James Franck and Hertha Sponer Franck - Session I

Franck:

The first question on the outline you have sent me is early life and family background, 1882-1896, and I do not remember to have seen you around at that time [Referring to H. Sponer (?)]. Then, how I became interested in science, when did I decide to make a career out of it, what science was taught at the Wilhelm-Gymnasium, what mathematics, and so on. These questions I want to try to answer. Actually, I became interested in physics much earlier than I knew the word physics. I remember that I was always astonished about everything that I saw around me. One of the things I remember is that we had a (newel) in the staircase; it was a round sphere. And I liked to do some things with my hands, to saw, to make a small thing. Not really carpentry, but a little bit. And I looked at this thing, and I said, “How can I rake it this way if I really had nothing but my file and these things? And I know that I stood there for hours really and looked at it and invented for myself the lathe, or something like that.

The beginning of such things then was how things have been made. And then came other things. And especially I misbehaved in school in that I dreamed always about some question which puzzled me. One morning in June I found a pot standing in the backyard. We had a thermometer in the place where the lowest temperature occurred. And although it was never below five degrees centigrade, still there was ice in the pot. How did this come about? Now, I do not know whether I found the answer. I looked around then other days earlier and later. And (when there was a frost—) “but” it never was under a tree. It was just around). And it would have something to do with that, but I did not find the answer. That I remember. But then I played around with shadows. If the sun shone one could play with fingers. Now when the two fingers came near together then one could see that even before they touched the two half-shadows overlapped. And that I found out by experimenting. You see, such things. I remember when I was 12 years old we had the first lessons in Greek, which I hated very much at that time. Then I saw in one of my notebooks prepared at school that there was a spot of fat on the paper. I became angry with myself that I was careless with this lunch we always took to school. But then I could see the writing on the other side, and then I solved that problem. That I solved during that hour. Namely, I did not know anything about scattering and so on, but knew where I had seen such things. One could look through ice but not through snow. Something must be between the’ two different pieces of snow, or whatever it is, or paper, and make it more homogeneous, and that then you could see. At that very moment that I was elated that one could understand such things. Then I was asked a question in Greek, and I had not the lightest idea. And n teacher, who really accompanied me - to my regret - - through my whole school time, said, “Now, I see you are again asleep.

Go ahead, dream. Dream right on.”... I got a very bad note. And I remember—just to tell the story—that my parents were very, very angry with me. And there was a fair in Hamburg, and I was not permitted to go there because I dreamed about other things during school. [more talk about recorder] What I have said means only that I did not study books about physics when I was quite young. But I tried to think about it, and I made experiments in chemistry. There was a chemical set one could get. And I got things of that type. I may say, when I decided that I had to become a physicist was about the time when I was 13 years old. At that time I broke my arm, and it was the same time when I read in the newspaper that one could see the bones with X-rays. In 1896 Roentgen made his discovery. And in the newspaper it said one could see how much money a man had in his purse and the bones and so on. Now in Hamburg at that time existed a little— what one may say—local bureau of standards. Hamburg was a state town. I always was interested what they do in these laboratories there. But I didn’t dare to come in. But I befriended the janitor, and asked him what everyone does in there. And then when somebody passed, he said, “That is a physicist.” “What does he do?” “0h, he works with glass tubes and pumps and so on.” So I decided that is the man I have to approach. He probably would do something. The name of that man was Walter. And Walter and Pohl were actually the first ones who tried to get with the narrow slit the diffraction of X-rays. Anyway, I went to that man and said, “Here I am. I have broken my arm. I would like to see the bones. Here you such a tube?” And he said, “I made one. I made one. And it’s just ready. And if you want to have that done, I am very willing to do it. But will your parents permit it?” And I said, “I don’t know about that. Let us do it anyway.” And it turned out that the bones were sitting sideways, and they had to be broken again.

That was done in quite a crude way. Two doctors came and broke it again and put it again better together. Now anyway, at that time I decided I must go into physics. Before all that I heard about physics was that it was more or less dead like a doornail. One knew everything. All the principles were known. Here I quote Kohlrausch, who was the president of the German Physikalische Technische Reichsanstalt, the Bureau of Standards. He said, “Nothing else has to be done in physics than just make better measurements.”

Kuhn:

People practicing physics thought that I know. But I wonder how a boy—?

Franck:

You see, this was a time— I know from later; I did not know then — when there were great discoveries. There were Hertz’ experiments about electromagnetic waves that really confirmed the ideas of Maxwell. All these things I learned later. But it did not impress people. And actually, the textbooks written in that time and the lectures given for beginners at that time, were absolute. One would see that there is a building erected and there is no possibility to add something or to take something away. That is what it is. I remember the lectures of Emil Warburg and all the other people at that time. They gave the same type of lectures that were introduced before by (Magnus). (Magnus) was the first one who gave really lectures with demonstrations, and very well, for that time. But the man who changed that was Robert Pohl, my colleague. And from that time on it was done in a much better way. And (???) has also done something earlier. But anyway, the lectures did not interest me at all. I found it nice, and I read them. I always liked much more to read books than to read lectures. And nothing really exciting was in there. At the time when I started to study in 1901, the lectures were given in the old-fashioned way. It is in agreement with the books which were written at that time. Very few people, like Prude, like Planck, wrote new textbooks, in which really electro-magnetism and other things played a role. The older people insisted always that the elastic theory of light would be absolutely correct. And they were so prejudiced in favor Of it because everyone had the impression that everything must go back to Newton’s mechanics. And beyond that there is nothing. And one does not know everything—how it works—but it will all be Newton’s mechanics.

Kuhn:

Before one had access to Prude and to Planck’s books, what books did people mostly use? What was the previous generation of books that one read with lectures?

Franck:

I don’t know by own experience, because I grew up with these books in which already that had been done. But I know what the people said about Maxwell. And I net old people, older than I, but anyway 10 years ago, who still insisted— and it is true— that Maxwell’s essays were written in a style which is absolutely undigestible. And the man who brought that in order was mostly H. A. Lorentz. He took the essential things out of it. And I understand why exactly, without having read Maxwell myself, it was an intellectual jungle, as Ehrenfest called it. Namely, he tried, on all sides, to explain why he had to make changes. He used so much of the old picture and of the new, together, that the whole thing became a hodge-podge. Planck, for instance, decided and told us in his lectures that he wanted to start with Maxwell’s equations and see how everything could be explained with it. It of course comes from different roots. All should then give that equation. Also, nobody was aware of the way of mathematics Maxwell used at that time. Physicists learned not so much mathematics. That changed, yes, that changed.... When I started, we had. to hear mathematics right from the beginning. But before it wasn’t that way.

Kuhn:

Could we go back now again to the time when you were 13 or 14. How much science did you actually get before you got to the university?

Franck:

I must say practically nothing. I went through a Latin and Greek school. And. I was unhappy. There were two teachers in science and mathematics. One was good end one was bad. I had the good one only for one year. The other one was no good; wasn’t a good teacher. And I must confess that after a short time I was convinced that I would know much more physics than he did. I mean I understood, better what physics meant than he did. And furthermore, at that time people did not appreciate science at all at the Latin school. I remember when I finally went for my (???) exam, the final examination. The same two teachers said, “Now Franck, do you want only to study physics? If you wanted to go in a decent profession, I would be against that you try to pass such an examination. (However, under the circumstances), try it!” I mean, this was the attitude that we learned. And it is still there. And there were many in the humanities who do not understand that to know somewhat about science is nowadays absolutely necessary for a humanist. And to know something of humanities is absolutely necessary for the scientist. But anyway, I may say the school has not encouraged me at all.

Kuhn:

How much mathematics would your own curriculum there have included?

Franck:

Oh, we learned much more mathematics than children learn here now. We began a little bit with calculus, very little. But we had geometry very well, and we had a lot of things.

Mayer:

Trigonometry, algebra.

Franck:

Trigonometry. Oh yes, but all at a low level. Anyway, I had no difficulties with mathematics. But I had very much difficulties with languages. I must say that I am glad that I was forced to, because one must say that if one only does what one likes, one probably also doesn’t do much in one’s own field. There are always slow and tedious things to do which one has to do,... I never was very good in mathematics. I was, at least in my school, good enough that other boys in school, when it cane to the final examination, hired me, who was decidedly a very bad pupil, saying, “Now please give us a survey about mathematics. We have forgotten all that.” And so I had a kind of a course with them. So they knew that I was. But I was also not very good in my mathematics in class because sometimes I made an error with numbers or so. I mean I was careless. But I understood mathematics relatively well, but never was good. And that you remember, that my mathematics is very mediocre.

Mayer:

That’s not true.

Franck:

Ah, I think so, I think so. You will agree?

Sponer:

No, it’s not always so, not always so.

Franck:

But anyway, I did what I had to do. But I have seen right now a boy of 10 years old of a colleague of mine, who worked not only on calculus but on number theory and principle of relativity. And he understands what he is doing. I have never seen a boy of that type.... This is an astonishing boy. I met him in Pittsburgh. The boy is ten, and his sister is eight. And the sister is normal and has great difficulty to say what is 8 x 10. But the boy learns more mathematics than I ever tried to learn.

Kuhn:

In the science curriculum, which you say you had very little of, how much was one supposed to know when one got out?

Franck:

I studied geometry, algebra, spherical geometry, and plane geometry.... it is certainly true that we learned a little bit of astronomy and chemistry; practically nothing. But chemistry I knew because I made experiments at home and had also a book which I studied. I went on doing experiments at home all the way through gymnasium. And several tables of my parents suffered very much. I did my work on them. Some of these things happened, of course. I may say, science and mathematics were practically absent. As compared with the schools here it was not absent. But it was absent compared with the intensity with which we had to learn Latin and Greek and French and English.

Sponer:

No, you couldn’t learn French and English at the same time.

Franck:

In Hamburg we learned French and English, yes. We learned more than in most schools...We had to learn it. I must say, I still remember the French and English teacher as one of the very acre cable men. He not only gave us lectures that he was supposed to do but he brought French coins with him and showed them. And asked us which we liked better, the German money or the French money. And all unusual things lie also predicted, when I once was bad in English, “You don’t know what will happen to you in your life. You might later regret that you learned not enough.”

Kuhn:

You said that in school there was not much sympathy for the scientific career. How about at home? Did your parents approve of your dedication to science?

Franck:

You see, my father wanted to study when he was young, but he had not the money. He was a banker and was quite well-to-do. But he hoped that his boys would study. But he thought more to convince me whether I would not become a lawyer. And that was the last thing I wanted to do. But anyway, my father was a very logical man, and he said, “How do you know that you don’t like law if you have not tried?” I was in Heidelberg in my first term. So I heard a few lectures on law and was not interested at all. Enough just to tell my father it’s out. Here you ask the question why I started with chemistry. Now, I was a little bit accustomed to it, and furthermore, my father said it was right. If you go in physics, you have no chance whatsoever to make a living if you don’t become a professor. The probability to become a professor is very small. And especially at that time the government disliked to give professorships to a Jewish boy to a non-Christian. So he was quite right. But my answer to my father was, “If I don’t study physics, then I am unhappy from now on. And if I study physics, I might become unhappy later. But anyway I have a few years of that which I like.”

Kuhn:

Did you know that already when you went to Heidelberg, that you wanted physics and not chemistry?

Franck:

Yes, I knew. But I thought that it would be good to have as much chemistry as possible so that there would be a way out if it didn’ t work in physics. So I wanted to go as far as this (Amts) exam in chemistry. It is an intermediate examination for a position, more or less like a technician. I wanted to go that far. But I gave it up because I was not interested in that. I’ had to learn so much by heart at that time. It might be interesting to know how long a time it took between a great discovery and the teaching of it. In Heidelberg, the professor of chemistry was Curtius. And he was the successor of Bunsen. Now (Winder), a professor of organic chemistry in Gottingen, a good friend of ours, said, “Bunsen ruined chemistry.” Anyway, one should think that that would be the case hearing the lectures of Curtius, because we had not, in inorganic chemistry, heard a word about Arrhenius’ work, about the positive and negative ions and how they played a role. When I came to Berlin after a year and wanted to continue a little bit with chemistry, the professors there asked me about these things. I had not the slightest idea that it existed. And then I read about it and was fascinated by it. So I may say the chemistry time I had was not lost, because during my whole life I had always an interest in the physical background of chemistry. So a little knowledge about it was quite good. But I did dislike wholeheartedly to become a chemist.

Sponer:

You insisted that almost all your assistants have some chemistry, didn’t you? Everyone who took the Ph.D. with you, you highly recommended that they take chemistry.

Franck:

Yes, that is quite true. I did, because I know it was important. And especially at that time in which gas discharge and spectroscopy and so on were really one of the means to learn something about atoms and molecules. Therefore one should know a little bit of chemistry.

Kuhn:

I want to know more about chemistry. But there’ a one question that arises for me, and it’s actually one that Professor Mayer and I talked about earlier. We notice quite how many Jews there are involved in these developments and were wondering to what extent it is aspects in the family background of the Jew in Germany in this period that brought quite so many people into the sciences at this time?

Franck:

Maybe I missed your question halfways.

Kuhn:

There were a lot of Jews involved in the development of physics in Germany, It isn’t yet a question, but I’d be terribly interested in what comments you have about—

Franck:

I would like to say that my interest in studies of physics started then in Berlin. I don’t mean so much the general lectures. I mean especially the so-called colloquium. That colloquium was the greatest event in my life. There all the professors of physics, and not only of the University but also of the Technische Hochschule and also of the Bureau of Standards — everyone who was interested in science came to these things. And this was a meeting every week of maybe 40 people. Of course there were much more in the Reichsanstalt, but they had no interest. These people who came together included the people engaged in their dissertations. Even a little bit earlier, before they started the dissertation they were admitted to come there and hear. And there really we could see how the great men of that time had all struggled with their problems. And this was such an informal thing. Every l2 days there was the Physical Society meeting in the evening — Berliner Physikalische Gesellschaft . But there more formal talks were given. But we heard Planck for instance, not only in the very beginning. I came in 1902.

That was the time in which Planck always struggled whether he could not avoid quantum theory, whether he could not at least make the influence of the quantum theory as little as possibly could be. And whether he could not for instance say it might be only the emission but not the absorption. I mean a lot of things he tried out. He was really trained in classical physics, and if ever there was a classicist in character, it was he. And he was a revolutionary against his own will. And I remember that always he came with attempts to see whether one could not avoid—with some resignation, but also with looking ahead. He finally came to the conclusion, ‘It doesn’t help. We have to live with quantum theory. And believe me, it will expand. It will not be only in optics. It will go in all fields. We have to live with it.’ That was the consequence. And now, for young people to see one man, for whom we had the highest regard, whose lectures we heard, whose clarity we admired, had to struggle so hard. It was all the inborn honesty of this man, to see whether one could not avoid this thing which really grew out of his own mind. This was a very strong impression. And furthermore, the younger people were treated there as younger members o the same order, as men who wanted to study and to learn the truth as far as that is possible. And this was not only in Planck, that was in all those things.

We had men coming there from all over the world— England, America. People came and visited and spent one afternoon or two, as long as they were there and told about their things. Later came Einstein—that was a good deal later. But the honesty of Einstein in all these things—I remember once later I made somewhere an error which I had to correct. And I told Einstein, “You know it’s not so agreeable when one has to admit that one made an error which one could have avoided.” It wasn’t too bad, it was a mix-up of two terms in the case of helium-metastable and the other one. And he said, “Franck, if you don’t want to commit errors, then you better stick to measuring accurately known constants only a little bit more accurately. There you are on safe grounds.” I remember a discussion with Nernst. I don’t know whether I should mention it. Nernst had to give a talk on something which was based on an idea which Einstein published a few months before. And when he was ready, Einstein said to Nernst, “I regret very much that I misled you, but this what I have published here is wrong. It isn’t so.” And then Nernst became angry. “Einstein, you can’t do that. You have published that. You have to stick to that.” And Einstein in his way said, “Now colleague Nernst, what do you recommend to me? Shall I start an argument with the Lord that he has not made the world the way I thought he should have done so four months ago?” Now all these things impressed us then, and that I believe, I always looked forward to that afternoon, because it was the greatest event. Later too many people came. It was then not run the same. We had to go from the one long table around which we were sitting to a classroom and so on. They tried very much. And we tried later on in Gottingen to have colloquia of that type, but it never was as the Berliner colloquium was at that time. I believe the reason that many of us who went into physics at that tine tried to do something with quantum theory, is that we went to that colloquium.

Kuhn:

You think it was really the colloquium itself that affected so many of you?

Franck:

I think so. Furthermore, there was another thing. Everyone who went into physics at that time went into physics because he had to. He couldn’t help himself. He had to. There was no attraction to go. I mentioned before what my father told me. There was no industrial position for a physicist at that time, even the great German electrical companies maybe hired one man, but not more. And the others, if they were a scientist, they were a physical chemist because they should know some metallurgy, and so on. And the physics, that was not so important. So whoever went to study physics went because he felt he cannot be happy in any other way. And that means quite a selection of people. I remember when my friend Pohl, who did his dissertation the same time as I, found a small new item, of very little interest, about electrical discharges. I was elated and told the Privatdozent, whom I met outside of the room, “Have you heard about Pohl’s results? And he asked, “What is it?” I told him. He said, “Now, look here. That is quite nice, but Pohl won’ t be shattering the world with it.” I said, “No, it is not that, but that we young people really can find something new; this is what shatters me.” And he said, “You are right.” I mean, this is the spirit in which we lived. We were from morning ‘til evening there. We were ‘til midnight still there. One of us went out to buy something, and all together there in the room we ate some supper. At noon we went for a short time in a restaurant near by. We lived there. (Warburg) came in sometimes at midnight or so, to see if somebody was there and said, “Oh, I just thought about it and—.” It was that atmosphere. And therefore at that time we grew up with the times. We grew up with the great men. It was unavoidable.

Kuhn:

Who else appear as dominant figures at the colloquia? You’ve spoken of Planck, and I assume Warburg was another.

Franck:

Warburg was another. Warburg was not inspiring in his way, rather dry in his way. But I think I can give you an example of what type of man he was. I told it yesterday to my wife. Warburg had a laboratory full of men, and many Americans were there. I remember (Peekam), for instance, [J.T.] Tate, and—

Sponer:

Lindemann.

Franck:

Lindemann was not from America. He was from England. He, Lindemann went to school in Germany. Lindemann came from Lorraine, and his parents went to England. But he disliked many things he saw in Germany. I remember when we heard a discussion about Friedrich den Grossen. And he defended his point of view, “Frederick the Great was a scoundrel. You can see it by the fact that he played the flute. His father broke the f1ute over his head, and he still insisted in doing it. That’s a scoundrel.” Always an astonishing view. But Lindemann was later happy, not at that time. Lindemann was exceedingly quick in the colloquium, especially with astronomy. He knew all the distances and calculated it in his head very quickly and could say, ‘that and that must be wrong,” and so on. He was very intensive and very quick… Now Warburg wanted to give topics to begin with, which were not interesting.

He had the laboratory full of people working on gas discharges. He said that I should study the point discharge— which he had studied before—in such a way that I would see the distribution of the current arriving on a circular electrode with isolated rings. I was to see whether that would change when one goes to higher potentials where the beginning of the transition to the spark would occur. Now I studied that and I found some changes but it was nothing really, a few measurements to make. I went to him and said that I have done so and whether he would not be kind enough to tell me how he thought that one could go further with it. Now I don’t know, he must have misunderstood me and thought that I wanted to graduate or get my thesis with this (menial) research. Anyway, he was decidedly unkind and said, “Oh, that’s your dissertation. It’s up to you to do something with it.” And that drove me mad. And I made a formal bow to him and said, “Herr Geheimrat, I am very glad that you tell me that. Now I know that I can only rely upon myself.” Which was an impudence. But just that I was a little bit quick tempered. At that very day I found something that I could use. I tried to suck some air through in the hope that maybe some gases—ozone—could be removed from that little apparatus.

And I found that the whole figure shifted. I had read something which influenced very much all of us, namely the book of J. J. Thomson, Electricity through Gases. I knew that mobility of ions had been studied. And I knew furthermore from the discharge that in the region where the luminosity was that there could not be normal ions there. There would be electrons, and so on. (Townsend’s) theory existed already. So I thought that if one changed that. Instead of a point discharge takes a discharge from a thin wire and, connects a cylinder, that one could probably study the mobility of the ions and compare it with the mobility of ions in other cases and see to what distance for instance the electrons move very quickly, or the positive ions are accelerated, and migrate with the velocity proportional to the field strength. And that became the dissertation also. But to come back to Warburg, in spike of the fact that I misbehaved the day before, when I told him that he said, “Yes, that’ s a good idea.

Yes, go ahead and do that. And by the way, there is a paper of such and such man in Philosophical Magazine, read that.” Now this shows that he was very much Der Herr Geheimrat, but if physics were concerned, he forgot all about this. And this made also a great impression on us. And it often made an. impression on us to see that the older people were as always much slower than we. So if somebody gave a talk, we knew, but Planck and Warburg and the other people inquired again. So we came to the conclusion, “How these old people are certainly slow. But, if they say it is right, then you can rely upon it.” So, it was always in the laboratory said, if you go to the chief, it will take some time to convince him. But if you can convince him, then you can forget all about your worries, then it’s all right. So that was the attitude in which people influenced us. Then there was, as you said, other people. The astronomer Schwarzschild. When he came he made a great impression upon us. Rutherford came. J. J. Thomson came. It was just a wonderful time. A wonderful time.

Mayer:

Was Drude there?

Franck:

It took one year of interregnum after Warburg left before Drude came. And Drude was refreshing, he was by no means a Herr Geheimrat. I once was there without jacket and waistcoat and apologized to him. And he said, “So far as I am concerned, you can come in your nightgown, if you only work.” But in that interregnum my dissertation was practically ready. And Drude was very nice. I had found the electrons moved much further in pure nitrogen than in oxygen. And. I said, what is the influence of oxygen? And so we discussed it back and forth, Drude and I. And one of us, I do not know who, he or I, said it might be the magnetism of the oxygen. Or it might be that it combines quicker with an electron by other reasons. I mean, we discussed that back and forth, but that’s the only discussion we had about the paper. Otherwise he said I should write it, and he gave me a very good note for the paper. But I was not too good really in the examination. Because I had learned theory in Planck’s way, and Drude used it in his books another way. And I read both of them, so I was by no means really good in the examination, but not too bad anyhow.

Kuhn:

That couldn’t be a later conversation with Drude on some of the later ion mobility?

Franck:

No, no. And actually, also Warburg had found already that the discharge in pure nitrogen was different than it was in air. So it was something known about it. But my dissertation was of great importance for my way of thinking. Because I came very quickly to the idea that the gas discharges are too complicated. One should not study the gas discharge alone, but one should study the kinetics. And therefore I went on and studied ionic mobility with Rutherford’ s method just alternating current and the amplitude, so to say, before they reach the other electrode.

Kuhn:

Was the quantum the big problem in Berlin when you were a student? How early would you yourself have been aware of it? Not immediately in 1902 I suppose.

Franck:

I would say, I may say, at least by l904 it was a burning question. One really said, this was the field in which one has to go. And I remember that when later Einstein came— I forgot in what year it was he came… 1913 he mast have been there, because I remember that he was present when I gave a talk about the Franck-Hertz experiment—the first one…I remember also the first impression I got from Einstein. Then I was 75 years old, another man of that age, or two or three years younger, wrote me a letter— I can’t tell you his name. And said that I influenced him by one story he kept in his mind. Namely, I had read early in the morning the first paper of Einstein. And I had to tell it to somebody, and I was early in the laboratory and only he was there.... This was the first paper on principle of relativity. And this influenced me very much. I went to this man— he quoted that, and I remembered afterwards that it actually was so. I came down and said, “I have seen a paper this morning of a man who should make us all ashamed of ourselves.

Not that any one of us could solve the problem that he has put before us, but we have not seen that there was a problem about absolute velocity and space.” Newton was quite right to say that the coordinate system of the world is that of the fined stars. But we have heard Schwarzschild and other people talking about Doppler effect of the stars, and we know that they move. And still we learned and believed to understand Newton and have not seen that there was a problem at all. And there he has made us ashamed. I have never heard his name; I don’t know where he is or what he is; but I must say he solved for us the problem. I don’t believe that I understand what he says. It becomes complicated, but I will study it further and. understand it. But this I have to tell you, that one never should really accept something just on authority, that one always should be skeptical and should be inventive oneself.” And that he said had influenced him, and this was the attitude of the first paper. When he came, it was as the man who has done this. Einstein was very impressive.... The older people of that time at the Colloquium—Rubens came. And from the Reichsanstalt some people. There was also the man who went to Breslau, Lummer. And then there were some people working on gas discharges, and all these things played a great role. But practically nothing was said about radioactivity.

I remember that when I was in the colloquium; in the colloquium it was always this way—one didn’t report only on his own papers, but the younger people especially had to present papers which Warburg assigned. “These are the papers which we want to discuss. Who wants to take that paper? Who wants to take that paper?” And we all did, as good as we could. Then he said, one day, “I think it’s time that we take this radioactivity seriously. Until now we have never discussed that.” I can’t tell you when it was, but it must be around 1904 maybe, or ‘05.... He said, “All this talk about it, and I believe we have to take it seriously. Who wants to speak on this?” Mentioning the older people, I should not forget Goldstein. I don’t know whether he came often to the colloquium. I don’t remember that. There was some tension, I believe, between him and Warburg. But we went often to Goldstein in his little laboratory. And he showed us about canal rays and what arc all these things.

Sponer:

Oh, it is a forgotten name, but he did beautiful things. For example, at the present moment people who work in phosphorescence and in luminescences of a number of complicated things, have to mention and do mention Goldstein. He was in many ways the first one. Not that he knew what kind of luminescence it was, but he had discovered it.

Franck:

He was quite an interesting man, Goldstein. He was one of the men who looked at discharges and found always nice new things. But there was no order in the whole system. But anyway, the canal rays, which Thomson and Willy Wien and other people did so much with— and Stark. He found them first, and he knew what he had, and it is a pity that his name is more or less forgotten.

Kuhn:

He was at the University?

Franck:

No, he was not at the University. He had a special laboratory which the government gave him. He worked alone with a glass blower. He made lots of experiments. But he was nothing for the orderly mind of Emil Warburg. You know Emil Warburg was the man who first found the (???) of magnetism, and then later he went into gas discharges. But I can understand why Goldstein and Warburg never got along. Warburg had a laboratory— actually a small apartment somewhere—which was paid under the name of astronomy, I mean it was a special part of the astronomical studies. There he studied gas discharges and all that. He was a man from whom we borrowed the little quartz spectrograph which we used for the line 2537 because we had none in the laboratory. And when he met me in uniform later he said, “You see. I told you. One always should be orderly. I have your signature here. If something happens to you, I get my quartz spectrograph back.” Anyway, he was an original, very interesting man.

Mayer:

You said that in the colloquium you wanted to take up radioactivity, and then it was suggested that somebody talk about it.

Franck:

Yes, that was relatively late. And you see, people became somewhat disillusioned. Because after the X-rays bad been found, then very quickly, and directly as a consequence of it, came the discovery of radioactivity. Then came a lot of other things. People found N rays and what not. All the stories, you know, about (Ira W. Woods) and so on. People became crazy. And especially if one uses very small intensities, one is apt to make—

Kuhn:

You think it was in part then disillusionment over N rays and over some of the other strange radiations that may have kept people skeptical?

Franck:

I know that Warburg disliked that people were sensational and tried to make a lot of things. But you asked whether foreign periodicals were read in Germany. Yes, they were. Especially the English ones, American ones were practically absent. The only thing which was read was Astrophysics. That was absent practically, with the exception of Schwarzchild. There was nobody really there. Otherwise, certainly, Philosophical Magazine—we all had our own copy of Phil. Mag. We had also Proceedings of the Royal Society which we read always.

Kuhn:

How about French journals?

Franck:

French, much less. Much less. Of course, I read the thesis of Langevin, and the work of Madame Curie and of Curie himself. That we read. But not directly. Later on. The astonishing thing with France was that it went so very quickly down. After having so many great people, it went very quickly down. And it went down particularly for two reasons. Whenever a man came to Paris he gave up. He didn’t do anything more, because one could not reach a higher goal. And then, they had no co-workers, because Doctor’s degree was very difficult. It was much more like the medieval doctor degree, much more difficult. Therefore practically nobody who studied made a dissertation. So the professors had no co-workers. And since at that time science became democratic, there you needed also some hands to help. That France did not do. They remained high in mathematics where people worked alone by themselves at the desk. But they did not do it in the other things.

Kuhn:

Can we try to come back for, a minute to the quantum? You speak of the sense of excitement in watching Planck wrestle with the problem.

Franck:

We had no doubts about the great importance. My friend Hertz mentioned some time ago that if you look for instance in this (Landolt-Bornstein), l906 or ‘o8, I’ve forgotten now. If you look under Loschmidt’s number or what not, you find no mention of Planck’ a formula. All the standard works did not use it for years and years—for determination of charge and connected with the Loschmidt number and so on. And you see it also, that when Hertz and I wrote our paper on mercury, we had not read Bohr’ s article which was published maybe already 2 or 3 months before. When we wrote our paper, we had not seen it. And nobody told us. It took longer time. And there was also a kind of bias against it. Nobody could make models for atoms. I was told that Sommerfeld wrote a letter to Bohr, congratulated him for the nice formula he derived. But he said, “You shouldn’t try to get a model of an atom. We know that doesn’t work.”… I know that there is a letter, but I do not know whether Bohr has it, or I even don’t know exactly whether Bohr told me or whether Sommerfeld told me. I know only that I’ve heard about that from quite a reliable source.

Kuhn:

Back now before the Bohr atom, you don’ t remember now particular conversations about the quantum?

Franck:

I remember one with Einstein. And he shook his head and said, “In the principle of relativity, everything is so clear. But in quantum theory it is horrible. What a mess it is in.” That was before he wrote his article that was before the war, or was it in the war? I was a soldier but I came home sometimes. Anyway, he said this, and my answer was. “You are certainly right. But you see, as an experimentalist, I am of the opinion that it pays to fish in muddy water. And with the principle of relativity, for the time being we cannot make any experiments. The astronomers can but we can’t.”

Kuhn:

What were the relations of the experimentalists and the theoretical physicists and the mathematicians in Berlin?

Franck:

With the mathematicians we had not much relation. But with the theoretical physicists, they were always close. It was not that great difference that later developed, that an experimentalist would say, Oh, I stick to my guns.” We regarded it as really our absolute duty to know what is going on in theory, and vice versa. Of course it was possible at that time.

Kuhn:

Planck writes somewhere that when he came to Berlin initially there was difficulty because nobody had heard of theoretical physics as a specialty.

Franck:

Planck was the first theoretical physicist employed as such by the University. We always told each other a story, which I have not the slightest idea whether it was true, that Planck tried once to make experiments. He wanted to find the melting point of certain substances, and the best substance he could think of was to take (seal wax), which decidedly is not the best thing. But this was maybe an invention. But it shows a little bit how astounding it was for us to see a man who did nothing else but just always think on theory. Rubens and Kurlbaum studied also once the N rays and tried to find out whether there was something in it. They made a lamp with so many screens and opaque glasses that very little light was visible. And they wanted to know whether one can at all measure small intensities with the eye, or see whether they change. Rubens changed an electrical resistance, and the lamp became brighter and darker. But he did not tell Kurlbaum in which direction. Kurlbaum got the right answers. Kurlbaum always could say brighter, darker, and so on, according to that what he did. Then Rubens thought, maybe be is influenced by the noise it makes if one changes the resistance. It was a gliding thing, that made a certain noise. So when he did it, brighter, darker, he made the same noise going with his thumbnail over the surface of this coil. Kurlbaum continued to say brighter, darker, brighter, darker, without the resistance being changed.... I did not know this story. Rubens told me the story later. But he must have written it to the French people, because the French people said the Teutonic mind was not fine enough to find that. Rubens was so pleased about ‘the Teuton mind’ as applied to him. He laughed and laughed about it. [Break for tea]

Kuhn:

Why was it that you chose Heidelberg in the first place?

Franck:

Actually because I never lived in south Germany and I thought Heidelberg would be nice to begin with, just to have some carefree days. You see at that time I met in the lecture hall the mathematician Max Born, and we became quick friends. Born got a visit from his sister, and I must confess that his sister contributed considerably to my pleasure at Heidelberg.

Mayer:

Frau Konigsberger? Frank: Ja, Frau Konigsberger. [mumbled exchange in German] And we always made excursions. I studied in Heidelberg also a little bit geology, which I liked. You see, I always liked to look at my surroundings. I never planned to become a geologist, but the professor there asked me whether I wanted to go into that because he saw some interest. I think especially he became interested when I brought him a piece of rock from the bottom of the Neckar River. Because he said, “Down there must be that and that stone.” For he knew. So I took a hammer with me, and I always liked to swim and brought him a piece of that. And that interested him. I knew a good deal of the geology of the surroundings of Heidelberg. We went to the Eifel and on excursions. All these things I liked very much to do, but I never wanted to be a geologist not at all. And I forgot practically all I have learned, but I still remember a few things with pleasure. And I even went to mineralogy, but mineralogy I disliked much all my life.

I heard a lot of lectures at that time. It is quite different how we were at that time. Now they have so very much to learn that they cannot make excursions in literature or history of art and so on. We did. I heard one man talking about Goethe. All such things we did. We even went to zoology and heard one famous lecture about this. I don’t know what all I did. I nipped here and nipped there. It was more or less not really very industrious but not lazy. I had a lot of things that interested me and got finally the freedom from school to do what I pleased. I took mathematics and physics. I must say, the lectures in physics were no good. Who was the man? Quincke. Quincke. Acoustics, such things. I remember once we made an excursion during the night. I went in the morning to the lecture and fell asleep, and he sent his laboratory aid to wake me. Anyway, I was not impressed by Quincke’s lectures. He was already quite old. And one must say, the lecture system, though good as it was for the time before us, it was too late for the time in which we lived. The old story about a professor: His wife complained, ‘Now look here, my husband gives the same lectures now for 30 years. The students liked it very much. And he has not changed it and still they don’t like it anymore.” This was the same situation. You wanted to know why I went to Heidelberg. I mentioned it. The beautiful surroundings. I went again and visited Heidelberg on this trip, and some of my pupils are professors there. And my pupils are already now in the stage of being slowly retired.

Kuhn:

It would really be then in the following year, when you came to Berlin, that you feel your real scientific education in the university started?

Franck:

In Heidelberg I just enjoyed the freedom to do what I pleased and really got some impression for later on, to think. Especially the beautiful surroundings—the way we always in the evening went down the river. I always liked to swim. Under the old bridge there was a terrific current. I took, always, a canoe and tried to go through that bridge against the current. And it never ended another way than that I capsized and swam back. And after a time people didn’t even look any more. “It’s the crazy student there. We know, he comes along.” But I wanted to get there. And then with Max Born, we had these certain rocks. They had these holes in there from the water. And I told them about so-called (Strudel-Kopfe). And so Max Born called me “the Strudel-Kopf.” Which was true. I was running around everywhere. Max Born was much wiser than I was.

Kuhn:

What then took you to Berlin next? Was Berlin then the place to go for physics?

Franck:

It was, yes. I went there with the intention to work and to work and to work and to work. And that was a university where people did it. In Heidelberg there were too many distractions. So I said that has to stop now. I have really to go somewhere— I really want to work.

Sponer:

They called it “Arbeits-Universtat.” Remember the name? There were certain universities which had the name “Work Universities”, and Berlin was one of them.

Kuhn:

Would there have been, in this period, for somebody who knew he wanted to do physics and was ready to work at it, any other place he might have picked instead.

Franck:

Munich. Was there already Willy Wien at that time there? Yes, I think so. Yes, he was there. And later Sommerfeld—but at that time not. But Munich had a reputation, yes. But Berlin had the greatest reputation at that time.

Kuhn:

When you went to Berlin, whose lectures did you take?

Franck:

I had Warburg, I had Planck, I had some lectures of Mommsen and such historians and so on.

Sponer:

Was Drude there?

Franck:

Drude was not there. Drude was in Giessen at that time. He came one year after Warburg left, and then he was only one year there, and he died— suicide.... I really never knew why. I thought it might be something in the family. They were afraid about his son, who broke away from physics at that time. He started physics and broke away because he couldn’t stand to be always, “Oh, yes, yes, you are the son of—.” He left Germany. He disappeared.... But he became an applied scientist and a very good one. He was in industry.

Sponer:

But you know, one daughter took her life, isn’t that right? One Drude daughter? Eine von den Tochtern in Gottingen.

Franck:

But she died by cancer, or—

Sponer:

Zwei Tochter, und die eine war immer in (Gefahr).

Franck:

There was something, some trend in the family. Why he did it? There is no reason whatsoever that you can think of. He had a happy family life and he had four growing children and he had success and everything. I don’t know.

Kuhn:

In the physics courses and lectures at Berlin, what would the standard subjects have been?

Franck:

Planck gave all the lectures in theoretical physics, and it started with mechanics and went to thermodynamics and went to acoustics and then electricity and electromagnetism and then— it was a course in five terms. And we all went there every morning. And this was really something that influenced us very much. Then mathematics. Mathematics was not so very agreeable for me because it was a little bit too abstract, and I was not too much attracted by that. But I learned the mathematics. I practically learned more by myself with books. I must say I had not heard Warburg’ s lectures about physics for beginners. I never got to the end. There was no real control of what a student did. He only had to prove that he knows something, that was all. Later it became more strict and there were some examinations. And now they have several examinations…

Kuhn:

Krigar-Menzel also gave lectures in theoretical physics at Berlin in these years, did he not?

Franck:

Krigar-Menzel, oh yes. I never heard of him. He was also there, but we all went to Planck’s lectures. Oh, there were also some other people, Privatdozenten and so on. I heard here and there lectures, but nothing really which influenced me as much as Planck’s lectures and the Praktical, the experimental physics where one could do some experiments himself. And then I said when I was in the Praktikum and I was a beginner, I said, “What a time in which Faraday lived. All the simple experiments he could do!” I did not realize how much that meant to do the simple experiments, about electrolysis. An experiment one could do in five minutes. It took some time before one matured enough to understand that. Then, you ask about the time in Berlin. You see, we were really a kind of fraternity, everyone in the laboratory. We went in the evening to the theatre together. We had some Americans with us, especially (Tuckerman) of the Bureau of Standards. He was in the same room as I. We worked in the same room together. And he was quite original, with a long beard. I remember that I brought him home to my parents. I asked him whether he could not go ahead alone because I had to finish some experiments, and I would come soon. He should tell my parents I would come soon. And when I came, my mother was in desperation; my father enjoyed himself very much. (Tuckerman) was sitting there with his legs on a polished mahogany table. And my father enjoyed it, because (Tuckerman) told him of the immorality of being a banker…My father had retired from banking and they lived there for years in Berlin.

Kuhn:

This fraternity in Berlin, did it include really the people who were oriented more toward theoretical physics as well as the experimentalists? Or was it now the people working in the laboratory?

Franck:

There were a few theoretical people there, there were a few. Laue was one of them. He came a little bit later, but anyway he was an assistant of Planck. Lise Meitner was for a time an assistant of Planck. Originally she planned to be a theorist, and then under the influence of radioactivity in Vienna and the arrival of Otto Hahn— But at that time Emil Fischer—he was in chemistry—didn’t want to have women in the building. They went into the so-called woodwork shop in the cellar. There they had isolation, and there they worked together. And they always were in a hurry. Of course with radioactive decay— when they came to the laboratory they rushed down (Luisenstrasse) and came out of breath there because they had to—We had a nice group of people together. My wife was a pianist, so we had some music at home. I remember that Einstein played also several times. And an old friend whom I saw now in London, came and played the violin also, or played cello, I forgot. Then Lise Meitner introduced us the (Brahm’s songs), which we did not know at that time. And the whole time we were all together always, in one or another way. It was a group of friends. [A discussion of Roentgen’s discovery is here omitted]

Kuhn:

You said earlier that Planck himself was trying to restrict the scope of his break. Did you yourself and other people around you feel this way then about what he was doing? Did you already have the sense that he does not realize how important this is?

Franck:

Yes, I think we did. We talked about it. And felt so strongly that he was influenced by his old experience. You see, what he did in the old field of statistics and thermodynamics.... It is certainly true that he was lucky in that respect, that people in the Physikalische Technische Reichsanstalt wanted to have a new unit which was better than the candle, you see. And so they thought the radiation of a black-body would be a much better unit. Actually, everything was connected with technique in this case. They wanted to have a better unit for measuring the intensity of different lights and light sources. This is after all a funny thing. Usually we people who work in non-applied science do often not realize how much applied science has influenced us. If you take now the new things, about electronics, the way that developed, it would not have developed without industry that way....

Kuhn:

But the Lummer-Pringsheim work was started in a search for a better intensity unit?

Sponer:

Yes, for a better unit. And a more accurate unit. The (Hafner) Kerze was the standard, but they wanted a better measure.

Franck:

It is quite astonishing that one had to use a candle. There was a certain way in which you make them, so that it is more or less responsible. It is astonishing that that worked for a long time. We usually paired in the laboratory. Then we had less apparatus necessary and the one can do better one thing and the other the other thing. We worked always in pairs if we could.