had always contact. When something was there Hilbert came. And Hilbert had then somebody who explained to him details when he didn’t follow, but he was very much interested. And this certainly had an influence. It had also an influence that the students who came to Max Born and so on had mathematical training, and that was not only due to Hilbert. Herglotz was there, very good mathematicians. All that helped a great deal.

Kuhn:

I’ve talked to a few people about somewhat earlier times at Gottingen, and it then appeared that Hilbert was also very much involved with appointments. For example, there are one or two occasions I’ve been told of when Hilbert and a physicist went to interview or to talk with a candidate for a job.

Franck:

Yes, for instance I was asked, as I said, to come there and give a talk. And of course Hilbert was there. Also, when Debye came, Hilbert was the man who wanted to have Debye there. And he had a great influence in that. Of course he made some remarks which some people did not like, but which were true, that physics is much too difficult for the physicist.

Kuhn:

That remark has apparently rankled with many people, because I keep hearing it.

Franck:

You see, it is true. It is true. On the other hand, it is now true really that biology is now too difficult for the biologist. There are always transition states of one and another. Then, don’t forget also the fact that Courant was there. Courant, with his great affinity to millionaires and what not, always brought money to the town. And he brought the Rockefeller Foundation to build a mathematics building, and add a wing to the physics laboratory. Courant was I don’t know what I should say—(betriebsam)—and that’s what he did also again in New York. He made a great school of applied mathematics, and has now a kind of a skyscraper there for a mathematics building. Such people must be there. He is a good friend of mine, and sometimes I anger with him and tell him “you scatter too much of your effort for these things. You should stick to your mathematics.” But anyway I don’t know whether I am right or not, such men are very important.

Kuhn:

He certainly is.

Mayer:

And also in Gottingen there were very good mathematics lectures given for beginners, for beginning students, which you just do not find in this country. In this country, usually the physics department will give its own mathematics lectures, because the mathematicians cannot talk, or will not lecture in a straightforward way to a group of students.

Franck:

But you see, if I say that the lectures were good for physicists always in Gottingen, I would say decidedly I would think that Landau’s lectures were much too abstract for the students.

Mayer:

Well not all the lectures were good for physicists, but the beginning course was usually given in such a way that a student could really get something out of it. Which is not what is done in this country.

Franck:

I may say the book of Hilbert—Courant, the way their calculus is introduced is so superior. When I read it I read it not the whole, but I mean what I read I said what a pity that I have not such a book available when I was a student. The lectures which have been given in Berlin at that time, also the lectures I heard in mathematics in Heidelberg, did not appeal to me. But the way in which it was presented there, that appealed to me. And so a lot of things came together. And I would like to say the indirect influence of the mathematicians is very great. You know already before there was Minkowski. His contribution to the Principle of Relativity. There was Klein, with his great interest in all educational questions. And I don’t know how much Klein has done to shape the way in teaching mathematics in Gottingen, I don’t know that. It was before your time, and it was also before my time. But Klein at that time still regarded himself as the Pope. And when I came, he didn’t go to any of the faculty meetings, where he had also not officially the right to go as an emeritus. He could go, but nobody would mind. But he had nothing really to say about it. So when I came he said I should come to his house, and he told me ail what one has to do and not to do. And sometimes we did, sometimes we didn’t.

Kuhn:

What sort of things did he tell you one must do and not do, do you remember?

Franck:

I can’t tell you, I can’t tell you. No, it would be not correct if I would say some particular things, because I don’t know any more.

Kuhn:

Did you and Born think together about the new physics…Were there programs either at that elementary level or at the more advanced level, that you and Born introduced?

Franck:

We thought that there were people—Privatdozenten—who could supplement the normal lecture course with advanced courses. I mean the thing was alive, and if something is alive and there is a nucleus there, it goes automatically. It couldn’t be helped, I don’t know in that respect how it was in Munich. I got once a call there, and I didn’t accept the call, because in one and another way I didn’t find that the atmosphere would fit to me so much as Gottingen.

Kuhn:

This was after you were at Gottingen?

Franck:

Oh yes, after, yes. You see that happened in Germany always. Men who did all right were asked at other universities. It was a great help that I was asked in many, several I was asked in Heidelberg and Munich and Berlin, so it was help, because that helped the laboratory again.

Mayer:

Berlin didn’t.

Franck:

Berlin not, that is true, because that was also a Prussian University, I did not accept but asked the man whether he could not do a little bit more for Gottingen, and he said “You cannot ask that now that you have not accepted Berlin that we should make it easier for you to stay in Gottingen.” Anyway, I took my revenge, because he came and visited us. He saw the laboratory and found it in much better shape than in Berlin. And I said “It is.” And he said. “Why is it?” I said, “I will tell you a secret. This drawer here in my desk is the drawer where all the admonitions came in and I collected them and never looked at them when I overstepped my budget.” He smiled and took it.

Kuhn:

I guess I don’t know enough about the organization of the University to understand this. Your budget was approved in Berlin?

Franck:

That’s it, yes. It was approved in Berlin and it was by no means really great, but it didn’t need to be too great at that time. And when I think about it do you remember Fraulein Richter? She was the secretary. The secretary had a ledger, and there she wrote in everything we borrowed, of apparatus. And I never was interested how we stood. I told her only, if we have only few hundred marks left, let me know, then I’ll write a letter to Berlin And I write to them “If I don’t get so and so much more, depending on the amount, I have to close the laboratory, because what shall I do? I can’t work.” And so what happened?

Mayer:

Any good director of any institute always overstepped his budget. (Tammann) was always proud that he did not overstep his budget.

Franck:

The result was that his laboratory was horrible. But on the other hand, it is quite astonishing what that man, who has a number of broken—down apparatus, could do to shape (metalodine). It can be done in one and another way. And if I think what we had at that time what we had in Berlin. Later in Gottingen we had more. But what we had in Gottingen still was so little, but it worked out. One could do it and could make simple experiments. One didn’t t need really millions as one does now. And it is understandable, because the problems are different.

Mayer:

Of course the pride and joy was the big spectrograph. The Rowland grating.

Franck:

That remained from Voigt. Voigt had already the grating. But we got a new one still. But anyway, in optics the remnants from Voigt were already quite good, and so we added a vacuum spectrograph and a few other things, which we constructed ourselves. Then other things we bought in England, and from Zeiss something. But these were also sometimes not from the normal budget, because, especially after the war, it was also one of the great ideas of Haber, who was also a practical man, to establish the Notgemeinschaft der Deutschen Wissenschaft. That is a kind of a society which included donors and acceptors, and the donors were industry. Haber was interested to see whether or not after the war, one could get an understanding of industry that they should give to this society enough money so that they could dissipate money. This dissipation was managed so that for physics every year or every two years another man or two men had to judge the requests which came in and see that there was some justice in it. Laue was very busy in these things too, and very good. I found a time ago a postcard [by Einstein] which Haber gave me, and which I sent to a man in Berlin who wanted to have it so very much. In it he said, “Please see to that, that Franck gets his support for that, because he deserves it.

He wrote that letter from Leiden, and he said to Haber, “It’s so very nice to be here in Leiden and to have a discussion with Lorentz and with Ehrenfest. A wonderful atmosphere.” I mean it was an interesting postcard, and since that man wrote about (Zernike?), I sent that to him. He was very grateful for that postcard. You see, all these things helped. And if one did something, then one got some other money, some extra money. I told you also that we got a visit once from the research director of General Electric, he died —— ...It might interest you. Langmuir was in General Electric under this Director. And when he was there first, he went to him and said he wanted to resign. And he said “Why?” Langmuir answered, “I have worked now for two years on electron emission of glowing wires. I cannot see any connection with the interests of General Electric in this case. Therefore I want to resign. I want to continue research work, and therefore I want to resign.” Then this man, whose name I at the moment can’t tell you, who died two or three years ago, said, “You stay if that is your reason. You wait and see.” And from the foresight of this man came then the development of the tungsten lamp… And he visited us this — man. Then suddenly he asked whether we wanted to have a few thousand dollars for the laboratory. And I said, “Now, if you ask me, we are always of course starved for money. But tell me, how can you give us money for the work we are doing, because we do not want to work for General Electric. How can you do that?” He said, “Oh, I can do it. You see, we know that wherever decent physics is done, they do something for us, whether they know it or they don’t.” This is the attitude held…

Kuhn:

If you will forgive me, I want to say something on the tape for a moment. For the record, in this same connection. Because if somebody listens to these years a hundred years from now, they will not take for granted what I take for granted. You spoke, in our very first day, of talking with your father, before you went to the university, and your father saying there was some pressure towards chemistry, because after all in physics there was nothing to be done, unless you get a job as a professor or, and unless you worked in the university. One of the things which I think people may not now realize, or may not realize a generation from now, is that that situation was still, in this country at least, almost identical when I went to the university. And I can remember talking to my father in 1939, and again having my father say, “But look. If you are a physicist...” I rather wanted to be a mathematician at that point, and we compromised on physics. But still even in physics there was nothing except applied research, yes. But if you wanted to do pure research it was still a matter of the university, except that there were a very few jobs at Bell and at General Electric. Coming back now to Gottingen, would you tell us more about your own work there? By the time you got to Gottingen, or at least very shortly after you were there, you were almost entirely concerned for a while with collisions of the second kind.

Franck:

I think I really became interested in that during the visit, between the time in Berlin and my going to Gottingen the three months in Bohr’s laboratory. Discussions with Klein and Rosseland, and with Niels Bohr, influenced me very much. On the other hand my interest remained always the same. Namely, the energy exchange between particles colliding whatever it is. Kinetic energy transforming light energy; light energy used for photochemistry, and light—energy used for fluorescence and for phosphorescence and all these things. And so I came automatically to it. I would like to say, the time in which we studied systematically the electron impacts on atoms and on molecules was replaced now by the use of excitation (???)for different types of purposes, And so came sensitized fluorescence, so came the Franck—Condon principle, so came my own relation to spectroscopy—which was always lose one—, so came pre-dissociation—so far as my contribution to this which were small compared to that of (???), But anyway, the whole studies of potential curves, and the cutting of the potential curves, and what happens there, and what that means. Then that influenced also a little bit the pars in which Born became interested. So your dissertation on the free-free transitions, which are now very fashionable again—you don’t probably know it in this plasma work. All these things were the natural next step to continue. And you see, if I enumerate, the electrons were in the first resonance level, then the higher levels, then ionization; mean free paths and all that connected with it. The whole thing connected with kinetics.

Then of course came the meta-stable states, and the meta-stables became how one reaches the meta-stable states, directly or indirectly? Then again this connects with R. W. Wood’s work, who also studied fluorescence. And then I was several times in Holland, where my friend Hertha was busy with Phillips. They had asked me also whether I would go there, but I didn’t want to. And all these things with neon light was on the role of meta-stable states, and selection rules. Then the exchange of this energy at surfaces meta-stable states liberating electrons. Then for instance Haber’s experiment where he had some sodium surfaces react with chlorine giving electron emission. Then came the connection with Polanyi, and Haber, about chemi-luminescence. Haber started it and then Polanyi continued in an excellent way. Then came energy fluctuations in-. side of complex molecules, and I became more interested in complex molecules. Then it came to photo—chemistry of these things, and to fluorescence, and then the connection again with Gilbert Lewis and his work; so automatically it went from the simpler to the more complicated things. The methods changed, but in principle it was always energy exchange between particles at collision or interrl1y internal conversion and all these things played quite a role in it.

Kuhn:

The Franck-Condon principle grows out of work that you and he did together?

Franck:

No, no. We never worked together. It happened in another way. It happened that I had an Englishman, Dymond, there, and let him work about the band spectrum of iodine. And another one, Turner, from Princeton, worked also on these things. Turner worked first on (the magnetic quenching of) the fluorescence of iodine. Of course there was also a cutting of potential curves, but the selection rules forbid the transition in a magnetic field. Now that was Turner’s paper. Then came these other things with Dymond, and he followed the band spectrum and saw how the bands came nearer and nearer together and then went over in a continuum; and so, I asked, what happens now, if the excited molecule comes to the continuum? That there must be dissociation was evident. But that was not the one where potential curves cut, but it was just so many oscillations that in the excited states the thing dissociated. We found these things, and I published a paper. Let us say Mr. Dymond published his paper, and I published a general paper, about band convergence and about the continuous spectrum—which would be excitation plus dissociation—and so on.

The atoms in a diatomic molecule must get potential energy because the binding changes and the thing starts to oscillate if the binding becomes looser or tighter by the excitation. And so I said all right, this is just a consequence of the law of conservation of momentum, and gave examples of how that looks in iodine, bromine, chlorine and so on. And gave the general principle. I was aware by Woods’ observations about resonance spectra, and our own work together with Wood (about impacts getting the whole band spectra because now rotational energy was added). I knew from that that it isn’t so simple, quantum-mechanically, to just say so much oscillation is transferred. I knew the uncertainty principle. I knew the potential curve. But if one wanted to do that quantum-mechanically one should do more than I was able to calculate over lap integrals and so on. I was not too much interested and left it there. And Hertha went at that time, as a Rockefeller stipend, to California. And she worked on these things—band convergency—together with Birge. And they gave then different types of heat of dissociation and so on; did very important and nice work in continuing these things. Condon was a student of Birge at that time, or in the laboratory, and heard about that work. And decided that he wanted to translate my classical language into the quantum mechanical language; quantum mechanics there was practically no quantum mechanics. It was quantum theory. The overlapping of these things. And that he did. And so it was right because the one had given the classical idea and the other had translated it—that it became then the Franck-Condon principle.

Kuhn:

This raises a question I had wanted to ask you. How much did you yourself follow the sort of paper that Dr. Sponer spoke of yesterday which Debye told her to read; the Schwarzschild paper on action and angle variables, and then Epstein’s treatment of the Stark effect?

Franck:

I must say usually I glanced just over the things. I never tried really to follow the mathematical calculation in detail, but saw where they were driving at, and what the consequences might be. And so far I kept track of that what happened, but I never could, on my own account, repeat the calculations, or would even try really to go in all the details.

Kuhn:

So that if questions of selection rules arose for you, as they must have, these you would take from existing calculations?

Franck:

Let us say, how I came to the meta-stable state. It was an example; when I wanted to write a paper about it which was correct also in the mathematics, then I (sent) it with a good man, like Reiche, I said “I know, I understand. I see from the spectrogram that there must be such a thing as a meta-stable state there, and I am now busy trying to prove that experimentally with electron impact. But I feel a little bit at a loss. Could we not work together?” So that happened. Or let us say when I was interested in such things like (exciton) movements there is a paper which became quite well-known and often used, from Teller and myself. I must say, it is written Franck and Teller, but it should have been written Teller, Teller, Teller and Franck, because he much more contributed to it than I. But I started with the problem and I came to him with the problem and said “Help me. I can’t understand (Peierls) and I want to know how that is, I need it and must use it also for other things. Can we not do that together?” And so we went through it together and I may say, I could not have done it without Teller. And Teller would not have done it without me, but he couldn’t have done it without me, I mean, if he were aware of the things and the implications. And so that was my way to doing things. And usually I may say, I like, if I put my name on something, that my contributions were really at least half, or possibly more…I wanted him to publish it alone, but he didn’t want to. You know, Teller was always so full of ideas, and he didn’t care really how much was his contribution and how much was the other. He was a wonderful man, and he is a little bit by this whole situation—yes, I do not agree with his political attitude.

Mayer:

Yes, he has trouble getting back to physics.

Kuhn:

What was the impact upon your own work and your own thinking about your work, of the coming of the new quantum mechanics? What in particular is the impact or the reaction to things like the Heitler-London paper? Does this make a big difference?

Franck:

The Heitler-London? Certainly, because this influenced the potential curves. All these things one knew much better by that; what to do and how to go at it. Generally, the idea about chemical bindings. I was never quite content, and never agreed entirely to the way in which the chemists now always speak of using the way of writing these formulas dawn as Gilbert Lewis did it. Always saying, one takes an electron from here to there and so on, because it makes a great difference whether you take really an electron away and get charges or get none especially in chemistry. And therefore I find the expression, which the enzymologist have, ‘the electron flow in photosynthesis’, or whatever it is, much too oversimplified.

Kuhn:

Let me then come back and ask you what sort of difference in the whole way you think about these problems, the new quantum mechanics may have made? Or it may have made very little.

Franck:

It made very little. But anyway, it will be of great importance for instance, if I want to at all understand a system of (conjugated) double bonds I must say. First one said, ‘here is a double one, here is a single one. Then the resonance between them.’ What does that mean, the resonance, if one doesn’t use the new quantum mechanics? I mean, so if one wants to go to complicated cases, one cannot avoid to use it.

Kuhn:

Would it be fair to say that for particular elements like this things for which the older quantum theory could say nothing you take them out of the new quantum theory now, but that you continue very much to talk about these in semi—classical terms as before.

Franck:

That’s it. I mean, roughly spoken, I still live in the age of the correspondence principle, and use the deviations from that which are necessary. But my way of thinking is still the way of thinking before all these new developments occurred. But I am aware of this, and careful not to use the old picture where I have not the right to do it. But I start with these things always from quasi—classical pictures, and add to it what has to be, because I am aware of the new development. But my wife is much more theoretical than I am. She would start with all the symmetry relations to begin with, and then draw the consequences. For me it is the opposite. I was invited from (???) to come to a meeting on plasma my old relations to electrons. And Joe was there too; we both, remember that, three years ago? And we both, Joe and I, were assigned to be the referees one morning to one part of the (papers). Joe came there one day before, and I two days before. So I read that paper before and had my ideas about it and spoke with Joe about it. We both came to that meeting to speak about something with which I had not before had any direct contact, but which had to do with your old paper with the(free — free)transitions. Now, there was a Hungarian, a young theoretical physicist, I mean, he was born in Hungary…Whatever his name is, Joe will know. And he gave a talk in which he tried to interpret theoretically these situations, And then I said something, and then Joe enhanced all these things.

I said from my way of thinking, I approach these problems in the old way. And I said of that you forget with your approach the triple impacts and such considerations. I don’t know the details. But anyway, people later said they were so astonished to hear that the old way to look at this would give new information. And so we managed Joe and I— to get through these things without being told that this was not our field. There was also an astronomer who spoke then with me, who said he was quite astounded about it. This was a younger man. How could one approach these things with correspondence ideas and so on. And that is the way I went to all such things. When something comes up, I cannot help to regard it for me as a great advantage that I understand classical physics. And I sometimes am sorry for people who have to learn it and start right with psi functions. And if you ask from where do they come?”They are there.” Now on the other hand, maybe I am unjust, because that is the way, as I mentioned the other day, that we learned Maxwell’s equations. And it might be that it is unavoidable to do it. But for me it is easier to think it first through classically. And I have the impression that even Bohr does that.

Kuhn:

One further aspect of this, Was there any problem for you in fitting into this picture certain of the things exchange forces and so on— that did come out of the wave mechanical picture? Did that fit in easily when people did it, or was it difficult to fit it in to the way of thinking you had used?

Franck:

I believe I had no great difficulty. But I sometimes went through a time of rebellion. I remember that I was very disillusioned at that time in which the problem came first up, ‘is it a particle or is it a wave?’ That is, that there was no question to ask. It took me at least four weeks of rebellion against it, to agree that things which I always believed one should know about it, and it would be fine to find out whether it is that or that, was meaningless. It was a hard blow for me! Otherwise I would like to say no, nothing was a hard blow for me. But that was a hard blow.

Kuhn:

That’s a quite philosophical issue, and I don’t believe in a sharp distinction between the philosophical and the technical. But how about the question as to whether the electron should really be attributed to this nucleus or this nucleus?

Franck:

No, I mean, then one has a picture with both. Let us just say, if I say I have a sodium chloride lattice, I can with a very good approximation say the sodium has lost an electron and the chlorine has it. And the probability to find it at the sodium is so small that I can forget it. And therefore I say that is an idea, ‘hetero—polar binding’. If I on the other hand do that with HCl, then I don’t have it any more. And I would like to say, this is already more complicated, and there is a heteropolaric component in it and another component. And I of course know of Pauling’s book and his interpretations, but I had always difficulty to read Pauling. Pauling was a genius, and really an excellent man, but I have difficulties to follow his way of thinking. Sometimes I feel as Teller said, “Pauling doesn’t care very much to neglect (one squared against one)”. He really does in his earlier books funny things. On page 40 he says, “I want to calculate the difference between the part which the heteropolar binding contributes to the binding—” and finds that the sign is wrong. And then he said “All right, we see it doesn’t work, but if I add a constant factor of let us say 40 calories to it, then the thing becomes all right.” Then later—in later pages he has entirely forgotten that he had added there with no theory whatsoever; “As we said on page 40, that—.” This disturbed me very much. But on the other hand, I must say he is really a genius. He is a naughty genius.

Kuhn:

You knew Heisenberg when he first came to Gottingen?

Franck:

Yes…

Kuhn:

His reputation had travelled ahead of him for you and for Born?

Franck:

Oh yes, oh yes. That you would say?

Mayer:

Oh yes.

Franck:

But I would like to say, there were times in which I did not agree with Heisenberg. And also the way he behaved during the war; he thought some things which I would like easily to permit a more stupid man. But there I was somewhat shocked that a man of his mental qualities did that. But he is exceedingly ambitious. And it might be that one should forget about such things. But anyway, I must say when he gave a talk right now in (Lindau) I could not help I (loved) him, in spite of the fact that I was sometimes angry. I knew Born from the time in Heidelberg, and in spite of the fact that he is a few months younger, he started in a year before I did with studies because I had to repeat one class, as I mentioned, in the gymnasium. So he was already more mature when we met than I was. But he was in mathematics, and in his clarity, his way to express himself, in his way to use beautiful language, he was always by far my superior. But I would think that if I compare him with Heisenberg, Heisenberg is the greater genius. Would you not think this same?

Mayer:

That is probably true.

Franck:

Born has not this monomania which Heisenberg has. This ‘he must go at it’. And again, the way this time he spoke, about what Pauli had said about the picture; there was a frame and nothing in it. But he was aware of it. I must say I had not so much contact with Schrödinger. I can say I had a high regard for him, in everything he did. Whatever he touched was good. His old work on color, and everything, was excellent. And what he said in what I might call his little book about biology, I regard as no good. What I think about his poems; they are not good. And it is so. I can criticize that man still. I would like to ask you both if you compare for instance Schrodinger and Heisenberg, the influence of Schrodinger’s way to write it, is much greater than Heisenberg’s.

Mayer:

Yes. Of course we learned Schrödinger’s equations in a cockeyed way. It was a transformation, from one system of coordinates to another.

Kuhn:

Max Born’s name has kept coming up again and again, and you knew him over so many years. Can you tell us things about him, as a person, as a scientist?

Franck:

As a person it’s a man who is a dear friend of mine, and has been since our early days in Heidelberg. So I can say I like him in every respect, and I admire him for his many abilities, and for his intelligence level, which is really so much superior to mine. You might think I also have one advantage (compared) to Born. I think that my imagination is a little bit stronger than Born’s. That’s what I believe. But otherwise, in intelligence level and everything, I cannot be together with Born without always learning something from him. And not just learning, but also the way he does it, I like very much.

Kuhn:

Tell me what you mean by the way he does it.

Franck:

To read a paper which Max Born writes is mostly even an aesthetic pleasure. It is not the way many people write — indigestible. I like that a scientist should be an educated man. You see, Born gave a talk there, in (Lindau) and he said, “I don’t know any more of these things, but I just looked at Goethe’s Farbenlehre and how it, came about and so on”. I disagree with him in one respect, but that doesn’t play a role. He has such a great knowledge of everything, and he said some remark about Goethe which seemed to be a little bit cruel. And certainly, from our point of view, quite correct. But he said, “If you think that I have not enough admiration for Goethe, you can, if you want to, test me. If you want, I can give a long talk quoting verbatim several acts of Faust.” And it was not as bragging, it was only because he shocked people a little bit with some remark. And he said he wanted to make clear that this does not at all influence his great admiration and his knowledge of Goethe. My wife always says w1n I quote something, “Why can’t you quote correctly?” I never can. I have read a good deal, and I regard myself as a man who knows for instance Goethe’s work very well, but not compared with Born.

Mayer:

You know I think in Gottingen there was one outstanding difference between you and Born; Born was not a happy man. You were much more serene and undisturbed…

Franck:

He had a more difficult life.

Mayer:

He had a much more difficult life.

Franck:

He had a much more difficult life, that is certainly true. That is fate to a part. I don’t know. We had such a nice group in the laboratory and were together much more. Theoretical physicists in general sit more alone at the desk. There were so many things in a laboratory which come to the attention every moment this and that. One has to be sometimes a little bit more versatile than one has to be if one sits on one’s desk the whole time.

Mayer:

In fact, Born worked at home most of the time.

Franck:

Yes, yes. This is true, but this is quite natural.

Mayer:

I hadn’t this experience, but other people have. They ask Born a question, wanted just some guidance and what did he think about it. And the next day he would hand them a paper in which he had worked it all out. Which is not what this particular student really wanted. He wanted guidance to do it himself.

Franck:

Yes, yes. But you see, the point is also that it is much easier to give in the laboratory tell him "Make your experiments that and that way.” But for Born, if he knows how to do it, he could probably not help to write it down. But anyway, I understand it is not right, that to do. Especially if he did it with you.

Mayer:

He didn’t do it with me.

Franck:

That is quite evident.

Mayer:

On the other hand, be gave excellent lectures.

Franck:

Excellent lectures, excellent lectures.

Mayer:

Not easy, but excellent.

Kuhn:

I’d be very much interested in your reaction to someone else who was not at Gottingen but who I gather came there often, and that’s Ehrenfest.

Franck:

Oh yes. Ehrenfest, I must say was probably one of the most intensive men and sometimes difficult to bear. Ehrenfest liked to teach, and was apparently a very good teacher. But when we were together, and we were on very good terms, I sometimes found it — I was afraid to ask him a question, because if I asked him a question, it took a terrific time. He didn’t let me out of his claws, I may say, until I really understood this thing I had asked and in each detail. Sometimes I didn’t want to understand each detail. I just wanted to have an answer to the question, I remember that when he visited us in Berlin, and so on, it was always nice, but very time—consuming; a simple question I gave up to ask Ehrenfest. I asked Ehrenfest only if it was really vital for me to understand it; but then I could not ask a better man.

Mayer:

But you realize that for a student it was wonderful that he would not let you go. If a student asked a question, it was the same thing. He would not let you go until you had really understood it, and that was wonderful.

Franck:

I did not only say that as a complaint, but to make clear that he was an excellent teacher, and he forced the people to understand. And the thing he hated most was if somebody said ‘yes, yes, I see already.’ “So if you see, then tell me…”And then, he had a great goodness in him. He was a man who really wanted to be just, wanted to be not conceited. He was the opposite. He was absolutely underestimated himself, but never overestimated himself. He was of course in his ways sometimes astonishing. When he came and I asked him something, and we went together and ate lunch together. He continued to discuss the matter. And I remember when we stood on the corner of the Friedrick-Strasse, and he leaned against a lantern with one hand, and told me then the whole time on the Friedrick-Strasse, all the traffic around him, about our problem. He forgot all about where he was. Apparently, if he would have had a piece of chalk, he would have written down something on the lantern. At all, he was really a maniac, and never made compromises in things. “Forget these things, let us forget about it. It is not of importance right now.” He would not do that; he must go to the roots. And I think all the great success he had as a teacher and all the good. pupils he had, and all the admiration they gave to him, comes from this side. On the other hand, he was very unhappy in his life. He was very unhappy. He had one child who was abnormal. He had. also a fixed idea that a man should not live longer than fifty years, because then he is a burden to everyone else, and his best years are gone, it is best he should go. And I never took it so seriously, but you know he died by suicide and he took the ill child with him.

Mayer:

Yes.

Kuhn:

I didn’t know that.

Mayer:

For us theoretical physics students in Gottingen, he was a wonderful combination with Born. I mean he was just the opposite of Born. From Born we learned essentially mathematical physics. And Ehrenfest spent a great deal of time with the students in Gottingen, (Vickie) Weisskopf and myself and a few others, and we learned physics from him —— in contrast to mathematics. And he would insist, “Look, don’t start with an equation. Tell me only what you are doing. Say first in words what you are doing, otherwise you don’t understand it.”

Franck:

If I describe him a little bit as a person: I came several times to him in Leiden and lived in his house. His house was a beautiful house, and his wife apparently came from a well—to-do Russian family. From his income as a professor, which was not too high in Holland, he could not have bought that house and bring it also in some shape. But suddenly then the revolution came, and the revolution then also cut off all the flow of money. And therefore the house had no wallpaper and no curtains and some of the things which one would expect in a house. The children, gifted children, some of them artistic, made pictures on the wall, on the whitewashed wall, and showed them with pride. And the only clock there was was in the dining room. It was a pocket watch hanging there. And at first I didn’t know where the family always looked to, then I saw that there was a clock.

Mayer:

Do you remember the guest room?

Franck:

The guest room, yes.

Mayer:

Where every guest wrote his name on the wall?

Franck:

Yes, my name is there too.

Mayer:

Mine is too.

Franck:

And Einstein’s name several times. The whole wall was covered with names who were guests. They ate. His wife, a good mathematician, and a little bit difficult to come along with her, because she never stopped talking about the things she was doing. They never stopped the Russian way. It went to infinity. And I am in exchange of letters still with her sometimes. Now I think their family life was not exactly happy. She was very much pro—communistic at that time. Nothing to say against it, if she felt that way. But I don’t think that he was that far. I could, think that some of the conservatives here would call him pinkish, or what. That he certainly was, because he had a very strong social feeling. I think always back to the time with great pleasure. And I understood entirely this postcard which Einstein wrote, that he felt happy there. Einstein was also quite independent whether there was a normal nice chairs there or what not. That he forgot, and he could be himself and do what he wanted to. And I may say that I was also very much impressed by H. A. Lorentz…

Mayer:

Do you remember when Fermi was in Gottingen?

Franck:

Yes, yes. We knew that he was a man of great importance. We did, not like when we came to the Volta Congress the way the Mussolini government spoke of Fermi in a positive way, exaggerated, you see. At that time it was still exaggerated. I mean if they later would have said it, then it would have been all right, but at that time it was in the future whether he would be all that what they said of him. I remember Fermi very well. And I remember that I visited in Italy the university where Fermi studied. I forgot where it was, one of the small and very old universities.