Fritz Reiche - Session I

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Interviewed by
Thomas S. Kuhn and George E. Uhlenbeck
Rockefeller Institute, New York, New York
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In footnotes or endnotes please cite AIP interviews like this:

Interview of Fritz Reiche by Thomas S. Kuhn and George E. Uhlenbeck on 1962 March 30, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA,

For multiple citations, "AIP" is the preferred abbreviation for the location. 


This interview was conducted as part of the Archives for the History of Quantum Physics project, which includes tapes and transcripts of oral history interviews conducted with ca. 100 atomic and quantum physicists. Subjects discuss their family backgrounds, how they became interested in physics, their educations, people who influenced them, their careers including social influences on the conditions of research, and the state of atomic, nuclear, and quantum physics during the period in which they worked. Discussions of scientific matters relate to work that was done between approximately 1900 and 1930, with an emphasis on the discovery and interpretations of quantum mechanics in the 1920s. Also prominently mentioned are: Niels Henrik David Bohr, Ludwig Edward Boltzmann, Max Born, Louis de Broglie, Byk, Compton, Albert Einstein, Arnold Eucken, Werner Heisenberg, Joe Keller, Hendrik Anthony Kramers, Krigar-Menzel, Werner Kuhn, Rudolf Walther Ladenburg, Alfred Landé, Stanislaus Loria, Max Planck, Radernacher, Rotzsayn, Clemens Schaefer, Hermann Amandus Schwarz, Otto Stern; Bad-Neuheim Conference, Naturforschertag (Salzburg, ca. 1909), Universitaet Berlin, Universitaet Breslau, and Universitaet Goettingen.



Dr. Uhlenbeck and I would most like to have you tell us about physics in Berlin in the early part of the century what the curriculum was, something of your own education there, your own life in science in Berlin. The whole question of what it is like to be a young student of physics in Berlin at the beginning of the century, is terribly important and interesting to us. There are not very many people who can tell us about it.


To speak of me instead of speaking of Planck I want first to say this. I left school, high school, only in October 1901, unfortunately one year after the prodigy child was born. I went first for one year to Munich. At that time, of course, Sommerfeld was not yet there. I was not quite clear about what to study, whether physics or chemistry. I attended lectures for two semesters, one year. I attended lectures by Roentgen; by Baeyer, Adolph von Baeyer, a big man in chemistry; and lectures in mathematics, of course. I had calculus, the two parts, with Lindemann. That's not the Lindemann who was later the Churchill adviser, but it is the Lindemann who proved the transcendence of e and pi. I even attended one of his special lectures.

I'm absolutely convinced now that I did not understand it correctly, because it was my second semester and it was too early. But anyway I had the impression. Then I attended some other lectures in economics by Brentano, Julio Brentano, who was a very famous economist, That was all, The main things I learned were the two calculus differential and integral — and the main basic things in experimental physics. Rontgen was not an agreeable but a very good lecturer. I mean that he made very interesting and good experiments, probably helped by his associate men in the laboratory.... In 1902 October, approximately, I went back to Berlin, where my parents lived. I think it was in the first semester in Berlin that I ran, by accident, into Planck's lectures.

He used to give the whole course in six semesters, three years, beginning in the usual way with mechanics, then mechanics of deformable media, etc. like the books are written. I came into the fifth one, which was thermodynamics. That was the first one I heard. I must say that in spite of the fact that I probably did not in my age completely grasp how well-prepared the whole thing was, and how consistent, yet I was very much attracted to this kind of lecture. And so I decided to stay with Planck and to attend all his six lectures. The next one, the sixth lecture, he called "System of the Whole of Physics," "System der Gesammiten Physik." I am not absolutely sure, but I think the next semester, if I am not in error, was the theory of heat radiation. And again of course I was very much attracted, though I am now pretty sure that I could not completely grasp everything.

I knew of course from the first semester which I attended thermodynamics - what entropy means, and so on. I saw that he used the relation between entropy and the energy of the oscillator, but the whole thing was for me like, say the empire State Building is for a man who never saw New York. I stayed there. But you might know that Planck was not of the same type as Sommerfeld. I never studied, unfortunately, with Sommerfeld. Sommerfeld was a man who was often sitting together with his students in the café, and suggesting problems and helping them solve problems. Planck was just the opposite of this. He was a type of (?) official, very reticent in everything. He never talked with anybody, except with those, perhaps, whom he knew already very well. I'm not quite sure who was his assistant at that time - I remember his face.... He had an assistant always, because be gave problems from week to week, as I remember.

The duty of the assistant was to look through the problems and then, obviously, show when be had found mistakes and so on.... Every student had to write them out. Usually, I think, if it was a too long problem he gave one, and otherwise be gave two, three problems from week to week. It was a class of about 100 students. It was very many students. I do not know exactly who was his assistant. I do know that Zermelo was one of his assistants, and his student once. But whether he was before me?... Certainly Max Abraham, whom I knew from sessions of the Physical Society and so on, was also for a certain time his assistant. Also before me, but not directly before me, probably, was Laue. That's a most regrettable thing, that he is not alive anymore, because he would be the man who was closest, no doubt, to Plank - not only as a brilliant physicist but also, I think, as a friend. There was a real friendship between them.


This course on the System of Physics, what did that contain?


I think he changed, as far as I remember, because I certainly attended it twice. Sometimes he gave relativity, but the first time I attended it I am pretty sure it was the whole theory of heat radiation with the introduction. You know how he represented it in his book? Of course the book has been changed enormously from edition to edition. Unfortunately I don't have anymore the first edition, which was probably the most original one.... Of course my whole feeling in this time was the feeling of a student who attended a series of wonderful lectures. I mean wonderful in the sense that they were certainly very well-prepared, very polished. I think he never made an error on the blackboard. And he was also a good talker ("Rhetor") - a good speaker.

It might be that he was not amusing, in a certain sense. I remember that once much later when I was in Breslau - an intermission - that Adolph Kneser, the mathematician, was always a little critical and against Planck. I do not know the real reason for that - the personal reason I do not remember. Kneser said "Well now Planck, Planck war auch nicht zum tot lachen!" Not to laugh to death. He means he was without humor. There is a certain point to this.... He was very reticent and not inclined to make jokes - at least certainly not during the lecture.

The lectures were serious and covered everything and went from point to point. And, as I remember, they were never erroneous. I attended of course still other lectures. I also worked a little on qualitative analysis in chemistry in a private laboratory at that time in Berlin, one of the leaders of this laboratory was a relative of mine. And so I learned at least to know a little about the elements of chemistry. I think [the fact] that I came to Planck was decisive, at least for my later career, because I decided on theoretical physics. However, I had no good adviser, and later I had the feeling, and have it now even more, that my mathematical preparation was not sufficient.

I attended lectures about function theory by the old Schottky, the father of W. Schottky. The old Schottky gave a lecture on the theory of complex functions. Also, for instance, I attended a lecture given by Issai Schur who was a very famous and very brilliant man, about ordinary differential equations. I didn't understand enough. I was a little bored by this, and after some time I left. And this unfortunately happened in several of the courses. For instance I attended first - it might be it was too early - a course given by Frobenius about number theory. He was a famous man in number theory, and I should have stayed but I didn't So I went out of it. However, I have the feeling that the things which are more in use now, like the different functions which I use in theoretical physics, and the whole theory of eigen functIons — all this — didn' t exist in lectures at that time.

The only thing which I can mention is a year's lecture on the theory of elliptic functions, given by the old Hermann Amandus Schwarz. He was a very funny man, an old man with a big white beard. And he had house shoes on his boots to save the soles. It was very funny. You always heard him through the halls of the university,... Another lecture by Schwartz which was very interesting was a very specialized thing about the hypergeometric series based on the real original Gauss paper. Later I decided to refresh my knowledge about calculus, and I went through differential and integral calculus, in a pretty later stage. That was still with old Hermann Amandus Schwarz. I stayed in Berlin until 1908. I started in 1902. In 1907 I was taking my Ph.D. with Planck.


What did you work on?


This was a very funny thing, a very specialized thing. Wien had made a statement which Planck did not believe. Namely that a semi-permeable plate, that means a plate which excludes certain regions of frequencies - let's say everything between 1 and 2 - gives, if one uses [it] as a piston in a vessel which contains black-body radiation,... a contradiction of the second law. Planck didn't believe it, and explained a little to me what he thought one should do. So I tried to do it. I did something at least. And it was accepted then as a Ph. D. thesis. I am not quite sure anymore what I discovered. I began to work In 1906, so I could have used the exact relativistic equations all right. But I didn' t.

And looking through again later I had the feeling there are quadratic terms in v over c and other terms which appear in relativity, which are essential, but did not appear [in my thesis]. Nevertheless Planck never made any contradiction to this. He accepted it, and later he gave the thing back to me to get rid of reprints.... An excerpt was published by Ann d. Phys., and I have it still, and I have still the original one which was printed. This was, I think, a duty to have it printed and to deliver it to the University.


While you worked on it did you see Planck regularly to talk about it?


This I want to tell you. No. I don't think that I saw him more than two times during the whole year. But this was very typical for him. He gave you the problem and told you aproximately what you had to do to tackle the problem. And then I saw him - I won' t say just two, it might be three times. The last time I said to him, "Now it is ready. I have to have it copied," and so on. This is very typical for him. I have another example which concerns a much later thing. I had worked for some time on the asytric top. According to the old quantum theory.

I ran into a Russian paper - Kolossof was the name of the man. Using his paper, I really could solve it under a certain restriction, which, however, as Planck later proved in a paper which is now published in his collected papers, is immaterial. This restriction according to his whole idea of how many quantum numbers you have to use in a certain system, that is, how many quantum conditions was immaterial. So actually his results and my results were in complete agreement. And that's what he also states.

But I didn' t know anything about his working on this. I think he wrote to me a letter or a postcard about this, telling me "I have worked on this from my standpoint of partition of the structure of the phase space, and I have come to your equations...." But this was very typical,... So this was my first development. Later, from 1908 to 1911, I was interrupting my Berlin stay, and went to Breslau, after having the Ph.D. There I worked together with Lummer, Otto Lummer. At that time Pringsheim was also there, Ernst Pringsheim, with whom Lummer had worked in the experiment there about the black body. Clemens Schaefer was there and Landenburg was there.... Then I went back again to Berlin and began to work on my "habilitation."

In 1913 I became privatdozent. In 1921 I received a call to Breslau as professor. There I remained until Hitler came, until '33. Then of course I had to leave, but was staying quite a time still in Germany. Unfortunately, by some reasons my mother was still alive then, and my mother- in-law was alive, and we didn' t want to leave them alone. So I stayed until '41. It's a wonder that we really came out in '41, but at last we succeeded with the help of different people here - mainly Ladenburg.

Ladenburg was very helpful. Also Einstein was very helpful, and so on. But coming back to the question which you asked me. After 1902 I was of course studying, and going to colloquia... There were regular colloquia. Now let me think it over. Who was at that time in the colloquium? Well, quite a lot of people. James Franck, Gustav Hertz, Peter Pringsbeim, and a man by the name of Westphal. The director, the chairman of experimental physics, might have been Emil Warburg.

He wrote a book which at that time was very famous, it was very much in use— Elements of experimental Physics. Later after his death there was Harold Drude..,. In the colloquium were discussed nearly always, papers which had appeared. They were distributed to different people, according to their interest and ability to give a talk on them. Also the other Lindemann - F.A. Lindemann was attending this for several years, I remember.


Wasn't Nernst there?


No, Nernst was at that time probably still in Göttingen. Later he became chairman not of the physics laboratory but of physical chemistry. Which was, by the way, in one block - all this was together.... In 1907, as I say, I made my Ph.D. It was the custom to send reprints from Ann d. Phys. to different known physicists. So I sent this thing about this semi-permeable plate....also to Einstein. This might have been the end of 1907 or 1908, I got back after some weeks, a card written by him. He thanked me very much for this very interesting paper, and he sent me some of his papers also.

It was a little envelope of this kind, and inside there were seven or eight relatively small papers: "Zur Elektrodynamik bewegter Koerper." The very small paper on E equals mc^2 containing I think only one and a half pages in Annalen, the paper about the specific heats, and about the photo-effects, and so on. Seven or eight things of first rank.... I still have them. Fortunately I still have them. So I began to read. I am again absolutely convinced that I could not at that time understand everything or estimate the value of them. I think the one that impressed me most was the special relativity.


Did both students and faculty come to the coiloquia? Planck himself?


Planck was very regular on all these things. He always came, but didn't say very much. He was not very talkative.... Later, when he had come to Berlin Einstein was very regular also, and very often he picked me up. He was living — all these things are now not existing anymore — in the so-called Bavarian part of the city. Then he came several times to pick me up and to go through the park, Tiergarten, — it no longer exists — to the colloquium,... There were not only the colloquia, but also from time to time the sessions of the so-called German Physical Society.

There of course not papers which had appeared were discussed by other people, but original papers were given. Einstein was mostly the man who was discussing, and very freely always discussing. I remember once he gave a talk about whether a certain function contains quasi-periodic parts, or aspects. After this somebody said to him, "Well all what you have said now is contained in the paper by so-and-so." "Oh, well then all that I said is old cheese." He was very very naive in these things. Whether he did it or another man did it was not of importance for him. The main thing was that it had been found. I do not know whether I should speak about the beginning of it.

This is before I was a student, and these things you know, I am pretty sure.... I used the last days to read a little in Planck' s papers. I have the whole three volumes.... [A description of the circumstances surrounding Planek's discovery of the radiation formula is here omitted.] By the way, to which one do you give the preference now, to which derivation of Planck's law? May I ask it?


Well, I have no special preference. I think the quantization as Debye does it is always the simplest. The simplest. Ja. Taking the number of states between V and V plus dV. Another one of course, which is pretty different, is Einstein's derivation. By the way this was very impressive. It was relatively late - about 1917. This was very impressive, especially in Germany,... to many people to whom I talked about this at that time. In the same way I can tell about my first seeing him, or meeting him, [Einstein].

This was I think in 1909 or 1910. I was still — after my Ph.D. — in Breslau, and studying and working with Lummer. We edited at that time the lectures by Abbe about microscopic image formation. In 1909 or 1910 there was a big meeting which was not the-usual Physical Society meeting, but it was called the Naturforschertag. This was of all natural scientists, and also medicine and chemistry everything. This was in Salzburg, in Austria, where the festivals are now every year. Einstein was invited to give a long talk, of 1 or 1-1/2 hours, about his new papers in which he showed the fluctuation formula consisting of two different terms, and this he proved in two or three different ways.... This was enormously interesting, for me at least, and also for those who were with me. We were together with Schaefer, and Ladenburg and so on. Einstein was at that time a not too well-known man, except for relativity of course. We had the feeling "it is really a very conspicuous proof, to say something like molecules of light."

These things have later been attacked. Of course if you take another statistics like the Bose statistics, you get automatically for the fluctuation the formula which consists of these two terms, But at that time this was the Boltzmann statistics, and he saw that nevertheless you get these two terms, One of them is exactly as if you have to do with single molecules, with single particles. The other term was proven later by Lorentz very very extensively to be the term which comes out of every undulatory theory.


Do you still remember at what time the papers 0f Bohr were discussed? The early papers of Bohr.


I would say at once, 1913, in the moment they appeared. They were at once taken up as enormously strange, but enormously important... I know that Ladenburg and myself discussed these things very much. I cannot tell in the moment how Planck directly reacted on this. I guess not negative, because he was not inclined to react negatively.


You told us earlier that you had heard early lectures of Planck's on blackbody radiation,..


.... I must say that I cannot remember that one had as a student the feeling he had some doubt.


No, but had you no feeling that it was completely new, something really revolutionary?


Yes, I think so. It is difficult to judge in retrospect. Of course one is not too critical if you learn [it by a] very long extended and not absolutely simple way coming from relation to relation and such. But I remember that it impressed me very much, these statements like "the oscillator, as a material thing, has entropy." He really stated, very exactly, the influence of the radiation, and that one can ascribe entropy not only to the blackbody radiation but also to the one particle.

Of course the one particle is only one of the whole group. To answer this question, I would not say that I had the impression that there is something doubtful, that he, Planck, had the feeling "I give you here something very new which is very funny and very complete break." I cannot remember that he just said this, that it is a complete break. One had the impression that one cannot speak of counted probability if you are not subdividing energy, at least in part.

On the other hand I must confess that, as you say, the rest of it was still restrospect. In view of the fact that we know now the things, it is difficult to say how the feeling was at that time. I don't think that he made the thing very convincing. This might have been his method of speaking, of so elegantly describing the whole derivation. This might well be — if I think it over — that we were not completely aware that there is an enormous break with everything that went before, that we learned before. This might be. [A discussion of Planck's second version of the quantum hypothesis is here omitted].

May I say one thing concerning the beginning. It has been often said, you know this of course, that Planek didn't know what he did. He did something very revolutionary and didn' t try to understand what he did. I had sometimes the feeling that Einstein was of this opinion. Now I have remembered, and found, fortunately yesterday, in the obituary written by Max Born, a thing which he has authoritatively told his son.... "Today I have made a discovery as important as that of Newton."