James Franck - Session II

Franck:

I want to speak a moment about this paper: This is the 1912 paper with Westphal, and that was before I started to work with Hertz, I think. At the same date I had two papers, one with Hertz and one with Westphal, on f1uorescence. [looking through reprints] Let me see, 1912…NO, 1911. There are two papers, and I do not have the first paper with Hertz. I couldn’t find it, but the other one on which you have remarked is a note we made about the connection between ionization and the quantum hypothesis. That is the one with Hertz in which we say that Stark had first said something about it but we overlooked it. [The first paper with Hertz employing the selective photo effect is not well remembered by Franck and a discussion of it is here omitted.] The point is this; I believe that neither what Stark said nor what we said at that time or in our first paper I do not remember what we said makes any sense… I understand that you are as much interested in the things we made wrong as we made right. This is correct. But I would say that, this you should, according to my impression, put into the field where we were 100% wrongs.

This is a little remark which Hertz and I made to pacify Stark. He wrote us a letter that we were not really decent not to quote him. We had overlooked what he has said. So we wanted to correct it. But this front page doesn’t make any sense. On the other hand, the paper with Franck and Westphal makes much more sense, because we see there a difference between ionization and resonance of an electron in an atom or a molecule. We would like to say, while we would think that the fluorescence has to do with the resonance in it, ionization (simplifies because the molecule or the atom contains all the resonance frequencies so that the ionization by electron impact would occur at a lower potential.) But we now would say, if an atom or a molecule is excited the energy needed to take the electron away is smaller. And that is said here quite clearly. How can one say the one thing and the other together, at the same date? That I don’t understand at all, because this really makes a lot of sense, and that was before Bohr’s paper and so on, and I was astonished that we had that much intelligence in writing this paper.

On the other hand, this paper reminds me of a funny history. This man (Sashti) in India found the same effect which we found; that the irradiation of iodine vapor would change the electric current of a discharge at low pressures, I forgot his name. And he had the whole University busy working on this (Sashti) effect for about 25 years. It’s astonishing how many papers have been written about it and how little new things came out, I had, to read these things because he sent me the papers, as dissertations. You know the Hindu universities have always to ask the opinion of some man outside. Now as much as possible I was lenient, and I told him only ‘Yes, it might be quite of interest to study this and this thing, but finally it became too much for me, and I said “Please don’t send me any more of these papers, because there is nothing new in it.” And I said what I had not said before, “You can read that this effect is very old and already mentioned by us.” So, it remains the (Sashti), or whatever the name is, effect. They had, on the other hand, so little apparatus available, and that one apparatus had to serve generations of physicists without any change, so, I was as mild as I possibly could be, but finally gave up because it was hopeless. I told him that what we said at that time was not really right, because we know now that the iodine, with irradiation by the light we used, (dissociates) into atoms, and that if we make a lot of atoms instead of molecules, that the electric current might change, and so there was nothing really in it. Of course now we know exactly what wave1ength one should take.

And I told him all that and said he could see whether it occurs only if it goes to the convergence of the bands, and so on. Anyway, nothing came out of it. But at least as many papers as are in this volume are about it. Anyway, I am astonished that on the same day we sent in the one paper that doesn’t make sense and the other paper, that makes sense. So you see we groped around in the dark. I must say that we were all under the impression that spectroscopy was un-understandable. I remember when Max Born wrote a little article at that time in which he said an atom or molecule is much more complicated in all its frequencies than any piano with all its frequencies. And to bring sense in that, the only indications were just (these series). But what they mean nobody would understand and it is impossible to find out. That was the general attitude. And that was also the attitude when Bohr’s paper came, which was expressed in the letter of Sommerfeld to Bohr, “Dear Bohr, you have a wonderful formula which explains hydrogen, but don’t think it has anything to do with the structure of the atom. We know that is an impossible question that nobody can answer.” And it is this defeatist attitude which was so strong. Whether one had the picture of Thomson, who I understand had smeared out the positive charge entirely, whether one took this, these were just things one played with but one didn’t take them seriously.

Mayer:

When were Rutherford’s experiments?

Franck:

Rutherford, and also Lenard, had some idea that there is a nucleus in it. And Rutherford was quite clear, Lenard less clear, but he had it decidedly, with the idea that cathode rays could go through, and so on. But I do not know really—Lenard did not quote any Englishmen anyhow, —whether it was dependent, I would not know…I remember still an anecdote that I could mention. When the first World War broke out and I was in the army, I got a letter from Lenard. He said that we should especially beat the Englishmen, because the Englishmen had never quoted him decently. That was astonishing to me.

Kuhn:

Going back perhaps a bit into this early research, at the time when your main concentration is on ionic mobilities. One of the things that I noticed in looking at this work is the extent to which the problems and the references are to English papers.

Franck:

Yes. I may say J.J. Thomson was our physical Bible. We had to look at his things and to read it and reread it. The connection with X-rays and all these things came so much clearer than anything which was said before that I must say I have saved the old edition, or the first edition, of his book. This was of exceedingly great importance…And I think this was quite typical, I can’t say, but several had it. Several I know. And I think that I started to read it, and Pohl read it then with great interest, and others. After a short time all our circle had this book and we read and reread it. We read always. The periodicals we read in our circle were the Phil. Mag., which was the most important journal at that time. And of course our own two, Annalen and Phys. ZS. and the things of the Physical Society.

So, I would like to say for myself that I became very quickly clear about one point; That if we wanted to understand more of discharges and so on, that the time was ripe to study the kinetics of electrons and ions independently. Not in a discharge much too complicated. I hoped at that time that one would after first studying ionization potential, mean free paths, and all these things, become clear about the whole discharge. And not the other way around. And this fascinated me from the beginning. And so I came also to fluorescence. Then R.W. Wood came for a visit, and we worked together, and he gave a talk. I must say, you asked me once, in a letter why our paper was published in English too. I couldn’t help it, because R.W. Wood was always an original man, and when the paper was published in German, he went over and published it again, and didn’t ask me at all about it. So I never was a man who liked to publish the same paper in several places, but with R.W. Wood it couldn’t be helped. He published it sometimes in French and in English and in German.

Kuhn:

When you say that you were convinced from a very early stage that the discharge itself was too complicated to approach directly, that you must study kinetics, would you say that these early papers on ion mobility already come after that decision, and that they too are directed to the kinetics of the discharge?

Franck:

Yes, because you see I wanted to see what happened to the electrons. One of the things which Warburg already did was show that a negative discharge of nitrogen with a mixture oxygen is different than when pure nitrogen. So there was the first idea. There must be a possibility that the electrons are caught quicker by oxygen than they are caught by nitrogen and form negative ions. That the discharge would be especially formed by impacts of electrons with atoms and molecules and not by impacts of negative ions was clear. It was clear from the beginning, I suppose probably said by many other people before I came to it. And in the dissertation I was quite clear that in the region where I could see light, that there also would be ionization. (Because there was always light and ionization where all the discharges connected.) And that therefore there could be free electrons, or should be free electrons.

That was clear, very independently really—because Warburg was no more there and Drude came only later—it became clear to me when working on the dissertation that there would be a difference between the behavior of free electrons and of negative ions in ionization and acceleration and the kinetic energies they can acquire…If you have an electron and it collides elastically with an atom it practically doesn’t lose energy. This, and all these considerations were clear to us. Then, I must say, while I have no high regard for Lenard as a human being, his work influenced us also. His measurements of ionization potential are in principle made the same way we made it, only we were at that time already quite convinced that we should expect different ionization potentials in different gases. He found always the same thing, and we didn’t believe that that was right. And therefore we took it up again. The mean free path was only done because we found that in helium and neon—these were not studied by Lenard—the discharge occurred very easily. I remember when we got some neon. I must say that was long before the Hertz time. We had a mercury pump.

We could see whenever we moved the mercury in it the light of neon would be emitted. We had a discharge, that is, the break-down-potential was very small. I brought it together with the idea that if the electrons remain free as the ionic mobility showed, then it’s understandable that they are easily accelerated and can get the ionization energy. We took metal vapor also sometimes, but I have not really studied metal vapor. But we only concluded that if these monatomic gases behave that way, then metal vapor would also do it. And furthermore we had a kind of a scale of the electron affinity. We found that we could have mercury vapor in with the helium without it having any influence on the free electrons there. So we concluded the electrons should be free in the metal vapor too. So this whole thing was really ripe for research. And you see I was at that time just a young Privatdozent, and Hertz got just his doctor’s degree. It is certainly true that I instigated these experiments, and Hertz always had made certain notes, I mean he is such a decent fellow. And I would like to say that when we got the Nobel prize together, I was only pleased, because he had contributed so much and he was so much more able with experiments than I am, that we really supplemented each other quite well.

A few people asked me. In Stockholm they first thought they should give it to me alone, but they didn’t, because Hertz published then when he came to Holland, a lot of papers which showed what he can do for himself. And this is the reason why I insisted we had to separate, because he didn’t get enough credit. And so I am very pleased that it happened this way. I mean, Hertz and I sometimes tried, after we wrote one paper with each other, to find out what did the one do and what did the other do. And in all honesty, we couldn’t find out. It was such a mix-up between the one and the other that I could not say that. I can only say that what would happen, that one would have to study the mean free paths, the impacts, the ionization potential, elastic and inelastic impacts, and that there would be a connection to quantum theory, because light emission was there. And as you see from this paper, it was also clear that one would expect that fluorescence the emission of light could occur at lower energy than the ionization.

Only in the final paper we became absolutely confused about the question that in a mercury arc where the pressure is half an atmosphere or more, how could ionization occur? And we forgot this paper in which we said, “It can be that a second act occurs.” I would like to say, Hertz was much more able with his fingers. I mean the apparatus we wanted to use was clear to both of us. But to it, he was the stronger. And I was probably the stronger in having the ideas. That is how he himself looks at it, and probably it is true. We spoke about it. You know I had a fight with Warburg about this photosynthesis business. Warburg said to Lise Meitner that Hertz had told him that was neither a theorist nor an experimentalist, but what he actually had said was that I am a mixture of both, always a little bit in the theory and not entirely 100% experimental. And Warburg turned it around in this way, and Hertz said to me, “Look here. I brought you into that trouble. I have said to that man this. And of course he turned it around.” But you can see the connection and why I mentioned it? I was told by Hanle something that was touching to me.

This was when Hanle was assistant of Hertz when we got to know him first. Hertz told Hanle “I really don’t know whether I should be pleased or I should not be pleased. The ideas were Franek’s. And I did a little bit experimentally.” Something like that. But anyway, what Hertz can do, he has shown many ways alone. And so I like to say, the one thing I can claim without being unjust to Hertz, is that the picture stood before me in great clarity. Only we were uncertain about the question: If the first is inelastic impact in mercury—that is 4.9 volts corresponding to the line 2537 — then how can one come up to the higher energy of 10.3 volt? And there we said, there must be in one or another way a connection between that. We did not realize at all double impacts, triple impacts…

Kuhn:

I may be confused, but in your initial measurements on ionization in mercury you take the 4.9 volts to be the ionization energy.

Franck:

Let me see. I am a little bit doubtful. Have we not made the measurements on ionization potentials of gases before we made the 2537 experiment?

Kuhn:

Yes. In fact the ones you list are helium 20.5, neon 16, argon 12, molecular hydrogen 11, molecular oxygen 9, and molecular nitrogen 7.5.

Franck:

There it is probably all the excitation potential… With this arrangement at the moment in which you had metastable atoms you got, really, electron emission from the electrode. And so we thought this first act was the ionization. And in that case, therefore, we would have found probably with mercury also, if we would have done it, 4.9.

Kuhn:

And you did the next year. That is the famous experiment with the successive peaks. And you report 4.9, and report it as an ionization potential. Which makes terribly good sense. I think I should say at this point—you may not remember this— that as late as this summary paper in 1916, you are still reporting that as an ionization potential. And there—and so far as I know it’s the first time in your work that this occurs. You mention a suggestion of Bohr’s, that perhaps there is photo-electric emission from the electrodes. And you say no; the peaks are too sharp. It must be ionization. So as far as I know in your published work, it isn’t really until 1919 that you side with Bohr.

Franck:

When I think that during that time, l9l6-l9l9 we had no chance whatsoever to do anything. We were both soldiers. Hertz with his serious wound—…

Kuhn:

The reason I raise this is that you speak of reconciling your 4.9 volt measurement with a 10.3 volt ionization potential. But I think that problem must come only later, after 1916.

Franck:

We did, in other words, not know at that time Bohr’s theory at all. And therefore we didn’t know what line we would expect, and if we would have a line. I was only astonished to see in this paper right now the idea that there could be some excitation which was different from ionization was mentioned. In spite of that fact we have not really applied it to the mercury, and could not really apply it very well, because we had no idea how at a high pressure, with so many inelastic collisions at 4.9, an electron would get enough energy if it were higher. So we said there must be something—a connection between that—and we don’t understand it.

Kuhn:

You have said, and I know this must be right, that from a very early stage of the game, you were concerned with finding out as much about kinetics as you can. Yet as you tell this story, it seems to me thinking of the papers, that things that go all the way from 1906 which is the thesis, to 1911 or ‘12 are all combined in here. And I wonder whether there’s any way to follow more of the developmental order. For example, the very first concern with mean free paths at all, that shows in the papers, does not come until 1911, which you see is five years after the thesis. And initially almost ail of the work is first on ionic mobility. Do you remember that all? The notion of the ion as an aggregate of molecules.

Franck:

As a cluster, yes. This was I think some Englishman, I forgot now, whether the cluster hypothesis played in J.J. Thomson’s book a great role. And who introduced it I do not remember.

Kuhn:

I think Rutherford may have been the one who introduced it.

Franck:

That is quite possible that it was Rutherford. He was really under the influence of J.J. Thomson. He was first interested in the ionic mobility and made this nice apparatus there. And we extended it so that both ions, positive or negative, could be measured. And I was suspicious during the dissertation whether the gas would have what I called—I think the word did not exist at that time—electron affinity. I think I introduced that word. What it actually meant became clear only under the influence of Bohr’s theory, and done in an excellent way by Kossel… But electron affinity interested me very much, and I wanted to know really how the transition from an electron to a negative ion occurs. From Warburg’s old experience with point discharge and other things we tried to see whether very pure gases behave differently. And monatomic gases were the simplest ones. And the influence of moisture… How could the moisture have an influence if there would be not a cluster, if it would not do the same thing as it does in an electrolytic ion—water molecules surround the ion.

Kuhn:

But in 1910 you do an investigation on argon. And there you report that you find—and apparently with great surprise—that the negative ions have vastly more mobility than the positive ions.

Franck:

And it was clear to us that they would be electrons, free electrons.

Kuhn:

I ask this only because that seems a terribly important paper because you do from this point on talk about affinity. You also talk about the effect of oxygen in reducing the mobility of the negative ion. But it looks to me as though that idea may not have been nearly so clear until you did this paper on argon. Because you seem surprised in the argon paper to get this result. So I think that one may not go all the way back to the thesis.

Franck:

You see the point was that I was expecting that the electrons would form negative ions in argon too. But the difference between the point discharge and the paper is that this happened at atmospheric pressure and with very weak fields. And therefore that it was a surprise that there was electron affinity, but that there must be lower electron affinity that was expected. But not that there was really practically none, in spite of the millions and millions of impacts such a particle has to make to go through, that was the point where the surprise came in. And I may say that I went around to my friends and said “Please, repeat the measurement. This is an important result that I get. You make them over and see whether I am mistaken. How can you interpret that?” And I asked Pohl to make some measurements with it. And other people. And they said “Yes, It is there.” So I was aware and it was a great surprise to me, because this was just not something as other discharges at low pressures or very high voltage. It was for us with small voltages, without any ionization, without light emissions, and so there was no electron affinity.

Kuhn:

Your earliest collaboration I think was with Pohl.

Franck:

Yes. You can see that we always paired off, I mean in these beginning—I worked with Pohl and with Westphal and with Pringsheim; and Pringsheim with Pohl again. So we always did some work together.

Kuhn:

This was not only as a student but even after you would have your degree you would pair off?

Franck:

Yes, yes. We did that systematically…We did that because we had little money, and few apparatuses. One had one apparatus, another another. The one had one experience and things got quicker. I am astonished at how many papers there are in 1911 and 1912. This came only because one worked sometimes that way and it went quick. Simple experiments, and it went quite quick. It’s also so much nicer. One can discuss matters with somebody else.

Kuhn:

There is your thesis, and then almost immediately there is the ion mobility. You work on the Rutherford Wechselstrom method with Pohl.

Franck:

Yes, I am sure that in this case the idea was presented to Pohl: What did he think about it. And then we decided let us try it together…The Rutherford method was only for negative ions, And he used the photo-effect on the one band to get electrons in without high fields; and then used the method. [Franck illustrates the construction of the apparatus in order to apply it to both positive and negative ions] By this trick, we could use very small amounts of gases maybe—30 cubic centimeters…So that we could use also rare gases and other things which became then slowly available. Partly they came from America, from helium wells, and partly they came from (monasite) sand…And we cleaned gases. I always was so proud that I had had my chemistry a little bit, that I could make gases cleaner than the chemists did. We tried everything there how to do it. There was a book written by an Englishman which we also used very often to make pure gases. But we improved the methods a little bit… Then was the only paper I made with Lise Meitner. We tried to see what the effect of the mass is on the mobility. That was quite astonishing. A radioactive ion—whatever we used I forgot—quite heavy, shows in hydrogen the came mobility as the hydrogen ions.

So the mass doesn’t play a role. The mass itself. The radius and what-not, but not the mass itself. This astonishes me still. The funny thing is that later experiments have shown that most probably the positive ions we measured in helium were never helium ions. Because any tiny impurity after millions of impacts will exchange the charge. The helium has an ionization potential higher than anything else, so the charge migrates. The helium will be de-charged and the impurity will carry the positive charge. And that was also one of the effects which was difficult to overcome in ionization potentials. So we had first 20.5 volts as the meta-stable state in helium. Whether only the meta-stable state came to the surface or whether some impurity was there which was ionized, that we didn’t know. It was a nice time. I went slowly, got things. But in all that what we have discussed, it was not discussed and not mentioned how great Bohr’s influence was upon all of us. And if you don’t mind I would like to say a few words about it. I say that we didn’t know of Bohr’s paper. But we learned it when we were in the hospital I learned it. Hertz was too ill. When I was paralyzed, but otherwise quite all right, I read literature, and I found Bohr’s paper… That was 1916. As soon as the war broke out, we had become soldiers. So there was no possibility any more to do something.

Kuhn:

But you think you had not even heard of the Bohr atom, of Bohr’s idea, when you went into the army?

Franck:

I must say that I do not know that. I know that we have not heard of Bohr’s paper when we wrote our article. Whether I had in the mean time heard about it, I don’t know. I know only that there was no possibility to do something about it, and then we both went into the army. And I remember that I had a long discussion with Otto Stern. We met each other in (Laon). He was there for something—weather forecasting he had to do there. And I was in the mean time a lieutenant…Stern always liked to eat well, but in Laon, because he was not a lieutenant, he could not go in the good restaurants, so I took him with me. He said he never forgot that. Anyway, we went around there, and discussed and forgot all about war and everything Bohr’s theory together.

Part of that I knew already; part of that Stern told me more about. And he had more time to study that thing. It was just wonderful…This was probably ‘15 or at the beginning of ‘16. I really don’t know. Anyway that was before I was ill. So, I was burning really, to read things, to digest more of it, and to write this paper of 1916. And I sent it to Hertz then, and he made some changes and then we published it. He was in the hospital because he was shot in the leg, and complained bitterly because he had to lie for so very long. It was very bad, very dangerous infections and so on. “I have learned,” he said, “that it takes nine months to make a new man, but it takes much longer for me now to get an old leg again in shape.” That has not prevented him to go 40 or 50 kilometers a day, or even more, but he still limps. Then, the influence of Bohr. When finally the war was out, I started again with electron impact. Hertz was still in Holland. I must say so many things Bohr said when we met first.

He invited me to come to Copenhagen where his Institute was opened. We were sitting together and I must say, I never felt I can only say such a hero worship as to Bohr. Of course I knew that Rutherford was a very great man, and Planck was a great man, and Einstein was of course. But Niels Bohr. And the way Bohr talked. And I think I should just tell you how Bohr talked at that time, directly after the war, about his theory. As he said, in any of the directions in which one may look one can make every day new observations which should be incorporated. He was never a moment (conceited). This approach he had was only a beginning and was by no means right. He was not at all convinced, as we were, that that was the end and that’s all. He said “No, you can’t believe that. This is a rough approach. It has too much of approximation in it, and it is philosophically not right.” And he said a lot of things, right in the beginning, which later became clear to me, that there must be something entirely new.

That then came with Heisenberg and with Schrodinger and so on. He always said of himself, “You know, I am an amateur. If the people become too complicated with the theory, I don’t understand that at all.” But he did not say that it meant, “Anyhow I can think.”… These conversations were in 1918 or 1919 just after the war. And ‘20 I went to him as a visit. But the first conversations occurred when we invited him to come to Berlin. And the younger people wanted to have him a little bit alone. And so they said he could talk and do what he wanted to do, but he had to reserve at least two discussions with people who are not full professors. (Bonzenfreie Zusammenkunft) And at that time I was in Haber’s institute as an Abteilungsleiter. I mean I had the physics group of the physical-chemical laboratory of Haber. And I told Haber we invited Bohr. He asked whether he could come. “No,” I said, “you couldn’t come. No Geheimrat, no full professor. We want to have this man alone.” Then Haber was very decent and said all right, “But am I permitted to invite you all after the discussion to dinner?” I said that’s another matter. Anyway, in these discussions, this was really a nice group together. There was Hahn, and Lise Meitner, and Hertz—was Hertz there?—I don’t know.

But anyway, Westphal, who always liked history, had a picture of it some time ago. Six or seven of that group got the Nobel Prize. You see, we all became his pupils. And so was Heisenberg…There is none who has not really learned by Bohr, and by discussions with Bohr. One thinks of Bohr when one had a discussion with him. Sometimes he was sitting there practically like an idiot. The face became empty, limbs were hanging down, and you would not know this man even would see. You would think, that must be an idiot. There was absolutely no sign of life. Then suddenly one could see that a glow went up in him and a spark came, and then he said “Now I know.” It is astonishing, this concentration, Newton must have been— You have not seen Bohr in his early years. He could really get an empty lace; everything, every movement, was stopped. That was the important point of concentration. I am sure it was with Newton too.

Kuhn:

Your first actual contacts with Bohr were after the war?

Franck:

Yes, yes.

Kuhn:

But clearly, you somehow or other must have been in touch with him before this. You speak in the 1916 paper of Bohr’s suggestion that…there is photo-emission from the electrodes. Apparently this comes first from Bohr, and then later from (Van der Bijl). Now the (Van der Bijl) paper is published in this country, but the Bohr suggestion which comes first we know only through your mention of it.

Franck:

I must have been in touch With him but I do not remember. This was wartime, and whether letter writing from Copenhagen would have reached us. I must say, it might be that we had even before the war an exchange of letters which I have forgotten.

Mayer:

Since this paper is Franck and Hertz, it could have been a communication to Hertz.

Franck:

No, no, Because at that time I was so far the older, that no. It is certainly not that. But I do not know. I really do not know.

Kuhn:

Do you remember at all how your mind changed about the interpretation of these experiments? In the 1919 paper it’s perfectly clear that you were then interpreting them much the way one would interpret them now. And I wondered whether you recollect at all how that transition came about?

Franck:

How much I really knew of Bohr here I don’t know. Is here Bohr’s theory mentioned?...I thought we had it in 1916 already…I can’t say how it happened…because you see when I became ill, paralyzed, I had (dysentery in Russia). We know now that it would be avitaminosis which I had, and polyneuritis. And the army doctor said, first he didn’t believe in anything. He said “Oh no.” Then there was another, higher, army doctor who said “It is evident, you had syphilis and this is the paralysis which comes from that.” Now I knew that this was nonsense. I told it to the younger doctor and he said, “What I would do in your case. I know it is difficult for you to do it. But I’ll write something for you so that you can travel home for restitution of your health. If you come into a hospital here, with these idiots—He was a private doctor in normal life—The man who had treated me—this impudent fellow—answered to me in Latin. (‘Syphiliticus semper mendax”) “He is a liar.” I was mad, and said something like “medicos militaris semper stupidus”—or something like that. Because he was a captain and I was a lieutenant, but I was mad enough to give him such an answer. And he was a little bit astonished about the answer. But anyway, this younger doctor said “Try to take a normal train for furlough for restitution of your health. And go there. There is a very good doctor I know. You see to get that doctor.” And actually it was so difficult for me. I couldn’t go. Somebody had to lift me in the train, I couldn’t go into the train. I had so great pain in my legs that I finally decided no, I will go into a (Lazarett). But I couldn’t make it, and that was my luck.

So I finally came home. I didn’t want to frighten my wife. We lived on the second floor, and I believe I used two hours to crawl up the staircase finally. And one boy who lived below us said: “Na, Ihre Alte wird sich aber freuen wenn Sie so ankommen!” Anyway, I was there in bed, I couldn’t move at all anymore. It was impossible for me to move. And I was in danger to die. This man I forget his name was a very well known doctor in Berlin. He came, and he also had an influence as a doctor there, so I could stay there. And my wife at that time could also give me something to eat, and this was more important than anything else. At that time you know I could not move around very much to get books and so on. Only what I had in my things in my room I could get. I couldn’t even hold a book at that time. So I got the information I could get. But I didn’t get more of Bohr, only because it was in the Phil. Mag. we didn’t get it anymore. So I really don’t know what the matter was. I know only that I was highly astonished to see that at that time I had not the slightest idea. If I say “it is I because I wrote most of it—and Hertz approved it…But anyway, it shows such an ignorance of the whole theory of Bohr, that I am astonished how that came about. If this was before Stern— let me see. Now, it might be before that time, before I met Stern. I really don’t know. If you have occasion to see Stern, ask him when we met in Laon. He might remember. Because I was so much on one front and then on the other front, I don’t know anymore when that was. But Stern might know, and since it is really of importance in this connection, I would like to know myself.

Kuhn:

I have to tell you. I have spoken once with Professor Stern, but he has to a very great extent become a recluse. He has retired a good deal from talking to people, and he has not really been willing to talk with us.

Franck:

I ought to write him a letter.

Kuhn:

I’d be very grateful if you would, because I am sure he would answer the question. There is one question I wanted to ask you about your time with Haber’s group at the Kaiser-Wilhelm-Institute. Another person with whom we have talked is Fritz Reiche. I don’t know how early it began, but there was a good deal of talk there, and I wonder whether you remember it or participated in it, about some early experiments which would have used not inhomogeneous magnetic fields as Stern did, but inhomogeneous electric fields.

Franck:

I left Haber’s Institute in 1920 and I suppose that this experiment was a little bit later. You see, Reiche was a man who came to Haber’s institute. I don’t know who recommended him. I have the impression that I did, because I knew of this work and I spoke with him, and I knew he was what one needed in that laboratory. We called him “the little oracle.” Bohr was the great oracle, and he was the little oracle because he could interpret us a good deal. And do you know this little book he wrote early on quantum theory or so, about Bohr’s theory? It’s very nice and very simple… I met him some time ago. He was not in very good shape [speaking to M.M] Do you know, as a daughter of a medical man, can one have here in the esophagus little pockets as in the intestines? Many people have that in the intestines. Eisenhower had that when he had an operation. Such extensions in the intestines. Now he had it there, and if he gets something in that, he cannot swallow any more. I invited him for lunch, and the only thing which he could take was the soup and oysters. He had not thought of oysters. I invited him to oysters, and he said “That’s wonderful, I will take that now all the time.”

Kuhn:

You think that very probably any discussion of those experiments came after you left?

Franck:

I suppose so.

Kuhn:

Was Stark in the early days of your work a very influential figure?

Franck:

I may say influential in what respect? He was feared everywhere as a man with whom one couldn’t get easily along. It is true that he was very sensitive that somebody did not quote him, and he was a most disagreeable fellow in speaking about other people and of the work of other people. He was in every respect a pain in the neck. But on the other hand I must say he had good ideas. And early. He had the idea that photochemistry would be a quantum process. Not as clear as Einstein, but he had it. And the Stark effect. I must say about the Stark effect that I was working at that time when he published the Stark effect on the same problem. However, I had read a paper of Voigt, and Voigt had said that one could not find, with normal electric fields an influence in analog to the Zeeman effect. The effect would be too small. The only at in which it could work turned out to be the one Stark took; hydrogen, I believed that Voigt was right.

It was a very long paper and difficult to read. I said “This method”, which was identical with the Stark method and which I wanted to build, “I give up.’, that will not work. I will only do it in studying molecular fields, and the spectral lines should be broadened by molecular fields, and that I discussed with Rubens, when I was assistant then. He said “Stark has made a great discovery. Why have you not made it?” I said ‘Oh, I will tell you. It is because I read this paper. But I will, on the other hand, show you how Stark did it.” I put on the blackboard this method and it was exactly how Stark did it. This was just something that was in the air at that time. But he has done other good things. He has done with canal rays things which were very good with the Doppler effect and so on. The man was full of ideas. But he was in German one would say “ein Querulant.”… When Bohr came Stark didn’t want anything. And Bohr said, “The funny thing with Stark is, first he says he has seen all that before I did. At the same time be says that what I say is all nonsense. If he only would make up his mind what it is.” He was very difficult, always very difficult.

And when he got the Nobel prize, then he stopped with all science and decided to become rich. And so he bought a factory to make porcelain, and ran into difficulties with it. But the whole laboratory where be was at that time had to work on something which be would use in his factory for porcelain manufacture. He was a high Nazi. I remember the letters which Laue always wrote, Hahn and Laue whenever there was a possibility I got letters from them during the Nazi time. And I remember how he called Stark. He called him Giovanni Robusto. The news of (Giovanni Robusto) came always in such letters. And I remember a letter from Mrs. Hahn where she said the only things we like is to go to the opera, we hear much of Wagner’s operas. Oh, we wait so much for the “Gotterdammerung”… Stark couldn’t stand for somebody else to get results. Also Lenard. The people in Sweden told me—a long time before Lenard became such a Nazi—they told me “You have really funny colleagues in Germany. You know when we asked Lenard he should make proposals for Nobel prize we always got the answer, “The only good papers which have been written in the last years are mine. And I have it already. Therefore there is no sense to propose somebody else.” This was Lenard. This was crazy. But the thing which I have heard (Kopferman) told me. When the Americans came to Heidelberg they also gave Lenard a hearing about finding out why he was such a fervent Nazi. And he said he couldn’t help it. He was a fervent Nazi because his pupil Becker led him astray. We called Becker always the Hausknecht. Ramsauer told always a story about Becker, only to show what Becker was…This man Becker had no own will at all, and when Lenard said something against which be wanted to protest, he went down into the cellar. There was a soundproof little room, and there he banged his fist on the table. That was all he could do.

Mayer:

Do you mean the Becker who was at Gottingen?

Franck:

Now the Becker in Gottingen, the theoretical man, was another person. He had nothing to do with this Becker. This other Becker was a stupid ass. But the theoretical man was excellent. No, no, no, no. But we always made jokes about that man Becker. Do you remember in there was once a picture of (Dereswige Privatdozent). There was a man bent over and always the bold Herr Geheimrat and so on. That was Becker. When Lenard’s daughter told him he should come to a funeral of a man she knew, a Privatdozent in Heidelberg “What do you expect? Me to go to a funeral of a privatdozent?” I have seen his laboratory. When he left I got a call to Heidelberg at that time. To avoid difficulties I went around the building only when I found out when he was not there. And I remember seeing with Kopfermann a sign lying there (“Mitgliedern der sogenannten Deutschen Physikalischen Gesellschaft ist Zutritt zu diesem Gebaude verboten.”) Then the elevator was only for his personal use. If somebody wanted to use the elevator for transporting apparatus they had to go to him and get the key for it… But what I did not know— Pohl told me about it—is this. Lenard came from Hungary and people were interested to find out about him. And they looked in the books of the church for baptizing and so on.

They couldn’t find it. Finally they came to the idea to look in the Jewish records. And there he was. He was born as a Jew, and became so super-Nazi just to— and I said to Born, ‘Born, I have a new idea I would like to tell you about.” I started to tell the story. And then he continued with it. And I said “Born, I never knew that you were that quick to understand exactly what it is and how it goes on. What happened to you?” He said, “You see, it was not so difficult for me because I told you the same story. It was my idea yesterday!” Such things we are good friends you see. There is no doubt about that it was so. But it shows only how difficult it is often to know whether one half heard a thing and then thought about it doesn’t know from where one got it and so on. It is really very difficult.

Mayer:

Joe, as a student, had this experience with Gilbert Lewis. He proudly told Gilbert Lewis something, and Gilbert Lewis just smiled at Joe, and then it turned out that Gilbert Lewis had essentially mentioned it to Joe the day before. He hadn’t understood it. But then he thought about it, and then it had come back to him as his own idea. And completely honestly I think.

Franck:

So it is, absolutely honest, I mean, there is no doubt about it. But it gave me a lot of thinking, that that can happen.