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Oral History Transcript — Dr. Martin Schwarzschild

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Interview with Dr. Martin Schwarzschild
By Spencer Weart
At Princeton University
June 3, 1977

Listen to Schwarzschild reminisce about Enrico Fermi and what it was like to work with him.

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Martin Schwarzschild; June 3, 1977

ABSTRACT: Life of his father, Karl Schwarzschild; father's scientific relationships in Göttingen (Felix Klein, David Hilbert); move to Potsdam, 1909; relations with Potsdam and Berlin scientists (Albert Einstein, Karl Sommerfeld); father's Jewish background concealed. M. Schwarzschild's youth in Göttingen and Berlin; early education, interest in astronomy and mathematics. Undergraduate at Göttingen Universität (Hans Kienle, Richard Courant, Neugebauer), 1930-1933; graduate work at Gottingen Observatory, 1933-1935; his reaction to Nazism. Introduction to astrophysics (Arthur Eddington), interest in stellar interiors and stellar evolution; contacts with other astronomers from Gottingen Observatory (Otto Heckmann, Kienle, Rupert Wildt); comments on general relativity; interest in pulsating stars; leaves Göttingen, 1936. Postdoctorate at Oslo (Svein Rosseland); Jan Oort, Ejnar Hertzsprung; mechanical analog computer for computations in astrophysics and celestial mechanics; comments on development of theory of stellar interiors, 1939-1950. To Harvard College Observatory (Harlow Shapley), 1938; C. Payne-Gaposchkin, Bart Bok; comparison of European and American observational style, social scene; Barbara Schwarzschild's difficulties as female astronomer; contacts with S. Chandrasekhar and other astronomers. Tour of the United States; visits Mt. Wilson Observatory (Wilhelm Baade, Rudolph Minkowski, Edwin Hubble, Milton Humason), 1940; Shapley's relationship with Mt. Wilson staff. Harvard (Fred Whipple), 1938-1941; Shapley as a leader; astronomy summer school at Harvard; work on Cepheid variables in M3 (Bok, Chandrasekhar); overall impact on Schwarzschild of Harvard period. Columbia University (Jan Schildt, I. I. Rabi), 1940-1942; difficulties there; origin and funding of Thomas Watson Astronomical Computing Center; discussion of cosmology in the late 1930s; contacts with physicists (Enrico Fermi). In U.S. Army, 1941-1945; enters as private, teaches math to recruits; refuses invitation to Los Alamos; transferred to Aberdeen Proving Ground, dissatisfaction there; to officers training school, does bombing analysis for Italian campaign. Work relating to stellar interiors and evolution, 1938-1946; nuclear energy source ideas (Hans Bethe, Fermi); Eddington, Gerard Kuiper, Chandrasekhar, G. Keller; German astronomers during World War II (Ludwig Biermann). Discussion of wife's career and her role in his career. Early ideas about red giants (Öpik, Herman Bondi, Fred Hoyle), 1946-1950. Work on acoustic wave energy transport (R. Richardson, Gold); work on chemical composition differences in stellar populations. To Princeton University (Spitzer, H. N. Russell), 1947; Project Matterhorn (start of bomb and fusion projects); relationship with Russell. Stellar evolution work in the 1950s; computer work (John Von Neumann, Richard Härm), mid-1950s; collaboration with Allan Sandage evolving a stellar model, 1952; computing towards red giants; observational cluster work, 1951; ages, metallicity, and the Big Bang; beginnings of "astrophysical" cosmology. Evolution theory after late 1950s; effect of computers on theoretical progress; relation of evolution theory to cosmology; general comments on his work in stellar evolution; interactions with Robert Dicke; views on cosmology, general relativity. Need for better solar convection work leads to use of balloons (James Van Allen); post-Sputnik funding; on cooperation with industry and engineers; Stratoscope II (Bob Danielson, Spitzer). Years advising the National Science Foundation, President's Science Advisory Committee, 1959-1976, and National Aeronautics and Space Administration (Von Neumann), to 1969; The International Astronomical Union, 1964-1970; American Asronomical Society, 1967-1973. Informal advisor to various observatories: Kitt Peak National Observatory, Mt. Wilson-Palomar Observatories, Carnegie Southern Observatory. Recent work on galactic structure. Reflects on importance of ethical standards; his feelings about religion and nature.

Transcript

Session I | Session II | Session III | Session IV

Schwarzschild:

You will have to stop me often, of course, because I do not remember.

Weart:

Right. Well, we had about finished Gottingen, except for one thing that I hadn't asked you about the Gottingen period that I wanted to, which was about your work there on the Delta Cepheids. I know you were interested in pulsating stars already from reading Eddington and so forth, but I don't know how you happened to pick exactly this problem to work on. Did Wildt suggest it? Did you suggest it to him? Were other people involved?

Schwarzschild:

No. Nobody there was really at all versed in the stellar interior. I still think it was one of these foresighted steps for Professor Kienle, noticing that I was interested in that type of theoretical work, to advise me to read Eddington's book. I think what actually happened was that Eddington, in his chapter on pulsation, states one unsolved problem. And that was just the challenge I needed; it came right out of Eddington's book.

Weart:

I see. You hadn't read other literature on this?

Schwarzschild:

No. And I stopped in that chapter, and never read the rest of Eddington's book. So it was really one clearly stated unsolved problem, in that chapter of the book, that got me on that track.

Weart:

Then you seem to have done both theory and observations of Alpha Ursae Minoris.

Schwarzschild:

The observations in Gottingen were entirely because Professor Kienle would not let anybody get away without observing, quite irrespective of what might be the (student's) main strength. A point that has helped me no end. Actually, I think Professor Kienle would have insisted on my completing an observational thesis, but then the political pressure became so that it seemed urgent that I finish as soon as possible. And since I had progressed quite well on the theoretical side by myself, he finally decided to let me finish that as the thesis. Then I finished the quite small observational program only as a side issue. As a matter of fact I finished the reduction of the observations only after I was already not any more permitted to enter any university building. Professor Kienle had the measuring instrument brought at night to my mother's apartment.

Weart:

I see. In your paper you mentioned that you were impeded both by some difficulties of the instruments, and also by the Gottingen observational conditions, "beobachtungsbedingungen" Were you referring to the political situation perhaps? Or were there other instrumental difficulties in making these measurements?

Schwarzschild:

I do not remember exactly what I was thinking of at that time. The Gottingen instruments were very small, and the Gottingen weather is atrocious. So the total number of photometric nights is even fewer than here. I didn't know any other state, so I think I took it as it came. But it made an observational thesis quite hazardous, because you just didn't know when you got enough nights.

Weart:

I see. How did you like observing?

Schwarzschild:

Well, I always enjoyed it quite enormously. And have continued to enjoy it; even now, I have been involved again in regular ground-based observing. I continue to enjoy it.

Weart:

Just being at the telescope.

Schwarzschild:

Yes, and trying to make the instrument really behave — top level (that?) and trying oneself to make — few mistakes as possible, during the night, is really sort of a challenge of one's capabilities in a mixed fashion. It calls both on one's psychological stamina and one's understanding of the technical points.

Weart:

Of the instruments. I see. You consider yourself then in part as an instrumental person?

Schwarzschild:

Oh, very much so, because I would have never gone through the balloon project —

Weart:

— the Stratoscope. But I was thinking of the earlier period, back in Gottingen and in the thirties.

Schwarzschild:

In Professor Kienle's school, the idea of a division into pure theoreticians and pure observers was never considered healthy. Lyman Spitzer here is of exactly that same kind. Indeed, it was a whole generation, I think, to which I belonged, where this separation really disappeared. In many ways, I think of the group more or less of my age — Chandrasekhar is probably the clearest straight theoretician. Of course, there are many straight observers. But the purest absolutely non-theoretical observers really are one generation earlier.

Weart:

I understand. For example, you mentioned that Kienle would have insisted that you have an observational thesis.

Schwarzschild:

Right.

Weart:

Was that generally the thing at Gottingen, or perhaps even around Germany and so forth?

Schwarzschild:

I don't know whether it was quite general all through Germany, but with Professor Kienle that was quite definitely so. But not in a one-sided way. He at the same time led me, in an extremely effective way, into theoretical work — without any guidance by himself, because he was not a theoretician.

Weart:

I understand. OK, is there more to be said about the work on the Cepheids? The next thing I have here is that you moved to Norway and so forth.

Schwarzschild:

Right. But actually I continued the theoretical work on Cepheids, both in Oslo and even in Harvard. I finished my PhD in December '35. And no possible position was apparent at that time. I myself was entirely dependent on what other astronomers in Germany, particularly Professor Kienle, might find outside the country. At that time I was already completely banned from any German university. Professor Kienle had contacted a variety of outside astronomers, I do not know whom. By spring of '36, Professor Rosseland in Oslo, then quite a leading theoretician, particularly for the stellar interior, offered me a one year post-doctoral fellowship. That was of course terribly exciting and it was an extremely happy circumstance for me. I think that Professor Rosseland went quite out of his way to find the means to give me a chance to come out of Germany. Actually, on the way to Oslo, but also immediately after my PhD, twice, Professor Hertzsprung invited me to come to Leyden for a week or two, which were for me very big events. These were personal visits. I mean, as the son of my father, who was the closest astronomical and personal friend of Hertzsprung. For me, those visits were extremely important, because I had a chance of seeing the work in Leyden. That is, Hertzsprung's school, very much observational, and in fact mostly on variable star8 like Cepheids. But also, it was my first chance of meeting Oort, which gave me an enormous introduction to his interests, his field.

Weart:

Oh, is that so? Did you feel even already at that time that he was an outstanding person?

Schwarzschild:

I wonder whether I even asked myself that question? I think all that I can remember is that he seemed to me personally terribly exciting, and that he was very patient, and gave me just a marvelous introduction to his field. I do remember one short scene, one of our discussions at that time, where he had described at length one of these big projects he then was engaged in regarding analysis of proper motions, and finally he said, "I'm getting a little tired of it." I was terribly surprised and told him so, because what he had told me seemed to me all terribly exciting and very new. When I said that I did not understand how he could be tired of that kind of research, he said, "Well, it has been a little long." You know the way Oort can smile, and that finishes that remark.

Weart:

He had been doing it for quite a while, too, that's true.

Schwarzschild:

By that time, right. Then, going to Oslo was for me an entirely new experience, because suddenly I was in Rosseland's institute, which was essentially entirely theoretical.

Weart:

Is that so?

Schwarzschild:

It had a few theoretical astronomers, but also a group of theoretical meteorologists were there. Indeed, the older Bjerknes, who was retired and who had done his great work in Bergen, had retired to Oslo. And there was a very active young group. So I learned a lot of theoretical hydrodynamics at that time.

Weart:

In taking courses or working with people?

Schwarzschild:

No, just talking. We had luncheons fairly regularly together, all the young group in any case. So I had a first experience of being together with people who were mainly theoreticians. It was, I think, enormously helpful, and it gave me the next step in my education. Professor Rosseland was just an extremely warm person. I did not see all that much of him, but the occasional hours spent with him made a very important impression on me.

Weart:

In terms of your scientific knowledge?

Schwarzschild:

Yes.

Weart:

He would advise you in terms of the work you were doing and so forth?

Schwarzschild:

Very much so. Mostly just by asking here and there a question. He was a very wise teacher. He knew how to teach youngsters who had their own ideas, by not forcing his point on them, but by asking questions. He definitely led. It was for me, I think, a very happy year, because Norway is not as big a step from Germany as coming directly to this country would have been. As an intermediate step, it was very wonderful. Also, I enjoyed skiing no end, and that winter in Norway was marvelous skiing.

Weart:

You'd already done some skiing in Germany.

Schwarzschild:

Yes, but nothing like that, that one glorious winter of skiing. It was beautiful. And even Rosseland was a very good skier.

Weart:

These Norwegians of course are very athletic.

Schwarzschild:

Yes.

Weart:

Were there other social interactions? Were there seminars, dinners at people's houses?

Schwarzschild:

Not all that much. But after a month or two I could move into what was called a student's home — a university-run home for about 200 students, quite close to the new complex of physical sciences buildings, and in that home, life was very friendly and very lively. So I did not feel lonesome the moment I moved to that.

Weart:

I suppose the Gottingen atmosphere by that time must have been rather depressing, so it must have been quite a contrast.

Schwarzschild:

Oh, that is entirely right. The last years in Gottingen, for me social life had essentially been reduced to cautious contacts with very few friends. Of course, the danger for them to be together with a Jew was getting higher and higher. So it was quite different. But at the same time, the step of a change from one cultural surrounding to another, I felt quite strongly also, you know, in Oslo. I invited my mother for a couple of weeks around Easter time, and we had a very nice time, but of course basically she was already in an extremely worried state about what would happen to us three children.

Weart:

Yes, particularly the younger one who was still there.

Schwarzschild:

My brother was still in Germany. But also the worry whether my mother would be able to maintain any contacts with my sister and myself. Actually, during that short spell came the offer from Shapley for a three year fellowship.

Weart:

I see, during that —

Schwarzschild:

Just when my mother was there, which was a very hard blow for her —

Weart:

— because it would take you farther —

Schwarzschild:

— because the distance seemed so enormous. And in fact, I was extremely unhappy about that offer, because my picture of this country was so, that I was quite sure I would not want to spend my life in the United States.

Weart:

This was your picture of American astronomy you're talking about, or your picture of the United States in general?

Schwarzschild:

The picture of the United States. Not at all from the astronomical point of view. I had just a simplified picture, to exaggerate a little, that the United States consisted of Indians, gangsters, and Mt. Wilson. It was quite clear that I wanted to visit Mt. Wilson, but the character of the country, as it was abstracted in in my mind — and I think that was somewhat typical from the German point of view — was a country without any culture.

Weart:

I was just going to say, a country with no "kultur."

Schwarzschild:

Right. And therefore, the idea of having this offer, professionally obviously very fine, but from this country, with the likelihood that that might decide my permanent stay, was a very hard one. And I did persuade Professor Rosseland to send a telegram to Eddington, who had indicated the possibility to stay in England for one year, but with the indication that there was no long-range future that he could foresee. Rosseland did telegraph Eddington, and Eddington telegraphed back that I should accept Shapley's offer, and that made the decision.

Weart:

I see. Before we get a little further into that, I wanted to ask you a little more about Rosseland's institute and what you did there. In the first place, did Rosseland's institute seem at all out of the way, off the beaten track? Or did you get foreigners, various people, coming through there, did you feel in contact with the rest of the astronomical world?

Schwarzschild:

I do not remember meeting foreigners there, except that simultaneous with me, a young Finnish astronomer, Tuominen, was there. But I didn't feel at all out of contact, because Rosseland himself had excellent contacts, and the meteorological dynamics school had very strong contacts. Also, Professor Stormer, one of the very early observers and theoreticians for the question of particles coming from outside into the earth's magnetic field and making aurorae, which were spectacular phenomena in Norway — that whole group had strong outside contacts. So I can't remember any trace of feeling outside the general scientific scene.

Weart:

I see. You would have been glad to stay there if you could have, I suppose.

Schwarzschild:

Oh, yes. I mean, emotionally, much rather than come to the United States. There was one other interesting technical phenomenon — just the year that I was there, a mechanical analog computer, was finished. Rosseland had become very interested in extended computing devices. Bush at MIT had developed the first major general mathematical mechanical analogue computer, and Rosseland had decided to order one for himself.

Weart:

Identical to Bush's model?

Schwarzschild:

Right. And it just got into operation when I was there. I asked Rosseland whether we could try on that machine a simple problem, again in pulsation theory, and he said "Yes." I remember extremely well the excitement, and I think Rosseland was as excited as I, and so was Gunnar Randars, who —

Weart:

Gunnar Randars was there?

Schwarzschild:

You know probably —

Weart:

— I know him from the nuclear fission side.

Schwarzschild:

That's right. That is where he went after the war. He was a very gay companion, about my age, an extremely happy and outgoing person. The three of us tried to run that first computer that I ever had contact with (other than ordinary old-fashioned desk calculators).

Weart:

In Gottingen you used the hand-cranked kind?

Schwarzschild:

Yes.

Weart:

Turn the handle —

Schwarzschild:

— yes. No electric motors in Gottingen.

Weart:

I see. So this was quite a step forward.

Schwarzschild:

This was very exciting. I do remember that Professor Kienle, before I left Germany, had reported to us that Rosseland was building this machine. And I still remember a remark of Kienle's, that if one needed that complicated a computing machine, he felt one probably didn't have the right theory. It must have made quite an impression on me, because I was not all that certain whether on that point Kienle was right. And it worried me, because at that time, what Kienle said carried weight with me. But then, using that machine — as a matter of fact, this pulsation problem was the very first one that Rosseland put on the machine — was a particularly exciting experience. It worked well enough; the accuracy was fairly poor, but just sufficient for that one problem that we tried, and I published a paper on the results with it. [1]

Weart:

What do you think now, thinking back, about that statement of Kienle's — for the state of astrophysics at that time?

Schwarzschild:

I feel that there Professor Kienle did not have the appreciation of theoretical astrophysics; that in astrophysics we cannot choose the experiment about which we want to make computations. In astrophysics, we have to take the experiments that Nature presents us with. A star, for example, is just intrinsically a very messy experiment. Even in the idealized form in which my Uncle Emden had attacked it already, required very extensive hand computations, at his time. And if I wanted to proceed further, one would get into more and more computations. It seemed to me rather clear. Also, of course, astronomers were used to extremely elaborate computations in celestial mechanics.

Weart:

That's a very interesting point. Some of it may have come over from that side.

Schwarzschild:

At least we were sort of mentally prepared. Though to a degree, there was a division between those in that classical branch of astronomy and the astrophysicists. Professor Kienle by temperament being quite an impatient man, would not likely personally appreciate longish computations.

Weart:

But for example, there were hand-cranked machines at Gottingen. Were they originally intended for celestial mechanics problems? Or did Rosseland expect that his machine would be used for celestial mechanics?

Schwarzschild:

The first question, I do not know. Not very much celestial mechanics was done in Gottingen in the times preceding Professor Kienle's time. For example, when my father was head of the Gottingen Observatory, I'm not aware of very extended computations that were carried out during that time. And I do doubt that Rosseland ever imagined his computing machine to do celestial mechanics, because the accuracy was just not high enough. You might reach three significant figures, but the fourth one, I think, was quite out. And that is just not the accuracy that is required, by several significant figures, for any celestial mechanics. So Rosseland's machine was for straight astrophysics. But including, for example, such problems as Stormer's interest in electron orbits in the earth's magnetic field. Indeed, that was one of the main applications to which the machine was aimed.

Weart:

Quite a problem, too.

Schwarzschild:

That's right. And I am somewhat skeptical whether, for that problem, the accuracy really was sufficient.

Weart:

The reason I questioned how far one could go in the thirties, even given the ideal computing machine, was because of the lack of understanding of the energy sources, the lack of nuclear physics.

Schwarzschild:

That certainly is absolutely fundamental, a fundamental question. And I do not know whether I mentioned last time already, that in afterthought, I think it was not a wise choice of myself to go into the interiors —

Weart:

— Yes, you did mention that —

Schwarzschild:

— because that key physical item was missing. And (there was) no way, in any case, for me to predict when the physicists would get to the point where those data would be understood and available to us.

Weart:

You seem to have had some feeling about that. While you were in Oslo, you wrote this paper on the creation of energy in stars, "Uber die Energieerzeugung in den Sternen," [2] in which you get some very broad limits on what the energy production might be. I wonder how that came about?

Schwarzschild:

Right. Well, I think we all were interested in that question. That paper, by the way, I think is an extremely incompetent paper. At that time, I still was very strongly under Eddington's influence (through his book, essentially entirely). All stars were constructed according to his so-called standard model. One had no imagination that other stars, particularly the red giants, could be constructed completely differently. Taking Eddington's standard model far too seriously, I came to the conclusions of that particular paper, which were physically (as in afterthought it is clear) completely unreasonable. And by the way, that was the paper that was extremely sharply attacked, in print, in a violent way, by Opik, who understood the physics very much better. In one of his two famous — well, now famous — papers of 1938, [3] he just dismissed my paper with the words that the author clearly does not understand what he is writing about. It was a quite hard blow for me, but I think somewhat typical of Opik at that time, with the consequence that not only I, but also the rest, ignored these papers, very much to the detriment of the development of the field. There, I think, psychological personal frictions just blocked the effectiveness of Opik's work, and left people like myself, but also others, to flounder about for more years than necessary.

Weart:

This would apply even into the 1950's?

Schwarzschild:

No, I would say that quite independent of Opik's work, the development started. Partly in this country, late during the war. Because in '38 — that is, the same year of Opik's papers, quite immediately afterwards — came the papers by Bethe and by von Weizsacker. But then, however, everybody got very preoccupied by the war, so that only in the early forties — well, Gamow and his colleagues and Chandrasekhar and his colleagues started computing models of a kind quite different from Eddington's model. And Hoyle and his school about the same time (but for physically quite different and, we think now, wrong reasons) started the same type of model development.

Weart:

We'll have to get back to that.

Schwarzschild:

Right.

Weart:

I do want to ask you about these developments. I was interested, though, in this paper, although the conclusions were wrong, simply in the spirit behind it of trying to learn something about what the energy generation must be.

Schwarzschild:

I think that I probably understood at that time the importance of the lack of our understanding of the nuclear sources, and tried to see whether we could find conditions for it, purely from the astronomical side — which turned out to be fruitless.

Weart:

You can't do it.

Schwarzschild:

A fruitless attempt.

Weart:

OK, well, now maybe it's time to talk about your move to Harvard, and how that offer from Shapley came about.

Schwarzschild:

As I learned only much later, during those years Shapley really took a leading role in trying to help German immigrants in astronomy. One way or another, mostly by trying to find funds to bring them to this country. In astronomy the number was not large. But there were not so many (people), I think, that looked out for German Jewish scientists, other than the famous scientists. They had easier offers. But young unknown people, and also the less famous older scientists, had a very much harder time. And in that regard, my personal respect of Shapley is really enormously high. It was the beginning, I think, of Shapley's development into the broader public frame that then became, isn't that right, a very strong preoccupation for him, and after World War II made difficulties. This first major involvement was, in any case, for a person like myself, an entirely decisive one. I assume that he learned to know about me, possibly by Professor Kienle writing to him, but Miss Payne — she was not yet married at that time and was on Shapley's staff — had come to the German Astronomical Society meeting that happened to be in Gottingen, and I had met her at that time. So had my sister and my sister spoke fluent English. I couldn't speak any English, so my contact with Mrs. Payne-Gaposchkin was very small. But my sister talked extensively to her, and in fact, Miss Payne got a fellowship for my sister.

Weart:

For your sister?

Schwarzschild:

For my sister, directly then, and for my sister it was really terribly important to get out of Germany — for a girl at that time it was impossible.

Weart:

Oh, even worse than for —

Schwarzschild:

Even worse. Because she was older and social contacts were much more important. I mean, for me to be a little separated for a few years at that age was no tragedy.

Weart:

So she got a fellowship in —

Schwarzschild:

In Cambridge, England, in the same college to which Miss Payne had belonged.

Weart:

That was in your sister's field?

Schwarzschild:

— No, the college —

Weart:

— Yes, but your sister was in —?

Schwarzschild:

Is in classics, comparative philology. But Miss Payne has a very broad view. Obviously, I suspect, that she must also have given a description of me to Shapley. But never anything was described in detail.

Weart:

So did this letter simply arrive, or had Rosseland already been in contact with Shapley?

Schwarzschild:

For me, as I remember, the letter offering that fellowship simply arrived.

Weart:

Out of the blue?

Schwarzschild:

Yes.

Weart:

As a tremendous surprise; you didn't even know Shapley knew about you?

Schwarzschild:

Yes. I don't remember in detail, but any of the correspondence that, on my behalf, was going on — I knew that efforts were being made, but that was as far as I was told. And that seems proper.

Weart:

— Yes —

Schwarzschild:

So that any of the "no's" would not be too embarrassing for me or anybody else.

Weart:

Yes. It's just not done that way these days. Well, perhaps you can tell me, while you were making up your mind or just before you came to Harvard, I'm curious as to what sort of an image you had of American astronomy. You mentioned Mt. Wilson. Did you have any other ideas about American astronomy?

Schwarzschild:

Well, by that time, of course, I knew a lot of the various kinds of work that was going on in this country, and my respect for American astronomy was not limited to Mt. Wilson. Obviously I had a picture of Shapley's early work, and was aware that Harvard was a big observatory; indeed, Harvard under Pickering had been a very clear picture. So much of the observational work on variable stars came from that group, for example.

Weart:

Oh, that's true. You would have been very familiar with that.

Schwarzschild:

So, I think I had a lively picture of American astronomy. And no picture of American life.

Weart:

But American astronomy seemed to you to be equal with astronomy in other countries?

Schwarzschild:

Oh, yes. On the observational side, I think there had been a strong feeling of an inferiority complex in Europe, relative to America.

Weart:

I see. Because of the big telescopes.

Schwarzschild:

Oh yes. Big telescopes and, at least in part, excellent climate. But on the theoretical side, in the States, there had been nothing like as much work as in Europe, taking Europe together. So from the purely theoretical point of view, the States still looked rather inferior to Europe — which I think is a description that one would accept, even now, for that time.

Weart:

For that period, yes. Well, I'm curious now as to how America, and particularly American astronomy, appeared after you arrived at Harvard — what sort of surprises you found, or what particular things struck you in contrast. But first, is there anything in particular about your trip over or your arrival at Harvard?

Schwarzschild:

Well, many funny small accidents, but none of very major importance. Except maybe that before I even arrived at Harvard, I visited Rupert Wildt here in Princeton, and met Russell for the first time. It took the very characteristic form of Rupert Wildt telling me that I would have to present myself to Russell the very first morning. So around 10 o'clock I was presented to Russell, who dismissed Rupert Wildt, started immediately to talk to me, with very few questions about myself, and with great enthusiasm describing what his interests were. I could hardly understand him at all. My English was extremely poor and Russell spoke extremely fast. He invited me to come to lunch. His family was already in their summer home on Rhode Island. So he continued speaking during lunch, except for maybe 30 seconds of a quiet prayer. Then after lunch he took me over the entire campus, gave me the whole history, in a setting of American history which I didn't know. And by 4 o'clock he let me go. We were back at the observatory. And I was so exhausted that I asked Rupert Wildt to give me a chance to go to bed. So that was my first meeting with Russell — entirely characteristic, with Russell, I think, having no idea how little of anything that he had said I could possibly have understood. But then promptly on the 1st of July, which I understood was my official date of engagement in Harvard, I appeared there, and was promptly, in the most friendly way, taken in. The first supper I had with the Greensteins, who had just finished, that is, Jesse Greenstein had just finished his PhD there and was ready to leave. Then I was invited out to their country station for the 4th of July celebration, and met Shapley out there.

Weart:

This is Oak Ridge?

Schwarzschild:

The Oak Ridge Station, yes; now it is called the Agassiz Station. I remember my first meeting with Shapley. He had come out of the woods with an enormous axe, so he looked quite formidable. Also, he knew practically no German, and I still practically no English, so our communication was fairly non-existent, except for, I think he understood that I thanked him for the offer. Mrs. Gaposchkin, who by that time was married, was right from the beginning extremely friendly to me, and so was Bart Bok. I think these two, Mrs. Gaposchkin and Bart Bok, probably were the most helpful mentors all through the three years. In very different ways, according to their characters. But I had much more contacts, both scientific and personal, with the two of them, than either with Shapley himself or with Dr. Menzel, who was in another branch of astrophysics from I.

Weart:

Could you tell me, this is interesting, about how Mrs. Gaposchkin and Bart Bok helped? How did they function as mentors, as you say?

Schwarzschild:

Mrs. Gaposchkin, much more from the scientific side. She was then very actively interested in variable stars. She always has had an unbelievable memory and a very wide interest. So with her, I could discuss my work, and learn an enormous amount of, you know, not random observations. I think one of her main strengths lies in digesting observational materials and finding the patterns, finding the relevant relations, from the theoretical point of view. Also, I just personally liked her very much. And got very used to Sergei Gaposchkin, who was a lively and quite special character whom I really liked very much when I was alone with the Gaposchkins. When I was together with Sergei Gaposchkin and others, he had a way of steadily embarrassing everybody. But when you took him as he was, we really got along extremely fine, so there was no difficulty. But together with other people there was, to an appreciable extent. Bart Bok's field was quite a different one, galactic structure, much more from the Dutch school. Basically the Kapteyn, van Rijn, type of school. But Bok always has been a marvelous teacher, from the point of view of really taking the personal side into account. One of the very big steps he did in advising me was, after I had been nearly one year there, and had essentially continued the theoretical work in pulsations, he suggested that maybe it was time, at least for the time being, to close if off and possibly think of an ambitious observing program. Which I never would have done by myself. He said, "You decide what you want to do scientifically, and if it takes the 60-inch" (which was the big instrument in Harvard then, and not a small instrument from any point of view) "If it takes that, ask Shapley. He always can say no. In this country, one asks, on a reasonable basis, and is not embarrassed if one gets a no. And that turned out to be, for me decisive advice. Indeed, there was one program I did get very eager about, and it did require the 60-inch, and Shapley did give me the necessary nights.

Weart:

That's on variables in M 3?

Schwarzschild:

Right. I had gotten somewhat convinced that a certain type of variable stars might be pulsating not in the fundamental mode, but in an overtone. Dr. (Ted) Sterne, who was then in Harvard, rather bet against me. But somehow, I guess I was a stubborn enough youngster at that time not to let myself be too easily deterred, and so I laid out this observing program. I remember Hertzsprung came through at the time, just before I started that program, but it was already all arranged and settled, Hertzsprung was really terribly nice to me. I think that was a straight consequence of transferring his feelings for my father to me. Indeed, for his one-month stay, where he used that enormous Harvard plate collection for his variable star work, he had been given an office in the top floor; but had asked to be transferred down in the basement, where my desk was, and took the next desk. Not that we really had much personal conversations, but just working on neighboring desks was —

Weart:

You just felt that contact —

Schwarzschild:

Apparently. I think I woke up to it only later, that there was a more emotional connection than I realized at that time. But of course, it gave me a marvelous chance of discussing matters. After I had described that program to Hertzsprung, Hertzsprung asked me "What accuracy do you need?" And I told him what was needed to answer the theoretical question. And he looked at me and said, "You think that that can be achieved in Harvard?" Which gave me the first inkling that he did not think all that much of Shapley's style of accuracy in observing, even though he clearly admired Shapley for his broad sweep.

Weart:

If we can, I'd like to get back to comparing Harvard with Germany, in terms of what were the contrasts in the kinds of facilities and career opportunities, the approaches people had to teaching and research, the social environment.

Schwarzschild:

On the astronomical side, I would not say that the Harvard style surprised me all that much, with the exception possibly of a couple of very large-scale programs, one under Shapley and one under Bart Bok, that employed lots and lots of people, mostly girls. And which I slowly got a little worried about — whether in that way observational quality could be maintained.

Weart:

Because the program was so large?

Schwarzschild:

It was large, and carried out by persons whose scientific judgment was not, in all cases, that high; some extremely fine and extremely faithful persons, indeed most of them of that kind. I understood then that it was really a long tradition; Shapley had not introduced it to Harvard. Pickering had worked very much in the same way, and indeed, Miss Cannon was still at the observatory, and I got to know her fairly well and just, as a person, was enchanted with her. But except for these couple of programs — none of which I ever got involved in, even though I heard, of course, the results reported, I interested myself to understand enough of what was going on, of what their aims were — I would not say that it struck me as all that different from Gottingen, for example. Of course, it was completely different from Oslo, which was a purely theoretical institute.

Weart:

But in terms of the interaction between theory, experiment and instruments and so forth?

Schwarzschild:

I think the attitude, set by Shapley, to a strong relation toward the theoretical side, even though he himself did not participate, was again not so unsimilar from what I was used to in Germany. On the social side the differences struck me as quite enormous. Missing classical music and many things of that type played a very depressing role for me. Even though by nature I think I am a person more normally happy than otherwise, I felt not at all personally comfortable for at least a year or two.

Weart:

Was this specifically relating to the Harvard College Observatory? Or was this just Boston and Cambridge in general?

Schwarzschild:

It was very largely the observatory. My contacts did not reach beyond the observatory, but the observatory was then a big group, full of young people roughly my age or a little older, so I was not alone at all. Indeed, the friendliness of the people, and the patience to get my English improved, was terribly actively friendly. They did everything to take me in, and make it happy for me. But that doesn't change that their style and their interests were very different from the group that I had left.

Weart:

Not as astronomers, but just as people

Schwarzschild:

Yes, right. So my acclimatization to this country came slow and really quite hard. I remember that after one year, I did go back to visit my mother.

Weart:

In Germany?

Schwarzschild:

In Germany, and my sister came at the same time. I remember one short discussion in which both my sister and I described our non-professional life. At that time, my sister felt quite as unsettled, in other ways, in England as I was in America. My mother really was terribly unhappy that the two of us had personally such a difficult time. I think for me that basically changed when Barbara (Cherry) appeared on my personal scene, even though really very slowly.

Weart:

That was during the Harvard period?

Schwarzschild:

Yes. She had finished her undergraduate studies, was a graduate student for one year and then an assistant to Dr. Bok for another year, and then decided to go into teaching. She was not convinced that, she was fit for a research person. But she was at the Harvard observatory.

Weart:

I see. Let me ask you about that, because that was during this period. Do you think that the fact that she was a woman played a role in that decision — the way she was treated?

Schwarzschild:

In a mild or indirect sense, yes. Because there were many women in the Harvard Observatory; the vast majority were in these giant programs, which Barbara did not want anything to do with. Indeed, in spite of being very definitely Bart Bok's student, she never did any of the star counting. Actually, when Barbara did decide to leave for teaching, Bart Bok very much tried to persuade her to continue as a graduate student and get her PhD. By that time, the Annie Cannon Award of the American Astronomical Society had been instituted, by a gift from Miss Cannon herself. And Bart Bok mentioned that, "You, Barbara, may eventually win that award." To Barbara, in her quiet and not dogmatic way, somehow, this as the aim of her life seemed not what she wanted.

Weart:

I see. Were there difficulties in women who wanted to observe, to use the 60-inch, for example?

Schwarzschild:

In the days that Barbara was an undergraduate and beginning graduate student, women were not permitted to observe at the Agassiz Station, or Oak Ridge Station as it was called then. They were only permitted to observe with the smaller instruments, right around in the Yard of Harvard Observatory. Actually, during the three years I was at Harvard, that changed, and —

Weart:

— How did that change come about?

Schwarzschild:

I do not know, but I think essentially, between Shapley and Bok, they decided that maybe the time had come. But I was hardly aware of those problems.

Weart:

— You were not privy to their conversations.

Schwarzschild:

And I had not woken up, you know, to those larger scale problems. During the Harvard years, I was exposed to whole new branches of astronomy. But there was one very important influence for me going simultaneously, and that was, the very first summer that I was there, during the summer school that I attended — which were really fascinating lectures — Kuiper came from Yerkes. He and I had very lively discussions, and he invited me for Christmas vacations to come to Yerkes. I was of course very excited to have a chance to see one other very major observatory. And it was a question of — I don't know, two days or so, even though I was the guest of the Kuipers — and from then on, I was essentially daily with Chandrasekhar.

Weart:

At Yerkes.

Schwarzschild:

At Yerkes, right.

Weart:

Was this your first meeting with him?

Schwarzschild:

Yes, indeed. I remember the first time meeting him very strongly. It was, I don't know, the second or so evening I think the Struves invited us in the evening. That was probably the first time that I was actually in the same room with a non-white person in my life. And I got very aware that there was some instinctive reservation in my mind. But Chandra's impression as an astronomer was immediately there. And I thought later that night, very much, how, well, basically unethical my natural reaction had been. And decided that I had to overcome it. On the moment I made up my mind; there was no difficulty even the next day, when we had made an appointment to talk astronomy. From then on he became really my basic teacher in the theory of the stellar interior in any case. And in many wider fields, later on. It was a very gay time. He's only just a little older than I am, a couple of years or so. So we were sufficiently contemporary personally, but scientifically, of course, he was much more advanced.

Weart:

I see. For the first few years, then, you would only see him for a few days at a time.

Schwarzschild:

I think the next year he and Lalitha Chandrasekhar invited me, but I think for two weeks, to their house, and I was quite often, for spells of one or two weeks, in the house, all the subsequent years.

Weart:

I see, and you also corresponded between times?

Schwarzschild:

Somewhat. Not all that much. But we met then at meetings. From then on, it was very rare that we did not see each other, at least for a day or two, roughly twice a year. And that has been going on till now.

Weart:

Till now. And then one has the telephone as well.

Schwarzschild:

That's right. Yes.

Weart:

I suppose that's a post-war phenomenon.

Schwarzschild:

That is certainly true. Indeed, more recent than that, that we both could feel free.

Weart:

The fifties? The sixties? I'm curious.

Schwarzschild:

I would rather think, the sixties.

Weart:

I'm curious as an oral historian, because the letters begin to disappear at this point, with the talking on the telephone. Well, whom else did you associate with particularly, among your colleagues, during the Harvard period?

Schwarzschild:

There was a young group. Jesse Greenstein just was finishing, and left — of course, I kept meeting him again and again. Leo Goldberg was a graduate student. Lawrence Aller was a graduate student, and so was James Baker, who later went into optics and became one of the leading optical men. Roderick Scott was an advanced undergraduate at the same time. He, during the war, went into industrial work, and ended up to be the key scientist for many years in Perkin-Elmer. So it was an extremely lively and bright group, most of them students of Menzel.

Weart:

Is this simply because you happened to fall in with this group who were Menzel's students? Or —?

Schwarzschild:

I think Menzel had the brightest students in Harvard at that time.

Weart:

Simply by his personal characteristics?

Schwarzschild:

No, I think more by the field. I think Bart Bok in many ways cared more for the students, from the personal side. But his work then was really sort of running the end of scientific development, that really needed a new turn. And in that way, at that period, he did not attract the best students. After World War II, when he went into radio astronomy in a very short period, before he went to Australia, his was the first American radio astronomical school, and then had some of the finest students. But that was after World War II. Before World War II, I think Menzel had the brightest.

Weart:

How was Menzel regarded by the students and by the people around the observatory?

Schwarzschild:

I think he was considered extremely highly. As a leading astrophysicist, which he was at that time. And that group, like Leo Goldberg and Aller and Baker, quite particularly, were deeply attached to him.

Weart:

When you say you interacted a lot with these people, where did you interact? Where would you exchange ideas?

Schwarzschild:

The daily life, at least for me, was: I would get up very late, would make dead sure that I went to the one restaurant where we always had breakfast and lunch. Some of them had their lunch. I had breakfast. Quite a group of us would go then, around 6 o'clock, for our main meal, whether it was the middle of the day or the end of the day, and those of us who were on the late schedule would, around midnight, go to Harvard Square and have a final small third meal. During the meals were the absolutely regular contacts. Some of them I met on weekends for — oh, for example, trips to New Hampshire, or other hiking expeditions. But also, we got together in the observatory. Shapley organized what was known as the "Hollow Squares" which were, I think, once a week, through most of the year. Maybe two-hour sessions where he asked three or four people to give very short reports, so that everybody really heard what was going on in the various parts of the observatory. It was one of the most stimulating arrangements of exchanges that I have encountered.

Weart:

Would this be the main place where you would encounter the senior people?

Schwarzschild:

Yes, though with Mrs. Gaposchkin I had many scientific conversations, most of the time. I mean, very very frequently, and the same with Bart Bok, because he had a whole new field, isn't that right, for me to learn. He is so outgoing. With Menzel I had less scientific discussions, but enough so that I could follow what he and his school were doing. Anyhow his students of course always discussed with me what they were doing.

Weart:

Did you think of yourself as being attached particularly to one person, to Bok, for example?

Schwarzschild:

Not on the scientific side. Indeed, that work which in a way continued in variable stars and pulsation theory, even in the observational work, really only Dr. Sterne was at home in that field. But he was a more difficult person, and very much on the mathematical side. Very different from me, so that our contacts were not all that strong.

Weart:

I see. Well, there are a lot of other questions. I guess one thing I'm curious about is, when you got together, did you talk about subjects outside astronomy — biology, philosophy?

Schwarzschild:

What I do remember strongly was that I was very struck by the type of political interests that the young Americans shared, very different from the political interests that I was used to from Germany — where it always was very philosophical, very abstract, and very removed from any actual knowledge of the individual persons in politics. I remember, I was just flabbergasted when they could, you know, discuss in detail the politicians and the members of the administration in Washington, and the members of the state government. It was just, to me, a completely new aspect, and a very interesting one. And they certainly discussed politics in those years, very lively. After all, it was fast approaching the European war, and the beginning of the involvement of this country in the war. So those matters were very much in the foreground. There was a small group getting interested in classical music. It was sort of slowly developing, that people actually started to listen to even classical German music.

Weart:

Records?

Schwarzschild:

Largely on records, but there was one small music school, quite a famous one, the name of which I now forget, and we used to attend their small concerts. I used to go to the Boston Symphony reasonably regularly — but that, rather, by myself.

Weart:

About the politics, did you feel that there was a clear, uniform viewpoint, a position that people took? Or were there divisions of opinion in the observatory?

Schwarzschild:

Within the observatory, divisions developed fairly fast between those who wanted this country to stay out of the European War, and those who wanted to go in. I doubt that I fully understood it. Bart Bok for a long while was the most outspoken person against this country going into the war. Ted Sterne, on the other hand, though being Jewish, was in the National Guard, and left before Pearl Harbor to let himself be called up.

Weart:

To the regular Army?

Schwarzschild:

Yes. Though he immediately was assigned a research assignment in the Aberdeen Proving Ground.

Weart:

So he was the first astronomer at Aberdeen Proving Ground?

Schwarzschild:

That I do not know, but certainly the first one from Harvard. He might have been the first. Later, of course, there was a much larger group.

Weart:

Right. I see. These divisions — what about the left-right positions of people?

Schwarzschild:

I do not remember, and I would not be surprised if I just did not understand that spectrum, except, you know, in semiparallel to the German situation. But of course the German situation was so much more polarized that it really did not give any picture. I mean, I would not have known who was a Republican and who was a Democrat, at the observatory, at that time. There was one other, for me, very important influence, which came (in 1940) after I'd been two years in this country. I decided to put the money that by that time I had saved into a trip, the grand tour of the country. Mostly going from observatory to observatory, with the one exception that I stayed for three days at the Grand Canyon. And that trip, I think, made a very big impression. A general impression of the country, particularly the West, which really, since I loved the outdoors, was a very big impression on me. My love, particularly of the Southwest, I think has stayed from that time on. But in a sense more important, to see the big observatories, particularly in the good observing climates, most of all Mt. Wilson, was very…

Weart:

You spent several days at Mt. Wilson?

Schwarzschild:

Actually, I think it was something like ten days. The staff then was still very largely the original staff, as appointed by Hale, with a few of the oldest ones already missing, and exactly two, I think, or three later appointments. The famous Hale staff, though it was becoming old, was still there. That visit, I think, was a very fast widening seminar. I was forward enough that I just plain decided whom I would visit the next morning, and the next afternoon, and in the evening read one or two of their most recent papers in the library, and then I found very fast a couple of leading questions into their work, and I would get a free half-day lecture on their field. I was very much struck by the difference in style between the spectroscopists on the upper floor of the Santa Barbara St. offices (Hale's observatory offices) which contained Adams, Joy, Merrill, and Sanford, with Olin Wilson being the youngster added — and the lower floor, which contained a funny mixture of Hubble, and Humason, and added Baade and Minkowski. A very heterogeneous group on the lower floor, of quite a different character from the upper floor. On the upper floor the doors always used to be closed, with unbelievably little interchange. Indeed, I remember that the last day, I went back to one of those whom I had visited earlier and pointed out that one difficulty he had described to me, if I understood it right, had been solved by one of his colleagues a couple of doors down the hall. There that was little interchange. While downstairs, Baade and Minkowski, both very active and noisy, open door German-style talkative persons — persistent discussions. Always sounded like they had a fight even though they were extremely good friends. Humason, who by nature was much more quiet, I think soon appreciated the two very much and adjusted himself quite marvelously to the two, even though he stayed quiet, as he had been.

Weart:

But he would still interact with them.

Schwarzschild:

Would interact very much. The relations with Hubble, I think, were very much more complicated. They were persistently friendly, but Hubble's style was more like an English gentleman. Therefore in all his preferences and all his behavior he did not integrate with the rest of the group, even though the straight scientific interaction, I think, was very positive. Hubble had just finished his most famous, sort of concluding papers, one with Tolman I think in '35 and '36. In some sense, he was in an intermediate state, waiting for the 200-inch. Which he in fact never got to use: I don't remember the timing.

Weart:

I believe that's right.

Schwarzschild:

So in a certain sense, Hubble was distinctly not a driving force over the years that I was there, and his whole style and preferences were fairly foreign to me.

Weart:

And also to the other people there, do you feel?

Schwarzschild:

Well, to Baade and Minkowski, very much so. I think it took really a very fine effort of all three of them to stay on active scientific good interconnections.

Weart:

This is in terms of personal style, but were there also differences of scientific style?

Schwarzschild:

Well, as to scientific style, Baade was the perfectionist observationally, and fitted Humason in that regard exactly. They were as finicky and careful with the big telescopes and how they handled the dark room — you could just look into the dark room, and you knew which of them was having the telescope. Minkowski came from physics, brought many of the new ideas into the Mt. Wilson observatory. He was very clumsy with instruments. Indeed, we always jokingly maintained, "When Minkowski tightens a screw, it's 50 percent that he has the screwhead in his hand — broken off." Indeed, I remember Humason describing — but that was later, when Barbara and I —

Weart:

— isn't this true, that you're talking not only about your first visit, but sort of right through the forties, when you were

Schwarzschild:

Yes, that's right

Weart:

— That's fine, please continue.

Schwarzschild:

Humason once, an evening that Barbara and I spent at his house with Mrs. Humason and Humason, felt that Minkowski really should not be permitted to work with the 100-inch, because it was too dangerous for him, and too dangerous for the 100-inch. And told terrible things —

Weart:

— That almost happened, or had happened —

Schwarzschild:

Had happened, yes. I think Minkowski had the singular record of driving the prime focus platform onto the north pier of the 100-inch so that it could not be unlodged, other than by some engineer.

Weart:

I see.

Schwarzschild:

Which just horrified Humason. Humason, you know, had no actual formal education at all, and therefore he approached it all from a very different side. (gestures)

Weart:

I see, with great respect.

Schwarzschild:

Great respect, and he really was an unbelievably fine observer. Hubble, as an observer, was in a way quite different. He was not orderly, and indeed, I learned that it was always a horrible assignment for the photographer at the observatory, if Hubble insisted on publishing an actual photograph or a spectrum that he had developed himself, because it was all scratched up and had to be all retouched for publication.

Weart:

Which is very dangerous actually.

Schwarzschild:

It is, but of course the measurements were taken on the original plates, so the measurements were not affected by the published plates. So in that sense, it was not scientifically dangerous. But also, he was not as dangerous to the instrument as Minkowski was. For Hubble's work, actually the observations of Humason were the basic ones.

Weart:

You make it sound as if these famous papers, Hubble and Humason, Baade and Minkowski — you make it sound like very natural combinations.

Schwarzschild:

Yes. No question. But to come back just to the early time — that ten days were a very important introduction into a quite different branch of Ameri6an astronomy, basically coming entirely from the observational side. And particularly with spectroscopists, they were absolutely dissociated from theory — and didn't, indeed, appreciate theoretical aspects.

Weart:

So the spectroscopists not only were closed off from one another, but they were completely separated from the lower floor, as you say.

Schwarzschild:

And the lower floor was not that much for theory, either. So in that sense, any discussion of stellar interiors would not have made any sense there at all.

Weart:

I understand.

Schwarzschild:

By the way, Baade and I had met once before in my last year of high school. My class made a trip to Hamburg, and I had gotten permission to spend one afternoon at the Bergdorf Observatory near Hamburg, through writing to Baade. When another classmate of mine (who also was interested in astronomy but did not enter it eventually) and I appeared, Baade immediately gave us to an assistant. The way he tells the story — I do not remember it quite that way — four hours later, he accidentally saw that his assistant was still with the two of us. He says he immediately went to us, dismissed the assistant, and then dismissed the two of us, very fast too. But he remembers that event, I do not remember it. I remember gratefully that he gave us a chance and had no feeling that we had overstayed our welcome. But he kidded me about it later.

Weart:

Meeting these spectroscopists must have been rather a new thing for you also. You hadn't really dealt much with spectroscopy up to that point.

Schwarzschild:

Yes. Not at all. It was a hard training, because they tended to assume that I knew something, and let me look at spectra under the microscope, and talked about this line and that line, and I never knew what line they were talking about. But I still, I think, really learned a lot.

Weart:

Tell me also, when you went to Mt. Wilson, were you made aware, or did you know even before you went, about the difficulties between Shapley and Mt. Wilson?

Schwarzschild:

The only thing that I realized, which surprised me a little, was that Shapley was not all that enthusiastic about my idea of making this trip and staying the longest spell at Mt. Wilson. But that, I think, was the only surprise I had. Nobody made any remarks that I remember, at Mt. Wilson, regarding Shapley, though later on I got very badly in the middle between them.

Weart:

This was after the war. Or even earlier?

Schwarzschild:

No, after the war.

Weart:

After the war, right. OK, we can come back to that then. Let's see — we've covered practically everybody at Harvard, to get back to Harvard. Whipple was there, was he not?

Schwarzschild:

That is right. That was very much a mistake, not to mention him, because indeed, I had a lot of contacts with him. He had just a little before been divorced from his first wife, so he very much lived a bachelor's life, and the age difference was not large enough, so he was in this group with whom I had (at least) meals daily. He must be substantially, noticeably younger than Bok and Menzel.

Weart:

He was born in 1906, so he's the same age as Bok, in fact, and a few years younger than Menzel. But I gather that the impression was, if only because he was a bachelor, he was going around with —

Schwarzschild:

That may very well exactly have been the reason.

Weart:

He didn't have students of his own?

Schwarzschild:

He had amazingly few. I never quite understood it, because he had a very lively astronomical mind. I did not have, outside astronomy, that much contact with him. He was not an outdoors person, and that was a strong selecting criterion for me, for the weekends. Neither do I remember that he participated very much in anything musical at that time. But he was terribly friendly to me, particularly with regard to getting over the language barrier. He was one of the patient ones.

Weart:

I see. What was Shapley's style as a leader?

Schwarzschild:

There was no question that Shapley was the director. And it did not particularly surprise me, from my German background. But in the American setting I think, as an afterthought, he was unusually strong, and somewhat authoritarian, I think, in the American setting. There was just no doubt that he made the decisions.

Weart:

Didn't people have any reaction to this?

Schwarzschild:

I think both Menzel and Bok, who were really the key members, and also Fred Whipple, accepted him. Because none of them had anything like the standing of Shapley, so it was very natural. And Cecilia Payne-Gaposchkin I think admired Shapley enormously. Indeed, she came to Harvard because she wanted to work with Shapley. In fact, their research fields were very separate. I think the group really stayed with Shapley, with some question possibly arising in the politics of the war. Then it became more complicated.

Weart:

You mean the politics of entering the war?

Schwarzschild:

Yes, that, or not to enter the war. The participation prior to entering.

Weart:

I see. Shapley was for intervention?

Schwarzschild:

I'm not really certain. I really do not remember which side he was on.

Weart:

OK. Well, let's see now. I wanted to ask you about some of the scientific things going on at that time, but first, anything more about Harvard during that period?

Schwarzschild:

No. One should mention that the summer schools that Shapley did run during those years were scientific high points. It was really at that time the most outstanding postgraduate finishing school you could have. Russell gave a course. Robertson gave a course in general relativity. One of the Harvard physicists, Slater, in quantum mechanics.

Weart:

Oh, Shapley had him over to do that?

Schwarzschild:

Yes. And then, other astronomers, Rosseland, after he had to leave Norway and came to Princeton, came to summer school. Oort gave one course in one of the summer schools. These are several summer schools.

Weart:

And then there would also be people coming to attend them, I suppose.

Schwarzschild:

Oh yes, younger people. Quite often previous graduates would return for the summer school.

Weart:

I noticed Wildt came for a year also, 1938, I believe. Is that right?

Schwarzschild:

(pause) For a year?

Weart:

I don't know whether for a year. I have here that Rupert Wildt came as a visiting lecturer in 1938. Maybe it was very brief?

Schwarzschild:

I don't think he was there a year. But he came to Harvard a number of times.

Weart:

I see. He would come visit and so forth.

Schwarzschild:

He and I kept in contact with each other, even though our research fields were quite separate.

Weart:

I see, a friendly relation.

Schwarzschild:

Right.

Weart:

Well, setting aside for a minute your own work, I suppose you were very aware of the things that were going on, because you would be going to Yerkes and Mt. Wilson, so you pretty much were in on things. What was particularly exciting to you? What sort of discoveries and announcements in that period particularly impressed you? It's a very important period, great advances made.

Schwarzschild:

That's a question that I have a hard time answering, because there were so many new things, isn't that right, and to sort out exactly what was my catching up with fields, and what were actually new things — I would have a hard time separating out. It was, scientifically for me, a very exciting time. It was right at the beginning of getting into research personally, and just an enormous opportunity of seeing new fields, and exactly —

Weart:

So you were encountering everything at that stage, at whatever stage it was in at that time.

Schwarzschild:

Yes.

Weart:

OK. That's fair. Maybe I should ask you now about your own work. There are several things. Perhaps particularly interesting is on the light curves of Cepheids, and I wondered how you came to the problem of the phase difference in Cepheids? [4]

Schwarzschild:

That was really the conclusion of the work that started in Gottingen, when I reached in Eddington's book that chapter where Eddington said that the phase relation was an unsolved problem. So that was really the conclusion of that work. Bok felt, I think, at that time, that I should close that, that it was –-

Weart:

He felt that because you had in fact come to a solution, or come to a —?

Schwarzschild:

In part, but in other part also, he perhaps felt that it was too specialized, that I had worked long enough on that problem, and maybe he felt that I should go into a research field that was more clearly recognized. With some suggestion towards observational work. And I think he was exactly right. I think that one very big (for me) observing program that led to that one single paper, in which the first overtone pulsations were found, was the right way of getting into American astronomy.

Weart:

Oh, why so?

Schwarzschild:

Because that was the type of observational work that you could present as an observational feature. And if you then also, of course, presented it as fitting theoretical, plausible expectations — that fitted in the frame of American astronomy.

Weart:

I see, particularly that it came as an observational thing.

Schwarzschild:

Yes.

Weart:

I see.

Schwarzschild:

In that sense, that was a terribly important step that Bart Bok helped me with, not to continue on the purely theoretical side, but to go into a direction that would bring me closer to what was going on in this country, in astronomy at the time.

Weart:

And how was it to use the 60-inch? How did that work?

Schwarzschild:

The Harvard 60-inch, I think, had already become somewhat famous for being a very poor instrument. Indeed Shapley, after he left Mt. Wilson, apparently left with a feeling that one can build big instruments with very much less funds, very much cheaper. He built one 60-inch that never worked at all, an extremely inexpensive one that, sort of as a wreck, was still there when I first arrived at the observatory in Cambridge. And then he built the 60-inch at the Agassiz station for total funds that just were enormously less than for Hale's 60-inch at Mt. Wilson. And it was an instrument that could be used for very little research. One of the difficulties was that the mirror mounting was completely inadequate. It squeezed the mirror, and the images were extremely poor. It was quite a challenge, and I did not realize at all when I asked for the 60-inch what difficult observing it would be. But I had the very great luck that a young astronomer was responsible for the 60-inch and did most of the observing. Emberson was his name. He was terribly nice and ready to help me. He himself had a bolometric instrument on the telescope, officially working under Sterne, but Sterne practically never came out to do any observing.

Weart:

Emberson was not a night assistant, he was actually an astronomer working there?

Schwarzschild:

Yes. Emberson and I worked together, that is, he volunteered two or three hours. I had the (part of the) night, you know, just when Messier-3 was high enough. He just wanted to help, and it turned out to be absolutely essential. That mirror mount was so poor that what we did was to go to a star, a bright star, a little ahead of Messier-3. Emberson would go out at the focus with a knife edge and look at it with a Foucault type test, where you directly see the shape of the mirror, and he would call out the names and I, with a big wrench, would turn by his commands. So we would squeeze the mirror into shape for that night. Then when Emberson said, "All right," we would go to Messier-3 and then take two hours worth of plates.

Weart:

It sounds like a very modern technique, just what they're trying to do nowadays. (laughter)

Schwarzschild:

Right. Exactly. We jokingly have made that remark now before: it was the first flexible mirror. But it wasn't intended that way. The set of plates that, by this method, was obtained was, at least for a long time, said to be the best plates taken with that telescope. I did not realize how touchy the situation was until I made, one time or another, in front of quite a group, some remark that the mounting of the telescope was really pretty terrible. Then Bart Bok took me to the side and said, "That is not something that you have to pronounce. It's a point of difficulty and hurts Shapley. You are given time with that instrument; your judgment you keep to yourself." And that was very good advice — again.

Weart:

I see. The skeleton in Harvard's closet, so to speak. Another thing you did mention — you did thank Emberson; you also thanked Chandrasekhar for advising you to pay special attention to short-period Cepheids. Perhaps when you were out at Yerkes you discussed it with him?

Schwarzschild:

I am quite sure. In detail, I do not remember that, because Chandrasekhar was, for me, just the one, to try to discuss any stellar interiors problem' Because you know, that was his field then; until towards the end of the war he was entirely in that field, so that there was practically no topic in the stellar interior that he wouldn't have discussed, and obviously we discussed my interests too.

Weart:

I have another thing on that same subject. Eddington, in his IAU report for the 1938 IAU meeting, mentioned the problem of stellar interiors. He mentioned that, "Problems of central density condensation are studied through Cepheids." Did you at any time see your study of Cepheids as having some relation to studies of what was going on in the stellar interior, conditions in the interior? Did you see the pulsations as being a probe of the interior?

Schwarzschild:

No. And I think, already by the integrations that we did in Oslo, I started to learn that the pulsations were dominated by the envelope and not the interior. I'm not too sure how clearly I understood it. But I do not remember ever having considered that the Cepheids were — I considered them a very good tool to test the outer portions of the star, but I do not remember connecting them up with the key question of the energy sources, which is at the very center. At least, I do not remember. Now, how clearly I separated them as early as that, I do not know.

Weart:

I don't remember whether I asked you this last time, but when you became interested in this problem of the phase in the outer envelope of Cepheids and so forth, was that in part because this had been something that your father had in fact observed in his early work?

Schwarzschild:

No, I didn't even know my father's work very well. That came quite clearly by Eddington stating it as an unsolved problem in the pulsation chapter of his book.

Weart:

I see. Now, the next big break I have is your move to Columbia, but first, is there other of your scientific work, or anything up to that period, we should talk about more?

Schwarzschild:

Nothing that I remember.

Weart:

OK.

Schwarzschild:

I think the Harvard years, besides the work, were probably the most widening, scientifically, of the years — if you include particularly Chandrasekhar's influence, and the beginning of learning to know other astronomers outside Harvard.

Weart:

Did you also attend scientific meetings around the country?

Schwarzschild:

Yes. That is, the American Astronomical Society meetings I started to go to, very fast, and liked them enormously.

Weart:

Uh huh, they were very useful to you?

Schwarzschild:

Yes. They were still of the style, you know, that had only one session at a time, always described as "the glorious old days", isn't that right, when you could listen to everything. But they never emphasize that you had to listen to everything. It was, particularly for a youngster, not so easy to just go out. Oh, you sat through paper after paper, you know this eclipsing binary or that eclipsing binary, that comet orbit there were plenty of not so interesting papers. But at the same time, I think it gave me a marvelous overview of what was done in general, and then of course, there were marvelous papers.

Weart:

But you also got a broader view of the field.

Schwarzschild:

Quite right.

Weart:

What journals would you read regularly?

Schwarzschild:

I think the ASTROPHYSICAL JOURNAL was already then becoming the most important one. But Shapley did not permit anyone in Harvard to publish outside the Harvard publications, and particularly not in the ASTROPHYSICAL JOURNAL. Because, you know, it was based on Mt. Wilson, Yerkes and Lick, and he considered it the house organ of those three.

Weart:

The ASTROPHYSICAL JOURNAL he regarded as standing in the same relation to-those three observatories as —

Schwarzschild:

Yes, but clearly it was different. Because these were three giant observatories publishing in one journal, where Shapley, Harvard being a giant observatory in its own right, had three publications. In that sense it was disadvantageous, because those were just not read as much as the ASTROPHYSICAL JOURNAL.

Weart:

What other journals? Was the ZEITSCHRIFT.FUR ASTROPHYSIK still of interest?

Schwarzschild:

Yes. I am sure I followed the ZEITSCHRIFT. But the MONTHLY NOTICES of the (English) Royal Astronomical Society played an important role, particularly on the theoretical side.

Weart:

Yes. Any other journals that you would look at?

Schwarzschild:

I do not remember.

Weart:

The ones we've mentioned — would you read them from cover to cover?

Schwarzschild:

No, I never have been a very patient reader at all.

Weart:

You would look for particular articles or particular names?

Schwarzschild:

Generally. Or read abstracts of the papers. But I never learned to —

Weart:

— I just wondered, because you made me think, you'd been talking about listening through all the meetings — whether you read all the articles — but of course it's quite different.

Schwarzschild:

Then, my personal characteristic is that once I am in a room and somebody is speaking, it is nearly impossible for me not to listen. I have just a single track mind. So once I am there, I will take it all in, that is, all that is presented. But in reading you have the choice. And in general, I never read literature very much. In that sense, personal contacts with other scientists have played an overwhelmingly stronger role for me personally.

Weart:

So this is where you would normally hear of a new development or learn of something?

Schwarzschild:

Mostly by personal contacts. That has been so all my life.

Weart:

Tell me, to get back to the personal contacts at the meetings and so forth — aside from the number of sessions, the number of papers presented, what differences do you feel there are between current AAS meetings and the meetings as they were at that time, in the late thirties, let's say?

Schwarzschild:

I doubt that I would feel that they are so terribly different. The sheer number of people and papers makes the external appearance very different, and somewhat more complicated both for the organizers and for the attendants. But basically I think they are still an extremely powerful tool, just as they were then, to really get (information) — not just the formal publishable part, but in the discussions, both the formal discussions after presentation, and of course infinite discussions at meals and in the evenings —

Weart:

Do you think these are pretty much the same now as they were then, both the formal discussions and the meals and so forth?

Schwarzschild:

At least for persons of my make-up they are. Simply because they provide the possibilities of listening to each other and discussing with each other, which, for me, has been always the basic means. And I think, for very many people, it's a rather basic means of really getting new stimuli.

Weart:

Since the opportunity's there, you would use it in the same way as you always did.

Schwarzschild:

Yes.

Weart:

I see. Now, what about then the move to Columbia? Maybe first I should ask, what was your family's situation by that time? This is 1940 now. Your mother was still in Germany?

Schwarzschild:

My mother and my brother were all through in Germany. I had not seen my mother since '38, that last summer vacation that we were together — actually, '39 the European War started. We could still correspond till Pearl Harbor, regularly, and my mother and I corresponded weekly. My sister and I corresponded very much more rarely — except, of course, that my mother quoted us to each other.

Weart:

I see. Did your sister stay in Britain?

Schwarzschild:

Right. She finished in Cambridge — let me see — no, she actually got her final degree while she was already in Edinburgh, teaching. There is where she met her husband, who was then preparing to become a minister.

Weart:

I see. OK. Well, tell me then about your move to Columbia. How did that come about?

Schwarzschild:

Jobs in those days were not easy. It was the end of the Depression, and in the abstract sciences like astronomy, isn't that right, the recovery is delayed.

Weart:

Was there a feeling of this, by the way, among the students at Harvard? Was there a feeling that jobs were hard to find?

Schwarzschild:

Yes. There was no question. And that year, I remember very well, Leo Goldberg and I were both needing jobs. And there seemed only to be one opening, at Columbia. Eckert had moved to become the head of the Naval Observatory, and Professor Schildt, who was the head of the department, looked for somebody. It is always a little uncomfortable to be so clearly competing with each other, but that was essentially out of our hands. I don't remember in detail. I remember that I was invited to give a colloquium, and Bart Bok told me that was the method of looking me over, which I would never have understood at that time. And then I got an offer, and there was just no question about me accepting or not accepting. It was the only —

Weart:

That was the position that was open at that time.

Schwarzschild:

Right. Leo Goldberg was taken care of by Shapley, in a temporary way. Shapley was really marvelous in looking after young people. And then very soon, a year or so later, he got a position in Michigan, and before you knew it became the director (that was only after the war). The observatory at Columbia was essentially two men, as far as research staff was concerned, and in that sense not at all particularly desirable.

Weart:

Meaning in this case you and Schildt.

Schwarzschild:

Schildt and I. Fermi used to call us jokingly "Shildt and Schwarz Shildt," I mean because of the funniness of the names. Or, "The Director and the Directee." (laughter) In that sense, it was not the most desirable spot to be in. And to live in New York, I really hated.

Weart:

Is that so? You were living near Columbia?

Schwarzschild:

Actually, in one of the dormitories, because I didn't want to bother with an apartment or anything. Also, I'm not that sure I could have afforded an apartment at that time. To get out doors from Manhattan was —

Weart:

It's a long way.

Schwarzschild:

— so difficult. And there was no chance of me affording a car at that time. And that was not just me. That was normal. So that was quite a lonesome spell. With regard to Professor Schildt, who certainly is not an outstanding astronomer, I still must say that he tried very hard to give me a free hand. But at the same time, he was very stingy in spending money. For example, I tried to get a little nicer desks, maybe a room for the graduate students, which I was quite interested in, but there was no chance that Professor Schildt would spend it. So even though he tried to persuade me that I should take the lead in building up astrophysics and the graduate school in astrophysics — in part I was not myself aggressive enough or understood enough how to go about it, and on the other hand also, Schildt's own attitude against any empire building and against spending unnecessary funds — that, in combination made if effectively impossible. There was one very fortunate circumstance. Eckert had been one of the first of the astronomers in this country on the celestial mechanics side who really had gotten into then modern digital machines. They were still semi-mechanical, semi-electrical, and of course nothing electronic about them. But he had persuaded the famous Watson of IBM to give free, including the service, a set of the best IBM machines of that time, as a Watson Astronomical Laboratory — not to be confused with the later big Watson Scientific Laboratory —

Weart:

Right, the Thomas Watson Astronomical Computing Center.

Schwarzschild:

That sounds like the right name.

Weart:

I wanted to ask you about that. I'm very curious about it — not only I, but I know someone who's very interested in history of computers, and it's not only important to history of astronomy but also to history of computers, this Center.

Schwarzschild:

Yes, it was. And there the initiative really came from Eckert. I did not take any subsequent initiative, but I exploited it, and in a field that was of more interest to a wider group of scientists. And in that sense, I may have helped a little. But I mean, the existence of all the machines that I ever used came from Eckert.

Weart:

They were there when you arrived. How was it funded? How did the funding work, during the time you were there? Eckert you say had already left.

Schwarzschild:

Left, but Watson kept that center.

Weart:

I see, and he continued to pay for the maintenance and so forth?

Schwarzschild:

Yes.

Weart:

Do you know why Watson was interested in doing this? Did you ever have any dealings with him?

Schwarzschild:

No, I never had. But I rather think that Eckert had persuaded him, and rightly so, that the scientific use would become a major one.

Weart:

I see. But you were not directly involved in this.

Schwarzschild:

No. I fear that I was still really fantastically naive, and completely inactive in anything administrative. In a certain sense that may have been also the reason why I did not manage to really build up astrophysics at Columbia.

Weart:

Well, you didn't have a very long time before the war.

Schwarzschild:

That is true, too.

Weart:

But to get back to your work on computing machines, was it simply that the machines were there, and of course you had a problem, with Cepheids and so forth.

Schwarzschild:

Yes. Right. But I did get interested in the machines, as machines, and what one could do with them. There was a very good operator there, Lillian Feinstein was her name — from Eckert's time — and she and I got very fast into very good personal cooperation with each other. She made extreme efforts to teach me what the machines could do in principle, and then when I had figured out what therefore basically one could attempt, we worked together.

Weart:

I see. Did she understand linear differential equations and so forth?

Schwarzschild:

No. But after I had gotten the linear differential equations down to straight algebra, and we had figured out what were the capacities of, particularly, the one most advanced machine that happened to be there, then she knew how to do the wiring. It was actually done by plugboard wiring.

Weart:

I see, right. Did she do the wiring, then?

Schwarzschild:

She did all the wiring. She knew those boards, so fast that —

Weart:

I see. Was there anybody else there, or was she the sole operator?

Schwarzschild:

I think she was the sole operator, though occasionally, in some of the very large statistical research that Professor Schildt himself did, they may have had some hired students for night runs. But I do not remember that.

Weart:

You ran it at night sometimes also?

Schwarzschild:

If I can remember right, that is so. Professor Schildt did statistical research, somewhat in the field of Bart Bok's but of a rather different character.

Weart:

But I'm interested that the demand on the machine was great enough so that it was worth running day and night.

Schwarzschild:

Yes. But they were slow.

Weart:

Yes, I realize that. But it's interesting that as soon as the computer appeared, already it was being run around the clock.

Schwarzschild:

Well, maybe not all the way around the clock, but in any case —

Weart:

— at least into the night.

Schwarzschild:

Oh yes. But it happened that just at the end of Eckert's time, one machine was added which was built by IBM just as a prototype, in consequence of a patent threat to their multiplying system. The patent was owned by an individual inventor who threatened IBM. So IBM set an engineering group to invent a different multiplying system, which they did, and put into one machine. It was slightly less efficient than the other one, and by the existence of the new one, the patent trouble disappeared. That machine, however, was built by apparently outstanding one or two IBM engineers. One of them I met later, and he described to me that at the same time they had terrible troubles with every customer wanting something slightly different in algebraic operations. He had gotten angry and said, "If they can't agree, I just give them a choice of a sequence of (I think) six steps, and they can plug that sequence in as they want to," not realizing that that was the heart of programming.

Weart:

He had a stored program of six steps.

Schwarzschild:

Yes, but he maintained he did it in anger at the customers. And it was that feature that, after Lillian Feinstein explained it to me, made it possible to go into the automatic solution of at least a limited class of differential equations. And it happened to be the class that I was very much interested in. I then went back to the pulsations, and did basically that the very beginning of which we did in Oslo, but now with digital accuracies. I forget how many digits we had, but I mean, oodles; that made it possible.

Weart:

This time you really did it.

Schwarzschild:

Right.

Weart:

In fact, this is one of your more cited early papers, it turns out, in the Science Citation Index. [5]

Schwarzschild:

I see.

Weart:

Of your early papers, this is the one that's still most referred to.

Schwarzschild:

I see. I think I mentioned to you that I never have used the Science Citation Index because it has that psychological effect that I want to avoid.

Weart:

Right. I don't recommend it for things other than for us, to find out which papers written in 1940 are still being cited. Then I can go back and make sure that I ask about them. I also notice that this is your first paper published in the ASTROPHYSICAL JOURNAL. Was it automatic that once you left Harvard, you could start publishing there?

Schwarzschild:

Yes. It was quite clearly by that time the natural place to publish in. I should say that through Professor Schildt, and his frequent visiting friends, Eckert but also Clemence (Naval Observatory) and Brower (Yale), all in celestial mechanics, I got a very strong course in some of the basic problems — the hunt for the inertial frame of reference, which really interested me, as a fundamental phenomenon, even though I never had worked on it.

Weart:

Are you speaking in the general relativistic sense, or are you just talking about celestial mechanics?

Schwarzschild:

Basically, celestial mechanics. But it was this funny time when general relativity was the thing, and Einstein, so to say, had forbidden talk about an inertial frame of rest. All frames were equally good. For, the development of general relativity, that emphasis was obviously a key point. But it played havoc with how to think about what one in fact did, in celestial mechanics.

Weart:

I see, so you —

Schwarzschild:

— You very clearly used something equivalent to an inertial frame of rest. I was very interested in that problem, and Professor Schildt really understood that field well. I think the man who put it the most clearly, but in part, I think, on my questioning what the relation was, was Clemence. By now, that is an old problem. Though if you ask a theoretical physicist or an astronomer: the famous Mercury perihelion rotation, relative to what? — very few can answer it. So that was another branch of astronomy, there.

Weart:

It's interesting that they were concerned with that. Tell me, for this whole Harvard period and also the early years at Columbia, did you talk much with people about cosmology, or was there anything to do with extragalactic astronomy?

Schwarzschild:

Oh yes. During the Harvard time particularly. Shapley was doing these major surveys of galaxies, having accepted by that time that they are galaxies as we understand them now. So there, that whole field was very much in the background. Questions of galaxy clusters and indeed questions of a metagalaxy, as Shapley called it then, or superclusters as we would call it now was very much in the foreground. Lemaitre visited a number of times in Harvard, and gave me very long lectures on his developments, which I only vaguely understood. But he loved to talk, and it didn't matter for him all that much whether the listener understood. He was a very gay and active person. So the question of cosmology was clearly there. In that sense, the specific problem of what in fact were these reference frames that one did use in astronomy and still uses in astronomy, seemed to me a very provocative interest that I wanted to get clear in my head, even though I never worked in any of the fields connected with it.

Weart:

How did you feel about the Big Bang? Did that seem to be the only possible theory? Or did there seem to be problems with it?

Schwarzschild:

I was fascinated with it, but I do not remember to what degree I was convinced of it. And also, at that time it did not have any direct astrophysical connection. It was really classical cosmology, which had only the fields of the red shifts of the galaxies as a function of distance and of galaxy counts. It was essentially the Hubble-Tolman early approach, with no connection to the origin of the elements or anything of that kind.

Weart:

Right. Well, there was some problem with the age of the universe, I suppose, getting things the right age.

Schwarzschild:

That's right, but at that time there were no astronomical ages. There was the beginning of the age of the earth and of the meteorites.

Weart:

But not really involving astronomical problems.

Schwarzschild:

Of course, there was the beginning worry that the times jive, because after all, the meteors and the earth —

Weart:

Seemed rather old, yes. I see. To get back to Columbia then and your relations then, a question I ask everybody, but particularly you since you were at Columbia — when did you first hear about the discovery of nuclear fission?

Schwarzschild:

That must have been before 1938.

Weart:

No, it would have been in early 1939. Let's see, that's right, you would have been at Harvard still then, yes. Nuclear fission was discovered in early '39, so you would have still been at Harvard, that's right.

Schwarzschild:

No, excuse me, I think I should correct myself. I suspect, but I don't remember, that I heard of that only from the physicists at Columbia. That would be starting in the fall of 1940.

Weart:

You went to Columbia in the fall of '40, so Fermi was still there, there would have been some talk.

Schwarzschild:

Yes, indeed. That is, I think, for me one very important feature of that year and a half in Columbia before I got into the Army. And that was that the two astronomers were permitted to have luncheons at the table with the senior physicists.

Weart:

— at the Faculty Club?

Schwarzschild:

At the Faculty Club, quite regularly. And that played for me an extremely exciting role. I mean, just to get a feeling for the thinking and approach of people like Rabi and Urey and Fermi (very different as they were) and younger men like Lamb and Anderson, and Pegram (though he was mostly administration then), was a really important personal experience. To see really outstanding scientists at work; particularly their singlemindedness of dedication was very impressive. And it had one other peculiar feature. At that time (isn't that right?) they were already engaged in their preparation of a pile.

Weart:

Very much so.

Schwarzschild:

mp3

And had agreed already, initially among themselves and then officially, to keep it secret. That meant that at the luncheons they couldn't talk about that work. And therefore, astrophysics came up rather more often than under normal conditions it would have been. So that in many ways, Fermi, particularly, was very ready to talk astrophysics. And a couple of times he helped me, just straight scientifically helped me, over key hurdles.

The impression that Fermi made on me was absolutely enormous, as a person. Scientifically that group was so phenomenal that it really didn't make any difference how phenomenal they were. The moment somebody is so much better than your own intelligence, it doesn't really make that much difference, isn't that right. But Fermi in addition was such an extraordinary person.

If you asked him a scientific question, he would put all his brain into transmitting what he understood into your brain — and making absolutely sure that you got it. He had a way of explaining something, and then looking at you and saying, "Have you understood it?" And then saying, "No!" And then automatically he'd work on you until you had it. Without any faking — I mean, there was no question that he knew that he was the brighter brain, and he would never flatter you, but he would just make it a job between you. So it was never embarrassing to ask Fermi a question. It became a common undertaking, to get into your head what he understood. It was unbelievably impressive.

He was a keen observer of people, and never could stay serious for more than half an hour at a time. It was a marvelous group, and he learned fast that I, by nature, am also towards the happy and gay side, that I didn't mind my leg being pulled. It became a really very enjoyable, but also very impressive, experience.

I remember one day, when I asked Lamb, who was then doing his critical experiments —

Weart:

— this is after the war then?

Schwarzschild:

Oh, excuse me. That's right. Fermi was not there anymore, but Rabi had returned. And Lamb, in his quiet way, explained one thing after the other, and I said, "But how could you be sure that —?" and then Lamb would go on — and finally, I was quite convinced that it was something exciting. But Lamb had been so very calm and, you know, low-tone about it. Finally I turned to him and I said, "But isn't this terribly exciting?" Then Lamb just burst out laughing, because of course everybody else had understood that it was terribly exciting. I finally had gotten there.

Weart:

I see. Had you encountered physicists much when you were at Harvard? Had they joined your talks?

Schwarzschild:

Not many, though Philip Morse had, largely through Menzel, become fairly interested in astrophysics. He had started at that time, if I remember the timing right, to compute one of the first somewhat more accurate tables of opacities, which is one of the parts of physics that I needed for the stellar interior. But except for Philip Morse and Robertson, who came for a very impressive course on general relativity for summer school, I don't think I had much contact with physicists.

Weart:

Would they come to the Hollow Square, or some of these things?

Schwarzschild:

Very rarely. Indeed, Shapley was not at all strongly convinced of the need of astronomers to get deeply into physics. Neither was Bart Bok. In that sense, I think, they were behind. Menzel in particular, and to a somewhat lesser degree, Whipple, was more convinced of the importance of physics. But the students were not sent to physics courses, even the graduate students. What physics Menzel felt they should know, he taught them himself.

Weart:

I see.

Schwarzschild:

Columbia, of course, with a small department, that was quite different. It was quite impossible.

Weart:

You were thrown in with the physicists.

Schwarzschild:

Yes, but also you would send the students into physics courses, of course. The connection was enormously stronger.

Weart:

During your early period at Columbia, with whom else did you have relations? Did you get to Princeton much, for example, during that period?

Schwarzschild:

Yes. Indeed, there was one semester I went every week to a regular colloquium, for one semester. Chandrasekhar was here that semester, as a visitor, and that was an additional attraction. By that time I was already under some restrictions as an enemy alien. I actually had to get permission to go to Princeton. I also went back to Harvard a fair number of times, though I don't think that last period — I don't know how long it was, half a year or so, when the restrictions had become quite tight.

Weart:

Now, Wildt was here at that time. Wasn't this just about the period he was doing his H minus work? I'm not sure.

Schwarzschild:

In Princeton, yes. That is right, I was at Columbia then. He of course told me about it in full detail. How important it was, I don't think I appreciated at that time. During the early part of Columbia the question, what I should do with regard to the war? became a very severe problem in my mind. And I had a very hard time; should I join in the war, for example, through the Canadian Army, or go into the American Army before there was a draft? It did run me down. I became so uncertain that I finally found that during one lecture I became dizzy, and to finish the lecture I had to concentrate extremely hard. That made up my mind that I had to make a decision. I decided that I would stay out of the war until this country came into the war. But the moment this country would go into the war, irrespective of what other people told me, I would go into the American service. After I had made that decision, everything went very easy. I mean, I found my balance again. I asked in Columbia if they wanted to use me, for example, in physics for teaching.

Weart:

This was before Pearl Harbor?

Schwarzschild:

Before Pearl Harbor, right. Because I couldn't be cleared, and there was no particular reason for anything else. At Columbia they were extremely eager to maintain their staff, not to have them leave too much, because quite a few left, like Rabi himself, for the Radiation Lab (at MIT). So they were very eager to keep as much of the staff together. So, to be sure that I wouldn't disappear into the Army — which I had somewhat discussed with Professor Schildt, who had then discussed it right away with Rabi — to make it attractive to me, they gave me the top section of a very big physics class, which was one of the most exciting teaching that I ever have done. You know, a big course, and they go by the grades of a previous semester, and just to make it attractive for me they gave me the top group. It was emotionally extremely exciting to have so good a group. You could get them excited about any part of the course. Of course, I did not give the main course. I followed —

Weart:

— a section —

Schwarzschild:

But it had the effect that it made it psychologically absolutely unthinkable that I wouldn't go in the Army when these youngsters would get called up. So in a certain way — Rabi never was a very good psychologist. I mean, he's a terribly nice man, but he did exactly the wrong thing. But maybe that would have been expecting too much, that he would see how it would really make it absolutely impossible for me to imagine that I, as a German Jew, could stay out of the war, when this group would be called.

Weart:

I understand.

Schwarzschild:

So it confirmed my decision. And the moment Pearl Harbor happened — well, I tried to get, that very day, to enlist, but the lunch hour was not long enough for the line. And then I went a couple of days later to the draft board (I was officially in the draft pool but exempted) and persuaded the draft board to draft me. They were very afraid of Columbia. I was not entirely honest, I told them that I had cleared it with the university, which in fact I hadn't, but then they drafted me, and then I told the University that I was drafted. Then I told Professor Schildt, and that day at lunch Schildt said, "Schwarzschild is going into the Army." A terrific discussion, whether it was right or wrong, happened, and when I wanted to say something Fermi, in his marvelously understanding way, turned to me and said, "Schwarzschild, you cannot participate in this discussion. It's all about you. Which in a way, of course, was — I mean, I think he saved me from becoming emotional and overwrought.

Weart:

OK, so then you went in and you were assigned.

Schwarzschild:

I just plain went in the regular way — being still an enemy alien, because I hadn't been five years in the country. There was no question but that I went in as a buck private, as they called it at that time. I had no idea what the Army was about. I didn't know the different branches or anything. But somebody had the bright idea that with my background, they should put me into one of the branches of gunnery, where at least some bit of mathematics is used. Contrary to the experience of very many educated people in the American Army in the last war, I felt that I was being as well used as you can expect, under the very bewildering circumstances when such large masses have to be handled. The fact that I did get into the Army from the bottom up I think had, for me as a person, a very essential influence. It was the very first time that I actually lived outside university circles. I was not that young, isn't that right, for that experience. And that experience was extremely essential and I think it really made me aware of people in a way that was entirely essential for my later work as a teacher in particular.

Weart:

Because you were thrown into contact with different types of people?

Schwarzschild:

Yes. And I got so much more, by necessity, aware of how people think and how people work. From the purely personal side, the American Army was an enormous education for me. And quite a staggering one, because I had not yet lost my German class consciousness, to the degree that I lost it in the Army. I was then in anti-aircraft gunnery and was very fast put into teaching at night, while I was still in basic training. That math teaching was cancelled whenever I was on kitchen duty, because that went through the evening, and kitchen duty has priority over anything else, I think, by the rules. But it didn't make any difficulties for me psychologically, because I wanted to participate in the war, and that gives you an emotional background that makes all these funny things or illogical things that happen very easy to take. I had a clear wish to be effective, and it was very clear that you had to get along with your top sergeant or whoever, and if you have a clear aim, it makes it much easier to do things that otherwise would be enormously grating. For example, these arrangements that I got into, the evening teaching. I took the initiative, because I wanted to be occupied to the extreme. Otherwise it becomes somewhat unbearable.

Weart:

I understand.

Schwarzschild:

That in itself was very good training, how to teach under very difficult circumstances. Then suddenly an order came from Washington to transfer me to the Ballistic Laboratory, which I was very unhappy about, and became more so after I was there.

Weart:

This was at Aberdeen?

Schwarzschild:

At Aberdeen, because there they had access to any first-class engineer or scientist. I mean, von Neumann came regarding computers, and Veblen was there most of the time, and oodles of experimental physicists. So I felt that I surely wasn't needed. It's time I was in good physical shape, which helped with some of the experimentation, having gone through basic training not long before, which is a good way of getting yourself into good physical shape — (otherwise one) couldn't execute these bomb tests, for example, to which I was put. So I felt really thoroughly convinced that even though it was extremely interesting, purely technically interesting work, that it was not using me effectively, since I had, by circumstances, to be in uniform. I thought that I could do very much more in the places and in the units where there was absolutely no scientific or no technical background, where I bad been before. Even, you know, ordinary trigonometry — there was just nobody. I developed one way of reducing wind data from a balloon, which was very primitive, essentially just a bit of algebra. From a very clumsy way — they normally made a mistake and gave the batteries wrong winds to correct for — to a much simpler way that more often came out right.

Weart:

This was while you were at Aberdeen, you developed that?

Schwarzschild:

No, this was still before, in the training camp, Camp Stewart in Georgia. There was nobody in that camp who could check that algebra. But an officer had to endorse it, if it was to go on. There was one young Georgian officer who trusted me, just by way of knowing my background and by way of my teaching. He signed it, even though he couldn't check it. That's how it became, within half a year, the general method.

Weart:

I see, the idea was, they would send up a balloon and track it?

Schwarzschild:

Well, that was always done. But when we had the tracking data, the old method was a complicated plot on elaborate graph boards, many steps, it took something like an hour, and during that hour —

Weart:

— the winds would change?

Schwarzschild:

No, we would make mistakes. And just give them quite wrong data. I was then assigned to a small platoon to do that work for a whole regiment. I saw that unless I did everything myself — and then was terribly careful, I had difficulties not making mistakes — the others, who had nothing like my training, would never come out.

Weart:

I see. So you found a way to do it much quicker.

Schwarzschild:

Right. But I cite that only to show what enormous lack there was of trained people in the operating forces. I think the pendulum, from the experience of World War I, where the scientists had been dumped into the infantry, had swung way over the other way. There were not enough trained people in the forces to receive all the developments and really put them into acting. I was terribly eager to stay there. The Aberdeen time, which was only half a year, was quite complicated in other ways. Because I was in uniform, most of the rest there were not, and I was only a sergeant by that time. Even though, again, the relations were terribly friendly. The Army's head ballistician, a very gay, older man, became very fond of me. But he also loved to make complications for the system, so he used me to get some of the high-ranking officers, like for example the head of the Ballistic Laboratory, and me into uncomfortable situations. He would send me officers to give them exams to see whether they should be in our group. Chandrasekhar, by the way, came part time to the Lab.

Weart:

Was that because you were there that you knew about him to come, or?

Schwarzschild:

No, that was independent.

Weart:

Were there other astronomers that they brought in also?

Schwarzschild:

Hubble was there, for example, in the instrumentation group, to measure rocket flights. There were quite a number more, and it just swarmed with good scientists. So the only way of getting out was to apply to officers' school, which by that time I could, because I had become a citizen The five years were over. That is a right that no commanding officer can refuse, if you qualify as an enlisted man. Those were the rules then in the Army, and by applying to the anti-aircraft gunnery officers' school, I had a way of getting out. It was a somewhat difficult step to take, because the colonel who headed the laboratory was very much against it, and persuaded von Karman for example to give me a long lecture why I should stay. It was one of those situations were von Karman didn't know how loud he was speaking, and he took me under the arm and marched me up and down the hall, passing the colonel's office, shouting in my ear why I should stay, and I couldn't shout back why I shouldn't stay! But in any case, I went through Officers' Training School, which was extremely hard on the physical side and extremely easy on the instructions side, for me. Then I was right away assigned back to the same camp where I had my basic training, got a very fast and very interesting assignment, connected with fire control when the radar is blanketed out, and very soon thereafter again an order came to come back to Aberdeen. By that time I was real furious. But then when I arrived in Aberdeen, it turned out that it was just a month of preparation to go for a special assignment with the 12th Air Force to Italy. So that is where I spent a year and a half, till the end of the war.

Weart:

What was your assignment?

Schwarzschild:

What one then started to call operations analysis. In the main theater in Europe these were civilians put in uniform but not reporting to commanders in the field, but to a central operation analysis office here in the States, so they were relatively independent. In the smaller theater, in Italy, no such group was set up. Actually I was the only person sent for that purpose, and was put into the ordnance section of the Air Force.

Weart:

You mean the anti-aircraft came under the Air Force?

Schwarzschild:

No, this was a shift. At that time, you know, the Air Force was still part of the Army and the anti-aircraft of course is part of the Army, so I was in the Army. No, it had nothing to do with anti-aircraft then any more. It was essentially to try to. find out what bombs, what fuses, how much bombing was necessary to knock a railroad line out and keep it out.

Weart:

I see.

Schwarzschild:

I felt very satisfied with that assignment, because it used my technical training and the judgment of what observations are relevant and what are not. It was physically at times quite tough, because to really get the data, to really see what happened, I had to go immediately behind the infantry quite often, to find the targets of our bombing and find out what actually had happened.

Weart:

You couldn't tell just from air observations?

Schwarzschild:

No. We used the air photography an awful lot, and I became very acquainted with air reconnaissance techniques. But the pilots' reports are just — when somebody is under fire, his judgment is no good. That was the humanly hard side, always having to say that the achievements were just factors below what the reports indicated. It made some real difficulties, persuading the commanding officers that my statistical findings were right. In one case, indeed, I was ordered that the report was not to be sent outside the headquarters. I felt very bitter about it, I mean bitter in the sense of disappointed, because I thought it was a useful report. I made a prediction how much it would take to close the Brenner (Pass), the main supply line, and they were convinced it was at least a factor of two, too pessimistic. But if that report had become available to other air forces — there was at least one case, I learned, when another air force spent their whole effort for one month on an attempt at the Rhine to isolate a main traffic center, which, from our experience,, one could have known would never work.

Weart:

I see.

Schwarzschild:

But somehow, from the commanding general's point of view, it sounded critical of our Air Force.

Weart:

Well, it was a general problem during the war, wasn't it, this over-confidence in the effects of aerial bombardment.

Schwarzschild:

Yes. And that part is natural. But the question is whether one has the courage to at least exchange these survey data. As it was organized in the main theater, it didn't go through the commanding generals. It went through the center in the States, and from them to the commanding generals as orders, superior orders. And that was not the case (in Italy).

Weart:

Do you feel that in the Italian Theater, your studies were made use of? In general?

Schwarzschild:

Yes. Never as far as they might have, but the efficiency in a war is so low anyhow.

Weart:

You did feel you were having an effect?

Schwarzschild:

Oh yes.

Weart:

You were dealing mainly at what level, at the headquarters level of the 12th Air Force?

Schwarzschild:

Right. But that was also the tactical headquarters of all the Allied Air Forces.

Weart:

In Italy?

Schwarzschild:

In Italy, the Italian Front. So I belonged to the 12th Air Force, but actually it affected all the air operations on that small front.

Weart:

I see. We're almost to the time we stop — maybe though I should say, is there anything more about the war before we get into postwar things, or shall we stop at that?

Schwarzschild:

I don't think so, except for wanting to re-emphasize the enormous personal impact that contacts with low-educated people made on me in comparison with people who had gone through famous colleges. The lack of correlation of personal strength and character and honesty, uncorrelated with educational level, was something absolutely enormous for me. During the most dangerous of these surveys, at the Front, where we quite often had to go through uncleared mine fields —

Weart:

— Where was this, by the way?

Schwarzschild:

Starting a little north of Rome, then going to Florence, and then one winter we were just north of Florence, where the last Winter Line was, and then past that line all the way to the Alps. But during the last more dangerous period, they gave me one enlisted man who was always with me, and we had a jeep and a small trailer; we were completely independent and I was given entire freedom. They gave me a New York truck driver — very crude exterior and completely uneducated, but with a reliability and a brightness of sense and a courage that's unbelievable. And there was just tacit understanding, for example, that we would alternate who went first in the mine field. There is a certain distance you keep, so that if somebody gets killed, not both get killed. There was just absolutely no question of it. Also, the rank differences disappear under such circumstances, it's very natural, and it just becomes a common undertaking. But common sense, he had. Just terrific. For example, he realized — this completely uneducated, fairly uncouth fellow, and a giant of a man — that I had a somewhat nervous character. And he after a while asked me, could we make an agreement: he would keep his pistol loaded, but would I mind if I didn't load mine? (laughter) It was sort of an insight, isn't that right? And putting it that way, entirely acceptable for me. It was clearly the safest for both of us.

Weart:

I understand. Did your contact with the commanding officers and so forth, do you think that had a major effect on you, in terms of later people that you had to deal with and so forth?

Schwarzschild:

I don't think so, because there again the mixture was enormous. I had one short contact, for example, with a Naval captain — that was during my Aberdeen days — who was unbelievably impressive and open, and for him rank played no role. And a very fine Army colonel who was reasonably, you know, according to the rules during daytime, but asked me whether I would give him some math lectures at night. In many ways, some of them really spoiled me. Then, some were just small men, who could not stand very easily that somebody might understand some things better. As a whole, there were essentially no bitter experiences. In that sense, I think, nothing negative was left.

Weart:

OK, well, I think we should close off here. Let me just say for the tape recorder, and also for the next time we meet, there are two main things I want to ask you about, and that's about your move to Princeton, and about the astronomical environment here; and the second is I know you want to tell me, and I want to ask, about the whole development of stellar evolution, starting from the late thirties and then particularly in the post-war era, 1945-1955 period. We'll do that.

Schwarzschild:

Right.

[1]"Zur Pulsationstheorie," ZEITSCHRIFT FUR ASTROPHYSIK 15 (1938), 14-31.

[2]ZEITSCHRIFT FUR ASTROPHYSIK 13 (1937), 126-31.

[3]E. Opik, PUBLICATIONS DE L'OBSERVATOIRE ASTRONOMIQUE DE L'OBSERVATOIRE DE TARTU 30, no. 3 (1938); no. 4 (1939).

[4]See HARVARD COLLEGE OBSERVATORY CIRCULAR No.'s 429, 431 (1938), 437 (1940).

[5]"Overtone Pulsations for the Standard Model," APJ 94 (1941), 245-52. See also REVIEW OF SCIENTIFIC INSTRUMENTS 12 (1941), 405-408 "Automatic Integration of Linear Second-Order Differential Equations by Means of Punched-Card Machines," with L. Feinstein.

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