James Franck - Session III

Kuhn:

I’d be very glad for anything you can add to yesterday’s discussion.

Franck:

I want to say that in 1919 I have read already all the things the people have made in the United States in the meantime. And especially it was Tate and it was Foote and Mohler. Foote and Mohler had extended it to get other one line spectra and they did very nicely. Now Tate I do not know exactly what he did but he continued with it and got nice results. And I saw Tate and asked him, “How did you get so quickly alert to this phenomena?” And he said “Don’t you know that just before the war I was in Germany and you told me all about it, so that I was well prepared. And then I saw also the paper of Bohr.” And so on, I forgot that entirely. He said we planned that we would work together or he would work with me in Berlin at that time. So that facilitated the quick progress. I got that literature later, but I knew already that Bohr’s theory had to be. And this point remains uncertain, whether it hangs theoretically together with Stern or whether I read it myself, that I do not know. But anyway I know that I spoke with Stern at Laon and we had discussions about this. It was also very interesting because Stern told me about his ideas of the atomic rays and exactly the same idea I had. But be had worked it out much more in detail. So I left my fingers out of that. So you see such things hang in the air sometimes. And these Dunoyer atomic rays; that one could do a lot with it, that was known.

Kuhn:

You knew the papers of Dunoyer on atomic beams? And Stern knew them also?

Franck:

Yes, yes.

Kuhn:

Because they appeared in the Radium, and I have no notion whether this was a journal that people knew or not.

Franck:

At that time, early or late we read everything. Not everything, but we looked through the journals and read the few things which we were interested in and left the others out. But that was a time in which one really could follow the literature still.

Kuhn:

When you talked with Stern at Laon, do you remember at all whether this was about the Bohr atom in general, or whether it also included questions about the relation of the Bohr atom to your experiments with Hertz?

Franck:

Oh, certainly that came up. Anyway, why was I against the idea in ‘16 that...it was ultraviolet light; that, as Bohr said, it was a photo—electric effect. Ultraviolet light is so strongly absorbed and scattered at the pressures one has there, that I didn’t think that it could be photoeffect at the electrodes. And the photo—effect at the electrodes has also a small yield. On the other hand, I think that if one has the higher pressure, and has directly by electron impact excited the level of 2537, the middle of the triplet, then the atom comes by impact with other mercury atoms into the meta-stable state. And the meta-stable states therefore are made in the neighborhood of the electrodes. They have a much better yield of taking electrons out of the electrodes. And so I think it was probably not the light but it was the meta-stable state. And with helium especially, that I know. I will write the letter to Stern to find out the date...I have to ask him this question. He feels apparently Lise Meitner told me — unhappy that he could not go on with attempts to deduce quantum theory from thermodynamics, and that mathematics is too difficult for him. That’s what I was told...Stern was a mixture between a physical chemist and a theoretical physicist. And he changed his position several times. In one university he was a physical chemist and in another he was a theoretical physicist. And he was in a small university first. His first call was Rostock...And he felt quite unhappy there, and then got quickly the call to Frankfurt.

Kuhn:

Excuse me, he was at Frankfurt before Rostock. Frankfurt first, Rostock very briefly, and then to Hamburg.

Franck:

Anyway, that he came to Hamburg was connected with two things... I mentioned earlier to you that he had the ability to sit at his desk and construct the apparatus and the detail and answer all the questions what trouble will there occur. I remember that in Laon we talked about the following point. I did not at all understand, if one wanted to measure with this method, whether one would get the Maxwellian distribution. The evaporation— And he explained that to me in detail. And I was always impressed by him. He really was very good in general physics, whatever it was; he would not easily make an error. I also spoke with him about space quantization because I had also thought about it. But again absolutely not in any detail. So I thought the best thing would be iron atoms and so on. You see the whole thing was that he had thought it through and I had only a vague idea tout it. So I learned a great deal by that discussion in Laon from him…And I am a little bit vague—yes, the spin was—when did the paper occur then from Uhlenbeck and Goudsmit?

Kuhn:

…It’s 1925.

Franck:

Now, how is it possible then? Of space quantization there was already something mentioned before?

Kuhn:

Oh yes. The earliest mention of space quantization is really 1916... But is there any possibility that this conversation at Laon may have been at the very end of the war or even just after the war?

Franck:

No no no no!...We were both in uniform in Laon. I think it must have been around ‘16. I imagine ‘16. The end of the war was not in sight. We both had no doubt about the outcome, but we were just defeatist.

Kuhn:

Do you remember how Stern at that time felt about space quantization? There’s been a good deal of testimony to us that he himself was terribly surprised by the positive outcome of that experiment, that he had been very skeptical about space quantization.

Franck:

I can’t tell you. I mean, I thought of the question, so far as I remember,[Very loud airplane, nothing understandable] and he had already planned to do all that. But what exactly he wanted to do I can’t tell you…

Kuhn:

You thought of iron because of paramagnetism?

Franck:

That's it. And it shows you how little one saw it through. And then he corrected me and said everything that he thought about it. But to tell you the details of it is impossible… I remember, I got first a postcard of Stern and Gerlach, where it said “guess what this is?” It showed these separated beams on it. I couldn’t guess of course. Then at the end they said “after wrong guessing” or something like that. And actually it was Stern who had the idea. Gerlach on the other hand was very able with his hands. And whether Stern alone could have done the experiment I don’t know. I really don’t know…

Kuhn:

You do have then some letters going back to that period?

Franck:

Yes. I sent a very few to a man in Berlin who wanted to have it for a collection which was lost in the meantime A quite interesting man. A young Privatdozent at Humboldt University. It is now set in the east. He wrote a few papers about Einstein, I think Herneck is his name. And he is very good. Something that shows how strongly he was convinced of communism is one sentence which he wrote in one of the things about Einstein: “One cannot help, one must accuse Einstein, that he could not see the greatness of dialectic materialism and did not follow Mach directly in the positivism, but appealed to the idealistic ideas.” I wrote him a letter and said “Please include me too in the people wham you have to accuse.” And I got a very nice answer from him. I blush a little bit to tell it “Yes, to my regret I have seen that many great physicists are blind in that spot.”, or something like that. I meant only the first part that he called me a great physicist. This is his personal opinion. Not mine.

Kuhn:

It’s widely held.

Franck:

Now, you see I was not bad in ideas. I know that. But I had never the clarity of the real one.—And you can see that in this thing with Bohr. With me, you see, sometimes the idea was pretty nearly right first the excitation, and then the energy for ionization and then that was forgotten again. So, I experimented with ideas… Now anyway, about Stern. Stern had a great number of people around him, and it was always something, He came often to the meetings of the northwest part of the Physical Society it was Hamburg and Gottingen and (???). We had meetings together. And Stern was always one of the men. In spite of the fact that he• had two left hands, I regard him the best experimental man we had for 10 years, in Germany...Hertz was very good, but he was not there at that time. I would like to say (Stern was an experimentalist) with the understanding of ideas, and with an understanding of theory. And I regret so very much that nowadays in so many fields, people say ‘that’s theory, let the others do it. Let the theorists do it. I’ll do my experiments.’ And this was not the attitude then.

Mayer:

It isn’t really the attitude now either.

Franck:

In nuclear physics.

Mayer:

In nuclear physics, certainly (???). The theoreticians suggest something, and 20 people immediately do the corresponding experiments. I mean, the Yang and Lee non-conservation of parity is an example.

Franck:

You may be right. I am a little bit influenced for instance by Pohl, who always had the idea that theory is paper physics and forget about it. He used theory himself, but he pretended that he didn’t use it.

Kuhn:

Was this an individual idiosyncrasy of Pohl’s, this attitude toward theory? Or was it widespread in some circles in Germany?

Franck:

It seems that we both have a little bit of difference of opinion about it.

Mayer:

I think it was individual.

Franck:

I have seen it relatively often. But I can’t tell exactly who had the idea.

Mayer:

Have you ever seen it as intensely as with Pohl?

Franck:

No, no.

Mayer:

You remember that Born would not let any of his students ever give a lecture in the seminar, because Pohl always lit into them in such a way, that Born felt he couldn’t defend them.

Franck:

I spoke With Pohl about it several weeks ago and said that he made his life much more difficult by not admitting theory. And he said, “Yes, it might be right.” Seitz told me about this interesting and very important work of Pohl, about color centers and so on. And he said “I never understood. If one takes a theory, then one can understand how one paper follows another. But he doesn’t mention a word of theory, and still one can see he must have had it.” And this is true. This is true…I remember Kopfermann told me a story about a session of the biweekly colloquium at which talks were to be given by Heisenberg and Pohl. And it was the following: Heisenberg gave a talk, a very abstract talk. And he overstepped his time somewhat. Pohl had to give the second talk, and Heisenberg apologized that he used a little bit too much time. He asked Pohl “I hope you will give us a talk anyhow...We don’t mind sitting a little bit longer. I didn’t look at the time.” And so Pohl answered “No Heisenberg, let me wait fourteen days.

You see my paper is still right in a fortnight.” This was a little bit the attitude. And you must say that there is also something in it. Some experimentalists, including me, saw red when Dirac spoke of negative probability and so on. That hurts. And I spoke at that time with Pauli. You see, how can one go so far with formalisms that one speaks of negative probabilities? This is by definition nonsense. I was glad to hear that in his talk now Heisenberg mentions that also with practically the same words, that there is no sense in that. And it is also somewhat difficult to speak of negative energies. I will say this might be just facon de parler; this might be not so bad to do it. One can become accustomed to this. But negative probabilities that was too much. There I exploded too!

Kuhn:

How did Pauli feel in this conversation about negative probabilities?

Franck:

I had some presence that he disliked it, but I can’t tell you exactly. Anyway, he understood my troubles. That I remember…

Kuhn:

I’d be very grateful, if you would like to, if you would continue talking about people.

Franck:

I would like, anyhow, to speak somewhat about Bohr. I believe I started yesterday, and said that everyone of us became his pupil then, including such men as Sommerfeld. By the way, I find it absolutely always unjust that Sommerfeld didn’t get the Nobel prize for the fine structure. He should have.

Mayer:

I agree.

Franck:

I made myself several times the proposal. I really don’t know why it didn’t work out. In my own case I must say that we became friends, and Bohr talked often quite over my head when we discussed. And then I asked questions and then he said “no.” I had to start again from the beginning, because it turned out that my question showed him that I misunderstood it… I remember also that Bohr made a remark once when Wigner spoke in one of the meetings. He told me he did not understand a word of it, and said “You know, I am really an amateur. And if they go really into high mathematics I can’t follow.” And this is the great strength of Bohr, and to some degree the great strength of Rutherford. Both of them were in some respect amateurs. If I say amateurs, I mean they have much greater independence than people who learned things and then stick to their guns and go ahead...Take Einstein. The first idea: saying it makes no sense to speak of absolute velocities in space. That was the beginning. That he then solved the problem, that he used four—dimensional things, there it happens as Hilbert once said…He said “Now, if Einstein only would have studied in Gottingen, he would have known Riemann’s four-dimensional mathematics. Every boy on the street here knows it,” he said “But, Einstein didn’t know it. But he did it. That’s because it was Einstein.” This is what Hilbert said! And there is something in it....

Kuhn:

When Bohr spoke about the limitations of the Bohr theory, and said that this can’t be right, did other people and yourself in particular agree with this, or did you think that the Bohr atom was much more solid than he did?

Franck:

I personally thought it was much more solid, but when Bohr said it was not, I said, “he may know.” But without him, I would become one of the disciples who always take the word of the master verbatim, and make a religion of it and everywhere make trouble with it. And I think that this attitude of many people who underestimated later Bohr’s contribution was because they themselves were as blind as I was. But Bohr was not blind.

Kuhn:

Can you tell me about some of the conversations, or some of the things that were said that would underestimate Bohr’s contribution?

Franck:

I wish you should also discuss that matter with Hertha, because she has more to do with the young people. And it seems so that some of the things which happened when I was young, with Maxwellian theory, are repeated in this case. I told you that Maxwellian theory was written in a way which was practically not understandable, and that it has to be reedited and re-thought through first by Lorentz. I tried to tell this in Chicago once to our president, Hutchins, who always wanted to go back to the sources. He said people should read really not a textbook about philosophy but they should read the author. It is certainly true that one should when one studies philosophy. But often you cannot give people Plato to read without knowledge about the old Greek situation and a textbook had to clarify that. Now something of that type I said is also true in science, where a new idea doesn’t come out of the ocean like Venus in full beauty or Aphrodite, in this case. But it is first a shadow and gains flesh and the full development is slower. And I mentioned this to Hutchins at that time when I was there. If somebody waits now to learn quantum theory and starts to read Planck, he certainly will have very great difficulties. I told you about Planck, that he tried really to smother his own brain child all the time…The same Planck who did that knew, on the other hand, like a prophet that “We cannot help it. It will come. It will be born; it will influence all thermodynamics and everything. And quantum theory will be (in acoustics) wherever you want.”

Kuhn:

Planck did say this, did he?

Franck:

He did say that.

Kuhn:

In his lectures, or in colloquium?

Franck:

No, always in the colloquium. There he opened his heart and said really where his qualms were and how it would come. And he said it with the idea “how nice it will be”. The opposite. “We cannot help that it will come that way.” He was really a rebel against his own wish. Paschen was also a man of great importance, but he was so careful. For instance Bohr said once that one of the things attributed to hydrogen was due to helium ions. And the paper which Paschen wrote about it said in the title “Bohr’s helium ions.” This was not only to mention Bohr, but also not to take over the responsibility to agree. He wanted to say “Bohr calls this helium ions and I find that and that.” So Paschen was excellent, but with all the distrust in things he could not do with normal physics. Therefore he called it “Bohr’s helium ions.” Actually I didn’t understand the title that way. I thought he wanted to give credit to Bohr. But somebody else who was against Bohr told me “You misunderstood that. This is not the opinion of Paschen. He only wanted not to take the responsibility.” And he was right. I looked at it again.

Kuhn:

In the early years of the century how seriously was the aether still taken at Berlin?

Franck:

In Berlin one didn’t speak more of this aether and that. But you must remember that Planck taught us that way. And his influence was in Berlin great enough that we discarded right from the beginning the aether.

Kuhn:

I take it then, on this same general line, that there was also no question in anybody’s mind about the reality of atoms?

Franck:

No, but there was anyway Ostwald, who in 1905 or something like that still didn’t want to know anything about it…But this certainly did not influence the physicists in Berlin.

Kuhn:

Did you find that the chemists thought differently about the atom? You had a good deal of contact with chemists also.

Franck:

Mostly I had contact with physical chemists. And there was no doubt about it; one regarded it as a kind of craziness to have any doubts about it.

Kuhn:

Tell me about Nernst if you will.

Franck:

Nernst — a highly intelligent man. But I may say he had not really the soul of a scientist. I can tell you one story that shows Nernst’s attitude and his wish to win in discussions, and to impose his will if possible. Now there is one story that Nernst used at that time that was unheard of eight calculating machines to prove that Planck’s formula is wrong. He gave a talk on it in the Physical Society, and Planck was not very much impressed. But he became curious enough to calculate it back, and in spite of the eight calculating machines he found an error. Some mix-up of a sign of correction. And if one took that into account, then Nernst’s calculations of all the results fitted very best—so good as never before with the prediction of Planck’s formula. So he went to Nernst and told him about it, or wrote him a postcard. I don’t know. No, they spoke about it. And Nernst said that Planck was wrong.

Then Planck said he would make a bet with him. Now Nernst said “Yes, all right. It us make a bet.” Then Planck in his way proposed one bar of chocolate, and said, “Take it home. Calculate it back yourself. And let me “And Nernst sent him, without any word, a bar of chocolate. He never took it back in colloquium or so. And I will speak about his personality, because it is a mixture of greatness and smallness. During the Nazi time he was so upset about the Nazis that when Wehnelt, who became a Nazi, paid him a visit and wanted to discuss something with him Nernst said, “How do you dare to come into my house, you Nazi. Out with you” He threw him out of his house. Anyway, he had courage. And he didn’t mind at all that one caught him on some dishonesty. If you can’t do it that way, all right. He never pretended to be nice. There was one story with the third law of thermodynamics, which he always called (Mein Warmehauptsatz)—with his hands so. And he had a diamond here, and it was inside, not outside. He flashed that. Ah, he was so funny. When one was invited by him he went around among the company with two boxes of cigars, and offered the good cigars from full professor up; the lower ranks got the cheap cigars.

Mayer:

He did invite the lower echelon though, did he?

Franck:

Yes, at the same time....At the 80 years anniversary of the Physical Society, I was invited. And he said I should sit at that table because I was a full professor in Gottingen. But I had some friends who were not in that category, and I wanted to sit with them. I said “No, pardon me, I have some friends. I want to sit at that table.” And Nernst told me he had prepared everything. “But you see, the food is better on this side.” And I found out that everyone paid the same price, but for the Bonzen the food was better. He was an impossible man. And I met the son Nernst lamp of one of the men, who was the director of the AEG. Nernst sold his(???) land for a million to them. It was a tremendous amount of money at that time. And while it was really a tremendous sum, it didn’t last long. Do you, Maria, remember that thing which was out into the table in the lecture hall in Gottingen? Nernst was in Gottingen professor of physical chemistry at that time. Tammann succeeded him. And in that lecture hall there was a long table. A young man cut into the wood: (“Der du hier sitzt im Schein des Nernstlichts gib acht, mein Sohn, du lernst nichts.”)… Nernst got the co-name among his pupils “Chronos”, because he ate his own pupils.

He ate his own Sons, scientific sons, like Chronos, who eats his children. And it is true that he was not on good terms with all his best pupils, with (???) with Eucken, with everyone; everyone who showed some independence... Lindemann worked with Nernst, and did very good work. And Nernst had a very good impression of him. And Lindemann was a very impressive man, but he learned what he wanted to learn and left out other things, and was prejudiced in many respects. But anyway, since Nernst regarded him as one of his strongest pupils, he wanted that he should get his doctor’s degree in Berlin. And Lindemann said “I am not interested in a doctor’s degree." Which was unusual enough for a student. And Nernst said “But Lindemann, you have made such nice papers. You can use one of them for a dissertation, and can have your examination any day you want to.” Lindemann said “All right with me. I have no objection, but one thing I would like you to know. I do not want to prepare myself for the doctors examination. I don’t want to go over a lot of things that I always can look up again in books when I need them, which I have now forgotten.

If you have no objection that I will probably fail in the examination, let us try. But I don’t prepare myself.” Now Nernst said that was all nonsense and he should come. So he made an appointment and he came. And he didn’t know anything that Nernst asked. And Nernst was really- upset, “But Lindemann, you must know that. It is so simple. You have to know that. How is this possible, that you don’t know that?” And Lindemann said only “See, I told you so.” Now Nernst regarded it as a shame not to give him a doctor degree—that he would try and fail. So he got it. But this was one of the men who was not impressed by Nernst’s bluffs and so on. He called the bluff and he won. And Nernst was always good in it. If somebody called his bluff, then he accepted it… Nernst was always very difficult in the examination. I must say when I became Privatdozent, Nernst told me he regrets he was unable to come but he had to make a trip. And he apologized to me that it was not lack of interest. But I was happy like a lark that he would not come, because he always made great trouble and great difficulties.

Kuhn:

How did people think about his law of thermodynamics?

Franck:

They all thought that it was of utmost importance, but they didn’t think that his proofs were too good. (And Nernst’s favorite example was the way we have iodine.) Stern had a pupil and gave him as a dissertation to look into that matter (of the way- we have iodine). He found out that it was by no means a good example, but it was by some reason I have forgotten an apparent contradiction which one could explain. But since Nernst had used that always as his best example) he was mad about it. And when Stern came to Berlin, the first question which Nernst asked was “Oh, Colleague Stern, sind Sie schon Voll-Professor? Sind Sie schon(Ordinarius)?” “Ja so,” sagt Stern, “Ich bin (Ordinarius).” So so, then you tell your pupil that the paper he has written is impossible, and that I will ruin his career. “And Stern said “But, this was his dissertation, and I am responsible for that dissertation. And I urged him to publish it because that is the situation. That doesn’t mean that he has any doubts of the importance of the third law of thermodynamics. Neither have I. But just that iodine is not a good example.” “That doesn’t help. I will ruin his career.” And then Stern smiled and said “You can’t. You can’t. You overestimate your importance.” And then Nernst said “Certainly I can. I ruined the career of that and that man in Holland.” Stern’s pupil was a Dutchman, “No,” Stern said, “you haven’t. That he did himself.” But he took such discussions very nicely. And from there on Stern and Nernst came very nicely along. He tries all ways. He was mad at me.

I was called as his successor to Berlin. He was mad because I said “now the laboratory is not in good shape, and if I accept it I would take the house in which he lived and which connected with the laboratory, and make laboratory rooms out of it.” And Nernst said if a man accepts here this position he must keep the house. This house has a great tradition. Here lived Helmholtz and I. How will you invite the Herr Minister if that house is not there?” And I said “I probably will not invite the Herr Minister at all.” And so he became mad and decided that I was not the right man. And there was also the point, that the professor, the head professor, had always the obligation to give the lectures for beginners. I learned in Gottingen how that could be done. But Pohl really renewed the way of presenting of experiments and so on, and did a remarkably good job. And I knew that this was not a thing I could do easily, and it would take much time. Most professors took it because it was the greatest source of income. You see, you could always get four or five hundred people and made a great amount of money. But I said I would like to give it to somebody who can do it better, I don’t do it well and it takes too much time. (And if they insist that I give the beginning lectures, I will not take the job.) Now Nernst knew that. Then he thought that is the way to see that I will not get the appointment. I wrote him a letter in which I said “I understand why the faculty would like to have a man who gives these lectures. But in my case I cannot do it by that and that reason, and I don’t want to do it.” Nernst mentioned in the faculty meeting, when it was discussed, “Oh, I am convinced Franck will accept the position. He wrote me a letter in which he”—and now he read one sentence—“says he “understands very well that people wanted to have a man who would give the lecture.” and left out the rest. But since I knew Nernst, I had written a copy of that letter to somebody else, to Peter Pringsheim.

And Pringsheim then stood up and said “I believe that Professor Nernst must not have read this letter carefully, because the letter continues this way—“. And so I got the call at that time but I did not accept. Nernst was not at all flustered. He said. “Oh yes, that might be, that might be.” Then he went to Pringsheim, “Of course, of course. You are quite right. Of course we have the same opinion.” And there is nothing in it. He tries. And this was the human side, which I disliked in some way, but felt always at least he was honest. It wasn’t dishonesty.

Kuhn:

When was this? When was the call to Berlin?

Franck:

Oh, this was when my children were quite small, and I wanted that they should grow up in a small town and not in Berlin. And I furthermore saw that it was very difficult to make out with this laboratory which was not in very good shape.

Mayer:

You were in Gottingen...You got a Fackelzug, a torch parade with the students.

Franck:

No, that was probably with the Nobel Prize.

Mayer:

You got it both times. I remember it twice.

Franck:

I can’t say that is so. It might be, but I don’t know that anymore. Now that must be ‘25 or so, something like that time. You were still in school.

Mayer:

No, I (wasn’t) a student. ‘25 might be right. I started studying in ‘24.

Franck:

Maria Mayer went to the same school as my children, and she was a few years ahead. So she is at least a niece.

Kuhn:

Was Nernst an attendant at the colloquium?

Franck:

He came always, and it was always interesting what he had said. And I cannot agree with Maria that he ruined physical chemistry…

Mayer:

But why is physical chemistry so weak in Germany now?

Franck:

That’s another reason. It is weak in Germany because the chemists are ruined by the great tradition of organic chemistry. This is an interesting question. The old tradition in Germany, is that the main professor is an organic chemist…Of course there was also the physical chemist, the Dutchman, who made the structure of molecules. I forgot right now his name. I met him often. Van’t Hoff. Van’t Hoff was the predecessor of Einstein. He had a professorship without any obligation to teach, you see, from the Academy. When I say I met him, that’s not true. I believe I have never spoken a word to him, but I saw him for a year or so daily because he ate at the same place, in the same restaurant as I did. So I looked at him, but I believe I have never spoken with him. Anyway, he did a remarkable job, but his fame was really greater in the world than it was in the chemistry circles. Think only that a man like (Windaus), an excellent man you know, as a person, an ideal man in every respect, could say without blushing that Bunsen ruined chemistry in Germany or tried to. This was the attitude one had towards physical chemistry. Mostly it was not a full professorship. And only in a few places it became a full professorship. And the point is just that the chemists did not learn enough mathematics, and don’t now. They have no position of theoretical chemist in the whole country, I believe now, as they have in several places here.

They did not learn enough, and they had to be so much in the laboratory, and learn so much of the technique. That was the attitude. I remember a discussion with (Willstatter) when I read a paper of his on how he isolated the chlorophyll. And he used, in the one spot, (glacial acetic) acid. And I said, “Why did you take that solvent at all?” I mean I just wanted to know. And he said “Oh, laboratory experience.” And I said “Now does that mean that you used all the reagents on the table and found that often does it?” “Yes, about that way.” You see, it was in that case experience and intuition, I must confess that if we are so proud about what physics did to chemistry, it did very little really to organic chemistry. It always showed that the crude pictures, foolish crude pictures, that the chemist had, were a good approach to the truth. Take for instance the non-rotating of a double bond. One cannot be more off with the crudeness of this idea. But still, what they did with it. And so it was in other things. Physical chemistry was really made into a discipline under the influence of Ostwald. Like Sommerfeld was a promoter of Bohr’s ideas and extending them, so Ostwald was a great promoter of the ideas of Arrhenius. Nobody paid any attention to Arrhenius before Ostwald did, even in Sweden. And Arrhenius is another example, an astonishing example, of a man who in his life has with two short papers, not longer than the papers of Roentgen on the Roentgen rays, changed the whole aspect of chemistry with the heat of activation and with the introduction of ions as reactants. All the other things and he has written volumes are of no importance.

Kuhn:

Would you talk about Einstein?

Franck:

Einstein once told me, “You know, it is not astonishing that I found the principle of relativity.” “Usually children here in the cradle become acquainted with the problem of space and time. And after that they are so accustomed that nobody asks any questions anymore about it. I was so slow in my development that I started to be astonished about it when I was around 20. So it’s not astonishing that I was a little better off by that slow development.” And there is some truth in it. He was in some respects always a child, and a wonderful child. He was a physicist at heart, and he could enjoy any result of physics, which others got or he got with the greatest aesthetic pleasure. When one visited him, he said “Now tell me a little bit about this and that.” The last visit with him there was also my son-in-law von Hippel there. And he remembered that Hippel had written something about (cinder stones) many years ago. And he asked him, “Can you tell me what one now believes about (cinder stones)?” He was just as interested to hear that as anything else…

Kuhn:

How early did you first know Einstein?

Franck:

I knew him when he came to Berlin. And he came to Berlin when did he come?—It was before the war that I knew him already at the colloquium. And we often went together after the colloquium and had a cup of coffee. And I remember that once Born was also there at that time. Born and Einstein and I went and had a coffee together. And then they started about higher details of the principle of relativity, and I couldn't follow at all. And I became a little bit—how shall I say it—depressed. There are two physicists; Born, an old friend of mine, and Einstein, friendly to me. They talk about physics and about the most important research, and so far as I am concerned it could be just gibberish. I could not follow at all. And I told them so. And they consoled me, they said that one could do physics in different ways too. Anyway, Einstein was pleased about the details.

He was invited by Warburg to come to his house because Warburg made at that time some experiments to see whether Einstein’s predictions about photochemistry were right...Einstein had to come to an official invitation. He told us, “Look here. Yesterday was really a kind of a new event in my life. The first time in my life I had to wear tails. And I think that we should celebrate that together and have a piece of cake to the coffee today. “He had really a childlike pleasure in situations. On the other hand, he could be very outspoken against the politics in Germany. And he never had any wish not to say exactly what he thought. Sometimes he was a little bit careless, because he had such a name and so on, people came to him, consulted him. His second wife I never knew his first wife was not too good at protecting him against all kinds of interviews.

Mayer:

Rather on the contrary. She liked to exhibit him.

Franck:

And I tried to tell him why he mustn’t give an interview to everyone who comes to him. And I said that it does damage to him and to the whole situation by doing that. And he said “You know, I know that these men have a dirty profession, or a dirty job to do, but they must eat anyhow. And if they can use what I tell them all right, let them do it.” I said “Now, do you also read what they print about your interview?” “No, never.” Then I took something out of my pocket, “Then read that here.” And it was some remarks he made about the Academy. And said “Do you really say it this way?” Now he became really mad about what was written there...He didn’t realize what damage could be done by misrepresentation. He always said “What do I care what the people believe of me?” It is certainly true that the German professors used to be very conservative and very nationalistic on the average. You, Maria, come from a professor’s family, but I am sure it was not in your house…[At Professor Franck’s request the name of the physicist referred to in the following incident is omitted] I made a trip once to England with ———. I came home so angry about my discussions with him. It isn’t important to go into details, but anyway, I told my wife, “I believe if one tells a German professor that it is in the interest of the nation to throw their own children out of the Window, they will do it.”…The universities were in general very conservative, and nationalistic. And the professors had not good judgment. Would you agree to that?

Mayer:

Yes. Also, it is certainly true that among non—scientists at universities Einstein’s name was ——-. I mean they didn’t know anything really about his science, but they disliked thoroughly his attitude, his speeches and so on, which after all were printed everywhere.

Franck:

But on the other hand one couldn’t be together with Einstein without knowing that he was unique, and charming and friendly and kind, yes, and naive.

Kuhn:

At what time did people begin to take him really seriously? Hevesy said that it was only in 1910 when Nernst came all the way from Berlin to Zurich to see Einstein about specific heats that they began to take Einstein seriously in Zurich.

Franck:

That would be also absolutely in line with Nernst’s attitude. If a man does really very good work, he would recognize it. He only was disagreeable to his own pupils, because he couldn’t stand that they became independent of himself. But otherwise, he only disliked if somebody had a greater name than he had.

Kuhn:

But did people not realize that this was one of the great minds?

Franck:

This is so difficult for me to answer because Planck took him so seriously…The men in which I had trust, like Planck, like the professors in Berlin, they all had the highest regard. And you see, one would not give a very young man this position as Professor of the Academy otherwise. He had not to teach, but was just a professor of the Academy of Science, and a member of the Academy of Science. This would not have happened if people were not convinced, and if Planck would not have convinced all the others that he was a great man. It is not only that some people disliked Einstein as a person, but it was so very difficult for people to give up things they took as granted. Everyone knew about Kant and that the three—dimensional space was really pregiven. And they were really offended. And I must say that I a little bit understood…I have seen the same thing in myself in these discussions in Gottingen at the time with Born and with Heisenberg, and then the Schrodinger equation. Then it came in a nutshell; the result that the question whether something is a particle or a wave is meaningless.

It was hard to swallow for me. We lived with this problem, (and then we were so astonished at the result.)...I was somewhat disillusioned. But with the previous experience I had of the changes with time, it didn’t affect me too much, But I had the feeling V always, “I wish it would be not that way.” I can give you another example how widespread the disgust was. Einstein never got the Nobel Prize for the principle of relativity, because one man in the group was so opposed to the principle of relativity. They said, all right, then we’ll give it to him for his work on the photo—effect. They had no objection. So there was emotion in it. This man was a—the Swede—I met him but I forgot his name now. He was a metallurgist or something like that a crazy fellow. To show you what kind, of fellow that was, I can say that he had a laboratory and he had a very big lecture hall. He had certain ideas about how a lecture hall should be and how the demonstrations should be made. And good ideas. And he had a workshop working only for that thing. And so I asked him how many lectures he had to give. And he said “two”. Arid I said “two?”— “Do you mean two courses or two lectures?” “Two lectures.” “In what time, in a week?” “No. In a year.” So his main job was to build a beautiful lecture hall in which one could do anything whatsoever, in spite of the fact that he had no lecture obligations at all. Now this man was against Einstein. A harmless individual, but it was against his philosophy.

And if I would not have seen that happen several times during my life the end of the transition to the Maxwel1ian theory, the quantum theory, the principle of relativity,—if I would, not have gone through all that, then my attitude toward the question we discuss right now—is it a wave or an electron would probably be more like (Pohl’s). And it can’t be helped. And I suppose that right now there is again therefore some feeling in the people who do not work in the field of nuclear physics, that there is something unrealistic or overestimated in it. I personally don’t.

Mayer:

Yes, but you see this situation is still the groping, as before quantum mechanics.

Franck:

Yes. I know, I know. But I was very much impressed in this case by Heisenberg’s talk. And I was impressed by a talk I heard years ago by Yang, and I knew of your work and of Jensen’s work and so I know what is going on a little bit. But I believe that that is true, that is a great difficulty, that of 100 people who work in that field of nuclear physics, only one should go into it. The others go in because of the glory and so connected with it, and don’t help very much. Of course the teamwork is absolutely necessary in the experimental work. But on the other hand I regret it, that one gives a student for his dissertation a small corner of a paper which is written by 20 people; this is not the right attitude.

Mayer:

No, it isn’t.

Franck:

Let me say one thing. You say Nernst ruined physical chemistry. No. Physical chemistry was ruined by the organic chemists. On the other hand it is always in the history of science, so far as I can see, that a great man, a real great man, or a group of great men, always after their work was introduced did some damage to their own fields.

Mayer:

After all, physical chemistry in the United States was essentially built up by one man, namely Gilbert Lewis.

Franck:

If I may permit to say something about the bad influence of Gilbert Lewis. There is his greatness and all that which he has done. I only want to say that always a great man has also some bad influence. And the bad influence of Gilbert Lewis was that his students did not learn how to read the literature, because he didn’t. And he said “I am disturbed if I read the literature.” “At the end one should consult the literature a little bit when one writes the paper, so that one sees whether that is new or not new, but otherwise don’t read too much, and so on.” And the result is that some of the people in California have the attitude that the new life starts with them.

Mayer:

That is true.

Franck:

And this really also you can read in (Wallenstein)…

Mayer:

They were actually trained that way. The young student was encouraged to think about something, and he would usually come out with something that was well-known. If it was known to Gilbert Lewis, the student was told so.

Franck:

I met Segre in Germany, and I like Segre. Whatever I could do to promote his things I did, may I say in retrospect. But anyway, when he got the Nobel Prize I said he got it for the wrong thing…And I told him it was for the wrong thing. I said that he deserved it, but not for that. Because he had the machine. He agreed, 100%.

Mayer:

It’s a shame that he didn’t get it for something else. I mean anyone who had access to the machine could do it.

Kuhn:

You speak of Gilbert Lewis’ students being trained not to read the literature. How was it in Berlin? Were you brought up yourself as a scientist to read the literature carefully?

Franck:

Yes, yes. You asked once about the struggle that Pohl and I had with Marx. We were not only brought up in the idea that one should not permit that something is printed which is misleading. And actually, this was an error, because if one wants to use the time to take away things which are just wrong it doesn’t work.

Kuhn:

But then we wondered that you had not known the Stark paper at the time when you and Hertz did that, first paper in 1911 on the relation of ionization potential to quantum theory.

Franck:

Yes. It was of course an oversight. But Stark made it easy to forget some of his papers, because he wrote in abundance and a great mixture of good and bad things…There is no excuse that we had not seen Bohr's paper before. We could have seen paper if we had been better. But actually our reading was more that we took some weeks off after a paper was finished and then caught up with the literature. And about Stark I really don’t know. Stark drove one mad the whole time. I think we apologized really enough and sufficiently clear. But I must say it is astonishing that a man becomes always so mad if he is not quoted who himself does not quote.

Kuhn:

Before, in speaking of attitudes toward Einstein, you said that anti-Semitism played a role. Was the anti-Semitism there from the very start, or does it get worse and worse as the situation develops?

Franck:

Anti-Semitism I must say probably became worse and worse. I do not know. But I know in my youth in Hamburg in school I didn’t have any impression of it. I am sure some groups did not always come together socially with some other groups, but one had in Hamburg a generally more liberal attitude, Take for instance the father of (Hertz). He was a senator, and was he not also Bugermeister? The senators in Hamburg and so on, were the elite of the elite. And I think that he was baptized, most probably. But anyway, later it was less possible. But there was in Germany much less social anti-Semitism than there was official anti-Semitism. So for instance, that a Jew would become a reserve officer, was practically out of the question. In the war it was different. I was promoted quite quick. Under the emperor, as long as they could avoid electing a Jewish professor, they avoided it. But if a man was baptized, then it was all right. You see it was not as in the Hitler time. The King of Bavaria made great difficulties when Willstatter got a call to Munich. He was persuaded to sign that, but he said ‘that’s the last Jew I want to admit.” But in the Weimar Republic that was not the case. When my father told me, “You will never be a professor. You know how the conditions are. And therefore would you not try to study law or whatever it is.” He was quite right, the probability was very small. I think there and more social anti—Semitism in this country than there was in Germany in the time of my youth, and most probably also in the Weimar Republic.

Mayer:

Father relates that in Berlin, I mean in their house, the word Jew was never mentioned. It was just that you never considered whether anybody was a Jew or not. You were sort of forbidden to use that word altogether. You never discussed that.

Franck:

I mean the point is just that. It was really socially practically nothing.

Kuhn:

Was it also true, Sir, in your own house, that the word Jew was not much used.

Franck:

Oh no, oh no.

Kuhn:

There was no religious upbringing?

Franck:

The point is just that, my grandparents were very orthodox Jews. My parents were not orthodox Jews, but there was no doubt in us that we belonged and that we were of Jewish descent and that we wanted to remain Jews. Later, one of the officers in the army, when he heard that I would become an officer asked if I would not do him the favor to get baptized. And I smiled and asked whether he believed that I would be a better officer if against my own conviction I would be baptized to do him a favor. And he couldn’t help to say he doesn’t think so, but anyway it would show that I do belong to them. I said that I feel that I belong here, whether I am an officer or not. I have not asked for it. If they want to make me an officer, it is all right with me. My colonel, who was very nice, said I should go to an officer’s school.” He said “Why not?” I said “I can stand war if necessary, but in peacetime to be trained by some people who think that to be a soldier means that you salute smart—…I can’t.” And he laughed and said, “No then, you’ll have to make an officer without going there.”

Kuhn:

In the earlier part of the war, what were you doing?

Franck:

Oh, you see, I had served a quarter of a year training as an engineer. In 1906 I was for a quarter of a year a soldier. At that time I thought I should go to something which was entirely new. Namely, they had, only for Einjahriger only for people who had special examinations in school they had a regiment where they introduced wireless telegraphy. And I had to learn physics again then. But then a horse was kind enough to throw me out of the army. In the beginning of the war I said never would I go there again. This was too horrible; the way we were taught physics. And I had to swallow all that. I met my old lieutenant again—he was in the meantime major—during the war. And he said why I didn’t come back to that regiment? I said “I couldn’t do it.” So I was what one calls a (Kriegsfreiwilliger) in the beginning. That means a private. And I wanted to go into the war not because I liked the war. I hated it. But because I thought I could not exclude myself from this general fate. And early or later they would get me anyhow. Therefore, better right away. And there were all such things in it. When one had an idea what one should do with this and that weapon, then one had to proceed in the following way. One should take a furlough to tell the people in Berlin about it, but not go there, because that made the bad impression that you would find a good way to leave the front, you see. I mean all such things. But let us not discuss.

Kuhn:

Have you any impression about why in this particular period there should have been quite so many Jews involved in the development of quantum mechanics?

Franck:

I met a mathematician from Hungary at the time in which in Hungary they had (numerus clausus)—only so and so many Jews would be admitted to the university. And I asked how it was with the professors, because he was of Jewish descent, or at least I suppose he was. And I said, “Did they have numerus clausus in mathematics, too, for professors? And were there difficulties? He said “Yes, they have. They have numerus clausus in mathematics they are all Jews.” It was so that also in Germany under the Kaiser in mathematics they admitted Jews. There were not enough to go around...It’s an old tradition, it’s an honor for the Jewish family to have somebody who does something of abstract interpreting the Talmud and such things. My father had not studied. He became a banker and was well to-do. But when he was young there was no money in the family so that he could study, and so he wanted that his boys should study. And when I was a bad pupil in school, my father was alarmed about it…It never occurred to him that there would be a possibility that if I get bad marks, that also there could be in principle some error by the teacher.

The teacher is a learned man and he is right and the child is wrong in that case. You see? I may say, the tradition is I believe to do something abstract, which my father didn’t want for us, He said his children could be lawyers or something like that. Because he liked law and had a very sharp mind and a very logical man. What I mean is, it is an old tradition in early childhood which surely has an influence. But let us come back to Einstein, He had such an independence of mind, which in practical life sometimes made difficulties…but meant that he was not influenced by any kind of fashion. And so he was not disturbed that all other people thought he was on the wrong path. He said quite openly to me, “I might be wrong, but that doesn’t play a role. I would like to do that and find out how far I can come.” And he was quite tolerant, at least to me, because I certainly was not a man who could discuss matters with him as Bohr did. But anyway he knew that I believed much more in Bohr’s point of view than in his point of view, and he had no objection to that. But he would say “you are mistaken.”...

Kuhn:

If I might, I’d like to ask you briefly about one other person. You said yesterday that you thought that people in this country did not sufficiently appreciate R.W. Wood.

Franck:

Wood was quite an astonishing man. And of course he was a practical joker, and he made so many practical jokes that many people hated him. And especially I believe Millikan couldn’t stand him at all. But that was vice versa also. And he was always pleased when he could tell a nasty joke about Millikan. One story is so nice that I can tell it. Namely he said he came to the campus in Pasadena, and a crank had written on one of the machines for road repair in big letters “Christ Saves.” And he said a student had written below that, “and Millikan gets the credit for it.” Millikan was a very good man but. Wood was at least as good. And they tell always the story whether it is true or not I don’t know that (dinosaurs) had the brain partly in the tail and partly in the head. Wood had the brain in his fingers. Wood has never passed an official a examination. He failed absolutely mathematics. And to go beyond sines and cosines, that was already the end of his mathematics.

Mayer:

An exponential he did not know.

Franck:

Quite possible that he would not—An exponential, probably yes. But anyway, once when I was in Hopkins he asked us all if it would not be a good idea that the young students come in contact with each member of the faculty in physics. And so he said, how would it be if he gave an introduction in a kind of modern physics to undergraduates of the second year or third year. Every one of us takes two hours of the course. Now they discussed that, and I don’t know what everyone did, but I remember what Wood wanted to do. He wanted to speak about coupled pendulae. And Dieke and I, and Herzfeld, whoever was there we believed to know that he just couldn’t do it. Coupled pendulae involves, really, quite a lot of mathematics. And we tried to persuade him to take another topic. Resonance or such things, where he had done so much. And he was intelligent enough to find out why we wanted to persuade hint not to do it, but he insisted he wanted to do it. Now we could not very well come to the lecture and flock all in there to see how he did it. But since we were on good terms, I said later to him, “Wood, why don’t you tell us in our colloquium what you told to the people. We would be interested how you did it.” And I must say I never have heard or read such a nice talk about coupled pendulae as Wood gave without using mathematics. All the physics behind it became clearer to me, who knows a little bit about it, than it was ever before.

Kuhn:

Did he use models?

Franck:

Yes. He always was three months during the summer in Long Island. He had there a little house and there was an old stable. And his wife let him do in this old stable whatever he wanted to. And he made experiments ail the time. But there he built coupled pendulae just two strings and little hooks on it at the end, and coupled with an old spring. And studied the behavior and looked at it. And for months he has not done anything else than just studied coupled pendulae. But at the end of the three months he knew more about it than any one of us. This was the way in which he worked. He had an instinct where interesting things could be. He was also to some degree crazy. Now, who is not. But his craziness was that he could not differentiate between the important things and the unimportant things he did. He regarded his practical jokes— the book “How to tell the Birds from the Flowers”,—as equally important than his physics. Pringsheim and I knew him quite well. And he wrote once a letter, I believe to me, or to Pringsheim, I forgot. But it was directed to us both. We should see to it that his biography in the Encyclopedia Britannica would brought up to date. It was too short and so on and so on. Now this astonishing anyhow, that one writes that.

But anyway, we were sitting together and wrote down a better version. And persuaded the people to take it, But he complained later that we had not put in this book “How to tell the Buds from the Flowers” and so on. You see? He told us his greatest achievement as a young man. He was Associate Professor in Minneapolis. And you know it is very cold there in winter. And in the house of the President as everywhere else the water pipes froze in the ground. And they always had to dig them up and so on. But he took just a transformer and sent a big current through it and that did the job very well. He wrote a book Physical Optics, which practically did not contain any mathematics. But he finally improved it and asked a lot of people to help with it here and there. And a man who had a good sense to judge it, Otto Stern, said “What happened to the wonderful book of Wood? He ruined it with putting in lots of mathematics.” He had asked Dieke and me to put little things in. It had been such a wonderful style. And the way he worked! It was quite right when we said “Give Wood a dollar and send him to the five and ten cent store.

He comes back with a laboratory.” This was not good for a Chairman, because there was practically no apparatus. That I went into photosynthesis was because I got two empty rooms and at least (???) were there and one could study a little bit fluorescence and so on, So I became attracted to that field. But if you saw the wonderful photograph he has made, and then seen in his room what kind of spectrograph he used. He took two razor blades for a slit, which he adjusted with his fingers in seal wax. Either it was a quartz prism or a glass prism, both of them damaged. He attached them with seal wax on the table. The only thing he had was a plate holder. And then the whole thing was covered with a piece of black cloth.

Mayer:

It was not always even covered with a black cloth. It was just done in the dark.

Franck:

And he told me, “You know I always work with a safety coefficient of five percent.” But he did not understand at all other people. For instance I know—what was the name of the man who died? Pfund. Pfund had an X-Ray tube and complained once bitterly to me. When Wood needed a little palatium tube which was rare at that time; there was little money—he cut that off and used it. Wood told him he could blow it on again. What it meant at that time to pump out an X—ray tube so that one could use it, he had no sense. When he had a student or students of other people, he stole from them something which these people adjusted. He stole the prism for instance and used it, and if the student complained about it, “Oh the prism is there.” It had of course some fingerprints on it. And he didn’t know that that poor boy would use fourteen days to adjust an instrument, because he could put it there and look a little bit at it and in a moment it was done. I mean it was quite an astonishing thing. And what he did with this was really wonderful.

Kuhn:

Do you remember this also from your days with him in Berlin?

Franck:

When I was in Berlin with him together, we needed a quartz lens, and the only quartz lens which was in the laboratory belonged to Rubens. And he knew that Rubens had a quartz lens because he had mentioned it in publications. And it was rare. And he said “Oh, you go to Rubens and tell him we need that quartz lens, and ask whether he would not give it to us.” But I knew how Wood was treating apparatus and so I went to Rubens and said, “Wood would like to have that for our work. We really need it.” He said “All right, if you take the responsibility for it.” I said, “I can’t. That’s impossible. I can’t.” And it took only fourteen days; then the lens had a crack. And I told Wood, “Now look here. I warned you to be careful, and now it has a crack, Rubens bought that quite cheap. And it is so difficult to get a new one.

And he will really be quite unhappy. I think you had better tell him about it,” “No,” said Wood, “you tell him. But you said he paid 40 marks for it. Tell him I will buy it for 20 marks because it has now a crack.” He was impossible in many respects. And I must say I went to Rubens and told him the story. And Rubens, while he was upset about it laughed so hard about this man. He was not always agreeable, as I told you. We wrote two papers together. It should be one paper, but since it was in German, I wrote it. And I wrote down, because it was partly my idea, and then the a, b, c. I wrote Franck and Wood. And he saw that, and said “let me write the second half,” in which were more interesting things. There he wrote Wood and Franck on it. He was impossible in many respects. But be was a child, and I liked him very much in spite of all his naughtiness. He was a naughty child, but a genius with his hands and his fingers, and a genius in smelling something of importance.

Kuhn:

Just one more question about that work with him. In those papers there is rather more talk about models than in your own earlier work. More remarks about the systems of electrons, about coupling forces and so on. Did he do that too or is that from you?

Franck:

That was I. That was not Wood. That he wouldn’t do. But you see the point is, this was my first contact with molecules. And I knew molecules would do other things than atoms. And so I tried to grope my way through…

Kuhn:

This bit of the tape needs two annotations both of which were supplied as we drove away by Maria Mayer. In the first place, the phrase used by Franck “Einjahrige” is a standard term involving compulsory military training in Germany. The standard period for trainees was three years. However, those who passed a special exam in school taken before, perhaps two years before the time that the university would start, needed to serve for only one year. That exam was the Einjahrige exam, or so I understand, and the corresponding service was Einjahrige service. In addition, Professor Mayer added the story about Wood to which she had referred when making the remark that he knew no exponentials. In practice, it turns out that he knew them at least well enough, but had no confidence in them. She reports that the two of them once did, an experiment together and that she recorded the data and then converted it to exponential form, turning over to Wood both the raw data itself and the converted form which could be presented in a vastly more economical way. Wood turned the article in to be printed and left out all of the converted data, giving only the raw data. As a result the article was a great deal longer than it needed to be. Somehow be found the computed results untrustworthy in some sense that the initial raw data was a thing in itself.