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Interview of Heinz Pick by Kris Syzmborski on 1982 October 5, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/32929
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In this interview, Heinz Pick discusses the scientific style of Robert Pohl's institute at Göttingen. Topics discussed include: Olexander Smakula; Rudolf Hilsch; Richard Becker; Walter Schottky; Wilhelm Jost; Paul Görlich; Wilhelm Röntgen.
The first concern the scientific style of Pohl and Pohl's school. And I have a series of questions. I just... I am very curious to know how this school worked. What was the mechanism, what method, what pattern was used starting from the recruitment of new students for instance.
I can take my example how I came to his group. I had been a student in Cologne, in Munich, and then I went to Gottingen for several years. And in Gottingen I had to do further studies and I did some laboratory work. And one of Pohl's assistants was one of the main guiding laboratory men, who was it? Herwig. He is in Damstadt, a professor in Damstadt. He did especially work on; it’s not interesting for you, no?
He did work and he's still, no he's now retired, but he did work on rare earth spectra. Rare earths in crystals, rather complicated crystals with low symmetry. So there are enormous field gradients… was his main interest. He guided my work and he was an assistant. The normal thing was that Pohl asked his several assistants who could be an interesting student to work with us and so Herwig told PohI you should look at Pick.
How many assistants assisted Pohl?
Very few, I think two or three, not more. Pohl had some additional money from foundations and he paid for most of people who had a Ph.D. from corporations. At that time, it was hard to find work, we had many unemployed people.
It's not very easy now.
Very similar to now. I think there were more at that time. And so, it was a rather cheap thing to get scientists to work. And so there were always few who were not as official assistants, but just a scientific associate.
And so it was Pohl who looked for promising students.
Pohl and his assistants had to look; the assistants had to look for people. And then you were just asked to come to the institute for a little while discussion and start some work. He gave me the problem just to measure the spectra of the solution of the… of selenium photocell. Sit down with some equipment, measure distribution. So I had some work to do —
This was sort of a test or examination.
This was a kind of test. He never said it was a test… very much, but it was. I was immediately accepted as a Ph.D. man, and it came to me that Pohl had no idea about color centers, didn't know anything. And he and a few of his people were just moving to Stuttgart, there was a German Physical Society meeting, and so that he had no time and his ... had no time… but your problem would be to measure the quantum efficiency of the transition of… but then soon people came back I had long discussions with several people. So very slowly, I became familiar with —
But do you have any idea of what type of students Pohl looked for? He was interested in people who were good experimenters or who had good theoretical knowledge?
Certainly, probably as I see it, he looked for people who were willing to work hard to go into the experiments, not…occasionally… some instrument was destroyed. This wasn't important, but it was very important that they did something. And you were keen enough to try what would be done, and I think. this was the main... that they worked hard to come into the field, to be ready for discussions, we had very many discussions, it was a small group, as I said a few assistants and a number of…candidates at that time, only Ph.D. candidates, and the number of Ph.D. candidates were four certainly no more than six, I think something like four or five, plus three assistants, one or two who worked additionally with some very little money. So we had never more than ten people working in the laboratory. And we had quite a lot of people in the machine shop. We have no… glass blowers, so most of the normal and most simple glass blowing work was done by us. I personally visited every Saturday morning, a school in Gottingen which trained machinists so I learned in a very short one-year course every Saturday morning, I learned what a machinist must know.
This was initiated by Professor Pohl?
This was not, but it was considered not especially from him but from the people working there that this would be a good thing to learn to be able at least to understand what the machinists… or to tell them how to make it if something new came up. And the same with glass blowing. I did some courses in glass blowing, there was a man who lived near several institutes, as a private entertainer and he taught us how to make it and by the way I learned quite a lot of glass blowing work and such special techniques from Hilsch. I think he was the man who had the biggest influence on the development on my ability to experiment. Pohl at that time did no experiments. None at all, and as far as I know he stopped rather early to do experiments by his own, but he was in the Institute, discussed with people which means, he always looked at what had been measured, and it could be that he came five times a day if he was just interested in a special thing to inspect what had measured And occasionally one of his assistants joined the group and then there was more heavy discussion and then we had every afternoon. We had a coffee, as is today in most institutes, and he did not join this coffee break but this was a very general discussion of all people who were working in the institute the scientists and we discussed not only physics but all things which had some interest. But this was the main place to discuss things.
I will ask you about this discussions a little bit later in more detail, but coming back to the recruitment, do you know of any special selection of people do. You know of any case that someone wanted to work with Pohl and was not accepted?
No, no. He had to be convinced that the man. Which of the people, it's hard to say. A friend of mine, for instance, Teltov, he tried to come to the Institute, and was not accepted, I don't know why. And he finally was accepted by Jost. And later on he joined Stali…Looking back on the development of this, I would say he did right not to accept him, he was a very slow man, he had more theoretical, intellectual attitude, but he was always hesitating to make some decision or to just go through and try how it works. He tried always to make sure not to fail. He was very anxious to fail at some point. And I was not so overanxious. I liked very much to do something that occasionally didn't work.
And for students it was a very attractive possibility to work for Pohl. What was the hierarchy of prestige at Gottingen at that time?
You see at that time, ordinary professor at an institute was one of the highest absolute independent rank. He could do whatever he wished, with respect to lectures, with respect to science, to personnel and so forth, in the framework of the money he could get. But nothing else could stop him if he wished to do something. And the assistants were really assistants; they had to assist the professor. Nevertheless, and then there was one step in between, if the assistant had worked for several years successfully, he could apply for habilitation, you know what this is?
This did not mean any better position, but it meant some higher reputation, but nevertheless in Pohl’s institute, the independency or the freedom of his co-workers in the framework of the general work which is done was extremely high. As soon as they had shown that they could do something. So if one wished to do something else in the framework, okay why not discuss it. Some discussion more with Hilsch and Molwo (these were older co-workers) and Pohl joined but he didn't really impose on his people, and then as soon as you reached a certain level of experience. You could do…
But for instance one day he decided this was in connection with… the literature of Smakula or…crystals and so forth not Smakula Smekal, I decided to make crystals with additions of strontium. He said, "Okay, go do it." So Molwo he wished to look for these anions, and okay he did, but it was always in this area. You could… strontium and calcium and so forth. You could go do something else, I once had a student, oh yes he did Ph.D. work, Glaser he's no professor…, at, I think…, and we had discussions about interference patterns and we looked for a nice model to show people group velocity so something completely different but at least it was in the framework of a lecture. This was a big interest of Pohl to write books and make nice experiments in his elemental lecture. And I was giving a lecture and this was a problem. Molwo had made some apparatus to show group velocity and I thought there must be something better. And I discussed this with Glaser and he did it. It was a very tough mechanical, he had done some master's work in the United States which was poor mechanical work, it made no sense for me. But he was a very clever man, a very intelligent person; you know he has done very nice work on superconductivity later on, Tinkham and Glover… superconductors measured by radiation. So you see the independency in the type of work and the direction was rather free and I think this is the explanation that in Pohl's school so many sideways were done. Experimentally all was solved. So it was not a straight line given by Pohl, we do that and that and that and then we come to this. But there always people wishing to do something else, a little bit else, and so it came a bundle of things came together. And Hilsch was a very independent person. He liked very much to make mathematical applications to results. He had learned physics in Stuttgart and at that time there was a very good technical mathematics and he learned differential equations and such things and he like always to play with that, and so finally he did some work about photoconductivity and gave secondary… you may have seen… quite heavy on the other hand he always liked experiments and technical work. For instance, he with my assistance, he changed… liquid air to liquid hydrogen. For weeks it didn't work. Finally it did. This he like also very much; he was a very interesting man. Unfortunately he died a few years ago.
How many hours a day did you spend in the institute?
All day. It was completely free when we came. But normally, a few of us had something to do with lecturing or assisting in lectures or just being in the lecture to have discussions with Pohl about lectures so I was rather frequently very early in the morning half past seven or eight at the latest in the lecture hall and inspected experiments and was sitting almost giving lectures, I was giving my own lectures, so for some of the people we started at about eight o'clock. But several like Molwo, he didn't like to be there early. He came at maybe ten or eleven. And then normally we together moved to lunch so we went to the restaurant or to the student's restaurant. And then we had our coffee then slowly we began to work. And then was no end. So occasionally at about eight o'clock or so, someone said oh, let's go to have some meal and then we went to a neighboring restaurant had some meal and came back and worked. Some went home at ten or eleven, some twelve; it was completely free. This was very hard as soon as people got married. But all the women had to learn at that time.
It was the same way in all institutes, not only in Pohl's?
It was similar, yes. It was not in all, you see in Gottingen we had two experimental institutes, and one applied institute, and that applied institute was different. This was more ordinary working time, but the two physics institutes in general it was the same.
When you met at this coffee and had discussions, did you usually discuss physics?
As you said we discussed all the things that happened, politics for instance, normally in Germany we would have discussed this very intensively and would have been fighting quite a lot. But I think the normal discussion was either on something new was reported by some, not officially reported, but he had read some paper or some journal he told about and then it was discussed. But the normal discussion was about the work which was done. You see, several of us were sitting in a coffee room there was a seminar room where we had our coffee. We’re sitting to look at their curves, because several of the rooms where we worked had to be darkened because of photoelectric measurements and so forth. So we couldn't sit over there, so we took our paper went to this room and calculated and drew our curves. So this was always you look at that what happened and so we discussed. So it was always a general procedure to go ahead in the work of all people. Whether it was… or whoever it was. So we knew what the situation at that moment is. In addition we had regular seminars and these seminars were mainly about newer experimental techniques for physics around the field oh we had a special program for several talks which followed a few weeks or so but completely free or any given order so we decided what shall we do?
Did you discuss theoretical problems like quantum mechanics?
No, not at all. There were, at that time, no lectures in quantum mechanics. None at all. You see, I came to Gottingen in '34. Born had left, Franck had left, we had Jost came about that time and he was a little bit interested in theoretical physics or let's say, in the mathematical treatment of theoretical physics so we learned a lot from Jost. We joined with the mathematician Kaluza and they both decided to write the book on the Introduction to Mathematics and because what the mathematicians told Hilbert, Klein and Weyl… we couldn't understand so we were happy to… was a wonderful man but he had… we knew his book. It was a brilliant book and this was one understood. But Hilbert was far away from us. And so we were very happy that Jost and Kaluza wrote this book which was a very nice general book for physicists to make use of mathematics. It was a rather low general standard and I do not think that one of the people that ever worked in Pohl's institute had deeper familiar knowledge about quantum mechanics, the wave function was something —
What about Becker?
Becker came later. Becker was very special teacher in mechanics especially in electrodynamics he learned optics in Gottingen and I remember that I showed him… not reflection Beugung diffraction at a slit.
Yes, I know. Diffraction.
Diffraction, yes. I showed him diffraction at the end of a plane he came to me. “Oh Pick could you show me is it possible to see with your eyes the diffraction at the end of a plane.” Certainly, I've done it in the lecture. And so I made some equipment put it together and showed him and he said ah… and he was quite happy. So he learned optics. He had been working in industry so he was a very good theoretician but had not a broad training at that time. And the same with thermodynamics. He never had really learned thermodynamics. And then he began to study. And then he wrote a wonderful book on thermodynamics, so we got quite a lot from Becker and from Jost who had some more theoretical interests.
.... working on magnetism, I think.
Yes, he worked and created a group and especially Sauter and Leibfried. Sauter was for a period of time the only man in Gottingen who knows, the only man who gave theoretical courses on mechanics and theoretical I think it was thermodynamics and electrodynamics. And occasionally optics. No quantum mechanics, he had no lecture on quantum mechanics. Becker has never given a lecture on quantum mechanics. So we were completely free of it.
Did you meet people from these institutes at your seminars?
This was on the second level not on the, we had colloquia, and there was always a rather interesting public and lecturers and there was quite a lot of discussion mainly stimulated by Pohl. Pohl was a man who was keen enough to ask crazy questions. “Ah, I didn't get it, please tell me again.” And then he put the several points. And then we realized that we just hadn't understood but he was a man who was keen enough to ask these simple questions and then things became much clearer. So he was a very stimulating man but he never on a very high theoretical level but this was true for the most of the people staffed at Gottingen at that time. So there was if you take the time before I came… from my own experience. But there was a complete separation between few highly intelligent persons doing theoretical physics. Something very crazy very special only for specialists and then the real physics. And that's what we did. And this was as far as I can think the situation later on also. Very slowly theoretical considerations came into experimental physics. The only thing that we did was mere mathematical treatment of experiment but not real theoretical.
Do you remember any discussions about F-center models before the Bristol conference?
Teichmann has asked me this question several times and first I reacted very spontaneously and found out I was wrong. I had shifted in history. So I am at the moment quite unsure when we, it must have been around '36-'37 when Pohl and Hilsch had been in Bristol, but I don't know how far we have gone because in our publications following that time, nothing is… but you must see we had man—different discussions about what it is in the microstructure. But this was just a play for us. Many ideas were not good enough to write down or take seriously because you couldn't measure it. For us, the situation was if you can measure something, it’s okay. Otherwise it's noise, hypothesis, speculation, however you may call it, but it has no worth in itself until you can prove it, observe it. So it may be that we discussed it in detail, but it has not any real effective reaction.
I think it's usually so that during the discussions you talk much more than you publish.
Oh, yes. Now the publication is something special.
Yes, that's my next question, how the publications were written. But my impression was when I read the papers published in the 20s and 30s that they were very cautious in making any theoretical statements. And I just wondered if some problems were discussed but not published.
As I said there was much discussion but only very little came into the published papers. And as you see the published papers most of them have the same general type, that is, Pohl's type.
I wanted to ask you how technically it was done, how a paper was written at Gottingen.
I would say a lot of papers, a large fraction of papers, were written by Pohl, if had done the work or not. Especially if the man who had done the work was not able to give reasonable manuscript—he'd throw it away and write it by himself. But if the man who had done the work gave a first draft a reasonable manuscript then there was a discussion and then Pohl had his very personal meaning about how to write first of all you had always to refer to some work by Hilsch and Pohl, or Gudden and Pohl and as we said years ago and so forth and slowly you started. And you can find this in all papers. So nevertheless also if you were more capable to write your own paper, it was at least fractionally and in the whole construction it was a paper with Pohl by Pohl or in tight connection with Pohl. Only people who had been working for a longer period of time and had become more and more independent like Hilsch and Molro then they wrote it and he discussed it very carefully as well as from his understanding of physics as from the syntax. And so then always there were some changes.
I'm interested in what Pohl tended to eliminate from the papers he wrote.
Do you recall any specific case that people wanted to tell something a little bit more than Pohl would accept?
No I couldn't remember for the moment some special case. Because it was so in the normal case that nothing was very special and there was no fighting. Pohl was a very strong personality. And in formal times, people feared Pohle. They began fluttering the moment they heard he was coming from his apartment. He came down the stairs; this was not true for a certain group of people like Hilsch and Molwo they were very soon completely partners but the younger people practically all those who did one work, Ph.D. work or so they always were very anxious when he'd come. This changed in the course of time quite a bit and I would say especially after the war his general attitude was very much changed. I had good contact with him before the war. This began when he one day called me and said “oh, Pick you have assisted in the course in the lecture please tomorrow you will have to go for me. I am sick, I can't go!” I was not in any way prepared. So what should I do? I went there and gave the lecture. And roughly from that time on, we were partners. He accepted me completely and whenever I said something, he took it seriously. So it was rather early, I was just a young man but this was the period of a certain transition in his strong attitude, and he became more and more gentle man, but if take this there is not much discussion about what should or should not be written down.
Because everybody knew more or less what he would accept.
Yes, yes. He was called lieber Gott. He was joking, but there was something in it. But you see, he always took full of care that the people working in his institute came to reasonable positions and he had contacts later on with all people who were interested by themself so he was the big father of a good family.
As he was getting older, I think it became more difficult for him to introduce new methods.
And I am interested specifically in the work done in '39 by Jensen in Jost's institute.
Jensen was in…
Jensen was in the second institute
But not in the first. Oh you said Jost.
Do you remember Jensen's work on the paramagnetism of colored crystals?
I do not remember that we discussed that work at that time. It has certainly been discussed between the older members because between the assistants of Jost's group and Pohl's group there was good contact and also between let's say Hilsch and Molwo and myself and Sauter and later on Becker's people and I had personally a good contact with Becker. There was no contact between Becker and Pohle. There was some contact between Jost and Pohl and they wrote some papers together not on solid state physics but on teaching and so forth. So I don't remember the paper of Jensen at the time. It became more and more interesting for me much later. So if I say oh yes I remember then it's something that happened much later.
Because this was a new method which from theoretical view was quite interesting.
It's interesting and became very important.
Later on because of resonance methods, but what about resonance methods? I heard that Pohl did not get interested.
You see, this came up after the war, and I learned about the existence of resonance when I was in the United States in 1953 and in fact I saw it some care for the first time in California in 1953 I visited Kip and Kittel and I had never seen such equipment as microwave techniques big magnets very big in my consideration so Kip told me what he was doing and I… and then I came to Kittel he was a very kind man a little big stuttering so it was hard to follow his talk but he went to the board and gave formulas and gave a wonderful picture. I went home… and began to study what that was and this was the stimulus for me to go further from that what I had done in Gottingen before the war and after the war also. At that time I did some x-rays in… and so forth and for that time I was for several years the eldest member of the institute and I had to take care of all the Ph.D. work because Pohl at that time had practically retired to do work on his books. Occasionally published one or the other, but I remember that many times we were sitting in his office I… and others and we tried to explain what holes is and so forth. This was not really in his head. And so we tried to bring him as near as possible to what was going on at the institute but what really happened… we decided completely independently. But he was interested.
But even going back to your first papers in Gottingen my first impression was when I looked through all Gottingen publications that in your papers you cited you referred to the Schottky and Wagner and I think it was for the first time.
It was for the first time. This is probably because it must have been shortly before I finished my Ph.D. work that we had a meeting of the Physical Society of the northern part of Germany in Klaustal in the Harz mountains. And I think it was it must have been about '38 or so. I don't know exactly. At that conference, Shotky appears. He had been rather unknown for us completely especially he had been as far as I can remember that it was told he had been away from the public because of some brain disturbance in some hospital or so. What I remember was told so I was a little surprised there, and Pohl introduced me to him. I didn't know what his interest in that field was because I didn't know the letter that Shottky had written to oh. So it was at the beginning it was completely foreign man for me, but Pohl seemed to be interested that Schottky learned what I had done. So we were sitting in a restaurant with a piece of paper and I told him what I had done. And I believe to remember but it's very unsure that he gave some opinion about the structure but…
But anyway I think that these two lines of development meet about the time you published your work on F-centers, the work on color centers and work on the mechanism of diffusion in alkali halides and you brought this —
Well it's more or less the first group of questions concerning Pohl's school and his scientific style. But what I'm interested in how different was for instance Jost's institute and Becker's group; did they have different habits/different style?
Jost was always in some opposition to Pohle I think that they had no real personal contact. They had to work together because they were main physicists, but he was in principle anxious he always felt the influence of Pohl to be too strong. Pohl's influence was strong at the University. There were three people one of the chemists… Pohl as a physicist, a medical man… a physiological chemist, and these four men they… the university at that time, which was a good thing because they could many things which other people could not have. But Jost was an additional person and he was always anxious to be also a member of the community and then he had a special character, he could be a very angry person. And then he came… after a year whole-faced, dark, and occasionally he was shouting terribly. I remember once he had some discussion I don't know the… he had some discussion with Pohl and certainly he was so angry with Pohl that he left his room shouting running through the corridor down to his group in his office. It was an experience.
But it was a discussion about physics?
It was certainly no discussion about physics at all. And there was not much discussion about physics. No discussion with Becker and Pohl, some discussion with Becker and Jost not very much and what else Jost and Pohl very little. There was some discussion on the second line. For instance, I had much discussion with Telltov and with Hellviger who was later on not…with Pohl but then he was with Jost and so forth. So we all knew each other quite well for instance Sauer who did the work with Stativ on regards… for mixed crystals… so we knew each other and met occasionally at lunch also. And there was a deep discussion on the physics we did, but what we did do occasionally we visited the other side and we found that I would say the quality of equipment and I would say the order in the experimental array was much better than it was in Jost's group. There was so much dust and we didn't like that. So we were always proud certainly and the others were angry or whatever it was. There was always a competition.
You know the opinion of people from Becker's institute the first institute is governed by a dictator.
By a dictator, yes.
And that I think discipline in Pohl’s group was much higher than in Becker's group.
We learned discipline very early and we kept it.
Maurer told me that there was a joke that they had a notice on the door that…
I will tell you. Becker's group was anxious if you wish democratic group and I came together with Becker much more intensively after the war and this started because at that time many soldiers coming back looked for acceptance in the university and we had to select too many and in physics this was done mainly by Becker and myself and so all students came to Becker and nearly all students came to me. And we had just a free discussion. Whatever way you thought… a series of questions about physics but we tried to find out if the personal structure was good enough to take such a study. And then Becker and myself we came together and we… our notes about these different persons every day we had to take… ten or more. And… he was a very different person from me. And his activity was in pure theoretical physics and mine in experimental physics but we had some estimation and I was in his family and my wife and his family quite a big but never Pohl but he accepted I don't think that he liked it. But I was independent enough to do what I liked at that time. So he didn't oppose. So we knew each other well and I think there was some estimation. What the story is when Becker died and his not Becker Koppeman, Jost was followed by Koppeman in the Second World War, and the relation between Koppeman and Pohl was very, very good. A very personal contact and Koppeman was a very bright and intelligent person and he grew to take Pohl without going too deep. And Pohl respected Koppeman completely as an extremely excellent experimentalist and physicist and Koppeman... was dirty. So this was still the same situation. But Koppeman made wonderful physics which he could explain also so we began to see that he was an extremely good man… When he left to go to Heidelberg then he was followed by another man, what's his name? Oh, I'll get it later. And he did the following. He asked his assistants to come every Monday morning with a fresh white laboratory kitted.
I don't know how it is in English.
And then the door to come into the Institute from now on had to be closed and you had to ring the bell the secretary came to the door and opened the door. This was completely unnormal for us. All the houses were open. You could go where you wished. From now on the second institute was a closed community and the whole attitude was nothing could be done in the institute without the director sitting taking care of things. Between the rooms of the theoretical group and this… were on the same floor there was a few steps and a door. Normally this door had been open and especially Koppeman had been interested in theoretical physics much more so there was a going on and back. And then the door was closed and then the theoretical people made a big paper that said “Hier verlassen Sie den demokratischen Sektor.” At that time Sektor was part of German, the Russian sector, the American sector, the British sector, the French sector, and so they wrote "Hier verlassen Sie den demokratischen Sektor."
This was not to the first institute, but to the second institute.
Nevertheless, the first was on the first floor, and second was on the ground floor. And so Becker's connection was with the second institute. Nevertheless, there was little connection between Becker and Pohle But between the people of Pohl's and Becker's group, there was quite a lot of contact. But it was interesting when Koppeman left, there was an intermediate period of time before his successor came and I had to take care of that institute for a period of time. And I saw how it was. They had put out all the nice instruments as far as they could be transported and all the rest was there. It was a mess. But nevertheless, they did wonderful physics. And then Pohl retired at his 68th birthday… and he had recommended to the faculty that I take care of the institute and I did. The next morning Becker came for the first time to the first floor. Ah, hello, Pick. What are you doing? And I for the first time brought him around and showed him what was done in the first physics institute. You see this was the relation between Becker, Pohl and Becker and the others.
You don't know from your own experience what the relationships were between people in Gottingen before '33. But you mention in one of your papers that there was some sort of competition between
This was… was reported that Pohl, Franck, and Born I wrote… friendly competition. This still was existiert, Franckte and asked what does it mean? So I came to this information.
I know from… the paper that was not published that there was some incident with… work published in '33 concerning… that there was some conflict between Molwo and Frohlich. You don't know about that.
No. I don't remember that.
Do you know anything about broader relations of Pohl to other groups elsewhere outside Gottingen? In particular, I am interested in his opinions about Smekal's work. Did he follow the work done in other centers?
I don't know if Smekal's work was really known in Gottingen and if I became familiar with Smekal's work by Pohl or the discussion with people in Pohl's group at least doing work on these D centers I read these papers and at least if by my own discussions I don't know. We thought this is not what we think is a good experimental work and so forth.
Can you explain your attitude why did you criticize these papers? Because I am interested in finding some objective measures of the quality. I think they were not as good papers as at of the Gottingen school. There was too much speculation probably. But when you read them first what was your impression?
It's hard to know what I was thinking at that time. But I think in general it was he measured a few spectra curves which moved a little bit, shifted… without a very strong parameter on one side and… on the other side. You see, we always we had learned you have to measure a wonderful… of measured points, before you sign a curve. Not three points it doesn't make a curve because you have a theory or something like that. But really measure it, so you have measured your curve 10 times or 20 times to be curve it is. And then you have to ask what is it? What have you put into your experiment? You have to change the crystal to be sure. And this is indeed one of the main attitudes you must be that if you publish that what you tell is the truth. In the framework of our knowledge. So you have to be sure that the point is correct and that seemed to be very weak in Smekal's in the work of Smekal’s group. So it was broader and we found oh you can do a little bit… but this is not a strong controllable parameter. This was the basic meaning and then when we found that there is some shift. And I started to do my measurements I could say why is there a shift or why is there a broadening. So I gave my manuscript or letter to him but I finished very soon my discussion because I felt that there is nothing else to come out. And this was the general attitude, there was no real respect.
Did you have any contacts with Smekal?
We had no personal contact; I don't think we ever met him. I think we exchanged two, maybe three letters. I think the first letter was exchanged by Pohl, and then I wrote two letters and there was one or two others not by me what was the other man.
No, I don't think so.
There was a whole group working there.
And then in addition we were not interested in mechanical work not at all neither elastic nor plastic deformation. We didn't find this of very special interest. So there are two reasons, one was the quality and the other was the special field that didn't seem to be interesting. But this was such a general attitude in an institute that is strongly guided by a few strong persons. It is not objectively right, I agree. But this was the attitude.
I know very little about Smekal's school, but I know that he had a very difficult personality. He engaged in arguments quite often. And also he wanted to explain everything using one not very precise concept.
Exactly. You see, what we did not like and we learned this from Pohl certainly I would say from others also, but what we did not like to make a few points from a measurement and then a lot of speculation and finally we know all things. There was very little amount of real knowledge and a mass of speculation and explanation and this was the same as with theory. First measure something real and if you are really sure then you can do some speculation but wait the next man will do other measurements and will… change it a little bit. So it's enough time to come to speculation first it's kind of a moral attitude what is the task of an experimentalist to search good experiments that in fifty years it's still a reasonable good thing and not in ten years, all will forget it. This was forbidden; and I think this is the strength of the institute that we always were quite sure. So if we came to a conference we could precisely explain it is this way. You see my work is an interesting example. I did quantum efficiency. And what did we expect? All people would expect either one or smaller compared with one, or maybe some little change against these two… and I measured I was really able to I got something near two, it didn't fit into any picture. So I told finally I… told it to Hilsch… Do it again. And then Pohl came, that is, he told Hilsch oh please Hilsch join Pick for a complete set of measurements. So Hilsch came to my small room and we did all steps from on the first beginning we worked all together. We were very anxious when did Hilsch find the fault in my… couldn't find it? We measured at one point… eight or something. We didn't know. And I too. It was a few days or a few weeks later I was thinking it was so trivial… only in the morning just coming up I always had the best ideas when I then I said it's very simple. One gives the electronic… the other takes it so the spinor and the acceptor are the same things. I went to… I was very familiar with Stasir played chess every weekend early in the morning before Sunday. And nothing against it. Then slowly we tried to make this clear to others. And it was unacceptable.
It was just before the Bristol conference because Pohl brought this idea to Bristol.
That the acceptor and the spinor were the same things. This was very proud that I had brand new idea.
What do you know about Pohl's attitudes and opinions about other scientific schools in Germany and outside Germany? What was Pohl's ideal of a good physicist? Who he respected most?
I think there was a strong competition between Munich and Gottingen. Munich was governed by Gerlach. And Gottingen was governed by Pohl. People coming from these two schools spread over Germany depending on the contacts that these two persons had. Pohl had as far as I remember a good contacts to the Berlin Industry, AEG, not so much to Jiemins (?), but some, Wien had contact with the optics industry and was also for instance came later on to Kiel which was a company making ultrasound detectors for ships under water this was at the beginning of the war before this company had started. In addition to the ultrasound detection they have done normal sound detection on planes with acoustic detectors and from they made a jump to infrared it had been done before I came there and Pohl was the man when I said for certain reasons I would leave Gottingen gave me two addresses the one was… in Dresden, Stazy was there at that time, Pohl gave me the names of the person I should call.
Smakula I think was at Zeiss also.
This was Zeiss in Nina, and Stasis was at Zeiss in Dresden. And the other was Dr. Hecht in Kiel. I visited first Zeiss in Dresden, and had a discussion with Gerlach was later was one of the highest personalities of the scientific world of the Deutsche Demokratische Republik. He’s still alive. The other was Dr. Hecht. This was not the Dr. Hecht that published with Pohl but this was a completely different person. And Pohl and he knew each other. He had good contact —Hamburg boat people. Much more than I knew went on. But he had broad knowledge and he had quite a lot of guests people like Gyulai (?) from Hungary and so forth. So he had quite a lot of contact but if you look for the physicists in Germany who was a highly estimated person in Germany he always told me that he had excellent contact with Sommerfeld, but this must have been a purely private contact because there is a nice picture it was in his home or his office. He and Sommerfeld in the mountains somewhere not just climbing but walking through the mountains and so there was probably a very good contact without special theoretical feel. By the way he estimated Lenard, Lenard at that time was attacked by many people especially because of his political attitudes and his lines of force. And Pohl was one of those who always praised the high quality of Lenard and I remember that there was real fighting but Pohl was very strong and said oh, forget it, as a scientist he's a brilliant man in such things he was always independent. He had a good contact with the Berlin people still.
He came from Berlin, so he worked with Prigshein(?) but I don't know who he considered his teacher and master. He was impressed by Rontgen's work.
He was very impressed by Rontgen's work, yes. And he knew Rontgen's work quite well. He knew that nobody could understand Rontgen. It is very complicated if you read these 100 pages paper, you understand that it was very hard and very tough, but he knew quite well and so I think he knew all people in Germany but which people were especially respected by him I don't know. If I could go through the names I could only make a few marks but in fact Gottingen was rather isolated.
I put it here in one of my questions, the isolation; because this I think that there were very few physicists that Pohl referred to in his papers and these were Rontgen and Lenard in the beginning. And then his work became so almost autarchic. He set his own standards. Nobody could even interact with him because the quality of Smekal's and Pzibram's (?) work was different was much more descriptive and not…
It was more the older type. You see in a certain sense Pohl's activity was a beginning of a more strong type of physical experimentalism with the exception of the people that did spectroscopy and atomic physics.
Like Franck and many others in Germany and other countries. But outside the atomic physics and later the nuclear physics it was one of the most severe experimental.
I have one speculation in mind but when Pohl started his work on alkali halides he could not have been sure that he was opening a new branch a new field of physics.
I don't think so. This came up slowly.
It's very difficult. But it's just a speculation, he must have had some attitude he was trying to become very independent, work in his own field and without any interference from any other people, that's my original impression.
In my desk I have tapes I asked Pohl about the first years of his Gottingen period he was invited to go to Gottingen during the war, or nearly the end of the war, then it took years until he finally came.
Yes, he came in '19.
It was certainly a very tough period for him. Because there was some personal pride in Gottingen in physics and in the vicinity of physics. Pohl was a young man and a tough man all attitudes of a dictator. And he gave me some information but closed informations and so I understand that he had difficulties as to well to be respected as to be really accepted as an outstanding person. And this gave a reaction in his person to show that what he can do and so he was very ambitious and went his own way. Always trying to be… a few very personal things connected with his marriage… he married the nicest girl that could be seen in Gottingen she was honored by all people in the university and otherwise. This again gave some conflict to his surroundings and so she was much younger than he was, 18 years younger, at that time it was surprising. And so forth you see his own personality his attitude his fighting against the surrounding all this seems to me as a big influence on his attitude so he was I think very happy always to find always people who were willing to join him and to go with him and just through and you find all these names just from the beginning. The first was Gudden who was working at the Institute of Mineralogy and then joined Pohl and he was a good man a strong man and a man with fantasy. So if he carefully looked through these publications that there is always influence from his co-workers with ideas which he accepts and then goes further and something new. So it broadens out. For instance the idea with crystal growth this was not primarily Pohl's idea. But there was a man telling him, there is a young man working with Tomman (?) he possibly could make crystals for us, so…
It was Kyropoulos?
It was Kyropoulos who then joined Pohl’s group.
I think before Kyropoulos joined Pohl’s institute, there was some contact with Vesey.
This I have never realized. I don't know. But this was the breakthrough. And you see Gudden had a friend in the institute of mineralogy. Who made contact to get… so this work on diamond this was I don't know now much Pohl really did. But at least he had a good understanding if there was something which could be good for our work. You see this is I think the best quality of Pohl to immediately realize what is good for our work and to all things to come to a connection with these people or with possibilities and this is the same as all the experimental development so he understood to stimulate his young co-workers to give the whole fantasy and the whole constructive
But to a certain extent they had to subordinate to a general —
At least at the beginning there were concrete. This is not true for Gudden. I think Gudden was old enough and Pohl I young enough that it was probably from the first beginning a friendship and partnership. And this also is true for Hilsch. Hilsch had worked in the machine shop of the institute as a student and there Pohl met him and found him very clever machinist and so he was independent very early. But for instance Gyulai(?) was always friendly. And did what Pohl wished.
For him it was a big chance to be able to do good work in Gottingen.
Oh yes, this was a big chance for many people who came from outside.
Because of his reputation very soon became very high but physicists colleagues of the other fields oh this crazy physics.
These people were coming from abroad. There were very few people coming from other institutes in Germany.
The reputation in Germany was always less than later on… the same than it was in other countries. We had more friends in England than we had in Germany…
Yes but I think that to some extent that was Pohl's policy.
If it was his policy or the result of his personal attitude I don't know.
How do you think that he was more open to foreigners because they were not in competition?
This is a part of the picture I think so, yes.
I know for instance one year Gregory Wannier Pohl came to Basel and gave a lecture. He travelled to the Soviet Union and had good contact with Leningrad but I don't know about his close contact with other institutes in Germany.
I think at all conferences of the Physical Society Pohl's group appeared. He himself gave lectures. And as I told you in Stuttgart there were four lectures from the Pohl school.
…I remember this from the bibliography.
So they gave their lectures, but there was no strong reaction. So it was a rather complicated feeling of the co-workers who in the group itself feel quite sure of what they did is okay but on the other hand they realized that the respect given from outside was rather less much less and we younger co-workers we projected part of this to this figure of Pohl because we knew of his strong attitude and he repelled easily people who were not on his line. We at least understood how to manage him directly or indirectly because we worked together every day. And then you learn how to make things, but people coming from outside they feel easily repelled.
This… isolation appears very often. For example in Hitsch’s talk in Urbana in '65 I listened to the tape and he said that in the early 30s they felt very isolated because other people were running through the library to look through new journals and seeing if other people did not anticipate their results.
They didn't interact very much with any other school and they felt isolated. They had a lot of time to work to make good experimental work. But then, when this isolation was broken, I think in the late 30s?
Yes. It was a little bit broken in the late 30s I think through the contact to Britain. And then strongly after the war.
Do you remember how these contacts were first established with Britain?
This must have been through the conference in Bristol. And I think…
Pohl was already invited to this conference.
I cannot remember British people came to Gottingen to look at us.
I think that Mott did not want to come to Germany at that time, for political reasons. But he invited Pohle But this was Mott's initiative. But you don't remember how it was received by Pohle.
I think we all, and Pohl also, was very happy to go to Britain. You see had very carefully prepared his talk and some additional remarks. At that time he engaged privately a young lady… a Hungarian girl about 25 years of age wonderful nice girl all were attracted to her, and Pohl also by the way, and he engaged this girl to teach him English. So every morning in his home he had a lecture was taught by the girl to speak English. So before going to England he had tried the best to learn English and this girl I think for a year in his home and gave him information about the English language.
What was her name? Blanche…
Blanche Semptreur(?). She was a very attractive person to us young physicists. We always were trying to come together with the girl. And Pohl was a little bit anxious that we had too much interest with her. And occasionally he realized that he was unable to entertain the girl and then asked me and my friend Rauch who was doing some work on the oxides spectroscopic work to take the girl for the weekend for a dance. We did it, and he paid all. And then after the war, I made a visit to another country with Pohl also to Bristol. And we tried hard to find out the address of Blanche Semptreur who meanwhile had been married in England and finally we found the address you see we were very interested to see the girl what she had done. But this was a very short visit and this was the last contact.
What year was it, this first visit?
I think that at a certain point of the development of color centers —
So I think that at a certain point it was necessary to use a different approach continuing Pohl's approach it would lead to nowhere because experimental facts were more and more complicated and you had to use some theoretical speculation to propose some order and that's what Seitz did. And Seitz in his interview he suggested that perhaps because of this new theoretical insight, you went back to color centers research.
You see I left Gottingen because of the political situation I had either to try to join the party complex to—or to leave Gottingen. And I left Gottingen and worked for five years in industry. Did… and so forth. Then I was I had no contract so after the war I was free completely free and lived as a private person in the home of my wife's parents. I always had contact with Pohl during the war I visited him several times and always had the hope that I could continue some of the work which was interrupted at Gottingen and so one day I got a letter from Pohl telling me we are now in the situation to start our work again. They also had to stop for a period of time. Seitz visited him, and why don't you come to Gottingen. I was very happy; I was just looking in Frankfurt for a position as a teacher in a school. I thought oh I've learned enough physics and enough mathematics for a school. I have tried to find a position. And I had contact with the group in Weilburg (?) a small place along the Rhine River and hoping that possibly I could get a position there. And then I got a letter from Pohle and I was real happy and said yes I'll come. Then I began in '46 left my family and wife to… to Gottingen and started to work. The institute at that time had a few people like… and other young men whom I knew from my visits who had partly… Stuckman had… activity he had taken some work upon zinc oxide and such and so I began this beginning was primarily reconstruction of experimental setups. Part of the institute had been during the war for the government and was closed and closed for the public. Molro was working in that and other people…
What kind of research?
I never really have got the experience because it was close during the war and nobody told me and after the war it was still closed and finally it was taken by the British. There are some reports in crazy journals of Herman Goering who was one of the man who wished to make a very big science institute in Berlin or in Munich and Pohl in fact was selected as one of the persons to take over I think the optics branch in a very broad sense and he was not really willing to go to Berlin but to stay in Gottingen and he finally succeeded in… persons accepted him to stay in Gottingen and to run a small group in Gottingen. But this was closed and was closed by the British Government. So nobody came into these rooms and Seitz has told about the batteries and so forth. And the other things had dropped down; there was no need especially for liquid air and so forth. So my work and Molro had left Gottingen as a soldier during the war and then… was invited… so in Gottingen there was only very little Stuckman who the only person who had some experience but he mainly done only photoconductivity in zinc oxide and similar things and he began to be interested in semiconductor.
And Petrov was there.
Petrov was a guest and he was there during the war. But I think he had to leave near the end of the war and when I came we had Pohl had showed me a lot of papers of Petrov. Oh we have to do something please go through this and find out what we can do. And I had hard work to do to select and find out what he had done and what the ideas were. And then we wrote an article under the name of Petrov.
It's one of the most frequently cited articles in aggregate centers.
And then information from the United States slowly came over. And so this was mainly the reason we decided we have to publish it we cannot leave it. Petrov was not available we had no contact with him at that time so we had to publish.
What he did later?
He was professor of physics in Bulgaria I think in… and I think I didn't meet him after the war but I had contact through correspondence. He has invited me twice to come there for some conference. In fact I have not been there. One conference has been visited by one of my co-workers but in fact I have never visited him I had contact with his son-in-law who came to me on a conference we had in Berlin. He was a young man coming to me. He said hello I'm the son-in-law of Petrov and then best regards from my father-in-law and so forth. And then he gave me some more contact and he was always interested that I would come but I was not really interested. I was in several of these eastern countries but I have no interest in going to Bulgaria because I had not the feeling that I could learn anything over there. And my personal contact with Petrov was very little because he had come to Gottingen during the war and was only a visitor occasionally. So the only tight contact was with his work to bring it to a manuscript.
What is interesting in this paper of Petrov is that you didn't try to interpret the data and it was just reported in the pre-war, Paul school style. At that time already Seitz' paper had appeared.
Which was unknown to us.
You didn't know about his '46 review paper?
We didn't have it at the time. This was the crazy situation that we very slowly came to contact and I told you about the conference in '49 that we were so hungry finally to see people whose names we knew and so you have seen the program and this was an attempt... we must come into contact with… journals, nothing was available at the beginning. So very slowly we had the possibility to make contact and so for the first time that I have ever seen… Maurer came also and the Germans came and Schottky was one of the persons who came. We were very wondering that he came… the names. And so we didn't know what had been done so slowly we came upon information and it was very complicated for us to get… which has never been published… Seitz and I don't know who mentioned it to us and then I wrote a letter to von Hippel that we could get a copy. And I think we got the copy but Pohl must have kept a copy I have never seen it later on. So it disappeared from me. But we knew what had been written and slowly we realized that so forth. Dorendorf's work and then we really inspected what was on the long wavelength side of the ultrasonic absorption. But normally we were just a little behind.
For some time. But would you agree with Seitz that perhaps you would not work in color centers if this new developments didn't happen in America?
During my last years in Gottingen, I started a new field these organic crystals and I did work on the conductivity… napthalene and so on. And I thought it would be wise to take different type of material and I looked for the simplest organic materials and the idea was assume we make the jump from these inorganic crystals which normally are something similar to minerals… if you wish to make a jump we have to go to organic chemistry because there you have a wonderful chance to change… and make a whole set of parameters to… many principles… and I started I would say with the wrong idea can we come from normal organic material like anthracene which at least available as a crystal or easy to produce as a crystal to finally crystals with high electronic conductivity and so we investigated conductivity and tried to find is there some activation energy this now was quite common in our mind that… is a principle question? Is there activation or not? And is there defect structure and so on? So I just started to grow crystals and to make investigation on these organic materials.
So normally you wouldn't have continued work on alkali halides.
I continued and I found a few questions and for me you know the work of Matisse and so forth on photochemistry. But one 'question seemed to be but this was given by my work during the wartime what is… radiation? Why don't we have some luminescence from the F centers? And it was quite clear if you could hope to find some luminescence you had to go to… I was an expect so it was quite normal to ask the question is there efflorescence what is the efficiency if there is one, is it small or is there nothing. And then would come the question what is the reason that it is there or not there. So I started with the work of… and I think it was Christmas '52 I planned to make the experiment I needed two spectrographs. After the war I had… institute he didn't like to agree but finally he did and Becker on the spectrometer we normally had built our equipment monochrometer and I said now we have to go further and I have a nice offer to buy an instrument completely finished and I said Pohl we have to try this. He didn't like that, but at that time I was strong enough to say we have to do it. And he agreed, so I bought that instrument. And then we had some infrared equipment and so forth. And then I these instruments were distributed to do some special work. And when Christmas came I thought now I could buy equipment together so I put my… laboratory room where I worked and put together equipment whatever I needed for the luminescence and it was in the few days before Christmas. I was sitting there working and working hard putting together all things. And then finally I was ready to do the measurement. I fought fluorescence. I calculated it, it's small. I… and then I stopped it, Christmas was over I had to build the instrument… kept it from me. Pohl knew what I did certainly but didn't publish anything but I knew and then appeared a paper it was Klick that the quantum efficiency of the florescence probably is there but the efficiency is very small, less than l% or something like that. I was quite happy. And then '53, I came to the United States and I also visited that group and I went to the laboratory and they showed me how they had done the measurement. They had much more equipment than I had at the time but I had… was the main reason. I borrowed… from Kiel one of the last… and it had to be cooled to low temperature to nitrogen temperature and I went to the laboratory and looked at it and said… why do you get such small quantum efficiency, and then immediately I realized I had forgotten the angle. They had calculated only the radiation which they had measured and forgotten there was an isotropic of radiation. Not isotropic, but at least the… in space you know what I mean. And I told that to these people and much later on they had measured it and people from Netherlands had measured and I was next was going to Stuttgart I had no chance to… further in Stuttgart I immediately it was still in Gottingen I immediately started a young man who made his… degree, Becker. And then he came with his physics equipment. We took all our equipment from there to Stuttgart and finally we gave it back but Hilsch was willing to give it to me until I had started my own equipment. Because I came here and there was nothing… completely new one had to build a new building so it was very little available so I took what I could get and Becker started and he was a very slow man careful but very slow and I had to do so much work building the faculty and so forth so I was happy to everyone who did the measurements and then meanwhile published from the first but I'm quite sure I was the first to have… the quantum efficiency. Stuttgart okay this was one part, this was one thing you could do. Finally we measured ...