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Oral History Transcript — Dr. Ira Bowen

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Interview with Dr. Ira Bowen
By Charles Weiner
At Pasadena, California
August 9, 1968

Listen to Bowen describe how the Great Depression had an effect on his work building large telescopes.

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Ira Bowen; August 9, 1968

ABSTRACT: Family background; undergraduate work at Oberlin College AB 1919; graduate work on vacuum spark spectra under R.A. Millikan at University of Chicago 1919-21; at Caltech as Millikan’s research assistant: cosmic ray work (1922), vacuum spectrograph (1923); determination of Bowen ratio leading to PhD thesis 1926; nebulium research: origins of interest, conclusions, follow-up at Lick Observatory-- determination of H as most abundant element in stars (1934), development of image slicer 1938, observation of “forbidden lines;” research results channel interests closer to astronomy; teaching positions and duties at Caltech; war work and disruption of research; postwar seminars relating nuclear physics to astronomy; appointment as Director of Mount Wilson-Palomar Observatories 1946, priority of constructing 200 inch Hale telescope, administrative details. Session II: post-war organization of Observatories, administrative committees, funding, division of project time and organization of staff, senior staff members Hubble, Baade, and Adams, incoming staff; achievements in astronomy: final constructing, testing, and setting into operation of 200 inch, developing auxiliary equipment, building Schmidt telescope, revision of distance scale of universe, rise of radio astronomy; communication within field; public interest in astronomy; personal research after retirement in 1964.

Transcript

Session I | Session II

Weiner:

Today is August 9, 1968, and this is a tape-recorded interview with Dr. Ira S. Bowen. We are sitting in Dr. Bowen’s office at the Mt. Wilson and Palomar Observatory building on Santa Barbara Street in Pasadena. This interview came about spontaneously. Neither of us are fully prepared, but we’ll start in from the beginning. What I wanted to do was to ask a little about your early home life and your background. I know you were born in Seneca Falls, New York.

Bowen:

Yes.

Weiner:

What kind of a community was that and what kind of a school system did it have?

Bowen:

I only lived in Seneca Falls for a little over two years. My father was a Fundamentalist minister, and, at one time, he was almost a circuit rider, because from Seneca Falls we moved down to the little village of Millview in the Appalachian Mountains in Northern Pennsylvania where he preached at seven different schoolhouses and churches in that neighborhood. At some he preached every fourth Sunday, some every other Sunday. We lived there for about four years. Then he became sort of business manager for this little denomination and had his headquarters in Syracuse. Due to the fact that my older brother was in high school at that time we established a residence in the village of Houghton, New York, which is on the Genesee River south of Rochester, where this particular church maintained a high school and junior college, Mother and I spent part of the time in Syracuse with Father and part of the time in Houghton with my brother. Because of this I wasn’t able to enter school and was taught at home. It happened that my mother was a normal school graduate, so it was quite legal as she had a license to teach. So I had my first six grades with home teaching. No, the first four grades, I should say. And then, unfortunately, Father died when I was nine, and this, of course, posed rather serious financial problems because due to the denomination’s feelings he didn’t carry any insurance, and there was relatively little money ahead. The only thing that saved the day was the fact that Mother had a license to teach, and she immediately got a job teaching in this high school and junior college at Houghton. I took the rest of my grades, my high school, and the first three years of college there.

Weiner:

What did you do for books at home during the first four grades?

Bowen:

Well, Mother had the usual textbooks, and she would set me problems to work out and things of that sort. She had taught school quite a little before she was married, and, as I say, she was a normal school graduate. Then, due to the fact that this was just a junior college, they could not give degrees so we all went away for our senior year in college in order to get a degree. I was ready for my senior year in 1918, and that, of course, was the war year, so went to Oberlin. It happened that the President of this college was an Oberlin graduate and had actually taught at Oberlin. He taught mathematics and physics at the place and was one of the finest teachers I’ve ever had. He started a great many people on their way that way, going to Oberlin and other colleges.

Weiner:

What was his name?

Bowen:

James S. Luckey. One other reason, of course, for going to Oberlin was that it was a war year, was of draft age, and Oberlin had a SATC unit, which is essentially an Army Officers’ Training Unit, so went there and enlisted in that, but was only in for about ten weeks when the war was over, and I chanced to be mustered out on my twentieth birthday. Then I continued for the rest of the year and took my degree under Sam Williams, who was head of the department there at Oberlin, and who is a very interesting fellow, He frankly was a very poor lecturer, but I think he sent more people away for their doctor’s degrees than practically any other person in the country, because he was doing a small amount of research, largely in magnetism, and he took all junior and senior students in with him, In fact, published my first paper on the basis of work that did as a senior under him. It was a joint paper with Dr. Williams and Hatfield on the magnetic properties of manganese steel, published in the Proceedings of the Royal Society. He was also very, very thoughtful of his students.

For instance, he called me in on January of that year and said: ‘What are you going to do next year, Bowen?’ Well, said, I haven’t thought much about it with the war and everything else. Then he went on to say: “You’ve made a good record here. We’d be most happy to have you, and I’ll see that you get a fellowship if you want to stay on for your master’s degree here. Frankly, my advice is: don’t take it; we haven’t anything more for you here,” And I’ve always been most grateful to him for saying it because as look back, I realize it was much better for me to go ahead into a real graduate school. And on talking it over, decided to try for Chicago. I had seen Millikan at that time, Millikan was also an Oberlin graduate. He’d been there and talked once during the year was there. He gave a chapel talk. And so went on to Chicago. I was a little bit late getting my application in, so I was given a scholarship for the first year. I managed, by working summers and everything else, to squeeze out money. Of course, there wasn’t too much money in the Bowen family in view of the circumstances. I had a brother who also took a Ph.D.--in geology. When I got to Chicago--about a week after I was there--Millikan called me into his office and said: “My research assistant, Dr. Ishida, is leaving on January 1st. Would you be interested in the job?” Well, naturally, I was. It was a wonderful opportunity. And so I immediately began to understudy Ishida. He was working on the oil drop experiment, using it somewhat backward to measure the viscosity of various gases. He filled the oil drop condenser with various gases and then used to assume the value of the electron. Ishida was using it for that purpose, if remember correctly. I assisted him a little during the fall of that year.

Then he left, and Millikan was interested in this vacuum spark. Ralph Sawyer had been there working with Millikan but had completed his degree and had left for Michigan just before I arrived. He had set up the vacuum spark equipment, although I think they hadn’t gotten too much out of it until that time. So I was then put on the job of getting it going and getting some results. And most of my time for the next two years, or twenty-one months that remained in Chicago, was working on that. A good deal the first year was getting the bugs out of it and getting it going. We were just nicely going, however, when Millikan decided to come out here.

Weiner:

During this period when you worked on it, did Millikan himself have much to do with it?

Bowen:

No, it was rather rarely that he came down and actually did anything with the equipment. On the other hand, he was always very much interested in what we were getting, and would come around pretty regularly and ask questions about what we were getting, and so on. So he kept pretty closely in touch, but he’d almost never come down and touch the equipment, for instance, put in a plate or anything like that.

Weiner:

How many graduate students were involved in research at this time?

Bowen:

I would guess there were 20 or 25 there in Chicago, most of who were working under Millikan. Michelson, of course, didn’t like graduate students, and, as far as know, didn’t have any. Millikan was the other senior person there so he had most of them. I think possibly Dempster might have had one or two, But most of them were working under Millikan.

Weiner:

Pretty much all the same class of problems?

Bowen:

Well, as I remember it, quite a lot of them were built around the oil drop experiment, in the sense that they were things like measurement of viscosity of gases, and that sort of thing. Millikan was getting a little interested in cosmic rays at that time, but not there. You see Millikan had already started his connections out here. They had the four quarter system there and staff members were free to take off any one quarter they wanted. Millikan always took off the winter quarter and came out here and taught here from January through March in those two years, and I think possibly one year before. And he had started Russell Otis and one or two other students out here. Russell Otis, I think, received the first Ph.D. in physics from Caltech working on cosmic rays. And there may have been some other things that my memory isn’t good enough to recall right now.

At Chicago there were two or three people working under Gale. Ralph Smythe, for instance, who has just retired from Caltech, was working under Gale on spectroscopic things. In fact, it was rather amusing. Gale was a very emotional person, a rather explosive person, and his field was spectroscopy. And when Millikan started his spectroscopy, Gale was a little bit jealous about it. And since I was the one who was actually doing it, I got in between. They were both of them friendly as far as I was concerned, however, but Gale would occasionally come into my office--he was a very profane man--and he would start cussing Millikan out in a most violent way. The ergot just blew about the place. Then, after about five or ten minutes, he’d say, “Well, I feel better now.”

Weiner:

You were sort of the sounding board.

Bowen:

He’d sort of use me as a sounding board to vent his feelings on. Mostly he was very friendly to Millikan but he would occasionally blow off steam a bit. Well, he worked along on that until Millikan, in the spring of 1921 decided to come out here, and he immediately asked me to come with him and offered me an instructorship out here and I was very glad to come because he had this program going; so I came out.

Weiner:

You had no family at that time?

Bowen:

No, I was only 22 at the time. In fact, I wasn’t married until I was 30. Well, we came out here, and at the time we came out, Bridge Laboratory was up, that is, the concrete poured, but I think the shop was the only thing finished off. There was a good deal of plastering and window sills to be put in and the usual things. I started teaching a course in general physics, and we taught in Throop Hall because Bridge wasn’t finished. Then in January ‘22 we got into Bridge. Because the only thing that was done was the shop, we then got started on this high altitude cosmic ray work. And Millikan started me on that. I may be a little confused by plus or minus a year as to the relative order of these things, but as I remember, since the shop was going, Julius Pearson made us up some things, and In the spring of ‘22, we went to San Antonio, Texas, and sent up these balloons.

We went out to the Meteorological Service--either the Meteorological Service of the Weather Bureau or the Air Force, I forget which--and we operated from their base because they had the hydrogen for balloons. They were using balloons a great deal at that time for measuring weather conditions aloft and they had the general facilities for launching. So we went there; but he came back before I did, because we had to wait until the balloons were returned. We just released these, with a tag on that there would be a $10 reward to ship them back to us. And we got, I think, the first record from sounding balloons of cosmic rays at that time, and got a definite evidence for an increase as you went up, and so on. As far as I know, that was the first sounding balloon. Aerial work had been done by Hess and Kolhorster from manned balloons but they weren’t able to get as high.

Weiner:

How did that idea to do it with sounding balloons come about?

Bowen:

I think Millikan was responsible. He’d had Otis working on cosmic rays from the ground and Otis had made measurements here, gone up in the High Sierras, and also, I think, Otis had started to work on sending the electroscope down in the lakes. There were some very high lakes in the High Sierras, some over 12,500 feet and very deep. The trouble with working on the ground is that, at this level, radioactivity on the ground is about ten times that of cosmic rays, or on that order. And as you go up, you get over different kinds of rocks, and the radioactivity varies a great deal, and, in general, while you get a sort of general increase as you go to higher elevations, any quantitative values are pretty well masked by the radioactivity in the ground.

And their idea of dropping it into the lake was to get rid of that local radiation because the water is very pure and shields off local radiation; that is, if you have a meter of water between you and your ordinary radioactivity it is pretty well shielded. And that was the idea--to get an absorption curve in that way by going up as high as you could, and then getting the absorption curve below that by going into the lake. I was out on one of those cosmic ray expeditions with Otis in the fall of ‘22. We went up Mt. Whitney, although went along just to help carry the equipment, and so on. Well, that was the first cosmic ray story. Then, shortly after that, we built a new vacuum spectrograph out here. I understand one of Hale’s inducements to get Millikan to come out was that he would rule him some gratings. There was a ruling engine here at Mt. Wilson. So we started out using some Mt. Wilson gratings with it which were ruled down in the basement here. We got that going a year or so after that and more or less dropped the cosmic ray things as far as I was concerned. There was another group, Otis, Cameron, and finally Victor Neher, who continued with that. And I was brought in. We had another balloon expedition in 1932, in which we went to Dallas, Texas, to send them up, but aside from that, I wasn’t involved in the cosmic rays very much, because the vacuum spectrograph got going strong, would guess, about the first of ‘23.

I concentrated pretty heavily on that from then on. First of all, we tightened up our technique. Before, in order to get anything through at all, we’d been using wide slits and our resolving power was poor. And, as we got to understand it more, we got a little more power in our sparks. First of all, we got better slits, and then tightened, narrowed them down, so that we really began to get high resolution, resolution down to about the limit that our plates would give. We had a slightly longer focal length in the camera, and we began to get a great deal of new data. About that time--you see the Bohr theory had come out in about 1913, I believe it was, but it didn’t have too much impact at first because it only explained the hydrogen atom--then, starting about that time, the Russell—Saunders vector model, Hund theory, all that series of developments began to come through so that we began to be able to analyze our spectrum. Before you just got a spectrum, and there was often uncertainty as to just what our spectrum was due to. I remember one amusing incident which happened while we were still working in Chicago--there we were still working in the dark. I put aluminum electrodes in one day and took a plate--it usually took all day to get a plate--and developed it. The next day I put in some very pure magnesium electrodes and got practically an identical spectrum. Well, Millikan, who is always a little bit inclined toward the spectacular, immediately got quite excited that we were transmuting one element into another. I think about that time hi started off for a trip. I was a little more skeptical and began running some tests on it, such as trying thallium, in which I got the same spectrum, and so on.

Obviously we hadn’t transmuted this. The thing which misled us was that in the visual and ordinary ultraviolet (6000A- 2000A) the metals have their strongest lines due to transitions to the ground states. On the other hand, the non-metals, such as oxygen and sulphur and things like that, have only very high level lines in this region, and consequently, unless you have some pretty strong excitation they don’t come out, and if they do, they’re very weak and tend to be suppressed by the metal. On the other hand, when you get down to this region from five hundred to two thousand angstroms where we were operating, there the metals have very few lines but the resonance lines of carbon and hydrogen and oxygen all occur. And what we were getting were the oxygen lines, because you can’t handle a piece of magnesium or aluminum in the air without getting it oxidized, so there was a nice layer of oxygen, or aluminum oxide, on the outside and a rather violent spark would naturally break it down and we were getting some beautiful oxygen spectra, occasionally with a little carbon thrown in, due to periods of handling it. But on that account, just because you didn’t know what to expect until this theory began to come out, and due to these anomalous things, it was pretty hard to straighten out the thing and know just what you were getting.

Weiner:

Was this tendency of Millikan to jump to that spectacular conclusion--you know there are certain ways one could have interpreted it if you didn’t know the answer--was this a tendency of his to look for something that he thought was a fundamental new idea?

Bowen:

I think it was partially that, and partially, of course, when he first got out here, he was very much concerned with the money-raising problem, and I think he felt any good publicity was good. I don’t think he thought of it selfishly, but it was good for the projects he was responsible for.

Weiner:

To increase the chance of continuing the support of them. How were these projects supported at the time?

Bowen:

Well, of course, in getting Millikan out, they got hold of a man who I think was the president of the Board of Trustees then, named Fleming, who had no children, and he promised to endow the Department to the tune of $100,000 a year, and that was the promise that got Millikan out; and that gave a fairly good start. In addition at that time the Carnegie Institution, as well as running its own departments, such as Mt. Wilson and DTM and so on, also made fairly substantial grants to other research people. I think my salary as research assistant was paid from Carnegie for quite a while. I never knew the details because I didn’t see the bookkeeping of the Institute, but I understand that I got quite a lot of my salary from them. Millikan had a grant, I think--my memory is something like $30,000 a year for several years during that period.

Weiner:

Was that grant earmarked for specific research projects or was it a general grant?

Bowen:

I think it was sort of a general grant to get the department going.

Weiner:

When I interrupted you, you were telling about the specific work on aluminum and magnesium where you determined, in effect, that the similarities were due to the oxygen.

Bowen:

I brought that in as showing why we had a little difficulty getting going in interpretation. Then, however, along came the Bohr theory and those other theories, and then one of the first things we noticed was that as we were working with a group of isoelectronic substances-- the first one, as I remember it, was the sodium ionized magnesium doubly ionized aluminum triply ionized silicon and so on--we began to notice similarities between them. We didn’t at the time realize quite what the stages of ionization were, but it turned out that our spark, which was a condensed spark with a big condenser across it, was giving us ionization up to 6 or 7-fold. And one of the first things we noticed was that each one of these had a prominent pair of lines, and then we noticed that on writing down the frequencies that there was a linear relationship between the wave lengths of each pair, of sodium 1, magnesium 2, aluminum 3, silicon 4, phosphorus 5, sulphur 6, chlorine 7. And the first thing that we began to get in the winter of ‘24 were these so-called isoelectronic sequences, and we were immediately able to relate them to the similar ones which they had gotten long before in the X-ray field and show that they were the so—called regular and irregular doublets, one of which went up linearly (in which the separation in wave numbers went up linearly), and the other one went up as a fourth power. And so we were able then to begin to relate this to the atomic structure theory that was developing at the same time; and of course, getting these rules of these separations immediately helped the theorists in setting up what they were due to, which were spin doublets, which were other types of doublets, and so on. As I remember, we published an article, and I went East to report to the Physical Society in the April meeting of ‘24 on these isoelectronic sequences. We got quite a lot of others, for instance, the magnesium 1 aluminum 2, and so on, in which we got these patterns running through it, and we were also able to set up a Grotian diagram and the term system for these things.

Weiner:

This was the Washington meeting in the spring?

Bowen:

Yes.

Weiner:

In the course of the work, how did you collaborate on this? You said, “we.” Are you referring here to Millikan and you?

Bowen:

Yes. Most of the papers were gotten out jointly, in fact, practically all of them were during this period. Millikan was very busy, and while he supported it a great deal, he never came into the laboratory except to look around. In fact, often he didn’t quite know what was doing until got ready to write an article and I’d go around and say: “I’ve got an article, How about coming around tonight?” He was always busy in the daytime, so he’d appear about nine o’clock in the office and we’d work until midnight writing the article. He always wrote the article, and as I say, he did very little of the actual work on it, such as taking the plates, measuring them, and so on, though he always kept pretty closely in touch with it. As I say, I was working as his assistant and so we worked together and published jointly.

Weiner:

What about when you were ready to take another step? Did you initiate any of these new steps on your own, or was it…

Bowen:

Well, I tended to sort of get the jump on him because I was much more closely in touch with it naturally than he was, and so was in a rather better position to initiate the new step, though he followed it right along, but often--well, not quite to the extent of seeing just what the next move was. Then, although I don’t say this at all in a disparaging way, he was just a very busy man but he did try to understand anything that he wrote first pretty closely, and we would work together in the evening that way. Then, that was about the time of the Russell-Saunders article and the vector model, and this was then generalized by Hund, and there was a whole series of names that generalized it, and we naturally began applying it to the more complicated atoms. For the one and two electron ones, which were the series mentioned thus far, you didn’t particularly need it except for the interpretation of the doublets, but as far as the analysis you do.

When this came out, however, as remember in ‘24 or ‘25, we jumped into it. Because of the fact that the main lines of these elements were in our region--it was the only place you could observe them—-we went after the things to the right of the table, that is, the carbon, nitrogen, oxygen, fluorine, and so on, and the next row, the silicon, phosphorus, sulphur and chlorine, and we did quite a few other things like beryllium. Metallic beryllium became available just at that time and we got one of the early samples and ran a spectrum of beryllium. As remember, in the fall of ‘26 and the spring of ‘27, we went after these elements to the right, and using the Hund theory, were able to get the spectrum and analyze most of the ground states. I published an article-- that article I published over my own name--and then a summary was published over our joint names later with a detailed technical analysis. I published over my own name in the spring of ’27, I believe.

Weiner:

That was the Physical Review?

Bowen:

The Physical Review.

Weiner:

All of this time you still hadn’t received your Ph.D.? You were working toward it?

Bowen:

Well, I received my Ph.D. in ‘26. Due to the fact that things were going so well with research, didn’t want to take time off to get my language requirements, and the usual oral exam. For one thing, my oral exam was a little more of a problem for me because I had taken all my courses at Chicago and was to be examined by the people out here, Epstein and Millikan, and Millikan was the only common one, which meant that didn’t know what they were thinking about too much. But finally, in the summer of ‘25, I decided I had better get the damned fuss over with, so I took a month’s vacation and took a German book along. I spent quite a lot of the vacation reading it, and came back and passed my German. I’d already passed my French. And then that fall got busy and brushed up and took the examination.

Weiner:

Took your oral examination?

Bowen:

Yes.

Weiner:

Can you take some time and give me an idea of how it went and who were the examiners?

Bowen:

Well, there was Epstein, Tolman, Millikan. I’ve forgotten just who the others were--one or two mathematicians, because I minored in math. Fundamentally, they were very friendly to me, remember Tolman asked me--he was teaching Relativity which was something hadn’t specialized in-—a very technical question, and Millikan turned around and said: “Say, you better try that on the committee first,” Well, knew that I had been on the faculty for quite a while and almost certainly they wouldn’t flunk me. On the other hand, due to the fact that knew I was presumably going to stay on the faculty, didn’t want to discredit myself. And actually, had published over 20 articles when took my degree. My thesis was a rather amusing one. It was on the ratio of heat losses by evaporation and by conduction from water surfaces.

Weiner:

Where does that fit in to all of this?

Bowen:

Well, it was rather funny. We had a graduate student here, by the name of Cummings, who was an older man. I think he’d been with the Weather Bureau, and he got me interested in this problem. He’d come here, and wanted to get his degree, and he wanted to do a thesis on evaporation. And he went out on the campus and would set out pans of water, insulating them in various ways, measuring the evaporation. And he had a theory that evaporation was primarily set by the amount of radiation that came in from the sun, and you could just take the amount of radiation from the sun and divide it by the heat of evaporation, and that was it. Millikan was busy. In spite of the fact that I was also a graduate student, Cummings was given to me to supervise his work. I got interested in it and succeeded in working out a theoretical formula for the ratio of heat lost by evaporation and by conduction to the air, and it turns out that you can determine this more or less uniquely by determining the temperature of the air and the temperature of the water and the humidity. It happens to have had quite a lot of use in oceanography. The meteorological literature has quite a little about it still. It’s known as the Bowen ratio. [The Earth as a Planet, G. P. Kulper, Ed. p. 232, University of Chicago Press, 1954]. And it happened when I got ready to take my degree that was the paper that was going to press so it was my thesis.

Weiner:

Really you directed your own thesis, then, because it came out of your directing someone else, and so then the work you did in the process became your thesis. It was something that Millikan didn’t itiate.

Bowen:

No, he had nothing to do with that.

Weiner:

It was very interesting the way it worked out. Did you ever consider that field any more?

Bowen:

No. Well, to come back to the spectroscopy…

Weiner:

I think I interrupted you. You were around 1927 but I got interested in your Ph.D.

Bowen:

I just mentioned that we had just published the spectrum analysis or the series analysis of the higher stages of ionization of carbon, nitrogen and oxygen. Well, all through, even when we were back in Chicago, everybody was much interested in, of course, what the nebular lines are due to, and any time we’d get something new, the first thing we’d do is check it out, that is, everybody would think about it. It was one of the outstanding problems in astronomy. Here were the strongest lines in a lot of these objects and nobody knew what they were due to. Originally, the reason they got the name of nebulium was that they thought it was like the helium which was discovered on the sun before it was here, They thought it was another element.

However by 1920 the X-ray work had established the sequence of the elements, 1, 2, 3, 4, and there just wasn’t any room until you went off the upper end and you knew that these were very rare elements, which couldn’t produce the strongest lines in an object; so that everybody was out looking for them. Well, as it turned out, of course, having published the carbon, nitrogen and oxygen of these stages, naturally I had the inside track, since I had all the analysis and all the data of all the lines so that could check things; if this predicted certain new lines, the data was all there. So that what happened was that I went East again for a short vacation. Shortly after I got back--I’d always been somewhat interested in astronomy and these things--I bought these books, which had just come out then. They are the standard texts.

Weiner:

These were the three Princeton men, weren’t they? Russell, Dugan and Stewart.

Bowen:

Yes. It was largely Russell that was responsible for it. And after got back used to read them through in the evening after got home from work.

Weiner:

What’s the formal title, just for the record?

Bowen:

Just Astronomy, by Russell, Dugan and Stewart. And it happened that Russell, who was one of the leading spectroscopists--you see, he and Saunders started the vector model off--was very knowledgeable about these things. He wrote a very nice summary about what we knew about such things in here. [Reference to text]. Well, for instance, that paragraph in small type there is very suggestive.

Weiner:

Let me read it aloud as long as I’m reading it to myself. “The suggestion is tempting that the nebular lines may be emitted only in gas of very low density. This would happen, for example, if it took a relatively long time as atomic events go for an atom to get into the right state to emit them, and if a collision with another atom in this interval prevented the completion of the process. In such a case it might require a great thickness of the very rarified gas to emit these lines strongly enough to be visible and ordinary vacuum tubes might be far too small to show them.” That was on page 838 of Volume II.

Bowen:

Well, you see he saw pretty well what the problem was, and so I just read that. As I said, we’d been watching for this for years. Then, one night I went down to work and came home about nine o’clock. I lived a half mile away from the campus. You see here is the structure of Oxygen II and Oxygen III, in which these are forbidden lines, that is, there is no way according to the theory to get from here to here. I got home about nine o’clock and started to undress. As I got about half undressed, I got to thinking about what happens if atoms get into one of those states. Are they stuck there forever? Then it occurred to me, having read this, maybe they can jump if undisturbed in a nebulae, but we can’t see them here because of collisions.

We’d done a lot of work in the physics laboratory about collisions a second time which took atoms out of these states. Well, I quickly put a reverse on my dressing and went down to the lab again. Since I had these levels it was very easy to take these differences and check them up for where there is… for instance, this is a double; there are three levels there and there should be two or three lines with a known separation between them. And, of course, having published the stuff and having all the other data, it was a matter of minutes to establish it. For instance, certain of the things I had gotten I forget now whether it was this one or not… I hadn’t found any transitions to this level, but I could predict about where it was from this I got this one right away, and I got these right away, and I could predict roughly where this one was, assuming this is the value of this line, and that fixed this level, add then I could predict certain lines here. Well, I just went to my table and there they were within a hundredth of an angstrom. I worked until midnight and I knew I had the answer when I went home that night.

Weiner:

How long, had you been thinking about this problem prior to this?

Bowen:

Well, off and on, practically ever since I’d been in graduate school working in spectroscopy, I should say. It was the problem that most spectroscopists knew was an outstanding problem and almost any spectroscopist kept his eye on it and as new things came up, thought: can this be the answer? And that was true, I think, of most spectroscopists. But the fact that I had just completed the analysis of those atoms gave me the inside track.

Weiner:

Did most people make the assumption that since there was apparently no other element, that this was an element unique to the galaxy? That nebulium, in fact, was an element that was not known and not likely to be found? There was no challenge in that part of it, was there?

Bowen:

No, I think Russell said it very well here. Also, one thing that was coming out more and more was the fact, which spectroscopy had qualitatively already proved, that the universe is reasonably uniform. After all, the elements you get in the sky are the same as we have here in general. And everything pointed that way. And then the X-ray data, and to a certain extent, this data that we were getting following up on it, was the same sort of thing but not as extensive. It showed that you get these progressions of the X-ray lines in which each one is ... if you take the square root of the frequencies they get a nice straight line with a step of Just one, but you can’t have a double Jump somewhere there without knowing it.

Weiner:

So, from many independent developments, it was apparent that there had to be another explanation for nebulium. The name itself is almost a facetious term.

Bowen:

It was patterned after helium, you see, which was discovered in the sun first, and then found on earth some period afterwards.

Weiner:

But in this case-—this is the point I am trying to make—-the important distinction was that you did not expect nebulium to be found on earth.

Bowen:

No. I think up till probably 1910 or ‘20, they did think of it as a new element. Then, however, as the X-ray data which was coming out-- the X-ray spectroscopy, as I remember, it was around 1914 when Moseley started that off, or started off getting the sequences. You know that date probably better than do.

Weiner:

No, off-hand, I don’t. [Moseley’s paper was published in 1913.]

Bowen:

And by the early twenties, that was really soaking in. People realized that that meant certain things, and that’s why I think Russell wrote as he did. Russell was one of the keenest minds at that time; that is, of those who were working in this particular field, and he was working very much in astronomical spectroscopy from a theoretical standpoint.

Weiner:

What did you do when you knew you had it after you’d gone back to the…

Bowen:

went back and went to bed.

Weiner:

No telephone calls? No sharing the word with anyone?

Bowen:

Well, I was put a little bit on the spot. Millikan was in Europe at the time. Up till that time, three-quarters, anyway, of our publications had been joint. I was his research assistant and hired as such. That was my official title. As say, I was quite on the spot because it was obviously the sort of thing, if somebody else got the idea, that was the end, since it’s one of these things that doesn’t require a lot of work to put it through. It’s an idea, and if somebody else gets it before you get into print with it, it’s just too bad. On the other hand, I was very reluctant to send it out without discussing it with him and seeing whether he wanted his name on it or not, didn’t dare put his name on it without his knowing it. Well, had quite a discussion with several of the other older men down there, Millikan wasn’t to be back for months. Of course, in those days, there was no air mail and things of that sort. It would take months to get word back from him. We finally decided the only thing to do was to get an article out, so in a couple of days I sent it right off to Nature, which was then our fastest publication.

Weiner:

Was that fastest in terms of all fields, physics and astronomy? Here’s a paper that had to do with both fields. Other than it being fastest, would Nature still have been the most appropriate journal for that particular article?

Bowen:

We used it. You see the Physical Review at that time was a rather slow publication. It was used quite a lot for publication of doctor’s theses, and frankly, we didn’t think very much of it. We tended to publish in the Phil Mag, or things that were spectroscopic in the Astrophysical Journal, so it was the normal thing for fast publication at this time.

Weiner:

And a prestigious publication too.

Bowen:

A few days later I sent off another one to the Publications of the ASP, and then, however, having got this short note off-—the one that sent to Nature as published was less than a page long since it didn’t take very much to give the basic ideas--then later, after Millikan got back, and I‘d had a chance to study other possibilities of other lines and so forth, published a long article in the Astrophysical Journal that winter.

Weiner:

What was his reaction when he finally learned of this?

Bowen:

He was fine. He didn’t object at all.

Weiner:

Was his reaction a positive response to this?

Bowen:

Oh, yes, he was happy about it.

Weiner:

Did you hear from people other than the people in Pasadena?

Bowen:

I had a beautiful letter from Russell. He got quite excited about it, of course. He was writing his series of articles for the Scientific American at that time. He wrote it up twice.

Weiner:

It was considered a hot new discovery?

Bowen:

Yes.

Weiner:

Well, how about publicity? Was there any local newspaper publicity?

Bowen:

No, particularly in view of the Millikan situation, we held off completely on that. At that time, we didn’t have any publicity department. In fact our policy in general, particularly at that time, was not to announce to the newspapers until it had come out in the scientific press.

Weiner:

During this period you weren’t a teaching assistant, yet you were teaching, though you were a research assistant to Millikan?

Bowen:

My title was: Instructor and Research Assistant to the Director of the Norman Bridge Laboratory of Physics. I had the longest title in the catalogue.

Weiner:

What did you do in instructing; was this undergraduate work?

Bowen:

Yes, it was undergraduate work in which I had a very interesting time. About l924, I think it was, they decided to segregate their students. Caltech always has the policy of very small classes of 20 students, which meant they had eight sections, because they had about 160 students in each class. That year they decided to pick the top men into the A section, the second class into the B section, and after that, they didn’t differentiate. I was given Section A to teach that year, and I never had quite such a run for my money. In the class was Ed McMillan, Robley Evans--I’m afraid I can’t remember all of them, but I think fully half of them are now heads of departments in big universities, and so on.

Weiner:

And you still hadn’t your Ph.D. by this time?

Bowen:

No. In fact, there was one man who was in about the middle of the class that I hadn’t heard from. I’d just completely lost touch with him, until when I retired four years ago, I got a very nice letter from him on the letterhead of the President of Rensselaer Institute. It was quite an unusual class. You see, Tech has the three-term system, and the first two terms we covered what the rest of the class did, and in the last term we set up a lot of research experiments, a little oil drop experiment, e by m experiments, that sort of thing.

Weiner:

At what level of the undergraduate was this?

Bowen:

Sophomores.

Weiner:

And this was based on first year performance?

Bowen:

Yes.

Weiner:

Well, how many hours a week did you put in on this sort of thing?

Bowen:

The class met three times a week, plus one laboratory, if I remember rightly, but keeping ahead of that group took quite a little time, as you can imagine.

Weiner:

I should imagine. This was your only class?

Bowen:

Yes, I never taught more than one class.

Weiner:

And so the rest of the time you were free to do research. Was this a unique position because you came as Millikan’s research assistant or were other faculty…

Bowen:

Some of the sections were taught by graduate students and the other people teaching were largely holdovers from the old regime. They were not too much involved in research, which was the reason I was given this assignment, I think, was always rather proud that at that time Ed McMillan was planning to major in chemistry. After that course he switched to physics. And then was quite irritated when they gave him the Nobel Prize in chemistry.

Weiner:

Getting back to his origins. But he got the Nobel Prize in chemistry for work that was really physics.

Bowen:

Well, it was on the borderline between them. He was a most brilliant fellow. He and Robley Evans were the top men in the class generally. You know who Evans is?

Weiner:

Is that the MIT…

Bowen:

MIT, yes. Robley was one of these people who--this shouldn’t be published--was always interested in getting as many grade points as he could. He was the most skillful person I know in getting A minus in a large number of courses. Ed was just the other way. What he was interested in, he would get A double plus in, and that was that. We all recognized Ed as the most brilliant fellow in the class, although often his grade point average wasn’t as high as Robley’s.

Weiner:

Had they both come out to study at Caltech as undergraduates?

Bowen:

Yes, though Ed was a local boy. His father was a physician here in town. I’m not sure what Robley’s background was.

Weiner:

Did you continue teaching this advanced section in later years?

Bowen:

Yes. I taught that till about ‘29 as I remember, though I never had a class like that again. Then in ‘29, Walter Whitney, who was teaching the optics, left. He was one of the holdovers from the older regime; he wasn’t too much interested in research, and they arranged for him to transfer to a nearby college. He had taught the graduate course in optics, and so they asked me to take over the optics.

Weiner:

By this time, had your position changed? You got your Ph.D. in 1926.

Bowen:

Well, I became Assistant Professor then. And then in 1928 I went to Associate Professor, and in ‘31 to full Professor.

Weiner:

And then, once you had your Ph.D., you were no longer a research assistant?

Bowen:

I forget now. I think the title continued for two or three years anyway.

Weiner:

On the outcome of the nebulium work, you pursued it through and refined it somewhat, didn’t you?

Bowen:

Oh yes. Actually, that took care of perhaps half a dozen of the strongest lines in the nebular spectrum, and explained the main ones. On the other hand, there were quite a few, a lot of fainter lines, some of which were hydrogen and helium lines, regular permitted lines which are observed In the laboratory, but there are also a good many more fainter lines. So after that, I went after analysis of other elements that might be likely to take care of some of these fainter lines. In fact most of the period up till the war, that is In the thirties, was spent on further analysis, quite definitely slanted toward getting the elements that might provide the explanation of the fainter lines, and I did get a great many more.

Weiner:

This brought you a lot closer to astronomy. Did you remain in close touch, as a result of this specialized work, with developments in astronomy? Did you get in touch with them more than you had in the past?

Bowen:

Yes, somewhat more. Well, the other thing that I did at that time was the fluorescence mechanism in nebulae, which came around ‘34 or ‘35. I had noted that the strong lines of helium plus, the resonance lines at three hundred and four angstroms of helium plus, coincided within one or two hundredths of an angstrom of certain lines in oxygen three, and had wondered what it might do. Let’s see if we can find you a diagram. This line coincides with this line here, which means…that is, there are several components to this and one of them coincides with the helium line within less than a couple of hundredths of an angstrom. If the helium line is then going through the gas in this stage, it should shoot an electron up to here and populate one of these three levels but not the others.

Then it can return to this position, not directly it can return directly, but it may return by these paths. It should give certain lines of these multiplets. I had noticed this coincidence and wondered what might happen. It happened that got a letter from W. H. Wright, who was then director at Lick, and who was one of the chief observers of nebular spectrum lines, and they had just put on the Crossley a new aluminum coat. John Strong put it on for them. It was the first large mirror aluminized. And he immediately started observing the ultra-violet. I got a letter from him one day. He said: “I’ve got these new lines in the ultra-violet.” You see these are down around 31 and 33 hundred and hadn’t been observed before because they’re down in the region where silver reflects very poorly. “I can’t understand it, they don’t have the normal intensities.

Do you have any explanation?” was happy to write back immediately and say, well, this is the explanation; because I‘d had the explanation but hadn’t had the evidence. So I kept quiet about it. So that settled that particular point. Then in 1938 Wright asked me to come out on the Morrison fellowship and spend the summer up there at Lick. And did, and he assigned--since I was pretty green at the observation work--he assigned Art Wyse (he was killed during the War as you know), who was a very promising young astronomer there, to work with me. It happened at that time some new very fast panchromatic film, which was much faster than anything available for the green, yellow, and red, had just come on the market. We set up a program for observing nebulae in that region, and picked up a lot of additional lines observationally, which in several cases, had the identification for from this study in the laboratory. So that was my first real observational work.

The other thing was that the funds for the 200-inch had been given in 1928. Hale supervised it for a while, as long as his health permitted, and kept in very close touch with it himself, although there were some committees set up. I was a member of one of the general advisory committees, largely because was teaching optics and spectroscopy. You see this was rather an anomalous situation in that the money vas given to Caltech, but Caltech had no astronomers on the staff, so all through, the committees set up for handling the 200-inch was usually made up about half from Mt. Wilson astronomers and half from either engineers or physicists from Caltech. And I was on that first advisory committee. Then around ‘36, Hale became incapacitated and they brought Mason out to head it up.

Weiner:

Max Mason?

Bowen:

Max Mason. He set it up a little more formally. First of all, there was the top committee which was largely trustees; there was Dr. Adams, and two or three of the trustees from Caltech and so on, and they had to give the final approval to spending major sums of money and so on. But the top scientific committee was the Policy Committee. And then there was a Construction Committee which was largely engineers, but which any member of the Policy Committee was free to sit in on any time he wanted to. The Policy Committee consisted of Mason as chairman; from Mt. Wilson there were Hubble and Adams; and from Caltech were Tolman and myself. And that was my first real dip into astronomy you might say. People often wonder why that telescope works so well, but there was a tremendous effort went into it. Both the Policy Committee and the Construction Committee from that time on met for half a day a week, really going into details.

Weiner:

From ‘36 on?

Bowen:

From ‘36 on, until the War started. And after the War they continued meeting quite often.

Weiner:

And so there were physicists and engineers and astronomers involved?

Bowen:

I asked Rule once: How much engineering time went into that telescope? He looked it up for me. I think it was 75 man years. They had a whole staff of engineers of detailers or people of that kind. Then on this Construction Committee was Pease, who had been chief engineer at Mt. Wilson, Sinclair Smith, who was a very instrument-minded astronomer from up here, a younger fellow, and think two or three other engineers, plus various members of the Policy Committee used to sit in. I sat in on it quite often any time there was anything felt could contribute to.

Weiner:

Were the meetings held on the campus?

Bowen:

On the campus, in Robinson.

Weiner:

Just prior to this, by ‘34 anyway, you had done work establishing that hydrogen is the most abundant element in the stars.

Bowen:

That was really Russell who did that.

Weiner:

Well, you were able to demonstrate it though.

Bowen:

Well, Russell had done it for the sun. He had come out with the first real abundance study. Then Mrs. Gaposchkin in her book on stellar atmospheres did it. It’s true that these first attempts were rather qualitative, but all showed that hydrogen was by far the most abundant. As far as most of those within the nearest factor of ten they were probably doing pretty well. They had pretty well established the order of things. The only thing that I did was on the basis of this work of Art Wyse’s and mine. We had calibrated our plates and measured intensities, and then we essentially extended the work that Russell and Mrs. Gaposchkin had done for the sun and the stars to the nebulae. But the original work was all Russell’s.

Weiner:

I see. But the statement that you demonstrated that the hydrogen was most abundant in the nebulae, that statement itself holds?

Bowen:

Yes; or think I prefer to state it that the composition of the nebulae was about the same as the sun and stars.

Weiner:

When did the image slicer come in? Was this ‘38?

Bowen:

‘38 or ‘39. I worked with Dr. Ted Dunham on that, I got the idea, chiefly on the basis of some discussions with these committees at Caltech, of the limitations on speed. Actually, it hasn’t been used as much as we thought it would be at that time. The slicer itself worked all right, but the condensing lens to take advantage of it, which was a cylindrical lens to go in front of the plate, caused difficulties. The slicer itself doesn’t increase the intensity on the plate; it simply widens the spectrum. Then in order to increase the speed you have to narrow that down with a cylindrical lens, and we ran into some problems with that. In the meantime, we were able in designing the 200-inch telescope to very greatly speed up the spectrographs in other ways, so that the need for the slicer was much less. And for our very fast ones the slicer wouldn’t have been very effective anyway; for these very long focus ones it is effective.

Weiner:

You used it at Lick?

Bowen:

Yes, we used it at Lick. It has been coming back recently, however, for the spectroscopic photoelectric work, because for the photoelectric work, it is total amount of light that strikes the cathode, and not the concentration of light that determines the speed. There they use it regularly and it has quite an advantage because since you take in all the light you’re not affected by seeing, which causes your image to expand like this. With a narrow slit the amount that goes through varies, which is rather upsetting for their analysis and often occurs rapidly. It is upsetting for measurement. The fact that you get practically all the light through makes it more uniform, so that they are using it for that purpose, but not for the one we originally set it up for.

Weiner:

Did the result of the work at Lick--where you talked about iron and magnesium and you found their distribution really in small amounts, and established that the distribution in the nebulae and the sun and stars are similar--did this have some impact at the time on cosmological theory?

Bowen:

don’t know that the fact we found the abundance the same had any great impact on that. I think the important thing was the original work, as I say, of Russell and followed up by Mrs. Gaposchkin, which we established for the others. Of course, it was of interest that these were the same, but think most people would have guessed it. The only thing was that when the first work identifying the forbidden lines came out, due to the fact they were oxygen and nitrogen, there was a little tendency to say these were more abundant there than they are in the other things. One trouble being, as I mentioned earlier when I was discussing this misidentification of the transmutation of magnesium, the oxygen and nitrogen and carbon lines are not in the region in the visual range. So it’s very difficult to determine in the laboratory or in the sun or in the stars, before we had the vacuum spectrograph. It’s still pretty hard to determine.

In fact, in the sun now, I think probably the best determination is the forbidden line in absorption, because that is a transition to the ground state. One of the troubles is due to the very high level of the states in oxygen, the lowest one that you can observe through the atmosphere has an excitation potential of something like ten volts, For the sun, the Boltzmann factor of that is about l09 and it is the ratio of that line up here to transition of the ground state. But that Boltzmann factor depends on the exact value of the temperature which we don’t know accurately. And so even though you do observe some of those high level lines the uncertainty of this correction is so great that it is pretty hard to fix the abundance. On the other hand, these forbidden lines which drop to the ground state in oxygen 1, or to very low levels, don’t have that factor, The ground state has no correction at all, you see, I think I was the first one to observe them in the sun, which I did in ‘47. There was some Frenchman who did it about the same time.

Weiner:

But you did it here. You were describing the sequence of work up till about 1938-1939-—I was just wondering, did this begin to be a different period? Or when would you say the sequence of work changed, where was there a change of scope in what you were doing?

Bowen:

Well, I kept up on this work of observing this vacuum spectra right up till the War. I was still Professor of Physics over at Caltech, and was just observing the spectrum and working through on that problem. I did one or two things jointly with Edlen in Sweden because there were certain things that he could do that I couldn’t. And then the War came along, and we stopped other things, starting about the fall of 1940, and while I kept up a little bit the winter of ‘41, it was at a reduced pace. In the fall of ‘41 Charlie Lauritsen’s big group got going and I got head over heels in that and never went back to the spectra.

Weiner:

What contact had you had with the work that Lauritsen was doing from the early thirties on? You were in the same department.

Bowen:

We were in the same department, but he was over in the high voltage laboratories, so I didn’t have too much contact with him. Oh, we were good friends. We used to meet at the Atheneum occasionally, at the department meetings, but it wasn’t at all intimate.

Weiner:

What else was going on then--this was when Oppenheimer would be here for one term, or for six weeks anyway, and would generally bring some of his students down with him? Did you have much interaction with this group?

Bowen:

Not a great deal. He was, as I remember, interested more in nuclear physics than he was in the atomic physics, by atomic I mean the extra-nuclear electrons, which is what I was interested in at that time, so I never had too close contact with him. My chief contact with Charlie and Willie (Charlie Lauritsen and Willie Fowler) was just after the War. Of course we had this big War project which we were all pretty heavily mixed up with. Charlie was in charge and Willie was second in command, and the War suddenly stopped, and we realized that we, all of us, had pretty well gotten out of our old fields and needed to have a certain amount of refresher to get back into it again. And I had been appointed up here, in fact, I had taken over on January 1, 1946.

Well, one of the things that was just beginning to come in then was the application of nuclear physics to stellar interiors. There had been a few stabs at it back in 1938 but pretty crude stabs, and everybody had just forgotten their own work completely for four years and were pretty rusty and were naturally sort of casting about--where do we go from here-—often not quite wanting to go back into the old field again. So we organized a seminar which met up at my house in the evening once a week for most of that winter and spring with several of the astronomers like Paul Merrill and Baade and Joy, or people who were interested in atomic structure and so on, and Charlie and Tommy Lauritsen, and Willie Fowler. We discussed these problems of the relationship of nuclear physics to astronomy, all the astronomers giving their information: what is the chemical abundance, what is the composition of these various objects, and what are their other characteristics, their temperature and so on; and Willie and Charlie re- viewing some of these early papers on the nuclear explanation of it, giving their own ideas.

Weiner:

Including Bethe’s carbon cycle?

Bowen:

Yes. I think it was largely because of those seminars that Willie took his present turn. It happened to fit in very nicely with their needs… You see, Caltech had never gone in for very high voltage things such as Ernie Lawrence had and the result is they weren’t able to compete on a lot of those high voltage problems. On the other hand, these reactions in the sun, after all, only have a few tens of thousands of volts to operate them, for the hydrogen to helium reaction. And consequently they fitted in very nicely with their equipment to investigate them. And, Willie has done the outstanding work in that field since then in getting out cross-sections and so on for these various reactions of these light elements that take place in the sun.

Weiner:

And then from that, drawing conclusions on relative abundances…

Bowen:

Well, predicting relative abundances…

Weiner:

…which is very significant for cosmological theory…

Bowen:

from that, getting data: why do stars have the characteristics they do, why do they have the surface temperature, the rate of emission or evolution of energy, the temperatures that they do, and so on. He got tied up with the Burbridges who were working on it from the more purely stellar interior standpoint. And they have done, as you know, pretty outstanding work in that field.

Weiner:

That’s one of the things that is interesting in the history of science. All of that work on stellar evolution and cosmology involving Fowler and the Burbridges and all of that team…

Bowen:

Yes. That was, I think Willie would say, started from that series of seminars which lasted for maybe six months.

Weiner:

Prior to that, from the time that you arrived in the twenties, what kind of communication had existed on the campus in terms of either seminars, or anything like a Journal club, or discussing the latest developments; was there anything much like that?

Bowen:

Well, Millikan was great for seminars, and there were two physics seminars, if I remember rightly, on Tuesdays and Thursdays at 4:45, which were largely Journal clubs, or where one of our own people if he had important research to report, he would report it there. But Millikan was quite a reader and he would get some reprints in and he would come around to some graduate student: here, you report this a couple of weeks from today, and so on. Then we had also, throughout that period through the twenties and thirties, what we called the Astronomy and Physics Club, which was a Joint meeting of the Physics Department down there and the Observatory people here. As I remember, it met alternately up here in the library or down in the physics lecture hall, and I think that was Friday afternoons. It came once a week too.

Weiner:

Who led those discussions? It wasn’t clear what role Millikan played in the physics seminars other than making assignments.

Bowen:

Well, they were largely reports. On the other hand, Millikan was rather fast on the uptake and he was often the one who would ask some questions at the end.

Weiner:

How about when Lauritsen developed his tube, the Lauritsen tube? Was that reported? Did you follow his work?

Bowen:

I haven’t a specific memory of a particular seminar, but I am sure it was.

Weiner:

But that would be the sort of thing?

Bowen:

That would be the sort of thing, anything of that sort would be reported, and then basically our own reports, that is, reports that were worked on here would take priority. And then they would use important articles from outside to fill in, because with two meetings a week or really three meetings a week, the work here wasn’t enough to really keep them all busy.

Weiner:

In other words, the meetings that you established at your house after the War were, in a sense, a continuation of a tradition?

Bowen:

Well, this one up there was a small rather intimate group. I presume there were never over ten or twelve people there, largely senior people, and people very actively interested in these problems. There were four or five people from here: Baade, I think Minkowski was there and Merrill and Joy and one or two others of the primary spectroscopists, and then there was Charlie and Willie and Tommy, and possibly one or two of their people from down there, and myself.

Weiner:

How long did this keep up?

Bowen:

Four to six months; forget now.

Weiner:

How about visitors to campus? You heard me mention at lunch today the visiting lecturers. Apparently Millikan’s policy was to bring in well known people. What do you recall about that?

Bowen:

Well, there were a good many. I remember the first year we had Raman for a year. And then there was this Norwegian meteorologist, the senior. It was a father-and-son team named Bjerknes. The father was here. He was rather a quiet fellow. And then at other times Millikan had Einstein in. I think not for that long, but maybe for three months. And Sommerfeld was over a couple of times. Sommerfeld was always a very fruitful fellow. You’d have to get the catalogue for that period to go through to get all of them.

Weiner:

I have a copy of a list that was prepared by Millikan when he was seeking some additional support from the Rockefeller Foundation and this was one of the things that he was demonstrating, But I was particularly interested in things that stood out in your mind, For example, you said that Sommerfeld was fruitful, in the sense that his lectures were good and were of interest to people.

Bowen:

Yes. Well, you see he had written the standard text on all this atomic structure business at that time. It was the thing that we were all reading. I remember that summer that I went home to study up on my German. A new edition had just come out and I took it home and read it through that summer. After that I passed my German exam.

Weiner:

The Atombau und Spektrallinien?

Bowen:

Yes.

Weiner:

How did you feel about the geographical location of Caltech? Was there any sense of isolation and if so, was this enhanced when you came in contact with visiting lecturers who gave you an impression of what was going on elsewhere?

Bowen:

I don’t think we felt isolated, except possibly for the first two or three years. You see, when I first came out and when Millikan came permanently, Epstein had just come, and I think Tolman came that year. They were about the only outstanding physicists here. There were several other people: Gilmore, who Just taught the undergraduate things, and Whitney, and Watson were here, but Watson had always largely been in administrative work rather than attempting to do very much research. For two or three years it was somewhat more isolated compared to Chicago where there was a somewhat bigger department. But that very quickly changed as we began to get other people in the staff and these visitors. Another thing that helped a great deal in building it up were the National Research Council Fellows. At one time, of the fifteen National Research Council Fellows in Physics, ten were at Caltech.

Weiner:

They could choose where they wanted to go, so apparently they were attracted here.

Bowen:

At least that’s my memory of it at one time. But that was exceptional, of course. Ordinarily, there were in the order of half a dozen there. One thing that Tech was very lucky about right then was that, just after he got out here, Millikan got the Nobel Prize, the second one given in physics in this country, in 1923. That, of course, carried a great deal of weight all over the country. And also here was a new place that had, compared to a lot of the older places, plenty of money for research. They didn’t think they were too flush, but I think compared with a lot of places they were, at least to the extent that they could put a much larger fraction of it into research than other places could.

Weiner:

I think $100,000 a year in the budget for a physics department, by anyone’s standards was very, very good.

Bowen:

At that time. And so a great many people did come out, because there was money to get people equipment and so on, and also Millikan’s name carried a great deal with it.

Weiner:

What about European fellows, people who came over on Rockefeller Fellowships or other international fellowships?

Bowen:

We had quite a few of those.

Weiner:

How did these people who came as fellows, either NRC fellows or the foreign fellows, get into the local situation here?

Bowen:

I think they fitted in pretty well. I think one or two stayed: Goetz and Zwicky.

Weiner:

I know Zwicky stayed.

Bowen:

The other was Goetz. Goetz never did quite so much. He was one of those who was a little bit too much endowed with the German spirit of lack of cooperation. He stayed and think there may have be some others.

Weiner:

Dieke spent some time here. He was at Berkeley but he also spent some time here.

Bowen:

Then up here at the Observatory, there were quite a few Commonwealth fellows at that time, Englishmen, most of whom have made names for themselves, I remember one of them was Sir Richard Woollie, who is now Astronomer Royal, and Sir John Carroll. He came over but he worked with me for some reason on this vacuum spectroscopy for a year. He’s been head of the Navy research in Great Britain. He’s now retired.

Weiner:

You’re talking now of this earlier period; we’re talking of the l93Os.

Bowen:

Yes, these were all here in the late twenties and thirties.

Weiner:

What about your teaching duties during the period. Did they tend to change very much? Was the load increased or decreased?

Bowen:

No, as mentioned, I switched to teaching a graduate course in optics in ‘29, a 2-term course in optics, and 1-term in spectroscopy, which meant was teaching just one course at a time. The fall and winter term was optics and the spring term was spectroscopy, I taught that right through, from ‘29 until we stopped at the War, In fact, taught a little bit after the War. They had difficulty getting a replacement for me, so for a year or two taught the spectroscopy after had moved up here,

Weiner:

Still your major time was devoted to research?

Bowen:

Yes, Of course, the first time you teach a graduate course like that, particularly as I’d never had the course, you work practically full time at it the first year, then after that it doesn’t take very much time getting organized and so on. The way to learn a subject is to teach it. You learn about three times as much when you teach it than if you took it.

Weiner:

What about the students during this period? The student body, of course, increased in number but not tremendously.

Bowen:

They had a definite policy of accepting 160 freshmen. They’d often have a thousand applicants, but they’d accept 160, I think now, since the War, they’ve gone up to 180 or maybe even 200, but it’s still essentially the same.

Weiner:

What about the effect of the Depression?

Bowen:

Well, we took some salary cuts and so on, but we kept going.

Weiner:

Did this affect the research budget?

Bowen:

Oh, I’m sure it did, but most of us by that time had gotten equipment and programs going so that it wasn’t necessary to have too much major new money. At least, in my work was using essentially the same equipment.

Weiner:

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I guess the real expensive thing was the cost of building large telescopes on the one hand, and then the high voltage work ate up a lot of money; but that paid for itself in a way because of the cancer grants that were made for it.

Bowen:

In a way, our telescope really benefitted by the Depression. In fact, we'd have been a little bit hard put too, I think, if the Depression hadn't come along. But just because of the Depression, a lot of these big companies were very anxious to keep their top technical people together and so were willing to accept these jobs for cost or even less, to keep their very best people hired, which I'm sure that in times like this wouldn't have happened. And I know, over and over again, some company would almost give us stuff or do it for what we knew was very much below their cost because here was the world's largest telescope. It was good advertising to participate in it and also there was this factor that it was the Depression and they were having trouble getting enough to keep their top technical people together so that after the Depression was over they’d have something to start with, I know we came out very well on a lot of things.

Weiner:

You are speaking from the time when your experience in this started, about 1936, was it?

Bowen:

Well, had some connections before. But it was in 1936 that was really intimately involved, though was on some committees before but they didn’t meet very often. But from ‘36 on we met very often and were really following the details of the thing.

Weiner:

I want to give you an idea of the sort of thing that I’d like to talk about now if you think that it is logically next--a little bit about the effect of the War and some general idea of how you related what you know about cosmic rays and optics to War work, how the War affected the 200-inch project, and then how it came about that you received the appointment as Director-—these all sort of fit in.

Bowen:

Of course, practically everything stopped as far as pure science research goes. They did up here. Dr. Adams was scheduled to retire in the middle of the War but naturally he didn’t. He stayed on, and there were one or two people who couldn’t be involved in war work. For instance, there was one of our most brilliant people, Baade, who was a German citizen actually. Naturally, the telescope time is very valuable and very hard to get so they wanted to keep it moving along, and Baade, in particular, got a great deal of time. He was undoubtedly our most expert observer here, and so it was lucky that he was available. They had to get permission for him to go more than five miles from home so he could go to the mountain, so he kept going on the mountain that way. And I think some of the other people, even though they were doing war work, had a few small projects here so they’d manage to get up and do a little observing now and then to keep the telescope busy during the War.

So, as far as the Observatory was concerned, that was the impact. Down at Caltech, it was even more so, because we were a little more heavily involved. It had this big project. Many of the rooms were actually cleared out because they needed the rooms for war work. So everything just stopped down there essentially. But most of us got into the war work. The big project was one of rockets which again drifted over into the atomic bomb at the end, but due to the fact my background was optics, had charge of the exterior ballistics. Of course, due to the fact that the rockets accelerate after they leave the launcher, you want to get as much information as you can as to how the acceleration is, how the path is, how it deviates from the path, and so on. And so we developed special cameras for getting pictures at accurately spaced intervals large enough so that you could measure them accurately, and from that, measure the accelerations, Oh, for instance, a rocket blew up. Was it due to something wrong with the powder that caused the pressure to go too high, which would cause a little sudden acceleration before it blew up, or was it just a weakness of the steel? There were a lot of questions of that sort so that the more we could find out about the behavior of the rocket, its motion, and so on, the better. Therefore we developed a rather elaborate set of entirely new types of cameras for that purpose, and the crew I was in charge of took the pictures, assessed them, and so on.

Weiner:

Were there other physicists on the crew, or were these engineers?

Bowen:

Well, most of them were younger people. One of them was Johnny Irwin, who is an astronomer now. He was at Indiana for quite a while. He’s now at Arizona. And Crandall, who had almost taken a doctor’s degree in mathematics, and then got interested in photography. He’s a very expert photographer, but he had the mathematical background. And then we had several other people with a physics background for taking the camera out, setting them up, and taking the pictures, then measuring them up back here.

Weiner:

Any substantial innovation resulting from this war work that was more widely used as a result?

Bowen:

Oh, I don’t think so. A lot of these cameras that we developed have been taken over by the Navy and Army, and are used for their present military work. They are doing a lot of rocket work too, so they need either these cameras or a later generation of them.

Weiner:

How about the cosmic ray work? Did you do any of that?

Bowen:

No, I had pretty thoroughly dropped that around 1933 or ‘34. We had one other expedition, which I mentioned before, to Dallas with these balloon things, but that’s the last active work I did with that, Millikan began to get out of it. Neher got very expert with it and was putting his full time on it, and so there wasn’t too much point in my doing it. I was getting more and more involved on the astronomical side of things.

Weiner:

Anderson too, by this time, was getting involved?

Bowen:

Yes.

Weiner:

That brings me to a question I meant to ask before, and that is, the reaction, as you recall it, to certain major events in the thirties, One is in 1932, the discovery of the positron. Do you remember discussions at that time?

Bowen:

Oh, in a general way. One discussion I remember was the objection of a good many people to the name because it is a mixture of Latin and Greek roots.

Weiner:

Did they have a better proposal than that?

Bowen:

I don’t think so. There was quite a little discussion at that time about it. The purists didn’t like it because the first part was Latin and the last part was Greek.

Weiner:

Well, it was just a contraction of positive electron. What about the neutron discovery? Did this make much of a stir?

Bowen:

I don’t remember much about that. I wasn’t following that field too closely at that time.

Weiner:

When did it become clear to you what your next steps would be in the post-war period?

Bowen:

Well, the war was still on when in the spring of ‘45, I was approached as to whether I’d be interested in the job up here. We all knew Dr. Adams was already a couple of years past his normal retirement, and I was approached. I was a little dubious at first because I’d assumed Hubble would have it, but I found out that the decision had already been made that probably he wasn’t the man for it. On thinking about it and realizing that the first big job would be getting the 200-inch going, I felt that possibly could do it as well as anybody. I had the optical background, and so on.

Weiner:

And you’d been closely associated with it?

Bowen:

I’d been fairly closely associated with it. I knew this before the end of the War, so naturally I didn’t think about going back to ordinary spectroscopy. In fact, I had been officially appointed before the War was over. It happened that Bush was out to see the Trinity Test and stopped out here and told me I had the job.

Weiner:

Was any construction done during the War?

Bowen:

No, it just stopped dead.

Weiner:

I could imagine that the contracting that had been let out would have to be stopped.

Bowen:

They just stopped. See, with all this work at Caltech, on particular rocket projects, and some other small ones, they needed all the shop work that they could get a hold of, and consequently, the big shops were just taken over for the war work with all their personnel. In fact, if I remember rightly, the big machine shop where the 200- inch was being built in, was put on extra shifts,

Weiner:

So you had the problem immediately after the War of sort of picking up all the pieces and beginning over again after this lapse. I imagine a lot of momentum was lost.

Bowen:

Oh, there was, a great deal.

Weiner:

You saw as your main task the completion of the 200-inch but yet it was very clear that there was also the question of the observatories. It was easy to understand your role in the newer one being built, especially in the stage of your involvement in the kind of optics that was really needed there, but the other one was an ongoing thing. It was a sort of astronomers’ institution. Was there any resentment that a physicist--with leanings to astronomy, but a physicist—-was coming and taking over as the head of an astronomical institution?

Bowen:

Well, not that I know about. Naturally, that sort of thing was not told to me to my face, There may have been, but didn’t know about it. I would rather guess, not too much) because of the situation. You see Hale had started the Observatory here in 1901+ and had staffed it between 1904 and 1920, but it happened when came up here that three- quarters of the staff were older than I was. They all knew they were going out soon, that is, three-quarters or 8o% of them retired before I did, and so they were rather relaxed about it. They realized they were past the age of taking on administrative work, and so on. And, of course, they knew I had dipped into astronomy a good bit before, and most of them were pretty good friends of mine. We had worked together from time to time on various things. Merrill, in particular, I knew very well. Hubble and Adams had been on a policy committee with me for years and I had worked with them pretty closely, and so on. And they also knew that they were going out before too long.

Weiner:

It seems to me that we’re at the point where we are beginning a whole new chapter from 19136 on. want to ask your advice whether we should get started on this.

Bowen:

I’m not sure just how...that is, a lot of the purely administrative details aren’t too much of concern. My actual main scientific work, you might say, was first of all testing out the 200—inch and getting it into adjustment and then doing a lot of the designing of the auxiliary equipment, particularly spectrographs, which was done between ‘46 and ‘52 or ‘53, when we got it into full operation; plus, of course, learning how to run an observatory.

Weiner:

Well, there are a lot of things, even in the administrative aspect, that think are of fundamental importance: concepts that are involved in sharing time for the use of the instrument, and so on. When you have under your wing the world’s largest astronomical instrument, the problems must be immense and the responsibilities must be immense in terms of how it’s used.

Bowen:

Well, there was of course the problem of operating two observatories which were owned by different institutions and under different control as one unit. On the other hand, it was felt very strongly that it was a big advantage to operate them as one unit. For one thing, we had up here all of the experienced astronomers. Caltech had--well, Zwicky, who like myself had started out like a physicist and had done a little observing with telescopes--they had no astronomers at all. We had quite a large staff up here, including a large proportion of the astronomers in the world that had had experience with large instruments.

Obviously, it was very much too bad to turn the 200-inch loose without being able to apply this experience, and on the other hand, it would be very much too bad even after they’d got a staff down there, to just have the 200-inch, because after all the great bulk of your programs (anywhere from 502 to 90 of it) can just as well be done with a small telescope. It would be very much too bad for the people down there to have to use the 200-inch for jobs that could as well be done using the smaller one. So it was obvious to everybody that the two observatories should be operated as a unit, and with complete freedom of the staff to go back and forth; that is, that the people on the Caltech staff should have no more special priority at Palomar than our people at Mt. Wilson, t was just so obvious to everybody that it had to be that way.

Fortunately, we were both private institutions and so we could be pretty informal about it, and also fortunately, we also had some pretty imaginative men at the head of them, namely Bush and Lee DuBridge. You see the basic principle set up was that Caltech would be responsible for the running expenses at Palomar, and Carnegie at Mt. Wilson, and each one would hire as large a staff as their budget would allow. Problems like this would come up: obviously our astronomers have to go back and forth from Palomar to Mt. Wilson so we need to run a car to each mountain about twice a week, changing astronomers, taking supplies, photographic plates, and what have you. It’s rather inefficient to hire two drivers and have two sets of cars, so talked to Lee and Van about it, and the agreement was that Carnegie would hire the drivers and Caltech would buy the car. Things were handled as informally as that. Often small purchases were needed, maybe about $20 worth for each mountain a year. One time we’d order it and charge it to Carnegie, and the next time we’d order it and charge it to Caltech, and split the orders. Well, we tried to keep this basic principle there. There was no penny-by-penny accounting on the thing, which made it very much easier to operate. Actually, it would have cost us a good deal of money to operate it, if we’d had to do it as it is done in the government.

Weiner:

just asked that question about the administrative side to indicate to you that there really is a lot to talk about on that end that probably is not in print anywhere, and at the same time there is a lot to talk about on the technical aspects of the work. I really think it’s the subject for another session and my suggestion is that, since the tape is about to run out, that we call this to a close now , and that I prepare for another session with the idea in mind that we’ll really talk about the history of your directorship.

Bowen:

That might be the best thing, and then you might have some questions on the earlier stuff.

Weiner:

You were continuous and coherent and the story held together well, but there are a lot of things in it that I didn’t want to ask because I didn’t want to interrupt the narrative. They’re minor things, but they’re still of interest. Next time when I come back, maybe we can start with those and fill them in, and then take the story from Mt. Wilson on. To do it properly, I have to reread a lot of things.

Bowen:

Yes.

Session I | Session II