Linus Pauling Interview, January 16, 1991

THOMAS HAGER: Interview with Linus Pauling. Wednesday, January 16th, 1991. Let's see, I wanted to- we were going to pick things up from about the time you left for Europe on the Guggenheim. But when I was going through the materials for that, I thought of one sort of background question I wanted to ask first, and that is about model building. You were very interested, in your letters back to Dr. Noyes from Munich in the collection here at Oregon State, you mentioned several times your interest in Selmayr models that you saw there, his molecular models, and you also mentioned that you had - last time we talked - that you had shown a model that you had designed of the water molecule to Sommerfeld when he visited Caltech in 1924. I was curious if that was the first molecular model 00:01:00that you had built, or if you had done others before that. Before 1924.

LINUS PAULING: Well, Selmayr's models were of the structure of crystals. Crystal structure models, not molecule models.

TH: Ah, I'm sorry.

LP: Except the structure that Dickinson had determined of hexamethylenetetramine. That was a crystal structure, but it showed the molecules of hexamethylenetetramine. I think I told you at the previous phone call that Dickinson had been making very primitive models of crystal structures.

TH: Uh-huh.

LP: He had taken a board, piece of wood about 20 inches square, and put a 00:02:00vertical steel 8-inch rod, probably Bessemer steel with copper coating, or other steels rods in. And then - in various positions in the two dimensions of the wood - and then he put - and sometimes he put wires across too - then he put plasticine balls. He made plasticine balls at various places, so as to have a representation of the crystal structure. Well, I did the same thing. I used those models. Other people may have been using them. Then there were molecular models available at that time. Perhaps, I think it may be that you could even 00:03:00buy them, consisting of wooden balls with holes bored in them, and sticks.

TH: They're the ball and stick idea.

LP: The ball and stick models. I didn't invent them. I'm not sure who did.

TH: Were you - did you use them?

LP: Well, I used them to some extent perhaps in my teaching. I don't remember. But since I wasn't - I was working on inorganic compounds then. And sometime, along about then, I began making ball and stick models of crystals too, to take the place of these models with vertical rods that Dickinson used. So, the model molecule that you're talking about I presented at a physics seminar in the fall 00:04:00of 1924. I had two of them. One was to show the neon atom with two inner electrons and eight outer electrons as four electron pairs. The other was almost identical. It had rubber balls to represent the protons in the loops that corresponded to the electron pairs. And the models were about two feet in diameter. That is, the wires that represented the tetrahedral orbitals, what I would call tetrahedral orbitals seven years later in 1931. These wires extended 00:05:00out about 16 or 18 inches from the center, which was a wooden block in which I had bored some holes. A wooden cube in which I had bored holes. I had loaned one of these models to the Smithsonian Institution. I thought it was a loan, but they've never returned it.

TH: [Laughs] uh-huh.

LP: The other one I have here in the next room. These may have been the first models attempting to reconcile G. N. Lewis's static atom with Bohr's dynamic atom because, as Lewis I think said later, his static atom that had electrons 00:06:00out in certain positions represented sort of the mean positions of the electrons. So, I have these wires, each of which was to show where two electrons were moving in a long, elliptical orbit, and the four orbits were directed tetrahedrally. I published a paper, too, about 1925. I don't remember whether I had a figure representing that, but in that paper, I proposed a structure of benzine based on these elliptical orbits extending around one nucleus and a second nucleus. Well, it must have been a good model for benzene, especially not 00:07:00good for naphthalene, but it shows that I was trying to find out what the electrons were doing in the molecule.

TH: Along that line, when you applied for the Guggenheim when you were trying to decide where to go, you had mentioned that you had written both to Bohr and to Sommerfeld. Is that correct?

LP: That's correct. I wrote, just on an ordinary lined sheet of paper, handwritten, to Bohr and to Sommerfeld. And Bohr didn't answer the letter, but Sommerfeld did. The Guggenheim Foundation asked that you get permission if you're going to work in someone's laboratory or institute that you're [inaudible]. And at that time, the Guggenheim Fellowships were for study abroad. 00:08:00It wasn't until the second world war that they were changed to permit studying and working in the United States, for Americans. And so, they required getting permission, or they asked that you get permission, and Sommerfeld answered my letter saying that I could come and work in the institute. So, that's what determined my going to Sommerfeld. Very fortunate accident, in a sense, because I think I told you that Sommerfeld's institute was a far better place for a beginner, a young person, than Bohr's.

TH: Yes. Would you- it almost seems as though at the time, looking back to your thought processes at the time of the application, that Bohr's institute might 00:09:00have seemed to you, at that time, a better place to go. It seems as though his concerns would have been more directly focused on questions of atomic structure, the sort of electron position questions that you were just talking about being concerned with at the time.

LP: No, I don't think so. Bohr, in 1913, I think it was, had developed the Bohr atom for hydrogen and ionized helium, the one electron going around the nucleus. Sommerfeld had, in 1917, first developed an improved method of applying the old quantum theory for conditionally periodic systems, and had introduced the 00:10:00concept of elliptical orbits and used it to account for many of the details of spectra of atoms and ions. And there was great interest in what Sommerfeld had done. It's a little surprising that Sommerfeld didn't receive the Nobel Prize, in my opinion, even though, of course, his theory of elliptical orbits and of the fine structure of spectral lines wasn't quite right. It didn't involve the spinning electron.

TH: Right. That would have been before.

LP: So, it probably was proper for the Nobel to postpone a decision about 00:11:00Sommerfeld and then, later, to give Nobel Prizes to the three or four... the three people who had invented quantum mechanics, Heisenberg, Schrödinger, and Born. And Dirac. The four of them. First two, Heisenberg, Schrödinger, and Dirac, and then 13 years later, I think when I received the Nobel Prize in Chemistry, Born was given half of a Nobel Prize.

TH: Before you left that spring, you spent a Christmas, apparently, with Dr. Noyes in Pasadena.

LP: Yes, my wife and I. He had us over to dinner.

TH: On Christmas day, was it?

LP: I'm not sure that it was Christmas day.

TH: And was that just- was it a large party, or was that just the two of you and Dr. Noyes?

LP: It was just my wife and me and Dr. Noyes.

TH: Okay. When you left, the decision was made to leave Linus Jr. in the care of his grandmother-

LP: Yes. But I think Linus Jr. was at the Noyes' home too [both laugh]. We didn't have a babysitter. But he was how old? Nine months old.

TH: Right.

LP: So, he was still pretty young.

TH: Yeah. Tell me about how the decision was made not to bring Linus Jr.

LP: Well, my wife said to me, perhaps along about that time - December, possibly earlier - at any rate, she said to me that she thought we shouldn't take Linus 00:13:00Jr. with us; that it would just be too hard for us to handle the job of taking care of a small baby, and that she had arranged, or would arrange, to leave him with her mother. And that we would pay $25 a month to her mother for care of Linus Jr. That sounds like a small amount of money, but of course it was more than 10 times that now, the dollar.

TH: Oh yes, yeah.

LP: It was perhaps $300 a month, or $350 a month. There's been more than tenfold inflation since then.

TH: Yeah. And had that crossed your mind before she brought it up?

LP: No-

TH: What was your feeling about it?

LP: Well, I was shocked [laughs] at the idea. But after thinking about the problem - after all, we'd never been away from the Pacific Coast - we didn't know what life would be like in a foreign country. We perhaps knew enough about traveling in along the Pacific Coast, staying in various hotels, my wife and me, or setting up residence. We knew that there were problems, and we knew by that time that there were problems about taking care of a baby. And of course, this was great experience, it turned out, for my wife and me. I think at this 00:15:00Christmas dinner, or approximately Christmas dinner with Dr. Noyes, he laid out the schedule for us to follow. He gave us copies of Baedeker for Italy and Germany, and perhaps England, and told us what we should do; take a ship to... to Naples, an Italian ship, and it stopped at two places, three places on the way. So, we had the experience of seeing three different parts of the world for a few hours one day, in each place before arriving at Naples. Then stay in Naples for a week and go to Rome, stay there for a week, go to Florence, stay 00:16:00there for a week, and visiting Pisa, and from Naples to Pompeii, and so on. And then to Venice for a week. So, we were in Italy traveling, getting educated about the Renaissance and about the museums and paintings and things of that sort for a month before we arrived in Munich. I think Dr. Noyes even indicated to us where we should stay in these places.

TH: Well, I do have a copy of his itinerary for your walks around Switzerland, in which he not only mentions the specific trains you should take but exactly how many miles to walk on foot to various places. So, he was thinking in detailed terms.

LP: Yes. So, all of this would have been impossible if we had had the baby along 00:17:00with us. We didn't have money enough, of course, to arrange for babysitters or anything of that sort.

TH: How did you have money? I know that you picked up your Guggenheim money when you reached Munich. How did you pay for things prior to getting to Munich?

LP: The institute, which probably means Dr. Noyes himself, gave us I think $1,000, possibly $1,500, to pay for the fares. The steamship- railroad, and steamship fares, and to pay for travel hotels and trains, third-class, of course, in Italy, and to keep us going for about a month in Munich, I think, 00:18:00before which the letter of credit arrived from the Guggenheim Foundation.

TH: I see. And was that grant money to you, or was it a loan?

LP: It was a... well, it was a salary, I think. A gift. I was appointed I think Research Associate at the institute, so it was probably a check from the institute as an advance of payment for a year as Research Associate.

TH: Was it unusual to be given that month, or was it common practice for postdoctoral fellowships at that time to take that much time just to travel and enjoy Italy and learn before you got to your destination?

LP: Well, that question may be two questions. I think it was unusual for a 00:19:00person only eight months out from his Ph.D. degree. First, it was unusual to be given a Guggenheim Fellowship at that early age. There's another man my age, a composer who received a Guggenheim Fellowship in that first batch too, and he died just a couple of months ago. This composer musician, Copland, was in that group of about-

TH: Oh, really? Aaron Copland?

LP: Aaron Copland- of about a dozen Guggenheim Fellowships. The first time that there were applications sent in for Guggenheim Fellowships. And the woman 00:20:00biologist, anthropologist whose name has slipped my mind.

TH: Is it Margaret Mead?

LP: Margaret Mead was in that group too.

TH: Uh-huh.

LP: I don't remember who the other people were. So, this was quite unusual, and during following years, the years when I was a member of the committee of selection of the Guggenheim Foundation, I don't remember a single scientist with less than a year of postdoctoral experience receiving a fellowship. But of course, I've read recently some statements made by Dr. Noyes in letters of that time in that book, From Ostwald to Pauling.

TH: Yes, I just finished that.

LP: Noyes is quoted as saying that I was the most promising student that he had ever had contact with. You remember?

TH: Yeah. In fact, I remember something even more lavish in its praise, which was the later comment that he made, that if the whole department were wiped away except for you, it would - this was after you came back, of course - that it would still be one of the outstanding departments of physical chemistry in the nation.

LP: Yes.

TH: Yes.

LP: Yes, that's right. I remember reading that in that book. So, my situation was essentially unique. I don't think that I realized it at the time, other that I was being-well, I think I knew I was being given special treatment. For 00:22:00example, Paul Emmett got his doctorate the same time that I did, and Oliver Wulf I believe the same year, and two or three others in chemistry. I was the only one that Dr. Noyes tried to keep at Caltech. Others went other places, and some did postdoctoral work somewhere else. But most of them took jobs somewhere else.

TH: And he tried to keep you to the extent, apparently, of making sure that G. N. Lewis didn't pick you up and spirit you a-

LP: Yes. Well, first he kept me from going to Berkeley on my [laughs]-

TH: Yes [laughs].

LP: -National Research Council Fellowship.

TH: Uh-huh.

LP: And then he managed to browbeat Lewis into not offering me a job [laughs].

TH: Uh-huh. I want to make sure I'm clear about the NRC Fellowship. You were 00:23:00awarded the fellowship immediately after gaining your Ph.D.?

LP: Well, I was awarded it before getting the Ph.D., so it began immediately that I got the Ph.D. that June.

TH: And the object of the fellowship was to take you to Berkeley, was it not?

LP: That's what I applied for. I said I would go to Berkeley, yes. And Noyes then - well, this is in the record - Noyes said to me that I had a good bit of unpublished results on the crystal structures and that I ought to write this up. They didn't have X-ray apparatus at Berkeley. There was no use in my planning to go there and start some work, so I ought to stay in Pasadena for a few months. Of course, it turned out to be eight months, and then he told me that I should resign, even though I didn't have the Guggenheim Fellowship, I should resign 00:24:00from the [laughs] National Research Council Fellowship.

TH: Which irritated the people who gave the NRC Fellowship, I guess.

LP: That's right. I got a very critical letter about my resigning. But, so he was determined that I not go to Berkeley [laughs].

TH: If you were to suppose about what it was that made this impression on Dr. Noyes during your graduate work - by the time you got your Ph.D. he obviously, as you said, singled you out from the group and was intent on keeping you - why do you think you had that impression on him?

LP: Well, I think even during my first year as a graduate student, the first of three years, even during that year - I've seen this only recently, probably in that book - Noyes had made a statement about their having a very unusual 00:25:00graduate student.

TH: Yes, yeah.

LP: So, why/what? Well, I was eager to do things [laughs]. I was eager to understand. I worked hard. And my coursework, you know, I felt I should take advantage of opportunities of learning mathematics, physics, and chemistry, physical chemistry, then in dynamic chemistry, which Noyes himself taught that first term, the fall of 1922. The last course he ever taught was that term. And I settled down I think Dickinson, who was perhaps astonished that in a couple of months I had learned how to determine crystal structures, essentially what he 00:26:00had to teach me. He only had to show me something once and then I knew it. And of course, pretty soon, not then but a couple of years later, I began trying to think of ways of making X-ray crystallography more powerful. So, within three months I had finished a job with Dickinson, determination of a structure, and was branching off on studies of my own. I perhaps was rather brash, as I recall, but... I don't think that I was egotistic. I think I was just interested in 00:27:00knowledge and reasonably smart. So, it's not surprising that I made an impression.

TH: Yeah. That's- you had mentioned the summer before you arrived in Caltech, Noyes had sent you the proof sheets for his book, yes?

LP: Yes.

TH: And you had worked through all the problems in that book. Is that correct?

LP: Yes. They're all there in Corvallis.

TH: Right. And was Dr. Noyes aware of that as well?

LP: Well, he had written to me, sending the proof sheet, perhaps of the first nine chapters, not the other four, and suggesting that I ought to work those problems during the summer, the problems in the first nine chapters. He did the same thing with Paul Emmett. He sent him the proof sheets and Paul presumably 00:28:00worked the problems. We weren't in the same place that summer. And whether Paul retained his copies of the problems I don't know, but Pauline might know. I think some of his papers were given to Oregon State University.

TH: Yeah. But did you give those- when you worked the problems, did you give them back to Dr. Noyes for review?

LP: I mean Portland State University.

TH: Uh-huh, yes.

LP: Not Oregon State University. No, I just kept them and took them with me. I went to Pasadena. And I don't think they ever were checked by anybody. In the collection of these worked problems that I have given to Oregon State, there are 00:29:00also the problems for the last four chapters, and those were corrected by Badger. Richard Badger, and his comments, or corrections, or grades, are noted on them.

TH: I see.

LP: But that was a remarkable book by Noyes and Sherrill, in that it was ideally adapted to self-study. The problems, in general, were stated, and then the authors gave some suggestions about how to attack each problem in a series of steps. So, I had no difficulty. I would work perhaps two or three hours every evening and the weekends, during the summer in Warrenton. And I got them all 00:30:00done. As I say, Paul probably did too. I don't know.

TH: One more question about Dr. Noyes before we move back to Munich, but you know, he was unmarried and childless; you were fatherless. The temptation is there to look for a kind of father/son relationship or some sort of bonding there that would have those elements to it. How would you respond to that kind of thought?

LP: Well, I didn't have any feeling of that sort about him. And I'm not sure that he had about me. For example, he- I learned after his death when his will was read that he had loaned a large sum of money to Ernest Swift, who had been 00:31:00his student, and was then a perhaps assistant, or associate professor of chemistry. And the part that hadn't been repaid, Noyes canceled the debt in his will. He said any unpaid sums. And Noyes hadn't ever given me or loaned me money. Well, there was one-I think he may possibly-[tape ends].

TH: Uh-huh.

LP: I had talked with the chairman of the Guggenheim Foundation.

TH: Mr. Moe.

LP: No, not with him. With Aydelotte.

TH: Oh, okay.

LP: Moe was his secretary.

TH: Ah.

LP: Aydelotte was the president, I think. He was also President of the Rhodes 00:32:00Trust, Aydelotte was, and was President of Swarthmore, you know. And I had talked with him in perhaps the fall of 1925. Millikan and Noyes and Aydelotte had me to dinner in the old faculty club. A farmhouse on the Caltech campus that served as a faculty club up unto the time the Athenaeum was built. And they- this may even have been in the spring of 1925, rather than the fall. The spring of 1925. And the Guggenheim Foundation did appoint a few, perhaps a half a dozen 00:33:00Guggenheim Fellows that year before they had made announcements. So, I think I was under consideration for getting a Guggenheim Fellowship just as soon as I got my Ph.D., but it was decided by Noyes, I guess, that it would be better for me to wait a year, or eight months. So...

TH: Now, you had- one of the letters from Ava Helen back to Dr. Noyes, when you reached Munich, was that you were looking much, much better than you had been. Were you ill during your trip?

LP: No, I don't think so, except seasick perhaps [laughs]. Well, I know I was seasick. I might have caught a cold. I tended to catch colds.

TH: Okay. But there was no indication of anything like the later kidney trouble or anything like that at this early day?

LP: No, no. No, I don't remember. I don't know what she was talking about.

TH: Yeah, I couldn't tell either. When you got to Munich, during your initial meeting with Sommerfeld, you wrote that he was going to propose a problem to you, as he did with many of his students when they first arrived. And you mentioned that you proposed one to him first [laughs], which he ignored. Is that correct?

LP: Well, I think so. He suggested- see, these spinning electrons had just been discovered, and a man named Abraham, a theoretical physicist named Abraham, had published some ideas before the spinning electron was discovered about the 00:35:00structure of the electron, pre-quantum theory, pre-quantum mechanics. So, Sommerfeld suggested that I examine Abraham's work and see if I could make something out of it. I had told him, I believe, that I had published a couple of papers on the difficulty-[audio glitch].

TH: Are you there?

LP: Yeah. The difficulty with the old quantum theory. And a number of these difficulties were turning up at that time. Mine related to the effect of a magnetic field on the dielectric constant of a gas such as hydrogen chloride.

TH: Right, right.

LP: So, I did work on that the first few months that I was in Munich, finishing up. And Sommerfeld gave me some help, suggested some mathematical papers to me to read. So, I published that in Physical Review. And of course, I also wrote an interesting paper that was published in 1926 on a discussion of a paper by Wentzel...

TH: Yes.

LP: ...that I had run across in the Zeitschrift für Physik, and I found an error in what Wentzel had done and corrected it. And it was the basis of quite a 00:37:00lot of work that I carried out during the next five years. An effort to make quantum mechanics applicable to atoms containing many electrons. I published a number of papers as a result of having seen that Wentzel's treatment could be corrected and used in various ways. So, Sommerfeld became interested in me then. There were some Americans there who were either plodding along or were quite unsuccessful in their efforts.

TH: Who were the other Americans who were there? You've mentioned, let's see, 00:38:00there was a fella who was a physicist, who you mentioned gave a seminar that was sort of almost hooted down. Not hooted down, but the audience began shuffling their feet and making noise and so forth.

LP: Yes. I think he was a sort of remittance man perhaps, I'm not sure.

TH: What does that mean, remittance man?

LP: Well, it comes from England where younger sons were shipped - especially if they had a weakness for alcohol or something like that - were shipped off to the South Pacific and sent a check every month. A remittance. Well, this fellow, Cranford I think was his name - that may not be exactly right - he just didn't understand what was going on [laughs] in physics. So, he disappeared after the 00:39:00first year. There were two Americans working with Sommerfeld. Brothers named Guillemin.

TH: Oh yes, okay.

LP: Ernie Guillemin and Victor Guillemin.

TH: Right.

LP: And they both got their Ph.D.s, I think, in 1927. Ernie became Professor of Electrical Engineering at MIT, and he published a textbook. Victor Guillemin, I don't know. He was working... I think in Dayton, Ohio, the Aeronautics Laboratory.

TH: Ah, uh-huh.

LP: He is dead. His son, I had some correspondence with his son, Victor 00:40:00Guillemin Jr., I think. So, Ernie and Victor were the ones that we knew best. And there were other Americans who were sort in and out. One of them was Otto... well, let me... he became a professor of chemistry at Stanford and died a few years ago after retiring. Otto... I'll have a little trouble.

TH: No, no, that's okay. I can try and check it out through the records of the institute, too.

LP: Then there were others. One of them became President at MIT later. He took his Ph.D. I think in Switzerland, but he was around in Munich for a little while. We got acquainted with him. And of course, a good number of others, Americans who just passed through, like Benson [?].

TH: Well, was Slater ever there at that time?

LP: Who?

TH: I'm trying to remember which other physicists were over in Europe around that time. Let me see.

LP: Well, there's a book by Katherine Sopka, I think is her name.

TH: Oh right, Quantum Physics in America.

LP: Yes. That concentrates on 11 young theoretical physicists. I was one of them, but mentions about 20 altogether who were in Europe when quantum mechanics was being developed.

TH: Where did you live in Munich?

LP: We lived-we had a room rented from the landlady on the second floor, or the first above the ground, on about a four-story building at Adelbert and Marler [?] Strassen. Adelbert Street and [Marler] Street, about four or five blocks from the university.

TH: So, it was just a single room? Very-

LP: Just a single room.

TH: Very small.

LP: Well, it was a good-sized room [laughs]. Must have been 20 feet square, perhaps. Corner-well, we started out Victor and Ernie had that room when we arrived, and we had a smaller room next door, but for some reason then they changed rooms with us. So, we had this larger room.

TH: That's, in some of the letters back, Ava Helen mentioned that there were two American boys who lived upstairs. Would that have been the Guillemin brothers?

LP: Yeah. Well, they lived on the same floor. They were right next door.

TH: Okay. You went with Sommerfeld to the Deutsches Museum and were impressed, according to your letter back to Noyes, with all of the atomic molecules that were there, some of the presentations that they had made. Was that in the nature 00:44:00of a social occasion with Sommerfeld, or was this part of the work?

LP: I don't think that we went with Sommerfeld. At least I don't remember.

TH: Well, I believe that's what it said in the letter.

LP: Oh. But we went there several times later when Sommerfeld asked us to take visitors to the Deutsches Museum, especially Japanese. So, we went to the Deutsches Museum a good number of times.

TH: Yeah, it said, "Yesterday, I went with Professor Sommerfeld to the Deutsches Museum. On introducing me to one of the officials, he said, 'Dr. Pauling is from America, but he speaks very good German." This is in a letter that you wrote in May of '26 back to...

LP: Wow, yes.

TH: So, your German was sufficient to get along.

LP: Well, it was pretty poor. I had studied German at Corvallis for two years, but not really conversational German. And within a few months, I was speaking moderate- well, poor German, but getting by. And Ava Helen was too, without ever having studied German [chuckles], except I had my German textbook along and she studied it by herself and talked with the landlady quite a bit.

TH: For the two of you, without the baby, was this sort of in the nature of a honeymoon, would you say, or was this-I mean, what I'm asking I suppose is was this a highly enjoyable experience for the two of you, being in Europe together, or was it in the line of just sort of being work?

LP: Well, we'd been married for three years by that time. I think we enjoyed everything that went on much more than if we hadn't been together [laughs].

TH: She came to seminars with you, correct? On occasion, at the university?

LP: She attended some lectures with me, mainly not those with Sommerfeld, but somewhat more general lectures, such as [inaudible] on relativity theory. And they were not classes for me. I just attended those and she came along too. And we went together to meetings of the Physical Society, the German Physical Society.

TH: What did you learn about- during your time in Munich when you're observing how Sommerfeld ran his group, did you pick up things that you later brought back with you? Not now speaking of quantum mechanical theoretical ideas or research ideas. I'm talking about managerial ideas, laboratory setup ideas. Were there things that impressed you about the model in Munich that you later tried to incorporate?

LP: Oh, I doubt it. Sommerfeld Institute was the Institute of Theoretical Physics. He had an instrument maker, Selmayr, because it was in that Institute of Theoretical Physics that Laue discovered X-ray diffraction. So, Sommerfeld 00:48:00had been able to set up a... I'm not sure what Selmayr did, other than to make these models.

TH: Yeah, you had said that he was basically a mechanic.

LP: Yes. And the graduate students working with Sommerfeld had- well, they did do a little X-ray diffraction. There was one privatdocent for Sommerfeld who published some papers on crystal structure. And I expect that it's experimental work. I think they may have had an X-ray diffraction apparatus, but I didn't make use of it. I concentrated on theory while I was there.

TH: I'm speaking more of the way that Sommerfeld interacted with his students, dealt with postdoctoral students, and so forth.

LP: Well, I think I was impressed by his lectures, and of course, my book Introduction to Quantum Mechanics is pretty much based on his lectures. Parts of it are. So, I was impressed by his grasp of theoretical physics, mathematical physics.

TH: Okay. Speaking of quantum mechanics, now you had been aware of the problems with the old quantum theory. Ehrenfest had come to Caltech before you left, is that correct?

LP: Yes.

TH: Yeah. And-

LP: My wife and I had Ehrenfest come to dinner with us.

TH: Oh, while you were at Caltech before you left?

LP: Yes.

TH: What sort of fellow was he? Was he a good dinner companion?

LP: [Chuckles]. Yes, I think so. The... he was quite intense, Ehrenfest, and he was a good lecturer. I can remember his marching back and forth behind the lecture desk in the physics lecture room during his seminar. And I've forgotten, he was showing a light wave perhaps... bucking the waves. I don't remember, but he obviously was pushing against something when he walked to the left and then being carried along when he speeded up, walking to the right. I don't remember what this was about. But he had a special lecturing technique, just as Tolman 00:51:00had. But Ehrenfest was quite a showman. And of course, you know that he committed suicide.

TH: Yeah.

LP: And I think it's thought- well, he had a son who was mentally retarded, but I think it's thought that he committed suicide because of a feeling that he had not succeeded in making an important contribution to physics. When he was in Pasadena, he and Tolman talked a good bit about their difficulties with the old quantum theory. But they didn't succeed in solving them.

TH: Mm-hmm. When you arrived in Munich, then, obviously it was the topic of current interest. Sommerfeld's lectures oriented around it. You-

LP: Well, this is Ehrenfest I was talking about.

TH: Sure, no, I understand that, but talking again just about quantum mechanics and the revisions to the old quantum theory.

LP: Yes.

TH: Umm...[audio glitch]. ...new quantum mechanics, where I think that atomic and molecular chemistry will require it. This was right after you arrived in Munich. Was this then your first major exposure to just sort of all of the basic thinking that was going on at the time in terms of quantum mechanics? You mentioned that Tolman brought up some of the problems-[audio glitch]. ...seen the light, I guess, in terms of-

LP: Well, Sommerfeld had talked about the difficulties when he was in Pasadena, and Ehrenfest of course had, but then when Sommerfeld was there, he mentioned 00:53:00Heisenberg. But it was before Heisenberg had discovered matrix mechanics. But he mentioned Heisenberg in connection with the problem of the hydrogen molecule with the old quantum theory. Both Bohr and Heisenberg, also others, have tried to - and Tolman, too, had tried to solve the problem of the hydrogen molecule, the nature of the bond, and without success. But Born lectured in Pasadena probably in December of 1925 about matrix mechanics. I have notes which I've sent up to Corvallis that I took, and I couldn't see any way of using matrix 00:54:00mechanics to attack the problems that I was interested in.

TH: Simply because of the diffi- I mean, it was tremendously difficult.

LP: It was very difficult. For example, Heisenberg had not been able to treat the hydrogen atom by matrix mechanics. Pauli did succeed. I think I told you this before. Pauli did succeed in treating the hydrogen atom with matrix mechanics. Probably after Schrödinger had treated it with wave mechanics. Well, by the time- so, I knew about matrix mechanics, but I didn't make any effort to use it. It was just too difficult. So then, by the time that I arrived in Munich, Schrödinger had published a couple of his papers, and immediately I 00:55:00became interested, read them carefully, and Sommerfeld began lecturing about wave mechanics. Probably the first lectures ever given on wave mechanics. Born had been lecturing about matrix mechanics. Of course, in this book about quantum mechanics in America, it mentioned that my talk, my course on quantum mechanics at Caltech, beginning 1927, was the first course in the Chemical Department. Chemistry Department.

TH: Mm-hmm. Oh, yeah.

LP: And just about coincident with the first courses at Physics Department too.

TH: Let me go down a list of names of the people who were active in Europe at 00:56:00that time. I just want to check and see if you made contact with these people during your time there. Okay?

LP: Okay.

TH: All right. Certainly, Sommerfeld and Bohr we know. And you did see- did you go to Göttingen and see Born when you were in Europe?

LP: Yes.

TH: Okay. And Schrödinger in Zurich?

LP: Well, I spent- we spent the summer of '27, I was supposed to be working with Schrödinger, yes. And Debye of course was there.

TH: You were supposed to be working with Schrödinger?

LP: Yeah. I think I went to see him once, and that's all.

TH: Huh. And-

LP: I may have gone to some of his lectures, but he was so busy with his own work that I didn't make any effort to talk with him.

TH: Okay. And you went to the summer conference on magnetism with Debye?

LP: Yes. In the fall of '26. Sommerfeld went to it and then sent a telegram saying that we should come to tour it.

TH: Heisenberg, did you meet him while you were in Europe?

LP: Yes. Yeah, I met him. I don't remember where. He gave me the proof sheets of his paper on the uncertainty principle.

TH: Oh, the proof sheets. Okay.

LP: Yes.

TH: You were impressed by him. I remember in one of your letters you said he was a fine young man.

LP: Yes.

TH: But this was just a single meeting?

LP: Well, I may have met him several times. I'm not sure.

TH: And would this have been in Munich, as well?

LP: I think he came to Munich and I saw him there, but I believe it was in Göttingen that he gave me the proof sheets of his paper.

TH: Okay. Was Teller there at that time?

LP: Teller was with Sommerfeld in 1930 when I was there for several months.

TH: I see, but not during your earlier trip.

LP: I don't think he had arrived in '27.

TH: Was Szilárd there at that time?

LP: No. I don't think I met Szilárd until later.

TH: How about- you did meet Hans Bethe [pronounces as "BETH-ay"]. Is that the correct pronunciation?

LP: Bethe [pronounces as "BAY-tuh"]. Hans Bethe.

TH: Bethe, yeah.

LP: Well, he was a graduate student with Sommerfeld in 1926 and '27, and then was assistant in 1930. So, I saw him all of those times.

TH: On both of those. Pascual Jordan? Did you see-

LP: Who?

TH: Jordan. Pascual Jordan. Am I mispronouncing again?

LP: Jordan [pronounces as "YORE-dahn"]? I think I met him in Göttingen.

TH: So basically-and Dirac, was he a-

LP: Dirac was in Göttingen too. I saw him at Göttingen.

TH: So, you met bas-

LP: Oppenheimer was in Göttingen at that time, 1927, so I talked a good bit with him there.

TH: Basically, all of the major players.

LP: Well, there are various Americans that you haven't mentioned that- most of whom came through Munich, or whom I had met in Göttingen too.

TH: Uh-huh, for instance, oh, Johnny von Neumann. I mean...

LP: I don't think I met Johnny von Neumann until later one when he was in the 01:00:00laboratory. He was perhaps in Budapest at that time.

TH: Okay. Some of the other Americans that passed through Munich or Göttingen, do you remember any other names?

LP: Well, let me see. Ed Condon.

TH: Uh-huh, Condon. Okay.

LP: Van Vleck. Johnny Van Vleck came through both 1926 and 1927. And... well, I mentioned [00:29:10 Jerome], who became President of MIT. I've forgotten his last name. He was around. Otto Koenig was the one who took his Ph.D. I think in 01:01:00chemistry in Munich and then became Professor at Stanford. Frederick Otto Koenig. And an American from Chicago named Hammichurst [?] did some work in X-ray crystallography. He came around, was around for a few weeks, I think. He later went into social science in Chicago. And David Dennison came, spent some time in Munich. He's the one who worked out the theory of heat capacity of 01:02:00gaseous hydrogen. Very interesting fellow. And there were others. Phil Morse, from MIT. So, I think I knew all of the young Americans who are mentioned in that book on quantum mechanics.

TH: And was the topic of conversation consistently the new interpretations that quantum mechanics made possible at that time?

LP: Well, they were, everybody was interested in that, yes. But topics of conversation were sometimes how much money you had, whether your stipend had come through the mail, and things of that sort too.

TH: [Laughs]. What was your social life like in the evenings when you were in Europe? Was there a- I've seen mentions of just a couple of birthday parties and events like that, but-[tape ends.

LP: -restaurant. I once... Karl Compton, President of MIT, came to Munich, and he took several of us out to dinner. He was looking for staff members for MIT.

TH: [Laughs] prospecting.

LP: Yes.

TH: You had mentioned going, having a party when Heitler got his Ph.D. after his doctoral exams.

LP: Yes. Well, Heitler invited London, his close friend London, and Ava Helen and me. That was the party, to dinner at [restaurant's name], the good restaurant to celebrate his having passed his doctor's examination.

TH: How did you meet Heitler and London?

LP: Well, they were there at Munich. I don't remember when we first met them, but during the winter '26, '27, the four of us went by train to... a place at the foot of the mountains and then climbed up to the Dreitorspitze and stayed 01:05:00overnight in a ɡästhous on the mountain. But mostly my wife and I were just by ourselves, and we spent the evenings with me working and her studying German or something like that.

TH: Did you stay in touch with Heitler and London after you left Europe, after you returned to Pasadena from that first trip? Did you correspond?

LP: No, I don't think so. We saw Heitler a few times, and London once, perhaps. But we didn't stay in touch by correspondence.

TH: You had mentioned in an earlier interview that when you did see them, you did talk about structural questions. The sorts of early chemical bond thinking that you were doing at the time and that they were doing. That was a topic of conversation with them. Is that correct?

LP: Maybe. I wasn't too happy about the work that Heiter and London did to extend their theory to polyatomic molecules. For one thing, I think they concentrated on the normal states of the atoms, and they use group theory, which I wasn't very happy with because it's hard to understand what the group theoretic equations mean [chuckles]. So, my 1931 paper, also my 1928 paper, 01:07:00represented my efforts to attack these quantum mechanical problems in a different way.

TH: The three-year gap that - I know you've been asked about this before by other people - between your 1928 paper and the appearance of the 1931 series of papers, is it- the explanation that I've seen given was that it was a three-year period between sort of the birth of the idea and its elucidation in a much more complete form was due to your working on the mathematics to sort of make that fuller picture and sort of base it on a sound basis. Is that approximately correct? Is that...

LP: Well, at least partially. I suggested to Sturdivant, who had taken his Ph.D. 01:08:00with me and was doing crystal structure work, but who had a master's degree in mathematics, that he try to handle the problem of the tetrahedral carbon atom, say. I can remember that, that one effort I made was to see if Sturdivant would have some ideas.

TH: Uh-huh [chuckles].

LP: He didn't. [Both laugh]. He didn't come through with anything. So, it wasn't until 1931, or the end of 1930, that I finally saw how to simplify the equations, and then I wrote my 1931 paper. But I was doing a number of other things.

TH: Yeah, yeah.

LP: In 1929, I published my rules about the structure of complex ionic crystals, the silicates, and so on. The rules that upset Lawrence Bragg...

TH: Yes, the Braggs were not happy.

LP: ...so badly.

TH: Yeah.

LP: And publishing a good number of experimental results with crystal structures and carrying on other theoretical studies too. So, I would think about that problem from time to time, but my experience has been that if you have a difficult problem of that sort, just sitting down day after day and trying to attack it may not get you anywhere. You have to wait until you have a good idea.

TH: You visited the Braggs in Manchester on your way back, is that correct? On your '26, '27 trip, did you visit the Braggs' laboratory?

LP: No. We didn't get to Manchester.

TH: Oh, okay, because I knew that was on the original- in your original thinking before you went. I knew that was sort of on the list of...

LP: We were in London. I think I visited the Royal Institution, but I'm not sure that I met W. H. Bragg, who was director of it. I think our about a week in London was sort of sightseeing for us. Well, I'm... I think I'm confused there. 01:11:00I'm not sure we got to England at all.

TH: Ah, okay.

LP: In '26, '27. I may be confusing it with the 1930 trip. The reason that I say that we may not have got to England is that we sailed back from Bremen.

TH: Oh, okay. All right. So, you wouldn't have gone. I just saw sort of, in an initial list of places that you'd hoped to visit, it included, you know, obviously Munich and Zurich and Göttingen. I thought the last place on the list was to try and see the Braggs, but I'll try and check that out.

LP: Well, I can't remember definitely just what we, how... let's see, I think we came back from the 1930 trip on the Queen Mary. Perhaps we had gone over on the Queen Mary, too [laughs]. So, here I don't remember just what we were doing.

TH: That's fine. It's just interesting. I'll try and track down it, to see if I can find anything to know if you first met Bragg before or after that 1929 paper.

LP: I don't think I met him 'til 1930.

TH: Okay, all right.

LP: And I was disappointed, as you know, when we went to Manchester for a month, that nothing much happened.

TH: In what way? Nothing much intellectually, or...?

LP: Well, there were no seminars in the Physics Department. Bohr visited Manchester one day, and there was a meeting of physicists, the Physics Department, in which Bragg introduced Bohr, and he gave a short talk about what 01:13:00he was interested in. But here I was at Manchester for a month; I never had, during that month, a talk with Bragg about the structure of silicates or other problems of the sort.

TH: Huh.

LP: He didn't ever invite me to come and talk with him.

TH: Hmm.

LP: And, in particular, he didn't ask me to give a seminar talk about my ideas about the silicates and other crystals, which I had published the year before. So, things were just much different from Caltech.

TH: Yeah. You got along much better with Bragg the younger, is that correct?

LP: With who?

TH: With Bragg the younger.

LP: Well, this is Bragg the younger.

TH: Oh, I'm sorry. Okay.

LP: Lawrence Bragg. He was a professor of physics, head of the department at Manchester.

TH: Right. Okay. Last question. When you were in Munich, you had sent back a paper on inter-ionic attraction theory for Noyes to take a look at, and he apparently passed it onto Tolman, who was critical of the paper, and you never published it. Is that correct?

LP: Yes. I have the paper here in the other room.

TH: Uh-huh. Was that the only- did that sort of thing ever happen at any other time, where you had received criticism of a paper prepublication, and therefore decided not to publish it? Or was that the only occasion?

LP: Well, I'm trying to think back... I... I can't think of any similar case. 01:15:00But as I have probably refrained from time to time from publishing some of my ideas, but I can't remember a case where I've written a paper and it's been criticized, and then I failed to publish it.

TH: On another occasion, you were irritated at Tolman for a remark he made to Roscoe Dickinson about sort of disparaging the kind of crystal structure work he was doing, and implying he sort of should have done some more sort of theoretical work, I guess. There was an occasion where they were talking about, 01:16:00I think it was Duane's, some of Duane's work, and also that you mentioned on another occasion that Tolman and Noyes had very different temperaments from one another. Did you and Tolman get along?

LP: Oh yes, we got along fine. [Laughs] I mentioned to him once that I had carried out an analysis of some band spectra of molecules at his suggestion and that it had never been published. And it was old quantum theory. He couldn't remember ever having made the suggestion to me, apparently. He seemed not to remember. We published a paper together, of course, on entropy of super-cooled liquids and crystals, and that was the only time when our ideas- when we collaborated.

The episode with Roscoe Dickinson was at a seminar where mention was made of a treatment of diffraction by crystals; X-ray diffraction carried out by Duane at Columbia University involving the old quantum theory of Sommerfeld's method of quantization was discussed. And Dickinson- or Tolman turned to Dickinson and said, "Now, that's the sort of thing that you ought to be doing." And I thought - and of course, Dickinson wasn't really a theoretician, a theoretical physicist 01:18:00- I thought it was unfair of Tolman to have said that. And somewhere I may have said that, and in the course of time, I recognized that Tolman could have said, "How about an electron scattered by a crystal?"

TH: Oh, really?

LP: Because he could have used Duane's arguments, or Duane could have used Duane's arguments to get a value for the wavelengths of the electron before de Broglie. Of course, I could have too. I just wasn't at the point in my development where I could generalize a treatment or apply it to other problems the way that I've become accustomed to later on. I might have discovered the 01:19:00wavelengths of the electron.

TH: [Laughs] well, that's interesting to know it was brought up at that early date, in that context. Later, of course, you did some work trying to use a similar approach to finding the wavelength of a proton. Is that right?

LP: Yes. After the wavelengths of the electron was discovered, I suggested to our graduate student that he carry on the experiment, set up an apparatus to see if he can get diffraction of protons. Well, he didn't succeed, but he wasn't very far along.

TH: But in theoretical terms that should have worked. Is that-

LP: Oh, yes. Yeah. Of course, it's been done since then. Well, there's one discovery that I might well have made but didn't, the discovery of the 01:20:00wavelength of the electron. I think I mentioned in my, perhaps in my freshman... in one of my books, perhaps in Quantum Mechanics, I mentioned that Duane's argument could have been applied to the electron and would have led to the discovery of the wavelengths of the electron.

TH: That's a fascinating period of time. You know, there were so many ideas floating around, being mentioned at so much informal or seminar-related talking about various problems, it's interesting to see the ones that got captured and the ones that got sort of got away from people.

One last question, then I'll let you go. This has been great. While you were in Munich, your mother passed away. And among the letters you had let me take a 01:21:00look at when I was down visiting you before, among the correspondence was a letter from you to Lucile about that time, talking about your mother's financial state at the time she passed away and mentioning that Pauline was making some sort of accusations about how you might have taken better care of your mother in her last days. Does that ring a bell with you?

LP: No. No, I don't remember.

TH: Ah. But I'm just- apparently there was, among all the emotions of that time, there was some bad feeling between you and Pauline about how things worked out in relation to the death of your mother and the finances at that time. I'm just- I was going to ask how long that bad feeling lasted between you and Pauline.

LP: [Laughs] well, I don't remember it all, so I can't answer [laughs].

TH: Okay, all right. That's fine. Listen, thank you so much. This has been a very, very good session, and I'm going to, if I don't get in touch with you again, I will see you at the end of next month. I'm coming down to Pasadena for the events surrounding your 90th, so I'll probably at least say hello to you down there. I'm going to do some archival research as well.

LP: You know Lucile is in bad shape, physically.

TH: Yeah, I had heard. I talked to your cousin, Richard, a few weeks ago.

LP: Yes.

TH: And haven't checked in since then, and hoping that no news is good news. How bad is she, and when was the last time you spoke to her?

LP: Well, I don't know. Her son has come from New Jersey two or three times in the last month or two to check up on her.

TH: Yeah. Yeah, that's unfortunate and I'm sorry to hear that. So, I will speak 01:23:00to you later. I do want to send you a package. I'm going to copy off a couple of chapters from this dissertation that I mentioned last time on the-

LP: the Kay's. Okay.

TH: Yeah, Lily Kay's dissertation, and I'll give you a copy of a couple chapters you may find interesting.

LP: Fine.

TH: All right, nice to talk with you.

LP: Bye, Tom.

TH: Bye-bye.