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Interview of Karl Herzfeld by Bruce Wheaton on 1978 May 11, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/4669
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Education at the Universities of Vienna, Zurich and Gottingen; taught at University of Munich 1926. Early interest in the application of statistical analysis to physical problems. One of the earliest emigree physicists to come to America, taking positions at Johns Hopkins University and the Catholic University of America. In addition to scientific articles he has written a number of studies on the philosophical and theological implications of modern physics. Also prominently mentioned are: Niels Henrik David Bohr, Kazimir Fajans, Fritz Hasenoehrl, Theodore von Kármán, Frank Rice, Arnold Johannes Wilhelm Sommerfeld, Otto Stern, Edward Teller, Theodore von Kármán, Wilhelm Wien; Los Alamos National Laboratory, United States Army, United States Navy, United States Office of Scientific Research and Development-National Defense Research Committee, Universität München, Universität Wien, and Universität Zürich.
Professor Herzfeld, you were going to tell me something about your grandparents.
Yes. My paternal grandfather worked as a doctor in public health. The separation between Austria and Hungary occurred in 1878, and therefore, he had to leave Guns and move to Vienna, where he was the physician for the police. After that, he went into practice for himself, and finally retired, devoted himself to his children, and lived in Prague.
Very fine looking grandparents. He reminds me of Sommerfeld a bit.
This is my grandfather, father and I.
This was approximately 1896.
Do you recall from your family’s discussions what the circumstances were when your father was born? Was your grandfather in Vienna already?
My grandparents had 11 children, of which three died young, and the oldest one was a lady called Aunt Marie. I have her picture here. She was a writer. She was vice president of the Austrian Penwomen. Originally she translated mainly from Scandinavian literature. But, then she changed over to the Renaissance. She wrote a book on Leonardo da Vinci.
LEONARDO DA VINCI, DENKER, FORSCHER UND POET.
She became editor of a series of translations. This is a series, and she was the editor of that series.
This is the series: DAS ZITALTER DER RAISSANE. AUGEWAHLTE QUELLEN ZUR GESCHICHTE DER ITALIANISCHEN KULTUR. Herausgegeben von Marie Herzfeld. Was Marie an important cultural influence in your family?
Well, I don’t know what you call important.
Did she have any particular influence on you when you were very young?
I don’t think so. When I was ten, I had scarlet fever, and went to a doctor called Reumer. That meant that I could not do any physical exercises. I was in practice forced to read.
This was from age 10?
This was when I was 10. And there was one particular thing. At that time in Vienna, the street cars changed over from horse-drawn to electricity, and that intrigued me very much; this underground, how should I call it, channel, where the contact was made.
The third rail for electrical connections?
Yes. And there were little booklets on electricity, which I studied. This was really my start.
Do you by any chance recall the names of any of these books?
No. These were little popular books, the size of a postage stamp.
I see. They always tended to be small, for small hands.
And from then on, I was interested and studied physics.
What did your father do?
My father was a very well known obstetrician. Here, I’ll show you something. This is my aunt.
This is my father. He was a very well known obstetrician, with particularly a practice extending very much to the east. He was for example, a fairly good friend of the King of Bulgaria. And brought the second son of the King of Bulgaria into the world. This is a Nekrolog for my aunt.
What year did she die?
Oh, she died late; somewhere around 1940.
I see, 1940. And your mother?
My mother died when I was 12, and we had then a governess. And there was a little difficulty, because the governess was not interested in books.
I had a brother, two years younger. This is my brother. I wanted to show you another picture of my father.
These are very nice books that you have assembled. Nice to have it all in one convenient place. You have also written a descriptive text on your family to go with the photographs. Very nice.
Well, you know that the Austrian educational system was different. I didn’t go to public school. We had a private teacher for elementary school. Then I went to the Gymnasium, a Benedictine school, and they were very favorable to intellectual activity.
Do you recall what subjects you studied in the Gymnasium?
There was no choice — Greek, German, mathematics, natural science, physical science, history, geography and religion.
I see. That’s a fairly modern curriculum for a Gymnasium at that time, I think, compared with German ones.
No. No. The curriculum was state prescribed.
I see. But you had relatively modern history, and you had natural science?
There are many Gymnasiums in Germany at the time where one got no science at all.
There were two halves, the lower part and the upper part, and there were two years in each, of natural science, that is to say, biology and botany, and two years of chemistry and physics.
Do you recall your teacher for physics? Do you recall what particular subjects were discussed in physics?
No. It was a general physics course.
I see. Mechanics, failing bodies?
Yes. I had studied calculus privately. In the course, they didn’t expect calculus in high school. And my physics teacher helped me with the calculus, so when I got out of the Gymnasium, I could know calculus.
I see. This ordinarily was not part of the Gymnasium curriculum.
No. Not at that time.
These schools were all in Vienna?
In Vienna. This is any early picture of my father at the department of gynecology of the university.
Your family was in medical practice in Vienna in the early 20th century. Was there any contact with the Freudian circle and Freud’s approach to medicine?
I’m thinking of Schnitzler. I noticed for example the Briefe from Marie Herzfeld and Hugo von Hofmannstahl.
And I was wondering if that cultural connection with the Hofmannstahl, Schnitzler circle had any impact on your family?
Let me think a moment. I cannot remember any contact. There was none, I think.
Your first introduction to physics was by reading these small books on electricity? Was this done entirely on your own? Or was there someone, an uncle or sister or brother, who encouraged you to read?
You were fascinated by the electric tram, and began studying electricity. Did you think at that time of studying physics seriously?
I assume so. At one point my father very much advised me to get into medicine. And so, when I was about 16, I thought of the possibility of going into physiology instead of physics. But that only lasted for two years.
Did your brother become a doctor?
No. My brother had bad luck. He wanted desperately to become a Navy officer, but his eyes were too bad to be accepted at the Naval Academy. So he went into the Military Academy and became a professional Army officer. In the war in 1918 he was an artillery officer. Well, I then started studying at the University of Vienna, and stayed there for two years.
1910 to 1912?
That’s right. And in 1912 I went to Zurich.
In Vienna, with whom did you study? Was Franz Exner there?
In Vienna, there were two experimental and one theoretical [physicists]. The experimental, the first one was a man named Lang. He was a very old man. When he retired, he was replaced by Lecher. In the other department was a man named Exner. Exner and Hascheck. Does that mean anything to you?
I know Exner. Exner is a very interesting gentleman.
The work here was mainly measuring spectral lines. In the other department, there was also Ehrenheft. Then there was a man named Stefan Meyer who was teaching an elementary course in theoretical physics, but was mainly studying radioactivity.
Yes. Was von Schweidler still there?
Schweidler? No, he had left for a professorship at Innsbruck. But he used to work with Meyer. My main teacher was a man named Hasenohrl. He was killed in the war, an infantry officer.
His widow married an American, and then moved to America. And his son studied law, and married the daughter of a dean of the Washington Cathedral. I think he’s still in the telephone directory. The name Hasenohrl is rather funny. You know what Hasenohrl said? In 1683, Vienna was overtaken by the Turks, and Hasenohrl’s ancestor was supposed to be a man whose original name was Hasan Ovry. And he stayed behind and founded a coffee shop, which was new to Vienna.
I see. Subsequently the coffee house became an important part of Viennese culture. What did you study with Hasenohrl?
They were general courses in advanced theoretical physics.
And you had already had elementary physics in your first years?
I had a one year course in elementary theoretical physics under Stefan Meyer. Then in 1912 I went to Zurich.
What induced you to go to Zurich?
This was specifically to study with Einstein?
Yes. I want to show you.
A list of lectures attended. Now, differential equations. When was this?
In Zurich, 1911-12.
You took lectures with Zermelo and Max von Have. And Einstein of course.
And Kullman, an electrical engineer. He was still there a few years ago.
You took thermodynamics from Einstein, and a physics seminar. What was the subject of this seminar?
I don’t know.
How did you hear of Einstein and decide that you wanted to go to Zurich to study with him?
Oh, everybody knew Einstein.
Even in 1912?
Yes. The special theory of relativity was 1909, wasn’t it?
Well, 1905 was the first.
But the reason that I asked goes very deeply into your own subsequent work. Your work from the very beginning was very heavily oriented toward statistical mechanics.
My reading of papers at the time indicates that there were not very many people who were using statistical arguments in physics at that time.
Well, of course, in Vienna that was different, because of the inheritance of Boltzmann. And Hasenohrl did.
Hasenohrl developed statistical mechanics in the Boltzmann fashion, Boltzmann wasn’t at the University when you were there, he had already died.
Boltzmann had committed suicide in 1905.
And Ehrenfest had left.
Ehrenfest was never a teacher.
Yes, he was just a student. I noticed the one photograph that you had.
He came to Zurich for a time.
Were you induced to study with Einstein because of Einstein’s work in statistical mechanics? Were you already interested in the statistical approach to physics?
I was already interested.
And that was the best place to go?
Yes. And of course Laue was there.
How did you find your work with Einstein? Was he helpful?
Well, yes. But it was a general stimulus.
Were there many people studying with him at the time?
He was the professor of theoretical physics at the Institute of Technology.
That’s the Eigenossische Technische Hochchole?
Yes. The experimental man there was Pierre Weiss. That was very funny. You know, Pierre Weiss was born in Alsace in 1870. And he remained a fanatical Frenchman. In 1870, of course, France lost Alsace, and the result was that all Pierre Weiss’s assistants had to be French.
Well, I had a very close personal relationship with the Laue family.
Are there any memories you have that you’d care to share about him?
Oh yes. The Laues had a sailboat on the lake, and we went sailing. And usually, the wind died around noon, and Laue had to pull the sailboat back. And then, if there was one weekend, we went skiing. One of the great stimuli for me was the fact that Stern was with Einstein.
How was that a stimulus?
Well, they talked, and I learned probably more from Stern than from Einstein himself.
Stern was also very much interested in statistical approaches to theory.
And in the applications to chemistry.
Yes. I noticed that at just about that time, 1912, when you were in Zurich, you began publishing papers.
I had published before that.
You had published when you were still in Vienna?
Yes. My first paper was rather a dud. It was the scattering of light by ellipsoids. The formula there for the scattering of light, by Shields. But then I had another paper, which still is good, I think which [could not locate] was much more interesting. At that time, a man named Kupelewieser — a rich steel man — donated the Radium Institute. There was a girl named Friedmann who measured the statistical variations of the path lengths.
For alpha particles?
For alpha particles. And in the paper, which was my first statistical paper, I explained numerically the fact that the path lengths meant a fixed number of collisions. It was statistical [analysis] over what distances the collisions occurred.
The range of the alpha particles?
Yes. When I went to Zurich, I had already published something like four papers.
I see. I remember the one on electro-chemistry of dilute solutions, in which you thanked Einstein and Stern both at the end of the paper. From the very beginning, you had taken a strongly statistical approach to physics.
You feel that that came more from Hasenohrl?
Did you feel that it was unusual to be doing statistical analyses in physics?
No. You see, there was Boltzmann, and that was statistical.
Yes. But when you went to Zurich and later when you went to Gottingen, did you find—
Gottingen was in that respect a disappointment.
Do you think it had anything to do with the fact that statistical argumentation was unusual in Gottingen?
No. The people in Gottingen were Riecke and Voigt. I went there because I was interested in spectroscopy, and they gave a seminar on the details of diffraction gratings. But unfortunately, I didn’t get anything from Born.
Born had just come, hadn’t he?
Well, he must have been there I think two years. But he was interested in relativity, which I was not. In addition Mrs. Born had her first child, which distracted him.
This was just the time of the Bohr theory of the atom. Do you recall when you first heard of the Bohr theory?
I can’t remember, I’m sorry to say.
In Gottingen did you do experimental work on spectroscopy?
I did experimental work which didn’t receive results.
Can you tell me about that.
Yes, I was trying to get experimentally the statistics of the solid state rectifier. I hoped to get the statistics of rectification. But that didn’t work out. I worked in the Institute of a man named Simon. The reason [it failed] is the frequency is so high that the rectifier doesn’t rectify it any more.
You were trying to use a crystal as a rectifier?
No. I was trying to get the statistics of rectification.
But in a crystal?
You say that your time in Gottingen was a disappointment?
Was this due to matters other than not making contact with Born?
Well, the reason was because I was not interested in relativity. What I gained in Gottingen was function theory under Caratheodory.
Your experience with Einstein had not induced an interest in relativity?
I don’t know why it was.
Then after Gottingen you went back to Vienna?
Yes, just to finish my doctor’s degree.
That would be just to write your dissertation?
Well, then it was possible to use already published work for my dissertation. I forget which one it was. It was a statistical one.
And at that point you expected to habilitate and become a Privatdozent in some place; ideally in Vienna or in Germany?
Well, I tried in Austria. It is a somewhat delicate point which I’m going to make. There was a man named Kohlrausch, and he told me that there was no use going on in physics, because with a name like Herzfeld, I would never get a call.
After you received your degree in Vienna, the war started. Can you tell me something about your war experiences?
The situation in Austria was so that if you were studying at the university, you needed only one year of service. And what’s more, you could choose when to do that year. And you could choose where to do that year. I had fortunately chosen to do it after my PhD, so I lost relatively nothing. That is to say, if the war had not started I would have anyway gone into the army. I had arranged to serve in Pola. There is a triangle — the Istrian Peninsula — Trieste at end and Pola at the southern tip. Pola used to be a Roman walled town under Emperor Hadrian. It had a beautiful Roman amphitheatre.
That’s not Split today?
Split is much farther [south]. So I went to Pola and served. I’ve forgotten to say one thing. When I entered the University of Vienna, Schrodinger had just finished, and was starting his own army service.
That would be 1910?
1910, yes. But I went to Pola and stayed for a year. We were then transferred to Galicia, and that was the end of the 1915 offensive. There are parallel rivers in Galicia. We advanced over two rivers. There were some counter offensives and finally it settled down to trench warfare. At the end of 1915 we were pulled out, and transported south for the Balkan offensive, Montenegro became a friendly ally, and we stayed then at that time in Montenegro, then we went south to Albania and stayed for a few days in Skutari.
Were you an officer?
Yes. I became an officer after about a year and a half.
1915. What was your reaction to the war? How did it sit with your own political views at the time?
We were a very patriotic family.
How long were you in Albania?
Perhaps three months. And then I was sent to get new guns to Vienna. While we were down there we ate anti-malarial drugs. In Vienna, when I got out of it I stopped, and there the malaria broke out. So I didn’t get back. It was pretty bad. 250 got malaria and 12 died.
Do you know the anti-malarial drugs? Were you taking quinine?
I think it was just quinine. Therefore I stayed for a time in Vienna. Then I went in to the south, the mountains, and I stayed in the pass, at 8000 feet. It was beautiful but cold. For two weeks we were cut off, until we were almost ready to leave.
What sort of scientific work were you going to undertake in the army?
At that time the Germans had developed the so-called “Big Bertha,” 42 centimeter [gun]. We calculated the ammunition for that. Ammunition — you see, this is a question of the rate of warming, that is, the rate of development of pressure —
— and heat, inside the gun?
Inside the gun.
Were you working with German physicists then?
This was all Austrian?
This was Austrian. I was there until the breakdown, and then I had to bring the battery back to the revolutionary interim [government] which was pretty bad.
Back to Vienna?
Back to Vienna.
Well, those are most interesting photographs. I’m sure that any number of historians of the war would be very much interested in these.
When I got out of the army, there were no real jobs in physics to be had, and so I thought I would go into chemistry. I was told, if I wanted a job in chemistry, I would have to learn more analytical chemistry. I thought that if I had to do that, I might just as well do it in another place, an interesting place. And so I went in December 1918 to Munich. This was enormously important for my later career, because it meant that the people in Munich got to know me: Sommerfeld and Wien and Fajans. There was then the revolution in Munich. I left Munich in February 1919. I tried to get habilitated in Austria. Vienna was too full, and I went to Innsbruck, where Schweidler was, but he wasn’t interested. Then I got an offer to go to Munich, and that was not only to get habilitated, but also an assistantship on which I could live. [So I went back.] In Munich I was private assistant to Fajans. Then I preferred to become laboratory assistant.
Which institute was this?
This was the Chemical Institute.
The Chemical Institute, I see.
Wilstatter was the boss, and Fajans had the physical chemistry. Theoretical physics was Sommerfeld. And then, next, in 1923, Sommerfeld had his first invitation to the United States, and I gave his lectures, in substitution.
I see. How had you gained entree into Sommerfeld’s Institute?
I was Privatdozent for theoretical physics and chemistry.
In both institutes?
Yes. My pay came from the chemical.
You didn’t teach physics courses?
Oh yes [I did].
Would you not have received payment from the students in the physics courses too?
Sure, but this is obvious, the pay which you get from the courses is minimal.
The pay you’re speaking of is as an assistant in the Chemical Institute. But you participated in the Mittwochs Kolloqium at Sommerfeld’s Institute?
How did people interact with one another at Sommerfeld’s Institute at that time?
Well, you see, they had three people essentially there. I forget now the name of the ranking oldest one. [Rontgen until 1920. Then Wien.] The second one was Ewald whom I knew very well. In addition, there was in the Institute of Technology a man named Kossel.
Walter Kossel who developed the explanation of X—rays on the basis of the Bohr atom?
I recall him mainly because he developed the systematics of a kind of bonding; the difference between chemical bonds on the one hand, and the purely electrostatic bonding. At the Chemical Institute, we had a lot of American visitors. For example, there was Conant, the president of Harvard. And Fues.
When did you become ausserordentlicher professor?
I got the title professor in 1923, when Sommerfeld had gone to America and I gave his lectures.
That was for one year?
I think it was only for one semester…
Do you recall what lectures you gave?
Yes. That was very funny. There was a cycle, and it so happened that thermodynamics [was due]. That was very funny. Among the students was Heisenberg, and he appeared in one of my lectures. When Heisenberg later took his PhD, Sommerfeld asked him something about thermodynamics, and he knew nothing. (laughter)
When did you first hear that story?
It might have been in 1925. I don’t know. When Heisenberg got his degree.
When Sommerfeld came back, then what did you do?
What I did before. I gave lectures in physical chemistry, and in physics; not the main lectures but smaller lectures. And I was again assistant in chemistry.
Did you find there was more sympathy for statistical argument on the part of the chemists, or on the part of the physicists?
The interests of the Sommerfeld group didn’t at that time need much statistics. Afterwards quantum statistics came in, and they talked about electron theory — then of course the Sommerfeld group needed statistics quite a bit. But as long as they did just atomic theory, spectral theory, they didn’t need statistics. In chemistry of course we were interested, I was interested in reaction rates.
And that requires statistics.
When did you read Gibbs?
I don’t know. Gibbs had no influence [on me].
But Einstein did?
Einstein and Boltzmann.
Well, this was a very interesting period of time to be in Munich, 1920-26.
Yes, very interesting.
Are there specific things that come to mind? Atomic theory seemed to be failing.
Of course, the main influence was the Bohr theory.
What for you made it particularly interesting? Did you do any work on spectroscopic analysis of atoms while you were at Sommerfeld’s Institute?
I’m afraid I can’t remember.
Were people at Sommerfeld’s Institute aware of the difficulties for atomic theory? Did they go around discussing the fact that there was no consistent solution to many of the problems that they faced?
I think so. I don’t remember. It was a very interesting time in Munich because we had as students Wolfgang Pauli, Heisenberg and LaPorte.
What are your memories of Pauli? Did you have any close contact with him?
Oh, Pauli was very undisciplined. There might be a class at quarter past 11, and that was in a classroom which was steep, with an entry on the side. And Pauli appeared at quarter to 12, and then stood there in the middle and looked at the clock, and finally sat down.
Even as a student?
Even as a student.
Well, this must have been distressing to the instructor.
Yes, which was Sommerfeld. Pauli’s father was an associate professor of medical chemistry at the University of Vienna. Heisenberg’s father was the professor or Byzantine of Greek at Munich, and I often walked home with him. We had part of the way in common.
What did you talk about when you walked home with him? Did you talk about physics.
No, his father knew nothing of physics.
Oh, I see. I thought you were talking about Heisenberg. Just about the time of Heisenberg’s matrix mechanics, you were working very seriously on dispersion theory.
Yes, I was. But my memory’s so bad, I don’t remember anything any more about it.
That isn’t the sort of work that one would associate with Munich at that time. Did you feel that you were doing that work completely on your own?
Well, not completely, because, I mean, essentially dispersion theory is connected with secondary waves, scattering of coherent secondary waves or particles. This is probably what I was trying to do, to see how that would appear in quantum theory.
But there is a serious difficulty with the Bohr atom and secondary radiation, because there is no necessary correlation between the incoming frequencies, and the secondary frequencies.
This would be a problem with the basic coherent radiation, which has nothing to do with excitation.
This is purely scattered?
It would be a disturbance on the Bohr orbit.
Were you conscious of Kramer’s and Heisenberg’s work on dispersion theory in 1925?
Well, Heisenberg was in Munich at that time. I must have been. I’m sorry, my memory’s so bad.
It was through dispersion theory that Heisenberg eventually came to what became matrix mechanics. I’m very much interested in the reaction to matrix mechanics.
I can’t remember.
Why did you decide to come to the United States?
There was a banker in New York with connections with Frankfurt, and he decided after the First World War, that there was still too much resentment. He gave $50,000, for the purpose of inviting a German each year as visiting professor. He first offered it to Columbia, but the president of Columbia was to prejudiced and refused it. And then he offered it to Johns Hopkins. Hopkins took it, and they offered me the first one.
I read something that made me feel that it was a possibility that you might have gone to Tubingen.
No, there was no call to Tubingen. I visited Gerlach, but there was no question of a call.
So your decision to come to the United States was influenced by the lack of prospect for a call anywhere in Europe?
Yes. In any case, Hopkins was very attractive at that time. And [it was] a certain kind of adventure.
Was the attractiveness limited to Hopkins, or would it have been true of any institution in America?
It would probably have been any institution in America.
Was any of your decision to leave Germany due to feelings of anti-Semitism in Munich or elsewhere?
You mentioned the episode [with Kohlrausch] that made me feel there might have been something like that.
Well, I’ve never felt it personally. There was a problem of anti-Semitism in Munich. That’s a complicated story. Three years before I left there was a vacancy in Munich. There had been a very old professor of mineralogy and he was retiring at the age of 80 or so. As usual in Germany there was a committee making up a list. And the first man on the list was, I forget his name. Not popular but very spectacular man, who lived in Scandinavia and he was Jewish. He was put first on the list, and when the faculty made the recommendation, they left him out. And Willstatter felt that this was a sign of anti-Semitism, and resigned his position. And there was a big to-do.
Was there ever any evidence of a similar phenomenon in the physics faculty?
No. I mean, Willstatter blamed to a large extent the Professor Willy Wien who was professor of physics, and influential with the professoriate. But not specifically in physics. Of course not at all in theoretical physics, at Sommerfeld’s Institute.
Did you have enough contact with Wien and his institute for experimental physics that you could see whether anti-Semitism was important?
No, I’m sure it wasn’t in the institute. In the spring a weekly ski group, and Willy Wien was one of the leaders…
Was your appointment at Hopkins for a year?
No, only three months. And so, of course I took it. I was only a Privatedozent. I came then to Baltimore to Hopkins.
Had you not become a professor?
This is only a title.
It was my understanding that as an ausserordentlicher professor, you would receive a salary.
There is one professor with only a title, and one which has a salary. [I came then to Hopkins] in the spring of 1928, and when my visiting professorship in June was over, they then offered me the permanent position. There was a man named Ames who used to be professor of theoretical physics, and he became the vice president and provost. So they offered me the position as professor of theoretical physics.
Who else was at Hopkins in physics at that time?
Yes. And then there was Pfund, who did infra-red work, and then there was a man named Bliss, who did the undergraduate teaching. There was a close connection with the electrical engineers.
What was your impression of America when you came, as far as physics is concerned?
Hopkins was completely dominated by Cambridge. And of course Cambridge was somewhat behind the times.
Do you mean Cambridge, Mass. or Cambridge, England?
Cambridge, England. And they didn’t know anything about Bohr. So what I had to do was to introduce Bohr, and German physics.
I see, so they were not keeping up with developments in physics?
This was politics, you see. There was still a big resentment against Germany.
So that the papers were not even read? One didn’t even know about the Bohr theory, let alone quantum mechanics. How long did it talk you to introduce these topics at Johns Hopkins?
I don’t know if I can put a date to that.
But you tried from the beginning. This was your intention?
Before you had come to America, did you expect to find more understanding of modern physics?
You didn’t expect to find that?
I didn’t know anything about it, I mean, I knew of course Wood.
Then, once you had arrived and completed that three month period, you were offered a permanent position. Since you had no permanent position at home, you decided to stay?
Yes, of course, a full professorship.
Were there other factors involved, other than purely economic ones, that led you to decide to leave Germany and Austria and come to the United States?
Other German positions were fairly crowded at that time. The chance was not too good.
Were you worried about the economic state in Europe at the time? Germany had finished a terrible inflation.
Did it affect your ability to do physics when you were in Munich?
The value of the Mark was halved every day. We got our pay on the first, and three days later we got the pay again. Every three days, And when you got your pay, you rushed out and tried to spend your money as quickly as possible, because 24 hours later it would be only half its worth. Then there was a strike of the government printing office which printed the money. So we didn’t get any salary. And the assistants in Munich would hang around to wait until the money arrived. When it finally came, it came as five billion marks. Five people got one bank note, and you had to go into town and try to change it so you could split it.
All five of them had to go in together?
There was a visitor a Spaniard who was enormously rich because he had Spanish money. But he didn’t want to change that. So he would borrow German money from his colleagues, so he was as badly off.
Did the inflation affect the work in physics that was done at the institutes?
Well, I don’t know about the experimental institute, but it didn’t affect the work at Sommerfeld’s Institute.
Was this one of the reasons that a number of people were induced to go on trips? Sommerfeld left in 1923 to go to America.
He only went for a visit. And ‘23 wasn’t quite as bad.
After you had arrived at Johns Hopkins, did you find that you were able to continue your own theoretical work in statistics?
Did you find that your statistical approach was accepted more readily in that period after quantum mechanics?
No, I don’t think so. I was particularly interested in reaction statistics, cooperating with Frank Rice.
Was most of your work done in theoretical chemistry?
Not most of it, because R.W. Wood made song high frequency sound experiments, and told me I could do ultra-sound.
Was there an expectation that there would be an application of this work in ultra-sound? Or was this purely theoretical?
That was purely theoretical. Somewhat later on, there came of course applications, to mine detection.
That was work that you did during the war?
Not really. It applied to the work I did after the war. What I was doing during the war was quite different.
Were there other things about your stay at Johns Hopkins that you feel we should discuss?
Yes. I was stupid and tactless. Originally, they offered me the head of the department. But I said I couldn’t take that, with Wood there. But then I acted as if I had it, you see. Wood was a genius. But he was a very undisciplined person, and I forced his people to come to the seminars. So I made myself very unpopular. The other thing I did was to bring in too many foreigners. After I’d been a year at Hopkins, I was invited for an interview at Princeton. G.I. Taylor and K.T. Compton offered me a job. And I didn’t take it. It was to the advantage of the United States I didn’t take it, because that was the job which they then gave to Wigner.
This was early, then.
It was within my first year or two. So they offered it to Wigner. But I used it to get a number of things at Hopkins.
What sorts of things did you feel were lacking at Hopkins?
Well, there were no significant young people. I asked for three — one in theoretical physics, one in experimental physics, and one so-to-speak traveling. Those were appointments only a short time.
These were some of the foreign people that you brought?
No, not at that time. One of the young people I got, I forget his name now, was an X-ray man.
An American. But when Wood returned, must have been in 1936 or so, then I arranged to get in his place James Franck.
Yes indeed. He had already come to the United States?
No. He had resigned from Gottingen and had no job.
I see. I hadn’t realized he had stayed in Gottingen that long.
No, he was living somewhere in Scandinavia. And I got him to Hopkins. But I didn’t consult everybody. I felt that it was worthwhile to get a Nobel Prize man. But then he got another job. And then there was a change in the presidency at Hopkins. Bowman became president instead of Ames. Joe Mayer was in chemistry, and at Hopkins, the wife couldn’t have a regular position, so Maria Mayer was an associate. I had always tried to push her, and that was always resented.
Do you mean you were trying to get her to a regular position?
No, I couldn’t do that. I tried to help her out in faculty meetings, tried to get her Phi Beta Kappa. Well, anyway, I was told that she wouldn’t be re-appointed for next year. I said, “If she goes, so do I.” I had a suspicion that that was their real aim. They wanted to get me out. Because nobody made any attempt at keeping me.
You did get James Franck over.
He was a regular professor for two years.
And then he went to Chicago?
Yes. After I had gotten out, all these people left: Franck went to Chicago, the Mayers went to New York,
There was someone else who came. I wanted to ask you at some point about your interaction with Paul Ehrenfest.
Only when I was a student at Zurich.
He would come and visit? In that period of time, I think in 1928 a student of his, Gerhardt Dieke, was appointed to Johns Hopkins.
Yes, that’s right.
Did you take a role in that appointment?
Yes. He was a young man.
He had studied with Ehrenfest.
I’d forgotten that. He came as my successor at Hopkins, and after that became head of the department, and unfortunately died suddenly. I was very fond of Dieke.
He also did spectroscopy, did he not?
I think so.
Had you already arranged at the Catholic University, in the event that your ultimatum about Maria Mayer was rejected?
No. At that time I was confident, that I could get either to Fordham or to Catholic University. Fordham fortunately didn’t work out. Catholic University did. The Rices were on good personal terms with the archbishop, who was chancellor of the university. The Rices just told the archbishop that I was ready for Catholic University.
At Catholic University, did you manage to find good students?
Well, there were very few students at that time. But you see, that was a time when the employment of physicists increased very much, and I put all the advanced courses in the evening. Before that time, the advanced students went to Hopkins and had to spend, say, three days out of the week there. This was bad from the financial standpoint. We arranged to have all the advanced courses at night or on Saturdays, which meant an enormous increase.
Had there been any advanced courses in physics at the Catholic University before you came?
Yes, I think so.
But nonetheless the students would go to Hopkins.
He got a lot of the government people, who were then attracted to the University because of the advanced courses given by my husband in the evening. Our students didn’t go to Hopkins. It was the government people who later became our students.
You could continue your own research there at the Catholic University?
I know very little about your experiences at the Catholic University.
Well, yesterday we are celebrating the 300th Ph.D. in physics.
Was there much undergraduate interest in physics?
Perhaps 12 a year or so.
This would be in this period, the late thirties, when jobs in industry particularly were just beginning to pick up again after the Depression?
Most of our graduate students were people who had jobs. The people came to Washington to get a job in the government laboratory with their bachelor’s degree.
Then would work in the evenings to obtain an advanced degree.
So it wasn’t so much a problem of finding academic jobs for these people. Most of them already had jobs.
Some academicians for example, most of the physicists at American University — and I can’t remember about George Washington University — are CU graduates. There were some people who came from Annapolis at night, and — a good bit of the faculty of the Naval Academy I’d say were from Catholic University.
Is that where you first formulated your connection with the Navy?
How did that come about? When you began doing war research, after 1940, it was mostly under the auspices of the Navy, was it not?
Well, we had done work for the government during the war, not only in ultrasonics, but in mechanics.
This was in connection with the mines department.
No, the strength and design of gun ammunition. We designed it so that the pressures inside the gun do not deform the [shell].
I see, this is closely related to the work you had done in World War I?
No, not really, because the factor there was chemical action in the powder. This here was, strength of the shell casing itself.
I was talking last year with Lother Nordheim, who was working at the same time on the theory of melting within gun barrels. Was there any connection between your work and his?
No. Only remotely.
Were you aware of the discovery of nuclear fission in ‘39, shortly before you began your war work?
I think so. Yes. Wasn’t that the famous seminar at G.W. that was then published in the SATURDAY EVENING POST?
There was a seminar when Bohr was here.
I was a good friend of Edward Teller. We used to fence together.
Had you known him in Europe?
I don’t think so.
But they became very good friends.
How were you approached by the National Defense Research Committee to begin doing this research?
They approached the director, and the director called us. We were then in the mountains.
So you were called back to work on this problem of deformation in guns.
How long did that work go on?
That went on till the end of the war.
Were there other things that you did in the way of war research, or was that the main problem on which you concentrated?
That was the main problem. There were some other smaller things which I’m not sure I remember.
You had a little model basin and did things under water, didn’t you?
Yes. This was sound propagation.
Sound propagation under water?
Was that work on sonar itself?
Were you aware at all of the other research projects that were going on at the Radiation Laboratory at MIT, radar research, or the Manhattan Project itself?
He was invited to Los Alamos. But he refused after he had investigated to see that heavy water had been knocked out in Norway. So the Germans really couldn’t get ahead, and he didn’t want to have anything to do with the bomb.
I see, so you know enough about the fission project to make a decision that you did not want to go to Los Alamos? That must have been in ’43. What was your feeling about the possibility that Germany would develop a fission bomb?
I didn’t like it. I didn’t want to have anything to do with it.
With the American effort.
I was invited by Teller to take part in the fission project, and I didn’t want to. So I went to see Tolman, and told him that I didn’t want to, except if he told me that the Germans were near to it. If it was a question of speeding it up a little, that an additional person might make the difference, then I would join. But Tolman then told me the Germans were not near.
On the basis of their lack of heavy water?
I don’t know. He didn’t explain. Tolman himself was of course one of the [leaders]. He didn’t explain why.
There are a few specific points that arose from our discussion of the other day, that occurred to me.
The question is, how von Laue got the title. His father was a civilian employee of the Prussian War Department, and his father, as such, got the title. And Laue inherited it from him. That was just about the time he was in Zurich.
If I recall, he was somewhat ambivalent about it.
Yes. You know how he died?
I don’t believe I do.
It was in an automobile accident. He was driving behind another car. He was trying to pass, there was another car coming in the other direction, and there was a collision.
What was your reaction to life in America. Were there any difficulties about anti—Semitism in the East?
Not at all. The man who had given that money on which I first came, was of course a Jewish man.
That influenced the process by which one might have been selected. I don’t know whether that would affect difficulties of living in the community.
No, there was no difficulty.
You became very much interested in Catholicism?
I had always been. It’s not correct to say I became.
That happened early in your life?
I went to the Benedictine school, and the interest ran back through the whole family. Then of course in Vienna, people there were formally Catholic but did not act as much so. That interest developed at the Benedictine School.
Do you feel that your beliefs in Catholicism have affected your physics at all, your interest in or approach to physics?
Some people would suggest that there might be some conflict between belief in a revealed religion, and work in the natural sciences. Did you ever feel such a conflict?
No, I don’t think so. There were occasionally difficulties on individual points.
What sorts of points would create difficulties? Can you give me an example?
The mood in the church, about the time of [Pope] Pius X, was not very favorable to what we call scientific freedom. But that was already more at the beginning of my stay at Catholic University.
Was this difficulty eventually resolved?
Well, it was resolved by a change in the attitude of the church. Pius XII was very influential in that respect. Pius X was originally a simple Italian priest, but Pius XII had been for many years Nuncio in Germany, and was quite affected by the German attitude to science. And so when he became Pope, there was a very great change.
Were you aware of this change at Catholic University?
Oh yes. Yes.
But before that time, there had been some difficulties in the Catholic university itself?
I don’t recall.
Well, the anti-modernist oaths.
Oh yes, yes. But it wasn’t a real difficulty. It didn’t affect you personally.
No, it didn’t affect me personally.
In 1934, just before you left Johns Hopkins, you wrote a paper with Maria Mayer on fusion. What was your view of fusion at that time? Did you feel it had any practical significance?
I know that wasn’t the purpose of your paper. Do you have any feelings about that now?
No. I deliberately omitted any contact with that.
Because of the potential for its use in armaments?
No, I felt I just didn’t know enough. I left knowledge of that field aside. There is one thing I wanted to mention. It had to do with your question about statistical mechanics. Does the name Muller- Pouillet mean anything to you?
Yes. The famous textbook.
While I was in Munich, I was asked to write a volume in kinetic theory of heat, which I did. This was about three-quarters the kinetic theory of gases, and it was a quarter or so statistical mechanics. This was actually my only real work in the application of the statistical mechanics. You see in chemistry the general applications are well known. What was really new around this time was the integration constants, which I couldn’t have gotten from classical physics. This I think I had essentially learned from Otto Stern, There was another thing that we did in the early time in Munich. We called it then the theory of valency: That was the possibility of calculating energies of compounds with polar bonds. There were several papers written, one in particular in which we showed that for example, sodium is monovalent. We showed that if you take sodium and chlorine, NaCl, has a much lower energy than for example Na2 Cl2. So, for the polar compound, we showed that it was an energy question; that the valency which is usually ascribed gave a much lower energy for the compound.
One knows at that time in Germany that there were very close connections between the chemical industry, and academic work in chemistry. Did that relationship between industrial application in chemistry and academic work in chemistry affect your work at all?
I don’t think so. We were on good personal terms with the people in chemical industry. There was a man in the chemistry department in Munich named Grimm with whom I worked and was very friendly, and he became head of the research department of Chemie Farben. He then left under the Nazis, the firm manufactured gas and he didn’t want anything to do with that.
You were still at Johns Hopkins when the race laws were passed in 1933? Was there an organized effort at Johns Hopkins to find positions for people?
Yes. There was a small group which was called the German Scientists Relief Fund. The administrator was a man named Ladenberg of Princeton, and I was a financial manager. What we mainly did was to finance the travel from Germany to the United States. We did that for quite a number of people.
Were you also successful in finding jobs for people in physics?
There were one or two where it was difficult. But this wasn’t our job. They’d gotten a job, and couldn’t finance [the travel). For some people we got jobs. But it was mainly a financial society.
You mentioned the other day that you had reservations about war work. You chose not to participate on Los Alamos, but you continued to work on the thermodynamics of guns and gun explosions. Was there ever any conflict in your mind about continuing with that research?
How did you make a distinction?
The distinction was the effect on civilians. Nuclear war affected civilians too, as you know from Hiroshima. A gun is purely for battle. So it was simply traditional war. You hear what I’m saying?
Yes. I hear what you’re saying, but I don’t fully understand it. I would seem to me that guns, especially large guns, can be used to bombard cities with civilians. And secondly, it wasn’t clear in 1943 that the possibility of a fission bomb necessarily appeared to be anything so much different from convention weapons of warfare.
Yes. I felt that to be the case.
I think it was essentially the distinction between aerial bombardment. I did not participate in development of aerial bombs, even explosive bombs. That is the point of it.
Was it clear to you in 1943 that a fission bomb was more than a remote possibility?
I didn’t know that much. But it was an aerial bomb.
So it automatically was not to be supported by you.
There is one point which I didn’t make clear probably, when we talked about the work on ammunition. A shell has a copper guiding bank. What was not known at all was the force involved to engrave it. This wouldn’t have happened in what is called smooth bore, but in a normal gun, you have rifling. It is a question of plastic deformation. And one just didn’t know anything about it.
This is one of the major problems on which you worked?
It was the major problem.
Was that the work that you did for the Navy?
No. That was done mainly for the Army. That was done in the civil engineering department at CU.
Were there other problems on which you worked?
The other problems came only with ultrasonics. That was for the Navy.
Was the National Defense Research Committee the official organization that brought you to do the work with the Navy?
Did you feel that there was any negative reaction to your statement that you did not wish to work at Los Alamos? Was it accepted at face value by Tolman or Condon?
Was there anything else that you did? I guess the Navy work went right through to the end of the war.
Yes. But of course, the relationship with the Navy was much more than purely scientific.
In what sense?
There were purely organizational questions: should the Navy introduce a mining specialty? In the work for the Navy, there were a lot of purely, shall I say, personal problems involved. There was a big naval establishment in Pensacola. Before we appeared they had never been visited by Chief of Naval Operations. We organized a visit, which made a lot of different for morale.
You were in Florida to do this work?
No, we visited there. I was the head of what was called the Mine Advisory Committee. It doesn’t exist any more, because it was formally transferred to the National Research Council. Under the new president [of the National Academy of Sciences). He didn’t like the independence that we had from the National Research Council.
So it was eliminated? The purpose of that committee was to oversee naval mining operations? And to evaluate the general program?
How long did you work for the Mine Advisory Committee go on?
Ten, twenty years. I’m not sure.
From your personal point of view, this was a matter of pure military weaponry. Mines, almost by definition, don’t affect civilians. This was the case?
Yes. There are other things which are not too well known. What happens in underwater explosions. What are the pressures? We did a lot of experimental work. We worked at the University on under water explosions. We had a little pond.
Shortly after the war you returned to Munich?
Yes. For not quite a year.
What were your reasons for doing that?
Fajans’ successor, as professor of physical chemistry suddenly left. They couldn’t replace him quickly, and were left without a professor of physical chemistry. So they invited me to take the job. And I was to give a class in theoretical physics.
And your reasons for accepting?
Well, adventurous. It was very nice. I lived in a military establishment, so there were no living difficulties.
You mean in the American military establishment.
Did you accompany him?
You stayed here?
At the end, they didn’t give me transportation, they asked whether I could be brought back by military means. They said I had to earn that. So at the end of Munich, I went for a month to the Office of Naval Research in London, and spent a month in England. During that time, I worked mainly on the problem of powder combustion and corrected the work being done in England on that. You might be interested in knowing that gunpowder doesn’t burn as a solid. The process consists in the gunpowder evaporating, and the vapor then burning.
Is it more than just the particles of the powder being dispersed? You’re talking about the particles themselves being broken up?
There is an actual vapor. And the reaction is a vapor reaction.
I didn’t know that.
Yes. Neither did I when I started out.
What was your reaction to Germany after the war?
Well, the students weren’t very hopeful. But they worked very hard.
What about the changes that you could see, in comparison with life in Munich in 1925 and in 1948?
Of course, the politics had completely changed.
Were issues about the war being discussed?
It was just put in the background, not brought up. Did you arrive before Sommerfeld died?
Did you see him?
I saw him. You know how he died?
I know some of the details of that.
He was very deaf, and he had been walking, and came out between buses, and a car hit him. He didn’t die immediately, but went to the hospital for four weeks. There was a slow accumulation of blood in his brain.
When you spoke with him, did you speak about anything other than physics? Do you recall anything of that meeting?
I’m sure I did but I can’t remember.
You returned ten years later to Munich, is that correct, in the late 1950’s?
Yes, I had another invitation.
Was it similar?
There was at that time the problem of whom to call in physical chemistry.
And so they wanted to consult you?
I think so. Yes. The man in charge was named von Bonhofer. He was a brother of Deitrich von Bonhofer who was involved, as you know, in the anti-Hitler conspiracy.
Were your experiences in 1958 considerably different from 1948?
Well, of course, in 1958 there was no army control any more and no army living. It all was civilian living. And this time Regina went with me.
If you have any comparative statements that you could make about how life had changed or how people had changed in that period of time, I would be interested to know them.
Well, I think the main important thing is that they had learned that the economy wasn’t hopeless.
At that point were people willing to discuss the war? Or was it still not discussed?
I can’t remember.
Today there’s a great deal of interest in Germany, at least in academic circles, about the events that brought about the Third Reich. I would be very much interested in any personal story that you might have or reaction that you might have. You say the story is basically very simple. I would be interested to know, simple in what sense?
You see, in the thirties there was a great resentment in Germany against the treatment which Germany had undergone at the end of the First World War. And one of the reasons Hitler succeeded was his protest against that. I don’t know whether you are familiar with some of these things. At the end of the First War, there was the problem of Upper Silesia. According to the Versailles Treaty, there was going to be a plebiscite in two years. The Poles didn’t wait; one of the Polish leaders assembled a private army and invaded Upper Silesia. Now, at that time, the French were very much for the Polish, and also, it was the Versailles Treaty. They didn’t oppose that invasion. So the German government couldn’t do anything. — This is one of the [reasons for] the rise of the Freikorps. This was an essential point. There was a collection of volunteers who formed an army, and opposed the invasion, there was a battle which is called the Battle at the White Mountain. The German volunteers beat the Polish volunteers and restored the free vote. Now, such things were resented very greatly in Germany. The early Hitler movement was to overthrow the Versailles Treaty. In those years you see the French tried to foster insurrection in Alsace, to get Alsace separated from Germany. And there were these volunteers who sabotaged the French.
Besides these political issues, did you feel that economic issues played an important role? The French occupation of the Ruhr?
They couldn’t be separated. There’s one thing, for example. In 1930, the Austrian government tried to unite the German and Austrian currency. The French reacted very badly by withdrawing all their money deposits in Austrian banks, which made for bankruptcies. Actually this involved me somewhat personally, because one of my uncles was a high official of a big Austrian bank.
I was curious to know after the war how soon these issues were discussed in Germany.
I think they were not discussed so much after the war. There had been so much discussion during the war and before the war. But there was not much additional.
Also, life was very diff cult for that first five or six years after the war.
I don’t recall political discussions [in 1958].
Did you see any other old physicist friends when you were in Germany besides Sommerfeld?
I can’t remember.
Did you have much contact with Einstein, since he was just up in Princeton?
You will see the letters in the file. I was very much interested always in the theory of elementary gas reactions.
There have been suggestions that, as a result of large projects during the war like the Manhattan Project, that the study of physics underwent a transformation. You no longer have individuals working on specific sorts of problems, but you have large groups of people working on closely related problems, or even large groups of people just doing a single experiment.
Well, of course that applies only to a very limited degree for Catholic University.
So in that environment you continued to work pretty much on your own, with a few students at a time?
Well, the whole faculty worked with them, together. Ultrasonics was our specialty.
When you say “our” you mean the whole faculty, or your group?
Yes, the whole faculty.
When you look outside Catholic University to physics as it is practiced today, what is your reaction?
Well, of course, nuclear physics is very popular, but it is a specialty from which I have kept away.
What about the industrial use of physics and physics research? One has large companies now that are built on very advanced abstract technology that came out of physics.
Do you think this has had any impact on the way physics is done and the sorts of problems that are addressed?
Sure. For example, as far as space is concerned.
Does that seem to you to be worthwhile to do?
Sure, But I haven’t participated.
What about energy technology? Investment in development of solar cells and fission reactors? What is your own personal reaction to that?
I think it’s good, but it needs a specialist.
Do you think that physics is substantially different today than when you were a student?
Oh, completely different.
In what ways do you find it different?
There was no quantum theory when I was a student. Or practically none. And there were no elementary particles.
Well, let me put it this way. Aside from the development of theory itself, do you see any differences in the way physics is approached, the sorts of values that are applied in physics research, now as compared to when you were a student? There certainly are larger numbers of people doing physics today.
If you were a student today, would you be interested in studying physics as it presently is constituted?
I think so.
So that what brought you into physics as a young student would still interest you today. I am very much interested in any stories that you might have about some of the people that we’ve discussed in the last two days: Einstein, Laue, people that you collaborated with.
Well, of course, the main change, as far as Einstein is concerned, was in his marriage. When I was in Zurich, I think he married his wife as a student, and she was of a low grade South Slavic family. When he got to Berlin, they were divorced, and he married an upper grade woman who in some way was related to him, I don’t know in which way. Her pre-marriage name was also Einstein, and she was very socially prominent. So that was the main change as far as Einstein was concerned.
What affect did this have on him, so far as you are aware?
I don’t know.
Were you in contact with the Einsteins much in this period in America?
I had some contact. That would be in the exchange of letters.
Were there other people that you had known in Europe that had come to the United States, with whom you had contact in this period?
Oh yes. For example, the Ladenbergs. Bethe was a student when I was in Munich.
What sort of contact did you have with Bethe in America?
Oh, just scientific contacts.
He married Ewald’s daughter.
That brought him even closer?
Heisenberg and Oldenberg.
If there are events that you recall with any of these people, that give an insight into their approach to physics or their values, I would be glad to hear of them.
No, I think that’s all so much taken for granted. Perhaps of more interest is von Karman, whom I know slightly in Europe. When I was in Vienna during the war, there was a big seminar, where all these people attended: von Karman and von Mises and then I met them again here. And von Karman told a story about his Air Force boss who asked, “I’d heard that a Hungarian Lieutenant Karman made an experiment in which helicopters supported” — I forget [how much weight] it was. “Could you find out something about that?” Karman said, “Don’t you know that Hungarian Lieutenant von Karman?”
How about the other story, after he was here?
Karman was told at a dinner that in Roman times, a number of martyrs were supposed to be attacked. So the first martyr was let in, and then the lion was released on him, and the lion bounded up to the prospective martyr. The martyr turned to the lion and mumbled something to him, whereupon the lion withdrew, and it was found impossible to get him to attack again. The Emperor was really astonished, and wanted to know what he had said to the lion. And the martyr refused to say, until he had gotten a promise that all his co-believers would be released. Then he said, “I only told the lion, ‘I assume that you will be asked to say a few words after dinner.’”
That’s not the story I meant.
What was the story?
Well, von Karman was here in the United States, and the Germans wanted to get him back again.
Before the war, von Karman was a visiting professor; half a year professor in Pasadena. And when the Nazis came into power, Goering wanted to get Karman back, and Karman of course didn’t want to. He said, “If he asks again, send him my profile!”
That’s all he can have.
[Then Goering wouldn’t invite him, the profile reveals he’s a Jew].
Mrs. Herzfeld, are there things that you recall? I would be particularly interested in anything that shed light on anyone’s approach to physical problems or their general attitudes toward life.
Well, we were very good friends with the Ewalds.
If particular events stand out in your memory as being particularly characteristic of these people, it might be nice to have them recorded.
Most of our work in recent years has been in ultrasonic. That has led to an understanding of the liquid state, and we are interested in the transition between the liquid and the gas.
And that’s work that you carried on up to your retirement?
Well, I haven’t done much. You see, I retired in 1969. Around that time and since, I’ve had three or five operations, which isn’t particularly favorable for scientific work.
Yes, of course. I understand.
I just recall the invasion of Poland, We were visiting the Mayers on a lake in New Jersey, and the Fermis were there. There was a big reservoir there, and there was a nice path to it. We often walked there. This particular day, we were going through. It was "No Trespassing" of course. We were going through this path that many people used anyway. Karl had hyperglycemia, and we needed some sugar for him right away, so we sat down to rest. That was our mistake, because the warden came along, and he was in a very bad mood that day. I think he’d had a little bit too much to drink anyway. So he arrested us. And instead of taking us to the office closest to the village where we were staying, where the Mayers were, he took us way far away. But on the way, we asked him if he wouldn’t let us stop at the Fermis’. Mrs. Fermi ran in and got some sugar for Karl. Joe Mayer had followed us. He hadn’t been with us on the walk, but he had followed the warden’s car, Maria was with us. Joe came along but he didn’t have any money either, because he had just dashed out, so fortunately, Fermi came along and bailed us out. Oh, that was funny. But we were all there at the time of the invasion of Poland, I remember we were at the Mayers, listening to the radio.
Oh yes, Mrs. Fermi — the children would be in bathing, and Mrs. Fermi would call them to come home, "Nella, Julio —" She had a very musical voice, and when she called them, you could hear her. Oh, we had a very pleasant visit.
Well, I’m sure there are many people who feel that Fermi bailed a lot of people out, in the next few years.
Oh yes. He did.
He was a remarkable man.
Shall we go look at the letters now?
Yes, that would be a good idea.